JPS5915913A

JPS5915913A - Objective lens of optical high density recording and reproducing device

Info

Publication number: JPS5915913A
Application number: JP12506582A
Authority: JP
Inventors: Yoji Kubota; 洋治久保田; Hidetoshi Hadama; 葉玉　秀俊
Original assignee: Nidec Sankyo Corp
Current assignee: Nidec Sankyo Corp
Priority date: 1982-07-20
Filing date: 1982-07-20
Publication date: 1984-01-27
Also published as: JPH0215044B2

Abstract

PURPOSE:To make a titled lens small-sized and light weight, and also to enlarge an operating distance of the lens and NA, by placing successively the first, the second and the third lenses toward a recording and reproducing medium side from a light source side, and constituting so that its focal distance and the radius of curvature satisfy a specified inequality. CONSTITUTION:An objective lens is constituted of the first lens L1 of a negative meniscus lens whose convex face is turned to a light source side, the second biconvex lens L2 and the third lens L3 of a positive meniscus lens whose convex face is turned to the light source side. When focal distances of the whole lens system, a composite system of the lenses L1, L2 and the lens L3 are denoted as (f), f1,2 and f3, respectively, the radiuses of curvature of each lens are denoted as r2, r3 and r5, respectively, and conditional inequalities (1), (2) and (3) are satisfied, the inequality (1) is a condition for keeping the spherical aberration satisfactory, the inequality (2) is a condition for keeping the operating distance satisfactory, and the inequality (3) is a condition for keeping a correction of a field curvature satisfactory. In this way, it is possible to obtain an objective lens which is small-sized and light weight, and to enlarge its operating distance and NA.

Description

【発明の詳細な説明】本発明はビデオディスク等の光学式高密度記録再生装置
の対物レンズに関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an objective lens for an optical high-density recording/reproducing device such as a video disc.

光学式高密度記録再生装置の対物レンズは、久。The objective lens of optical high-density recording and reproducing equipment is long-lasting.

−力レンズ等の制御駆動を必借とし必然的に小型軽量化
が要求される一方、上記制御駆動時におけるディスク面
への衝突などを避けるために作動距離が大きく、捷だ記
録再生の精確度金向」ニさせるためにＮＡの大きなもの
が要求される。本発明はこれらの要求に沿って、小型軽
量で作動距離が犬きく且つＮＡの大きな光掌弐箇密度記
録角生装置の対物レンズを提供するものである。- While it is necessary to use control drive such as a power lens, it is inevitably required to be smaller and lighter, but the working distance is long to avoid collisions with the disk surface during the control drive, and the accuracy of recording and playback is poor. A large NA is required to achieve "Kinmukai". In accordance with these requirements, the present invention provides an objective lens for an optical beam density recording angle generating device that is small and lightweight, has a long working distance, and has a large NA.

以下、本発明について説明する。本発明の対物レンズは
３枚のレンズより構成される。この３枚のレンズは光源
側から記録再生媒体側に向けて、第ルンズ、第２レンズ
、第３レンズの順に配置される。上記第ルンズは光源側
に凸曲を向けた負のメニスカスレンズにより、第２レン
ズは両凸レンズにより、第３レンズは光源側に凸面を向
けた正のメニスカスレンズにより各々構成される。The present invention will be explained below. The objective lens of the present invention is composed of three lenses. These three lenses are arranged in the order of the first lens, the second lens, and the third lens from the light source side toward the recording/reproducing medium side. The first lens is a negative meniscus lens with a convex surface facing the light source, the second lens is a biconvex lens, and the third lens is a positive meniscus lens with a convex surface facing the light source.

このような対物レンズにおいてζ上記第ルンズの記録再
生媒体側の曲率半径ｋ　ｒｚ、第２レンズの光源側の曲
率半径ｋｒ３、第３Ｖンズの光源側の曲率半径をｒ５、
第１及び第２レンズの合成焦点距入１ｔをｆｌ　＋、２
　、第３レンズの焦点距離をｆ’３、全レンズ系の焦点
距離をｆとしたとき、本発明の対物レンズは次の３宋件
を満足する。In such an objective lens, the radius of curvature of the second lens on the recording/reproducing medium side is krz, the radius of curvature of the second lens on the light source side is kr3, the radius of curvature of the third lens on the light source side is r5,
The combined focal length 1t of the first and second lenses is fl +, 2
, the focal length of the third lens is f'3, and the focal length of the entire lens system is f, the objective lens of the present invention satisfies the following three conditions.

（ｉ）　０．５５　＜　　”２／　　＜　０．９５３（ｈ）　ｏ、２１　＜　　”’　／　ｙｏ、２　＜　０
．ｄＢ（ｉｉｉ）　０．５６　＜　　ｒ５／（＜　０．
９７上記の条件（１）は球面収差全良好に保つための条
件である。上限をこえると球面収差の補正不足、下限を
こえると補正過剰となる。(i) 0.55 <"2/< 0.953 (h) o, 21 <"' / yo, 2 < 0
．． dB(iii) 0.56 <r5/(< 0.
97 The above condition (1) is a condition for keeping all spherical aberrations in good condition. If the upper limit is exceeded, the spherical aberration will be under-corrected, and if the lower limit is exceeded, the spherical aberration will be over-corrected.

