JPH09197264A - Objective optical system variable in thickness of disk substrate - Google Patents
Objective optical system variable in thickness of disk substrateInfo
- Publication number
- JPH09197264A JPH09197264A JP8020377A JP2037796A JPH09197264A JP H09197264 A JPH09197264 A JP H09197264A JP 8020377 A JP8020377 A JP 8020377A JP 2037796 A JP2037796 A JP 2037796A JP H09197264 A JPH09197264 A JP H09197264A
- Authority
- JP
- Japan
- Prior art keywords
- lens
- disk substrate
- thickness
- objective
- 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.)
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、大容量の光情報媒
体の記録，再生に適した対物光学系に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective optical system suitable for recording and reproducing a large capacity optical information medium.
【０００２】[0002]
【従来の技術】高密度，大容量の光情報媒体の記録，再
生には対物レンズのＮＡを大きくすることが有効である
が、このときレンズの光軸の傾きにより、収差発生量が
増大する。これを防ぐには光ディスク基板の厚みを薄く
することが有利である。以上の理由で近年ディスク基板
の厚みを薄くすることが試みられている。一方、現在普
及しているコンパクトディスク（ＣＤ）は、ディスク基
板の厚みは１．２ｍｍと厚い。この現在のコンパクトデ
ィスクと高密度光ディスク（ＳＤ）の両方を記録，再生
できる光ディスク装置が必要となった。しかるに、ディ
スクの基板厚みが変化すると球面収差が著しく変化する
ため、コンパクトディスク（ＣＤ）と高密度光ディスク
（ＳＤ）の両方を１つの対物光学系で満足することは不
可能であった。2. Description of the Related Art Increasing the NA of an objective lens is effective for recording and reproducing on a high-density, large-capacity optical information medium. At this time, the amount of aberration increases due to the inclination of the optical axis of the lens. . In order to prevent this, it is advantageous to reduce the thickness of the optical disk substrate. For the above reasons, attempts have recently been made to reduce the thickness of the disk substrate. On the other hand, compact discs (CDs) that are currently popular have a thick disc substrate of 1.2 mm. An optical disk device capable of recording and reproducing both the present compact disk and high density optical disk (SD) is required. However, since the spherical aberration changes remarkably when the substrate thickness of the disc changes, it is impossible to satisfy both the compact disc (CD) and the high density optical disc (SD) with one objective optical system.
【０００３】最近、対物レンズにホログラムレンズを付
加することにより、多焦点を得る方法として特開平７−
１９８９０９号公報，特開平７−９８４３１号公報等が
あるが、回折による光量低下の欠点を逃れることはでき
ない。また特開平７−１５３１１０号公報にはコリメー
タレンズと対物レンズの間に負の非球面を持つ補正板を
挿入することにより、ディスク基板の厚みの変更に対処
する方法が開示されているが、ディスク基板厚みが異な
る数だけ、それに対応した補正板が必要であり、その出
し入れの機構も複雑となる。また、ディスク基板と対物
レンズのセットを交換する方法も行われているようであ
るが、ディスク基板の厚みが異なる数だけ対物レンズと
のセットが必要であり、経済性の悪化と機構の複雑さは
免れない。Recently, as a method for obtaining a multifocal point by adding a hologram lens to an objective lens, Japanese Patent Laid-Open No. 7-
Although there are 198909 and Japanese Patent Laid-Open No. 7-98431, it is not possible to avoid the drawback of the decrease in the light amount due to diffraction. Japanese Patent Laid-Open No. 7-153110 discloses a method of coping with a change in the thickness of a disk substrate by inserting a correction plate having a negative aspherical surface between a collimator lens and an objective lens. Corresponding correction plates are required for the number of different substrate thicknesses, and the mechanism for loading and unloading them is complicated. Also, it seems that there is a method of exchanging the set of the disc substrate and the objective lens, but it is necessary to set as many objective lenses as the number of disc substrates having different thicknesses, which deteriorates economic efficiency and complicates the mechanism. Is inevitable.
【０００４】[0004]
【発明が解決しようとする課題】本発明は簡単な機構に
より異なった多数のディスク基板厚みに対応し、光量の
損失もなく、しかも良好な性能が得られる方法を提供す
るものである。SUMMARY OF THE INVENTION The present invention provides a method capable of accommodating a large number of different disk substrate thicknesses by a simple mechanism without loss of light quantity and good performance.
