JPH0210402B2 - - Google Patents

Info

Publication number
JPH0210402B2
JPH0210402B2 JP1430383A JP1430383A JPH0210402B2 JP H0210402 B2 JPH0210402 B2 JP H0210402B2 JP 1430383 A JP1430383 A JP 1430383A JP 1430383 A JP1430383 A JP 1430383A JP H0210402 B2 JPH0210402 B2 JP H0210402B2
Authority
JP
Japan
Prior art keywords
lens
group
focal length
disk
aberration
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.)
Expired
Application number
JP1430383A
Other languages
Japanese (ja)
Other versions
JPS59140414A (en
Inventor
Takahiro Sugyama
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Pentax Corp
Original Assignee
Asahi Kogaku Kogyo Co Ltd
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 Asahi Kogaku Kogyo Co Ltd filed Critical Asahi Kogaku Kogyo Co Ltd
Priority to JP1430383A priority Critical patent/JPS59140414A/en
Publication of JPS59140414A publication Critical patent/JPS59140414A/en
Publication of JPH0210402B2 publication Critical patent/JPH0210402B2/ja
Granted legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B13/00—Optical objectives specially designed for the purposes specified below
    • G02B13/001—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras
    • G02B13/0015—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras characterised by the lens design
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B13/00—Optical objectives specially designed for the purposes specified below
    • G02B13/24—Optical objectives specially designed for the purposes specified below for reproducing or copying at short object distances
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B2007/13727—Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Lenses (AREA)

Description

【発明の詳細な説明】[Detailed description of the invention]

