JP3552873B2 - Deformable mirror - Google Patents

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JP3552873B2
JP3552873B2 JP06519697A JP6519697A JP3552873B2 JP 3552873 B2 JP3552873 B2 JP 3552873B2 JP 06519697 A JP06519697 A JP 06519697A JP 6519697 A JP6519697 A JP 6519697A JP 3552873 B2 JP3552873 B2 JP 3552873B2
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JPH10261239A (en
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▲頼▼成 石井
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Sharp Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は、反射面の変形が可能な変形可能ミラーに関し、より詳しくは、例えば、記録再生装置に搭載され、ＣＤ（コンパクト ディスク）、ＤＶＤ（デジタル ビデオ ディスク）といった異なる基板厚さの光ディスクに対して正確な情報の記録・再生動作を可能にする変形可能ミラーに関する。
【０００２】
【従来の技術】
光ディスクは多量の情報信号を高密度で記録することができるため、近年、オーディオ、ビデオ、コンピュータ等の多くの分野において利用が進められている。図３０は、これらの装置に用いられている光ピックアップ装置（以下では光ピックアップと称する）の一従来例を示す。以下に、この光ピックアップ１００の構成を動作とともに説明する。
【０００３】
半導体レーザー１０１から出射した光はコリメータレンズ１０２により平行光１０３になる。平行光１０３は偏光ビームスプリッター１０４に入射することにより直進して、４分の１波長板１０５を通り、反射ミラー１０６で光路を曲げられ、対物レンズ１０７に入射する。対物レンズ１０７に入射した光は絞り込まれ、回転モータ１１３によって指示された光ディスク１０８の情報記憶媒体面上に光スポット１０９を形成する。
【０００４】
一方、光ディスク１０８で反射した反射光１１０は、再び、対物レンズ１０７と反射ミラー１０６及び４分の１波長板１０５を通って、偏光ビームスプリッター１０４に入射する。この反射光１１０は４分の１波長板１０５の作用により、偏光ビームスプッリター１０４で反射して、絞りレンズ１１１を通り、光検出器１１２に受光される。光検出器１１２は、反射光線の光強度を検出することによって再生信号を検出する。
【０００５】
ここで、上記の対物レンズ１０７は光ディスク１０８の厚みを考慮して設計されている。しかしながら、この設計値と異なる厚みの光ディスクに対しては、球面収差が生じて結像性能が劣化するため、記録再生を精度よく行うことができない。
【０００６】
従来、ＣＤやビデオディスクあるいはデータ用のＩＳ０規格光磁気ディスク装置等に用いられる光ディスクの厚みは、ほぼ同一規格（約１．２ｍｍ）であった。このため、一つの光ピックアップで種類の異なる光ディスク（ＣＤ、ビデオディスク、光磁気ディスク等）を記録再生することが可能であった。
【０００７】
ところで、近年、光ディスクのより高密度化を図るために、以下の方法が検討されている。
【０００８】
（１）対物レンズの開口数（ＮＡ）を大きくして、光学的な分解能を向上させる方法。
【０００９】
（２）記録層を多層に設ける方法。
【００１０】
ここで、上記（１）の方法では、対物レンズのＮＡを大きくすると、集光ビーム径は比例して小さくなるが、ディスクの傾きの許容誤差を同程度に収めるためには、ディスクの基板厚さを薄くする必要がある。例えば、対物レンズのＮＡを０．５から０．６にすると、基板厚さを１．２ｍｍから０．６ｍｍに減少させなければ、同程度のディスク傾き許容誤差を有することができない。
【００１１】
しかしながら、このようにディスクの基板厚さを薄くした場合は、その基板厚さの薄い光ディスクに対応する対物レンズを使用して、従来の光ディスクを記録再生すると、球面収差が増大して結像点が広がってしまい、記録再生が困難となる。したがって、従来の光ディスクとの間で互換性を保つことができなくなり、光ピクアップを２個使い薄型光ディクスと従来型光ディスクを別々の光ピックアップで記録再生せざるを得なくなる。
【００１２】
また、上記（２）の方法のように、記録層をある程度の厚さの透明基板を介して複数設けた多層ディスクを用いる場合は、１枚のディスクで記録容量が大幅に増加する。
【００１３】
しかしながら、各記録層で対物レンズから見た基板厚さが異なるため、上記同様の理由により、１つの光ピックアップでは正確な情報の記録再生ができない。
【００１４】
このような問題点を解決するものとして、特開平５−１５１５９１号公報に開示された方法があり、そこでは、変形可能ミラーにより基板厚さを補正する手法を採用している。
【００１５】
図３１は、この変形可能ミラーを用いたディスク装置の光学系を示す。以下にその構成を動作とともに説明する。半導体レーザー１０１から出射した光１０３はコリメータレンズ１０２、偏光ビームスプリッター１０４、４分の１波長板１０５を透過し、ビームスプリッター２０２に到達する。ここで、光１０３は、ビームスプリッタ２０２及び４分の１波長板１０５を透過して変形可能ミラー２００に達するような偏光で配向している。
【００１６】
変形可能ミラー２００は、ミラー表面が変形可能に構成されており、光ディスクの基板厚みが厚くなったときに変形可能ミラー駆動回路２０３によりミラー表面が変形されて、光１０３に基板が厚くなったことによって発生する球面収差を打ち消すような球面収差を与える。光１０３は４分の１波長板２０１を通って戻り、ビームスプリター２０２で反射されて対物レンズ１０７に達する。対物レンズ１０７に入射した光は絞り込まれ、光ディスク１０８の情報記録媒体面上に光スポット１０９を形成する。
【００１７】
一方、光ディスク１０８で反射した反射光１１０は、再び対物レンズ１０７とビームスプリッター２０２、４分の１波長板２０１、変形可能ミラー２００及び４分の１波長板１０５を通って、偏光ビームスプリッター１０４に入射する。この反射光１１０は偏光ビームスプリッター１０４で反射して、絞りレンズ１１１を通り、光検出器１１２に受光される。光検出器１１２は、反射光線の光強度を検出することによって再生信号を検出する。
【００１８】
図３２は、上記変形可能ミラー２００の具体的な構成を示す。これは、「”Ａｄａｐｔｉｖｅ ｏｐｔｉｃｓ ｆｏｒ ｏｐｔｉｍｉｚａｔｉｏｎ ｏｆ ｉｍａｇｅ ｒｅｓｏｌｕｔｉｏｎ”（Ａｐｐｌｉｄｅ Ｏｐｔｉｃｓ”，ｖｏｌ．２６，ｐｐ．３７７２−３７７７，（１９８７），Ｊ．Ｐ．Ｇａｆｆａｒｅｌ等）」に記載されたものである。
【００１９】
この変形可能ミラー２００は、表面にミラー面３００を形成した変形プレート３０１と、変形プレート３０１の裏側の複数箇所を加圧する圧電アクチュエータ３０２と、変形プレート３０１、圧電アクチュエータ３０２、変形プレート３０１を固定するベース基板等から構成され、各圧電アクチュエータ３０２に印加する電圧を変えることにより、変形プレート３０１上が初望の量だけ変位し、全体として変形プレート上のミラー面３００を初望の形状に変形させる。
【００２０】
また、変形可能ミラーの他の従来例として、本願出願人が、特願平５−２０５２８２号で先に提案したものがある。この変形可能ミラーは、後述の本発明と同様の参照面基板を備え、この参照面基板の曲面部（凹凸面部）の形状を特定し、これにより、変形可能ミラーの変形に要するエネルギーの低減を図る手法を採用している。
【００２１】
【発明が解決しようとする課題】
しかしながら、図３２に示した従来の圧電アクチュエータ３０２を用いた変形可能ミラーでは、駆動電圧が変動すると、その変位も変動してしまう、特に、各圧電アクチュエータ３０２間に電圧変動があると変形ミラー３００が所望の面から大きく外れてしまう。
【００２２】
また、環境温度の変化によっても熱膨張の影響によって各電圧アクチュエータ３０２の加圧力が変動し、ミラー面３００が所望のミラー面からはずれてしまうという問題がある。
【００２３】
更に、収差補正を行う光ビームの直径は４ｍｍ程度であり、変形可能ミラーの正確な変形形状を実現するには多数の圧電アクチュエータ３０２を直径４ｍｍの中に備えることが必要であり、組み立てが複雑になると共に、全体として変形可能ミラーのサイズが大きくなる。このため、光ピックアップの装置構成が大型化するという問題もある。
【００２４】
また、本願出願人が先に提案した変形可能ミラーは、必ず特定の収差を発生して収差補償しなければならない部分の形状として、非球面である比較的凹凸が浅いものを用いているため、組立て時の軸ずれに対して非常に敏感であり、不安定である。このため、組立に時間を要する結果、光ピックアップの低コスト化を図る上での制約となっていた。
【００２５】
本発明は、上記課題を解決するためになされたものであって、環境温度の変動や電気回路の変動の影響を受けにくく、高精度にミラー面を保持することが可能であると共に、小型、かつ簡単な構造で、安価に製造可能な変形可能ミラーを提供することを目的とする。
【００２６】
本発明の他の目的は、変形性を向上でき、結果的に弾性変形に要するエネルギーを低減でき、記録再生装置のランニングコスト等を低減できる変形可能ミラーを提供することにある。
【００２７】
また、本発明の他の目的は、局部的に大きな応力が発生することがなく、その寿命を向上できる変形可能ミラーを提供することにある。
【００２８】
【課題を解決するための手段】
本発明の変形可能ミラーは、表面に入射光を反射する反射面を有する弾性変形可能な可撓性部材と、該可撓性部材の裏面側に、該裏面と対向する形に設置され、該可撓性部材の変形を許す空間を形成するように中心部が可撓性部材側に突出した曲面部及び該曲面部の周縁部に該可撓性部材を平面性が維持された状態で支持する平面部が形成された参照面基板とを備え、該可撓性部材を該曲面部の表面に吸着させて変形させる変形可能ミラーであって、該曲面部の該参照面基板の中心部に対する片側断面における表面形状は、該参照面基板の中心部から半径ｒ１までの部分が、該可撓性部材が吸着することにより、該可撓性部材の反射面にて反射される光ビームに、必ず特定の収差を与える状態に該可撓性部材を変形させるように球面状に設定されており、半径ｒ１から半径ｒ２（ｒ１＜ｒ２）までの部分が該曲面部分においても前記特定の収差を発生させるべく設定されており、該中心部から半径ｒ３（ｒ２＜ｒ３）の部分に該曲面部の最深部が設けられ、中心部から半径ｒ４（ｒ３＜ｒ４）の部分に、該曲面部から該周縁部の該平面部へ遷移する部分が設けられて構成されており、該曲面部における半径ｒ１から半径ｒ３までの表面部分が、半径ｒにおける深さを示す関数ｆ（ｒ）で表される曲線で形成されており、該関数ｆ（ｒ）は、半径ｒ１から半径ｒ３までの間に変曲点が１つ存在し、該変曲点から半径ｒ３までの部分がｆ”（ｒ）＞０となっており、そのことにより上記目的が達成される。
【００２９】
好ましくは、前記平面部の最外側が中心部から半径ｒ５（ｒ４＜ｒ５）の部分に設けられており、前記参照面基板の前記平面部における水平部分の距離に相当するｒ５−ｒ４が、下記（１）式の条件
ｒ５−ｒ４≦０．２ｍｍ …（１）
を満足するように構成する。
【００３０】
また、好ましくは、前記参照面基板の半径ｒ３から半径ｒ４までの部分が、半径ｒにおける深さを示す関数ｇ（ｒ）で表される曲線で形成されており、該関数ｇ（ｒ）は、半径ｒ３から半径ｒ４までの間に変曲点が１つ存在し、該変曲点から半径ｒ４までの部分がｇ”（ｒ）＜０とする。
【００３１】
また、好ましくは、前記参照面基板の前記中心部から前記平面部の最外側までの部分が全て微分可能な断面曲線である構成とする。
【００３２】
また、好ましくは、前記参照面基板の前記中心部から半径ｒ４までの部分が、下記（２）式の条件を満足し、
ｒ４≧２×ｒ２ …（２）
かつ、ｒ３がその中間点、若しくは、該中間点より該中心部寄りに位置する構成とする。
【００３３】
また、好ましくは、前記参照面基板の半径ｒ１の部分の深さｄ１と、最深部に相当する半径ｒ３の部分の深さｄ３との差ｄ３−ｄ１が、下記（３）式の条件
０．５μｍ≦ｄ３−ｄ１≦１．５μｍ …（３）
を満足する構成とする。
【００３４】
以下に本発明の作用を説明する。
【００３５】
上記構成の変形可能ミラーにおいては、参照面基板の曲面部の断面形状に倣って可撓性部材、つまりこの表面に形成された反射面が変形する。このため、曲面部の形状精度を高く維持しておけば、反射面の変形精度を精度よく決定できるので、収差補償を精度よく行うことができる。
【００３６】
