JPS63192006A - Objective lens for optical disk - Google Patents
Objective lens for optical diskInfo
- Publication number
- JPS63192006A JPS63192006A JP2346387A JP2346387A JPS63192006A JP S63192006 A JPS63192006 A JP S63192006A JP 2346387 A JP2346387 A JP 2346387A JP 2346387 A JP2346387 A JP 2346387A JP S63192006 A JPS63192006 A JP S63192006A
- Authority
- JP
- Japan
- Prior art keywords
- lens
- disk
- thickness
- aspherical
- aspherical surface
- Prior art date
- Legal status (The legal status 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 status listed.)
- Pending
Links
- 230000003287 optical effect Effects 0.000 title claims description 18
- 230000004075 alteration Effects 0.000 abstract description 23
- 230000015556 catabolic process Effects 0.000 abstract 2
- 238000006731 degradation reaction Methods 0.000 abstract 2
- 230000006866 deterioration Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000005494 condensation Effects 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
Landscapes
- Lenses (AREA)
Abstract
Description
【発明の詳細な説明】
〔産業上の利用分野〕
本発明は、光ディスク用ピックアップに用いられる対物
レンズに関するものである。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an objective lens used in an optical disc pickup.
光ディスク用ピックアップに用いられる対物レンズは、
収差補正が十分になされておシなおかつ自動焦点、トラ
ッキングサーボの必要性から小型軽量でなければならな
い。The objective lens used in optical disc pickups is
It must have sufficient aberration correction, and be small and lightweight due to the need for automatic focusing and tracking servo.
特開昭５７−７６５１２号、特開昭６１−８８２１３号
に記載されている光ディスク用対物レンズは、非球面単
レンズを用いることにより収差補正が十分になされ、小
型軽量化されている。The objective lenses for optical discs described in Japanese Patent Laid-open Nos. 57-76512 and 61-88213 use an aspherical single lens to sufficiently correct aberrations and are made smaller and lighter.
しかし現在の光ディスクは、厚さが１．２稿のものと１
．２５１１１１のものがあり、対物レンズも光ディスク
の厚さに合わせた収差補正が行なわれている。However, current optical discs have a thickness of 1.2 mm and 1.2 mm thick.
．． 251111 is available, and the objective lens is also corrected for aberrations in accordance with the thickness of the optical disc.
そのため同一の対物レンズを用いて両方の光ディスクを
使用した場合、どちらか一方の光ディスクで著しい性能
劣化を生ずることになる。したがって光ディスクに合わ
せて２種類の対物レンズが必要になる。Therefore, if both optical disks are used with the same objective lens, the performance of one of the optical disks will be significantly degraded. Therefore, two types of objective lenses are required depending on the optical disc.
前述の従来例のうち、特開昭５７−７６５１２号に記載
されているような両面が非球面の対物レンズの場合、面
の偏芯による性能劣化が大きく、レンズを製作すること
が難しく、コスト高になってしまう。Among the conventional examples mentioned above, in the case of an objective lens with aspherical surfaces on both sides, such as the one described in JP-A No. 57-76512, the performance deteriorates significantly due to eccentricity of the surfaces, making it difficult to manufacture the lens and increasing the cost. It gets expensive.
又特開昭６１−８８２１３号に記載されている平凸の非
球面レンズは、片面が平面であるために面の偏芯による
性能劣化が小さく製作性が良くなっている。しかし光デ
ィスクの厚さの変化に対する性能の劣化が大きく厚さ１
．２ ｍｍの光ディスクと１．２５１１１１の光ディス
クの両方で同じ性能を出すことが出来ない。Furthermore, the plano-convex aspherical lens described in JP-A No. 61-88213 has one flat surface, so that performance deterioration due to eccentricity of the surface is small and manufacturing efficiency is improved. However, the performance deteriorates significantly with changes in the thickness of the optical disk.
．． It is not possible to achieve the same performance with both a 2 mm optical disc and a 1.251111 optical disc.
〔発明が解決しようとする問題点〕
本発明は、前記のような従来例の欠点を除去するために
々されたものであって一方の面のみが非球面でしかもい
ずれの光ディスクにても使用可能である光ディスク用対
物レンズを提供するものである。[Problems to be Solved by the Invention] The present invention has been made in order to eliminate the drawbacks of the conventional example as described above. The object of the present invention is to provide an objective lens for an optical disc that is possible.