本発明は光デイスク（高密度情報記録媒体）用
対物レンズに関するものである。 既に知られているとおり、光デイスクに記録さ
れた高密度の情報の読み取りに使用される対物レ
ンズは、高密度の信号を読み取らなければならな
いので1μ程度の分解能を必要とされる。従つて
対物レンズの開口数（NA）は0.48程度の明るさ
が要求される。しかも、この対物レンズはトラツ
キングやフオーカシングのために可動となつてい
る場合が多く、小型で軽量である事が要求され
る。又、この対物レンズが可動となつている場合
が多くなつている事から、対物レンズとデイスク
面との間隔、即ち作動距離は、ある程度以上に大
きくないと、対物レンズがデイスク面に当つてし
まうという実用上の不都合が生じる恐れがある。 本発明にかかるレンズは、以上の事を充分に考
慮に入れ、NAは0.48と明るく、作動距離は0.39F
〜0.40Fと充分に大きく、しかも小型・軽量であ
りながら、諸収差、特に球面収差を良好に補正す
る事に成功したものである。 本発明は、２群２枚構成レンズよりなり、第１
群は凸面を光源側に向けた正のメニスカスレン
ズ、第２群も凸面を光源側に向けた正のメニスカ
スレンズにより構成され、符号を、Ｆはレンズ全
系の合成焦点距離、F2は第２群の焦点距離、riは
第ｉ番目の曲率半径、diは第ｉ番目のレンズ肉厚
又はレンズ間隔、Njは第ｊ番目レンズの屈折率
とするとき、以下の条件を満足することを特徴と
する光デイスク用対物レンズである。 (1) 2.0F＜F2＜2.4F (2) 10F＜r2＜20F (3) 0.5F＜r4＜0.7F (4) N1，N2＞1.83 以下各条件について説明する。 (1)の条件は球面収差の補正を良好にするための
ものであり、本発明レンズが２群２枚構成レンズ
よりなる事から、第２群レンズの焦点距離を定め
れば、第１群レンズの焦点距離もほぼ定まり、各
レンズの度の配分がすべて定まつてしまう。今、
F2が上限を越えて大きいときには、第１群レン
ズの焦点距離が小さくなりすぎ、第１群レンズで
の負の球面収差の発生量が多くなり、球面収差の
補正が困難となる。又、F2が下限を越えて小さ
いときには、第２群レンズの焦点距離が小さくな
りすぎ、第２群レンズでの負の球面収差の発生量
が多くなり、球面収差の補正が困難となる。 (2)，(3)の条件は正弦条件を整えてコマ収差を補
正するための条件であり、光デイスク用対物レン
ズの収差の補正は、基本的にはレンズの光軸上の
像性能を良くするために球面収差の補正をすれば
良いわけであるが、レンズのセツテイングによる
光軸のずれは避けられないものであり、ある程度
の軸外の像性能を補正しなくてはならない。その
ためには正弦条件を整えてコマ収差の補正を良好
にしなくてはならない。今、(2)の条件のr2が上限
を越えて大きいときには、正弦条件不満足量が正
で大きくなりすぎ、コマ収差の増大をまねき好ま
しくない。又、r2が下限を越えて小さいときに
は、正弦条件不満足量が負で大きくなりすぎ、コ
マ収差の増大をまねき好ましくない。 (3)の条件のr4が上限を越えて大きいときには、
正弦条件不満足量が正で大きくなりすぎ、コマ収
差の増大をまねき好ましくない。又、r4が下限を
越えて小さいときには、正弦条件不満足量が負で
大きくなりすぎ、コマ収差の増大をまねき好まし
くない。 (4)の条件は球面収差を良好に補正するための条
件であり、N1，N2が下限を越えて小さいときに
は、同じ焦点距離を得るためには各レンズの曲率
半径が小さくなつてしまい、各面での球面収差の
発生量が大きくなつてしまい、目的とする球面収
差量に補正する事が困難となつてしまう。 本発明にかかるレンズは、前記(1)から(4)の条件
を満足し、諸収差を良好に補正した光デイスク用
対物レンズを提供するものである。 次に本発明レンズの実施例１、実施例２、実施
例３の数値を示す。 但し、Wtは対物レンズとデイスクのカバーガ
ラスとの空気間隔（作動距離）、ｔはデイスクの
カバーガラスの厚み、Ntはデイスクのカバーガ
ラスの屈折率である。また屈折率はすべて波長
800nmにおける数値である。 The present invention relates to an objective lens for optical disks (high-density information recording media). As is already known, the objective lens used to read high-density information recorded on optical disks must have a resolution of about 1 μm because it must read high-density signals. Therefore, the numerical aperture (NA) of the objective lens is required to have a brightness of about 0.48. Moreover, this objective lens is often movable for tracking or focusing, and is required to be small and lightweight. In addition, as this objective lens is increasingly movable, the distance between the objective lens and the disk surface, that is, the working distance, must be larger than a certain level otherwise the objective lens will hit the disk surface. This may cause practical inconvenience. The lens according to the present invention takes the above points into consideration, has a bright NA of 0.48, and has a working distance of 0.39F.
Although it is sufficiently large at ~0.40F, compact and lightweight, it successfully corrects various aberrations, especially spherical aberration. The present invention consists of a lens composed of two elements in two groups, and the first
The group consists of a positive meniscus lens with its convex surface facing the light source, and the second group also consists of a positive meniscus lens with its convex surface facing the light source. The following conditions are satisfied when the focal length of the second group, r i is the i-th radius of curvature, d i is the i-th lens thickness or lens spacing, and N j is the refractive index of the j-th lens. This is an objective lens for an optical disk characterized by the following. (1) 2.0F<F 2 <2.4F (2) 10F<r 2 <20F (3) 0.5F<r 4 <0.7F (4) N 1 , N 2 >1.83 Each condition will be explained below. The condition (1) is for good correction of spherical aberration, and since the lens of the present invention is composed of two lenses in two groups, if the focal length of the second group lens is determined, the focal length of the first group lens is The focal length of the lens is also almost fixed, and the power distribution of each lens is all fixed. now,
When F 2 exceeds the upper limit and is large, the focal length of the first group lens becomes too small, and the amount of negative spherical aberration generated in the first group lens increases, making it difficult to correct the spherical aberration. Furthermore, when F2 is small beyond the lower limit, the focal length of the second group lens becomes too small, and the amount of negative spherical aberration generated in the second group lens increases, making it difficult to correct the spherical aberration. Conditions (2) and (3) are conditions for correcting coma aberration by adjusting the sine condition, and correction of aberration of an objective lens for optical disks basically improves the image performance on the optical axis of the lens. In order to improve the image quality, it is sufficient to correct spherical aberration, but misalignment of the optical axis due to lens setting is unavoidable, and a certain degree of off-axis image performance must be corrected. To achieve this, it is necessary to improve the sine conditions and correct coma aberration. Now, when r 2 in condition (2) exceeds the upper limit and is large, the amount of unsatisfactory sine condition becomes too large and positive, leading to an increase in coma aberration, which is undesirable. Furthermore, when r 2 is smaller than the lower limit, the amount of unsatisfactory sine condition becomes negative and too large, leading to an increase in coma aberration, which is undesirable. When r 4 in condition (3) is larger than the upper limit,
The amount of unsatisfactory sine condition becomes too large and positive, which leads to an increase in coma aberration, which is undesirable. Furthermore, when r 4 is small beyond the lower limit, the amount of unsatisfactory sine condition becomes negative and too large, leading to an increase in coma aberration, which is undesirable. Condition (4) is a condition for good correction of spherical aberration, and when N 1 and N 2 are small beyond the lower limit, the radius of curvature of each lens becomes small in order to obtain the same focal length. , the amount of spherical aberration generated on each surface increases, making it difficult to correct the amount of spherical aberration to the desired amount. The lens according to the present invention satisfies the conditions (1) to (4) above and provides an objective lens for an optical disk in which various aberrations are well corrected. Next, numerical values of Example 1, Example 2, and Example 3 of the lenses of the present invention are shown. However, Wt is the air distance (working distance) between the objective lens and the disk cover glass, t is the thickness of the disk cover glass, and Nt is the refractive index of the disk cover glass. Also, the refractive index is all about the wavelength
This is the value at 800nm.