また、本発明が対象とする変形可能ミラーは、例えば記録再生装置に搭載されるが、この場合に、収差補償を要する領域は可撓性部材の中心部から対物レンズのＮＡに相当する領域であればよい。そのような領域は半径ｒ１内の領域となる。従って、半径ｒ１より外の領域は可撓性部材が変形しやすい任意の形状に設定することが可能である。
【００３７】
このような考えに基づき、曲面部の断面形状を、中心部から半径ｒ２までの部分が球面で形成され、かつ半径ｒ１から半径ｒ３までの部分がｒの関数ｆ（ｒ）で表され、半径ｒ１から半径ｒ３までの間に変曲点が１つ存在し、該変曲点から半径ｒ３までの部分がｆ”（ｒ）＞０となる曲線で構成すると、可撓性部材に無理な応力がかかることなく、スムーズに変形し、変形のためのエネルギーも少なくてすむ。なお、具体的な理由については、後述の実施形態で説明する。
【００３８】
また、必ず特定の収差を発生して収差補償しなければならない部分の形状が球面であり、組立て時の軸ずれに対して敏感でなくなるため、組立てが容易であり、その分コストダウンに寄与できる。
【００３９】
ここで、本発明が対象とする変形可能ミラーは、後述の実施形態で明かなように、例えば、可撓性部材の一部を形成する上部電極層と参照面基板に形成される下部電極層との間に駆動回路により電圧を印加することにより弾性変形される。このため、弾性変形に要するエネルギー、つまり駆動電圧を低減することが可能となる。この結果、記録再生装置のランニングコストを低減することができる。また、駆動電圧が低くなることにより、絶縁膜の絶縁破壊の可能性が低減されるので、装置の信頼性も向上できる。
【００４０】
また、参照面基板の平面部における水平部分の距離に相当するｒ５−ｒ４の部分は、後述のように、変形には影響しにくい。従って、この部分を小さくして全体の寸法を小さくするか、若しくは、半径ｒ４までの部分をその代わりに大きくするほうが、小型化若しくは駆動電圧の低電圧化の観点からは好ましい。このような要件を満足するｒ５−ｒ４の長さは、後述の本発明者等のシミュレーション結果によれば、ｒ５−ｒ４≦０．２ｍｍであることが確認できた。
【００４１】
また、曲面部の周縁部分で可撓性部材と下部電極の間隙がより小さくなるような構造にすると、比較的低電圧でも比較的大きな静電気力の発生が可能となり、低電圧化の観点から好ましい。このような構造は、参照面基板の半径ｒ３から半径ｒ４までの部分がｒの関数ｇ（ｒ）で表され、半径ｒ３から半径ｒ４までの間に変曲点が１つ存在し、変曲点から半径ｒ４までの部分をｇ”（ｒ）＜０となる曲線で形成することにより達成できる。
【００４２】
また、参照面基板の中心部から半径ｒ５までの部分が全て微分可能な断面曲線である構成にすると、このような形状は、より一層滑らかな形状であるため、角部での応力集中がなくなるうえ、更に、可撓性部材と参照面基板との密着性が向上するので、静電気力の伝達の観点から好ましいものになる。
【００４３】
また、参照面基板の前記中心部から半径ｒ４までの部分が、下記（２）式の条件を満足し、
ｒ４≧２×ｒ２ …（２）
かつ、ｒ３がその中間点、若しくは、中間点より中心部寄りに位置する構成にすると、本発明者等の後述のシミュレーション結果によれば、可撓性部材がより一層変形しやすくなることを確認できた。従って、このような構成によれば、弾性変形に要するエネルギー、つまり駆動電圧をより一層低減できる。
【００４４】
また、参照面基板の半径ｒ１の部分の深さｄ１と、最深部に相当する半径ｒ３の部分の深さｄ３との差ｄ３−ｄ１が、下記（３）式の条件
０．５μｍ≦ｄ３−ｄ１≦１．５μｍ …（３）
を満足する構成にすると、本発明者等の後述のシミュレーション結果によれば、静電気力と可撓性部材の曲げによる反力の釣り合いがとれ、弾性変形に要するエネルギー、つまり駆動電圧をより一層低減できることを確認できた。
【００４５】
【発明の実施の形態】
以下に本発明の実施の形態を図面に基づき具体的に説明する。
【００４６】
（実施形態１）
図１〜図１２は本発明変形可能ミラーの実施形態１を示す。まず、図１〜図４に従い本発明変形可能なミラーの概略構成について説明する。但し、図１は変形可能ミラーの平面図、図２は図１のＸ−Ｘ線による断面図、図３は底面図、図４は分解斜視図を示す。
【００４７】
この変形可能ミラー１は、シリコン基板５０、このシリコン基板５０の裏面側に取り付けられた可撓性部材２及びその下方に配置された参照面基板６を有する基本構成になっている。ここで、シリコン基板５０は内側が正方形状に開口５３された枠体状に形成されている。この開口部５３の中心はシリコン基板５０の形状中心から図上左側に少し偏位している。
【００４８】
可撓性部材２は、図４に示すように、平面視前記開口部５３よりも少し大型の正方形状をなし、その外周部がシリコン基板５０の平坦になった外周縁部に固着されている。より具体的には、シリコン熱酸化膜５１ａを介してシリコン基板５０の外周縁部に固着されている。なお、可撓性部材２は引張応力が付加された状態でシリコン基板５０に固着されている。
【００４９】
ここで、図２に示すように、可撓性部材２は上部電極層８とその上に積層された反射膜１０で構成されている。上部電極層８は、例えば８μｍ程度の厚みを有するＮｉ膜で作製されている。また、反射膜１０は、例えば１μｍ程度の厚みを有するＡｕ、Ａｌ等の薄膜で作製されている。
【００５０】
なお、反射膜１０を無くして、上部電極層８の表面をそのまま反射面として利用する実施形態をとることも可能である。このような構成によれば、部品点数を削減でき、製造コストを低減に寄与できる利点がある。
【００５１】
参照面基板６は、図４に示すように円筒状をなし、例えばガラスモールド法で作製されている。参照面基板６の表面、すなわち可撓性部材２と対向する表面には、下部電極層１２、配線部５５、配線パッド５６及びスペーサー層５４が形成され、これらの上に絶縁層９が形成されている（図２参照）。ここで、下部電極層１２、配線部５５及び配線パッド５６は連接されている。
【００５２】
図２等に示すように、参照面基板６の表面の外周縁部は平坦になっており、その内側には曲面部（凹凸部）３が形成され、ここに上記下部電極層１２が形成されている。また、平坦になった外周縁部の外周端には面取り部５９が設けられており、平坦部に配線部５５が形成され、面取り部５９には絶縁層９は設けられていない。従って面取り部５９上の配線パッド５６には絶縁層９は付着していない（図２参照）。
【００５３】
下部電極層１２とスペーサー層５４は、例えば０．１μｍ程度の厚みを有するＡｌで作製され、絶縁層９は、例えば０．５μｍ程度の厚みを有する酸化シリコンで作製されている。
【００５４】
ここで、上記の配線パッド５６は、下部電極層１２へ電圧を印可するための配線部５５と後述する下部電極用パッド５８とを電気的に接続す為に設けられている。なお、配線部５５及び配線パッド５６は下部電極層１２と同じ厚み・材料で形成されている。
【００５５】
可撓性部材２が固着されたシリコン基板５０と、下部電極層１２と絶縁層９が設けられた参照面基板６は、シリコン基板５０側の上部電極層８と参照面基板６側の下部電極層１２が互いに対向するように接着剤で接着されている（図２参照）。より具体的には、平坦になった外周縁部同士が密着して接着されている。可撓性部材２は、スペーサ５４上の絶縁層９の上面と下部電極層１２、配線部５５上の絶縁層９の上面で同じ高さで接触し、平面性を維持する。
【００５６】
前記接着剤には、例えば導電性のエポキシ系接着剤が用いられ、図２に示すように、接着剤５７ａは参照面基板６の面取り部５９上の配線パッド５６と、シリコン基板５０の裏面上に熱酸化膜５１ａを介して設けられた下部電極用パッド５８とを電気的に接続する機能も兼ねている。
【００５７】
参照面基板６の面取り部分５９は、シリコン基板５０との参照面基板６が接着された時に配線パッド５６を外部に露出させるとともに、接着剤５７ａ、５７ｂ、がこの面取り部分に入り込むことにより、接着の信頼性を向上させ、かつ配線パッド５６と下部電極用パッド５８との電気的な接続を確実にする機能を有する。
【００５８】
可撓性部材２の露出部分２ｂ（図３参照）と下部電極用パッド５８は、例えば半田等の手段により駆動回路７に接続されている。これにより、駆動回路７は可撓性部材２の露出部分２ｂと下部電極層１２との間に電圧を印加したり、印加を中止したりする。
【００５９】
具体的には、可撓性部材２の反射膜１０に入射する光ビームに収差を与えることなく反射させる場合は、駆動回路７は電圧を印加しない。この結果、可撓性部材２は付加された引張応力の作用で平坦のまま維持される為、入射してくる光ビームに収差を与えず、そのまま反射させる。これに対して、入射する光ビームに収差を与えるときには、駆動回路７は上部電極層８と下部電極層１２の間に電圧を印加する。これにより、両者間には静電気力が作用するので、可撓性部材２は参照面基板６側に変形し、結果的に凹凸面３に吸着し、入射してくる光ビームに所定の収差を与える。
【００６０】
次に、変形可能ミラーを記録再生装置に組み込んだ一構成例を図５及び図６に従い説明する。尚、ここでは厚み０．６ｍｍ（例えば、ＤＶＤ）と１．２ｍｍ（例えば、ＣＤ）の２種類の光ディスクに対応できる記録再生装置を例にとって説明する。
【００６１】
光ピックアップの光源である半導体レーザー５００から出たビーム５０４は、コリメータレンズ５０２、ビームスプリッター５０３、４分の１波長板５０７を通過して、ビームスプリッター５０６に到達する。このビーム５０４は、ビームスプリッター５０６及び４分の１波長板５０７を通過して、変形可能ミラー１に達する。
【００６２】
そして、この変形可能ミラー１で反射された光が４分の１波長板を通過し、ビームスプリッター５０６で反射され、対物レンズ５０８に入射する。そして、対物レンズ５０８で集光されて光ディスク５０９を照射する。この対物レンズ５０８は、ディスクの厚みが０．６ｍｍの光ディスクに対応するように焦点距離、ＮＡ等が設定されている。
【００６３】
ここで、本実施形態１では、装着された光ディスク５０９の厚みに応じて、変形可能ミラー１の状態を変えて、対物レンズ５０８の焦点をその光ディスク５０９に合致したものとする。即ち、ディスクの厚みが１．２ｍｍの時に変形可能ミラー１を変形させて、入射光に収差を与えて、ディスクに焦点が合うようにする。尚、この変形可能ミラー１は、無変形時には、平面ミラーを形成するものである。以下、その動作について説明する。
【００６４】
まず、光ディスク５０９の上側に設けられたディスクの厚み検知装置５１５により、その厚みが０．６ｍｍか１．２ｍｍかを検知する。このディスク厚み検知装置５１５は、例えば図６に示すような構成になっている。ディスク厚み検知装置５１５は、光源６００から光ビーム６０２を射出し、光ディスク５０９の上面で反射させる。この反射光は、光ディスク５０９の厚みが０．６ｍｍの場合は光路６０４をたどって光位置検出器６０１に入射する。一方、光ディスク５０９の厚みが１．２ｍｍの場合は、光路６０３をたどって光位置検出器６０１に入射する。従って、この反射光の位置を光位置検出器６０１で検出することにより、そのディスク５０９の厚みを判定することができる。
【００６５】
次に、システム制御装置５１６が、この基板厚み検知装置５１５から基板厚み情報を受け、変形可能ミラー１の駆動回路７を動作させる。このとき、駆動回路７は、光ディスク厚みが０．６ｍｍの場合は、変形可能ミラー１を変形させない。一方、ディスクの厚み１．２ｍｍの場合には、変形可能ミラー１を変形させる。即ち、変形可能ミラー１の可撓性部材２を参照面基板６の参照面に吸着させる。これにより変形可能ミラー１による反射光には所定の収差が与えられ、対物レンズ５０８の焦点をディスク厚み１．２ｍｍの光ディスクに合うようにする。
【００６６】
逆に、対物レンズ５０８に、収差が与えられていない光が入射した時に、ディスクの厚みが１．２ｍｍの光ディスク５０９に焦点の合うものを使用し、ディスクの厚みが０．６ｍｍの光ディスク５０９を使用した時に、変形可能ミラー１により収差を与えても良いが、ディスク厚みが０．６ｍｍの光ディスクは記録容量が大きいため、ディスクの厚みが１．２ｍｍのＣＤ等の光ディスクを再生する場合よりも、使用する光学部品に高い位置精度が要求される。
【００６７】
本発明者等のシミュレーション結果によると、ディスク厚みが１．２ｍｍの基板を再生するときに収差を与えた光を入射させた方が光学部品の位置精度がゆるくてすむ。従って、変形可能ミラー１が平面ミラーとなっているときに、ディスクの厚みが０．６ｍｍの光ディスクを再生し、変形可能ミラー１を変形させたときに、ディスクの厚みが１．２ｍｍの光ディスクを再生する方が望ましい。
【００６８】
この場合、変形可能ミラー１が平面ミラーとして働くときは、ミラー面深さ＝０μｍの位置に沿った状態であり、収差補償ミラーとして働くときは、図７の曲線で示すような凹凸面、即ち曲面部３に沿った断面形状になる。
【００６９】
ここで、曲面部３は、これに吸着した可撓性部材２のミラー面２ａが、前記所定の収差を発生するものであれば良い。
【００７０】
