CN100367383C - Object optical element and optical pickup device - Google Patents
Object optical element and optical pickup device Download PDFInfo
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- CN100367383C CN100367383C CNB2003801021382A CN200380102138A CN100367383C CN 100367383 C CN100367383 C CN 100367383C CN B2003801021382 A CNB2003801021382 A CN B2003801021382A CN 200380102138 A CN200380102138 A CN 200380102138A CN 100367383 C CN100367383 C CN 100367383C
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Abstract
Downsizing of an optical pickup device is made compatible with ensuring of aberration characteristics by irradiating an object lens (OBJ) with a light flux having a small divergent angle. More specifically, since its optical system magnification m1 is at least the lower limit (-1/7), a deterioration in aberration characteristics can be restricted even when, for example, a light flux from a light source is beamed with its center deviated or inclined from the axis of the object lens (OBJ). In addition, since an optical system magnification m1 is up to the upper limit (-1/25), a sufficient distance can be ensured between the object lens (OBJ) and an optical information recording medium (D).
Description
Technical Field
The present invention relates to an objective optical element that converges light flux to an information recording surface of an optical recording medium and to an optical pickup apparatus.
Background
In recent years, with the practical use of a short-wave red laser, DVDs (digital video discs) representing high-density optical information recording media (which are also referred to as optical discs) have been commercialized, which are the same size as CDs (compact discs) and have higher capacity.
In a recording apparatus for DVD, when a semiconductor laser having a wavelength of 650nm is used, the numerical aperture NA of the object lens on the side of the optical disk is 0.6 to 0.65. The track pitch (track pitch) and the shortest pit length (pit length) of the DVD are 0.74 micrometers and 0.4 micrometers, respectively, which means that the DVD has a higher density and the track pitch and the shortest pit length of the CD are half or less, the track pitch of the CD is 1.6 micrometers, and the shortest pit length is 0.83 micrometers. Also, in the DVD, the thickness of a protective mother board (base board) thereof is 0.6 mm, which is half of that of the CD, so that coma aberration, which is generated when one optical axis is tilted to the other, is controlled to be small.
In addition to the aforementioned CD and DVD, optical discs of various standards have also been commercialized, in which light source wavelengths are different from each other and protective mother plate thicknesses are also different from each other, such as CD-R, RW (compact disc read once), VD (video disc), MD (mini disc), and MO (magneto-optical disc).
Moreover, a technology for making the wavelength of a semiconductor laser shorter has been developed, and the development work of a high-density optical disc (hereinafter referred to as "high-density DVD") having a protective mother substrate having a thickness of about 0.1 mm, which employs a violet semiconductor laser light source having a wavelength of 400 nm and an object lens in which the Numerical Aperture (NA) on the image side is increased to about 0.85, and for a high-density DVD having a protective mother substrate having a thickness of 0.6 mm, which employs an object lens in which the Numerical Aperture (NA) on the image side is increased to 0.65, has been advanced.
Therefore, there have been proposed various types of so-called optical pickup devices having compatibility of converging two types of light fluxes each having a different wavelength and having only a single object lens on the information recording surfaces of the two types of optical discs.
As an optical pickup apparatus having compatibility, there is known an optical pickup apparatus in which a step structure (diffraction structure) composed of a staircase-like discontinuous surface is formed on a surface of an object lens or on a surface of an optical element disposed separately from the object lens (for example, see patent document 1 to patent document 3).
In the disclosed apparatus, recording and reproducing of information is performed on two types of optical discs having a single object lens in the following manner; that is, of the wavelengths of the two types of parallel light collimated by the collimator lens, a light flux having a certain wavelength on one side is condensed onto a prescribed disc through the object lens after passing through the hologram optical element, while a beam of light having a certain wavelength on the other side is diffracted so as to be diffused as it passes through the hologram optical element, and then, first order diffracted light is condensed onto the prescribed disc by the object lens.
Further, the aforementioned patent document 3 discloses an optical pickup apparatus provided with an object lens on which a diffraction structure composed of staircase-like steps (zone plates) is formed.
The apparatus is such that a light flux with a wavelength of 650nm is condensed to the recording surface of the DVD by the convex-shaped object lens and the object lens both surfaces of which are aspherical shapes, and a light flux with a wavelength of 780nm is condensed to the recording surface of the CD-R, wherein parallel lights with both wavelengths of 650nm and 780nm are collimated by the collimator lens.
(patent document 1)
TOKKATHEI No.9-54973
(patent document 2)
TOKKATHEI No.9-306018
(patent document 3)
TOKKATHEI No.2002-277732
(problems to be solved by the invention)
Incidentally, each of the apparatuses disclosed in patent documents 1 to 3 is an optical pickup apparatus of a so-called infinite system (infinite system), in which two types of luminous fluxes each having a different wavelength respectively emitted from different light sources are collimated into parallel light by a collimator and then, are caused to enter a hologram optical element provided with a diffraction structure or an object lens.
In an optical pickup apparatus of an infinite system, a problem of arranging an optical element such as a collimator lens for converting a light flux into parallel light between a light source and an object lens results in a large-sized and high-cost apparatus.
Further, there is a problem that, in an optical pickup device of a so-called infinite system in which divergent light enters an object lens, in the case of performing reproduction or recording on an optical disc, an image height characteristic is deteriorated in a process of following the object lens to move relative to the optical disc, and coma aberration and astigmatism are caused.
Further, there is a problem that, in the optical pickup apparatus of the finite system, spherical aberration caused by temperature change is larger than corresponding spherical aberration in the optical pickup apparatus of the infinite system.
Disclosure of Invention
In view of the problems set forth above, it is an object of the present invention to provide an optical pickup apparatus for performing reproduction and/or recording of information for two types of optical information recording media each having a different operating wavelength and reducing deterioration of image height characteristics and correcting spherical aberration caused by temperature variation, and also to provide an objective optical element.
Drawings
Fig. 1 (a) and 1 (b) are each a sectional view of an example of the objective optical element of the first embodiment.
Fig. 2 is a schematic configuration diagram of an optical pickup apparatus relating to the present invention.
Fig. 3 is a schematic diagram showing an example of an optical pickup apparatus relating to the second embodiment.
Fig. 4 is an enlarged view of a main portion (primary section), which shows the structure of a light source.
Fig. 5 is a side view of a main portion, which shows the structure of a problematic lens.
Fig. 6 (a) to 6 (c) each show an enlarged view of a main portion showing a discontinuous region.
Fig. 7 is a side view of a main portion, which shows the structure of an object lens.
Fig. 8 is a side view of a main portion, which shows the structure of an object lens.
Fig. 9 is an enlarged view of a main portion, which shows the structure of the object lens.
Fig. 10 is a schematic diagram showing an example of another optical pickup apparatus.
Fig. 11 (a) to 11 (c) show side views of the main part, which show the structure of another optical pickup apparatus equipped with phase modulating means (means).
Fig. 12 (a) to 12 (c) show side views of the main part, in which each figure shows the structure of another object lens.
Fig. 13 is a profile configuration view of an optical pickup apparatus equipped with the object lens 16 of the third embodiment.
Fig. 14 is a sectional view of the object lens 14 when converging light flux on the DVD 21.
Fig. 15 is a sectional view of the object lens 14 when converging light fluxes on the CD 21.
Fig. 16 is a plan view of the incident surface 241 of the object lens 14.
Fig. 17 is a cross-sectional view of the diffraction structure a on the coma aberration area 241a.
Fig. 18 is a side view of a main portion, which shows an example of the objective optical element relating to the fourth embodiment.
Fig. 19 is a top view showing the light condensing optical system and the optical pickup device.
Detailed Description
First, terms used in the present specification are explained below.
The optical element in the present specification means in this case an assembly such as a coupled lens, a beam expander, a beam shaper and a correction sheet, which constitute an optical system of an optical pickup apparatus.
Further, the optical element is not limited to an element constituted by only a single lens, but may be a lens group in which a plurality of lenses are combined in the optical axis direction.
The objective optical element means an object lens. The object lens means in a narrow sense a lens which has a light condensing function and which is disposed so as to face an optical information recording medium at a position close to the optical information recording medium under a condition that the optical information recording medium is loaded into an optical pickup apparatus, and means in a broad sense a lens, the lens and the aforementioned lens being pushed by an actuator in a direction of an optical axis.
The optical information recording medium means a general optical disc such as CD, DVD, CD-R, MD, and high-density DVD, which performs reproduction and/or recording of information by using a light flux of a prescribed wavelength.
Further, the reproduction of information means the reproduction of information recorded on the information recording surface of the optical information recording medium on which the information recording apparatus records information. Incidentally, the reproduction mentioned in this case includes simple reading of information.
The optical pickup device may be a device for performing only information recording or only information reproduction, or for performing recording and reproduction.
The discontinuous region means a structure composed of continuous staircase-like step portions in the optical axis direction when the cross section thereof is viewed from a plane (meridional cross section) including the optical axis and having a function of diffracting the light flux by a certain phase difference to a prescribed light flux entering the discontinuous region.
"optical system magnification" means the so-called lateral magnification, which is the ratio of the size of an object to the size of an image.
"diffractive structure" means a corrugation (relief) provided on the surface of an optical element such as an object lens so as to have a function of converging or diverging a light flux by diffraction. One well-known form of corrugation is represented by, for example, ring-shaped zones (rings) which have mainly concentric rings centered on the optical axis, each ring having a saw-toothed shape when viewed in cross section from a plane including the optical axis, including such shapes and which are particularly referred to as "diffractive ring zones".
The second optical information recording medium (also referred to as a second optical disc) means various kinds of optical discs of the CD type, such as CD-R, CD-W, CD-Video, and CD-ROM, while the first optical information recording medium (i.e., the so-called first optical disc) includes DVD-ROM and DVD-Video independently for reproduction, and also includes different types of DVD optical discs of the DVD type, such as DVD-RAM, DVD-R, and DVD-RW, for reproduction and recording. Further, in the specification of the present invention, the thickness t of the transparent mother plate includes t =0.
Further, the protective mother plate means an optically transparent parallel plane plate and is formed on the light flux entering side of the information recording surface so as to protect the information recording surface of the optical information recording medium, and the thickness of the protective mother plate means the thickness of the parallel plane plate. The light flux emitted from the light source is condensed on the information recording surface of the optical information recording medium by the object lens through the protective mother plate.
The numerical aperture of the image side optical element means a numerical aperture on the lens surface, which is disposed at a position in the optical element near the optical information recording medium.
Further, the numerical aperture is defined as a numerical aperture of a result in which a light flux contributing to spot formation at an optimum image point is limited by a member or element having a blocking function such as an aperture of a filter provided on the optical pickup device and a diffraction structure provided on the optical element.
When the optical pickup apparatus relating to the present invention is used as an optical pickup apparatus having compatibility with CDs and DVDs, the wavelength of the light flux having the first wavelength λ 1 is assumed to be in the range of 620nm to 680nm, and the wavelength of the light flux having the second wavelength λ 2 is assumed to be in the range of 750nm to 810 nm.
Hereinafter, examples for achieving the above objects of the present invention will be described.
(first embodiment)
The objective optical element of the optical pickup apparatus described in the item (1-1) is an objective optical element which has a first light source having a wavelength λ 1, a second light source having a wavelength λ 2 (λ 1 < λ 2), and a light converging optical system including a magnification conversion element and the objective optical element, and which is capable of performing information recording and/or reproduction when the light converging optical system converges a light flux emitted from the first light source on an information recording surface of a first optical information recording medium through a protective layer having a thickness t1, and is capable of performing information recording and/or reproduction when the light converging optical system converges a light flux emitted from the second light source on an information recording surface of a second optical information recording medium through a protective layer having a thickness t2 (t 1 ≦ t 2), wherein the objective optical element satisfies the following expression for a light flux optical system magnification m1 having a wavelength λ 1,
-1/7≤m1≤-1/25(1)
an optical system magnification M1 for a light flux having a wavelength λ 1 from a first light source to a first optical information recording medium in an optical pickup device satisfies the following expression,
|m1|＜|M1|(2)
and on the surface of at least one objective optical element, there are provided a common region through which a light flux emitted from the first light source and a light flux emitted from the second light source pass and form light converging spots on the information recording surfaces of the first optical information recording medium and the second optical information recording medium, respectively, and a dedicated region (exclusive area) through which the light flux emitted from the first light source passes and forms a light converging spot on the information recording surface of the first optical information recording medium, and through which the light emitted from the second light source passes but does not form a light converging spot on the information recording surface of the second optical information recording medium, on the common region, there is provided a common diffractive structure having a function of correcting so as to reduce a difference between spherical aberration caused by the light flux of wavelength λ 1 and spherical aberration caused by the light flux of wavelength λ 2, a light flux having a wavelength λ 1 passes through the common diffraction structure through the protective layer having a thickness t1 and is condensed on the information recording surface of the first optical information recording medium, a light flux having a wavelength λ 2 passes through the common diffraction structure through the protective layer having a thickness t2 and is condensed on the information recording surface of the second optical information recording medium, and on the dedicated area, a dedicated diffraction structure is provided which has a function of controlling spherical aberration, which increases as the ambient temperature increases, in accordance with a change in the wavelength λ 1 when the light flux having the wavelength λ 1 passes through the dedicated diffraction structure and is condensed on the information recording surface of the first optical information recording medium, and when the light flux having the wavelength λ 2 passes through the dedicated diffraction structure and the optical axis intersect at a point different from a light-condensing spot, which is on the information recording surface of the second optical information recording medium in the direction of the optical axis Is formed as above.
In the objective optical element of the optical pickup apparatus described in item (1-1), the optical pickup apparatus is downsized to be compatible with safety of aberration characteristics by emitting a light flux having a small angle divergence onto the objective optical element. To be more specific, deterioration of aberration characteristics can be controlled even if the light flux emitted from the light source deviates from the optical axis of the objective optical element at its center or enters obliquely toward the optical axis of the objective optical element, for example, because the optical system magnification m1 is not smaller than the aforementioned lower limit of expression (1). On the other hand, a sufficient distance between the objective optical element and the optical information recording medium can be ensured because the optical system magnification m1 does not exceed the upper limit. Further, in the present invention, the deterioration of spherical aberration caused by the difference between the thicknesses of the protective layers of the first optical information recording medium and the second optical information recording medium is controlled by the diffraction structure provided on the common area, and the deterioration of spherical aberration caused by the change in refractive index of the objective optical element in accordance with the rise in ambient temperature is controlled by the diffraction structure provided on the dedicated area, and therefore, recording and/or reproduction of information can be appropriately performed for different types of optical information recording media. Incidentally, "correcting to reduce the difference in spherical aberration" means correcting the spherical aberration to be smaller than in the case where a common diffractive structure is not provided and only a refractive interface is present.
In the objective optical element of the optical pickup apparatus described in the item (1-2), when an optical system magnification of the objective optical element for a light flux of a wavelength λ 2 is represented by m2, the following expression is satisfied.
|m1-m2|＜0.5(3)
In the objective optical element of the optical pickup apparatus described in the item (1-3), a first annular band region and a second annular band region, which are divided by steps in the optical axis direction and have centers on the optical axis, respectively, are provided on the aforementioned common region, and a common diffraction structure is provided on the second annular band region, which is distant from the optical axis, and a refractive interface is provided on the first annular band region, which is relatively close to the optical axis.
In the objective optical element of the optical pickup apparatus described in the item (1-4), an edge portion adjacent to the second annular band type region in the first annular band type region is positioned at a position closer to the light source in the optical axis direction than an edge portion adjacent to the first annular band type region in the second annular band type region.
In the objective optical element of the optical pickup apparatus described in the item (1-5), a third annular zone-shaped region having a refractive interface on the side away from the optical axis is provided adjacent to the second annular zone-shaped region, and an edge portion of the third annular zone-shaped region adjacent to the second annular zone-shaped region is positioned closer to the optical information recording medium than an edge portion of the second annular zone-shaped region in the third annular zone-shaped region in the optical axis direction.
In the lens optical element of the optical pickup apparatus of the item (1-6), the common diffractive structure has an optical characteristic that, as the wavelength of the light source becomes longer, it brings spherical aberration below the luminous flux passing through the common diffractive structure.
Now, with respect to the aforementioned examples of the objective optical element of the present invention, the following will be explained with reference to the drawings. Fig. 1 is a cross-sectional view of an objective optical element OBJ of the present invention. In fig. 1, on an optical surface S1 of an objective optical element OBJ closer to a light source, a central first annular band type region A1 including an optical axis X, a second annular band type region A2 surrounding the first annular band type region, and a third annular band type region A3 surrounding the second annular band type region are divided stepwise in the optical axis direction. The common area mentioned in the present invention corresponds to the first endless belt type area A1 and the second endless belt type area A2, and the dedicated area mentioned in the present invention corresponds to the third endless belt type area A3.
That is, when information recording and/or reproduction is performed on the first optical information recording medium D, the second and third annular band-type regions A2 and A3 form a light condensing spot on the information recording surface Dr through the protective layer Dp by the light flux of the first annular band-type region A1, as shown in fig. 1 (a). On the other hand, when information recording and/or reproduction is performed on the second optical information recording medium D, the light flux passing through the first annular band type region A1, and the second annular band type region A2 form a light condensing spot on the information recording surface Dr through the protective layer Dp, as shown in fig. 1 (b). In this case, the light flux passing through the third endless belt type region A3 becomes flare spot (flare) without forming a spot on the information recording surface Dr.
Each of the regions A1-A3 is composed of a refractive interface and is provided with a diffractive structure (however, the region A1 may be provided with only a refractive interface), and the second annular zone type region A2 is so shaped as to be displaced closer to the optical information recording medium D than the first annular zone type region A1 and the third annular zone type region A3. To be more specific, the edge portion P1 in the first endless belt type region A1 adjacent to the second endless belt type region A2 is positioned closer to the light source in the optical axis direction than the edge portion P1 in the second endless belt type region A2 adjacent to the first endless belt type region A1. Further, the edge portion in the second annular zone type region A2 adjacent to the third annular zone type region A3 is positioned closer to the optical information recording medium D in the optical axis direction than the edge portion P4 in the third annular zone type region A3 adjacent to the second annular zone type region A2. Due to this structure, the effect of changing the phase difference as described in the following items (1-6) or (1-7) can be achieved.
In the objective optical element of the optical pickup apparatus described in the item (1-7), a phase difference of a light flux of a wavelength λ 1 passing through the first annular zone type region and a light flux of a wavelength λ 1 passing through the second annular zone type region is 2 π × i (i: integer) on the optimal imaging plane.
In the objective optical element of the optical pickup apparatus described in the item (1-7), a phase difference of a light flux of a wavelength λ 1 passing through the first annular zone type region and a light flux of a wavelength λ 1 passing through the third annular zone type region is 2 π × i (i: integer) on the optimal imaging plane.
In the objective optical element of the optical pickup apparatus described in the items (1-9), all the common regions are provided with different diffractive structures.
The objective optical element of the optical pickup apparatus described in the item (1-10) is an objective optical element used in an optical pickup apparatus having a first light source having a wavelength λ 1, a second light source having a wavelength λ 2 (λ 1 < λ 2), and a light converging system including a magnification conversion element and the objective optical element, and by the light converging system, the objective optical element of the optical pickup apparatus capable of performing recording and/or reproduction of information when a light flux emitted from the first light source is converged on an information recording surface of a first optical information recording medium through a protective layer having a thickness t1, the objective optical element of the optical pickup apparatus capable of performing recording and/or reproduction of information when a light flux emitted from the second light source is converged on an information recording surface of a second optical information recording medium through a protective layer having a thickness t2 (t 1 < t 2), wherein an optical system magnification m1 of the objective optical element satisfies the following expression for a light flux having a wavelength λ 1,
-1/7≤m1≤-1/25(1)
the following expression is satisfied for an optical system magnification M1 of a light flux having a wavelength λ 1 from a first light source to a first optical information recording medium in an optical pickup device,
|m1|＜|M1|(2)
and on a surface of the at least one objective optical element, there are provided a common region through which a light flux emitted from the first light source and a light flux emitted from the second light source pass and form light converging spots on information recording surfaces of the first optical information recording medium and the second optical information recording medium, respectively, and a dedicated region through which the light flux emitted from the first light source passes and forms a light converging spot on the information recording surface of the first optical information recording medium and through which the light emitted from the second light source passes without forming a light converging spot on the information recording surface of the second optical information recording medium, the common region being divided into a plurality of annular refractive interfaces having steps in the optical axis direction, the 1 st, 2 nd, right, k (k is a natural number of 2 or more) surfaces in order from the optical axis, at least an edge portion of an nth (n is a natural number of 2 or more, n ≦ k) annular refractive interface is positioned closer to the optical information recording medium than an edge portion of an (n-1) th annular refractive interface in the direction of the optical axis, the (n-1) th annular refractive interface is farther from the optical axis, and the edge portion of the nth annular refractive interface farther from the optical axis is positioned closer to the optical axis than the edge portion of an (n + 1) th (surface of the dedicated region in the case of n = k) annular refractive interface in the direction of the optical axis, and a light flux having a wavelength λ 1 passing through the nth surface is condensed at a position different from the optimum image plane in the direction of the optical axis, the light flux having a wavelength λ 1 passing through the dedicated region forms a first light condensing spot on the information recording surface of the first optical information recording medium, while the light flux having passed through the dedicated area with the wavelength λ 2 does not form the second light converging spot on the information recording surface of the second optical information recording medium, the diffraction structure for temperature correction is formed on the dedicated area, and a function is provided which, when the light flux having the wavelength λ 1 passed through the diffraction structure for temperature correction is converged on the information recording surface of the first optical information recording medium, controls spherical aberration according to a change in the wavelength of the light flux having the wavelength λ 1, the spherical aberration increasing according to an increase in ambient temperature, and further, the light flux having the wavelength λ 2 passed through the diffraction structure for temperature correction intersects the optical axis at a position different from the light converging spot in the optical axis direction.
In the objective optical element of the optical pickup device described in the items (1-10), the optical pickup device is made to be reduced in size so as to be compatible with safety of aberration characteristics by emitting a luminous flux having a divergence of a small angle on the objective optical element. To be more specific, deterioration of aberration characteristics can be controlled even if the luminous flux emitted from the light source deviates from the optical axis of the objective optical element at the center thereof or inclines toward the optical axis, for example, because the optical system magnification m1 is not lower than the aforementioned lower limit of expression (1). On the other hand, a sufficient distance between the objective optical element and the optical information recording medium can be ensured because the optical system magnification m1 does not exceed the upper limit.
Further, in the explanation of the present invention with reference to the example shown in fig. 1, the first endless belt type region A1 is a first surface, the second endless belt type region A2 is a second surface, and the third endless belt type region A3 is a third surface, and therefore, in the case where n =2, the edge portion P2 closer to the optical axis of the endless belt type refractive interface on the second surface is positioned closer to the optical information recording medium D than the edge portion P1 in the optical axis direction, the edge portion P1 is farther from the optical axis of the endless belt type refractive interface on the first surface, and the edge portion P3 farther from the optical axis of the endless belt type refractive interface on the second surface is positioned closer to the optical information recording medium D than the edge portion P4 in the optical axis direction, the edge portion P4 is closer to the optical axis on the endless belt type refractive area on the third surface, and therefore, the effect of changing the phase difference can be obtained as described in the following items (1-10).
In the objective optical element of the optical pickup apparatus described in the item (1-11), when m2 denotes an optical system magnification of the objective optical element for a light flux of a wavelength λ 2, the following expression is satisfied.
|m1-m2|＜0.5(3)
In the objective optical element of the optical pickup apparatus described in the item (1-12), a phase difference of a light flux of a wavelength λ 1 passing through the nth surface and a light flux of a wavelength λ 1 passing through the (n-1) th surface on the optimum image plane is 2 π × i (i: integer).