【０００５】[0005]
【課題を解決するための手段】本発明はレーザ光源から
の発散光束がコリメータにより平行光になった光束を受
けて結像する対物光学系において、ディスク基板の厚み
の変化により増大する収差を除去し、多数のディスク基
板の厚みにも充分良好な性能が得られる光学系を極めて
簡単な構成で得られるものである。すなわち、本発明は
コリメータ側より順次に光軸上第１負レンズ，第２正レ
ンズ，対物レンズおよびディスク基板が配置され、ディ
スク基板の厚みの変化に対しては、上記第１負レンズと
第２正レンズの軸上間隔を変化させることにより、収差
を良好とするものである。According to the present invention, in an objective optical system in which a divergent light beam from a laser light source receives a light beam that has been converted into parallel light by a collimator and forms an image, aberrations that increase due to a change in the thickness of a disk substrate are removed. However, it is possible to obtain an optical system with a very simple configuration, which can obtain a sufficiently good performance even for the thickness of a large number of disk substrates. That is, according to the present invention, the first negative lens, the second positive lens, the objective lens, and the disc substrate on the optical axis are sequentially arranged from the collimator side. The aberration is improved by changing the axial distance between the two positive lenses.
【０００６】本発明のディスク基板の厚みの変化に対
し、収差補正が良好にできる理由を以下に説明する。こ
こでディスク基板の厚みの変化は対物レンズの球面収差
を著しく変化させることは当業界では周知であることを
前提とする。 （説明１）正の対物レンズの球面収差は入射する光の物
体距離によって変化する。無限遠物体に対する球面収差
に対し、物体が有限距離で正の対物レンズに近づくほ
ど、補正不足の球面収差が増大する。すなわち、球面収
差の近点変化であり、この逆の超無限遠光束に対しても
成り立つ。 （説明２）正の対物レンズは、ディスク基板の厚みの変
化により球面収差は著しく変化する。ディスク基板の厚
みが厚くなると補正過剰の球面収差が増大し、逆に薄く
なると補正不足の球面収差が増大する。前記説明１によ
り物体位置を変化させるときは球面収差が変化するの
で、異なったディスク基板厚みに対し、それぞれ球面収
差が良好となる物体位置が存在する。 （説明３）対物レンズに前置の第１負レンズと第２正レ
ンズの光軸上の間隔を変化させるときは、その合成レン
ズの焦点距離も変化するが、像点位置も変化する。The reason why the aberration can be corrected well with respect to the change in the thickness of the disk substrate of the present invention will be described below. Here, it is assumed that it is well known in the art that a change in the thickness of the disk substrate causes a significant change in the spherical aberration of the objective lens. (Description 1) The spherical aberration of a positive objective lens changes depending on the object distance of incident light. With respect to spherical aberration for an object at infinity, undercorrected spherical aberration increases as the object approaches a positive objective lens at a finite distance. That is, it is a near-point change of spherical aberration, and it holds for the opposite light beam at infinity. (Explanation 2) In a positive objective lens, the spherical aberration remarkably changes due to the change in the thickness of the disk substrate. If the thickness of the disk substrate is thick, the overcorrected spherical aberration increases, and if it is thin, the undercorrected spherical aberration increases. Since spherical aberration changes when the object position is changed according to the above description 1, there are object positions where the spherical aberration becomes good for different disk substrate thicknesses. (Explanation 3) When the distance between the first negative lens and the second positive lens in front of the objective lens is changed, the focal length of the compound lens also changes, but the image point position also changes.
【０００７】以上のことを総合，考察，集大成すること
により、本発明が生じたものである。大容量の光情報媒
体の記録，再生のためには、対物レンズは高ＮＡとし、
ディスク基板の厚みは小さい値を特定し、この組合せの
もとに収差を極限まで除去する。この場合、対物レンズ
に入射する光束は無限遠物体からの平行光束、有限距離
物体からの発散光束，および対物レンズの像側方向の物
体に向かう収斂光束（超無限遠光束）のいずれでも良
い。The present invention has been produced by synthesizing, considering, and compiling the above. For recording and reproducing large capacity optical information media, the objective lens has a high NA,
A small value is specified for the thickness of the disk substrate, and aberration is removed to the limit based on this combination. In this case, the light beam incident on the objective lens may be either a parallel light beam from an infinite object, a divergent light beam from an object at a finite distance, or a convergent light beam (super-infinite light beam) toward the object on the image side of the objective lens.
【０００８】次に本発明の光学系におけるレンズ配置に
ついて、図１を参照しながら説明する。対物レンズが前
記の特定ディスク基板厚みと組合されている場合は、コ
リメータからの平行光束を受ける第１負レンズと第２正
レンズによって作られる像点は対物レンズの設計時に用
いられた物体距離の近傍に得られるように第１負レンズ
と第２正レンズの光軸上の間隔を定める。この場合、第
２正レンズと対物レンズの光軸上の距離はあまり問題に
ならない。簡単のために、対物レンズと特定ディスク基
板厚みとの組合せが無限遠物体からの平行光束に対して
収差が補正されている場合について述べる。Next, the lens arrangement in the optical system of the present invention will be described with reference to FIG. When the objective lens is combined with the above-mentioned specific disc substrate thickness, the image point formed by the first negative lens and the second positive lens that receive the parallel light flux from the collimator is equal to the object distance used when designing the objective lens. The distance between the first negative lens and the second positive lens on the optical axis is determined so that they can be obtained in the vicinity. In this case, the distance between the second positive lens and the objective lens on the optical axis does not matter so much. For simplicity, the case where the combination of the objective lens and the specific disc substrate thickness is corrected for the aberration with respect to the parallel light flux from the object at infinity will be described.