所定の収差を発生する曲面部３の断面形状をシミュレーションで求めた結果の一例を図７に示すが、実際のデバイスとして用いる場合、中心部分が多少軸ずれを生じても問題ないよう、前記曲面部３の断面形状が球面となるものを用いるのが良い。即ち、曲面部３を球面にすると、軸ずれに対し安定であるうえ、更に焦点距離の補正もある程度可能であるため、本願出願人が先に提案した、曲面部が非球面である上記従来の変形可能ミラーに比べて、組立に要する時間を低減でき、その分、光ピックアップ装置等のコストダウンが可能になるからである。
【００７１】
ここで、一般に、例えば０．６ｍｍ基板厚のＤＶＤ等を再生するときは、例えば０．４５等の大きいＮＡが必要であるが、例えば１．２ｍｍ基板厚のＣＤ等を再生するときは、例えば０．３８等の小さいＮＡで良い。対物レンズの焦点距離を、例えば３．３ｍｍ、対物レンズのＮＡを前記と同じ、例えば０．３８とし、その範囲を収差補正するとすると、実際はミラーの変形により光線が曲げられるため、上記の数値より小さい値となるが、概算で、必要ビーム系は３．３×０．３８ｍｍで、半径約１．２５ｍｍの範囲が光ビームで照射されることになる。よって、図８（ａ）に示すような、曲面部３の形状にすればよい。
【００７２】
しかしながら、このままの曲面部３の形状で変形可能ミラー１を構成すると、可撓性部材２の変形が同図（ｂ）に示すようになり、可撓性部材２の曲面部３の周縁部に相当する部分において、無理な変形が発生する。このため、可撓性部材２の変形自体に無理が生じ、膨大なエネルギー（印加電圧）が必要となる。また、仮に変形したとしても、可撓性部材２自体に塑性変形等を生じ、その寿命を考慮すると、現実的でない。
【００７３】
よって、実際には、図９（ａ）〜（ｃ）に示すように、ＮＡ相当部分は収差補正するような面にし、その周りは可撓性部材２が変形しやすい断面形状にすればよい。
【００７４】
ここで、周縁部まで含めた曲面部３全体の形状としては、基本的に図９（ａ）〜（ｃ）の３種類のタイプのものが考えられる。以下にこれらの詳細を説明する。まず、図９（ａ）に示すものは、必ず特定の収差を発生して収差補正しなければならない部分の半径（曲面部３の中心からの半径）、即ち、例えば対物レンズのＮＡに相当する部分の半径をｒ１、曲面部３において、特定の収差を発生すべく設計された部分の半径をｒ２、曲面部３の最深部の半径をｒ３、曲面部３から周縁部の平面部３４へ遷移する部分の半径をｒ４、平面部３４の最外側の半径をｒ５（それぞれ同図（ａ）中に表示）とすると、中心部３５から半径ｒ２までの部分が球面で形成され、かつ半径ｒ１から半径ｒ３までの部分がｒの関数ｆ（ｒ）で表され、ｒ１からｒ３間に変曲点が１つ存在し、この変曲点からｒ３側の部分では、ｆ”（ｒ）＞０となる曲線で表される断面形状に形成されている。
【００７５】
また、半径ｒの位置に相当する最深部より外側では特に形状は問わないが、図９（ａ）に示すものでは、最深部と周縁部の平面部の入り口までを直線（傾斜面）で接続している。
【００７６】
また、図９（ｂ）に示すものは、半径ｒ２の位置より周縁部の平面部３４の入り口までを直線（傾斜面）で接続している。
【００７７】
また、図９（ｃ）に示すものは、半径ｒ４の位置まで前記球面をそのまま延長している。
【００７８】
なお、各部の諸寸法であるが、以降特に断りのない限り、可撓性部材２の厚みは８μｍ（実用的な範囲は５〜１５μｍ）、絶縁層９は、材質ＳｉＯ２で、比誘電率は４、ＳｉＯ２の厚みは０．５μｍ（実用的な範囲は０．４〜１．５μｍ）、半径ｒ１が１．１ｍｍ（実用的な範囲は０．５〜１．５ｍｍ）、半径ｒ５が３ｍｍ（実用的な範囲は１．５〜４ｍｍ）、特定の収差を発生して収差補正しなければならない部分の球面の曲率半径Ｒ＝１００ｍｍ（実用的な範囲は５０〜１５０ｍｍ）であり、これを基準にして、駆動電圧２５Ｖで変形可能ミラー１を変形させた場合の計算（評価）を行った。
【００７９】
図１０（ａ）〜（ｃ）は、評価結果（シミュレーション結果）を示す。但し、図１０（ａ）〜（ｃ）は、図９の（ａ）〜（ｃ）に示すタイプの評価結果をそれぞれ示している。
【００８０】
図１０（ａ）からわかるように、図９（ａ）に示すタイプのものでは、可撓性部材２は曲面部３の最深部以外はほぼ接触している。
【００８１】
これに対して、図１０（ｂ）からわかるように、図９（ｂ）に示すタイプのものでは、最深部付近の可撓性部材２の曲げによる反力が大きいため、特定の収差を発生して収差を補正しなければいけない部分の半径ｒ１内の中心部は問題なく接触しているが、半径ｒ１の周辺部は接触しにくいという現象が生じている。
【００８２】
また、図１０（ｃ）からわかるように、図９（ｃ）に示すタイプのものでは、曲面部３の周縁部分において、可撓性部材２と下部電極層１２との間隙が大きくなったことに起因して、この部分では可撓性部材２に静電気力はほとんど働かない。このため、可撓性部材２は、曲面部３の中心部から受ける静電気力のみで変形させねばならないことになる。
【００８３】
よって、静電気力を有効に活用し、できるだけ低い駆動電圧で可撓性部材２を駆動し、目的の収差補正を達成する観点からは、特定の収差を発生して収差を補正しなければならない部分、即ち半径ｒ１の位置から最深部、即ち半径ｒ３の部分までを滑らかな曲線で結ぶのが良いことがわかる。
【００８４】
ここで、曲面部３の中心部から最深部までの断面曲線をｆ（ｒ）とすると、特定の収差を発生する半径ｒ１（若しくは半径ｒ２）までは、球面の上弦であるので、常にｆ”（ｒ）＜０となる。できるだけ滑らかに最深部までつなぐためには、半径ｒ２からｒ３迄をｆ”（ｒ）＞０となる曲線を含む必要がある。即ち、半径ｒ１からｒ３間に、少なくともｆ”（ｒ）＝０となる変曲点が１つ以上存在する必要がある。
【００８５】
次に、前記変曲点が２つ以上存在する場合を調べた。図１１は半径ｒ１〜ｒ３間に変曲点が２つ存在する曲面部３を有する参照面基板６を示す。この場合は、半径ｒ１〜ｒ３間に突起が１つ発生することになる。また、図１２はその評価結果を示す。
【００８６】
図１２に示すように、可撓性部材２の変形がこの突起に邪魔されて、かえって変形しにくくなってしまうことがわかる。変曲点の数が更に増えると、突起もまた増え、より一層好ましくない結果が発生する。
【００８７】
よって、上記の考察より、曲面部３において、必ず特定の収差を発生して収差補償しなければならない部分の半径、即ち、例えば対物レンズのＮＡに相当する部分の半径をｒ１、曲面部３において、特定の収差を発生すべく設計された部分の半径をｒ２、曲面部３の最深部の半径をｒ３とすると、中心部３５から半径ｒ２までの部分が球面で形成され、かつ半径ｒ１から半径ｒ３までの部分がｒの関数ｆ（ｒ）で表され、半径ｒ１からｒ３間の部分に変曲点が１つ存在し、その変極点よりｒ３側ではｆ”（ｒ）＞０となる曲線で曲面部３を形成すると、変形に必要なエネルギーを少なくできることがわかる。
【００８８】
（実施形態２）
図１３〜図１６は本発明変形可能ミラーの実施形態２を示す。上記の実施形態１では、曲面部３の中心部から最深部までの断面形状が可撓性部材２の変形に与える影響を調べたが、本実施形態２では、曲面部３（中心部〜半径ｒ４まで）と平面部（半径ｒ４〜半径ｒ５まで）３４の水平方向の寸法比を変化させた場合の可撓性部材２の変形に与える影響を調べた。
【００８９】
具体的には、第１のパターン（タイプ）として、半径ｒ１＝１．０９、ｒ２＝１．１、ｒ３＝１．５、半径ｒ２までの収差補正用の球面の曲率半径がＲ＝１００ｍｍの参照面基板６を用い、第２のパターンとして、半径ｒ１＝１．３９、ｒ２＝１．４、ｒ３＝１．７、半径ｒ２までの収差補正用の球面の曲率半径がＲ＝１５０ｍｍの参照面基板６を用い、それぞれ半径ｒ４とｒ５の寸法を変えて、可撓性部材２と下部電極層１０間に３０Ｖの駆動電圧を与えて、変形のしやすさを調べた。
【００９０】
また、本実施形態２では、半径ｒ３〜ｒ４までの部分は、中心部３５から半径ｒ４まで連続となるような２次曲線を用いた。図１３〜１６にその評価結果を示す。
【００９１】
曲率半径Ｒが１００ｍｍと１５０ｍｍの場合それぞれにつき、図１３及び図１５では、曲面部３の水平半径を２．６ｍｍで固定して、平面部３４の長さを０．４ｍｍを中心に０．２〜０．６ｍｍまで変化させた。また、図１４及び図１６では、参照面基板６自体の大きさを決定する平面部３４の外周半径、即ちｒ５を３．０ｍｍで固定して、曲面部３の半径を２．６ｍｍ（平面部は０．４ｍｍ）を中心に２．４〜２．８ｍｍ（このとき平面部は０．６〜０．２ｍｍ）まで変化させた。
【００９２】
上記のシミュレーション結果によれば、曲面部３の水平方向に比べて、平面部の水平方向寸法が変形に与える影響はわずかであることが判明した。例えば、参照面基板６は、当然小型化が要求されるものであり、水平方向寸法には制限がある。この場合、平面部分を大きくすることよりも、曲面部３を大きくする方が可撓性部材２の変形に有利であることが判明した。
【００９３】
以上の考察結果より、平面部３４はできるだけ小さくして、全体の寸法を小さくするか、若しくは、その分、曲面部３を大きくするほうが良い。但し、平面部は参照面基板６の支持部としての機能も有するので、０〜０．２ｍｍ程度は必要な場合もある。よって、平面部３４の寸法は０．２ｍｍ以下とするのがよい。
【００９４】
（実施形態３）
図１７〜図２０は本発明変形可能ミラーの実施形態３を示す。本実施形態３では、曲面部３の最深部、即ち半径ｒ３の部分から、曲面部３から平面部３４への遷移部分、即ち半径ｒ５の部分までの断面曲線形状が可撓性部材２の変形に与える影響を調べた。
【００９５】
上記実施形態２の、例えば図１４〜図１６では、曲面部３の中央部分では、比較的、可撓性部材２が曲面部３に吸着しているのに対し、曲面部３の周縁部では、ほとんど接触していない。原因として、変形初期の可撓性部材２と曲面部３の間隙、換言すれば、可撓性部材２と下部電極層１０との間隙が曲面部３の中心部３５に比して周縁部では大きく、これに起因して静電気力が小さくなっているためと考えられる。
【００９６】
それ故、曲面部３の周縁部において、上記間隙が小さくなるような断面形状、即ち、参照面基板６の中心部に対する曲面部３の片側断面形状が、その断面曲線において、半径ｒ３から半径ｒ４までの部分がｒの関数ｇ（ｒ）で表されるとすると、ｒ３からｒ４間に変曲点が１つ存在し、その変曲点よりｒ４側ではｇ”（ｒ）＜０となる曲線で形成される断面曲線にすれば、周縁部においても静電気が有効に働くことが予想される。
【００９７】
図１７は前記事項を満たす断面形状を有する参照面基板６を用いた場合の評価結果を示し、図１８はそれとは逆の形状の断面形状を有する参照面基板６を用いた場合の評価結果を示す。但し、可撓性部材２の厚みは８μｍ、印加電圧は３０Ｖで行った。
【００９８】
図１７と図１８を比較すればわかるように、曲面部３の周縁部において、可撓性部材２と曲面部３が間隙が小さくなるように構成すると、可撓性部材２の変形にかなり効果的であることが判明した。また、曲面部３から平面部３４への遷移部分において、図１８のような変形状態であれば、応力集中が発生することが予想されるが、図１７の場合は、応力集中も軽減できるので、変形可能ミラーの信頼性の観点からも図１７に示す断面形状を有する参照面基板６が実施する上で好ましい。
【００９９】
但し、本実施形態３において、半径ｒ３の部分や半径ｒ４の部分では、比較的滑らかではあるが、完全に微分可能な曲線ではない。即ち、角部が存在する場合もある。
【０１００】
そこで、図１９、図２０に示すように、半径ｒ３、若しくは半径ｒ４において、角部が存在する場合と、完全に滑らか、即ち、参照面基板６において、中心部から半径ｒ５の部分までが完全に微分可能な曲線である場合の変形状態の比較を行った。
【０１０１】
ここで、図１９は中心部３５から半径ｒ５の部分までが完全に微分可能な場合の評価結果を示し、図２０は図１７と同一形状で、半径ｒ４の部分が微分可能でなく、角部が存在する場合の評価結果を示す。印加電圧のみ図１７、１８の場合より下げて２５Ｖで評価した。
【０１０２】
図１９と図２０を比較してみればわかるように、全体的に微分可能な断面形状にすると、曲面部３と可撓性部材２の間隙がより小さくなる方向になり、静電気力の有効利用の観点からより効果的であることが判明した。また、半径ｒ３、半径ｒ４の部分での応力集中もより軽減できることが予想されるので、変形可能ミラーの信頼性の観点からも好ましい。よって、図１９に示す断面形状を有する参照面基板６が実施する上で好ましい。
【０１０３】
（実施形態４）
図２１〜図２９は本発明変形可能ミラーの実施形態４を示す。本実施形態４では、曲面部３の最深部の位置が、可撓性部材２の変形に与える影響について調査した。即ち、上記実施形態１〜３では、最深部の位置は特に規定していないが、本実施形態４では、最深部、即ち半径ｒ３の部分の水平位置及び垂直位置が可撓性部材２の変形にどのような影響を及ぼすかを調べた。
【０１０４】
まず、最深部の水平方向の位置に関して、可撓性部材２の厚みを１２μｍ、印加電圧２５Ｖで調査した。また、半径ｒ２までの特定の収差を発生するように設けられた球面の曲率半径Ｒ＝１００ｍｍ、ｒ４／ｒ５＝２．８／３．０ｍｍとした。