The objective optical element of the optical pickup apparatus described in the item (1-13) is an objective optical element used in an optical pickup apparatus having a first light source having a wavelength λ 1, a second light source having a wavelength λ 2 (λ 1 < λ 2), and a light converging optical system including a magnification conversion element and the objective optical element, and capable of performing recording and/or reproduction of information when a light flux emitted from the first light source is converged on an information recording surface of a first optical information recording medium after passing through a protective layer having a thickness t1, and capable of performing recording and/or reproduction of information when the light flux emitted from the second light source is converged on the information recording surface of a second optical information recording medium by the light converging optical system after passing through the protective layer having a thickness t2 (t 1 ≦ t 2), wherein a magnification m1 of the optical system of the objective optical element for the light flux having the wavelength λ 1 satisfies the following expression,
-1/7≤m1≤-1/25(1)
the following expression is satisfied for an optical system magnification M1 of a light flux having a wavelength λ 1 from a first light source to a first optical information recording medium in an optical pickup device,
|m1|＜|M1|(2)
and on a surface of the at least one objective optical element, a common region through which a light flux emitted from the first light source and a light flux emitted from the second light source pass and form light converging spots on information recording surfaces of the first optical information recording medium and the second optical information recording medium, respectively, and a dedicated area through which a light flux emitted from the first light source passes and which forms a light converging spot on an information recording surface of the first optical information recording medium, and the light emitted from the second light source passes through it without forming a light converging spot on the information recording surface of the second optical information recording medium, and at least a part of the common area has a correcting function, which reduces spherical aberration caused when a light flux of wavelength λ 1 having passed through a common area is condensed on an information recording surface of a first optical information recording medium through a protective layer of thickness t1 in accordance with a wavelength difference between wavelength λ 1 and wavelength λ 2, and spherical aberration caused when the light flux having a wavelength of 2 that has passed through the common area is condensed on the information recording surface of the second optical information recording medium through a protective layer having a thickness of t2, then, at least a part of the dedicated area has a function of controlling, when the light flux of the wavelength λ 1 passing through the dedicated diffractive structure is condensed on the information recording surface of the first optical information recording medium, which controls spherical aberration according to a change in wavelength of a light flux having a wavelength λ 1, the spherical aberration increasing according to an increase in ambient temperature, and the light flux having the wavelength λ 2 that has passed through the dedicated area intersects the optical axis in the optical axis direction at a position different from a light converging spot formed on the information recording surface of the second optical information recording medium. The functions and effects of the present invention are the same as those described in item (1-1) or item (1-9).
In the objective optical element of the optical pickup apparatus described in the item (1-14), when m2 denotes an optical system magnification of the objective optical element for a light flux of a wavelength λ 2, the following expression is satisfied.
|m1-m2|＜0.5(3)
In the objective optical element of the optical pickup apparatus described in the items (1-15), the magnification conversion optical element is a coupling lens.
In the objective optical element of the optical pickup apparatus described in the item (1-16), the objective optical element is an objective lens.
In the objective optical element of the optical pickup apparatus described in the item (1-17), the objective optical element is made of plastic.
In the objective optical element of the optical pickup apparatus described in the items (1-18), the first light source and the second light source are disposed on the same motherboard as a two-laser one-package unit.
In the objective optical element of the optical pickup apparatus described in the item (1-19), the arrangement of the first light source and the second light source is the same from the viewpoint of the distance from the magnification conversion element in the optical axis direction.
The optical pickup apparatus described in the item (1-20) is an optical pickup apparatus in which a first light source having a wavelength of λ 1, a second light source having a wavelength of λ 2 (λ 1 < λ 2), and a light condensing optical system including a magnification conversion element and an objective optical element, and which is capable of performing recording and/or reproduction of information when the light condensing optical system condenses a light flux emitted from the first light source onto an information recording surface of a first optical information recording medium through a protective layer having a thickness of t1, and is capable of performing recording and/or reproduction of information by condensing a light flux emitted from the second light source onto an information recording surface of a second optical information recording medium through a protective layer having a thickness of t2 (t 1 < t 2), wherein an optical system magnification m1 of the objective optical element for the light flux having the wavelength of λ 1 satisfies the following expression,
-1/7≤m1≤-1/25(1)
the following expression is satisfied for an optical system magnification M1 of a light flux having a wavelength λ 1 from a first light source to a first optical information recording medium in an optical pickup device,
|m1|＜|M1|(2)
and on a surface of the at least one objective optical element, a common region through which a light flux emitted from the first light source and a light flux emitted from the second light source pass and form light converging spots on information recording surfaces of the first optical information recording medium and the second optical information recording medium, respectively, and a dedicated area through which a light flux emitted from the first light source passes and which forms a light converging spot on an information recording surface of the first optical information recording medium, and the light emitted from the second light source passes through it without forming a light converging spot on the information recording surface of the second optical information recording medium, a common diffraction structure is provided on the common area, which has a function of correcting so as to reduce a difference between spherical aberration caused by luminous flux having a wavelength λ 1 and spherical aberration caused by luminous flux having a wavelength λ 2, the luminous flux having the wavelength λ 1 passing through the common diffractive structure through the protective layer having a thickness t1 and converging on the information recording surface of the first optical information recording medium, the luminous flux having the wavelength λ 2 passing through the common diffractive structure through the protective layer having a thickness t2 and converging on the information recording surface of the second optical information recording medium, on the dedicated area, a dedicated diffractive structure is provided that, when a light flux of a wavelength λ 1 passing through the dedicated diffractive structure is condensed on the information recording surface of the first optical information recording medium, and the light flux of wavelength 2 passing through the dedicated diffractive structure and the optical axis intersect at a point different from the light converging spot, which has a function of controlling spherical aberration, which increases according to an increase in ambient temperature, in accordance with a change in wavelength λ 1, wherein the light condensing spot is formed on the information recording surface of the second optical information recording medium in the direction of the optical axis. The function and effect of the present invention are the same as those described in item (1-1).
In the optical pickup apparatus described in the item (1-21), when m2 denotes an optical system magnification of the objective optical element for the light flux of the wavelength λ 2, the following expression is satisfied.
|m1-m2|＜0.5(3)
In the optical pickup apparatus described in the item (1-22), the first annular zone type region and the second annular zone type region, which are divided by the step in the optical axis direction and are both centered on the optical axis, are provided in the common region, and the common diffraction structure is provided in the first annular zone type region positioned farther from the optical axis, and the second annular zone type region closer to the optical axis has a refractive interface.
In the optical pickup apparatus described in the item (1-23), the edge portion adjacent to the first endless belt type region in the second endless belt type region is positioned closer to the light source in the optical axis direction than the edge portion adjacent to the second endless belt type region in the first endless belt type region.
In the optical pickup apparatus described in item (1-24), the third annular zone type region having the refractive interface on the farther side from the optical axis is provided adjacent to the first annular zone type region, and the edge portion adjacent to the third annular zone type region in the first annular zone type region is provided closer to the optical information recording medium in the optical axis direction than the edge portion adjacent to the first annular zone type region in the third annular zone type region.
In the optical pickup device described in the item (1-25), the common diffractive structure has an optical characteristic that causes spherical aberration to be below a luminous flux passing through the common diffractive structure as the wavelength of the light source becomes longer.
In the optical pickup apparatus described in the item (1-26), a difference at the optimum image plane between a phase of a light flux of wavelength λ 1 having passed through the first endless belt type region and a phase of a light flux of wavelength λ 1 having passed through the second endless belt type region is 2 π × i (i: integer).
In the optical pickup device described in the item (1-27), a difference between a phase of a light flux having a wavelength λ 1 which has passed through the first endless belt type region and a light flux having a wavelength λ 1 which has passed through the third endless belt type region at an optimum image plane is 2 π × i (i: integer).
In the objective optical element of the optical pickup apparatus described in the item (1-28), all the common regions are provided with the diffraction structures.
The optical pickup apparatus described in the item (1-29) is an optical pickup apparatus in which there are a first light source having a wavelength λ 1, a second light source having a wavelength λ 2 (λ 1 < λ 2), and a light converging optical system including a magnification conversion element and an objective optical element, and information recording and/or reproduction can be performed when the light converging optical system converges a light flux emitted from the first light source on an information recording surface of a first optical information recording medium through a protective layer having a thickness t1, and information recording and/or reproduction can be performed when the light converging optical system converges a light flux emitted from the second light source on an information recording surface of a second optical information recording medium through a protective layer having a thickness t2 (t 1 ≦ t 2), wherein the objective optical element satisfies the following expression for a light flux optical system magnification m1 having a wavelength λ 1,
-1/7≤m1≤-1/25(1)
the following expression is satisfied for an optical system magnification M1 of a light flux having a wavelength λ 1 from a first light source to a first optical information recording medium in an optical pickup device,
|m1|＜|M1|(2)
and on a surface of the at least one objective optical element, there are provided a common region through which a light flux emitted from the first light source and a light flux emitted from the second light source pass and form light converging spots on information recording surfaces of the first optical information recording medium and the second optical information recording medium, respectively, and a dedicated region through which the light flux emitted from the first light source passes and forms a light converging spot on the information recording surface of the first optical information recording medium and through which the light emitted from the second light source passes but does not form a light converging spot on the information recording surface of the second optical information recording medium, on which common region there is provided a common diffraction structure, the common region being divided into a plurality of annular refractive interfaces having steps in the optical axis direction, 1 st, 2 nd,. Multidot.k (k is a natural number of 2 or more), at least an edge portion of an nth (n is a natural number of 2 or more, n ≦ k) annular refractive interface is positioned closer to the optical information recording medium than an edge portion of an (n-1) th annular refractive interface in the direction of the optical axis, the (n-1) th annular refractive interface is farther from the optical axis, and the edge portion of the nth annular refractive interface farther from the optical axis is positioned closer to the optical axis than the edge portion of an (n + 1) th (a surface of a dedicated region in the case of n = k) annular refractive interface in the direction of the optical axis, and a light flux passing through the nth surface with a wavelength λ 1 is converged at a position different from an optimum image plane in the direction of the optical axis, the light flux having a wavelength of λ 1 which has passed through the dedicated area forms a first light converging spot on the information recording surface of the first optical information recording medium, and the light flux having a wavelength of λ 2 which has passed through the dedicated area does not form a second light converging spot on the information recording surface of the second optical information recording medium, and the diffraction structure for temperature correction is formed on the dedicated area, and provides a function of controlling spherical aberration, which increases in accordance with an increase in ambient temperature, in accordance with a change in wavelength of the light flux having a wavelength of λ 1 when the light flux having a wavelength of λ 1 which has passed through the diffraction structure for temperature correction is converged on the information recording surface of the first optical information recording medium, and further, the light flux having a wavelength of λ 2 which has passed through the diffraction structure for temperature correction intersects the optical axis at a position different from the second light converging spot in the direction of the optical axis. The functions and effects of the present invention are the same as those described in items (1-10).
In the optical pickup apparatus described in the item (1-30), when the optical system magnification of the objective optical element for the light flux of the wavelength λ 2 is represented by m2, the following expression is satisfied.
|m1-m2|＜0.5(3)
In the optical pickup device described in the item (1-31), a difference between a phase of a light flux of wavelength λ 1 passing through the nth surface and a phase of a light flux of wavelength λ 1 passing through the (n-1) th surface at an optimum image plane is 2 π × i (i: integer).
The objective optical element of the optical pickup apparatus described in the item (1-32) is an objective optical element which has a first light source having a wavelength λ 1, a second light source having a wavelength λ 2 (λ 1 < λ 2), and a light converging optical system including a magnification conversion element and an objective optical element, and which is capable of performing information recording and/or reproduction when the light converging optical system converges a light flux emitted from the first light source on an information recording surface of a first optical information recording medium through a protective layer having a thickness t1, and capable of performing information recording and/or reproduction when the light converging optical system converges a light flux emitted from the second light source on an information recording surface of a second optical information recording medium through a protective layer having a thickness t2 (t 1 ≦ t 2), wherein the objective optical element satisfies the following expression for a light flux optical system magnification m1 having a wavelength λ 1,
-1/7≤m1≤-1/25(1)
the following expression is satisfied for an optical system magnification M1 of a light flux having a wavelength λ 1 from a first light source to a first optical information recording medium in an optical pickup device,
|m1|＜|M1|(2)
and on the surface of at least one objective optical element, there are provided a common region through which a luminous flux emitted from a first light source and a luminous flux emitted from a second light source pass and form light converging spots on the information recording surfaces of the first optical information recording medium and the second optical information recording medium, respectively, and a dedicated region through which the luminous flux emitted from the first light source passes and forms the light converging spots on the information recording surface of the first optical information recording medium, and through which the light emitted from the second light source passes but does not form the light converging spots on the information recording surface of the second optical information recording medium, at least a part of the common region having a function of correcting according to a difference between the wavelength λ 1 and the wavelength λ 2 so as to reduce a difference between spherical aberration caused by the luminous flux of the wavelength λ 1 and the luminous flux of the wavelength λ 2, the luminous flux of the wavelength λ 1 passing through a common diffraction structure via a protective layer having a thickness of t1 and converging on the information recording surface of the first optical information recording medium, the light flux of the wavelength 2 passing through the common diffraction structure and the dedicated region, and the recording medium having a wavelength of the recording medium changed when the light flux of the recording medium is changed by the diffraction of the second optical information recording medium, the special region having a wavelength 1 and the recording the light converging spot, the recording medium, the special information recording medium, the special region having a diffraction structure, and the recording medium, the special information recording medium having a recording temperature, and the special recording medium, the function and effect of the present invention are the same as those described in item (1-1) or item (1-10).
In the optical pickup apparatus described in the item (1-33), when the optical system magnification of the objective optical element for the light flux of the wavelength λ 2 is represented by m2, the following expression is satisfied.
|m1-m2|＜0.5(3)
In the optical pickup apparatus described in the item (1-34), the magnification conversion optical element is a connection lens.
In the optical pickup apparatus described in the item (1-35), the objective optical element is an object lens.
In the optical pickup apparatus described in the item (1-36), the objective optical element is made of plastic.
In the optical pickup apparatus described in the item (1-37), the first light source and the second light source are disposed on the same mother board.
In the optical pickup apparatus described in the item (1-38), the arrangement of the first light source and the second light source is the same from the viewpoint of the distance from the magnification conversion element in the optical axis direction.
The first embodiment of the present invention will be explained below with reference to the drawings. Fig. 2 is a schematic configuration diagram of an optical pickup apparatus relating to an example of the present invention. In the optical pickup apparatus shown in fig. 2, a first semiconductor laser 111 representing a first light source and a second semiconductor laser 212 representing a second light source are disposed on the same mother board 113, the first semiconductor laser 111 being for performing recording and/or reproduction of information on a first optical disc (e.g., DVD), and the second semiconductor laser 212 being for performing recording and/or reproduction of information on a second optical disc (e.g., CD).
First, when recording and/or reproducing of information is performed on the first optical disc, a laser light flux is emitted from the first semiconductor laser 111. The light flux thus emitted becomes a divergent light flux which is approximately parallel light flux through the polarization beam splitter 120 and the connection lens 115 representing the magnification conversion element. The light flux is blocked by the diaphragm 117 and converged to the information recording surface 122 by the object lens 116 representing the objective optical element via the transparent mother substrate 121 of the first optical disc 120.
The light flux modulated by the information pits (information pits) and reflected by the information recording surface 122 is transmitted again through the object lens 116, the aperture 117, and the connection lens 115 to the polarization beam splitter 120, is reflected there and is astigmatic by the cylindrical lens 180, and enters the light receiving surface of the photodetector 130 through the concave lens 150. A recording or reproduction signal of information recorded on the first optical disc 120 can be obtained by using an output signal from the photodetector 130.
On the other hand, when the second optical disc is reproduced, the laser light flux is emitted from the second semiconductor laser 212. The light flux thus emitted is converged on the information recording surface 122 through the polarizing beam splitter 120, the connecting lens 115, the aperture 117 and the object lens 116 via the transparent mother substrate 121 of the second optical disc 120 in the same manner as the light flux emitted from the aforementioned first semiconductor laser device 111.
The light flux modulated by the information pits and reflected by the information recording surface 122 is again emitted through the object lens 116, the aperture 117, the connection lens 115, the polarization beam splitter 120, the cylindrical lens 180, and the concave lens 150, and enters the light receiving surface of the photodetector 130. In this way, a recording or reproduction signal of information recorded on the first optical disc 120 can be obtained by using the output signal from the photodetector 130.
Preferred examples of the aforementioned embodiments will be explained as follows.
Both surfaces of the object lens are represented by aspherical surfaces, which are shown by the following "numerical value 1", where Z denotes an axis in the optical axis direction, h denotes a height from the optical axis, r denotes a paraxial radius of curvature (paraxalradius), κ denotes a conic constant, a 2i Representing the coefficients of the aspheric surface.
(numerical value 1)
Further, a diffraction structure is formed on the surface of the non-condition surface of the object lens on the light flux side. The diffraction structure is expressed by "value 2" in units of millimeters, and "value 2" represents an optical path difference function Φ of blazed wavelength (blazed wavelength) λ B. The second order coefficient represents the paraxial power of the diffracted portion. Further, the spherical aberration can be controlled by coefficients other than second-order coefficients, such as fourth-order coefficients or sixth-order coefficients. "controllable". In this case means that the spherical aberration is completely corrected by applying spherical aberration of opposite characteristics to that of the refractive part, the diffractive part, or that the spherical aberration is corrected by incident wavelength or blaze (flare) is caused by utilizing the wavelength relation (wavelengh-dependency) of the diffractive part. In this case, the spherical aberration caused by the temperature change can also be considered as the sum of the spherical aberration of the refractive portion and the change in the spherical aberration of the diffractive portion caused by the temperature change.
(numerical value 2)
(examples 1-1)
Example 1-1 described below is an example concerning an object lens, which can be applied to the above-described embodiments. Table 1-1 shows lens data regarding the objective lens in example 1-1, from now on (including the lens data in the table), an index of 10 (e.g., 2.5X 10 -3 ) Denoted by E (e.g., 2.5 XE-3).
TABLE 1-1
| f 1 ＝2.22mm | f 2 ＝2.23mm | M 1 ＝-0.1667 | M 2 ＝-0.1648 |
| NA1：0.60 | NA2：0.47 | m 1 ＝-0.1000 | m 2 ＝-0.0990 |
| Ith surface | Ri | di(670mm) | ni(670nm) | di(789nm) | ni(789nm) |
| 0 | 8.29100 | 8.29100 | |||
| 1 | -4.26577 | 0.80000 | 1.53921 | 0.80000 | 1.53587 |
| 2 | -3.48388 | 8.52546 | 1.0 | 8.89806 | 1.0 |
| 3 | 1.49581 | 1.50000 | 1.53921 | 1.50000 | 1.53587 |
| 3’ | 1.75416 | 1.51419 | 1.53921 | 1.51419 | 1.53587 |
| 4 | -3.88785 | 1.28150 | 1.0 | 0.90895 | 1.0 |
| 5 | ∞ | 0.6 | 1.57653 | 1.2 | 1.57047 |
| 6 | ∞ |
| Aspheric surface data | ||
| Second surface | ||
| Coefficient of aspheric surface | K＝-1.0865×E-1 | |
| Third surface 63 (h 0 ≦ 1.160mm | ||
| Coefficient of aspheric surface | K＝-5.0435×E-1 A1＝-1.3149×E-2 A2＝-1.3416×E-3 A3＝-6.5969×E-4 A4＝-8.3527×E-4 A5＝+5.6237×E-4 A6＝-1.4458×E-4 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
| Function of optical path difference (function of optical path difference) Coefficient of number: standard wavelength 1.0 mm) | C4＝-7.9254×E-0 A6＝+5.0701×E-1 A8＝-7.6729×E-1 A10＝+1.7882×E-1 | |
| Third surface (1.160 mm < h: DVD special area) | ||
| Coefficient of aspheric surface | K＝-4.8398×E-1 A1＝+3.8936×E-2 A2＝-1.3304×E-2 A3＝-1.8461×E-3 A4＝+5.5374×E-4 A5＝+6.3164×E-4 A6＝-2.1371×E-4 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
| Function of optical path difference (function of optical path difference) Counting: standard wavelength 1.0 mm) | C2＝-3.4110×E+0 C4＝+9.5563×E-1 A6＝-8.9185×E-1 A8＝-2.0852×E-2 A10＝+5.0103×E-2 | |
| The fourth surface | ||
| Coefficient of aspheric surface | K＝-1.6446×E+1 A1＝+1.9964×E-2 A2＝-1.2869×E-2 A3＝+5.2796×E-3 A4＝-1.2551×E-3 A5＝-1.6610×E-4 A6＝+6.1668×E-5 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
(examples 1-2)
Examples 1-2 described below are also about object lenses, which can be applied to the above-described embodiments. Tables 1-2 show lens data for the object lenses of examples 1-2.
Tables 1 to 2
| f 1 ＝1.65mm | f 2 ＝1.66mm | M 1 ＝-0.1665 | M 2 ＝-0.1648 |
| NA1：0.65 | NA2：0.50 | m 1 ＝-0.05 | m 2 ＝-0.05 |
| Ith surface | Ri | di(660mm) | ni(660nm) | di(785nm) | ni(785nm) |
| 0 | 7.67878 | 7.67878 | |||
| 1 | -20.64788 | 1.50000 | 1.54076 | 1.50000 | 1.53716 |
| 2 | -5.31143 | 5.00000 | 1.0 | 4.77290 | 1.0 |
| 3 | 1.12823 | 1.07000 | 1.53938 | 1.07000 | 1.53596 |
| 3’ | 1.07437 | 1.07136 | 1.53938 | 1.07136 | 1.53716 |
| 4 | -3.37604 | 0.77652 | 1.0 | 0.40360 | 1.0 |
| 5 | ∞ | 0.6 | 1.57718 | 1.2 | 1.57063 |
| 6 | ∞ |
| Aspheric surface data | ||
| Second surface | ||
| Coefficient of aspheric surface | K＝-2.21766×E-1 | |
| Third surface (h is more than or equal to 0 and less than or equal to 0.8774mm | ||
| Coefficient of aspheric surface | K＝-7.1436×E-1 A1＝-1.3733×E-2 A2＝-1.1346×E-3 A3＝-9.9466×E-3 A4＝-3.3590×E-3 A5＝+1.2870×E-2 A6＝-7.5424×E-3 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
| Function of optical path difference (function of optical path difference) Coefficient of number: standard wavelength 1.0 mm) | C4＝-2.5175×E+1 A6＝-3.2573×E+0 A8＝-5.1432×E+0 A10＝+2.3869×E+0 | |
| Third surface (0.8774 mm < h: DVD special area) | ||
| Coefficient of aspheric surface | K＝-5.8942×E-1 A1＝+4.4167×E-3 A2＝+1.9906×E-3 A3＝-6.9650×E-3 A4＝-7.4018×E-4 A5＝+6.1321×E-3 A6＝-4.2362×E-3 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
| Function of optical path difference (function of optical path difference) Coefficient of number: standard wavelength 1.0 mm) | C2＝-1.9480×E+1 C4＝+9.3550×E+0 A6＝+1.4926×E+1 A8＝-1.6118×E+1 A10＝+4.5614×E+0 | |
| The fourth surface | ||
| Coefficient of aspheric surface | K＝+4.6282×E+0 A1＝+1.4280×E-1 A2＝-1.2458×E-1 A3＝+1.4186×E-1 A4＝-1.2095×E-1 A5＝-5.7591×E-2 A6＝-1.1354×E-2 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
According to the first embodiment, it is possible to provide an optical pickup apparatus which has a compact configuration and is capable of performing recording and/or reproduction of information on different optical information recording media by using light sources each having a different wavelength, and an objective optical element.