【０００９】（ａ）ディスク基板厚みが特定値の場合 第１負レンズの後側焦点位置と第２正レンズの前側焦点
位置が合致する近傍に両者の光軸上の間隔を定める。 （ｂ）ディスク基板厚みが特定値より厚い場合 球面収差が補正過剰となる。第１負レンズと第２正レン
ズとの光軸上の間隔を狭めることにより、コリメータか
らの平行光束は有限物体からの発散光束となって、対物
レンズに入射する。前記説明２においてディスク基板厚
みに対し、球面収差が良好となる対物レンズの物体距離
の近傍になるように第１負レンズと第２正レンズの光軸
上の間隔を定める。この場合、第１負レンズを像側に移
動するか、第２正レンズを光源側に近づけるか、また
は、上記第１負レンズと第２正レンズの双方を光軸上で
移動しても良い。 （ｃ）ディスク基板厚みが特定値より薄い場合 球面収差は補正不足となる。第１負レンズと第２正レン
ズとの光軸上の間隔を拡げることによりコリメータから
の平行光束は対物レンズの像側方向の点に向かう収斂光
束（超無限遠光束）となって対物レンズに入射する。前
記説明２において、ディスク基板厚みに対し球面収差が
良好となる対物レンズの物体距離の近傍になるように第
１負レンズと第２正レンズとの光軸上の間隔を定める。
この場合、第１負レンズを光源側に近づけるか、第２正
レンズを像側へ移動するか、または上記第１負レンズと
第２正レンズ双方を光軸上で移動しても良い。(A) When the thickness of the disk substrate is a specific value: The distance between the optical axes of the first negative lens and the front focal position of the second positive lens is determined in the vicinity thereof. (B) When the disk substrate thickness is thicker than a specific value Spherical aberration is overcorrected. By narrowing the distance between the first negative lens and the second positive lens on the optical axis, the parallel light flux from the collimator becomes a divergent light flux from the finite object and enters the objective lens. In the above description 2, the distance between the first negative lens and the second positive lens on the optical axis is determined so as to be close to the object distance of the objective lens where the spherical aberration becomes good with respect to the thickness of the disk substrate. In this case, the first negative lens may be moved to the image side, the second positive lens may be brought closer to the light source side, or both the first negative lens and the second positive lens may be moved on the optical axis. . (C) When the disk substrate thickness is thinner than a specific value Spherical aberration is undercorrected. By expanding the distance between the first negative lens and the second positive lens on the optical axis, the parallel light flux from the collimator becomes a convergent light flux (ultra-infinite light flux) toward the point in the image side direction of the objective lens. Incident. In the above description 2, the distance between the first negative lens and the second positive lens on the optical axis is determined so as to be close to the object distance of the objective lens where the spherical aberration becomes good with respect to the disc substrate thickness.
In this case, the first negative lens may be brought closer to the light source side, the second positive lens may be moved to the image side, or both the first negative lens and the second positive lens may be moved on the optical axis.
【００１０】以上（ａ），（ｂ），（ｃ）の方法は、対
物レンズと特定ディスク基板厚みとの組合せの設計基準
の物体距離が有限距離からの発散光束の場合、および対
物レンズの像側方向の点に向かう収斂光束（超無限遠光
束）に対した場合においても成り立つ。これまでに述べ
た方法により高密度，大容量，高ＮＡにおいて、ディス
ク基板の厚みの変化に対しても球面収差は極めて良好に
補正することができるが、コマ収差には若干の影響もあ
り、トラッキング等で対物レンズを光軸と直角方向に移
動（シフト）した場合に性能が悪化することにも考慮す
る必要があるため、高ＮＡ（ＳＤ）においては、ディス
ク基板の厚さの変化は特定値の２０％以内が望ましい。
例えばＮＡ＝０．６でディスク基板の特定厚さが０．６
ｍｍのときは±０．１２ｍｍ位に止めるのが良い。The above methods (a), (b), and (c) are used when the object distance of the design reference of the combination of the objective lens and the specific disk substrate thickness is a divergent light beam from a finite distance, and the image of the objective lens. It holds even for a convergent light beam (super-infinity light beam) directed to a point in the lateral direction. With the method described above, spherical aberration can be corrected very well even with a change in the thickness of the disk substrate at high density, large capacity, and high NA, but there is a slight effect on coma. It is necessary to consider that the performance deteriorates when the objective lens is moved (shifted) in the direction perpendicular to the optical axis due to tracking or the like, so at high NA (SD), the change in the thickness of the disk substrate is specified. Within 20% of the value is desirable.