条件（１１）は作動距離を犬きく保つための条件である
。上限分こえると作動距離が小さくなり、フォーカシン
グなどの制御駆動に支障全きたす。また下限をこえると
第３レンズの負荷が犬きくなり各収差補正が困難となる
。Condition (11) is a condition for keeping the working distance close. If the upper limit is exceeded, the working distance becomes smaller, which completely hinders control drives such as focusing. Moreover, when the lower limit is exceeded, the load on the third lens becomes severe, making it difficult to correct each aberration.

条件（ｉｉｉ）は像面湾曲の補正を良好に保つための条
件である。上限をこえると像面湾曲の補正過剰、下限を
こえると補正不足となる。Condition (iii) is a condition for maintaining good correction of field curvature. If the upper limit is exceeded, the field curvature will be over-corrected, and if the lower limit is exceeded, the field curvature will be under-corrected.

本発明の対９りＪレンズは上記の３条件ヲ滴足すること
により、下記する実施例のように作動距離が大きく、且
つＮＡも大きな、所望の光学式高密度記録再生装置、ｔ
ｔめ対物レンズが得られたものである。By adding the above three conditions, the pair 9-shaped J lens of the present invention can be used as a desired optical high-density recording/reproducing device with a large working distance and a large NA as shown in the embodiments below.
A t-th objective lens was obtained.

第１図ＭＣ第１笑施例を示す。図示しない光源は図の左
側に置力）れる。符号ＬＪ、　Ｔ−ｒｚ、　　詔は第ル
ンズ、第２レンズ、第３レンズである。符号Ｇはカバー
ガラス、符号Ｍは記録再生媒体を示す。符号ｒｌＷ　ｒ
６は上記各レンズの曲率半径、符号ｒｆｒ８はカバーガ
ラスＧの表裏面の曲率半径、符号ｄｌ〜ｄ５は上記各レ
ンズの面間距離、符号ｄ６Ｆｉ第３レンズ込の記録再生
媒体側面からカバーガラスＧの表面までの光軸上の距離
、符号ｄ７Ｊ−ｊカバーガラスＱの表裏面間の距離を各
々示す。FIG. 1 MC shows a first embodiment. A light source (not shown) is placed on the left side of the figure. The symbols LJ, T-rz, and imperial commands are the 1st lens, 2nd lens, and 3rd lens. The symbol G indicates a cover glass, and the symbol M indicates a recording/reproducing medium. Code rlW r
6 is the radius of curvature of each lens, code rfr8 is the radius of curvature of the front and back surfaces of the cover glass G, codes dl to d5 are the distances between the surfaces of each of the lenses, code d6Fi is the distance from the side of the recording/reproducing medium including the third lens to the cover glass G. The distance on the optical axis to the surface of d7J-j and the distance between the front and back surfaces of the cover glass Q are shown respectively.

これらの具体的数値は以下のとおりである。These specific figures are as follows.

ｒｌ　　＝　　１．８９８ｄ１＝０．１９２　　ｎ１＝１．７８７８８　　）’ｔ
＝２５．５ｒ２　　＝　　１．０８８ｄ２＝０．０８４ｒ３”　　　１．５２５ｄ３＝　０．４４３　　　ｎ２＝１．６１８８８　　　
））ｚ　＝６０Ｊｒ４ニー５．２８２ｄ４＝＝　ｏ、　１７５ｒ５二　　０．７８８＋１５＝０．４７８　　　　ｎ３＝１．８２０７２　　
　Ｊ／Ｊ＝８７．８ｒ６＝　　　１．９９４ｄ６＝０．３８１ ’ｒ’７＝　　　　０Ｏｄ７＝　０．８　　　　　ｎ１１）−１，５１Ｑ３””
　　　（Ｘ）尚、　ｆ＝１．ｏｏｏ　　　　ＮＡ＝０．６　　　ＷＤ
＝０．８８上記において、符号ｎ１〜ｎ３Ｕ各レンズＬ
１〜尾の屈折率、ｎＱはカバーガラスＧの屈折率、シＩ
〜シ３は各レンズＬ］〜馳のアツベ数を各々示し、また
ＷＤは作動距離を示す。rl = 1.898 d1 = 0.192 n1 = 1.78788 )'t
=25.5r2 = 1.088 d2=0.084 r3" 1.525 d3= 0.443 n2=1.61888
)) z = 60 Jr4 knee 5.282 d4== o, 175 r5 two 0.788 +15=0.478 n3=1.82072
J/J=87.8r6= 1.994 d6=0.381 'r'7= 0O d7= 0.8 n11)-1,51Q3""
(X) Furthermore, f=1. ooo NA=0.6 WD
=0.88 In the above, symbols n1 to n3U each lens L
1 to tail refractive index, nQ is the refractive index of cover glass G,
3 indicates the Atsube number of each lens L], and WD indicates the working distance.

