WO2006008666A1 - Polarizing device - Google Patents

Polarizing device Download PDF

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Publication number
WO2006008666A1
WO2006008666A1 PCT/IB2005/052092 IB2005052092W WO2006008666A1 WO 2006008666 A1 WO2006008666 A1 WO 2006008666A1 IB 2005052092 W IB2005052092 W IB 2005052092W WO 2006008666 A1 WO2006008666 A1 WO 2006008666A1
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WIPO (PCT)
Prior art keywords
grating
polarizing device
light beam
polarizing
present
Prior art date
Application number
PCT/IB2005/052092
Other languages
French (fr)
Inventor
Andreas Drauschke
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2006008666A1 publication Critical patent/WO2006008666A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3058—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state comprising electrically conductive elements, e.g. wire grids, conductive particles
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1809—Diffraction gratings with pitch less than or comparable to the wavelength

Definitions

  • the present invention relates to a polarizing device arranged to produce a polarized light, beam from a source light beam that has a first and a second polarization direction, wherein the device transmits light of the first polarization direction and reflects light of the second polarization direction.
  • Prior art wire grid polarizers typically exploit the feature that a metallic grating comprised in the polarizer reflect one polarization state and transmit the other, if the grating period d, i.e. the center-to-center distance of generally parallelly arranged elongated elements that form the grating, is much smaller than the wavelength ⁇ of incident light on the grating.
  • the grating period d i.e. the center-to-center distance of generally parallelly arranged elongated elements that form the grating
  • Different propagation conditions of stimulated surface plasmons of the metallic grating are the cause of the polarizing effect.
  • the polarizing effect depends on a number of different grating parameters, in particular on the grating period d, the grating depth h, i.e. the thickness of the grating, the filling factor c (which equals the width/of the grating divided by the grating period d), the constant refractive indices ni and 723 of the respective medias separated by the grating, and distribution of refractive indices ri2(x, y, z) in the grating.
  • Fig. 1 Light is incident on the grating under an angle ⁇ .
  • light beams that are incident on a grating typically results in a number of light beams, both transmitted light beams 71,- to 3 ⁇ and reflected light beams R. k to Ri.
  • the angles ⁇ n for diffracted light beams are defined by the well-known grating equation:
  • Equation 1 shows that only diffractions of order zero ("zeroth-order") exist if the grating period is small enough, where m specifies the order.
  • R 2 refractive indices
  • m specifies the order.
  • the grating will function like a wire grid polarizer.
  • the grating production process defines a lower limit of the grating period d, the grating depth h and the filling factor c are the only design parameters which may be varied and experimented with.
  • a grating with a carrier grating period d c which is called the local period of the grating, can be modulated for each individual element in the grating. If the modulation frequency is not too high, such a grating propagates all energy in a direction specified in accordance with equation (1) using the carrier grating period d c . Because of the modulation, the energy distribution in that specified direction may be affected.
  • US Patent no. 6,108,131 discloses a polarizer apparatus having an arrangement of generally parallelly elongated elements disposed in a source light beam.
  • the elements interact with the electromagnetic waves of the source light beam to generally (i) pass light having a polarization oriented perpendicular to the length of the elements, and (ii) reflect light having a polarization oriented parallel to the length of the elements.
  • the passed light defines a passed beam with a first polarization and the reflected light defines a reflected beam with a second polarization.
  • the elements are located in generally parallel arrangement with a center-to-center spacing, or pitch, of the elements which is smaller than the wavelength of light.
  • the pitch will be less than 400 nm, and preferably less than one third of the wavelength of light, or approximately 130 nm.
  • each element has a width that may range from 10% to 90% of the pitch.
  • spaces separating the elements have a width that will range from 90% to 10% of the pitch.
  • An object of the present invention is to provide a polarizing device that solves the above given problems and which polarizing device has a high performance, but which uses a pitch that is greater than the wavelength of light incident on the device.
  • a polarizing device arranged to produce a polarized light beam from a source light beam that has a first and a second polarization direction, wherein the device transmits light of the first polarization direction and reflects light of the second polarization direction, in accordance with claim 1.
  • a polarizing device comprising a number of parallelly arranged conducting means, which means polarize the unpolarized light beam, wherein the number of conducting means has a pitch that is greater than the wavelength of the source light beam, and a carrier pitch that differs for at least two of the parallelly arranged conducting means.
  • An idea of the present invention is to provide a polarizing device, such as a grating, having a strong polarizing effect, but which device employs a relatively large grating period, or pitch, as compared with prior art polarizers.
  • the effective grating period of the polarizing device according to the present invention will be much larger than the smallest wavelength of the source light beam incident on the polarizing device. Due to the fact that a carrier grating is employed, contrast ratio and polarization efficiency can be maximized.
  • the polarizing device may advantageously be implemented in, for example, front and rear projection systems.