【０１０５】
そして、最深部の半径ｒ３として、ｒ３＝１．２、１．３、１．４、１．４２、１．５ｍｍの場合を例にとって評価した。その断面形状及び計算結果をそれぞれ図２１〜２５に示す。
【０１０６】
図２１〜２５に示す計算結果により、ｒ３＝１．４ｍｍの位置が曲面部３の片側断面の中間点となるが、その点よりわずかでもｒ３の位置がｒ４側に寄ると、可撓性部材２が変形しにくくなること（図２４、図２５参照）、逆にｒ３の位置が中間点となるのがベストであるが（図２３参照）、仮に中心点寄りになっても可撓性部材２が極度に変形しにくくなることは無い（図２１、図２２参照）ことが判明した。
【０１０７】
これは、可撓性部材２の変形が最深部に対し対称的で変形しやすいことや、曲面部３全体で可撓性部材２と曲面部３の間隙が小さくなることによる効果と考えられる。
【０１０８】
以上の条件が成立するには、半径ｒ４≧２×ｒ２となることが必要であるが、仮にｒ４＜２×ｒ２の場合は、最深部の半径ｒ３はできるだけｒ２側に設けるのが良い。
【０１０９】
次に、曲面部３の最深部、即ち半径ｒ３の部分の垂直位置、つまり曲面部３の深さが可撓性部材２の変形に与える影響について調べた。
【０１１０】
ここで、最深部の深さが深すぎると、前記間隙が大きくなるため、一定電圧で発生する静電気が弱くなり不利である。一方、浅すぎると、可撓性部材２の曲げに無理が生じ、ｒ１付近で接触不良を生じることが予想される。そこで、半径ｒ３の部分の垂直位置がどの位置にあるのが可撓性部材２の変形に効果的であるかを調べた。
【０１１１】
図２６は最深部の深さｄ３が６．５μｍの場合の可撓性部材２の変形状態の評価結果を示す。印加電圧は図２３の場合と同じである。図２７は最深部の深さｄ３が７μｍであり、それ以外は図２６と同一の条件で比較していることになる。図２６、図２７の評価結果によれば、可撓性部材２の曲げの反力で既に若干収差補正用に特定の収差を発生すべき部分、即ち半径ｒ１内の部分の周辺あたりが既に接触しにくくなっていることがわかる。
【０１１２】
図２８及び図２９は最深部の深さが深い場合（それぞれ、ｄ３＝７．５μｍ、ｄ３＝８μｍ）を示す。印加電圧は２１Ｖで行った。図２９に相当する８μｍの深さ程度から可撓性部材２の変形に悪影響が現れているのがわかる。
【０１１３】
ここで、最深部の深さ自体は、半径ｒ２迄の曲面部の曲率や、ＮＡによって変動するので、収差補正用の球面の端部、即ち半径ｒ１の垂直位置と最深部の垂直位置の相対関係で表すならば、半径ｒ１の部分とｒ３の部分の深さ方向の距離の差は、０．５〜１．５μｍの間が好ましいことが判明した。
【０１１４】
なお、本発明と本願出願人が先に提案した変形可能ミラーとの違いは、曲面部の中央部の形状と、深さの違い、特に深さの違いによるところが大きいことによる。例えば、先に提案した変形可能ミラーの場合、曲面部の深さが１μｍ以下であるため、静電気力の計算において、上下の電極層間の間隔＝絶縁層の膜厚として、可撓性部材〜曲面部の間隙を無視しても結果はあまり変わらないため無視しているが、本発明の場合は、可撓性部材〜曲面部の間隙が大きく無視できないため、上下の電極層間の間隔＝絶縁層の膜厚＋可撓性部材〜曲面部の間隙とし、更に変形により遂次静電気力が変動することを考慮にいれたシミュレーション方法により計算を実行している。
【０１１５】
【発明の効果】
以上の本発明変形可能ミラーによれば、参照面基板の曲面部の断面形状に倣って可撓性部材、つまりこの表面に形成された反射面が変形する。このため、曲面部の形状精度を高く維持しておけば、反射面の変形精度を精度よく決定できるので、収差補償を精度よく行うことができる。
【０１１６】
また、本発明が対象とする変形可能ミラーは、例えば記録再生装置に搭載されるが、この場合に、収差補償を要する領域は可撓性部材の中心部から対物レンズのＮＡに相当する領域であればよく、そのような領域は半径ｒ１内の領域となる。従って、半径ｒ１より外の領域は可撓性部材が変形しやすい任意の形状に設定することが可能である。
【０１１７】
そこで、本発明では、曲面部の断面形状を、中心部から半径ｒ２までの部分が球面で形成され、かつ半径ｒ１から半径ｒ３までの部分がｒの関数ｆ（ｒ）で表され、半径ｒ１から半径ｒ３までの間に変曲点が１つ存在し、該変曲点から半径ｒ３までの部分がｆ”（ｒ）＞０となる曲線で構成しており、可撓性部材に無理な応力がかかることなく、スムーズに変形し、変形のためのエネルギーも少なくてすむ。
【０１１８】
それ故、本発明によれば、弾性変形に要するエネルギー、つまり駆動電圧を低減することが可能となる。この結果、記録再生装置のランニングコストを低減することができる。また、駆動電圧が低くなることにより、絶縁膜の絶縁破壊の可能性が低減されるので、装置の信頼性も向上できる。
【０１１９】
加えて、必ず特定の収差を発生して収差補償しなければならない部分の形状が球面であり、組立て時の軸ずれに対して敏感でなくなるため、組立てが容易であり、その分コストダウンに寄与できる。
【０１２０】
また、特に請求項２記載の変形可能ミラーによれば、ｒ５−ｒ４≦０．２ｍｍの条件を満足するように曲面部を構成するため、装置構成の小型化若しくは駆動電圧の低電圧化を一層図ることができる。
【０１２１】
また、特に請求項３記載の変形可能ミラーによれば、参照面基板の半径ｒ３から半径ｒ４までの部分がｒの関数ｇ（ｒ）で表され、半径ｒ３から半径ｒ４までの間に変曲点が１つ存在し、変曲点から半径ｒ４までの部分をｇ”（ｒ）＜０となる曲線で形成する構成をとるので、曲面部の周縁部分で可撓性部材と下部電極層の間隙がより小さくなり、比較的低電圧でも比較的大きな静電気力の発生が可能となり、低電圧化の観点から好ましいものになる。
【０１２２】
また、特に請求項４記載の変形可能ミラーによれば、参照面基板の中心部から半径ｒ５までの部分が全て微分可能な断面曲線である構成をとるので、角部での応力集中がなくなるうえ、更に、可撓性部材と参照面基板との密着性が向上するので、静電気力の伝達の観点から好ましいものになる。
【０１２３】
また、特に請求項５記載の変形可能ミラーによれば、参照面基板の前記中心部から半径ｒ４までの部分が、下記（２）式の条件を満足し、
ｒ４≧２×ｒ２ …（２）
かつ、ｒ３がその中間点、若しくは、中間点より中心部寄りに位置する構成をとるので、可撓性部材がより一層変形しやすくなるので、弾性変形に要するエネルギー、つまり駆動電圧をより一層低減できる利点がある。
【０１２４】
また、特に請求項６記載の変形可能ミラーによれば、参照面基板の半径ｒ１の部分の深さｄ１と、最深部に相当する半径ｒ３の部分の深さｄ３との差ｄ３−ｄ１が、下記（３）式の条件
０．５μｍ≦ｄ３−ｄ１≦１．５μｍ …（３）
を満足する構成をとるので、静電気力と可撓性部材の曲げによる反力の釣り合いがとれ、弾性変形に要するエネルギー、つまり駆動電圧をより一層低減できる利点がある。
【図面の簡単な説明】
【図１】本発明の実施形態１を示す、変形可能ミラーの平面図。
【図２】本発明の実施形態１を示す、図１のＸ−Ｘ線による断面図。
【図３】本発明の実施形態１を示す、変形可能ミラーの底面図。
【図４】本発明の実施形態１を示す、変形可能ミラーの分解斜視図。
【図５】本発明の実施形態１を示す、変形可能ミラーが搭載された記録再生装置の構成を示すブロック図。
【図６】本発明の実施形態１を示す、厚み検知装置の検出原理を示す模式図。
【図７】本発明の実施形態１を示す、シミュレーションで求めた収差補償を行うための参照面基板の曲面部の断面形状を示す図。
【図８】（ａ）は変形可能ミラーの一例を示す、無変形状態の断面図、（ｂ）は（ａ）の変形可能ミラーの変形状態の断面図。
【図９】本発明の実施形態１を示す、（ａ）〜（ｃ）は種々の曲面部を有する参照面基板の例を示す断面図。
【図１０】本発明の実施形態１を示す、（ａ）は図９（ａ）の参照面基板を用いて可撓性部材を変形させた場合の評価結果を示す図、（ｂ）は図９（ｂ）の参照面基板を用いて可撓性部材を変形させた場合の評価結果を示す図、（ｃ）は図９（ｃ）の参照面基板を用いて可撓性部材を変形させた場合の評価結果を示す図。
【図１１】本発明の実施形態１を示す、片側に変曲点を２つ有する曲面からなる曲面部を有する参照面基板の断面図。
【図１２】図１１の参照面基板を用いて可撓性部材を変形させた場合の評価結果を示す図。
【図１３】本発明の実施形態２を示す、曲面部（中心部〜半径ｒ４まで）と平面部（半径ｒ４〜半径ｒ５まで）の水平方向の寸法比を変化させた場合の可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図１４】本発明の実施形態２を示す、曲面部（中心部〜半径ｒ４まで）と平面部（半径ｒ４〜半径ｒ５まで）の水平方向の寸法比を変化させた場合の可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図１５】本発明の実施形態２を示す、曲面部（中心部〜半径ｒ４まで）と平面部（半径ｒ４〜半径ｒ５まで）の水平方向の寸法比を変化させた場合の可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図１６】本発明の実施形態２を示す、曲面部（中心部〜半径ｒ４まで）と平面部（半径ｒ４〜半径ｒ５まで）の水平方向の寸法比を変化させた場合の可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図１７】本発明の実施形態３を示す、曲面部の最深部から平面部への遷移部分までの断面曲線形状が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図１８】本発明の実施形態３を示す、曲面部の最深部から平面部への遷移部分までの断面曲線形状が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図１９】本発明の実施形態３を示す、曲面部の最深部から平面部への遷移部分までの断面曲線形状が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２０】本発明の実施形態３を示す、曲面部の最深部から平面部への遷移部分までの断面曲線形状が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２１】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２２】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２３】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２４】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２５】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２６】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２７】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２８】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図２９】本発明の実施形態４を示す、曲面部の最深部の位置が可撓性部材の変形に与える影響を調査するための評価結果を示す図。
【図３０】従来のピックアップの構成を示す図。
【図３１】従来の変形可能ミラーを使用した光ピックアップの構成を示す図。
【図３２】従来の変形可能ミラーの構成を示す図。
【符号の説明】
１ 変形可能ミラー
２ 可撓性部材
３ 曲面部
６ 参照面基板
８ 上部電極層
９ 絶縁層
１２ 下部電極層
３４ 平面部
３５ 中心部分
５０ シリコン基板
５０８ 対物レンズ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a deformable mirror capable of deforming a reflecting surface, and more particularly to, for example, an optical disk mounted on a recording / reproducing apparatus and having a different substrate thickness such as a CD (compact disk) and a DVD (digital video disk). The present invention relates to a deformable mirror that enables accurate and accurate information recording / reproducing operations.