For example, when NA = 0.6 and the specific thickness of the disk substrate is 0.6
When it is mm, it is better to stop at about ± 0.12 mm.
【００１１】次にコンパクトディスク（ＣＤ）用として
用いるときは、使用波長が７８０ｎｍと長く、ＮＡ＝
０．４５が現状である。高密度光ディスク（ＳＤ）にお
ける波長は６５０ｎｍ，６３５ｎｍ等であるから、これ
らの波長を使用した場合、コンパクトディスク（ＣＤ）
に必要なＮＡCDは使用波長６５０ｎｍのとき ＮＡCD＝０．４５・（６５０／７８０）＝０．３７５ 使用波長６３５ｎｍのとき ＮＡCD＝０．４５・（６３５／７８０）＝０．３６６ で良いことになり、ディスク基板厚みが０．６ｍｍから
１．２ｍｍと大きく変化しても充分高性能の結果が得ら
れる。そのためには、第１負レンズの手前か第１負レン
ズと第２正レンズの間、または第２正レンズと対物レン
ズとの間に絞りを挿入すると良い。なお、ディスク基板
の厚みの変化に対する全系像点位置の変化に対しては対
物レンズの微少移動により行う。When used for a compact disc (CD), the wavelength used is as long as 780 nm and NA =
0.45 is the current situation. Since wavelengths in high-density optical discs (SD) are 650 nm, 635 nm, etc., when these wavelengths are used, compact discs (CD)
NA CD good at NA CD = 0.45 · (635/780) = 0.366 when the NA CD = 0.45 · (650/780) = 0.375 using the wavelength 635nm when the use wavelength 650nm necessary Even if the disk substrate thickness changes greatly from 0.6 mm to 1.2 mm, a sufficiently high performance result can be obtained. For that purpose, an aperture may be inserted before the first negative lens, between the first negative lens and the second positive lens, or between the second positive lens and the objective lens. The change in the image point position of the entire system with respect to the change in the thickness of the disk substrate is performed by a slight movement of the objective lens.
【００１２】次に条件式（１）について説明する。条件
式（１）は第１負レンズと第２正レンズの焦点距離の関
係を定めるものである。（ＳＤ）を対象に対物レンズが
ディスク基板厚みの小さい値を特定し、この組合せのも
とに収差を極限まで除去した場合、ディスク基板厚みが
増加する（ＣＤ）においては、球面収差が補正過剰とな
るため、対物レンズに入射する光は有限距離物体からの
発散光束とならなければならないが、条件式（１）の範
囲を超えて上記目的を達成させる時は第１負レンズと第
２正レンズの軸上間隔が負となり、実現不可能となるか
らである。Conditional expression (1) will be described below. Conditional expression (1) defines the relationship between the focal lengths of the first negative lens and the second positive lens. If the objective lens specifies a small value of the disc substrate thickness for (SD) and the aberration is removed to the limit based on this combination, the spherical aberration is overcorrected in the case of the disc substrate thickness increasing (CD). Therefore, the light incident on the objective lens must be a divergent light beam from an object with a finite distance, but when the above-mentioned object is achieved beyond the range of the conditional expression (1), the first negative lens and the second positive lens are used. This is because the axial distance between the lenses becomes negative, making it impossible to achieve.
【００１３】条件式（２）はコリメータからの平行光束
が入射する第１負レンズの第１面の曲率半径を負とする
もので、第１負レンズと第２正レンズで構成されるコン
バータと対物レンズとの相互偏心による性能低下を防ぐ
ためのものである。トラッキング等により対物レンズが
光軸と直角方向に移動（シフト）する場合、上記第１負
レンズと第２正レンズで構成されるコンバータも同時に
シフトできれば問題はないが、機構の複雑化を防ぐため
に、対物レンズのみをシフトするときは、偏心による性
能低下が生ずる。この量は第１負レンズの第１面の屈折
力が正となるとき性能低下が著しくなる。Conditional expression (2) is for making the radius of curvature of the first surface of the first negative lens on which the parallel light beam from the collimator is incident negative, and for the converter composed of the first negative lens and the second positive lens. This is to prevent performance deterioration due to mutual eccentricity with the objective lens. When the objective lens moves (shifts) in the direction perpendicular to the optical axis due to tracking or the like, there is no problem if the converter composed of the first negative lens and the second positive lens can be shifted at the same time, but in order to prevent the mechanism from becoming complicated. However, when only the objective lens is shifted, performance deterioration occurs due to decentering. This amount causes a remarkable deterioration in performance when the refractive power of the first surface of the first negative lens becomes positive.