  • the present invention is advantageous, since "binary", or unmodulated, gratings with a large grating period in comparison with the wavelength of the incident light do not show a strong polarizing effect.
  • a designer of gratings is not confined to small grating periods.
  • Fig. 1 illustrates a polarizing device in the form of a grating and parameters employed to define the grating used in the present invention
  • Fig. 2 shows a grating in accordance with an embodiment of the present invention
  • Fig. 3 shows a comparison of transmission efficiency of the zeroth diffraction order between a binary grating and a carrier grating for TE and TM polarization, depending on the wavelength of incident light;
  • Fig. 4 shows transmission efficiency of TE polarization depending on the wavelength of light incident on the grating according to the present invention
  • Fig. 5 shows transmission efficiency of TM polarization depending on the wavelength of light incident on the grating according to the present invention
  • Fig. 6 shows contrast depending on the wavelength of light incident on the grating according to the present invention
  • Fig. 7 shows an example of a projection display system comprising the polarizing device.
  • Fig. 1 illustrates a polarizing device in the form of a grating and parameters employed to define the grating used in the present invention.
  • Prior art wire grid polarizers typically reflect one polarization state and transmit the other if the grating period d is much smaller than the wavelength ⁇ of light L incident on the grating.
  • the grating period d is the center-to-center distance of parallelly arranged elongated elements E that form the grating.
  • the polarizing effect depends on a number of different grating parameters, in particular said grating period d, the grating depth h, i.e.
  • the light Z is incident on the grating under an angle ⁇ , and the incident light results in a number of light beams, both transmitted light beams 71; to 7 ⁇ and reflected light beams R- k to Ri.
  • Fig. 2 illustrates a polarizing device in the form of a grating in accordance with an embodiment of the present invention.
  • the new design approach introduced by the present invention combines the advantages of both wired grid polarizers in the prior art and a modulated high frequency carrier grating to create a polarizing device which may be adapted, and ideally optimized, such that is attains a specific optical function required to satisfy a specific optical requirement.
  • a carrier grating period d c of 72 nm has been employed.
  • the smallest wavelength ⁇ of the incident light is 400 nm.
  • the polarizing device proposed by the present invention a designer of gratings is given a greater degree of freedom, since he is not confined to using small grating periods in the design process.
  • Employing pulse density modulation or pulse width modulation to modulate the carrier grating may optimize the transmission efficiency.
  • These modulation techniques are known by the skilled person, and it should be clear that the skilled person realizes that any other known appropriate modulation technique can be employed.
  • the refractive index ni is that of glass and the refractive index «3 for a substrate in which the grating is located is 1.0.
  • the grating itself is formed of a mixture of glass and aluminum.
  • the thickness h of the grating is typically approximately 150 nm.
  • Fig. 3 shows that the efficiency of TM polarization advantageously may be maximized by employing the grating of the present invention.
  • the dotted curve shows the efficiency of a binary grating.
  • the efficiency of the binary grating peaks at 90% for a ⁇ /d ratio of approximately 2.2. For greater ⁇ /d ratios, the efficiency decreases rapidly.
  • the unbroken curve shows the efficiency of a polarizer employing carrier gratings.
  • the efficiency of the carrier grating continuously lies slightly above 90%, even though the ⁇ /d 'ratio steadily increases. This is highly advantageous.
  • An object of the grating of the present invention is to have a minimum contrast ratio C min of 300 and a maximum of transmission efficiency for TM polarization.
  • Fig. 4 shows transmission efficiency ⁇ of TE polarization depending on the wavelength ⁇ of light incident on the grating according to the present invention.
  • Fig. 5 shows transmission efficiency ⁇ of TM polarization depending on the wavelength ⁇ of light incident on the grating according to the present invention.
  • the minimum efficiency ⁇ m j, is 81.2%
  • the average efficiency ⁇ avg is 84.5%
  • the maximum efficiency ⁇ max is 89.2%.
  • Fig. 7 shows an example of a projection display system 10 for projection image information.
  • the projection display system comprises a light source 11 for generating a light beam, a reflector 12 and the new polarizing device 13.
  • the projection display system 10 comprises a reflective liquid crystal display panel 14 for modulation the polarization direction of the transmitted light beam with the image information.
  • An example of a reflective liquid crystal display is a liquid crystal on silicon (LCOS) device.
  • the projection display system comprises projection optics 15 for projection the modulated light beam and a screen 16. In operation, the light source 11 generates a light beam and the reflector 12 directs the generated light beam 17 to the polarizing device 13.
  • LCOS liquid crystal on silicon
  • the polarizing device reflects a first linearly polarized light beam having a first polarization direction and transmits a second linearly polarized light beam 18, having a second polarization direction perpendicular to the first polarization direction, to the LCOS device 14.
  • the operation of the LCOS device is well known to the skilled person.
  • the LCOS device 14 modulates the direction of polarization of the incident light beam and reflects the light beam towards the projection optics 15 via the polarizing device 13.
  • the polarizing device 13 reflects only the component of reflected light beam 19 with the first polarization direction and thus converts the polarization modulation in an amplitude modulation of the light beam.
  • the projection optics projects the modulated light beam 19 on the screen 16.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Polarising Elements (AREA)