[0002]
[Prior art]
Since optical disks can record a large amount of information signals at high density, they have recently been used in many fields such as audio, video, and computers. FIG. 30 shows a conventional example of an optical pickup device (hereinafter, referred to as an optical pickup) used in these devices. Hereinafter, the configuration of the optical pickup 100 will be described together with the operation.
[0003]
Light emitted from the semiconductor laser 101 is converted into parallel light 103 by the collimator lens 102. The parallel light 103 enters the polarization beam splitter 104, travels straight, passes through the quarter-wave plate 105, has its optical path bent by the reflection mirror 106, and enters the objective lens 107. The light incident on the objective lens 107 is narrowed down to form a light spot 109 on the information storage medium surface of the optical disk 108 specified by the rotation motor 113.
[0004]
On the other hand, the reflected light 110 reflected by the optical disk 108 passes through the objective lens 107, the reflection mirror 106 and the quarter-wave plate 105 again and is incident on the polarization beam splitter 104. The reflected light 110 is reflected by the polarization beam splitter 104 by the function of the quarter-wave plate 105, passes through the aperture lens 111, and is received by the photodetector 112. The photodetector 112 detects the reproduction signal by detecting the light intensity of the reflected light beam.
[0005]
Here, the objective lens 107 is designed in consideration of the thickness of the optical disk 108. However, for an optical disk having a thickness different from the design value, spherical aberration occurs and the imaging performance deteriorates, so that recording and reproduction cannot be performed accurately.
[0006]
Conventionally, the thickness of an optical disk used for a CD, a video disk, a data IS0 standard magneto-optical disk device, or the like has almost the same standard (about 1.2 mm). For this reason, it was possible to record and reproduce different types of optical disks (CD, video disk, magneto-optical disk, etc.) with one optical pickup.
[0007]
In recent years, the following methods have been studied in order to increase the density of optical disks.
[0008]
(1) A method of increasing the numerical aperture (NA) of an objective lens to improve optical resolution.
[0009]
(2) A method in which recording layers are provided in multiple layers.
[0010]
Here, in the above method (1), when the NA of the objective lens is increased, the diameter of the condensed beam is reduced in proportion, but in order to keep the tolerance of the tilt of the disk to the same extent, the thickness of the substrate of the disk must be reduced. Need to be thinner. For example, if the NA of the objective lens is changed from 0.5 to 0.6, the same disk tilt tolerance cannot be obtained unless the substrate thickness is reduced from 1.2 mm to 0.6 mm.
[0011]
However, when the substrate thickness of the disk is reduced in this manner, when recording / reproducing a conventional optical disk using an objective lens corresponding to the optical disk having a small substrate thickness, spherical aberration increases and an image forming point increases. Are spread, making recording and reproduction difficult. Therefore, compatibility with the conventional optical disk cannot be maintained, and two optical pickups must be used to record and reproduce the thin optical disk and the conventional optical disk with separate optical pickups.
[0012]
Further, when a multi-layer disc having a plurality of recording layers provided through a transparent substrate having a certain thickness is used as in the above method (2), the recording capacity of one disc is greatly increased.
[0013]
However, since the recording layer has a different substrate thickness as viewed from the objective lens, accurate recording and reproduction of information cannot be performed with one optical pickup for the same reason as described above.
[0014]
As a method for solving such a problem, there is a method disclosed in Japanese Patent Application Laid-Open No. H5-151591, in which a method of correcting the substrate thickness by using a deformable mirror is adopted.
[0015]
FIG. 31 shows an optical system of a disk device using the deformable mirror. The configuration will be described below together with the operation. Light 103 emitted from a semiconductor laser 101 passes through a collimator lens 102, a polarizing beam splitter 104, a quarter-wave plate 105, and reaches a beam splitter 202. Here, the light 103 is oriented with a polarization such that it passes through the beam splitter 202 and the quarter-wave plate 105 and reaches the deformable mirror 200.
[0016]
The deformable mirror 200 is configured such that the mirror surface is deformable, and when the substrate thickness of the optical disk increases, the mirror surface is deformed by the deformable mirror driving circuit 203, and the light 103 becomes thicker. Spherical aberration that cancels out spherical aberration caused by the above. The light 103 returns through the quarter-wave plate 201, is reflected by the beam splitter 202, and reaches the objective lens 107. The light that has entered the objective lens 107 is narrowed down to form a light spot 109 on the information recording medium surface of the optical disk 108.
[0017]
On the other hand, the reflected light 110 reflected by the optical disk 108 passes again through the objective lens 107, the beam splitter 202, the quarter-wave plate 201, the deformable mirror 200 and the quarter-wave plate 105, and passes through the polarization beam splitter 104. Incident. The reflected light 110 is reflected by the polarization beam splitter 104, passes through an aperture lens 111, and is received by a photodetector 112. The photodetector 112 detects the reproduction signal by detecting the light intensity of the reflected light beam.
[0018]
FIG. 32 shows a specific configuration of the deformable mirror 200. This is described in "Adaptive optics for optimization of image resolution" (Applied Optics), vol. 26, pp. 3772-3777, (1987), JP Gafferel, and the like.
[0019]
The deformable mirror 200 fixes a deformation plate 301 having a mirror surface 300 formed on the surface, a piezoelectric actuator 302 for pressing a plurality of locations on the back side of the deformation plate 301, and the deformation plate 301, the piezoelectric actuator 302, and the deformation plate 301. By changing the voltage applied to each of the piezoelectric actuators 302, the deformable plate 301 is displaced by an initially desired amount, and the mirror surface 300 on the deformed plate is deformed as a whole into a desired shape as a whole. .
[0020]
Further, as another conventional example of a deformable mirror, there is one proposed by the present applicant in Japanese Patent Application No. 5-205282. The deformable mirror includes a reference surface substrate similar to that of the present invention described later, and specifies the shape of a curved surface portion (concavo-convex surface portion) of the reference surface substrate, thereby reducing the energy required for deforming the deformable mirror. It employs a technique that seeks.
[0021]
[Problems to be solved by the invention]
However, in the deformable mirror using the conventional piezoelectric actuator 302 shown in FIG. 32, when the driving voltage fluctuates, the displacement also fluctuates. In particular, when there is a voltage fluctuation between the piezoelectric actuators 302, the deformable mirror 300 Will deviate significantly from the desired plane.
[0022]
In addition, there is a problem that the pressing force of each voltage actuator 302 fluctuates due to the influence of thermal expansion also due to a change in environmental temperature, and the mirror surface 300 deviates from a desired mirror surface.
[0023]
Further, the diameter of the light beam for performing the aberration correction is about 4 mm, and in order to realize an accurate deformed shape of the deformable mirror, it is necessary to provide a large number of piezoelectric actuators 302 within a diameter of 4 mm. And the size of the deformable mirror as a whole increases. For this reason, there is also a problem that the device configuration of the optical pickup becomes large.
[0024]
In addition, the deformable mirror previously proposed by the applicant of the present application uses an aspherical surface having relatively shallow asperities as a shape of a portion that always needs to generate a specific aberration and compensate for aberration. It is very sensitive and unstable to misalignment during assembly. For this reason, assembling takes time, which is a constraint in reducing the cost of the optical pickup.
[0025]
The present invention has been made in order to solve the above-described problems, and is less susceptible to fluctuations in environmental temperature and fluctuations in an electric circuit, can hold a mirror surface with high accuracy, and has a small size. It is an object of the present invention to provide a deformable mirror that can be manufactured at low cost with a simple structure.
[0026]
Another object of the present invention is to provide a deformable mirror that can improve the deformability and consequently reduce the energy required for elastic deformation, and reduce the running cost and the like of the recording / reproducing apparatus.
[0027]
It is another object of the present invention to provide a deformable mirror that does not locally generate a large stress and can improve the life of the mirror.
[0028]
[Means for Solving the Problems]
The deformable mirror of the present invention is an elastically deformable flexible member having a reflection surface for reflecting incident light on the surface, and is provided on the back side of the flexible member so as to face the back side, The flexible member is provided on a curved surface portion whose central portion protrudes toward the flexible member so as to form a space that allows deformation of the flexible member, and on a peripheral portion of the curved surface portion. With flatness maintained A reference surface substrate having a flat surface portion for supporting the flexible member, wherein the flexible member is Surface A deformable mirror which is deformed by being attracted to the mirror, wherein a one-side cross section of the curved surface portion with respect to a center portion of the reference surface substrate Surface The shape is such that the portion from the center of the reference surface substrate to the radius r1 is: The flexible member is set to have a spherical shape so that the flexible member is deformed so that a specific aberration is always imparted to the light beam reflected by the reflection surface of the flexible member by being attracted. Has been The portion from radius r1 to radius r2 (r1 <r2) is Also said It is set to generate a specific aberration, the deepest portion of the curved surface portion is provided at a radius r3 (r2 <r3) from the center, and a radius r4 (r3 <r4) from the center. A portion that transitions from the curved surface portion to the flat surface portion of the peripheral edge portion is provided, and the radius of the curved surface portion is from r1 to r3. surface Part Indicates the depth at radius r Represented by the function f (r) And the function f (r) is Between radius r1 and radius r3 Inflection point Exists, and the Inflection point The part from to the radius r3 is f ″ (r)> 0. Has become Thereby, the above object is achieved.
[0029]
Preferably, The outermost surface of the plane portion is provided at a portion having a radius r5 (r4 <r5) from the center portion, R5-r4 corresponding to the distance of the horizontal portion in the plane portion of the reference surface substrate is a condition of the following equation (1).
r5−r4 ≦ 0.2mm (1)
Is configured to satisfy
[0030]
Preferably, a portion of the reference surface substrate from a radius r3 to a radius r4 is: Indicates the depth at radius r With the function g (r) And the function g (r) is Between radius r3 and radius r4 Inflection point Exists, and the Inflection point G ″ (r) <0 from the point up to the radius r4 To be .
[0031]
Also, preferably, from the central portion of the reference surface substrate Outermost of the flat part It is assumed that all the parts up to are the differentiable sectional curves.
[0032]
Preferably, a portion of the reference surface substrate from the center to a radius r4 satisfies the condition of the following expression (2);
r4 ≧ 2 × r2 (2)
In addition, the configuration is such that r3 is located at the intermediate point or closer to the center than the intermediate point.
[0033]
Preferably, the difference d3-d1 between the depth d1 of the portion having the radius r1 of the reference surface substrate and the depth d3 of the portion having the radius r3 corresponding to the deepest portion is a condition of the following expression (3).
0.5 μm ≦ d3-d1 ≦ 1.5 μm (3)
Is satisfied.
[0034]
Hereinafter, the operation of the present invention will be described.
[0035]
In the deformable mirror having the above-described configuration, the flexible member, that is, the reflecting surface formed on the surface is deformed according to the cross-sectional shape of the curved surface portion of the reference surface substrate. For this reason, if the shape accuracy of the curved surface portion is maintained high, the deformation accuracy of the reflection surface can be determined with high accuracy, and thus the aberration compensation can be performed with high accuracy.
[0036]
The deformable mirror to which the present invention is applied is mounted on, for example, a recording / reproducing apparatus. In this case, the area requiring aberration compensation is an area corresponding to the NA of the objective lens from the center of the flexible member. I just need. Such an area is an area within the radius r1. Therefore, the area outside the radius r1 can be set to an arbitrary shape in which the flexible member is easily deformed.
[0037]
Based on such an idea, the cross-sectional shape of the curved surface portion is expressed by a function f (r) of r in which the portion from the center to the radius r2 is formed of a spherical surface, and the portion from the radius r1 to the radius r3 is r. between r1 and radius r3 Inflection point Exists, and the Inflection point When the portion from to the radius r3 is formed by a curve satisfying f ″ (r)> 0, the flexible member is smoothly deformed without applying excessive stress to the flexible member, and the energy for the deformation can be reduced. The specific reason will be described in an embodiment described later.
[0038]
In addition, the shape of the portion where the specific aberration must be generated and the aberration must be compensated is a spherical shape, and the shape is not sensitive to the axis deviation during the assembly, so that the assembly is easy and the cost can be reduced accordingly. .
[0039]
Here, the deformable mirror targeted by the present invention includes, for example, an upper electrode layer that forms a part of a flexible member and a lower electrode layer that is formed on a reference surface substrate, as will be apparent in embodiments to be described later. When a voltage is applied by a drive circuit during the period, the elastic deformation occurs. Therefore, it is possible to reduce the energy required for the elastic deformation, that is, the driving voltage. As a result, the running cost of the recording / reproducing device can be reduced. Further, since the possibility of dielectric breakdown of the insulating film is reduced by lowering the driving voltage, the reliability of the device can be improved.