(second embodiment)
The optical pickup apparatus described in item (2-1) of the second embodiment is represented by an optical pickup apparatus 10 which has a plurality of optical elements including an objective optical element (object lens 40) and is capable of performing reproduction and/or recording of a plurality of pieces of information by condensing a luminous flux having a wavelength λ 1 emitted from a first light source 11 by using the objective optical element on a first optical information recording medium 20 having a thickness t1 and a luminous flux having a wavelength λ 2 (λ 2 > λ 1) emitted from a second light source 12 on a second optical information recording medium 21 having a thickness t2 (t 2 ≧ t 1), wherein at least one of the optical elements provides at least two regions including a central region A1 and a peripheral region A2 whose centers are on an optical axis L, the peripheral area A2 is positioned around the central area, on at least one optical surface 41, staircase-like discontinuous areas 31 having a plurality of predetermined steps are periodically formed on the central area, each staircase-like step portion 31a forms a concentric ring centered on the optical axis, and a phase modulation device 30 is provided which converges light fluxes on a prescribed optical information recording medium under the condition that spherical aberration and/or wavefront aberration is corrected in conjunction with the objective optical element by letting at least one of a first light flux having a wavelength λ 1 and a light flux having a wavelength λ 2 have a phase difference, and the first light flux having the wavelength λ 1 and a second light flux having the wavelength λ 2 enter the objective optical element as divergent light.
The discontinuous region means a structure which is composed of discontinuous staircase-like step portions in the optical axis direction when viewed in cross section from a plane including the optical axis (meridional cross section), and which has a function of diffracting the light flux by allowing a prescribed light flux entering the discontinuous region to have a phase difference.
The phase modulating means is provided on only one of the one or more surfaces of one optical element.
Thus, for example, the phase modulating means may be formed on an optical surface on the light source side or an optical surface on the optical information recording medium side of an object lens representing an optical element, or further formed on a plurality of optical surfaces of an optical element constituting the optical pickup apparatus, such as forming the phase modulating means on both optical surfaces.
It is assumed in this description that the phase difference φ ranges between 0 ≦ φ < 2 π or- π < φ ≦ π.
From the optical surface on which the phase modulation device is formed, there are generated light diffraction lines expressed in an infinite number of orders including 0-order diffraction light, ± first-order diffraction light, ± second-order diffraction light,. And by changing the shape of the discontinuous region, the diffraction efficiency of a specific order can be made higher than that of the other orders, or in some cases, the diffraction efficiency of a specific order (for example, + first-order diffraction light) can be made substantially 100%.
Incidentally, the diffraction efficiency is a ratio indicating the amount of diffracted light occurring on the discontinuous area, and the sum of all orders of diffraction efficiency is 1.
In the optical pickup apparatus described in the item (2-1), even if the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 enter the objective optical element as divergent light, the phase modulation device provided with the staircase-like discontinuous region makes at least one of the light flux of the first wavelength λ 1 and the second wavelength λ 2 have a phase difference, and by incorporating the objective optical element, the light fluxes are condensed on the prescribed optical information recording medium under the condition that spherical aberration and/or wavefront aberration is corrected.
Therefore, an optical element such as a collimator lens used in a conventional infinite type optical pickup apparatus to collimate a light flux emitted from a light source into parallel light so that the light flux can enter an objective optical element proves unnecessary, and reduction in size and apparatus cost can be achieved.
At least one optical surface of at least one optical element is divided into at least two areas including a central area having a center on the optical axis and peripheral areas disposed around the central area, and at least one of two types of luminous fluxes respectively having luminous fluxes of a wavelength λ 1 and a wavelength λ 2, each of which passes through each of the divided areas, is given a phase difference as occasion demands by a phase modulation device, so that the luminous fluxes appear as diffracted lights on a prescribed information recording medium under the condition that the aberration is corrected.
The degree of freedom of aberration correction can be increased. It is further possible to control coma and astigmatism during tracking to control the occurrence of spherical aberration caused by temperature changes.
The optical pickup apparatus described in item (2-2) is the light described in item (2-1)Learning to pick up devices in which, when expressed by the phase function phi (h), discrete regions are formedThe ring is expressed by an integer part of phi (h)/2 pi, and the phase function phi (h) is defined as phi (h) = (B) 2 h 2 +B 4 h 4 +B 6 h 6 +...+B n h n ) X 2 pi, where h denotes the height from the optical axis, B n Coefficient representing the optical path difference function of the nth stage (n is an even number), and when B 2 When the coefficient of the second-stage optical path difference function is expressed, the value of | phi (h)/2 pi-B is kept to be less than or equal to 0 2 (h in ) 2 L is less than or equal to 10, and h in Indicating the height of the position furthest from the central region.
In the optical pickup apparatus described in item (2-2), the same effect as in item (2-1) can be obtained, and the number of the discontinuous regions provided on the phase modulation device can be limited to a certain number or less, and therefore, the amount of light of divergent light entering the discontinuous regions that does not enter the divergent light from the surface portion of the step portion can be controlled, which prevents a decrease in the amount of light.
The optical pickup apparatus described in item (2-3) is the optical pickup apparatus described in item (2-2), wherein | B is held 2 (h in ) 2 |≤18。
In the optical pickup apparatus described in item (2-3), the same effect as that in item (2-2) can be obtained.
The optical pickup apparatus described in the item (2-4) is the optical pickup apparatus described in one of the items (2-1) to (2-3), wherein a light flux passing through the central area among the second light fluxes having the wavelength λ 2 is condensed on the information recording surface of the second optical information recording medium, and a light flux passing through the peripheral area is condensed on the information recording surface of the second optical information recording medium.
In the optical pickup apparatus described in the item (2-4), the same effect as that in one of the items (2-1) to (2-3) can be obtained, and the second light flux having the wavelength λ 2 passing through the peripheral area can be condensed out of the information recording surface of the second information recording medium, and for example, when reproduction and/or recording of information is performed on a CD as the information recording medium, the numerical aperture can be adjusted without using an element such as an aperture adjusting filter, and therefore, the number of parts of the optical pickup apparatus can be reduced.
The optical pickup device described in item (2-5) is the optical pickup device described in one of items (2-1) to (2-4), in which a refractive structure 60 that refracts a light flux to a peripheral region is provided.
In the optical pickup apparatus described in item (2-5), the same effects as those in one of items (2-1) to (2-4) can be obtained, and the optical element provided with the phase modulating means can be manufactured more easily, and is relatively simple in configuration because the peripheral region is provided with the refractive structure, as compared with a case where it is entirely a staircase-like discontinuous surface or a diffraction blazed shape.
The optical pickup apparatus described in item (2-6) is the optical pickup apparatus described in one of items (2-1) to (2-4), wherein the same phase modulation device as that formed in the central region is provided in the peripheral region.
In the optical pickup apparatus described in item (2-6), the same effect as that of one of items (2-1) to (2-4) can be obtained, and spherical aberration caused by a wavelength change and a temperature change of diffracted light can be corrected more appropriately than that provided by the phase modulation device only in the central area because the phase modulation is formed in the peripheral area and the central area.
The optical pickup apparatus described in item (2-7) is the optical pickup apparatus described in item (2-6), wherein the number of steps of the discontinuous area provided on the phase modulating device is smaller than the number of steps of the discontinuous area on the central area.
In the optical pickup apparatus described in item (2-7), the same effects as in item (2-6) can be obtained, and the total number of steps formed on the optical element can be reduced as much as possible by reducing the number of steps of the discontinuous region on the phase modulation device provided on the peripheral region, which makes manufacturing easier.
The optical pickup apparatus described in item (2-8) is the optical pickup apparatus described in one of items (2-1) to (2-4), wherein a serrated endless belt 50 is provided on the peripheral region.
The optical pickup apparatus described in item (2-9) is the optical pickup apparatus described in one of items (2-1) to (2-4), wherein the peripheral region is provided with a discontinuous surface formed by moving a prescribed aspherical surface shape in a staircase form in a direction parallel to the optical axis.
The optical pickup apparatus described in item (2-10) is the optical pickup apparatus described in one of items (2-1) to (2-9), wherein the number of steps provided on the central area to at least one of the discontinuous areas on the phase modulation device is 4.
The optical pickup apparatus described in item (2-11) is the optical pickup apparatus described in one of items (2-1) to (2-10), wherein the number of steps provided on the central area to at least one of the discontinuous areas on the phase modulation device is 5.
The optical pickup apparatus described in the item (2-12) is the optical pickup apparatus described in one of the items (2-1) to (2-11), wherein the first wavelength λ 1 satisfies 620nm ≦ λ 1 ≦ 680nm, and the second wavelength λ 2 satisfies 750nm ≦ λ 2 ≦ 850nm.
The optical pickup apparatus described in item (2-13) is the optical pickup apparatus described in one of items (2-1) to (2-12), wherein the phase modulation device is formed on an optical element that is not the objective optical element mentioned above.
The optical pickup apparatus described in item (2-14) is the optical pickup apparatus described in one of items (2-1) to (2-12), wherein the phase modulation device is formed on the above-mentioned objective optical element.
The optical pickup apparatus described in item (2-15) is the optical pickup apparatus described in one of items (2-1) to (2-14), wherein an image forming magnification m of the optical system satisfies-0.149. Ltoreq. M.ltoreq.0.049.
In the optical pickup apparatus described in item (2-16), the same effect as that of one of item (2-1) to item (2-14) can be obtained, and a connection lens has proved unnecessary, resulting in a reduction in parts of the optical pickup apparatus.
Incidentally, it is more preferable to have the image forming magnification m in the range of-0.147. Ltoreq. M.ltoreq.0.099.
The optical pickup apparatus described in the item (2-16) is the optical pickup apparatus described in one of the items (2-1) to (2-15), wherein the phase modulating device on the central region does not cause the luminous flux of the first wavelength λ 1 to have a phase difference, or causes an absolute value of the phase difference due to a depth of one step in each step equal to the discontinuous region to be in a range of less than 0.2 pi radians.
In the optical pickup device described in item (2-16), the same effect as in one of items (2-1) to (2-15) can be obtained, the diffraction efficiency of each of the luminous flux of the wavelength λ 1 and the luminous flux of the wavelength λ 2 can be changed by making the phase difference in a range of less than 0.2 π radians, and a more preferable amount of light can be used for performing recording and/or reproduction of each information for each optical information recording medium.
The optical pickup apparatus described in the item (2-17) is the optical pickup apparatus described in one of the items (2-1) to (2-16), wherein the phase modulating device on the central region cannot make the luminous flux of the wavelength λ 2 have a phase difference or make an absolute value of the phase difference due to a depth of one step in each step equal to the discontinuous region in a range of less than 0.2 pi radians.
In the optical pickup apparatus described in item (2-17), the same effect as that of one of items (2-1) to (2-16) can be obtained.
The optical pickup apparatus described in item (2-18) is the optical pickup apparatus described in one of items (2-1) to (2-17), wherein the number of discontinuous areas on the phase modulating device provided on the central area is in the range of 3 to 18.
The optical pickup apparatus described in item (2-19) is the optical pickup apparatus described in one of items (2-1) to (2-18), wherein the phase modulation device is formed on a plurality of optical surfaces of the optical element.
The optical pickup apparatus described in item (2-20) is the optical pickup apparatus described in one of items (2-1) to (2-19), wherein-3.2 < R2/R1 < -1.9 remains unchanged when R1 denotes a paraxial radius closer to a curvature of an optical surface of the objective lens optical element and R2 denotes a paraxial radius of a curvature of the optical information recording medium side.
The objective optical element described in the item (2-21) is represented by an objective optical element of an optical pickup apparatus in which a plurality of optical elements are present and reproduction and/or recording of a plurality of pieces of information is performed by converging a luminous flux of a first wavelength λ 1 emitted from a first light source on a first optical information recording medium of a protective master of thickness t1 and a luminous flux of a second wavelength λ 2 (λ 2 > λ 1) emitted from a second light source on a second optical information recording medium of a protective master of thickness t2 (t 2 ≧ t 1), wherein at least one of the optical elements is provided with at least two regions including a central region and a peripheral region, the central region being centered on the optical axis and the peripheral region being positioned around the central region, the two regions being provided on at least one optical surface, staircase-like regions having a predetermined number of steps being formed discontinuously on the central region, and each staircase-like-shaped step portion forming a concentric axis, and therefore, a phase modulation means is provided which, in combination with the objective optical element, as a condition that the luminous flux of the first wavelength λ 1 and the second wavelength λ 2 are converged as a concentric ring.
In the objective optical element described in the item (2-21), even if the first luminous flux of the wavelength λ 1 and the second luminous flux of the wavelength λ 2 enter the objective optical element as divergent light, the phase modulation device provided with the staircase-like discontinuous region makes one of the luminous flux of the first wavelength λ 1 and the luminous flux of the second wavelength λ 2 have a phase difference so as to converge the luminous fluxes on the prescribed optical information recording medium under the condition that spherical aberration and/or wavefront aberration is corrected in conjunction with the objective optical element.
Therefore, an optical element such as a collimator lens for use in a conventional infinite type optical pickup apparatus in order to collimate the luminous flux emitted from the light source into parallel light so that the luminous flux can enter the objective optical element has proved unnecessary, and thus a reduction in size and cost of the apparatus can be achieved.
At least one optical surface of the objective optical element is divided into at least two regions including a central region centered on the optical axis and a peripheral region located around the central region, and at least one of two types of luminous fluxes respectively having a wavelength λ 1 and a wavelength λ 2 is given a phase difference as occasion demands by the phase modulation device, and therefore, the luminous flux appears on a prescribed information recording medium as diffracted light under the condition that the aberration is corrected, wherein the luminous flux of each wavelength passes through each of the divided regions.
The degree of freedom of aberration correction can be increased. It is further possible to control the occurrence of coma and astigmatism during tracking and thereby the occurrence of spherical aberration caused by temperature changes.
A second embodiment of the objective optical element and the optical pickup apparatus of the present invention will be explained as follows with reference to the drawings.
As shown in fig. 3, the optical pickup apparatus 10 emits a light flux of a wavelength λ 1 (= 650 nm) from the first semiconductor laser 11 (light source) to the first optical information recording medium 20 (DVD in the present embodiment), and emits a light flux of a wavelength λ 2 (= 780 nm) from the second semiconductor laser 12 (light source) to the second optical information recording medium 21 (CD in the present embodiment). Then, the optical pickup apparatus 10 lets these light fluxes enter as divergent light into an object lens 40 (objective optical element) which represents an optical element provided with a phase modulation device 30, to condense them on information recording surfaces 20a and 21a of a prescribed optical information recording medium, and thereby performs recording of respective pieces of information and reading of recorded information.
Incidentally, since the first semiconductor laser 11 and the second semiconductor laser 12 are used as light sources, as shown in fig. 4, the luminous fluxes of the wavelength λ 1 and the wavelength λ 2 emitted from the respective semiconductor lasers are collectively shown in fig. 3 by solid lines.
When information recording or reproduction is performed on the DVD, the light flux of the wavelength λ 1 emitted from the first semiconductor laser 11 passes through the diffraction grating 13 and is emitted by the single-direction see-through glass (half mirror) 14. Further, the light flux is blocked by the diaphragm 15 and condensed on the information recording surface 20a by the object lens 40 via the protective mother substrate 20b of the DVD.
In this case, the effect of the object lens 40 on the light flux of the wavelength λ 1 will be explained below.
Then, the light flux modulated by the information pits and reflected by the information recording surface 20a passes through the object lens 40, the diaphragm 15, the half mirror 14, and the diffraction grating (not shown) to enter the photodetector 16, and the signal output from the photodetector 16 is used to obtain a signal for reading the information recorded on the DVD.
Even if information is recorded or reproduced on the CD, the light flux of the wavelength λ 2 emitted from the second semiconductor laser 12 passes through the diffraction grating 13 and is reflected by the half mirror 14. Further, the light flux is blocked by the diaphragm 15 and condensed on the information recording surface 21a by the object lens 40 via the protective mother substrate 21b of the CD. Incidentally, for convenience, the protective mother board 21b for CDs and the protective mother board 20b for DVDs are shown with the same aperture in fig. 3.
The action of the object lens 40 on the light flux of the wavelength λ 2 in this case will be explained below.
Then, the light flux modulated by the information pits and reflected by the information recording surface 21a passes through the object lens 40, the diaphragm 15, the half mirror 14, and the diffraction grating (not shown) to enter the photodetector 16, and the signal output from the photodetector 16 is used to obtain a signal for reading the information recorded on the CD.
Further, the change in the amount of light caused by the change in the form and the change in the position of the spot on the photodetector 16 is detected for focus detection and track detection. Based on the result of the detection, a not-illustrated two-dimensional actuator moves the lens 40 so that the light flux emitted from the first semiconductor laser 11 or the light flux emitted from the second semiconductor laser can form an image on the information recording surface 20a of the DVD or the information recording surface 21a of the CD, and moves the lens 40 so that an image can be formed on a prescribed track.
As shown in fig. 5, the object lens 40 representing the objective optical element is a single lens of both aspherical surfaces, which constitutes the optical system of the optical pickup apparatus 10. On an optical surface 41 on one side (closer to the light source) of the object lens 40, the phase modulation device 30 is provided in a range of a certain height h or lower, centered on the optical axis L (referred to herein as "central region A1"), and a sawtooth-shaped diffractive annular zone 50 is provided in a range other than the central region A1 (referred to herein as "peripheral region A2").
To be more specific, the discontinuous regions 31 composed of the staircase-shaped step portions 31a in the direction parallel to the optical axis direction L form the shape of concentric rings centered on the optical axis L at the prescribed ring P, like the phase modulating device 30 on the central region A1.
As shown in fig. 6 (a), each discontinuous region 31 is composed of 5 staircase-like step portions 31a, the staircase-like step portions 31a being parallel to the direction of the optical axis. Incidentally, it is preferable that the number of the step portions 31a constituting one discontinuous region 31 is 5 or 6 (the number of steps of the discontinuous region is 4 or 5), but it may range from 4 to 7. Further, each discontinuous region 31 may also be composed of a step portion 31a having a different number of steps within the aforementioned range (4 to 7).
In the present embodiment, four discontinuous areas 31 of the phase modulation device 30 are formed at the prescribed ring P in the form of concentric rings, each centered on the optical axis L, as shown in fig. 5.
The ring P is specified to be represented by an integer part of phi (h)/2 pi, phi (h)/2 pi being a value obtained by dividing a phase function phi (h) by 2 pi, the phase function phi (h) being expressed by a value 3 using h and Bn, h representing a height from the optical axis L, and Bn representing a coefficient of an optical path difference function of nth order (n is an even number).
(value 3)
In this case, it is preferable when B 2 Coefficient h representing the second-stage optical path difference function in When the height of the position of the central area A1 farthest from the optical axis L is indicated, the following condition is satisfiedAnd (4) a foot.
0≤|φ(h in )/2π-B 2 (h in ) 2 |≤10
Further, it is preferable to satisfy the condition | B 2 (h in ) 2 |≤18。
By defining the ring P defined by the discontinuous regions 31 so that the aforementioned conditions are satisfied, it is possible to control the number of the discontinuous regions 31 within certain limits and thereby to facilitate handling of the object lens 40, and it is possible to prevent a drop in the light quantity by controlling the ratio of the amount of divergent light entering from a surface (optically functional surface) portion (for example, side edge) other than the staircase-like step portion 31a to the total light quantity in the light quantity entering the discontinuous regions 31.
Further, each of the discontinuous regions 31 is provided with a shape that does not give a phase difference to the luminous flux of the first wavelength λ 1 passing through the central region A1, but gives a phase difference to the luminous flux of the wavelength λ 2 passing through the central region A1.
Incidentally, the phase difference of the first wavelength λ 1 and the second wavelength λ 2 can be adjusted by adjusting the distance between the staircase-shaped step portions 31a constituting the discontinuous region 31, that is, by adjusting the depth d of one step of the staircase-shaped step portion 31a (see fig. 6 (a)). Therefore, the depth d of one step of the step portion 31a can also be adjusted so that the absolute value of the phase difference of the light fluxes at the first wavelength λ 1 is smaller than 0.2 π radians.
Incidentally, a method of designing the discontinuous region 31 satisfying the aforementioned conditions is already known, and thus an explanation of the method will be omitted.
On the peripheral area A2, a plurality of sawtooth-shaped diffraction annular zones 50 are formed, each centered on the optical axis L.
The diffractive annular band 50 is also provided with a form that does not diffract the light flux of the first wavelength λ 1 passing through the peripheral area A2, but diffracts the light flux of the wavelength λ 2 passing through the peripheral area A2.
Then, the effects of the object lens 40 on the light flux of the wavelength λ 1 and the light flux of the wavelength λ 2 are explained.
First, when divergent light of a wavelength λ 1 enters the peripheral area A2 and the central area A1 of the object lens 40, a light flux of the wavelength λ 1 passing through the peripheral area A2 is not diffracted by the diffractive annular zone 50, but is refracted by the aspherical surface of the object lens 40. The light flux of the wavelength λ 1 passing through the central area A1 is refracted by the aspherical surface of the object lens 40 because the phase modulation device 30 does not make it have a phase difference as before. Then, the light flux of the wavelength λ 1 entering the peripheral area A2 and the light flux of the wavelength λ 1 entering the central area A1 are condensed on the image recording surface 20a of the DVD, respectively.
On the other hand, when divergent light of the wavelength λ 2 enters the peripheral area A2 and the central area A1 of the object lens 40, the luminous flux of the wavelength λ 2 passing through the peripheral area A2 is diffracted by the diffraction annular band 50, and when the phase adjustment device 30 makes it have a prescribed phase difference, the luminous flux of the wavelength λ 2 passing through the central area A1 is diffracted.
Then, the light flux of the wavelength λ 2 passing through the peripheral area A2 is condensed by the diffractive annular zone 50 to the outer portion of the information recording surface 21a of the CD, and the light flux of the wavelength λ 2 passing through the central area A1 is condensed only on the information recording surface 21a of the CD under the condition that the aspherical aberration is corrected in combination of the diffractive action of the phase modulation device 30 and the refractive action of the object lens 40.
Incidentally, in the explanation given above, the phase modulation device 30 does not make the light fluxes of the wavelength λ 1 have the phase difference, but makes the light fluxes of the wavelength λ 2 have the phase difference. However, the present invention is not limited to this, and it is also possible to adopt a phase modulation device that does not cause the light fluxes at the wavelength λ 2 to have a phase difference, but causes the light fluxes at the wavelength λ 1 to have a phase difference.
The structure of the peripheral area A2 on the object lens 40 must be such that the divergent light of the wavelength λ 1 is correctly converged on the information recording surface of the DVD, and the divergent light of the wavelength λ 2 is converged outside the information recording surface 21a of the CD.
Thus, for example, the same phase modulation device 30 as that formed on the central area A1 may be formed on the peripheral area A2. In such a case, it is assumed that the phase modulation device 30 formed on the peripheral area A2 does not make the divergent light of the wavelength λ 1 have a phase difference, but makes the divergent light of the wavelength λ 2 have a phase difference and is diffracted.
In this case, it is preferable that the number of step portions 31a of the discontinuous region 31 provided on the phase modulation device 30 of the peripheral region A2 is smaller than the number of step portions 31a of the discontinuous region 31 provided on the phase modulation device 30 of the central region A1. It is further preferred that the number of discontinuous areas 31 provided on the phase modulation device 30 of the central area A1 is in the range of 3 to 18.
Generally, when the number of the discontinuous regions 31 increases, the number of the stepped portions 31a increases, and the diffraction efficiency improves. However, it is not necessary to improve the diffraction efficiency because the light flux of the wavelength λ 2 passing through the peripheral region A2 is not used for reproduction and/or recording of information, and the manufacturing cost of the object lens 40 can be controlled by limiting the number of the step portions 31a of the discontinuous region 31 to be within the aforementioned range.
Further, the structure of the peripheral area A2 may also be a structure having a refractive function, which is achieved by the aspherical surface shape of the object lens 40.
(example 2-1)
Next, a first example of the optical pickup apparatus 10 shown in the foregoing embodiment is explained.