Abstract

The present invention relates to a polarizing device arranged to produce a polarized light beam from a source light beam (L). An idea of the present invention is to provide a polarizing device, such as a grating, having a strong polarizing effect, but which device employs a relatively large grating period (d), or pitch, as compared with prior art polarizers. The effective grating period (d) of the polarizing device according to the present invention will be much larger than the smallest wavelength (X) of the source light beam incident on the polarizing device. Due to the fact that a carrier grating (dc) is employed, contrast ratio (CTM,TE) and polarization efficiency (rl) can be maximized. The polarizing device may advantageously be implemented in, for example, front and rear projection systems.

Description

Polarizing device
The present invention relates to a polarizing device arranged to produce a polarized light, beam from a source light beam that has a first and a second polarization direction, wherein the device transmits light of the first polarization direction and reflects light of the second polarization direction.
Prior art wire grid polarizers typically exploit the feature that a metallic grating comprised in the polarizer reflect one polarization state and transmit the other, if the grating period d, i.e. the center-to-center distance of generally parallelly arranged elongated elements that form the grating, is much smaller than the wavelength λ of incident light on the grating. Different propagation conditions of stimulated surface plasmons of the metallic grating are the cause of the polarizing effect.
The polarizing effect depends on a number of different grating parameters, in particular on the grating period d, the grating depth h, i.e. the thickness of the grating, the filling factor c (which equals the width/of the grating divided by the grating period d), the constant refractive indices ni and 723 of the respective medias separated by the grating, and distribution of refractive indices ri2(x, y, z) in the grating. For an illustration of these parameters, reference is made to Fig. 1. Light is incident on the grating under an angle θ. As shown in the same figure, light beams that are incident on a grating typically results in a number of light beams, both transmitted light beams 71,- to 3} and reflected light beams R.k to Ri. The angles θn for diffracted light beams are defined by the well-known grating equation:
tip,3]Sin θn = nisin θ + (mλ/d) (1)
Equation 1 shows that only diffractions of order zero ("zeroth-order") exist if the grating period is small enough, where m specifies the order. If the distribution of refractive indices R2(X, y, z) is complex, i.e. if one of the medias is metallic, the grating will function like a wire grid polarizer. Typically, prior art strategies for design of wire grid polarizers assume that the grating period should be as small as possible in order to achieve a high contrast ratio CTM/TE = ητιJητE and high efficiencies in transmitted transverse magnetic (TM) polarization. If the grating production process defines a lower limit of the grating period d, the grating depth h and the filling factor c are the only design parameters which may be varied and experimented with.
On the other hand, a grating with a carrier grating period dc, which is called the local period of the grating, can be modulated for each individual element in the grating. If the modulation frequency is not too high, such a grating propagates all energy in a direction specified in accordance with equation (1) using the carrier grating period dc. Because of the modulation, the energy distribution in that specified direction may be affected.
US Patent no. 6,108,131 discloses a polarizer apparatus having an arrangement of generally parallelly elongated elements disposed in a source light beam. The elements interact with the electromagnetic waves of the source light beam to generally (i) pass light having a polarization oriented perpendicular to the length of the elements, and (ii) reflect light having a polarization oriented parallel to the length of the elements. The passed light defines a passed beam with a first polarization and the reflected light defines a reflected beam with a second polarization. The elements are located in generally parallel arrangement with a center-to-center spacing, or pitch, of the elements which is smaller than the wavelength of light. In the disclosed arrangement, the pitch will be less than 400 nm, and preferably less than one third of the wavelength of light, or approximately 130 nm. In addition, each element has a width that may range from 10% to 90% of the pitch. Thus, spaces separating the elements have a width that will range from 90% to 10% of the pitch.