[0040]
Further, the portion of r5 to r4 corresponding to the distance of the horizontal portion in the plane portion of the reference surface substrate hardly affects the deformation as described later. Therefore, it is preferable to reduce the size of this portion to reduce the overall size, or to increase the size of the portion up to the radius r4 instead from the viewpoint of downsizing or lowering the driving voltage. According to the simulation results of the present inventors described later, the length of r5-r4 satisfying such a requirement was confirmed to be r5-r4 ≦ 0.2 mm.
[0041]
Further, if the structure is such that the gap between the flexible member and the lower electrode is smaller at the peripheral portion of the curved surface portion, a relatively large electrostatic force can be generated even at a relatively low voltage, which is preferable from the viewpoint of reducing the voltage. . In such a structure, the portion from the radius r3 to the radius r4 of the reference surface substrate is represented by a function g (r) of r, and the portion between the radius r3 and the radius r4 is Inflection point There is one, Inflection point Can be achieved by forming a portion from to a radius r4 by a curve satisfying g ″ (r) <0.
[0042]
In addition, when the portion from the center of the reference surface substrate to the radius r5 is configured to be a differentiable cross-sectional curve, such a shape is a smoother shape, so that stress concentration at corners is eliminated. Furthermore, since the adhesion between the flexible member and the reference surface substrate is further improved, it is preferable from the viewpoint of transmitting the electrostatic force.
[0043]
Further, the portion of the reference surface substrate from the center to the radius r4 satisfies the condition of the following expression (2),
r4 ≧ 2 × r2 (2)
In addition, when the configuration is such that r3 is located at the intermediate point or closer to the center than the intermediate point, according to the simulation results of the present inventors described later, it has been confirmed that the flexible member is more easily deformed. did it. Therefore, according to such a configuration, the energy required for elastic deformation, that is, the drive voltage can be further reduced.
[0044]
The difference d3-d1 between the depth d1 of the radius r1 portion of the reference surface substrate and the depth d3 of the radius r3 portion corresponding to the deepest portion is a condition of the following formula (3).
0.5 μm ≦ d3-d1 ≦ 1.5 μm (3)
According to the simulation results described later by the present inventors, the electrostatic force and the reaction force due to the bending of the flexible member are balanced, and the energy required for elastic deformation, that is, the driving voltage is further reduced. I was able to confirm that I can do it.
[0045]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
[0046]
(Embodiment 1)
1 to 12 show Embodiment 1 of the deformable mirror of the present invention. First, a schematic configuration of a deformable mirror according to the present invention will be described with reference to FIGS. 1 is a plan view of the deformable mirror, FIG. 2 is a sectional view taken along line XX of FIG. 1, FIG. 3 is a bottom view, and FIG. 4 is an exploded perspective view.
[0047]
The deformable mirror 1 has a basic configuration including a silicon substrate 50, a flexible member 2 attached to the back surface side of the silicon substrate 50, and a reference surface substrate 6 disposed below the silicon substrate 50. Here, the silicon substrate 50 is formed in a frame shape having an opening 53 in a square shape on the inside. The center of the opening 53 is slightly displaced from the center of the shape of the silicon substrate 50 to the left side in the figure.
[0048]
As shown in FIG. 4, the flexible member 2 has a square shape slightly larger than the opening 53 in a plan view, and its outer peripheral portion is fixed to the flat outer peripheral edge of the silicon substrate 50. . More specifically, it is fixed to the outer peripheral edge of the silicon substrate 50 via the silicon thermal oxide film 51a. The flexible member 2 is fixed to the silicon substrate 50 in a state where a tensile stress is applied.
[0049]
Here, as shown in FIG. 2, the flexible member 2 is composed of an upper electrode layer 8 and a reflective film 10 laminated thereon. The upper electrode layer 8 is made of, for example, a Ni film having a thickness of about 8 μm. The reflection film 10 is made of, for example, a thin film of Au, Al or the like having a thickness of about 1 μm.
[0050]
It is also possible to adopt an embodiment in which the reflection film 10 is omitted and the surface of the upper electrode layer 8 is used as it is as a reflection surface. According to such a configuration, there is an advantage that the number of parts can be reduced and the manufacturing cost can be reduced.
[0051]
The reference surface substrate 6 has a cylindrical shape as shown in FIG. 4, and is manufactured by, for example, a glass molding method. The lower electrode layer 12, the wiring portion 55, the wiring pad 56, and the spacer layer 54 are formed on the surface of the reference surface substrate 6, that is, the surface facing the flexible member 2, and the insulating layer 9 is formed thereon. (See FIG. 2). Here, the lower electrode layer 12, the wiring portion 55, and the wiring pad 56 are connected.
[0052]
As shown in FIG. 2 and the like, the outer peripheral edge of the surface of the reference surface substrate 6 is flat, and a curved surface portion (concavo-convex portion) 3 is formed inside the outer peripheral edge portion, where the lower electrode layer 12 is formed. ing. Further, a chamfered portion 59 is provided at the outer peripheral end of the flattened outer peripheral portion, a wiring portion 55 is formed on the flat portion, and the insulating layer 9 is not provided on the chamfered portion 59. Therefore, the insulating layer 9 is not attached to the wiring pad 56 on the chamfered portion 59 (see FIG. 2).
[0053]
The lower electrode layer 12 and the spacer layer 54 are made of, for example, Al having a thickness of about 0.1 μm, and the insulating layer 9 is made of, for example, silicon oxide having a thickness of about 0.5 μm.
[0054]
The wiring pad 56 is provided for electrically connecting a wiring portion 55 for applying a voltage to the lower electrode layer 12 and a lower electrode pad 58 described later. The wiring portion 55 and the wiring pad 56 are formed of the same thickness and material as the lower electrode layer 12.
[0055]
The silicon substrate 50 to which the flexible member 2 is fixed and the reference surface substrate 6 on which the lower electrode layer 12 and the insulating layer 9 are provided are composed of an upper electrode layer 8 on the silicon substrate 50 side and a lower electrode on the reference surface substrate 6 side. The layers 12 are adhered with an adhesive so as to face each other (see FIG. 2). More specifically, the flat outer peripheral edges are closely adhered to each other. The flexible member 2 makes contact with the upper surface of the insulating layer 9 on the spacer 54 at the same height as the upper surface of the lower electrode layer 12 and the upper surface of the insulating layer 9 on the wiring portion 55 to maintain the flatness.
[0056]
As the adhesive, for example, a conductive epoxy adhesive is used. As shown in FIG. 2, the adhesive 57 a is formed on the wiring pad 56 on the chamfered portion 59 of the reference surface substrate 6 and on the back surface of the silicon substrate 50. Also has a function of electrically connecting the lower electrode pad 58 provided via the thermal oxide film 51a to the lower electrode.
[0057]
The chamfered portion 59 of the reference surface substrate 6 exposes the wiring pad 56 to the outside when the reference surface substrate 6 is bonded to the silicon substrate 50, and the adhesives 57a and 57b enter the chamfered portion, thereby forming a bonding surface. And a function of ensuring electrical connection between the wiring pad 56 and the lower electrode pad 58.
[0058]
The exposed portion 2b (see FIG. 3) of the flexible member 2 and the lower electrode pad 58 are connected to the drive circuit 7 by means such as soldering. As a result, the drive circuit 7 applies a voltage between the exposed portion 2b of the flexible member 2 and the lower electrode layer 12, or stops applying the voltage.
[0059]
Specifically, when the light beam incident on the reflection film 10 of the flexible member 2 is reflected without giving an aberration, the drive circuit 7 does not apply a voltage. As a result, since the flexible member 2 is kept flat by the action of the applied tensile stress, the incident light beam is reflected as it is without giving any aberration. On the other hand, when giving an aberration to the incident light beam, the drive circuit 7 applies a voltage between the upper electrode layer 8 and the lower electrode layer 12. As a result, an electrostatic force acts between the two, so that the flexible member 2 is deformed toward the reference surface substrate 6, and as a result is adsorbed on the uneven surface 3, causing a predetermined aberration to the incident light beam. give.
[0060]
Next, an example of a configuration in which a deformable mirror is incorporated in a recording / reproducing apparatus will be described with reference to FIGS. Here, a recording / reproducing apparatus that can handle two types of optical disks having a thickness of 0.6 mm (for example, DVD) and 1.2 mm (for example, CD) will be described as an example.
[0061]
A beam 504 emitted from a semiconductor laser 500, which is a light source of the optical pickup, passes through a collimator lens 502, a beam splitter 503, a quarter-wave plate 507, and reaches a beam splitter 506. This beam 504 passes through a beam splitter 506 and a quarter-wave plate 507 and reaches the deformable mirror 1.
[0062]
Then, the light reflected by the deformable mirror 1 passes through the quarter-wave plate, is reflected by the beam splitter 506, and enters the objective lens 508. Then, the light is condensed by the objective lens 508 and irradiated onto the optical disk 509. The focal length, NA, and the like of the objective lens 508 are set so as to correspond to an optical disk having a disk thickness of 0.6 mm.
[0063]
Here, in the first embodiment, it is assumed that the state of the deformable mirror 1 is changed according to the thickness of the mounted optical disk 509, and the focus of the objective lens 508 matches the optical disk 509. That is, when the thickness of the disk is 1.2 mm, the deformable mirror 1 is deformed to give an aberration to the incident light so that the disk is focused. The deformable mirror 1 forms a plane mirror when there is no deformation. Hereinafter, the operation will be described.
[0064]
First, whether the thickness is 0.6 mm or 1.2 mm is detected by a disk thickness detecting device 515 provided above the optical disk 509. The disk thickness detecting device 515 has a configuration as shown in FIG. 6, for example. The disk thickness detecting device 515 emits the light beam 602 from the light source 600 and reflects the light beam 602 on the upper surface of the optical disk 509. When the thickness of the optical disc 509 is 0.6 mm, the reflected light follows the optical path 604 and enters the optical position detector 601. On the other hand, when the thickness of the optical disk 509 is 1.2 mm, the light enters the optical position detector 601 along the optical path 603. Therefore, by detecting the position of the reflected light with the light position detector 601, the thickness of the disk 509 can be determined.
[0065]
Next, the system controller 516 receives the substrate thickness information from the substrate thickness detector 515 and operates the drive circuit 7 of the deformable mirror 1. At this time, when the optical disk thickness is 0.6 mm, the drive circuit 7 does not deform the deformable mirror 1. On the other hand, when the thickness of the disk is 1.2 mm, the deformable mirror 1 is deformed. That is, the flexible member 2 of the deformable mirror 1 is attracted to the reference surface of the reference surface substrate 6. As a result, a predetermined aberration is given to the light reflected by the deformable mirror 1, and the focus of the objective lens 508 is adjusted to an optical disk having a disk thickness of 1.2 mm.
[0066]
Conversely, when light having no aberration is incident on the objective lens 508, an optical disk 509 having a thickness of 1.2 mm is used to focus on the optical disk 509 having a thickness of 1.2 mm. When used, an aberration may be imparted by the deformable mirror 1. However, since an optical disk having a disk thickness of 0.6 mm has a large recording capacity, compared to a case where an optical disk such as a CD having a disk thickness of 1.2 mm is reproduced. In addition, high positional accuracy is required for optical components used.
[0067]
According to the simulation results of the present inventors, when reproducing a substrate having a disc thickness of 1.2 mm, the position accuracy of the optical component can be loosened by entering the light having the aberration. Therefore, when the deformable mirror 1 is a plane mirror, an optical disk with a disk thickness of 0.6 mm is reproduced, and when the deformable mirror 1 is deformed, an optical disk with a disk thickness of 1.2 mm is reproduced. Reproduction is more desirable.
[0068]
In this case, when the deformable mirror 1 works as a plane mirror, it is in a state along the position of the mirror surface depth = 0 μm, and when it works as an aberration compensating mirror, it has an uneven surface as shown by the curve in FIG. It has a cross-sectional shape along the curved surface portion 3.
[0069]
Here, the curved surface portion 3 may be any as long as the mirror surface 2a of the flexible member 2 attracted to the curved surface portion 3 generates the predetermined aberration.
[0070]
FIG. 7 shows an example of a result obtained by simulation of a cross-sectional shape of the curved surface portion 3 that generates a predetermined aberration. It is preferable to use a part having a spherical cross section. In other words, if the curved surface portion 3 is spherical, it is stable against axial deviation, and furthermore, the focal length can be corrected to some extent. This is because the time required for assembly can be reduced as compared with the deformable mirror, and the cost of the optical pickup device and the like can be reduced accordingly.
[0071]
Here, in general, when reproducing a DVD or the like having a substrate thickness of 0.6 mm, for example, a large NA such as 0.45 is required, but when reproducing a CD or the like having a substrate thickness of 1.2 mm, for example, for example, A small NA such as 0.38 is sufficient. If the focal length of the objective lens is set to, for example, 3.3 mm and the NA of the objective lens is set to the same, for example, 0.38, and the range is corrected for aberration, the light beam is actually bent by the deformation of the mirror. Although the value is small, it is estimated that the required beam system is 3.3 × 0.38 mm, and a range of a radius of about 1.25 mm is irradiated with the light beam. Therefore, the shape of the curved surface portion 3 as shown in FIG.