In this example, the phase modulation device 30 is provided on the central area A1, which is on the optical surface on one side (closer to the light source) of the object condition 40, with a height of not more than 1.38mm from the optical axis L, the object lens 40 represents a single lens with aspherical surfaces on both sides, which is shown in fig. 5, and the sawtooth-shaped diffractive annular band 50 is provided on the peripheral area A2.
To be more specific, a plurality of discontinuous regions 31a composed of staircase-like step portions, which are parallel to the direction of the optical axis L and have a center on the optical axis L at the prescribed ring P, are formed in a concentric ring shape, like the phase modulation device 30 on the central region A1.
Incidentally, fig. 5 is a schematic diagram of the object lens 40 used in the present example. Therefore, on the object lens 40 in fig. 5, four discontinuous regions 31 are formed in the central region A1, but twelve discontinuous regions 31 are formed in the object lens actually used in the present example.
Further, each discontinuous region 31 is composed of five step portions 31a, and as shown in fig. 6 (a), the step portions 31a are arranged such that each step portion 31a projects forward as it approaches the optical axis L.
Further, the phase modulation device 30 is provided with a structure that converges the light flux of the wavelength λ 1 on the image recording surface 20a of the DVD by letting the light flux of the wavelength λ 1 have an arc of about 0.1 π at each step of the discontinuous region, and converges the light flux of the wavelength λ 2 on the image recording surface of the CD by letting the light flux of the wavelength λ 2 have a prescribed phase difference and thereby diffracting the light flux.
The diffractive annular zone 50 has a structure that diffracts the light flux of the wavelength λ 1 and thereby converges it on the image recording surface 20a of the DVD, and diffracts the light flux of the wavelength λ 2 and thereby converges it on the image recording surface 21 of the CD.
Lens data for the object lens 40 are shown in tables 2-1 and 2-2.
TABLE 2-1
Example (2-1)
| Focal length | f 1 ＝2.45mm | f 2 ＝2.52mm |
| Numerical aperture | NA1＝0.60 | NA2＝0.47 |
| Image forming magnification | m＝-1/6.8 | m＝-1/6.7 |
| Ith table Noodle | Ri | di(655nm) | ni(655nm) | di(785nm) | ni(785nm) |
| 0 | 10.0 | 10.0 | |||
| 1 | ∞ | 1.25 | 1.51436 | 1.25 | 1.51108 |
| 2 | ∞ | 7.86011 | 1.0 | 8.12781 | 1.0 |
| 3 | 1.67496 | 1.75 | 1.52915 | 1.75 | 1.52541 |
| 3’ | 1.70255 | 0.00294 | 1.52915 | 0.00294 | 1.52541 |
| 4 | -3.64079 | 1.53989 | 1.0 | 1.26219 | 1.0 |
| 5 | ∞ | 0.60 | 1.57752 | 1.20 | 1.57063 |
| 6 | ∞ |
＊ (ii) a "di" shows the distance from the ith surface to the (i + 1) th surface.
＊ (ii) a "d3" shows the distance from the third surface to the 3' th surface.
As shown in Table 2-1, when the first wavelength λ 1 emitted from the first light source 11 is 655nm, the object lens 40 established in this example has a focal length f of 2.45 mm 1 0.60 and an image forming magnification m of-1/6.8, and when the first wavelength λ 2 emitted from the second light source 21 is 785 nanometers, the object lens 40 established in this example has a focal length f of 2.52 millimeters 2 An image-side numerical aperture NA2 of 0.47 and an image forming magnification m of-1/6.7.
Each of the surface numbers 3,3' and 4 of the object lens is formed as an aspherical surface which is specified by an expression in which coefficients shown in table 2-1 and table 2-2 are substituted into the following expression (numerical value 4) and which is axisymmetric to the optical axis L.
(value 4)
In the above expression, X (h) represents an axis in the direction of the optical axis L (the direction in which light advances from the viewpoint of the symbol is positive), κ represents a constant of the cone, and a 2i Coefficients representing aspherical surfaces.
Tables 2 to 2
| Aspheric surface data | |
| The third surface (h is more than or equal to 0 and less than 1.38 mm) | |
| Coefficient of aspheric surface | κ＝-8.1403E-01 A4＝+3.2437E-03 A6＝-3.4518E-03 A8＝+5.1774E-03 A10＝-3.7006E-03 A12＝+1.3482E-03 A14＝-2.0334E-04 |
| Coefficients of optical path difference function | B2＝+7.5508E+00 B4＝-7.1441E-01 B6＝+7.9208E-02 B8＝-7.1571E-02 B10＝+1.8106E-02 |
| The (3') th surface (1.38 mm. Ltoreq. H) | |
| Coefficient of aspheric surface | κ＝-8.1000E-01 A4＝+4.4764E-03 A6＝-2.7908E-04 A8＝+2.0702E-04 A10＝-1.7861E-04 A12＝+7.4388E-05 A14＝-2.4519E-05 |
| Coefficients of optical path difference function | B2＝-8.4641E-03 B4＝-6.6051E-01 B6＝+3.4445E-01 B8＝+2.5278E-02 B10＝+4.7696E-02 |
| Surface No. 4 | |
| Coefficient of aspheric surface | κ＝-1.1984E+01 A4＝+5.6688E-03 A6＝-4.3010E-04 A8＝-3.2242E-04 A10＝-3.1994E-04 A12＝+7.6388E-05 A14＝-5.4308E-06 |
As described above, the prescribed ring P of the discontinuous region 31 is represented by the integer part of the value φ (h)/2 π by dividing λ by the optical path difference function φ (h), which is shown in the numerical value 1, with the coefficients shown in Table 2.
In the optical pickup apparatus and the object lens shown in the present example, a structure is provided in which the phase modulation device causes the luminous flux of the wavelength λ 1 to have a phase difference of about 0.1 π per step and causes the luminous flux of the wavelength λ 2 to have a prescribed phase difference. Therefore, regarding the light fluxes having the wavelength λ 1 and the wavelength λ 2 respectively passing through the central region, they can be condensed with a diffraction efficiency of about 85% for the DVD and the CD.
Further, in this structure, the diffraction annular band formed on the peripheral region is blazed for the light flux of the wavelength λ 1. Therefore, with respect to the light flux of the wavelength λ 1, for the DVD, it is possible to condense with almost 100% diffraction efficiency.
Further, for DVD and CD, it is possible to converge under the condition that spherical aberration caused by wavelength variation is appropriately corrected, because diffracted lights of the luminous flux of the wavelength λ 1 and the luminous flux of the wavelength λ 2 passing through the central area and the peripheral area can be utilized.
(example 2-2)
In the present example, as shown in fig. 7, the phase modulation device 30 is provided on a central area A1 and a peripheral area A2, the height of which from the optical axis L is 1.38mm or less, both the central area A1 and the peripheral area A2 being on an optical surface 41, the optical surface 41 being on one side (light source side) of an object lens 40 representing a single lens with aspherical surfaces on both sides.
To be more specific, a plurality of discontinuous regions 31 composed of staircase-shaped step portions 31a in a direction parallel to the optical axis L are formed in a concentric ring shape centered on the optical axis L at the prescribed ring P, like the phase adjusting device 30 on the central region A1.
Incidentally, fig. 7 is a schematic diagram of the object lens 40 used in the present example. Therefore, in the object lens 40 in fig. 7, four discontinuous regions 31 are formed on the central region A1, but four discontinuous regions 31 are formed on the object lens actually used in the present example.
Further, each discontinuous region 31 is composed of five step portions 31a, as shown in fig. 6 (B), which are disposed such that the step portions 31a project forward as they are farther from the optical axis L.
Further, even on the peripheral region A2, three discontinuous regions 31 composed of stair-like stepped portions 31a are formed in the form of concentric rings, which stepped portions 31a are parallel to the optical axis L direction with the centers of the concentric rings on the optical axis L at the prescribed ring P, as with the phase modulation device 30. Each discontinuous region 31 is composed of five step portions 31a, and as shown in fig. 6 (a), they are disposed such that the step portions 31a project forward as they are closer to the optical axis.
The phase modulation device 30 at the central area A1 is provided with a structure in which the light flux of the wavelength λ 2 is condensed on the information recording surface 21a of the CD without a phase difference, and the light flux of the wavelength λ 1 has a phase difference, and is thereby condensed on the information recording surface 20a of the DVD.
Further, the phase modulation device 30 on the peripheral area A2 is provided with a structure in which the light flux of the wavelength λ 2 is not diffracted and condensed outside the information recording surface 21a of the CD, and the light flux of the wavelength λ 1 has a phase difference, thereby being diffracted and condensed on the information recording surface 20a of the DVD.
Lens data of the object lens 40 are shown in table 3 and table 4.
Tables 2 to 3
Example (2-2)
| Focal length | f 1 ＝2.36mm | f 2 ＝2.38mm |
| Numerical aperture | NA1＝0.60 | NA2＝0.51 |
| Image forming magnification | m＝-1/8.0 | m＝-1/8.1 |
| The ith surface | Ri | di(655nm) | ni(655nm) | di(785nm) | ni(785nm) |
| 0 | 10.0 | 10.0 | |||
| 1 | ∞ | 1.25 | 1.51436 | 1.25 | 1.51108 |
| 2 | ∞ | 9.97544 | 1.0 | 10.34470 | 1.0 |
| 3 | 1.61368 | 1.80135 | 1.52915 | 1.80135 | 1.52541 |
| 3’ | 1.59522 | 0.00403 | 1.52915 | 0.00403 | 1.52541 |
| 4 | -3.40195 | 1.36321 | 1.0 | 0.99395 | 1.0 |
| 5 | ∞ | 0.60 | 1.57752 | 1.20 | 1.57063 |
| 6 | ∞ |
＊ (ii) a "di" shows the distance from the ith surface to the (i + 1) th surface.
＊ (ii) a "d3" shows the distance from the third surface to the 3' th surface.
Tables 2 to 4
| Aspheric surface data | |
| The third surface (h is more than or equal to 0 and less than 1.38 mm) | |
| Coefficient of aspheric surface | κ＝-7.6977E-01 A4＝+1.0250E-02 A6＝-1.8158E-03 A8＝-1.3917E-03 A10＝+1.9019E-03 A12＝-7.1677E-04 A14＝+1.1697E-04 |
| Coefficients of optical path difference function | B2＝-2.7871E-01 B4＝+1.0355E+00 B6＝-4.2129E-03 B8＝+4.6111E-02 B10＝-1.1018E-02 |
| The (3') th surface (1.38 mm. Ltoreq. H) | |
| Coefficient of aspheric surface | κ＝-8.6858E-01 A4＝+8.3450E-03 A6＝-1.5112E-03 A8＝+8.5363E-04 A10＝-4.0799E-04 A12＝+2.5325E-04 A14＝-3.9800E-05 |
| Coefficients of optical path difference function | B2＝+6.4315E+00 B4＝-3.6471E+00 B6＝+2.6586E-01 B8＝+2.2288E-01 B10＝-6.7202E-02 |
| Surface No. 4 | |
| Coefficient of aspheric surface | κ＝-3.0329E+01 A4＝-8.3902E-03 A6＝+3.5649E-03 A8＝+2.5562E-03 A10＝-2.4827E-04 A12＝-3.8271E-04 A14＝+3.3834E-05 A16＝+1.4882E-05 |
As shown in tables 2-3, when the first wavelength λ 1 emitted from the first light source 11 is 655nmMeter, focal length f of the object lens 40 established in this example 1 Is 2.36 mm, the image-side numerical aperture NA1 is 0.60, the image forming magnification m is-1/8.0, and the focal length f of the object lens 40 established in this example is when the second wavelength λ 2 emitted from the second light source 21 is 785nm 2 Is 2.38 mm, the image-side numerical aperture NA2 is 0.51, and the image forming magnification m is-1/8.1.
Each surface of the object lens 40 of numbers 3,3' and 4 is formed as an aspherical surface, which is specified by an expression in which coefficients shown in tables 2-3 and 2-4 are replaced to a value of 4, the spherical surface being axisymmetric to the optical axis L.
As described above, the prescribed ring P of the discontinuous region 31 is expressed by an integer part of the value φ (h)/2 π, which is obtained by dividing the optical path difference function φ (h), which is shown in the numerical value 1, wherein the coefficients shown in tables 2-4 are replaced with λ.
In the optical pickup apparatus and the object lens shown in the present example, there is provided a structure in which the phase modulation device formed on the central region does not cause the light fluxes of the wavelength λ 2 to have the phase difference. Therefore, with respect to the light flux of the wavelength λ 2 passing through the central region, it can be condensed with almost 100% diffraction efficiency for CD. Further, with respect to the light flux of the wavelength λ 1 passing through the central region, it can be condensed with a diffraction efficiency of almost 870% for the DVD.
Further, good correction of aberrations is possible because diffracted light of light fluxes of the wavelength λ 1 passing through the central area and the peripheral area is condensed on the DVD. It is further possible to obtain a sufficient amount of light for recording of information because the refracted light of the light flux of the wavelength λ 2 is condensed on the CD.
The compatibility with DVD and CD can be proven sufficient from the foregoing description.
(examples 2 to 3)
In this example, as shown in fig. 8, the phase modulation device 30 is provided on the central area A1 with a height of 1.25mm or less from the optical axis L, and on the optical surface 41 of one side (light source side) of the object lens 40, the object lens 40 represents a single lens having aspherical surfaces on both sides, and the refractive structure 60 serving as a refractive lens is provided on the peripheral area A2.
To be specific, as with the phase modulation device 30, on the central region A1, a plurality of discontinuous regions 31 composed of staircase-like step portions 31a are formed in the shape of concentric rings in which the staircase-like step portions 31a are parallel to the direction of the optical axis L, the concentric rings being centered on the optical axis L at the prescribed ring P.
Incidentally, fig. 8 is a schematic diagram of the object lens 40 used in the present example. Therefore, on the object lens 40 in fig. 8, four discontinuous regions 31 are formed on the central region A1, but three discontinuous regions 31 are formed on the object lens actually used in the present example.
Further, each discontinuous region 31 is composed of five step portions 31a, as shown in fig. 6 (B), which are arranged such that the step portions 31a project forward as they are farther from the optical axis L.
The phase modulation device 30 is provided with a structure in which the light flux of the wavelength λ 2 is condensed on the information recording surface 21a of the CD without a phase difference, but the light flux of the wavelength λ 1 has a phase difference and is thereby diffracted and condensed on the information recording surface 20a of the DVD.
Lens data for the object lens 40 are shown in tables 2-5 and tables 2-6.
Tables 2 to 5
Example (2-3)
| Focal length | f 1 ＝2.39mm | f 2 ＝2.40mm |
| Numerical aperture | NA1＝0.60 | NA2＝0.47 |
| Image forming magnification | m＝-1/10.0 | m＝-1/10.1 |
| Ith table Noodle | Ri | di(655nm) | ni(655nm) | di(785nm) | ni(785nm) |
| 0 | 10.0 | 10.0 | |||
| 1 | ∞ | 1.25 | 1.51436 | 1.25 | 1.51108 |
| 2 | ∞ | 15.03953 | 1.0 | 15.41078 | 1.0 |
| 3 | 1.61123 | 1.75 | 1.52915 | 1.75 | 1.52541 |
| 3’ | 1.60874 | -0.00045 | 1.52915 | -0.00045 | 1.52541 |
| 4 | -3.66417 | 1.35047 | 1.0 | 0.97922 | 1.0 |
| 5 | ∞ | 0.60 | 1.57752 | 1.20 | 1.57063 |
| 6 | ∞ |
＊ (ii) a "di" shows the distance from the i-th surface to the i + 1-th surface.
＊ (ii) a "d3" shows the distance from the third surface to the 3' th surface.
Tables 2 to 6
| Aspheric surface data | |
| The third surface (h is more than or equal to 0 and less than 1.25 mm) | |
| Coefficient of aspheric surface | κ＝-8.3747E-01 A4＝+4.5312E-03 A6＝+2.1482E-03 A8＝-1.4416E-03 A10＝+1.3269E-03 A12＝-5.3392E-04 A14＝+5.8100E-05 |
| Coefficients of optical path difference function | B2＝-2.2474E-02 B4＝+1.3947E+00 B6＝-2.9624E-01 B8＝+1.9503E-01 B10＝-5.1181E-02 |
| The (3') th surface (1.25 mm. Ltoreq. H) | |
| Coefficient of aspheric surface | κ＝-8.4706E-01 A4＝+3.2551E-03 A6＝+1.1222E-03 A8＝+3.1848E-04 A10＝-2.9650E-05 A12＝-4.3419E-05 A14＝-8.9795E-05 |
| Coefficients of optical path difference function | B2 B4 B6 B8 B10 |
| Surface No. 4 | |
| Coefficient of aspheric surface | κ＝-6.7689E+00 A4＝+1.9274E-02 A6＝+4.2139E-04 A8＝-2.6460E-03 A10＝-5.6909E-04 A12＝+5.6178E-04 A14＝-9.1534E-05 |
As shown in tables 2 to 5, when the first wavelength λ 1 emitted from the first light source 11 is 655nm, the focal length f of the object lens 40 established in this example 1 Is 2.39 mm, the image-side numerical aperture NA1 is 0.60, the image forming magnification m is-1/10.0, and the focal length f of the object lens 40 established in this example is when the second wavelength λ 2 emitted from the second light source 21 is 785nm 2 It was 2.40 mm, the image-side numerical aperture NA2 was 0.47, and the image forming magnification m was-1/10.1.
Each surface of the object lens 40 of numbers 3,3' and 4 is formed as an aspherical surface, which is specified by an expression in which coefficients shown in tables 2 to 5 and tables 2 to 6 are replaced to a numerical value of 4, the spherical surface being axisymmetric to the optical axis L.
As described above, the prescribed loop P of the discontinuous region 31 is expressed by an integer part of the value φ (h)/2 π, which is obtained by dividing the optical path difference function φ (h), which is shown in the numerical value 1, with the coefficients shown in Table 6 replaced with λ.
In the optical pickup apparatus and the object lens shown in the present example, there is provided a structure in which the phase modulation device formed on the central region does not cause the light fluxes of the wavelength λ 2 to have the phase difference. Therefore, with respect to the light flux of the wavelength λ 2 passing through the central region, it can be condensed with almost 100% diffraction efficiency for CD. Further, with respect to the light flux of the wavelength λ 1 passing through the central region, it can be condensed with high diffraction efficiency for DVD.
Further, good correction of aberrations is possible because diffracted light of light fluxes of the wavelength λ 1 passing through the central area and the peripheral area is condensed on the DVD. It is further possible to obtain a sufficient amount of light for recording of information because the refracted light of the light fluxes of the wavelength λ 1 and the wavelength λ 2 is condensed on the DVD and the CD of the peripheral area, respectively.
The compatibility with DVD and CD can be proven sufficient from the foregoing description.
(examples 2 to 4)
In the present example, as shown in fig. 9, the phase modulation device 30 is provided on a central area A1 and a peripheral area A2, the central area having a height of 1.42mm or less from the optical axis L, and on an optical surface 41 on one side (light source side) of an object lens 40, the object lens 40 represents a single lens having aspherical surfaces on both sides.
To be specific, as with the phase modulation device 30, on the central region A1, a plurality of discontinuous regions 31 composed of staircase-like step portions 31a are formed in the shape of concentric rings in which the staircase-like step portions 31a are parallel to the direction of the optical axis L, the concentric rings being centered on the optical axis L at the prescribed ring P.
Incidentally, fig. 9 is a schematic diagram of the object lens 40 used in the present example. Therefore, on the object lens 40 in fig. 9, four discontinuous regions 31 are formed on the central region A1, but three discontinuous regions 31 are formed on the object lens actually used in the present example.
Further, each discontinuous region 31 is composed of five step portions 31a, as shown in fig. 6 (B), which are arranged such that the step portions 31a project forward as they become farther from the optical axis L.
Further, three discontinuous regions 31 composed of staircase-like stepped portions 31a parallel to the direction of the optical axis L are formed just on the peripheral region A2 in the shape of concentric rings centered on the optical axis L at the prescribed ring P as in the phase modulating device 30. Each discontinuous region 31 is formed of five step portions 31a, which are disposed such that the step portions 31a project forward as they are farther from the optical axis L, as shown in fig. 6 (B).
The phase modulation device 30 on the central area A1 is provided with a structure in which the light flux of the wavelength λ 2 is diffracted and condensed on the information recording surface 21a of the CD with a phase difference, but the light flux of the wavelength λ 1 is diffracted and condensed on the information recording surface 20a of the DVD without a phase difference.
The phase modulation device 30 on the peripheral area A2 is provided with a structure in which the light flux of the wavelength λ 2 is made to have a phase difference and is thus diffracted so as to be condensed on the information recording surface 21a of the CD, but the light flux of the wavelength λ 1 has no phase difference and is condensed on the information recording surface 20a of the DVD.
Lens data for the object lens 40 are shown in tables 2-7 and tables 2-8.
Tables 2 to 7
Examples (2-4)
| Focal length | f 1 ＝2.80mm | f 2 ＝2.81mm |
| Numerical aperture | NA1＝0.60 | NA2＝0.47 |
| Image forming magnification | m＝-1/15.0 | m＝-1/15.1 |
| Ith table Noodle | Ri | di(655nm) | ni(655nm) | di(785nm) | ni(785nm) |
| 0 | 10.0 | 10.0 | |||
| 1 | ∞ | 1.25 | 1.51436 | 1.25 | 1.51108 |
| 2 | ∞ | 33.63106 | 1.0 | 34.01354 | 1.0 |
| 3 | 1.84007 | 1.90 | 1.52915 | 1.90 | 1.52541 |
| 3’ | 1.84007 | 0.0 | 1.52915 | 0.0 | 1.52541 |
| 4 | -4.92462 | 1.60894 | 1.0 | 1.22646 | 1.0 |
| 5 | ∞ | 0.60 | 1.57752 | 1.20 | 1.57063 |
| 6 | ∞ |
＊ (ii) a "di" shows the distance from the ith surface to the (i + 1) th surface.
＊ (ii) a "d3" shows the distance from the third surface to the 3' th surface.
Tables 2 to 8
| Aspheric surface data | |
| The third surface (h is more than or equal to 0 and less than 1.42 mm) | |
| Coefficient of aspheric surface | κ＝-8.0672E-01 A4＝+4.9515E-03 A6＝+1.3804E-04 A8＝+1.1130E-04 A10＝-4.4350E-05 A12＝+1.9589E-05 A14＝-4.9821E-06 |
| Coefficients of optical path difference function | B2＝-1.1116E+00 B4＝-7.3368E-01 B6＝-2.9250E-01 B8＝-2.0187E-01 B10＝+4.3038E-02 |
| The (3') th surface (1.425 mm. Ltoreq. H) | |
| Coefficient of aspheric surface | κ＝-8.0672E-01 A4＝+4.9515E-03 A6＝+1.3804E-04 A8＝+1.1130E-04 A10＝-4.4350E-05 A12＝+1.9589E-05 A14＝-4.9821E-06 |
| Coefficients of optical path difference function | B2＝+5.7606E+00 B4＝-3.8733E+00 B6＝+3.8208E-01 |
| Surface No. 4 | |
| Coefficient of aspheric surface | κ＝-2.6508E+01 A4＝+3.4985E-03 A6＝+2.4350E-04 A8＝-1.8017E-04 A10＝-8.7274E-05 A12＝+5.7455E-06 A14＝+3.2581E-06 |
As shown in tables 2 to 7, when the first wavelength λ 1 emitted from the first light source 11 is 655nm, the focal length f of the object lens 40 established in this example 1 Is 2.80 mm, the image-side numerical aperture NA1 is 0.60, the image forming magnification m is-1/15.0 when viewed from the second light source 21The focal length f of the object lens 40 established in this example when the second wavelength λ 2 of the emission is 785nm 2 It was 2.81 mm, the image-side numerical aperture NA2 was 0.47, and the image forming magnification m was-1/15.1.