本発明の光ディスク用対物レンズは、前記の問題点を解
決するために、第１面が正の屈折力を持つ非球面で第２
面が平面である凸平レンズよシなシ、前記非球面上の一
点から頂点の接平面に下した重縮の長さをＸ、入射元高
をＹ、非球面の頂点での曲率半径をｒとした時、前記非
球面が下記の式にて表わされ、又次の条件（１）乃至条
件（３）を満足するものである。In order to solve the above problems, the objective lens for optical discs of the present invention has a first surface that is an aspherical surface with positive refractive power, and a second surface that has a positive refractive power.
For a convex-planar lens whose surface is a flat surface, the length of condensation from a point on the aspherical surface to the tangent plane of the apex is X, the height of the source of incidence is Y, and the radius of curvature at the apex of the aspherical surface is When r is the aspherical surface, the aspherical surface is expressed by the following formula and satisfies the following conditions (1) to (3).
（１） １．７ ＜ ｎ
（２） ０．９ ＜α〈１
（３） −１≦に≦０．５
ただしｎはレンズの作動波長での屈折率、αは下記の式
にて表わされる値、ｋは後に示す非球面の式における円
錐定数である。(1) 1.7 < n (2) 0.9 <α<1 (3) -1≦≦0.5 where n is the refractive index at the operating wavelength of the lens, and α is expressed by the following formula. The value k is the conic constant in the aspherical equation shown later.
上記αの式のｆは全系の焦点距離、ＮＡは開口数、ｄは
レンズの中心厚、ｔ はディスクの厚さ、ｎｄはディス
クの屈折率である。In the above equation for α, f is the focal length of the entire system, NA is the numerical aperture, d is the center thickness of the lens, t is the thickness of the disk, and nd is the refractive index of the disk.
本発明の対物レンズは、偏芯による性能の劣化を小さく
するために前記のようにレンズの片面を平面にした。こ
の時開口数を０．５程度にした場合、レンズに用いる硝
材の屈折率は、１．７以上にしなくては非球面を用いて
もアプラナートなレンズを作ることは不可能である。つ
まシ条件（１）より外れるとアプラナートなレンズに出
来ない。In the objective lens of the present invention, one side of the lens is made flat as described above in order to reduce deterioration in performance due to eccentricity. In this case, when the numerical aperture is set to about 0.5, it is impossible to make an aplanar lens even if an aspherical surface is used unless the refractive index of the glass material used for the lens is 1.7 or more. If the condition deviates from condition (1), it will not be possible to make an aplanatic lens.
平凸レンズでは、焦点距離によって凸面の曲率半径が一
義的に決められるため肉厚を調節して正弦条件を補正す
ることになる。そのため条件（２）のように対物レンズ
とディスクの肉厚を定めることによシ最犬ロ径の近傍で
正弦条件が満足されるようになシこれによって軸外収差
を良好に補正できる。もし条件（２）をはずれた場合正
弦条件を満たすことが出来なくなり軸外収差を悪化させ
る。In a plano-convex lens, the radius of curvature of the convex surface is uniquely determined by the focal length, so the sine condition is corrected by adjusting the thickness. Therefore, by determining the thickness of the objective lens and the disk as in condition (2), the sine condition can be satisfied in the vicinity of the maximum diameter, thereby making it possible to satisfactorily correct off-axis aberrations. If condition (2) is not met, the sine condition cannot be satisfied and off-axis aberrations will worsen.
本発明の対物レンズは、非球面によって球面収差の補正
を行なっているが、高次の収差までは補正しきれない。Although the objective lens of the present invention corrects spherical aberration using an aspherical surface, it cannot correct high-order aberrations.
本発明では残存する高次の収差とディスクの厚み変化に
よって生ずる球面収差とを相殺させることによって性能
の劣化を少なくしている。そのためには、円錐定数ｋを
条件（３）の範囲に設定する必要がある。この条件の上
限又は下限からはずれると、非球面の高次係数を用いて
も゛高次の球面収差が大きくなシすぎて球面収差の補正
が困難になる。In the present invention, deterioration in performance is reduced by canceling out remaining high-order aberrations and spherical aberrations caused by changes in disk thickness. For this purpose, it is necessary to set the conic constant k within the range of condition (3). If the upper or lower limit of this condition is exceeded, even if high-order coefficients of the aspherical surface are used, the higher-order spherical aberration becomes too large, making it difficult to correct the spherical aberration.