【００１４】条件式（３）は第１負レンズの像側の面と
第２正レンズの光源側の面とによる空気レンズの屈折力
を正とし、この両面の間に発散作用を生ぜしめるための
もので、条件式（２）と同様に第１負レンズと第２正レ
ンズで構成されるコンバータと対物レンズの相互偏心に
よる性能低下を防ぐもので、この条件を超えるとトラッ
キング等により、対物レンズが光軸と直角方向に移動
（シフト）した時に偏心による性能低下が大きくなる。Conditional expression (3) is to make positive the refracting power of the air lens by the image side surface of the first negative lens and the light source side surface of the second positive lens, and to cause a diverging action between the both surfaces. As with the conditional expression (2), it prevents performance deterioration due to mutual eccentricity of the converter composed of the first negative lens and the second positive lens and the objective lens. When the lens moves (shifts) in the direction perpendicular to the optical axis, the performance is greatly reduced due to decentering.
【００１５】条件式（４）は第１負レンズと対物レンズ
との焦点距離の関係を定めるものである。第１負レンズ
と第２正レンズの屈折力が大きく、その和の絶対値が小
さいときは、ディスク基板の厚みの変化に対し、上記２
レンズ間の光軸上の間隔の変化量も小さくなり、よりコ
ンパクト化が可能となる。しかしコリメータからの平行
光束（無限遠光束）が第１負レンズと第２正レンズで構
成されるコンバータ系を通過し、平行光束（無限遠光
束）が対物レンズに入射する場合は第１負レンズの焦点
距離をｆC1，ＮＡをＮＡc1，対物レンズの焦点距離をｆ
M ，ＮＡをＮＡMとすると −ｆC1／ｆM ＝ＮＡM ／ＮＡc1 なる関係式が成り立つ。条件式（４）は第１負レンズの
ＮＡc1を対物レンズのＮＡM の１／２未満、すなわち対
物レンズのＮＡM ＝０．６のときは、第１負レンズのＮ
Ａc1が０．３未満に定めるもので、この条件式を外れる
と第１負レンズのＮＡが過大となり、球面収差を悪化さ
せる。なお、本発明対物光学系の第１負レンズ，第２正
レンズのディスク基板厚みの変化に際し、移動するコン
バータ系に非球面を導入して性能の向上をさらに図るこ
とは本発明の条件範囲を逸脱するものではない。ただ
し、トラッキング等により、対物レンズのみがシフトす
る場合には、上記コンバータ系と対物レンズの相互偏心
による性能維持への配慮が必要である。Conditional expression (4) defines the relationship between the focal lengths of the first negative lens and the objective lens. When the refractive powers of the first negative lens and the second positive lens are large and the absolute value of the sum is small, the above-mentioned 2
The amount of change in the distance between the lenses on the optical axis is also small, and it is possible to make the lens more compact. However, when the parallel light flux (infinity light flux) from the collimator passes through the converter system including the first negative lens and the second positive lens and the parallel light flux (infinity light flux) enters the objective lens, the first negative lens F C1 , NA is NA c1 , and the focal length of the objective lens is f C1
M, when the NA and NA M -f C1 / f M = NA M / NA c1 relational expression holds. Conditional expression (4) is such that when NA c1 of the first negative lens is less than 1/2 of NA M of the objective lens, that is, when NA M of the objective lens is 0.6, N 1 of the first negative lens is
A c1 is set to be less than 0.3, and if this conditional expression is not satisfied, the NA of the first negative lens becomes excessive and the spherical aberration is deteriorated. It should be noted that it is within the condition range of the present invention to further improve the performance by introducing an aspherical surface into the moving converter system when the thickness of the disk substrate of the first negative lens and the second positive lens of the objective optical system of the present invention changes. It does not deviate. However, when only the objective lens is shifted due to tracking or the like, it is necessary to consider performance maintenance due to mutual decentering of the converter system and the objective lens.