A problem to be solved in US Patent no. 6,108,131 is that the arrangement of generally parallelly elongated elements is confined to a small pitch, i.e. a pitch that is smaller than the wavelength of light, and preferably smaller than one third of the wavelength of light. The smaller the pitch, the more complex the production process will be in order to produce a functioning element arrangement.
An object of the present invention is to provide a polarizing device that solves the above given problems and which polarizing device has a high performance, but which uses a pitch that is greater than the wavelength of light incident on the device.
This object is attained by a polarizing device arranged to produce a polarized light beam from a source light beam that has a first and a second polarization direction, wherein the device transmits light of the first polarization direction and reflects light of the second polarization direction, in accordance with claim 1. According to a first aspect of the present invention, there is provided a polarizing device comprising a number of parallelly arranged conducting means, which means polarize the unpolarized light beam, wherein the number of conducting means has a pitch that is greater than the wavelength of the source light beam, and a carrier pitch that differs for at least two of the parallelly arranged conducting means.
An idea of the present invention is to provide a polarizing device, such as a grating, having a strong polarizing effect, but which device employs a relatively large grating period, or pitch, as compared with prior art polarizers. The effective grating period of the polarizing device according to the present invention, as will be shown in exemplifying embodiments, will be much larger than the smallest wavelength of the source light beam incident on the polarizing device. Due to the fact that a carrier grating is employed, contrast ratio and polarization efficiency can be maximized. The polarizing device may advantageously be implemented in, for example, front and rear projection systems.
The present invention is advantageous, since "binary", or unmodulated, gratings with a large grating period in comparison with the wavelength of the incident light do not show a strong polarizing effect. With the polarizing device proposed with the present invention, a designer of gratings is not confined to small grating periods.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.
Preferred embodiments of the present invention will be described in more detail with reference made to the attached drawings, in which:
Fig. 1 illustrates a polarizing device in the form of a grating and parameters employed to define the grating used in the present invention;
Fig. 2 shows a grating in accordance with an embodiment of the present invention; Fig. 3 shows a comparison of transmission efficiency of the zeroth diffraction order between a binary grating and a carrier grating for TE and TM polarization, depending on the wavelength of incident light;
Fig. 4 shows transmission efficiency of TE polarization depending on the wavelength of light incident on the grating according to the present invention; Fig. 5 shows transmission efficiency of TM polarization depending on the wavelength of light incident on the grating according to the present invention;
Fig. 6 shows contrast depending on the wavelength of light incident on the grating according to the present invention; and Fig. 7 shows an example of a projection display system comprising the polarizing device.
Fig. 1 illustrates a polarizing device in the form of a grating and parameters employed to define the grating used in the present invention. Prior art wire grid polarizers typically reflect one polarization state and transmit the other if the grating period d is much smaller than the wavelength λ of light L incident on the grating. The grating period d is the center-to-center distance of parallelly arranged elongated elements E that form the grating. As previously mentioned, the polarizing effect depends on a number of different grating parameters, in particular said grating period d, the grating depth h, i.e. the thickness of the grating, the filling factor c (which equals the width/of the grating divided by the grating period d), the constant refractive indices nj and ns of the respective medias separated by the grating, and distribution of refractive indices ri2 (x, y, z) in the grating. The light Z, is incident on the grating under an angle θ, and the incident light results in a number of light beams, both transmitted light beams 71; to 7} and reflected light beams R-k to Ri.