このようにして具体的にはディスクの厚さを１、２０
朋に設定した場合、球面収差は全開口数の８割程度まで
プラス側に補正し、それ以上に高次の収差がのるように
してマイナの方向に向かうように補正している。これに
よってディスクの厚さが１．２５１１１１１になった場
合には厚さの変化によって生ずる球面収差はプラス側に
作用す−るので、いずれの場合も全体としてフルコレク
ションに近い状態になる。In this way, specifically, the thickness of the disk is 1,20
When set to 5, spherical aberration is corrected to the positive side up to about 80% of the total numerical aperture, and higher-order aberrations are corrected in the direction of minor. As a result, when the thickness of the disk becomes 1.2511111, the spherical aberration caused by the change in thickness acts on the positive side, so in either case, the state as a whole is close to full correction.
本発明の光ディスク用対物レンズの各実施例は、第１図
に示す通シで次のデーター〇通シである。Each embodiment of the objective lens for an optical disk of the present invention is shown in the following data in the diagram shown in FIG.
実施例１
ｆ＝４．２９３、ＮＡ ＝ ０．５０、刀＝１．９４２
ｒｌ＝３．３７３２
ｄ＝２．７０ ｎ＝１．７８５６９ｒ２”（１）
ｔｄ＝ １．２５ 、 ｎｄ ＝ １．４８８６０
に−” ０．１６６６ 、 Ａ４ ＝ ０．１１５７１
Ｘ１０−２Ａａ ” ０．８５４１５Ｘ１０−’
Ａｓ ” ０．５０５８２Ｘ１０−５
Ａ＋ｏ ＝−０，３８２０Ｘ１０−’
実施例２
ｆ＝４．３００ 、 ＮＡ＝０．５０ 、 ＷＤ＝２
．０７８ｒｌ ＝ ３．２９３５
ｄ＝２．５０ ｎ”１．７６５９１ｒ２ ＝ω
ｔｄ＝ １．２０ 、 ｎｄ＝ １．４８８６０
、 ｋ ＝ ０Ａ４＝ ０．１８４６２Ｘ１０−
２
Ａｓ ” ０．１４５４３Ｘ１０−３Ａｇ＝ ０．
８６４８４Ｘ１０−’
Ａ＋ｏ＝−０，１１５０４Ｘ １０−’実施例３
ｆ＝４．５００ 、 ＮＡ＝０．５０ 、 ＷＤ＝
２．２２２ｒ＋＝３．４４６６
ｄ＝２．６０ ｎ＝ １．７６５９１ｒ２”の
ｔｄ＝１．２０ 、ｎｄ＝１．４８８６０ 、に＝
−０，１００５Ａ４ ＝ ０．１３１４７Ｘ１０−２
Ａｓ ” ０．９１９６７Ｘ１０−’
Ａａ ”−０，５３１７９Ｘ１０−５
Ａ＋ｏ＝−０，３８２１０Ｘ１０−’
上記実施例でｒｌ＋ｒｌはレンズの第１面と第２面の曲
率半径、ｄはレンズの厚さ、ｎは作動波長でのレンズの
屈折率、ＷＤは作動距離である。Example 1 f=4.293, NA=0.50, sword=1.942
rl=3.3732 d=2.70 n=1.78569r2” (1) td=1.25, nd=1.48860
ni-” 0.1666, A4 = 0.11571
X10-2Aa "0.85415X10-'As" 0.50582X10-5 A+o = -0,3820X10-' Example 2 f=4.300, NA=0.50, WD=2
．． 078rl = 3.2935 d=2.50 n”1.76591r2 =ω td= 1.20, nd= 1.48860
, k = 0A4 = 0.18462X10-
2 As” 0.14543X10-3Ag=0.
86484X10-' A+o=-0, 11504X10-' Example 3 f=4.500, NA=0.50, WD=
2.222r+=3.4466 d=2.60 n=1.76591r2” td=1.20, nd=1.48860, to=
-0,1005A4 = 0.13147X10-2 As "0.91967X10-' Aa "-0,53179X10-5 A+o=-0,38210X10-' In the above example, rl+rl is the curvature of the first and second surfaces of the lens The radius, d, is the thickness of the lens, n is the refractive index of the lens at the working wavelength, and WD is the working distance.