第２図に第２実施例を示す。符号Ｌｌ’　、　Ｌ２’　
、祐′は第ルンズ、第２レンズ、第３レンズを示し、他
の符号は第１実施例と全く同様である。FIG. 2 shows a second embodiment. Code Ll', L2'
, Yu' indicate the first lens, the second lens, and the third lens, and the other symbols are exactly the same as in the first embodiment.

これらの具体的数値は次のとおりである。These specific figures are as follows.

ｒｌ”　　１．８７７ｄ１＝　０．１７５　　ｎｌ＝　１．７８７３８　　Ｊ
ｔ　＝　２５．５ｒａ　＝１．０４６．１２＝　０．１２５ｒ３＝：　　１．５０５ｄ３＝　０．４５２　　　ｎ２＝　１．６　ｌ３８８　
　　Ｌｌ　＝　６０Ｕｒ４＝−５，２４２ｄ４＝　０．１８７ｒ５＝　　０．７８６ｄ５＝０．４３９　　　ｎ３＝１．８２０７２　　　シ
３＝ａ７．ａｒ５＝　　２．ｆｉ７８ｄ６＝０．４５０ｒ７−　　　″ ｄｙ＝ＯＪｒ８二　　（資）尚、ｆ　＝　１．０（１０、ＮＡ　＝　０．５　、　　
ＷＤ　＝　０．４５次に各収差図について述べる。第１
実施例に対する収差図を第３図に、第２実施例に対する
収差図を第４図に各々示す。また、第１実施例の波面収
差の等高線図を第５図に、第２実施例の波面収差の等高
線図を第６図に各々示す。これらの波面収差に関する図
のうち、（イ）は像高ｈ＝ｏすなわち光軸上の、（ロ）
は周辺部のそれぞれにおける波面収差を１厘位置の等高
線図で示したものである。rl” 1.877 d1= 0.175 nl= 1.78738 J
t = 25.5ra = 1.046. 12= 0.125 r3=: 1.505 d3= 0.452 n2= 1.6 l388
Ll = 60Ur4 = -5,242 d4 = 0.187 r5 = 0.786 d5 = 0.439 n3 = 1.82072 C3 = a7. ar5=2. fi78 d6=0.450 r7-'' dy=OJ r82 (fund) In addition, f = 1.0 (10, NA = 0.5,
WD = 0.45 Next, each aberration diagram will be described. 1st
An aberration diagram for the example is shown in FIG. 3, and an aberration diagram for the second example is shown in FIG. 4. Further, a contour line diagram of the wavefront aberration of the first embodiment is shown in FIG. 5, and a contour line diagram of the wavefront aberration of the second embodiment is shown in FIG. 6, respectively. Among these diagrams regarding wavefront aberration, (a) shows the image height h=o, that is, on the optical axis, and (b)
is a contour map showing the wavefront aberration in each peripheral area at one position.

[Brief explanation of drawings]

第１図は本発明の第１実施例を示す図、第２図は本発明
の第２実Ｍｑ例を示す図、第３図及び第４図は上記第１
及び第２実施例の収差図、第５図及び第６図は上記第１
及び第２実施例の波ｍ］収走の等高線図である。ｂｌ、塊、馳、　Ｌ１２．　Ｌ２ｊ、招電０、レンズＧ
・・カバーガラス、　Ｍ・・・記録丙午媒体特許出願人株式会社三協精機製作所第１図第２図　　　　　、６．。５第３図第４図勧ｏｏ＋ａ＊　　　　　　　−１＝ｏ、ｏ１２シＮＡ”
（Ｌｆ　　　　ＡＭ　Ａｓ第５図中１（（イ）第６図申ｉ（（イ）１１辺−（ロ）FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a second actual Mq example of the present invention, and FIGS. 3 and 4 are diagrams showing the first embodiment of the present invention.
and the aberration diagrams of the second embodiment, FIGS. 5 and 6 are the same as those of the first embodiment.
and wave m of the second embodiment] is a contour diagram of retraction. bl, lump, hase, L12. L2j, electrification 0, lens G
...Cover glass, M...Record Heigo media patent applicant Sankyo Seiki Seisakusho Co., Ltd. Figure 1 Figure 2, 6. . 5 Figure 3 Figure 4 Recommendation oo+a* -1=o, o12 si NA"
(Lf AM As 1 in Figure 5 ((a)) Figure 6 (i) ((a) 11th side - (b)

Claims

[Claims] A first lens, a second lens, and a third lens are sequentially arranged from the first light source toward the recording/reproducing medium, and the first lens has a negative meniscus 1/2 with a convex surface facing the light source. The second lens is a biconvex lens, and the third lens is a positive meniscus lens with a convex side facing the light source side.
The radius of curvature of the lens on the light source side is krv, the radius of curvature of the third lens on the light source side is r5, the combined focal length of the first and second lenses is fl, 2, the focal length of the third lens is f3, the focal point of the entire lens system Let the distance be f and 1. (i) 0.55 <
r2/ < 0.953 Ql) o21 < f3/ fl, 2 < o, a3
(iii) 0.56 < r5/f (0.97 ff: objective lens of an optical high-density recording/reproducing device.