Fig. 2 illustrates a polarizing device in the form of a grating in accordance with an embodiment of the present invention. The new design approach introduced by the present invention combines the advantages of both wired grid polarizers in the prior art and a modulated high frequency carrier grating to create a polarizing device which may be adapted, and ideally optimized, such that is attains a specific optical function required to satisfy a specific optical requirement. In an exemplifying embodiment of the present invention, a carrier grating period dc of 72 nm has been employed. However, the effective grating period d equals 8 x dc = 8 x 72 = 576 nm. The smallest wavelength λ of the incident light is 400 nm. Hence, with the polarizing device proposed by the present invention, a designer of gratings is given a greater degree of freedom, since he is not confined to using small grating periods in the design process. Employing pulse density modulation or pulse width modulation to modulate the carrier grating may optimize the transmission efficiency. These modulation techniques are known by the skilled person, and it should be clear that the skilled person realizes that any other known appropriate modulation technique can be employed. In the exemplifying embodiment of the carrier grating of the present invention, the refractive index ni is that of glass and the refractive index «3 for a substrate in which the grating is located is 1.0. The grating itself is formed of a mixture of glass and aluminum. The thickness h of the grating is typically approximately 150 nm. Fig. 3 shows that the efficiency of TM polarization advantageously may be maximized by employing the grating of the present invention. The dotted curve shows the efficiency of a binary grating. The efficiency of the binary grating peaks at 90% for a λ/d ratio of approximately 2.2. For greater λ/d ratios, the efficiency decreases rapidly. The unbroken curve shows the efficiency of a polarizer employing carrier gratings. The efficiency of the carrier grating continuously lies slightly above 90%, even though the λ/d 'ratio steadily increases. This is highly advantageous.
An object of the grating of the present invention is to have a minimum contrast ratio Cmin of 300 and a maximum of transmission efficiency for TM polarization. Fig. 4 shows transmission efficiency η of TE polarization depending on the wavelength λ of light incident on the grating according to the present invention. Fig. 5 shows transmission efficiency η of TM polarization depending on the wavelength λ of light incident on the grating according to the present invention. The minimum efficiency ηmj,, is 81.2%, the average efficiency ηavg is 84.5% and the maximum efficiency ηmax is 89.2%. These figures are comparable with the results of a pure binary grating having a grating period d of 70 nm. Fig. 6 shows the contrast C depending on the wavelength of light incident on the grating according to the present invention. For a wavelength λ of 400 nm on the incident light, the contrast C is approximately 363, which is well above the required minimum contrast ratio Cmin of 300.
Fig. 7 shows an example of a projection display system 10 for projection image information. For example, data images or video images. The projection display system comprises a light source 11 for generating a light beam, a reflector 12 and the new polarizing device 13. Furthermore the projection display system 10 comprises a reflective liquid crystal display panel 14 for modulation the polarization direction of the transmitted light beam with the image information. An example of a reflective liquid crystal display is a liquid crystal on silicon (LCOS) device. Furthermore, the projection display system comprises projection optics 15 for projection the modulated light beam and a screen 16. In operation, the light source 11 generates a light beam and the reflector 12 directs the generated light beam 17 to the polarizing device 13. The polarizing device reflects a first linearly polarized light beam having a first polarization direction and transmits a second linearly polarized light beam 18, having a second polarization direction perpendicular to the first polarization direction, to the LCOS device 14. The operation of the LCOS device is well known to the skilled person. The LCOS device 14 modulates the direction of polarization of the incident light beam and reflects the light beam towards the projection optics 15 via the polarizing device 13. The polarizing device 13 reflects only the component of reflected light beam 19 with the first polarization direction and thus converts the polarization modulation in an amplitude modulation of the light beam. The projection optics projects the modulated light beam 19 on the screen 16.
Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.