これら実施例の収差状況は夫々第２図、第３図、第４図
に示す通シである。又実施例３においてディスクの厚さ
が１．２５１１１１１の時の収差状況を第５図に示しで
ある。この収差状況と第４図に示す実施例３の１．２０
ｆｆ１ｆｉの時の収差状況とより明らかなようにディ
スクの厚さが１．２ Ｑｍｓ、 １．２５闘のいずれの
場合も収差が良好に補正されている。The aberration situations of these examples are shown in FIGS. 2, 3, and 4, respectively. Further, FIG. 5 shows the aberration situation when the thickness of the disk is 1.2511111 in Example 3. This aberration situation and 1.20 of Example 3 shown in FIG.
As is clearer from the aberration situation when ff1fi is used, aberrations are well corrected when the disk thickness is 1.2 Qms or 1.25 Qms.
本発明の光ディスク用対物レンズは、レンズの片面が平
面であるので面側芯による性能劣化が小するものである
。In the objective lens for an optical disk of the present invention, since one side of the lens is flat, there is little performance deterioration due to the core on the side.
第１図は本発明の光ディスク用対物レンズの断面図、第
２図乃至第４図は夫々本発明の実施例１乃至実施例３の
収差曲線図、第５図は実施例３のディスク厚１．２５ｆ
ｉの時の収差曲線図である。FIG. 1 is a sectional view of an objective lens for an optical disk of the present invention, FIGS. 2 to 4 are aberration curve diagrams of Examples 1 to 3 of the present invention, respectively, and FIG. 5 is a disk thickness 1 of Example 3. .25f
It is an aberration curve diagram at the time of i.
Claims (1)
成される凸平レンズで、前記非球面上の一点から頂点の
接平面に下した垂線の長さをＸ、入射光高をＹ、非球面
の頂点での曲率半径をｒとした時、前記非球面が下記の
式にて表わされ、又次の条件（１）乃至条件（３）を満
足する光ディスク用対物レンズ。 Ｘ＝Ｙ＾２／｛ｒ＋√［１−（ｋ＋１）（Ｙ／ｒ）＾２
］｝＋Σ＿ｉ＿−＿２Ａ＿２＿ｉＹ＾２＾ｉ（１）１．
７＜ｎ （２）０．９＜α＜１ （３）−１≦ｋ≦０．５ ただし、非球面の式におけるｋは円錐定数、Ａ＿２＿ｉ
は２ｉ次における非球面係数であり、又条件中のαは全
系の焦点距離をｆ、開口数をＮＡ、レンズの中心厚をｄ
、作動波長でのレンズの屈折率をｎ、ディスクの厚さを
ｔ＿ｄ、ディスクの屈折率をｎ＿ｄとしたとき下記の式
で与えられる。 α＝ｆ・ＮＡ／［（ｄ／ｎ）＋（ｔ＿ｄ／ｎ＿ｄ）］[Claims] A convex plano lens whose first surface is an aspherical surface with positive refractive power and whose second surface is a flat surface, in which a perpendicular line drawn from a point on the aspherical surface to a tangential plane at the apex. When the length is X, the incident light height is Y, and the radius of curvature at the apex of the aspherical surface is r, the aspherical surface is expressed by the following formula, and the following conditions (1) to (3) An objective lens for optical discs that satisfies the following. X=Y^2/{r+√[1-(k+1)(Y/r)^2
]}+Σ_i_−_2A_2_iY^2^i(1)1.
7<n (2) 0.9<α<1 (3) −1≦k≦0.5 However, k in the aspherical formula is the conic constant, A_2_i
is the aspherical coefficient in the 2i order, and α in the conditions is f for the focal length of the entire system, NA for the numerical aperture, and d for the center thickness of the lens.
, where n is the refractive index of the lens at the operating wavelength, t_d is the thickness of the disk, and n_d is the refractive index of the disk. α=f・NA/[(d/n)+(t_d/n_d)]
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2346387A JPS63192006A (en) | 1987-02-05 | 1987-02-05 | Objective lens for optical disk |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2346387A JPS63192006A (en) | 1987-02-05 | 1987-02-05 | Objective lens for optical disk |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPS63192006A true JPS63192006A (en) | 1988-08-09 |
Family
ID=12111213
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2346387A Pending JPS63192006A (en) | 1987-02-05 | 1987-02-05 | Objective lens for optical disk |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS63192006A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5371632A (en) * | 1992-07-31 | 1994-12-06 | Minolta Co., Ltd. | Single aspherical plano-convex collimator lens |
-
1987
- 1987-02-05 JP JP2346387A patent/JPS63192006A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5371632A (en) * | 1992-07-31 | 1994-12-06 | Minolta Co., Ltd. | Single aspherical plano-convex collimator lens |
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