Each surface of the object lens 40 of numbers 3,3' and 4 is formed as an aspherical surface, which is specified by an expression in which coefficients shown in tables 2 to 7 and tables 2 to 8 are replaced to a value of 4, the spherical surface being axisymmetric to the optical axis L.
As described above, the prescribed ring P of the discontinuous region 31 is expressed by an integer part of the value φ (h)/2 π, which is obtained by dividing the optical path difference function φ (h), which is shown in the numerical value 1, wherein the coefficients shown in tables 2-8 are replaced with λ.
In the optical pickup apparatus and the object lens shown in the present example, there is provided a structure in which phase modulating devices each formed on the central region and the peripheral region cause the luminous fluxes of the wavelength λ 2 to have a phase difference. Therefore, diffracted light of light flux of wavelength λ 2 passing through the central area and the peripheral area can be utilized, so that the light flux can be converged on the DVD under the condition that spherical aberration caused by the wavelength variation is appropriately corrected.
Further, a sufficient amount of light can be obtained for information recording because the light refracted by the wavelength λ 1 of the central area and the peripheral area is condensed on the DVD.
The compatibility of DVD and CD can be proven sufficient from the foregoing description.
The phase modulation device 30 on the central area A1 is provided with a structure in which the light fluxes of the wavelength λ 2 have a phase difference and are thus diffracted to be condensed on the information recording surface 21a of the CD, and the light fluxes of the wavelength λ 1 are condensed on the information recording surface 20a of the DVD without having a phase difference.
Further, the phase modulation device 30 on the peripheral area A2 is provided with a structure in which the light fluxes of the wavelength λ 2 have a phase difference and are thus diffracted to be condensed on the information recording surface 21a of the CD, and the light fluxes of the wavelength λ 1 are condensed on the information recording surface 20a of the DVD without having a phase difference.
Incidentally, the optical element on which the phase modulation device 30 is formed is not limited to the above-described objective optical element (object lens 40), and, for example, as shown in fig. 10, the phase modulation device 30 may also be formed in the form of a flat plate on an optical element 70 (see fig. 11 (a) -11 (C)) that is disposed on the adjacent object lens 40.
To be more specific, five discontinuous regions 31 composed of staircase-shaped step portions 31a parallel to the direction of the optical axis L are formed in concentric rings on a central region A1 of an optical surface 71 on one side (light source side) of a flat plate-shaped optical element 70 on the optical axis L at a prescribed ring center, as with the phase modulation device 30. Each discontinuous region 31 is composed of four step portions 31a, and the discontinuous region 31 shown in fig. 11 (a) is provided with a structure in which each step portion 31a projects forward as approaching the optical axis L, as shown in fig. 6 (C), and the discontinuous region 31 shown in fig. 11 (B) is provided with a structure in which each step portion 31a projects forward as approaching the optical axis L, as shown in fig. 11 (B), as farther from the optical axis L.
Further, the phase modulation device 30 may be provided on such a region A1 and the peripheral region A2, and the central region A1 may be provided with a structure in which the stepped portion 31a projects forward as it approaches the optical axis L, and the peripheral region A2 may be provided with a structure in which the stepped portion 31a projects forward as it is farther from the optical axis L, as in the case of the flat plate-shaped optical element 70 shown in fig. 11 (C).
As shown in fig. 12 (a), the discontinuous region 31 of the central region A1 may also be disposed so that the step portion 31a projects forward as it approaches the optical axis L, and the discontinuous region 31 of the peripheral region A2 may also be disposed so that the step portion 31a projects forward as it is farther from the optical axis L.
It is further possible to adopt a structure in which the discontinuous region 31 of the central region A1 is disposed such that the step portion 31a projects forward as it approaches the optical axis L, and the refractive structure 60 is provided in the peripheral region A2, as shown in fig. 12 (B).
The discontinuous regions 31 of the central region A1 and the peripheral region A2 may also be disposed so that the step portion 31a projects forward as it approaches the optical axis L, as shown in fig. 12 (C).
Further, the phase modulation device 30 may be formed on a plurality of optical surfaces of one object lens, however, for example, on each of the optical surfaces of the light source side and the optical information recording medium side, the description thereof is omitted.
Further, the image forming magnification m may be made in the range of-0.149 to-0.049.
When R1 denotes the paraxial radius of the optical surface of the objective optical lens on the light source side, and R2 denotes the paraxial radius of the optical surface on the optical information recording medium side, the following expression is preferably maintained.
-3.2＜R2/R1＜-1.9
According to the second embodiment, even if the luminous flux of the first wavelength λ 1 and the luminous flux of the second wavelength λ 2 enter the objective optical element as divergent light, the phase modulation device provided with the discontinuous region causes at least one of the luminous flux of the first wavelength λ 1 and the luminous flux of the second wavelength λ 2 to have a phase difference, and by incorporating the objective optical element, the luminous fluxes are condensed on the prescribed optical information recording medium under the condition that spherical aberration is corrected. Therefore, an optical element such as a collimator lens proves unnecessary, and reduction in size and cost of the apparatus can be achieved.
(third embodiment)
The light-converging optical system described in the item (3-1) is a light-converging optical system in which an optical element portion is provided, the optical element portion including at least an objective optical element and being composed of one or more optical elements, a light flux of a first wavelength λ 1 (630 nm ≦ λ 1 ≦ 680 nm) is converged on an information recording surface of a first optical information recording medium having a protective mother plate thickness t1, and a light flux of a second wavelength λ 2 (760 nm ≦ λ 2 ≦ 680 nm) is converged on an information recording surface of a second optical information recording medium having a protective mother plate thickness t2 (t 1 < t 2), wherein optical system magnifications m1 and m2 for light flux of a first wavelength λ 1 and light flux of a second wavelength λ 2, respectively, satisfy m1 ≠ 0 and m2 ≠ 0, respectively, and a common region is provided on an optical surface of at least one of the optical element sections, the light flux of the first wavelength λ 1 passes therethrough and is converged on an information recording surface of the first optical information recording medium, and the light flux of the second wavelength λ 2 passes therethrough and is converged on an information recording surface of the second optical information recording medium, a plurality of annular-band-type optical functional surfaces are continuously formed through the step surfaces, and x parallel to an optical axis of the step surfaces satisfies 5.5 μm ≦ x ≦ 7 μm, the annular-band-type optical functional surfaces having centers on the optical axis.
In the light converging optical system described in the item (3-1), a common region where the light flux of the first wavelength λ 1 passes through the optical surface of the at least one optical element portion and converges on the information recording surface of the first optical information recording medium immediately after the passage is provided in the light converging optical system, and the light flux of the second wavelength λ 2 converges on the information recording surface of the second optical information recording medium immediately after the passage is provided, and the common region is provided with an annular stripe type optical function surface and step surfaces each having a distance x which is parallel to the optical axis and satisfies 5.5 μm ≦ x ≦ 7 μm.
When the distance x parallel to the optical axis is less than 5.5 μm, the deviation from the distance becomes larger, the distance being substantially five times as large as the light flux of the wavelength λ 1, which lowers the utilization efficiency for the light fluxes of the wavelength λ 1 and the wavelength λ 2, which are condensed on the information recording surfaces of the first and second information recording media, respectively. Even if the distance x parallel to the optical axis is larger than 7 μm, the deviation from this distance becomes larger, and the distance is substantially five times as large as the light flux of the wavelength λ 1, which lowers the utilization efficiency for the light fluxes of the wavelength λ 1 and the wavelength λ 2, which are condensed on the information recording surfaces of the first and second information recording media, respectively. The light use efficiency is a ratio of the amount of light of the light-converging spot to the amount of light incident on the objective optical element of the light-converging optical system.
Therefore, the light flux of the first wavelength λ 1 passing through the adjacent annular band type optical function surface has an optical path difference of 5 × λ 1, but the light use efficiency can be enhanced because the phases are coincident with each other on the light condensing spot on the first optical information recording medium. Further, the light flux of the second wavelength λ 2 passing through the adjacent annular band-type optical functional surface has an optical path difference of 4 × λ 2, but the light use efficiency can be enhanced because the phases are coincident with each other on the light-converging spot on the second optical information recording medium.
Further, optical system magnifications m1 and m2 for the luminous flux of the first wavelength λ 1 and the luminous flux of the second wavelength λ 2, respectively, satisfy m1 ≠ 0 and m2 ≠ 0, respectively. Therefore, the light flux of the finite system is used to be condensed onto the first or second optical information recording medium, and thus, it is not necessary to provide an optical element such as a collimator lens for collimating the light flux, and it is possible to reduce the number of components and to reduce the size of equipment such as an optical pickup apparatus having a light condensing optical system, thereby reducing the cost.
The light converging optical system described in item (3-2) is the light converging optical system described in item (3-1), wherein the number of the endless belt-type optical functional surfaces is one of 4 to 60.
In the light converging optical system described in the item (3-2), the number of the endless belt type optical function surfaces is one of 4 to 60. Therefore, the number of the optical functional surfaces of the endless belt type can be made an appropriate value for varying the mother substrate thicknesses t1 and t2, and therefore, sufficient light utilization efficiency can be obtained and the optical functional surfaces of the endless belt type can be easily manufactured. When the number of the optical functional surfaces of the endless belt type is less than 4, it is difficult to realize a sufficient optical function of the optical functional surfaces of the endless belt type for the optical information recording medium having the thin protective mother substrate. When the number of the optical functional surfaces of the endless belt type is more than 60, the proportion of the area of the step surface through which the light flux does not pass becomes larger, and the light utilization efficiency is lowered.
The invention described in the item (3-3) is the light condensing optical system described in the item (3-1) or (3-2), wherein the optical element provided with the common region is a connection lens.
In the light converging optical system described in the item (3-3), the optical element provided with the common region is a connection lens. Therefore, it is possible to have other corrective effects by providing the optical functional surface of the annular band type and the step surface on the objective optical element, which are different from those described in the item (3-1) or (3-2). It is also possible to use a general and inexpensive objective optical element without either the annular band type optical function surface or the step surface.
The light converging optical system described in item (3-4) is the light converging optical system described in any one of items (3-1) to (3-3), wherein the optical element provided with the common region is the objective optical element described above.
In the light converging optical system described in the item (3-4), the optical element provided with the common region is an objective optical element. Therefore, it is possible to reduce the number of parts of the light converging optical system and achieve size reduction and cost reduction.
The light-converging optical system described in item (3-5) is the light-converging optical system described in any one of items (3-1) to (3-4), wherein the optical system magnification m1 satisfies-1/3 ≦ m1 ≦ 0.
In the light-converging optical system described in the item (3-5), the optical system magnification m1 satisfies-1/3. Ltoreq. M1. Ltoreq.0. It is therefore possible to prevent a large-sized light-converging optical system caused by the positive optical system magnification m 1. It is further possible to prevent the wavefront aberration of the light fluxes condensed on the first and second optical information recording media from being larger due to an error characteristic caused when the magnification m1 of the optical system is smaller than-1/3 and the light source is deviated from the optical axis.
The light-converging optical system described in item (3-6) is the light-converging optical system described in any one of items (3-1) to (3-5), wherein the optical system magnification m2 satisfies-1/3 ≦ m2 ≦ 0.
In the light-converging optical system described in the item (3-6), the optical system magnification m2 satisfies-1/3. Ltoreq. M2. Ltoreq.0. It is therefore possible to prevent the use of a large-sized apparatus of the light converging optical system due to the fact that the magnification m2 of the optical system is positive. It is further possible to prevent the wavefront aberration of the light fluxes condensed on the first and second optical information recording media from being larger due to an error characteristic caused when the magnification m2 of the optical system is smaller than-1/3 and the light source is deviated from the optical axis.
The light condensing optical system described in the item (3-7) is the light condensing optical system described in any one of the items (3-1) to (3-6), wherein a focal length f1 of the light flux for the first wavelength λ 1 satisfies f1 ≦ 4mm.
In the light converging optical system described in the item (3-7), the focal length f1 of the light flux for the first wavelength λ 1 satisfies f1 ≦ 4mm. It is therefore possible to make the focal length f1 small, thereby reducing the size of equipment such as an optical pickup device equipped with a light converging optical system.
The light condensing optical system described in the item (3-8) is the light condensing optical system described in any one of the items (3-1) to (3-7), wherein a focal length f2 of the light flux for the second wavelength λ 2 satisfies f2 ≦ 4mm.
In the light converging optical system described in the item (3-8), the focal length f2 for the light flux of the second wavelength λ 2 satisfies f2 ≦ 4mm. It is therefore possible to make the focal length f2 small, thereby reducing the size of equipment such as an optical pickup apparatus equipped with a light converging optical system.
The light converging optical system described in the item (3-9) is the light converging optical system described in any one of the items (3-1) to (3-8), wherein a numerical aperture NA1 on the image side for the luminous flux of the first wavelength λ 1 satisfies 0.55 ≦ NA1 ≦ 0.67.
The image-side numerical aperture is an image-side numerical aperture defined as a result of limitation of light flux that contributes to a light-converging spot on an optimum image point of the optical information recording medium. However, when a plurality of optical elements are present, the numerical aperture on the image side means the numerical aperture on the image side of the optical element which is closest to the optical information recording medium in the light converging optical system.
In the light converging optical system described in the item (3-9), the image-side numerical aperture NA1 for the light flux of the first wavelength λ 1 satisfies 0.55 ≦ NA1 ≦ 0.67. Therefore, the light flux can be appropriately condensed in accordance with the recording density of the first optical information recording medium for information.
The light converging optical system described in the item (3-10) is the light converging optical system described in any one of the items (3-1) to (3-9), wherein a numerical aperture NA2 on the image side for a light flux of the second wavelength λ 2 satisfies 0.44 ≦ NA2 ≦ 0.55.
In the light converging optical system described in the item (3-10), the image-side numerical aperture NA2 for the light flux of the second wavelength λ 2 satisfies 0.44 ≦ NA1 ≦ 0.55. Therefore, the light flux can be appropriately condensed in accordance with the recording density of the second optical information recording medium for information.
The light condensing optical system described in the item (3-11) is the light condensing optical system described in any one of the items (3-1) to (3-10), wherein the common region is provided with a diffractive structure portion in which incident light is diffracted by the annular zone type optically functional surface.
In the light converging optical system described in the item (3-11), the common region is provided with a diffractive structure portion in which incident light is diffracted by the annular band type optically functional surface. It is therefore possible to reduce beam aberration of the light flux, which is condensed on each of the first and second optical information recording media, by diffraction of the diffraction structure portion, and thereby to significantly reduce the position of the focal point on the optical axis to one point.
The light converging optical system described in item (3-12) is the light converging optical system described in item (3-11), wherein the order of diffraction K1 of diffracted light having the largest diffraction efficiency among diffracted light having the first wavelength λ 1 diffracted by the diffractive structure portion is 5, and the order of diffraction K2 of diffracted light having the largest diffraction efficiency among diffracted light having the second wavelength λ 2 diffracted by the diffractive structure portion is 4.
In the light converging optical system described in the item (3-12), the order of diffraction K1 of diffracted light having the largest diffraction efficiency among diffracted lights having the first wavelength λ 1 diffracted by the diffractive structure portion is 5, and the order of diffraction K2 of diffracted light having the largest diffraction efficiency among diffracted lights having the second wavelength λ 2 diffracted by the diffractive structure portion is 4. It is possible to enhance the light use efficiency of the luminous flux condensed on the first optical information recording medium because the diffraction efficiency is maximized by the fifth order diffracted light of the first wavelength λ 1. Along with this, the light utilization efficiency of the light flux condensed on the second optical information recording medium can also be enhanced because the diffraction efficiency is maximized by the fourth-order diffracted light of the second wavelength λ 2.
The light-converging optical system described in item (3-13) is the light-converging optical system described in any one of items (3-1) to (3-10), wherein each of the first wavelength λ 1 and the second wavelength λ 2 passing through the annular-band type optical functional surface appears in a direction refracted by the annular-band type optical functional surface.
In the light converging optical system described in the item (3-13), each of the first wavelength λ 1 and the second wavelength λ 2 passing through the annular band type optical functional surface appears in a direction refracted by the annular band type optical functional surface. Thus, the light flux refracted at the first wavelength λ 1, which has passed through the adjacent annular band type optical functional surface because the phases are coincident with each other on the light condensing spot on the first optical information recording medium, has an optical path length difference of about 5 × λ 1, but the light use efficiency can be enhanced. Further, the light flux refracted at the second wavelength λ 2, which has passed through the adjacent annular band type optical functional surface because the phases are coincident with each other on the light converging spot on the second optical information recording medium, has an optical path difference of about 4 × λ 2, but can enhance the light use efficiency. Further, the number of the optical functional surfaces of the annular band type can be reduced as compared with the case for providing the diffraction structure portion, so that the manufacturing of the light condensing optical system is easy.
The optical pickup apparatus described in the item (3-14) is an optical pickup apparatus having a first light source that emits a light flux of a wavelength λ 1, a second light source that emits a light flux of a wavelength λ 2, and the light condensing optical system described in any one of the items (3-1) to (3-13), wherein the light flux of the wavelength λ 1 emitted from the first light source is condensed by the light condensing optical system on an information recording surface of the first optical information recording medium so as to perform at least one of recording and reproduction of information, and the light flux of the wavelength λ 2 emitted from the second light source is condensed by the light condensing optical system on an information recording surface of the second optical information recording medium so as to perform at least one of recording and reproduction of information.
Information is recorded by condensing the light flux emitted from the light condensing optical system through the protective mother substrate of the optical information recording medium on the information recording surface and recording the information on the information recording surface.
Information is reproduced by condensing the light flux emitted from the light condensing optical system through the protective mother substrate of the optical information recording medium on the information recording surface and reproducing the information on the information recording surface.
The optical pickup apparatus described in item (3-14), which has therein a first light source that emits a luminous flux of a first wavelength λ 1, a second light source that emits a luminous flux of a second wavelength λ 2, and the light converging optical system described in any one of items (3-1) to (3-13), and converges the luminous fluxes on the image recording surfaces of the first optical information recording medium and the second optical information recording medium so as to perform at least one of recording and reproduction of information. Thus, the optical pickup apparatus has the effect described in any one of items (3-1) to (3-13), and condenses the light flux of the first wavelength λ 1 on the information recording surface of the first optical information recording medium by the light condensing optical system to perform any one of information recording and reproduction, and condenses the light flux of the second wavelength λ 2 on the information recording surface of the second optical information recording medium by the light condensing optical system to perform any one of information recording and reproduction.
The optical pickup apparatus described in item (3-15) is the optical pickup apparatus described in item (3-14), wherein the first light source and the second light source are integrally integrated.
In the optical pickup apparatus described in the item (3-15), the first light source and the second light source are integrally integrated. Thereby, the first light source and the second light source are integrally united, which makes the optical pickup apparatus small in size.
The third embodiment will be explained below with reference to the drawings.
First, the optical pickup apparatus 1 in the present embodiment will be explained with reference to fig. 13. Fig. 13 is a schematic configuration diagram of an optical pickup apparatus 1, the optical pickup apparatus 1 being provided with an object lens 214 relating to the present embodiment.
The optical pickup apparatus 1 in the present embodiment is an apparatus that condenses the light flux L emitted from the semiconductor laser light source 211 on a CD 221 or a DVD 220 to perform recording and reproduction of information, the CD 221 or the DVD 220 representing an example of an optical information recording medium.
As shown in fig. 13, the optical pickup apparatus 1 is composed of a semiconductor laser light source 250, a beam splitter 212, an aperture 213, an object lens 214, a two-dimensional actuator 215, a cylindrical lens 216, a convex lens 217, and a photodetector 230, the semiconductor laser light source 250 emitting a luminous flux, the beam splitter 212 transmitting the luminous flux emitted from the semiconductor laser light source 250 and branching off the luminous flux reflected by the DVD221 or the CD222, the aperture 213 for the luminous flux passing through the beam splitter 212, the object lens 214 representing a light converging optical system (optical element portion, objective optical element) converging the luminous flux passing through the aperture 213 on the DVD221 or the CD222, the two-dimensional actuator 215 moving the object lens 214 in the direction of the optical axis and in the direction parallel to and perpendicular to the peripheral edge of the information recording surface of the DVD221 or the CD222, the cylindrical lens 216 causing the luminous flux branched off on the beam splitter 212 to have astigmatism, and the photodetector 230 detecting the reflected light from the DVD221 or the CD222. Further, a DVD221 or a CD222 may be mounted in the optical pickup apparatus 1.
The object lens 124 is a single lens having both-side aspherical surfaces, and is composed of an incident surface 241 and a light exit surface 242 from which light flux emitted from the semiconductor laser light source 250 enters, and a flange portion 214a provided at the outer periphery from the light exit surface 242 at the DVD221 or the CD222. The flange portion 214a makes it possible to easily fix the object lens 214 to the optical pickup apparatus 1. Further, the flange portion 214a can enhance the accuracy of easy fixing because it has a surface extending in a direction substantially perpendicular to the optical axis L of the object lens 214. The optical axis of the object lens 214 in fig. 13 is assumed to be an optical axis L (not shown) which is separated from an optical axis L1 corresponding to the light flux of the DVD221 and an optical axis L2 corresponding to the light flux of the CD222. As a material of the object lens 214, a plastic of an optically transparent material, such as a paraffin type resin, may be used. By using plastic, it is possible to realize the object lens 214 with light weight and low cost, and easily produce the diffraction structure section S described below.
Further, in the semiconductor laser light source 250, a light source section 211 such as an LD (laser diode) that emits a light flux having an operation standard wavelength λ 01 of 655nm to be condensed on the DVD221, and a light source section 212 such as an LD that emits a light flux having an operation standard wavelength λ 02 of 785nm to be condensed on the CD222 are integrally provided (one package). In the standards for DVD and CD, respectively, the operating standard wavelengths λ 01 and λ 02 are standard wavelengths. The wavelengths of the light fluxes emitted from the light source portions 211 and 212 are actually the operating wavelengths λ 11 and λ 12, respectively. The operating wavelengths λ 11 and λ 12 are those wavelengths having deviations from the operating standard wavelengths λ 01 and λ 02, respectively, due to temperature changes and mode hopping in the light source sections 211 and 212.
The DVD221 is provided with an information recording surface 221a on which information is recorded, and a protective mother substrate 221b formed on the information recording surface 221a protects the recorded information. The CD222 is provided with an information recording surface 222a on which information is recorded, and a protective mother substrate 222b formed on the information recording surface 222a protects the recorded information. As a material of each of the protective mother board 221b and the protective mother board 222b, an optically transparent material such as polycarbonate resin (PC) may be used.
The object lens 214 has a structure for converging a limited type of light flux. In the case of such a structure in which a finite type of luminous flux is used, in the case of the luminous flux of the converging operating wavelength λ 11, the optical system magnification m1 satisfies m1 ≠ 0, and in the case of the luminous flux of the converging operating wavelength λ 12, the optical system magnification m2 satisfies m2 ≠ 0.
Now, the operation of the optical pickup apparatus 1 will be explained as follows, referring to fig. 13, 14 and 15. Fig. 14 is a cross-sectional view of the object lens 214 in a case where light is condensed on the DVD 221. Fig. 15 is a cross-sectional view of the object lens 214 in a situation where light is converged on the CD222. In fig. 14 and 15, the flange portion 214a of the object lens 214 is omitted. First, a case where information recording or reproduction is performed on the DVD221 will be explained.
First, the light flux of the operating wavelength λ 11 is emitted from the light source section 211 of the semiconductor laser light source 250. Then, the light flux passes through the beam splitter 212 disposed between the semiconductor laser light source 250 and the object lens 214, and it is blocked by the aperture 213 to proceed to the object lens 214.