【実施例 １】 r1＝1.543 d1＝0.572 N1＝1.84850 r2＝10.823 d2＝0.007 r3＝0.593 d3＝0.327 N2＝1.84850 r4＝0.675 Ｆ＝1.000 NA＝0.48 Wt＝0.352 ｔ＝0.289 Nt＝1.51 F2＝2.029[Example 1] r 1 = 1.543 d 1 = 0.572 N 1 = 1.84850 r 2 = 10.823 d 2 = 0.007 r 3 = 0.593 d 3 = 0.327 N 2 = 1.84850 r 4 = 0.675 F = 1.000 NA = 0.48 Wt = 0.3 52 t=0.289 Nt=1.51 F2 =2.029

【実施例 ２】 r1＝1.558 d1＝0.368 N1＝1.86796 r2＝13.099 d2＝0.014 r3＝0.617 d3＝0.325 N2＝1.86796 r4＝0.681 Ｆ＝1.000 NA＝0.48 Wt＝0.387 ｔ＝0.291 Nt＝1.51 F2＝2.256[Example 2] r 1 = 1.558 d 1 = 0.368 N 1 = 1.86796 r 2 = 13.099 d 2 = 0.014 r 3 = 0.617 d 3 = 0.325 N 2 = 1.86796 r 4 = 0.681 F = 1.000 NA = 0.48 Wt = 0.3 87 t=0.291 Nt=1.51 F2 =2.256

【実施例 ３】 r1＝1.626 d1＝0.309 N1＝1.87955 r2＝12.129 d2＝0.014 r3＝0.627 d3＝0.335 N2＝1.87955 r4＝0.681 Ｆ＝1.000 NA＝0.48 Wt＝0.398 ｔ＝0.291 Nt＝1.51 F2＝2.307[Example 3] r 1 = 1.626 d 1 = 0.309 N 1 = 1.87955 r 2 = 12.129 d 2 = 0.014 r 3 = 0.627 d 3 = 0.335 N 2 = 1.87955 r 4 = 0.681 F = 1.000 NA = 0.48 Wt = 0.3 98 t=0.291 Nt=1.51 F2 =2.307