[0072]
However, when the deformable mirror 1 is formed with the shape of the curved surface portion 3 as it is, the deformation of the flexible member 2 becomes as shown in FIG. Unreasonable deformation occurs in the corresponding portion. For this reason, the deformation of the flexible member 2 itself becomes unreasonable, and enormous energy (applied voltage) is required. Even if it is deformed, plastic deformation or the like occurs in the flexible member 2 itself, which is not realistic in view of its life.
[0073]
Therefore, in practice, as shown in FIGS. 9A to 9C, the portion corresponding to the NA may be formed into a surface for correcting aberration, and the surrounding portion may be formed into a cross-sectional shape in which the flexible member 2 is easily deformed. .
[0074]
Here, as the shape of the entire curved surface portion 3 including the peripheral portion, basically, three types shown in FIGS. 9A to 9C can be considered. The details will be described below. First, the one shown in FIG. 9A corresponds to the radius of the portion (radius from the center of the curved surface portion 3) at which a specific aberration must be generated and corrected for aberration, that is, for example, the NA of the objective lens. The radius of the portion is r1, the radius of the portion designed to generate a specific aberration in the curved portion 3 is r2, the radius of the deepest portion of the curved portion 3 is r3, and the transition from the curved portion 3 to the flat portion 34 at the periphery is made. Assuming that the radius of the portion to be formed is r4 and the outermost radius of the plane portion 34 is r5 (indicated in FIG. 5A), the portion from the center portion 35 to the radius r2 is formed as a spherical surface and the radius r1 is The part up to the radius r3 is represented by a function f (r) of r, and between r1 and r3. Inflection point Exists, and this Inflection point Is formed in a cross-sectional shape represented by a curve satisfying f ″ (r)> 0.
[0075]
Although the shape is not particularly limited outside the deepest portion corresponding to the position of the radius r, in the case shown in FIG. 9A, the deepest portion and the entrance of the flat portion of the peripheral portion are connected by a straight line (inclined surface). are doing.
[0076]
9B, a straight line (inclined surface) is connected from the position of the radius r2 to the entrance of the flat portion 34 at the peripheral edge.
[0077]
In the case shown in FIG. 9C, the spherical surface is extended as it is to the position of the radius r4.
[0078]
The dimensions of each part are as follows. Unless otherwise specified, the thickness of the flexible member 2 is 8 μm (a practical range is 5 to 15 μm), and the insulating layer 9 is made of a material SiO 2. 2 And the relative dielectric constant is 4, SiO 2 Has a thickness of 0.5 μm (a practical range of 0.4 to 1.5 μm), a radius r1 of 1.1 mm (a practical range of 0.5 to 1.5 mm), and a radius r5 of 3 mm (a practical range). The range is 1.5 to 4 mm), and the radius of curvature R of the spherical surface of a portion where a specific aberration occurs and the aberration must be corrected is 100 mm (a practical range is 50 to 150 mm). Calculation (evaluation) was performed when the deformable mirror 1 was deformed at a driving voltage of 25V.
[0079]
FIGS. 10A to 10C show evaluation results (simulation results). However, FIGS. 10A to 10C show the evaluation results of the types shown in FIGS. 9A to 9C, respectively.
[0080]
As can be seen from FIG. 10A, in the type shown in FIG. 9A, the flexible member 2 is almost in contact with the curved surface 3 except for the deepest portion.
[0081]
On the other hand, as can be seen from FIG. 10B, the type shown in FIG. 9B generates a specific aberration because the reaction force due to bending of the flexible member 2 near the deepest portion is large. The center portion within the radius r1 of the portion where the aberration must be corrected is in contact without any problem, but the peripheral portion of the radius r1 is hard to contact.
[0082]
Further, as can be seen from FIG. 10 (c), in the type shown in FIG. 9 (c), the gap between the flexible member 2 and the lower electrode layer 12 is increased in the peripheral portion of the curved surface portion 3. Due to this, the electrostatic force hardly acts on the flexible member 2 in this portion. For this reason, the flexible member 2 must be deformed only by the electrostatic force received from the central portion of the curved surface portion 3.
[0083]
Therefore, from the viewpoint of effectively utilizing the electrostatic force, driving the flexible member 2 with a drive voltage as low as possible, and achieving the target aberration correction, a portion where a specific aberration must be generated and the aberration corrected. That is, it is good to connect a smooth curve from the position of the radius r1 to the deepest part, that is, the portion of the radius r3.
[0084]
Here, assuming that a cross-sectional curve from the center portion of the curved surface portion 3 to the deepest portion is f (r), a radius r1 (or a radius r2) at which a specific aberration occurs is a cosine of a spherical surface. (R) <0 In order to connect as smoothly as possible to the deepest part, it is necessary to include a curve satisfying f ″ (r)> 0 from the radii r2 to r3. That is, at least f ″ (r) = 0 between the radii r1 and r3. Inflection point Must be present one or more times.
[0085]
Next, Inflection point Were examined when two or more were present. FIG. 11 shows the range between the radii r1 and r3. Inflection point Shows a reference surface substrate 6 having a curved surface portion 3 in which two are present. In this case, one projection is generated between the radii r1 to r3. FIG. 12 shows the evaluation results.
[0086]
As shown in FIG. 12, it can be seen that the deformation of the flexible member 2 is hindered by the protrusions, which makes it difficult to deform. Inflection point As the number of further increases, the protrusions also increase, producing even more undesirable results.
[0087]
Therefore, from the above considerations, in the curved surface portion 3, the radius of a portion where a specific aberration must be generated and the aberration must be compensated, that is, for example, the radius of the portion corresponding to the NA of the objective lens is r 1, If the radius of the portion designed to generate a specific aberration is r2 and the radius of the deepest portion of the curved surface portion 3 is r3, the portion from the center portion 35 to the radius r2 is formed of a spherical surface, and the radius from the radius r1 is The part up to r3 is represented by the function f (r) of r, and the part between the radii r1 and r3 Inflection point It can be seen that when the curved surface portion 3 is formed by a curve satisfying f ″ (r)> 0 on the r3 side from the inflection point, the energy required for deformation can be reduced.
[0088]
(Embodiment 2)
13 to 16 show a second embodiment of the deformable mirror according to the present invention. In the first embodiment, the influence of the cross-sectional shape of the curved portion 3 from the center to the deepest portion on the deformation of the flexible member 2 was examined. In the second embodiment, the curved portion 3 (from the center to the radius) was examined. The effect on the deformation of the flexible member 2 when the horizontal dimensional ratio of the flat portion (from r4 to radius r5) 34 and the flat portion 34 (from radius r4 to radius r5) was changed was examined.
[0089]
Specifically, as a first pattern (type), a radius r1 = 1.09, r2 = 1.1, r3 = 1.5, and a radius of curvature of a spherical surface for aberration correction up to the radius r2 are R = 100 mm. Using the reference surface substrate 6, as a second pattern, a reference having a radius r1 = 1.39, r2 = 1.4, r3 = 1.7, and a radius of curvature of a spherical surface for aberration correction up to the radius r2 of R = 150 mm. By using the surface substrate 6 and changing the dimensions of the radii r4 and r5, a drive voltage of 30 V was applied between the flexible member 2 and the lower electrode layer 10 to examine the ease of deformation.
[0090]
Further, in the second embodiment, a quadratic curve that is continuous from the center portion 35 to the radius r4 is used for the portion from the radius r3 to the radius r4. 13 to 16 show the evaluation results.
[0091]
In each of the cases where the radius of curvature R is 100 mm and 150 mm, in FIGS. 13 and 15, the horizontal radius of the curved surface portion 3 is fixed at 2.6 mm, and the length of the flat portion 34 is set to 0.2 around 0.4 mm. ０．６0.6 mm. In FIGS. 14 and 16, the radius of the outer circumference of the plane portion 34 that determines the size of the reference surface substrate 6 itself, that is, r5 is fixed at 3.0 mm, and the radius of the curved surface portion 3 is 2.6 mm (plane portion). Was changed to 2.4 to 2.8 mm (at this time, the plane portion was 0.6 to 0.2 mm).
[0092]
According to the simulation results described above, the influence of the horizontal dimension of the flat portion on the deformation is smaller than that of the curved surface portion 3 in the horizontal direction. For example, the reference surface substrate 6 is naturally required to be reduced in size, and the horizontal dimension is limited. In this case, it has been found that increasing the curved surface portion 3 is more advantageous for deforming the flexible member 2 than increasing the flat surface portion.
[0093]
From the above considerations, it is better to make the plane portion 34 as small as possible to reduce the overall dimensions, or to make the curved surface portion 3 correspondingly large. However, since the flat part also has a function as a support part of the reference surface substrate 6, about 0 to 0.2 mm may be necessary. Therefore, it is preferable that the dimension of the flat portion 34 be 0.2 mm or less.
[0094]
(Embodiment 3)
17 to 20 show Embodiment 3 of the deformable mirror of the present invention. In the third embodiment, the cross-sectional curve from the deepest portion of the curved surface portion 3, that is, the portion of the radius r3 to the transition portion from the curved surface portion 3 to the flat portion 34, that is, the portion of the radius r5, is the deformation of the flexible member 2. The effect on the was investigated.
[0095]
In FIGS. 14 to 16, for example, the flexible member 2 is relatively attracted to the curved portion 3 in the central portion of the curved portion 3, whereas in the peripheral portion of the curved portion 3 in FIGS. , Almost no contact. The cause is that the gap between the flexible member 2 and the curved surface portion 3 in the initial stage of deformation, in other words, the gap between the flexible member 2 and the lower electrode layer 10 is smaller at the peripheral portion than at the central portion 35 of the curved portion 3. This is considered to be due to the fact that the electrostatic force was reduced due to this.
[0096]
Therefore, in the peripheral portion of the curved surface portion 3, the cross-sectional shape in which the gap is reduced, that is, the one-side cross-sectional shape of the curved surface portion 3 with respect to the center of the reference surface substrate 6 is changed from the radius r 3 to the radius r 4 Is expressed by a function g (r) of r, between r3 and r4 Inflection point Exists, and its Inflection point On the r4 side, if a cross-sectional curve is formed by a curve satisfying g ″ (r) <0, it is expected that static electricity will effectively work even in the peripheral portion.
[0097]
FIG. 17 shows the evaluation result when the reference plane substrate 6 having the cross-sectional shape satisfying the above items is used, and FIG. 18 shows the evaluation result when the reference plane substrate 6 having the cross-sectional shape of the opposite shape is used. Show. However, the thickness of the flexible member 2 was 8 μm, and the applied voltage was 30 V.
[0098]
As can be seen from a comparison between FIG. 17 and FIG. 18, when the gap between the flexible member 2 and the curved surface portion 3 is reduced at the peripheral edge of the curved surface portion 3, the deformation of the flexible member 2 is significantly affected. Turned out to be relevant. In the transition from the curved portion 3 to the flat portion 34, stress concentration is expected to occur in the deformed state as shown in FIG. 18, but in FIG. 17, stress concentration can be reduced. From the viewpoint of the reliability of the deformable mirror, the reference surface substrate 6 having the cross-sectional shape shown in FIG.
[0099]
In the third embodiment, the radius r3 and the radius r4 are relatively smooth but not completely differentiable curves. That is, a corner may be present.
[0100]
Therefore, as shown in FIG. 19 and FIG. 20, when the corner is present at the radius r3 or the radius r4, it is completely smooth, that is, in the reference surface substrate 6, the portion from the center to the radius r5 is completely completed. A comparison was made between the deformation states when the curve was differentiable.
[0101]
Here, FIG. 19 shows an evaluation result in the case where the portion from the center portion 35 to the portion of the radius r5 is completely differentiable. FIG. 20 shows the same shape as that of FIG. 17, and the portion of the radius r4 is not differentiable. Shows the evaluation results in the case where exists. Only the applied voltage was evaluated at 25 V lower than the case of FIGS.
[0102]
As can be seen from a comparison between FIG. 19 and FIG. 20, when the overall cross-sectional shape is differentiable, the gap between the curved surface portion 3 and the flexible member 2 becomes smaller, and the effective use of electrostatic force is achieved. Was found to be more effective from the viewpoint of Further, since it is expected that the stress concentration at the radius r3 and the radius r4 can be further reduced, it is preferable from the viewpoint of the reliability of the deformable mirror. Therefore, the reference surface substrate 6 having the cross-sectional shape shown in FIG. 19 is preferable for implementation.
[0103]
(Embodiment 4)
21 to 29 show a fourth embodiment of the deformable mirror according to the present invention. In the fourth embodiment, the influence of the position of the deepest portion of the curved surface portion 3 on the deformation of the flexible member 2 was investigated. That is, in the first to third embodiments, the position of the deepest part is not particularly specified. However, in the fourth embodiment, the horizontal position and the vertical position of the deepest part, that is, the portion of the radius r3 are the deformation of the flexible member 2. Was examined to see what effect it had.