Then, the light flux enters the incident surface 241 of the object lens 214 and comes out of the light exit surface 242 to be condensed on the information recording surface 221a of the DVD221 as the focal point L1a. In both cases of information recording and reproduction to the DVD221, the light flux is condensed on the information recording surface 222 as the focal point L1a. The intensity of the light flux emitted from the semiconductor laser light source 250 is established so that the intensity in the case of recording information is higher than that in the case of reproducing information.
When reproducing information recorded on the DVD221, the light flux coming out of the object lens 216 is further modulated by the information pits and reflected to the information recording surface 221a. The reflected light flux passes through the object lens 216 and the aperture 213 again in order, and is reflected and branched by the beam splitter 212 serving as an optical path changing means. The branched light flux is given astigmatism by the cylindrical lens 216 and enters the photodetector 230 through the concave lens 217. The photodetector 230 detects incident light from the concave lens 217 to output a signal, and the signal for reading information recorded on the DVD221 is obtained by use of the output signal.
Further, a change in the amount of light caused by the change in the form and the change in the position of the spot on the photodetector 230 is detected, and detection for focusing and detection for recording tracks are performed. Based on the detection result, the two-dimensional actuator 215 moves the object lens 214 in the direction of the optical axis L1 so that the light flux emitted from the light source portion 211 can be aberrated into an image on the information recording surface 221a of the DVD221, the information recording surface 221a serving as the focal point L1a. Along with this, the object lens 216 is moved in a direction parallel to the information recording surface 221a and perpendicular to the periphery of the recording track so that the luminous flux emitted from the semiconductor laser light source 250 can be aberrated into an image on the prescribed recording track of the information recording surface 221a.
The foregoing also applies to a case for recording or reproducing information to the CD222. When recording or reproducing information to or from the CD222, the light flux emitted from the light source section 212 passes through the beam splitter 212 and the aperture 213, then enters the incident surface of the object lens 214 and comes out from the light exit surface 242 to be condensed on the information recording surface 222a of the CD222 as the focal point L2 a. When reproducing information of the CD222, the light flux reflected on the information recording surface 222a passes through the object lens 214 and the aperture 213 to be reflected and branched on the beam splitter 212, and enters the photodetector 230 through the cylindrical lens 216 and the concave lens 217.
In the case of applying a light flux onto the DVD221 in accordance with the recording density of the DVD221, the numerical aperture NA1 on the image side (on the optical information recording medium side) is required to be large. In contrast, in the case of applying a light flux onto the CD222 in accordance with the recording density of the CD222, the numerical aperture NA2 on the image side (on the optical information recording medium side) is required to be small. Therefore, as shown in fig. 14 and 15, when a light flux is applied to the DVD221, a light flux having a large diameter is caused to enter the object lens 214, the center of which is on the optical axis L1. When the light flux is caused to enter the CD222, the light flux having a relatively small diameter is caused to enter the object lens 214, the light flux being centered on the optical axis L2.
As shown in fig. 14 to 16, the incident surface 241 of the object lens 214 is an optically functional region having a shape of a concentric ring centered on the optical axis L. Fig. 16 is a top view of an entrance surface 241 in object lens 214. The incident surface 241 has therein a common area portion 241a through which light fluxes pass when the light fluxes are converged on the DVD221 and the CD222, respectively, and a DVD dedicated area 241b through which light fluxes pass only when the light fluxes are converged on the DVD221, respectively. On the common area portion 241a, a sawtooth diffraction structure portion S is formed which is composed of concentric annular bands. The diffraction structure portion S has a function of diffracting light fluxes, which enter the diffraction structure portion.
Fig. 17 is a cross-sectional view of the diffraction structure S in the common area portion 241a. As shown in fig. 17, the diffractive structure portion S that diffracts the incident light flux has an annular band type optical function surface S1 and a step surface S2 provided between the annular band type optical function surfaces S1.
Further, on the object lens 214, a base aspherical surface (base aspherical surface) is formed, which is expressed by the aforementioned numerical value 5 for the expression in the form of an aspherical surface.
Number 5
In this case, Z represents a distance in the optical axis direction (the advancing direction of the incident light flux entering the incident surface 241 is assumed to be positive). Further, h denotes a value (height from the optical axis) of an axis perpendicular to the optical axis direction. R is 0 Representing the paraxial radius of curvature. The symbol κ denotes the cone constant. A. The i Representing the coefficients of the aspheric surface. P i Denotes the index of the aspherical surface.
In general, the pitch of the annular bands is defined by the optical path difference function Φ. To be more specific, the optical path difference function Φ is expressed as the aforementioned value 6 in millimeters.
Sign lambda 0 Denotes the operating standard wavelength, an example of which is λ 01 And λ 02 . Sign lambda B The manufacturing wavelength (blaze wavelength) is shown. K represents the number of diffraction orders that makes the diffraction efficiency the largest of all diffraction orders. The manufacturing wavelength is such that the diffraction efficiency is 100% in the K order. The diffraction efficiency is a ratio of the light output of a predetermined order in the diffracted light of the diffraction structure portion to the light output of all orders of the diffracted light.
The number n of the annular bands can be expressed by the expression phi/lambda 0 And (4) obtaining. The order of diffracted light is positive in the direction toward the optical axis. C 2i Representing the optical path difference function coefficients.
Also, lens data of the object lens 216 is shown in the following table 3-1.
TABLE 3-1
| The jth surface | rj | dj(655mm) | nj(655mm) | dj(785mm) | nj(785mm) |
| 0 | 23.37 | 23.37 | |||
| 1 (numerical aperture) Footpath) | ∞ | 0.0(φ 4.674mm) | 0.0(φ 4.674mm) | ||
| 2 | 4.51893 | 2.90000 | 1.52915 | 2.90000 | 1.52541 |
| 2’ | 3.62857 | -0.01111 | 1.52915 | -0.01111 | 1.52541 |
| 3 | -6.37280 | 1.97 | 1.0 | 1.69 | 1.0 |
| 4 | ∞ | 0.6 | 1.57752 | 1.2 | 1.57063 |
| 5 | ∞ |
In Table 3-1, rj mm represents the paraxial radius of curvature, dj mm represents the distance of the optical axis, and nj represents the refractive index. Further, j represents the number of surfaces. With respect to the number of surfaces j,0 shows the object point, and 1 shows the aperture surface of the aperture 213. Further, regions showing the incident surfaces 241, j =2 and 2' of the object lens 214 with respect to each of the surface numbers j,2 and 2' are assumed as the second surface and the 2' th surface, respectively. The second surface shows a common area portion 241a of the incident surface 241. In this case, the common area portion 241a is assumed to be an area in which the height h from the optical axis shown in FIG. 14 satisfies 0 < h ≦ 1.763 mm. The 2' nd surface shows a DVD-dedicated area portion 241b of the incident surface 241, and in this case, the DVD-dedicated area portion 241b is assumed to be an area in which the height from the optical axis satisfies 1.763mm < h.
With respect to the number of surfaces j,3 shows the light exit surface 242,4 of the object lens 214 shows the protective mother substrate for the optical information recording medium (the protective mother substrates 221a and 222a for the DVD221 and CD222, respectively), and 5 shows the information recording surface for the information recording medium (the information recording surfaces 221b and 222b for the DVD221 and CD222, respectively). The distance dj on the optical axis shows the distance from the jth surface to the (j + 1) th surface. Specifically, the distance d2 'shows the distance from the 2 nd surface to the 2' nd surface.
The paraxial radius rj of curvature, the distance dj on the optical axis and the refractive index nj show values on the surface corresponding to the number j of surfaces, respectively. In particular, the wavelength λ corresponding to the operating standard is shown for the optical axis dj and the refractive index nj 11 (= 655 nm) and operating standard wavelength lambda 12 (value of (= 785 nm)),these two operating standard wavelengths correspond to DVD221 and CD222. When working standard wavelength lambda 11 When the light flux enters the object lens 214, the light flux goes through the objectThe focal length f1 on the optical axis L1 from the principal point of the bulk lens 214 to the focal point L1a on the information distance surface 221a is 3.40 mm. Further, when the standard wavelength λ of operation 11 When the light flux of (2) enters, the numerical aperture NA1 on the image side of the object lens 214 is 0.60. Further, when the standard wavelength λ of operation 01 When the light flux of (2) enters, the magnification m1 of the optical system is-1/6. The thickness of the protective motherboard 221b is 0.6 mm.
Further, when the standard wavelength λ of operation 12 When the light flux enters the object lens 214, the focal length f2 on the optical axis L1 from the principal point of the object lens 214 to the focal point L2a on the information distance surface 222a is 3.47 mm. Further, when the standard wavelength λ of operation 12 When the light flux of (2) enters the object lens 214, the image-side numerical aperture NA2 of the object lens 214 is 0.44. Further, when the standard wavelength λ of operation 02 When the light flux of (2) enters, the magnification m2 of the optical system is-1/5.9. The thickness of the protective motherboard 221b is 1.2 millimeters.
Then, table 3-2 shows the taper constants κ and aspherical surface coefficients A of the second surface, the 2' th surface and the third surface of the object lens 214 1 And an index Pi to be substituted into the expression Z of the basic aspherical surface of the previous value 5. Table 3-2 further shows the optical path difference function coefficient C i Coefficient of coefficient C i Will be substituted into the optical path difference function phi of the previous value 6.
TABLE 3-2
| Second surface (0 < h.ltoreq.1.763mm | ||
| Coefficient of aspheric surface | κ＝1.6560×E-0 A1＝2.9133×E-3 A2＝9.0124×E-4 A3＝-5.2721×E-4 A4＝3.2835×E-5 A5＝1.0713×E-5 A6＝-9.3059×E-7 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
| Optical path difference function (manufacturing wavelength lambda) B ＝1mm ) | C2＝-4.0745×E-0 C4＝1.7303×E-1 C6＝4.6687×E-2 C8＝-1.9946×E-2 C10＝2.7347×E-3 | |
| 2' surface (h > 1.763mm | ||
| Coefficient of aspheric surface | κ＝-1.8190×E-0 A1＝7.4752×E-3 A2＝-6.8159×E-3 A3＝2.0970×E-3 A4＝-2.7108×E-4 A5＝1.6262×E-5 A6＝-1.3867×E-7 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
| Optical path difference function (manufacturing wavelength lambda) B ＝1mm) | C2＝-7.2021×E+1 C4＝-6.4664×E-0 C6＝1.5091×E-0 C8＝-2.1705×E-1 C10＝3.4868×E-2 | |
| Third surface | ||
| Coefficient of aspheric surface | κ＝4.8233×E-0 A1＝1.7272×E-2 A2＝-1.0292×E-2 A3＝4.9860×E-3 A4＝-1.4772×E-3 A5＝2.4514×E-4 A6＝-1.6118×E-5 | P14.0 P26.0 P38.0 P410.0 P512.0 P614.0 |
Incidentally, the manufacturing wavelength λ B Shown together with the optical path difference appropriated coefficient Ci. Production wavelength λ in Table 3-2 B Is a trial value, which is 1 mm. Further, "E-t (t is an integer)" means "10 -t ”。
Then, the number xd of steps of the step surface S2 of the diffraction structure portion S on the second surface (common area portion 241 a) of the object lens 214 is shown in the following table 3-3.
Tables 3 to 3
| Number of endless belts | Initial height hs of circular band | Height hl of endless belt | Step amount xd at |
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | 0.000 0.222 0.314 0.385 0.445 0.498 0.546 0.591 0.633 0.672 0.709 0.745 0.779 0.812 0.844 0.874 0.904 0.934 0.962 0.990 1.017 1.044 1.070 1.096 1.122 1.147 1.171 1.195 1.219 1.243 1.266 1.290 1.312 1.335 | 0.222 0.314 0.385 0.445 0.498 0.546 0.591 0.633 0.672 0.709 0.745 0.779 0.812 0.844 0.874 0.904 0.934 0.962 0.990 1.017 1.044 1.070 1.096 1.122 1.147 1.171 1.195 1.219 1.243 1.266 1.290 1.312 1.335 1.357 | 0.00620 0.00620 0.00621 0.00622 0.00623 0.00624 0.00624 0.00625 0.00626 0.00627 0.00628 0.00628 0.00629 0.00630 0.00631 0.00632 0.00633 0.00633 0.00634 0.00635 0.00636 0.00637 0.00638 0.00639 0.00640 0.00640 0.00641 0.00642 0.00643 0.00644 0.00645 0.00646 0.00647 0.00648 |
| 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | 1.357 1.380 1.402 1.423 1.445 1.467 1.488 1.509 1.530 1.551 1.572 1.593 1.613 1.634 1.655 1.675 1.696 1.716 1.736 1.757 1.777 | 1.380 1.402 1.423 1.445 1.467 1.488 1.509 1.530 1.551 1.572 1.593 1.613 1.634 1.655 1.675 1.696 1.716 1.736 1.757 1.777 1.783 | 0.00649 0.00650 0.00651 0.00652 0.00653 0.00653 0.00654 0.00655 0.00656 0.00657 0.00658 0.00659 0.00660 0.00661 0.00662 0.00663 0.00664 0.00665 0.00666 0.00667 |
The data in tables 3 to 3 are values of the second surface (common area portion 241 a) in which the manufacturing wavelength λ is made B At 655nm, which represents the work function corresponding to DVDAs a standard wavelength lambda 01 The diffraction order K1 for maximizing the diffraction efficiency was 5, and the diffraction efficiency of the object lens 214 shown in tables 3-1 and 3-2 was 100%. Tables 3-3 show the number of annular zones per diffractive annular zone, the end height hl mm per diffractive annular zone and the step amount xd mm at the end height hl. The number of annular bands increases when each annular band is positioned farther from the optical axis. The start height hs, the end height hl, and the step amount xd are shown in fig. 17. The starting points for the starting height hs and the ending height hl are assumed to be on the optical axis L.
The object lens 214 having the diffractive structural portion S diffracts the operating standard wavelength λ 01 The diffraction structure part S is designed based on the starting height hs, the ending height hl, and the step amount xd for each diffraction annular zone in table 3-3. In the diffraction structure part S satisfying the data in tables 3 to 3, the wavelength λ was determined in accordance with the operation standard 01 For working standard wavelength lambda 02 For an operating standard wavelength λ corresponding to a CD 02 The number of diffraction orders K2 having the highest diffraction efficiency of (2) is 4. Thus, the objectThe lens 214 diffracts the operating standard wavelength λ corresponding to the CD 02 The fourth-order diffracted light is thereby caused to appear, and the diffraction efficiency thereof is 93%.
In the case where the step corresponding to the first-order luminous flux having the wavelength corresponding to the DVD is provided, the diffraction efficiency of the luminous flux having the wavelength corresponding to the CD becomes substantially 91%, as before. Thus, the step structure corresponding to the fifth order diffraction of the present embodiment has higher diffraction efficiency for the luminous flux corresponding to the wavelength of the CD, and therefore, the light use efficiency is also higher, as compared with the step structure corresponding to the wavelength corresponding to the first order luminous flux of the DVD. In practice, the operating wavelength λ 11 And λ 12 Into the object lens 214.
When providing the step corresponding to the fifth order diffraction on the step surface S2, it is preferable that the step amount xd nm satisfies 5.5 μm < xd < 7 μm. The reason for this is as follows.When the step amount xd nm is less than 5.5 μm, the deviation from the step amount, which is the operating wavelength λ, becomes larger 01 Is five times the luminous flux of (a) and is respectively lambda for the operating wavelength 01 And λ 02 The light utilization efficiency of the light fluxes of the two wavelengths, which are condensed on the DVD221 and CD 222D information recording surfaces, respectively, is reduced accordingly. The step amount xd shown in Table 3-3 satisfies the condition 5.5. Mu. M.ltoreq.x.ltoreq.7. Mu.m.
For the foregoing reason, the object lens 214 is provided with the diffraction structure portion S having the step amount xd shown in Table 3-3, and the object lens 214 diffracts light so that the fifth order diffracts the operating wavelength λ 11 The diffraction efficiency of the incident light flux is maximized. Thus, the light diffracted in the fifth order, which makes the operating wavelength lambda, can be condensed onto the DVD221 11 The diffraction efficiency of (2) is maximized, and the light utilization efficiency can be enhanced. Together with this, the fourth order diffracted light can be converged on the CD222, the fourth order diffracted light having the operating wavelength λ 12 The diffraction efficiency of (2) is maximized, and the light utilization efficiency can also be enhanced.
Further, the diffraction function of the diffraction structure portion S can reduce the optical aberration of light condensed on the DVD221 or the CD222. Therefore, the position of the focal point on the optical axis can be substantially made to be one point.
Further, the incident light fluxes of the finite system are used to be condensed on the optical information recording media so as to be used for the operating wavelengths λ, respectively 11 And λ 12 The optical system magnifications m1 and m2 of (2) satisfy that m1 ≠ 0 and m2 ≠ 0, respectively. Therefore, it is not necessary to provide an optical element for collimating the light flux, such as a collimator lens, and it is possible to reduce the number of components, and to reduce the size and cost of the optical pickup apparatus 1.
Preferably, the magnifications m1 and m2 of the optical system satisfy-1/3. Ltoreq. M1 < 0 and-1/3. Ltoreq. M2 < 0, respectively. When each of the optical system magnifications m1 and m2 is smaller than-1/3, wavefront aberration of the light flux to be condensed on the optical information recording medium becomes large due to an error characteristic caused by the light source deviating from the optical axis. When each of the optical system magnifications m1 and m2 is a positive value, the object lens 214 becomes larger. In the present embodiment, the optical system magnifications m1 and m2 are within the preferable ranges.
Further, a common area portion 214a having the diffraction structure portion S is provided at the incident surface 241 of the object lens 214. For this reason, compared with a structure in which the diffraction structure portion S is provided separately from the object lens 213, the number of components of the light condensing optical system can be reduced to achieve size reduction and cost reduction.
Since tables 3 to 3 show that the number of annular zones of the diffraction structure part S is 55, the number of annular zones is in the range of 4 to 60. Therefore, the diffraction structure portion S can be easily manufactured, and sufficient light use efficiency can be obtained. The foregoing reason is that when the number of annular zones is less than 4, it is difficult to achieve a sufficient diffraction function of the diffraction structure portion S for the DVD221 having a thin protective mother substrate, and when the number of annular zones is more than 60, the pitch thereof is small and it is difficult to manufacture the diffraction structure portion S. Further, when the number of the endless belts is more than 60, the area ratio for the step surface S2 where no diffraction is performed on the diffraction structure portion S becomes larger, and the diffraction efficiency is lowered.
The light source sections 211 and 212 are integrally integrated to form a semiconductor-structured light source 250, and the two light sources 211 and 212 each have a different operating standard wavelength. Therefore, the semiconductor laser light source can be reduced in size to reduce the size of the optical pickup apparatus 1.
Respectively for the operating wavelength lambda 11 And λ 12 The focal length f1 and the focal length f2 respectively satisfy f1 is less than or equal to 4 nanometers and f2 is less than or equal to 4 nanometers. Thereby, the focal length f1 and the focal length f2 can be made small to reduce the size of the optical pickup apparatus 1.
Further, for the operating wavelength λ 11 The numerical aperture NA1 on the image side satisfies 0.55. Ltoreq. NA 1. Ltoreq.0.67. Thereby, the light flux corresponding to the information recording density for the DVD221 can be condensed appropriately, so that the information of the DVD221 can be recorded and reproduced appropriately.
Further, for the operating wavelength λ 12 The numerical aperture NA2 on the image side satisfies 0.44. Ltoreq. NA 2. Ltoreq.0.55. Thereby, the light flux corresponding to the information recording density for the CD222 can be condensed appropriately, so that the information of the CD222 can be recorded and reproduced appropriately.
It is also possible to adopt a structure that provides a structural portion through which the direction of light emission is determined only by refraction, instead of the diffraction structural portion S on the common area portion 241a of the object lens 214. One of the foregoing examples is a structure that provides a phase shift structure section described in "patent document 1". In this case, there is a certain amount of step adjacent to the annular band-shaped concave portion or the annular band-shaped convex portion, the step corresponding to the operating standard wavelength λ 01 Of the fifth order of diffraction, the operating standard wavelength λ 01 Corresponding to a DVD. In other words, the standard wavelength λ is operated by the adjacent annular band-shaped concave portion or annular band-shaped convex portion 01 Has a certain number of steps, which is given as almost 5 times the optical path difference of the outgoing light, which results in the structure providing an annular band-shaped concave portion or an annular band-shaped convex portion having the number of steps on the common area. When the annular band-shaped concave portion or the annular band-shaped convex portion is provided with the number of steps, if corresponding to the operation standard wavelength λ of the CD 02 Is passed through an operation standard wavelength lambda adjacent to the concave portion or the convex portion of the annular band type 02 Is given an optical path difference equal in number to 4 times the light emission.
Thus, the operating standard wavelength λ of the optical functional surface of the adjacent annular band type is passed 11 Has a luminous flux of 5 x lambda 12 The optical path difference of (b), the light utilization efficiency thereof can be enhanced because the phases coincide with each other on the light converging spot of the DVD 221. Further, the operating standard wavelength λ of the adjacent optical functional surface of the annular band type is passed 12 Has a luminous flux of 4 x lambda 12 But the light utilization efficiency thereof can be enhanced because the phases coincide with each other on the light converging spot of the CD222.
In the case of providing the annular band-shaped concave portion or the annular band-shaped convex portion with a certain amount of steps, the operating wavelength λ to be converged on the CD222 12 The light utilization efficiency of the light flux is higher than that of the light flux to be condensed on the CD222 in the latter case where the amount of steps occurs in the light flux with the optical path difference of about 5 times the operating standard wavelength λ 01, and in the latter case where the annular band-shaped concave portion or the annular band-shaped convex portion is provided with the amount of steps occurring in the light flux with the optical path difference of about 1 time the conventional operating standard wavelength λ 01. That is, regarding the light use efficiency, the light use efficiency in the structure in which the light flux having the optical path difference of about 5 times the operation standard wavelength λ 01 occurs is higher than the light use efficiency in the structure in which the light flux having the optical path difference of about 1 time the operation standard wavelength λ 01 occurs. Further, when the annular band type concave portions or the annular band type protrusions are provided, the number of the annular band type concave portions or the annular band type protrusions may be madeThe number of portions is smaller than the number of the annular band-type optical functional surfaces S1 providing the diffraction structure portion S, thereby making the light converging optical system easy to manufacture.
Incidentally, the common area portion 241a is provided on the object lens 214 in the structure of the present embodiment, however, the present invention is not limited to this structure. For example, a structure may also be adopted in which an object lens without a common area portion and a separate connection lens with a common area portion are provided. In this case, it is possible to manufacture the object lens 214 having another correction effect by providing the optical function surface of the annular zone type and the step surface different from the optical function surface S1 of the annular zone type and the step surface S2, respectively, on the object lens 214. Further, a general and inexpensive object lens having neither an annular band type optical function surface nor a step surface can be used. A structure may also be adopted which uses a light converging optical system in which an object lens having no common area portion and a connection lens having a common area portion are integrally integrated.
The embodiments of the present invention have been explained above. However, the present invention is not always limited to the devices and methods in the aforementioned embodiments, and may be modified in accordance with the circumstances within a range in which the object of the present invention can be achieved and the effect of the present invention can be obtained.