【図面の簡単な説明】[Brief explanation of drawings]

第１図は実施例１のレンズ構成図、第２図は実
施例１のコマ収差及び波面収差図、第３図は実施
例２のレンズ構成図、第４図は実施例２のコマ収
差及び波面収差図、第５図は実施例３のレンズ構
成図、第６図は実施例３のコマ収差及び波面収差
図である。 Fig. 1 is a lens configuration diagram of Example 1, Fig. 2 is a coma aberration and wavefront aberration diagram of Example 1, Fig. 3 is a lens configuration diagram of Example 2, and Fig. 4 is a coma aberration and wavefront aberration diagram of Example 2. FIG. 5 is a diagram of the lens configuration of Example 3, and FIG. 6 is a diagram of coma aberration and wavefront aberration of Example 3.

Claims (1)

【特許請求の範囲】 １ ２群２枚構成レンズよりなり、第１群は凸面
を光源側に向けた正のメニスカスレンズ、第２群
も凸面を光源側に向けた正のメニスカスレンズに
より構成され、以下の条件を満足することを特徴
とする光デイスク用対物レンズ。 (1) 2.0F＜F2＜2.4F (2) 10F＜r2＜20F (3) 0.5F＜r4＜0.7F (4) N1，N2＞1.83 ここで、Ｆはレンズ全系の合成焦点距離、F2
は第２群レンズの焦点距離、r2は第１群レンズの
デイスク側面の曲率半径、r4は第２群レンズのデ
イスク側面の曲率半径、N1は第１群レンズの屈
折率、N2は第２群レンズの屈折率である。[Claims] 1. Consisting of two lenses in two groups, the first group is a positive meniscus lens with a convex surface facing the light source side, and the second group is also a positive meniscus lens with a convex surface facing the light source side. An objective lens for an optical disk, characterized by satisfying the following conditions. (1) 2.0F＜F 2 ＜2.4F (2) 10F＜r 2 ＜20F (3) 0.5F＜r 4 ＜0.7F (4) N 1 , N 2 ＞1.83 Here, F is the value of the entire lens system. Combined focal length, F2
is the focal length of the second group lens, r 2 is the radius of curvature of the side surface of the disk of the first group lens, r 4 is the radius of curvature of the side surface of the disk of the second group lens, N 1 is the refractive index of the first group lens, N 2 is the refractive index of the second group lens.
JP1430383A 1983-01-31 1983-01-31 Objective lens for optical disk Granted JPS59140414A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP1430383A JPS59140414A (en) 1983-01-31 1983-01-31 Objective lens for optical disk

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP1430383A JPS59140414A (en) 1983-01-31 1983-01-31 Objective lens for optical disk

Publications (2)

Publication Number Publication Date
JPS59140414A JPS59140414A (en) 1984-08-11
JPH0210402B2 true JPH0210402B2 (en) 1990-03-08

Family

ID=11857327

Family Applications (1)

Application Number Title Priority Date Filing Date
JP1430383A Granted JPS59140414A (en) 1983-01-31 1983-01-31 Objective lens for optical disk

Country Status (1)

Country Link
JP (1) JPS59140414A (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07119889B2 (en) * 1985-09-20 1995-12-20 コニカ株式会社 Condensing optical system for recording / reproducing optical system of optical information recording medium
JPH01262445A (en) * 1988-04-13 1989-10-19 Toshiba Corp Surface inspection device
JP3932578B2 (en) * 1996-10-24 2007-06-20 ソニー株式会社 Objective lens and optical pickup device
JP4506081B2 (en) * 2003-02-06 2010-07-21 コニカミノルタホールディングス株式会社 Optical pickup device

Also Published As

Publication number Publication date
JPS59140414A (en) 1984-08-11

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