【００１６】[0016]
【発明の実施の形態】次に本発明のディスク基板厚み可
変の対物光学系の実施例１から実施例８までを第１表か
ら第８表に示す。表中の記号は次の通りである。 ｒi ：順次に球面の曲率半径または非球面の頂点曲率半
径 ｄi ：順次にレンズの光軸上の厚みまたは空気間隔 ｎi ：順次にレンズの材質の波長６５０ｎｍにおける屈
折率 ｔ ：ディスク基板の光軸上の厚み ｎb ：ディスク基板の材質の波長６５０ｎｍにおける屈
折率 ＷＤ：作動距離 ｆ ：全系の焦点距離 ｆC1：第１負レンズの焦点距離 ｆC2：第２正レンズの焦点距離 ｆM ：対物レンズの焦点距離 ＮＡ：全系のＮＡ ＮＡM ：対物レンズのＮＡ Ｌ1M：対物レンズの設計に用いた物体距離（ｔ＝０．
６） （有限距離物体からの発散光束が入射するとき（−）） 非球面の形状の式は Ｘ：非球面上の点のレンズ面頂点における接平面からの
距離 ｈ：光軸からの高さ Ｃ：非球面頂点の曲率（Ｃ＝１／ｒ） Ｋ：円錐定数 Ａ2i：非球面係数 とするときDESCRIPTION OF THE PREFERRED EMBODIMENTS Next, Tables 1 to 8 show Examples 1 to 8 of the objective optical system having a variable disk substrate thickness according to the present invention. The symbols in the table are as follows. r i : Sequentially spherical radius of curvature or aspherical vertex radius of curvature d i : Sequentially thickness of lens on optical axis or air gap n i : Sequentially refractive index of lens material at wavelength 650 nm t: Disc substrate Thickness on optical axis n b : Refractive index of disc substrate material at wavelength 650 nm WD: Working distance f: Focal length of entire system f C1 : Focal length of first negative lens f C2 : Focal length of second positive lens f M : focal length of objective lens NA: NA of entire system NA M : NA of objective lens L 1M : object distance used for designing the objective lens (t = 0.
6) (When a divergent light flux from a finite distance object is incident (-)) The expression for the shape of the aspherical surface is: X: distance from the tangent plane at the apex of the lens surface of the aspherical surface h: height from the optical axis C: curvature of aspherical vertex (C = 1 / r) K: conical constant A 2i : aspherical coefficient
【式１】 で表される。なお、ディスク基板厚さｔ＝０．６のとき
の対物レンズの有効径をｔ＝０．５およびｔ＝０．７に
も使用し、ｔ＝１．２のときは絞りにより計算を行っ
た。(Equation 1) It is represented by When the disk substrate thickness t = 0.6, the effective diameter of the objective lens is also used for t = 0.5 and t = 0.7, and when t = 1.2, the calculation is performed using the diaphragm. .
【表１】 [Table 1]
【表２】 [Table 2]
【表３】 [Table 3]
【表４】 [Table 4]
【表５】 [Table 5]
【表６】 [Table 6]
【表７】 [Table 7]
【表８】 [Table 8]
【００１７】実施例１乃至６における対物レンズは共通
で特定ディスク基板厚み０．６ｍｍにおいて無限遠物体
（Ｌ1M＝∞）に対して収差を良好としたもので、この収
差曲線を図２に示す。実施例１の収差曲線を図３および
図４に、実施例２の収差曲線を図５および図６に、実施
例３の収差曲線を図７および図８に、実施例４の収差曲
線を図９および図１０に、実施例５の収差曲線を図１１
および図１２に、実施例６の収差曲線を図１３および図
１４に示す。実施例７における対物レンズは特定ディス
ク基板厚み０．６ｍｍにおいて対物レンズの第１面の手
前３００ｍｍの有限物体からの発散光束（Ｌ1M＝−３０
０）に対して収差を良好としたもので、この収差曲線を
図１５に示し、全系の収差曲線を図１６および図１７に
示す。実施例８における対物レンズは特定ディスク基板
厚み０．６ｍｍにおいて、対物レンズの第１面より像側
３００ｍｍにある物体に向かう収斂光束（超物限遠光
束）（Ｌ1M＝３００）に対して収差を良好としたもの
で、この収差曲線を図１８に示し、全系の収差曲線を図
１９および図２０に示す。いずれの実施例においてもデ
ィスク基板厚みが変化しても良好な性能であることがわ
かる。The objective lenses in Examples 1 to 6 are common, and the aberration is made good for an object at infinity (L 1M = ∞) at a specific disk substrate thickness of 0.6 mm. This aberration curve is shown in FIG. . The aberration curves of Example 1 are shown in FIGS. 3 and 4, the aberration curves of Example 2 are shown in FIGS. 5 and 6, the aberration curves of Example 3 are shown in FIGS. 7 and 8, and the aberration curves of Example 4 are shown. 9 and 10 show the aberration curves of Example 5 in FIG.
12 and FIG. 12 show the aberration curves of Example 6 in FIG. 13 and FIG. The objective lens in Example 7 is a divergent light beam (L 1M = −30) from a finite object 300 mm before the first surface of the objective lens when the specific disk substrate thickness is 0.6 mm.
The aberration curves are shown in FIG. 15 and the aberration curves of the entire system are shown in FIGS. 16 and 17. The objective lens in Example 8 has aberrations with respect to a convergent light flux (super-substance-finding light flux) (L 1M = 300) directed to an object located 300 mm from the first surface of the objective lens at a specific disk substrate thickness of 0.6 mm. FIG. 18 shows this aberration curve, and FIGS. 19 and 20 show the aberration curves of the entire system. It can be seen that in any of the examples, good performance is obtained even if the disk substrate thickness changes.