Claims

CLAIMS:
1. A polarizing device arranged to produce at least one polarized light beam from a source light beam (L) that has a first and a second polarization direction, wherein the device transmits light (T) of the first polarization direction and reflects light (R) of the second polarization direction, which device comprises: a number of parallelly arranged conducting means (E), which means polarize said source light beam, wherein said number of conducting means has a pitch (d) that is equal to or greater than the wavelength (λ) of said source light beam, and a carrier pitch (dc) that differs for at least two of said parallelly arranged conducting means.
2. The polarizing device in accordance with claim 1, wherein said pitch (d) is equal to or greater than the wavelength (λ) of visible light.
3. The polarizing device in accordance with claim 1, wherein said pitch (d) is greater than 400 nanometers.
4. The polarizing device in accordance with claim 1, wherein said number of parallelly arranged conducting means (E) comprise a grating.
5. The polarizing device in accordance with claim 3, wherein said grating has a thickness (h) of approximately 150 nanometers.
6. The polarizing device in accordance with claim 4, wherein the grating material comprises aluminum.
7. The polarizing device in accordance with claim 1, wherein a carrier employed in the polarizing device is modulated by means of pulse width modulation.
8. The polarizing device in accordance with any one of claims 1-6, wherein a carrier employed in the polarizing device is modulated by means of pulse density modulation.
9. Display system provided with a polarizing device as claimed in claim 1.
PCT/IB2005/052092 2004-07-13 2005-06-24 Polarizing device WO2006008666A1 (en)

Applications Claiming Priority (2)

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EP04103333 2004-07-13
EP04103333.3 2004-07-13

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0592075A1 (en) * 1992-09-28 1994-04-13 Sharp Kabushiki Kaisha A polarization detector
JP2000284117A (en) * 1999-03-30 2000-10-13 Fuji Elelctrochem Co Ltd Grid polarizer and its manufacture
EP1160589A1 (en) * 2000-05-31 2001-12-05 Canon Kabushiki Kaisha Diffractive optical element and optical system having the same
JP2002365416A (en) * 2001-06-06 2002-12-18 Asahi Glass Co Ltd Polarization diffraction element and optical head device
JP2003294947A (en) * 2002-04-08 2003-10-15 Ricoh Co Ltd Polarized light separating element and method for manufacturing the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0592075A1 (en) * 1992-09-28 1994-04-13 Sharp Kabushiki Kaisha A polarization detector
JP2000284117A (en) * 1999-03-30 2000-10-13 Fuji Elelctrochem Co Ltd Grid polarizer and its manufacture
EP1160589A1 (en) * 2000-05-31 2001-12-05 Canon Kabushiki Kaisha Diffractive optical element and optical system having the same
JP2002365416A (en) * 2001-06-06 2002-12-18 Asahi Glass Co Ltd Polarization diffraction element and optical head device
JP2003294947A (en) * 2002-04-08 2003-10-15 Ricoh Co Ltd Polarized light separating element and method for manufacturing the same

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 2000, no. 13 5 February 2001 (2001-02-05) *
PATENT ABSTRACTS OF JAPAN vol. 2003, no. 04 2 April 2003 (2003-04-02) *
PATENT ABSTRACTS OF JAPAN vol. 2003, no. 12 5 December 2003 (2003-12-05) *

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