(fourth embodiment)
In order to solve the above-mentioned problems, the present invention described in item (4-1) is an optical pickup device which performs reproduction and/or recording of a plurality of pieces of information by condensing luminous flux of a first wavelength λ 1 (630 nm ≦ λ 1 ≦ 680 nm) emitted from a first light source on a first optical information recording medium having a protective master of thickness t1 and condensing luminous flux of a second wavelength λ 2 (760 nm ≦ λ 2 ≦ 810 zxft 3242) emitted from a second light source on a second optical information recording medium having a protective master of thickness t2 (t 2 > t 1), by means of a light condensing optical system having a plurality of optical elements including an objective optical element, wherein optical system magnifications m1 and m2 of luminous flux of a first wavelength λ 1 and luminous flux of a second wavelength λ 2 for an objective optical element respectively satisfy m1 ≠ 0 and m2 ≠ 0, respectively, a plurality of annular-band-type optical function surfaces centered on an optical axis continuously form a step surface on at least one optical surface passing through one side of at least one optical element, and a common region is provided in which refracted light of luminous flux of the first wavelength λ 1 and refracted light of luminous flux of the second wavelength λ 2 generated by the plurality of annular-band-type optical function surfaces are converged on an information recording surface of a prescribed optical information recording mediumAbove and in COMA 1 (λ 1 rms) represents a COMA of a wavefront aberration of a light converging spot formed on an information recording surface of the first optical information recording medium by a light flux having the first wavelength λ 1 entering the light converging optical system with an inclination of an angle of view of 1 °, and 2 (λ 2 rms) denotes that the light flux having the second wavelength λ 2 entering the light converging optical system obliquely at the viewing angle of 1 ° is formed at the second optical information recordingSatisfying 0.8 x COMA on the assumption of COMA aberration of wavefront aberration of a light-converging spot on an information recording surface of a medium 2 ≤COMA 1 ≤1.2×COMA 2 。
On at least one optical surface of at least one optical element among a plurality of optical elements constituting a light converging optical system, a common region for emitting light flux of a first wavelength λ 1 and light flux of a second wavelength λ 2 as refracted light is formed and converged on an information recording surface of a prescribed optical information recording medium, and an annular optical function surface is formed by the common region.
The annular optically functional surface is represented by annular bands that are substantially concentric rings centered on the optical axis on the surface of the optical element. A radially continuous step surface is formed adjacent to the annular optically functional surface.
Although the light flux passing through each of the annular optical function surfaces is given a dimensional phase difference corresponding to the step surface, the annular optical function surface in the present invention has no function of diffracting the incident light flux, although it has a function of refracting the incident light flux.
The annular optically functional surface is formed only on at least the common area, and it may also be formed on other portions of one optical surface than the common area. The annular optical-function surface may be further formed on a plurality of optical-function surfaces of the plurality of optical elements.
Thus, for example, a ring-shaped optical function surface may be formed on an optical surface closer to the light source or an optical surface closer to the information recording medium provided on the object lens representing the optical element, and further a ring-shaped optical function surface may be formed on each of a plurality of optical surfaces of the optical element of the optical pickup device, such as a ring-shaped optical function surface formed on each optical surface.
In the present invention described in the item (4-1), the optical system magnifications m1 and m2 of the light fluxes of the first wavelength λ 1 mainly for DVDs and the second wavelength λ 2 mainly for CDs, respectively, satisfy m1 ≠ 0 and m2 ≠ 0, respectively, that is, in a limited type of optical pickup apparatus in which the light flux of each wavelength enters as divergent light or convergent light for the objective lens optical element, the light flux of each wavelength passing through the common area of the optical element is emitted as refracted light to the optical information recording medium.
Further, the light converging optical system is established so that a light flux of the first wavelength λ 1 entering the light converging optical system obliquely from the 1 ° angle of view forms a COMA of the wavefront aberration of the light converging spot on the information recording surface of the first optical information recording medium 1 COMA of wavefront aberration of light converging spot formed on information recording surface of second optical information recording medium for light flux of second wavelength λ 2 obliquely entering light converging optical system from 1 ° angle of view 2 (lambda.2 rms) at 0.8 × COMA 2 ≤COMA 1 ≤1.2×COMA 2 Within the range.
In the limited type of optical pickup apparatus, off-axis coma (off-axis coma) for reproduction and/or recording of CDs and DVDs can be appropriately corrected, and deterioration of optical performance in, for example, tracking can be prevented in advance. Further, the positioning of the object lens in the process of assembling to the optical pickup apparatus is easy, and thus it is possible to improve productivity and prevent deterioration of optical performance based on aging change due to mechanism abrasion caused by moving different types of lenses and light sources.
Further, as used in a conventional infinite type optical pickup apparatus, an optical element that collimates a luminous flux emitted from a light source into parallel light so that the luminous flux can enter a collimator lens of an objective optical element proves unnecessary, and a reduction in size and cost of the apparatus can be achieved.
The optical pickup apparatus described in item (4-2) is the optical pickup apparatus described in item (4-1), wherein the number of the endless belt-type optical function surfaces formed on the at least one optical surface of the optical element is one of 4 to 30.
In the optical pickup apparatus described in item (4-2), the same effect as in item (4-1) can be obtained, and the number of the optical functional surfaces of the endless belt type and the step surfaces can be limited to a certain number or less, and therefore, in the divergent light and the convergent light entering the optical surfaces, the amount of light entering the optical functional surfaces of the non-endless belt type (the step surfaces and the other surfaces) can be controlled, which prevents a decrease in the amount of light.
The optical pickup apparatus described in item (4-3) is the optical pickup apparatus described in item (4-1) or item (4-2), wherein the optical element provided with the common area is a connection lens.
In the optical pickup apparatus described in item (4-3), the same effects as in item (4-1) or item (4-2) can be obtained, and by providing a common region on the connection lens constituting the light converging optical system without necessity of disposing an optical element for providing the common region, it becomes possible to reduce the number of parts of the optical pickup apparatus.
The optical pickup apparatus described in item (4-4) is the optical pickup apparatus described in any one of items (4-1) to (4-3), wherein the optical element provided with the common area is an objective optical element.
In the optical pickup apparatus described in item (4-4), the same effects as any one of items (4-1) to (4-3) can be obtained, and by providing a common region on the objective optical element constituting the light converging optical system without necessity of disposing an optical element for providing the common region, it becomes possible to reduce the number of parts of the optical pickup apparatus.
The optical pickup apparatus described in item (4-5) is the optical pickup apparatus described in any one of items (4-1) to (4-4), wherein the first light source and the second light source are integrally combined.
In the optical pickup apparatus described in item (4-5), the same effect as that of any one of items (4-1) to (4-4) can be obtained, and sharing of the optical element by integrally combining the first light source and the second light source, making the optical path of the light flux of the first wavelength λ 1 and the optical path of the light flux of the second wavelength λ 2 the same makes it possible to reduce the number of components of the optical pickup apparatus.
The optical pickup apparatus described in item (4-6) is the optical pickup apparatus described in any one of items (4-1) to (4-5), wherein the optical system magnification m1 satisfies-1/3 ≦ m1 ≦ 0.
In the optical pickup apparatus described in item (4-6), the same effect as that of any one of item (4-1) to item (4-5) can be obtained, and the negative value of the magnification of the optical system is limited to a certain value or more, that is, the distance from the light source to the information recording surface is limited. Generally, the smaller the magnification, the more compact the optical pickup device is, but the larger the absolute value of the magnification, the larger the coma aberration in tracking, and the larger the deterioration of the light converging spot. Therefore, when the balance between them is taken into consideration, it is preferable that the optical system magnification satisfies-1/3. Ltoreq. M1. Ltoreq.0.
The optical pickup apparatus described in item (4-7) is the optical pickup apparatus described in any one of items (4-1) to (4-6), wherein the optical system magnification m2 satisfies-1/3 ≦ m2 ≦ 0.
In the optical pickup apparatus described in item (4-7), the same effects as any one of items (4-1) to (4-6) can be obtained, and size reduction of the optical pickup apparatus and prevention of deterioration of the light condensing spot are simultaneously achieved.
The optical pickup apparatus described in item (4-8) is the optical pickup apparatus described in any one of items (4-1) to (4-7), wherein a focal length f1 of the objective optical element for the light flux of the first wavelength λ 1 satisfies f1 ≦ 4mm.
In the optical pickup apparatus described in item (4-8), the same effects as any one of item (4-1) to item (4-7) can be obtained, and the distance from the objective optical element to the information recording surface is limited, which makes it possible to reduce the size of the optical pickup apparatus.
The optical pickup apparatus described in item (4-9) is the optical pickup apparatus described in any one of items (4-1) to (4-8), wherein a focal length f2 of the objective optical element for a light flux of the second wavelength λ 2 satisfies f2 ≦ 4mm.
In the optical pickup apparatus described in item (4-9), the same effects as any one of item (4-1) to item (4-8) can be obtained, and the distance from the objective optical element to the information recording surface is limited, which makes it possible to reduce the size of the optical pickup apparatus.
The optical pickup apparatus described in the item (4-10) is the optical pickup apparatus described in any one of the items (4-1) to (4-9), wherein a numerical aperture NA1 of a spot on which light of the light flux of the first wavelength λ 1 is condensed satisfies 0.55 ≦ NA1 ≦ 0.67.
The optical pickup apparatus described in the item (4-11) is the optical pickup apparatus described in any one of the items (4-1) to (4-10), wherein a numerical aperture NA2 of a spot condensed by light of a light flux of the second wavelength λ 2 satisfies 0.44 ≦ NA2 ≦ 0.55.
The optical pickup device described in item (4-12) is the optical pickup device described in any one of items (4-1) to (4-11), wherein the COMA 1 Satisfy COMA 1 ≤0.040(λ 1rms)。
The optical pickup device described in item (4-13) is the optical pickup device described in any one of items (4-1) to (4-12), wherein the COMA 2 Satisfy COMA 2 ≤0.040(λ 2rms)。
The optical pickup apparatus described in the item (4-14) is the optical pickup apparatus described in any one of the items (4-1) to (4-13), wherein a phase difference P1 caused when the light flux of the first wavelength λ 1 passes through the annular band type optical function surface satisfies 0.2 × 2 π ≦ P1, and a phase difference P2 caused when the light flux of the second wavelength λ 2 passes through the annular band type optical function surface satisfies 0.2 × 2 π ≦ P2.
The light converging system described in the item (4-15) is a light converging optical system of an optical pickup apparatus having a plurality of optical elements including an objective optical element and converging a light flux of a first wavelength λ 1 (630 nm ≦ λ 1 ≦ 680 nm) emitted from a first light source to a second light source having a wavelength of a light of a second wavelength λ 1 (630 nm ≦ λ 1 ≦ 680 nm)Reproducing and/or recording of a plurality of pieces of information is performed by condensing light fluxes of a second wavelength λ 2 (760 nm ≦ λ 2 ≦ 810 nm) emitted from a second light source on a first optical information recording medium of a protective master having a thickness t2 (t 2 > t 1), and by condensing light fluxes of a second wavelength λ 2 (760 nm ≦ λ 2 ≦ 810 nm) emitted from a second light source on a second optical information recording medium of a protective master having a thickness t2 (t 2 > t 1), wherein optical system magnifications m1 and m2 for light fluxes of a first wavelength λ 1 and light fluxes of a second wavelength λ 2 of an objective optical element, respectively, satisfy m1 ≠ 0 and m2 ≠ 0, respectively, and a plurality of annular band-type optical function surfaces centered on an optical axis are continuously formed on a step surface of an optical surface on at least one optical element side, a common region is provided in which refracted light fluxes of the first wavelength λ 1 and refracted light fluxes of the second wavelength λ 2, both of the plurality of annular band-type optical function surfaces, are generated on a prescribed information recording medium, and are condensed on an information recording surface of the prescribed optical information recording medium A 1 (λ 1 rms) represents the COMA aberration of the wavefront aberration of the light condensing spot formed on the information recording surface of the first optical information recording medium by the light flux having the first wavelength λ 1 entering obliquely at the angle of view of 1 °, and 2 (λ 2 rms) represents a COMA aberration of a wavefront aberration of a light condensing spot formed on an information recording surface of the second optical information recording medium by a light flux having the second wavelength λ 2 entering the light condensing optical system obliquely at an angle of view of 1 °, and satisfies 0.8 × COMA 2 ≤COMA 1 ≤1.2×COMA 2 。
In the light converging system described in the item (4-15), the optical system magnification ratios m1 and m2 of the light fluxes of the first wavelength λ 1 mainly for DVD and the second wavelength λ 2 mainly for CD respectively satisfy m1 ≠ 0 and m2 ≠ 0, that is, in the limited-type optical pickup apparatus in which the light flux of each wavelength enters as divergent light or convergent light for the objective optical element, the light flux of each wavelength passing through the common area of the optical element is emitted as refracted light to the optical information recording medium.
Further, a light converging optical system is established so as to be composed ofA luminous flux of the first wavelength λ 1 having an angle of view of 1 ° obliquely entered into the light converging optical system forms a COMA of a wavefront aberration of a light converging spot on an information recording surface of the first optical information recording medium 1 COMA of wavefront aberration of light converging spot formed on information recording surface of second optical information recording medium for light flux of second wavelength λ 2 obliquely entering light converging optical system from 1 ° angle of view 2 (lambda.2 rms) at 0.8 × COMA 2 ≤COMA 1 ≤1.2×COMA 2 Within the range.
In the limited type of optical pickup apparatus, off-axis coma (off-axis coma) for reproduction and/or recording of CDs and DVDs can be appropriately corrected, and deterioration of optical performance in, for example, tracking can be prevented in advance. Further, the positioning of the object lens in the process of assembling to the optical pickup apparatus is easy, and thus it is possible to improve productivity and prevent deterioration of optical performance based on aging variation due to movement of different types of lenses and light sources.
Further, as used in a conventional infinite type optical pickup apparatus, an optical element that collimates a luminous flux emitted from a light source into parallel light so that the luminous flux can enter a collimator lens of an objective optical element proves unnecessary, and a reduction in size and cost of the apparatus can be achieved.
The light converging system described in item (4-16) is the light converging optical system described in item (4-15), wherein one of the number of endless belt type optical function surfaces 4 to 30 is formed on at least one optical surface of the optical element.
The same effects as in items (4-15) can be achieved in the light converging system described in items (4-16), and the number of the endless belt-type optical function surfaces and the step surfaces can be limited to a certain number or less, and therefore, the amount of light entering the portion of the non-endless belt-type optical function surfaces (step surfaces and other surfaces) can be controlled among all of the divergent or convergent light entering the optical surfaces, which prevents the drop of the amount of light.
The light converging system described in the item (4-17) is the light converging system described in the item (4-15) or the item (4-16), wherein the optical element provided with the common region is a connection lens.
In the light converging system described in item (4-17), the same effects as in item (4-15) or item (4-16) can be obtained, and by providing a common area on the connection lens constituting the light converging optical system without necessity of disposing an optical element for providing the common area, it becomes possible to reduce the number of parts of the optical pickup part.
In the light converging system described in item (4-18), the same effects as in any one of item (4-15) to item (4-17) can be obtained, and by providing a common region on the objective optical element constituting the light converging optical system without newly disposing an optical element for providing the common region, it becomes possible to reduce the number of parts of the optical pickup device.
The light converging system described in item (4-19) is the light converging system described in any one of items (4-15) to (4-18), wherein the first light source and the second light source are integrally combined.
In the light converging system described in item (4-19), the same effect as any one of item (4-15) to item (4-18) can be obtained, and sharing of the optical element by integrally combining the first light source and the second light source, making the optical path of the light flux of the first wavelength λ 1 and the optical path of the light flux of the second wavelength λ 2 the same makes it possible to reduce the number of components of the optical pickup device.
The light converging system described in item (4-20) is the light converging system described in any one of items (4-15) to (4-19), wherein the optical system magnification m1 satisfies-1/3 ≦ m1 ≦ 0.
In the light converging system described in item (4-20), the same effect as in any of items (4-15) to (4-19) can be obtained, and the negative value of the magnification of the optical system is limited to a certain value or more, that is, the distance from the light source to the information recording surface is limited. Generally, the smaller the magnification, the more compact the optical pickup device is, but the larger the absolute value of the magnification, the larger the coma aberration in tracking, and the larger the deterioration of the light converging spot. Therefore, when the balance between them is taken into consideration, it is preferable that the optical system magnification satisfies-1/3. Ltoreq. M1. Ltoreq.0.
The light converging system described in item (4-21) is the light converging system described in any one of items (4-15) to (4-20), wherein the optical system magnification m2 satisfies-1/3 ≦ m2 ≦ 0.
In the light converging system described in item (4-21), the same effects as in any one of item (4-15) to item (4-20) can be obtained, and the size reduction of the optical pickup device and the prevention of deterioration of the light converging spot are simultaneously achieved.
The light converging system described in the item (4-22) is the light converging system described in any one of the items (4-15) to (4-21), wherein a focal length f1 of the objective optical element for the light flux of the first wavelength λ 1 satisfies f1 ≦ 4mm.
In the light converging system described in item (4-22), the same effects as in any of items (4-15) to (4-21) can be obtained, and the distance from the objective optical element to the information recording surface is limited, which makes it possible to reduce the size of the optical pickup apparatus.
The light converging system described in the item (4-23) is the light converging system described in any one of the items (4-15) to (4-22), wherein a focal length f2 of the objective optical element for the light flux of the second wavelength λ 2 satisfies f2 ≦ 4mm.
In the light converging system described in item (4-23), the same effects as in any of items (4-15) to (4-22) can be obtained, and the distance from the objective optical element to the information recording surface is limited, which makes it possible to reduce the size of the optical pickup apparatus.
The light converging system described in the item (4-24) is the light converging system described in any one of the items (4-15) to (4-23), wherein a numerical aperture NA1 of a spot converged by light of the light flux of the first wavelength λ 1 satisfies 0.55 ≦ NA1 ≦ 0.67.
The light converging system described in the item (4-25) is the light converging system described in any one of the items (4-15) to (4-24), wherein a numerical aperture NA2 of a spot converged by light of a light flux of the second wavelength λ 2 satisfies 0.44 ≦ NA2 ≦ 0.55.
The light converging system described in item (4-26) is the light converging system described in any one of items (4-15) to (4-25), wherein COMA 1 Satisfy COMA 1 ≤0.040(λ1 rms)。
The light converging system described in item (4-27) is the light converging system described in any one of items (4-15) to (4-26), wherein COMA 2 Satisfy COMA 2 ≤0.040(λ2 rms)。
The light converging system described in the item (4-28) is the light converging system described in any one of the items (4-15) to (4-27), wherein the phase difference P1 caused when the light flux of the first wavelength λ 1 passes through the optical functional surface of the annular band type satisfies 0.2X 2 π ≦ P1, and the phase difference P2 caused when the light flux of the second wavelength λ 2 passes through the optical functional surface of the annular band type satisfies 0.2X 2 π ≦ P2.
The objective optical element described in item (4-29) is an objective light of an optical pickup deviceAn optical element, the optical pickup apparatus performing reproduction and/or recording of a plurality of pieces of information by a light converging optical system having a plurality of optical elements, the reproduction and/or recording of the plurality of pieces of information being performed by converging a light flux having a first wavelength λ 1 (630 nm ≦ λ 1 ≦ 680 nm) emitted from a first light source on a first optical information recording medium having a protective master having a thickness t1, and by converging a light flux having a second wavelength λ 2 (760 nm ≦ λ 2 ≦ 810 nm) emitted from a second light source on the first optical information recording medium having a protective master having a thickness t2 (t 2 ≦ t 1), wherein optical system magnifications m1 and m2 respectively for the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 satisfy m1 ≠ 0 and m2 ≠ 0, respectively, a plurality of annular band-type optical functional surfaces centered on an optical axis are continuously formed on a surface on at least one side, a step area is provided, and a step area is formed by a step area is providedThe refracted light of the light flux of the first wavelength lambda 1 and the refracted light of the light flux of the second wavelength lambda 2 generated by the plurality of annular-band-type optical function surfaces are converged on the information recording surface of the prescribed optical information recording medium in the common region, and are in COMA 1 (λ 1 rms) represents the COMA aberration of the wavefront aberration of the light converging spot formed on the information recording surface of the first optical information recording medium by the light flux having the first wavelength λ 1 entering obliquely at the angle of view of 1 °, and 2 (λ 2 rms) represents a COMA aberration of a wavefront aberration of a light condensing spot formed on an information recording surface of the second optical information recording medium by a light flux having the second wavelength λ 2 entering the light condensing optical system obliquely at an angle of view of 1 °, and satisfies 0.8 × COMA 2 ≤COMA 1 ≤1.2×COMA 2 。
In the objective optical element described in the item (4-29), the optical system magnifications m1 and m2 of the light fluxes of the first wavelength λ 1 and the second wavelength λ 2, respectively, for the DVD and the CD, respectively, satisfy m1 ≠ 0 and m2 ≠ 0, respectively, that is, in the limited-type optical pickup apparatus in which the light flux of each wavelength enters as divergent light or convergent light for the objective optical element, the light flux of each wavelength passing through the common area of the optical element is emitted as refracted light to the optical information recording medium.
Further, the light converging optical system is set up so that a light flux of the first wavelength λ 1 entering the light converging optical system obliquely from the 1 ° angle of view forms a COMA of the wavefront aberration of the light converging spot on the information recording surface of the first optical information recording medium 1 Coma aberration of wavefront aberration of a light converging spot formed on an information recording surface of a second optical information recording medium for a light flux of a second wavelength λ 2 obliquely entering the light converging optical system from an angle of view of 1 ° (ii) is correctedCOMA 2 (lambda.2 rms) at 0.8 × COMA 2 ≤COMA 1 ≤1.2×COMA 2 Within the range.
In the limited type of light condensing system, off-axis coma (off-axis coma) for reproduction and/or recording of CDs and DVDs can be appropriately corrected, and deterioration of optical performance in, for example, tracking can be prevented in advance. Further, the positioning of the object lens in the process of assembling to the optical pickup apparatus is easy, and thus it is possible to improve productivity and prevent deterioration of optical performance based on aging change due to mechanism abrasion caused by moving different types of lenses and light sources.
Further, as used in a conventional infinite type optical pickup apparatus, an optical element that collimates a luminous flux emitted from a light source into parallel light so that the luminous flux can enter a collimator lens of an objective optical element proves unnecessary, and a reduction in size and cost of the apparatus can be achieved.
The objective optical element described in item (4-30) is the objective optical element described in item (4-29), wherein the number of the endless belt-type optical functional surfaces is one of 4 to 30.
In the objective optical element described in item (4-30), the same effects as in item (4-29) can be achieved, and the number of the annular belt-type optical functional surfaces and the step surfaces can be limited to a certain number or less, and therefore, the amount of light entering the portion of the non-annular belt-type optical functional surfaces (step surfaces and other surfaces) among all of the divergent or convergent light entering the optical surfaces can be controlled, which prevents a drop in the amount of light.
The objective optical element described in item (4-31) is the objective optical element described in item (4-29) or item (4-30), wherein the first light source and the second light source are integrally combined.
In the objective optical element described in item (4-31), the same effects as in item (4-29) or item (4-30) can be obtained, and the optical element can be shared by integrally combining the first light source and the second light source, making the optical path of the luminous flux of the first wavelength λ 1 and the optical path of the luminous flux of the second wavelength λ 2 the same, which makes it possible to reduce the number of parts of the optical pickup apparatus.
The objective optical element described in item (4-32) is the objective optical element described in any one of items (4-29) to (4-31), wherein the optical system magnification m1 satisfies-1/3 ≦ m1 ≦ 0.
In the objective optical element described in item (4-32), the same effects as in any of items (4-29) to (4-31) can be obtained, and the negative value of the magnification of the optical system is limited to a certain value or more, that is, the distance from the light source to the information recording surface is limited. Generally, the smaller the magnification, the more compact the optical pickup device is, but the larger the absolute value of the magnification, the larger the coma aberration in tracking, and the larger the deterioration of the light converging spot. Therefore, when the balance between them is taken into consideration, it is preferable that the optical system magnification satisfies-1/3. Ltoreq. M1. Ltoreq.0.
The objective optical element described in item (4-32) is the objective optical element described in any one of items (4-29) to (4-32), wherein the optical system magnification m2 satisfies-1/3 ≦ m2 ≦ 0.
In the objective optical element described in item (4-33), the same effects as any one of items (4-29) to (4-32) can be obtained, and size reduction of the optical pickup device and prevention of deterioration of the light condensing spot are simultaneously achieved.