【００１８】[0018]
【発明の効果】以上説明したように本発明によるディス
ク基板厚み可変の対物光学系は構成枚数も少なく、極め
て簡単な機構にもかかわらず、高密度，大容量の光情報
媒体の記録，再生において多数のディスク基板の厚みの
連続変化にも充分対応し、性能も良好となし得るもので
ある。本発明は第１負レンズ，第２正レンズがズームコ
ンバータの働きをし、ディスク基板厚みの変化に対応し
たズーム対物光学系と称することができる。また第１負
レンズや第２正レンズが偏心をしても性能低下が少ない
特徴もある。光源側に配するコリメータのＮＡの選択も
自由のため、光量も充分確保できるので、機構設計上の
自由度も多く、回折等による光量低下の欠点もない。As described above, the objective optical system having a variable disk substrate thickness according to the present invention has a small number of constituent elements and is extremely simple in mechanism for recording and reproducing a high density and large capacity optical information medium. It can cope with continuous changes in the thickness of a large number of disk substrates and has good performance. The present invention can be referred to as a zoom objective optical system in which the first negative lens and the second positive lens function as a zoom converter, and the zoom objective optical system can cope with changes in the thickness of the disk substrate. Further, there is also a feature that the performance is less deteriorated even if the first negative lens and the second positive lens are decentered. Since the NA of the collimator arranged on the light source side can be freely selected, a sufficient amount of light can be secured, so there is a large degree of freedom in designing the mechanism and there is no drawback of a decrease in the amount of light due to diffraction or the like.
【図１】本発明のディスク基板厚み可変対物光学系の実
施例１における構成断面図である。FIG. 1 is a sectional view showing the configuration of a disk substrate thickness variable objective optical system according to a first embodiment of the present invention.
【図２】実施例１乃至６において、対物レンズのディス
ク基板厚み０．６における収差曲線図である。FIG. 2 is an aberration curve diagram in Example 1 to 6 when the disk substrate thickness of the objective lens is 0.6.
【図３】実施例１のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 3 shows that the disk substrate thickness (a) of Example 1 is 0.
6 (b) is an aberration curve diagram at 1.2.
【図４】実施例１のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 4 shows that the disk substrate thickness (a) of Example 1 is 0.
5 (b) is an aberration curve diagram at 0.7.
【図５】実施例２のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 5: The disk substrate thickness (a) of Example 2 was 0.
6 (b) is an aberration curve diagram at 1.2.
【図６】実施例２のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 6 shows that the disk substrate thickness (a) of Example 2 is 0.
5 (b) is an aberration curve diagram at 0.7.
【図７】実施例３のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 7: The disk substrate thickness (a) of Example 3 is 0.
6 (b) is an aberration curve diagram at 1.2.
【図８】実施例３のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 8 shows that the disk substrate thickness (a) of Example 3 is 0.
5 (b) is an aberration curve diagram at 0.7.
【図９】実施例４のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 9 shows that the disk substrate thickness (a) of Example 4 is 0.
6 (b) is an aberration curve diagram at 1.2.
【図１０】実施例４のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 10: The disk substrate thickness (a) of Example 4 was 0.
5 (b) is an aberration curve diagram at 0.7.
【図１１】実施例５のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 11: The disk substrate thickness (a) of Example 5 was 0.
6 (b) is an aberration curve diagram at 1.2.
【図１２】実施例５のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 12 shows that the disk substrate thickness (a) of Example 5 is 0.
5 (b) is an aberration curve diagram at 0.7.
【図１３】実施例６のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 13: The disk substrate thickness (a) of Example 6 was 0.
6 (b) is an aberration curve diagram at 1.2.
【図１４】実施例６のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 14 shows that the disk substrate thickness (a) of Example 6 is 0.
5 (b) is an aberration curve diagram at 0.7.
【図１５】実施例７において対物レンズのディスク基板
厚み０．６における収差曲線図である。FIG. 15 is an aberration curve diagram for a disk substrate thickness of 0.6 for the objective lens in Example 7.
【図１６】実施例７のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 16: The disk substrate thickness (a) of Example 7 was 0.
6 (b) is an aberration curve diagram at 1.2.
【図１７】実施例７のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 17: The disk substrate thickness (a) of Example 7 is 0.
5 (b) is an aberration curve diagram at 0.7.
【図１８】実施例８において対物レンズのディスク基板
厚み０．６における収差曲線図である。FIG. 18 is an aberration curve diagram for a disk substrate thickness of 0.6 of the objective lens in Example 8.
【図１９】実施例８のディスク基板厚みが（ａ）は０．
６，（ｂ）は１．２における収差曲線図である。FIG. 19 shows that the disk substrate thickness (a) of Example 8 is 0.