The objective optical element described in item (4-34) is the objective optical element described in any one of items (4-29) to (4-33), wherein a focal length f1 for a light flux of the first wavelength λ 1 satisfies f1 ≦ 4mm.
In the objective optical element described in item (4-34), the same effects as any one of items (4-29) to (4-33) can be obtained, and the distance from the objective optical element to the information recording surface is limited, which makes it possible to reduce the size of the optical pickup apparatus.
The objective optical element described in item (4-35) is the objective optical element described in any one of items (4-29) to (4-34), wherein a focal length f2 of the light flux for the second wavelength λ 2 satisfies f2 ≦ 4mm.
In the objective optical element described in item (4-35), the same effects as any one of items (4-29) to (4-34) can be obtained, and the distance from the objective optical element to the information recording surface is limited, which makes it possible to reduce the size of the optical pickup apparatus.
The objective optical element described in item (4-36) is the objective optical element described in any one of items (4-29) to (4-36), wherein a numerical aperture NA1 of a spot condensed by light of a light flux of the first wavelength λ 1 satisfies 0.55 ≦ NA1 ≦ 0.67.
The objective optical element described in item (4-37) is the objective optical element described in any one of items (4-29) to (4-36), wherein a numerical aperture NA2 of a spot condensed by light of a light flux of the second wavelength λ 2 satisfies 0.44 ≦ NA2 ≦ 0.55.
The objective optical element described in item (4-38) is the objective optical element described in any one of items (4-29) to (4-37), wherein COMA 1 Satisfy COMA 1 ≤0.040 (λ1rms)。
The objective optical element described in item (4-39) is the objective optical element described in any one of items (4-29) to (4-38), wherein COMA 2 Satisfy COMA 2 ≤0.040 (λ2rms)。
The objective optical element described in the item (4-40) is the objective optical element described in any one of the items (4-29) to (4-39), wherein a phase difference P1 caused when a light flux of the first wavelength λ 1 passes through the optical functional surface of the annular zone type satisfies 0.2 × 2 π ≦ P1, and a phase difference P2 caused when a light flux of the second wavelength λ 2 passes through the optical functional surface of the annular zone type satisfies 0.2 × 2 π ≦ P2.
A fourth embodiment of the optical pickup apparatus, a light converging optical system and an objective optical element of the present invention will be explained below with reference to the drawings.
As shown in fig. 18 and 19, the object lens 310 representing the objective optical element is a plurality of lenses which constitute the light converging optical system of the optical pickup device 1 and have aspherical surfaces on both sides thereof. On one optical surface on the side of the object lens 310 (closer to the light source), there is provided an annular belt-type optical function surface 320 within a certain height range from the optical axis L (hereinafter referred to as "common area A1"). Incidentally, the range of the certain form of the non-common area A1 (hereinafter referred to as "peripheral area A2") is not particularly limited.
To be more specific, the optical function surface 320 of the annular band type centered on the optical axis L is continuously formed in the central area A1 in the radial direction by the step surface 330.
The number of the annular belt-type optically-functional surfaces 320 formed on the common area A1 is not particularly limited, and it may be appropriately modified according to the thickness of the protective mother substrate 302b or 304 b. However, it is preferable that the number is in the range of 4 to 30 from the viewpoint of preventing the drop of the light output amount and the ease of manufacturing the objective lens 310.
The dimension d (depth in the direction of the optical axis L) of the step surface 330 is established so that the luminous flux of the wavelength λ 1 and the luminous flux of the wavelength λ 2 or both the luminous fluxes passing through each of the annular band-type optical function surfaces 320 can appear as refracted light on the optical information recording media 302 and 304, respectively, under the condition that they are each given a prescribed phase difference, with the step surface 330 appearing between the two annular band-type optical function surfaces 320 adjacent to each other in the radial direction.
The optical pickup device 1 is a device for emitting a light flux of a first wavelength λ 1 (= 655 nm) from a first semiconductor laser 303 (light source) to a first optical information recording medium 302 (DVD in the present embodiment) representing an optical information recording medium and emitting a light flux of a second wavelength λ 2 (= 785 nm) from a second semiconductor laser 305 (light source) to a second optical information recording medium 304 (CD in the present embodiment) through a light condensing optical system, recording information on an information recording surface 302a of the first optical information recording medium 302 or an information recording surface 304a of the second optical information recording medium 304, or reading recorded information.
In the present invention, the light converging optical system is composed of an object lens 310, a beam splitter 306, and an aperture 307.
Incidentally, the first semiconductor laser 303 and the second semiconductor laser 305 are (integrally) united together as a light source.
When recording or reproducing information to or from the DVD, divergent light of a wavelength λ 1 emitted from the first semiconductor laser 303 is blocked by the aperture 307 after passing through the beam splitter 306, and passes through the common area A1 and the peripheral area A2 of the object lens 310 as shown by solid lines in fig. 19. Then, the light flux of the wavelength λ 1 having passed through the common area A1 and the peripheral area A2 is condensed to the information recording surface 302a as refracted light by the protective mother sheet 302b of the DVD.
Then, the light flux reflected by the pit modulation and information recording surface 302a passes through the object lens 310 and the aperture 307 again to be reflected by the beam splitter 306, and then is given astigmatism by the cylindrical lens 308 to enter the photodetector 340 via the concave lens 309, so that the signal output from the photodetector 340 is used to obtain a signal for reading information recorded on the DVD.
When recording or reproducing information to or from the CD, divergent light of a wavelength λ 2 emitted from the second semiconductor laser 305 is blocked by the aperture 307 by the beam splitter 306, and passes through the common area A1 and the peripheral area A2 of the object lens 310 as shown by the broken lines in fig. 19. In this case, the light flux of the wavelength λ 2 passing through the common area A1 is condensed on the information recording surface 304a as refracted light via the protective mother substrate 304b of the CD. However, the light flux of the wavelength λ 2 that has passed through the peripheral area A2 reaches a portion of the non-information recording surface 304b via the protective mother substrate 304b of the CD, and does not contribute to reproduction and/or recording of information.
Then, the light flux reflected by the information pit modulation and information recording surface 304a passes through the object lens 310 and the aperture 307 again to be reflected by the beam splitter 306, and then is given astigmatism by the cylindrical lens 308 to enter the photodetector 340 via the concave lens 309, so that the signal output from the photodetector 340 is used to obtain a signal for reading information recorded on the CD.
Further, a change in the amount of light caused by a change in the form of a light spot and a change in position on the photodetector 340 is detected to perform focus detection and tracking detection. Based on the detection result, the two-dimensional actuator 350 moves the objective lens 310 so that the light flux emitted from the first semiconductor laser 303 or the light flux emitted from the second semiconductor laser 305 can form an image on the information recording surface 302a of the DVD or the information recording surface 304a of the CD, and moves the objective lens 310 so that an image can be formed on a prescribed track.
Each optical element constituting the light converging optical system is designed in form and size so that the COMA is given when a light flux having the first wavelength λ 1 obliquely enters the light converging optical system at a viewing angle of 1 ° 1 (λ 1 rms) represents COMA aberration of wavefront aberration of a light condensing spot formed on the information recording surface 302a of the first optical information recording medium 302, and when a light flux having the second wavelength λ 2 obliquely enters the light condensing optical system at an angle of view of 1 °, COMA 2 (λ 2 rms) represents a COMA aberration of wavefront aberration of the light condensing spot formed on the information recording surface 304a of the second optical information recording medium 304, and satisfies 0.8 × COMA 2 ≤COMA 1 ≤1.2 ×COMA 2 。
Incidentally, COMA 1 Equal to ((third-order coma in case of wavefront aberration expressing the luminous flux of the ith wavelength λ i by Zernike polynomial expression)) 2 + (fifth-order coma in the case of wavefront aberration expressing the luminous flux of ith wavelength λ i by Zernike polynomial expression) 2 ) 1/2 Wherein i is 1 or 2.
Incidentally, a method for designing a light converging optical system satisfying the foregoing conditions is well known, and explanation thereof will be omitted.
For example, in the case of a liquid, COMA aberration of the wavefront aberration of the light converging spot formed on the information recording surface 304a of the CD as described above 2 Proved to be 0.030 (λ 2 rms), when the luminous flux of the wavelength λ 2 (785 nm) is caused to enter the light condensing optical system for CD, the light condensing is designedOptical system for use inThe luminous flux of the wavelength λ 1 (655 nm) of the DVD enters the light converging optical system at the viewing angle of 1 °, and the COMA of the wavefront aberration on the light converging spot formed on the information recording surface 302a of the DVD is described previously 2 In the range of 0.8X 0.030 (. Lamda.2 rms) to-1.2X 0.030 (. Lamda.2 rms).
In a limited type of optical pickup device having compatibility with DVDs and CDs in the present invention, a light flux of each wavelength passing through a common area of an optical element is projected as refracted light onto an optical information recording medium.
Further, the light converging optical system is set up so that a light flux of the first wavelength λ 1 entering the light converging optical system obliquely from the 1 ° angle of view forms a COMA of the wavefront aberration of the light converging spot on the information recording surface of the first optical information recording medium 1 COMA of wavefront aberration of light converging spot formed on information recording surface of second optical information recording medium for light flux of second wavelength λ 2 obliquely entering light converging optical system from 1 ° angle of view 2 (lambda.2 rms) at 0.8 × COMA 2 ≤COMA 1 ≤1.2×COMA 2 Within the range.
Therefore, in the limited type of optical pickup apparatus, off-axis coma for reproduction and/or recording of CDs and DVDs can be appropriately corrected, and deterioration of optical performance in, for example, tracking can be prevented in advance. Further, the positioning of the object lens in the process of being assembled to the optical pickup apparatus is easy, and thus it is possible to improve productivity and prevent deterioration of optical performance based on aging change due to mechanism wear caused by moving different types of lenses and light sources.
Claims (36)
1. An objective optical element for an optical pickup apparatus provided with a first light source having a wavelength λ 1, a second light source having a wavelength λ 2, where λ 1 < λ 2, and a light converging optical system including a magnification varying element and the objective optical element, wherein the light converging optical system converges a light flux emitted from the first light source onto an information recording plane of a first optical information recording medium through a protective substrate having a thickness t1 so as to perform information recording and/or reproduction on the first optical information recording medium, and the light converging optical system converges a light flux emitted from the second light source onto an information recording plane of a second optical information recording medium through the protective substrate having a thickness t2, where t1 ≦ t2 so as to perform information recording and/or reproduction on the second optical information recording medium, the objective optical element having an optical system magnification m1 for the light flux having the wavelength λ 1, and the optical system magnification m1 satisfying the following equation:
-1/7≤m1≤-1/25
|m1|＜|M1|
wherein M1 is an optical system magnification for a luminous flux of a wavelength λ 1 from the first light source to the first optical information recording medium in the optical pickup apparatus, and
the objective optical element includes on at least one surface:
a common area through which a light flux from the first light source and a light flux from the second light source pass together to form converging light spots on an information recording plane of the first optical information recording plane and an information recording plane of the second optical information recording plane, respectively; and
a dedicated area through which the light flux from the first light source passes so as to form a light converging spot on an information recording plane of the first information recording plane, and through which the light flux from the second light source passes so as not to form a light converging spot on an information recording plane of the second information recording plane;
wherein the dedicated area includes a diffractive annular zone having a function of suppressing an increase in spherical aberration caused by an increase in atmospheric temperature in accordance with a wavelength fluctuation of light flux of the wavelength λ 1 when the light flux of the wavelength λ 1 passing through the diffractive annular zone is condensed on an information recording plane of the first information recording medium, and
wherein a luminous flux of the wavelength λ 2 passing through the diffraction annular band and an optical axis intersect at a position different from a position of a condensing spot formed on an information recording plane of the second optical information recording medium.
2. The objective optical element according to claim 1, wherein the objective optical element has an optical system magnification m2 for a light flux of a wavelength λ 2, and the optical system magnification m2 satisfies the following formula:
|m1-m2|＜0.5。
3. the objective optical element according to claim 1, wherein the common region includes a common diffractive annular zone having a correction function for reducing a difference between spherical aberration when a light flux of the wavelength λ 1 passing through the common diffractive annular zone is condensed to an information recording plane of the first optical information recording medium via a protective substrate having a thickness t1 and spherical aberration when a light flux of the wavelength λ 2 passing through the common diffractive annular zone is condensed to an information recording plane of the second optical information recording medium via a protective substrate having a thickness t2, by a change in a diffraction function according to a wavelength difference between the wavelength λ 1 and the wavelength λ 2.
4. The objective optical element according to claim 3, wherein the common region is divided into a first annular region and a second annular region around the center on the optical axis by a step-like portion distributed in the optical axis direction, and wherein the first annular region located closer to the optical axis includes a refractive surface, and the second region located farther from the optical axis includes a common diffractive structure.
5. The objective optical element according to claim 4, wherein an edge of the first annular region contacting the second annular region is closer to the light source side than the second annular region contacting the first annular region.
6. The objective optical element according to claim 4, wherein a third annular region having a refractive surface is provided so as to be adjacent to the second annular region on a more distal side from the optical axis, and an edge of the second annular region contacting the third annular region is closer to the optical information recording medium side than the third annular region contacting the second annular region.
7. The objective optical element according to claim 2, wherein the common diffractive structure has an optical characteristic such that spherical aberration of light flux passing through the common diffractive structure is lower as the light source wavelength becomes longer.
8. The objective optical element according to claim 4, wherein an optical path length difference between a light flux of a wavelength λ 1 passing through the first annular region and a light flux of a wavelength λ 1 passing through the second annular region at an optimum image position is λ 1 x i, where i is an integer.
9. The objective optical element according to claim 6, wherein an optical path length difference between a light flux of a wavelength λ 1 passing through the second annular region and a light flux of a wavelength λ 1 passing through the third annular region at an optimum image position is λ 1 x i, where i is an integer.
10. The objective optical element according to claim 4, wherein the diffractive structure is provided on the entire surface of the common region.
11. The objective optical element according to claim 1, wherein the common region is divided into a plurality of annular refractive zones in the optical axis direction, which are arranged in order of 1 st, 2 nd, so, k-th annular refractive zones from the optical axis, where k is a natural number greater than 2, wherein at least the n-th annular refractive zone has a first edge closer to the optical axis and a second edge farther from the arranged optical axis, where n is a natural number and 2 < n ≦ k, so that the first edge is located on the optical information recording medium side than the second edge, and the second edge is located on the optical information recording medium side than the first edge of the (n + 1) th annular refractive zone closer to the optical axis, assuming that in the case of k = n, the first edge of the (n + 1) th annular refractive zone is an edge of a dedicated region, and wherein a light flux having a wavelength λ 1 passing through the n-th annular refractive zone converges at a position different from an optimal image forming position in the optical axis direction.
12. The objective optical element according to claim 11, wherein an optical path length difference between a light flux of a wavelength λ 1 passing through an n-th annular refractive band and a light flux of a wavelength λ 1 passing through an (n-1) -th annular refractive band at the optimum image position is λ 1 × i, where i is an integer.
13. The objective optical element according to claim 1, wherein at least a part of the common region has a correction function to reduce a difference between spherical aberration when a light flux of the wavelength λ 1 passing through the common region is condensed on the information recording plane of the first optical information recording medium via a protective substrate having a thickness t1 and spherical aberration when a light flux of the wavelength λ 2 passing through the common region is condensed on the information recording plane of the second optical information recording medium via a protective substrate having a thickness t2 in accordance with a wavelength difference between the wavelength λ 1 and the wavelength λ 2.
14. Objective optical element according to claim 1, wherein the magnification-changing element is a connecting lens.
15. The objective optical element of claim 1, wherein the objective optical element is an object lens.
16. The objective optic of claim 1, wherein the objective optic is formed of plastic.
17. The objective optic of claim 1, wherein the first light source and the second light source are disposed on a same motherboard.
18. The objective optical element according to claim 1, wherein the first light source and the second light source are disposed such that distances from the magnification-varying element along an optical axis are equal.
19. An optical pickup apparatus, comprising:
a first light source of wavelength λ 1;
a second light source of wavelength λ 2, where λ 1 < λ 2; and
a light condensing optical system including a magnification changing element and an objective optical element, wherein the light condensing optical system condenses a light flux from a first light source onto an information recording plane of a first optical information recording medium via a protective substrate having a thickness t1 so as to perform recording and/or reproduction of information on the first optical information recording medium, and the light condensing optical system condenses a light flux from a second light source onto an information recording plane of a second optical information recording medium via a protective substrate having a thickness t2, where t1 ≦ t2 so as to perform recording and/or reproduction of information on the second optical information recording medium,
the objective optical element has an optical system magnification m1 for a wavelength λ 1 and an optical system magnification m2 satisfying the following formula:
-1/7≤m1≤-1/25
|m1|＜|M1|
wherein M1 is an optical system magnification from the first light source to the first optical information recording medium for the luminous flux of the wavelength λ 1 in the optical pickup device, and
the objective optical element includes on at least one surface:
a common area through which the light flux from the first light source and the light flux from the second light source pass together to form a condensed light spot on an information recording plane of the first optical information recording plane and an information recording plane of the second optical information recording plane, respectively; and
a dedicated area through which a light flux from the first light source passes so as to form an information recording plane that converges light spot on the first optical information recording plane, and through which a light flux from the second light source passes so as not to form an information recording plane that converges light spot on the second optical information recording plane;
wherein the dedicated area includes a diffraction annular zone having a function of suppressing an increase in spherical aberration due to an increase in atmospheric temperature in accordance with a fluctuation in wavelength of the luminous flux of the wavelength λ 1 when the luminous flux of the wavelength λ 1 passing through the diffraction annular zone is condensed on the information recording plane of the first information recording medium, and
wherein a luminous flux of the wavelength λ 2 passing through the diffraction annular band and the optical axis intersect at a position different from a position of a converging light spot formed on an information recording plane of the second optical information recording medium.
20. The optical pickup device according to claim 19, wherein the objective optical element has an optical system magnification m2 for a luminous flux of the wavelength λ 2, and the optical system magnification m2 satisfies the following expression:
|m1-m2|＜0.5。
21. the optical pickup device according to claim 19, wherein the common area includes a common diffractive annular zone having a correction function to reduce a difference between a spherical aberration when a light flux of the wavelength λ 1 passing through the common diffractive annular zone is condensed on the information recording plane of the first optical information recording medium through the protective substrate of the thickness t1 and a spherical aberration when the light flux of the wavelength λ 2 passing through the common diffractive annular zone is condensed on the information recording plane of the second optical information recording medium through the protective substrate of the thickness t2 in accordance with a change in the diffractive function caused by a wavelength difference between the wavelength λ 1 and the wavelength λ 2.
22. The optical pickup device according to claim 21, wherein the common region is divided into a first annular region and a second annular region around a center on the optical axis by a step-like portion distributed in the optical axis direction, and wherein the first annular region located closer to the optical axis includes a refractive surface, and the second region located farther from the optical axis includes a common diffractive structure.
23. The optical pickup device according to claim 22, wherein an edge of the first annular region contacting the second annular region is closer to the light source side than the second annular region contacting the first annular region.
24. The optical pickup apparatus according to claim 22, wherein a third annular region having a refractive surface is provided so as to be adjacent to the second annular region on a farther side from the optical axis, and an edge of the second annular region contacting the third annular region is closer to the optical information recording medium side than the third annular region contacting the second annular region.
25. The optical pickup device according to claim 21, wherein the common diffractive structure has such optical characteristics that spherical aberration of a light flux passing through the common diffractive structure is lower as a light source wavelength becomes longer.
26. The optical pickup device according to claim 22, wherein an optical path length difference between a light flux of a wavelength λ 1 passing through the first annular region and a light flux of a wavelength λ 1 passing through the second annular region at the optimum image position is λ 1 x i, where i is an integer.
27. The optical pickup device according to claim 24, wherein an optical path length difference between a light flux of a wavelength λ 1 passing through the second annular region and a light flux of a wavelength λ 1 passing through the third annular region at the optimum image position is λ 1 x i, where i is an integer.
28. The optical pickup device according to claim 21, wherein the diffraction structure is provided on an entire surface of the common area.
29. The optical pickup device according to claim 19, wherein the common region is divided into a plurality of annular refractive zones arranged in the optical axis direction in the order of 1 st, 2 nd, so, k-th annular refractive zones, where k is a natural number larger than 2, from the optical axis, wherein at least an nth annular refractive zone has a first edge closer to the optical axis and a second edge farther from the arranged optical axis, where n is a natural number and 2 < n ≦ k, arranged such that the first edge is located on the optical information recording medium side than the second edge along the optical axis, and the second edge is located on the optical information recording medium side than the first edge of the (n + 1) th annular refractive zone closer to the optical axis along the optical axis, assuming that in a case where k = n, the first edge of the (n + 1) th annular refractive zone is an edge of the dedicated region, and wherein a light flux having a wavelength λ 1 passing through the nth annular refractive zone converges at a position different from an optimal image forming position in the optical axis direction.
30. The optical pickup device according to claim 29, wherein at the optimum image position, an optical path length difference between a light flux of a wavelength λ 1 passing through an n-th annular refractive band and a light flux of a wavelength λ 1 passing through an (n-1) -th annular refractive band is λ 1 × i, where i is an integer.
31. The optical pickup device according to claim 19, wherein at least a part of the common area has a correction function to reduce a difference between a spherical aberration when a light flux of the wavelength λ 1 passing through the common area is condensed on the information recording plane of the first optical information recording medium via a protective substrate having a thickness t1 and a spherical aberration when a light flux of the wavelength λ 2 passing through the common area is condensed on the information recording plane of the second optical information recording medium via a protective substrate having a thickness t2 in accordance with a wavelength difference between the wavelength λ 1 and the wavelength λ 2.
32. The optical pickup device according to claim 19, wherein the magnification-varying element is a connection lens.
33. The optical pickup apparatus of claim 19, wherein the optical pickup apparatus is an object lens.
34. The optical pickup apparatus of claim 19, wherein the optical pickup apparatus is formed of plastic.
35. The optical pickup apparatus of claim 19, wherein the first light source and the second light source are disposed on the same motherboard.
36. The optical pickup device according to claim 19, wherein the first light source and the second light source are disposed such that distances from the magnification-varying element along the optical axis are equal.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002318795A JP2004152443A (en) | 2002-10-31 | 2002-10-31 | Optical pickup device and objective optical element |
| JP318795/2002 | 2002-10-31 | ||
| JP335205/2002 | 2002-11-19 | ||
| JP339165/2002 | 2002-11-22 | ||
| JP345063/2002 | 2002-11-28 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1729520A CN1729520A (en) | 2006-02-01 |
| CN100367383C true CN100367383C (en) | 2008-02-06 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB2003801021382A Expired - Fee Related CN100367383C (en) | 2002-10-31 | 2003-10-24 | Object optical element and optical pickup device |
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| Country | Link |
|---|---|
| JP (1) | JP2004152443A (en) |
| CN (1) | CN100367383C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4297099B2 (en) | 2005-08-09 | 2009-07-15 | ソニー株式会社 | Optical pickup and optical disc apparatus |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002203331A (en) * | 2000-10-26 | 2002-07-19 | Konica Corp | Optical pickup device and objective lens |
| JP2002288867A (en) * | 2001-03-26 | 2002-10-04 | Konica Corp | Objective lens for optical pickup device and optical pickup device |
-
2002
- 2002-10-31 JP JP2002318795A patent/JP2004152443A/en active Pending
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2003
- 2003-10-24 CN CNB2003801021382A patent/CN100367383C/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002203331A (en) * | 2000-10-26 | 2002-07-19 | Konica Corp | Optical pickup device and objective lens |
| JP2002288867A (en) * | 2001-03-26 | 2002-10-04 | Konica Corp | Objective lens for optical pickup device and optical pickup device |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2004152443A (en) | 2004-05-27 |
| CN1729520A (en) | 2006-02-01 |
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