6 (b) is an aberration curve diagram at 1.2.
【図２０】実施例８のディスク基板厚みが（ａ）は０．
５，（ｂ）は０．７における収差曲線図である。FIG. 20 shows that the disk substrate thickness (a) of Example 8 is 0.
5 (b) is an aberration curve diagram at 0.7.
Claims (4)
第１負レンズ，第２正レンズ，対物レンズおよびディス
ク基板が配置され、ディスク基板の厚みの変化に起因す
る収差の増大に対しては上記第１負レンズと第２正レン
ズの光軸上の間隔を変更することにより収差を良好と
し、ディスク基板の厚みの変化による像点位置の移動に
は対物レンズを光軸上で微少移動することにより合焦す
ることを特徴とするディスク基板厚み可変の対物光学
系。1. A first negative lens, a second positive lens, an objective lens, and a disk substrate are sequentially arranged for a parallel light beam from a collimator, and the above-mentioned is provided for an increase in aberration caused by a change in the thickness of the disk substrate. Aberration is improved by changing the distance between the first negative lens and the second positive lens on the optical axis, and the objective lens is slightly moved on the optical axis to move the image point position due to the change in the thickness of the disk substrate. An objective optical system with a variable disk substrate thickness, which is focused by means of.
ディスク基板の厚みが増加するときは第１負レンズと第
２正レンズの光軸上の間隔を減少させ、ディスク基板の
厚みが減少するときは第１負レンズと第２正レンズの光
軸上の間隔を増加させることを特徴とするディスク基板
厚み可変の対物光学系。2. The objective optical system according to claim 1,
When the thickness of the disk substrate increases, the distance between the first negative lens and the second positive lens on the optical axis is reduced, and when the thickness of the disk substrate decreases, the distance between the first negative lens and the second positive lens is on the optical axis. An objective optical system with variable disk substrate thickness, characterized in that the distance between the two is increased.
おいて、第１負レンズの焦点距離をｆC1，第２正レンズ
の焦点距離をｆC2，対物レンズの焦点距離をｆM ，第１
負レンズと第２正レンズの曲率半径を順次にｒ1 ，
ｒ2 ，ｒ3 ，ｒ4とするとき −ｆC1＜ｆC2 ・・・（１） ｒ1 ＜０ ・・・（２） １．３ｒ2 ＜｜ｒ3 ｜ ・・・（３） ２ｆM ＜−ｆC1 ・・・（４） なる条件を満足することを特徴とするディスク基板厚み
可変の対物光学系。3. The objective optical system according to claim 1, wherein the focal length of the first negative lens is f C1 , the focal length of the second positive lens is f C2 , the focal length of the objective lens is f M , and 1
The radiuses of curvature of the negative lens and the second positive lens are sequentially set to r 1 ,
r 2, r 3, -f C1 <f C2 ··· (1) r 1 <0 ··· (2) when the r 4 1.3r 2 <| r 3 | ··· (3) 2f M <-F C1 (4) An objective optical system with a variable disc substrate thickness, which satisfies the following condition.
光学系において、対物レンズは収差補正の基準となる特
定ディスク基板厚との組合せにおいて、無限遠物体から
の平行光束に対して収差を良好とするものの他、有限距
離物体からの発散光束に対して収差を良好とするもの、
および対物レンズの像側方向の物体に向かう収斂光束
（超無限遠光束）に対して収差を良好とするもののいず
れでも良いことを特徴とするディスク基板厚み可変の対
物光学系。4. The objective optical system according to claim 1, wherein the objective lens, in combination with a specific disk substrate thickness serving as a reference for aberration correction, produces an aberration with respect to a parallel light beam from an infinite object. In addition to those that make good, those that make the aberration good for divergent light flux from a finite distance object,
And an objective optical system with a variable disk substrate thickness, which can be any of those that make a good aberration for a convergent light beam (ultra-infinite light beam) toward an object in the image side direction of the objective lens.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8020377A JPH09197264A (en) | 1996-01-11 | 1996-01-11 | Objective optical system variable in thickness of disk substrate |
| US08/740,351 US5818643A (en) | 1995-11-14 | 1996-11-08 | Optical objective lens system with variable disk thickness feature |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8020377A JPH09197264A (en) | 1996-01-11 | 1996-01-11 | Objective optical system variable in thickness of disk substrate |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH09197264A true JPH09197264A (en) | 1997-07-31 |
Family
ID=12025366
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8020377A Pending JPH09197264A (en) | 1995-11-14 | 1996-01-11 | Objective optical system variable in thickness of disk substrate |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH09197264A (en) |
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| WO2002033700A3 (en) * | 2000-10-16 | 2004-04-01 | Konishiroku Photo Ind | Objective lens, coupling lens, light converging optical system, and optical pick-up apparatus |
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