[0104]
First, with respect to the horizontal position at the deepest part, the thickness of the flexible member 2 was examined at 12 μm and the applied voltage of 25V. The radius of curvature R of the spherical surface provided so as to generate a specific aberration up to the radius r2 was 100 mm, and r4 / r5 was 2.8 / 3.0 mm.
[0105]
Then, evaluation was made by taking, as an example, the case where r3 = 1.2, 1.3, 1.4, 1.42, and 1.5 mm as the deepest radius r3. The cross-sectional shapes and calculation results are shown in FIGS.
[0106]
According to the calculation results shown in FIGS. 21 to 25, the position of r3 = 1.4 mm becomes the middle point of the one-side cross section of the curved surface portion 3, but if the position of r3 is slightly closer to the r4 side than that point, the flexible member 24 is hardly deformed (see FIGS. 24 and 25), and conversely, it is best that the position of r3 is the middle point (see FIG. 23). It was found that No. 2 was not extremely deformed (see FIGS. 21 and 22).
[0107]
This is considered to be an effect due to the fact that the deformation of the flexible member 2 is symmetrical with respect to the deepest portion and is easy to deform, and the gap between the flexible member 2 and the curved surface portion 3 is reduced in the entire curved surface portion 3.
[0108]
In order to satisfy the above condition, it is necessary that the radius r4 ≧ 2 × r2. However, if r4 <2 × r2, the radius r3 of the deepest part is preferably provided on the r2 side as much as possible.
[0109]
Next, the effect of the deepest portion of the curved surface portion 3, that is, the vertical position of the portion with the radius r3, that is, the depth of the curved surface portion 3 on the deformation of the flexible member 2 was examined.
[0110]
Here, if the depth of the deepest portion is too deep, the gap becomes large, so that static electricity generated at a constant voltage is weakened, which is disadvantageous. On the other hand, if it is too shallow, it is expected that the bending of the flexible member 2 will be unreasonable and a contact failure will occur near r1. Therefore, it was examined which vertical position of the portion having the radius r3 is effective for deformation of the flexible member 2.
[0111]
FIG. 26 shows an evaluation result of the deformed state of the flexible member 2 when the depth d3 of the deepest portion is 6.5 μm. The applied voltage is the same as in FIG. In FIG. 27, the depth d3 of the deepest part is 7 μm, and the other conditions are compared under the same conditions as in FIG. According to the evaluation results shown in FIGS. 26 and 27, a portion where a specific aberration should already be generated slightly for aberration correction due to the bending reaction force of the flexible member 2, that is, the vicinity of the portion within the radius r1 has already come into contact. It turns out that it is hard to do.
[0112]
FIGS. 28 and 29 show a case where the deepest part is deep (d3 = 7.5 μm and d3 = 8 μm, respectively). The applied voltage was 21 V. From the depth of about 8 μm corresponding to FIG. 29, it can be seen that the deformation of the flexible member 2 is adversely affected.
[0113]
Here, since the depth itself of the deepest portion varies depending on the curvature of the curved surface portion up to the radius r2 and the NA, the end of the spherical surface for aberration correction, ie, the relative position between the vertical position of the radius r1 and the vertical position of the deepest portion. In terms of the relationship, it has been found that the difference in the depth direction distance between the portion having the radius r1 and the portion having the radius r3 is preferably between 0.5 and 1.5 μm.
[0114]
The difference between the present invention and the deformable mirror previously proposed by the applicant of the present invention is due to the fact that the shape of the central portion of the curved surface and the difference in depth, particularly the difference in depth, are large. For example, in the case of the deformable mirror proposed above, since the depth of the curved surface portion is 1 μm or less, in the calculation of the electrostatic force, the distance between the upper and lower electrode layers = the thickness of the insulating layer, and Although the result does not change so much even if the gap of the portion is ignored, it is ignored. However, in the case of the present invention, since the gap between the flexible member and the curved surface portion cannot be largely ignored, the distance between the upper and lower electrode layers = the insulating layer The calculation is performed by a simulation method taking into account that the film thickness of the film and the gap between the flexible member and the curved surface portion are taken into consideration, and further that the electrostatic force fluctuates due to deformation.
[0115]
【The invention's effect】
According to the deformable mirror of the present invention described above, the flexible member, that is, the reflection surface formed on this surface is deformed according to the cross-sectional shape of the curved surface portion of the reference surface substrate. For this reason, if the shape accuracy of the curved surface portion is maintained high, the deformation accuracy of the reflection surface can be determined with high accuracy, and thus the aberration compensation can be performed with high accuracy.
[0116]
In addition, the deformable mirror targeted by the present invention is mounted on, for example, a recording / reproducing apparatus. In this case, the area requiring aberration compensation is an area corresponding to the NA of the objective lens from the center of the flexible member. It is sufficient that such a region is a region within the radius r1. Therefore, the area outside the radius r1 can be set to an arbitrary shape in which the flexible member is easily deformed.
[0117]
Therefore, in the present invention, the cross-sectional shape of the curved surface portion is defined by a function f (r) of r in which the portion from the center to the radius r2 is formed as a spherical surface, and the portion from the radius r1 to the radius r3 is represented by a function f (r) of r. From to the radius r3 Inflection point Exists, and the Inflection point The portion from to the radius r3 is constituted by a curve that satisfies f ″ (r)> 0, so that the flexible member is deformed smoothly without applying excessive stress, and the energy for the deformation can be reduced. .
[0118]
Therefore, according to the present invention, it is possible to reduce the energy required for elastic deformation, that is, the drive voltage. As a result, the running cost of the recording / reproducing device can be reduced. Further, since the possibility of dielectric breakdown of the insulating film is reduced by lowering the driving voltage, the reliability of the device can be improved.
[0119]
In addition, the shape of the part that must generate specific aberrations and compensate for aberrations is spherical, making it less sensitive to axial misalignment during assembly, making assembly easier and contributing to cost reductions. it can.
[0120]
Further, according to the deformable mirror according to the second aspect, since the curved surface portion is configured so as to satisfy the condition of r5−r4 ≦ 0.2 mm, it is possible to further reduce the size of the device configuration or lower the driving voltage. Can be planned.
[0121]
According to the deformable mirror according to the third aspect, a portion of the reference surface substrate from the radius r3 to the radius r4 is represented by a function g (r) of r, and the portion between the radius r3 and the radius r4. Inflection point There is one, Inflection point Is formed by a curve that satisfies g ″ (r) <0, so that the gap between the flexible member and the lower electrode layer at the periphery of the curved surface portion becomes smaller, and a relatively low voltage However, a relatively large electrostatic force can be generated, which is preferable from the viewpoint of lowering the voltage.
[0122]
In addition, according to the deformable mirror of the fourth aspect, since the portion from the center of the reference surface substrate to the radius r5 is all a differentiable cross-sectional curve, stress concentration at corners is eliminated. Further, the adhesion between the flexible member and the reference surface substrate is improved, which is preferable from the viewpoint of transmitting the electrostatic force.
[0123]
According to the deformable mirror of the fifth aspect, the portion of the reference surface substrate from the center to the radius r4 satisfies the condition of the following expression (2),
r4 ≧ 2 × r2 (2)
In addition, since r3 is located at the middle point or closer to the center than the middle point, the flexible member is more easily deformed, so that the energy required for elastic deformation, that is, the driving voltage, is further reduced. There are advantages that can be done.
[0124]
According to the deformable mirror of the sixth aspect, the difference d3-d1 between the depth d1 of the portion of the reference surface substrate having the radius r1 and the depth d3 of the portion having the radius r3 corresponding to the deepest portion is given by: Condition of the following formula (3)
0.5 μm ≦ d3-d1 ≦ 1.5 μm (3)
Is satisfied, the electrostatic force and the reaction force due to the bending of the flexible member can be balanced, and there is an advantage that the energy required for elastic deformation, that is, the driving voltage can be further reduced.
[Brief description of the drawings]
FIG. 1 is a plan view of a deformable mirror according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating the first embodiment of the present invention, taken along line XX of FIG. 1;
FIG. 3 is a bottom view of the deformable mirror according to the first embodiment of the present invention.
FIG. 4 is an exploded perspective view of a deformable mirror, showing Embodiment 1 of the present invention.
FIG. 5 is a block diagram illustrating a configuration of a recording / reproducing apparatus equipped with a deformable mirror according to the first embodiment of the present invention.
FIG. 6 is a schematic diagram illustrating a detection principle of the thickness detection device according to the first embodiment of the present invention.
FIG. 7 is a diagram illustrating a cross-sectional shape of a curved surface portion of a reference surface substrate for performing aberration compensation obtained by simulation, according to the first embodiment of the present invention.
8A is a cross-sectional view showing an example of a deformable mirror in an undeformed state, and FIG. 8B is a cross-sectional view showing a deformed state of the deformable mirror in FIG.
FIGS. 9A to 9C are cross-sectional views illustrating examples of a reference surface substrate having various curved surface portions according to the first embodiment of the present invention.
10A and 10B show an embodiment 1 of the present invention, in which FIG. 9A shows an evaluation result when a flexible member is deformed using the reference surface substrate of FIG. 9A, and FIG. FIG. 9B is a diagram showing an evaluation result when the flexible member is deformed using the reference surface substrate of FIG. 9B, and FIG. 9C is a diagram showing the result of deforming the flexible member using the reference surface substrate of FIG. 9C. The figure which shows the evaluation result in the case of having done.
FIG. 11 shows the first embodiment of the present invention, Inflection point Sectional drawing of the reference surface board which has the curved surface part which consists of a curved surface which has two.
FIG. 12 is a view showing an evaluation result when a flexible member is deformed using the reference surface substrate of FIG. 11;
FIG. 13 shows a flexible member according to a second embodiment of the present invention in which the horizontal dimension ratio between a curved surface portion (from the center portion to the radius r4) and a flat surface portion (from the radius r4 to the radius r5) is changed. The figure which shows the evaluation result for investigating the influence which it has on the deformation | transformation.
FIG. 14 shows a flexible member according to a second embodiment of the present invention in which the horizontal dimension ratio of a curved surface portion (from the center portion to the radius r4) and a flat surface portion (from the radius r4 to the radius r5) is changed. The figure which shows the evaluation result for investigating the influence which it has on the deformation | transformation.
FIG. 15 shows a flexible member according to a second embodiment of the present invention in which the horizontal dimension ratio of a curved surface portion (from a center portion to a radius r4) and a flat surface portion (from a radius r4 to a radius r5) is changed. The figure which shows the evaluation result for investigating the influence which it has on the deformation | transformation.
FIG. 16 shows a flexible member according to a second embodiment of the present invention in which the horizontal dimension ratio between a curved surface portion (from the center portion to the radius r4) and a flat surface portion (from the radius r4 to the radius r5) is changed. The figure which shows the evaluation result for investigating the influence which it has on the deformation | transformation.
FIG. 17 is a view showing an evaluation result for investigating the influence of the cross-sectional curve shape from the deepest part of the curved surface part to the transition part to the flat part on the deformation of the flexible member, showing the third embodiment of the present invention. .
FIG. 18 is a view showing an evaluation result for investigating the influence of the cross-sectional curve shape from the deepest part of the curved surface part to the transition part to the flat part on the deformation of the flexible member, showing the third embodiment of the present invention. .
FIG. 19 is a view showing an evaluation result for investigating the influence of the cross-sectional curve shape from the deepest part of the curved surface part to the transition part to the flat part on the deformation of the flexible member, showing the third embodiment of the present invention. .
FIG. 20 is a view showing an evaluation result for investigating the influence of the cross-sectional curve shape from the deepest part of the curved surface part to the transition part to the flat part on the deformation of the flexible member, showing the third embodiment of the present invention. .
FIG. 21 is a view showing an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 22 is a diagram illustrating an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 23 is a diagram illustrating an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 24 is a view showing an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 25 is a view showing an evaluation result for investigating the influence of the position of the deepest part of the curved surface on the deformation of the flexible member, according to the fourth embodiment of the present invention.
FIG. 26 is a diagram illustrating an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 27 is a diagram illustrating an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 28 is a view showing an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 29 is a view showing an evaluation result for investigating the influence of the position of the deepest part of the curved surface portion on the deformation of the flexible member according to the fourth embodiment of the present invention.
FIG. 30 is a diagram showing a configuration of a conventional pickup.
FIG. 31 is a diagram showing a configuration of an optical pickup using a conventional deformable mirror.
FIG. 32 is a diagram showing a configuration of a conventional deformable mirror.
[Explanation of symbols]
1 Deformable mirror
2 Flexible member
3 Curved surface
6 Reference board
8 Upper electrode layer
9 Insulation layer
12 Lower electrode layer
34 flat part
35 Central part
50 silicon substrate
508 Objective lens

Claims (6)

表面に入射光を反射する反射面を有する弾性変形可能な可撓性部材と、該可撓性部材の裏面側に、該裏面と対向する形に設置され、該可撓性部材の変形を許す空間を形成するように中心部が可撓性部材側に突出した曲面部及び該曲面部の周縁部に該可撓性部材を平面性が維持された状態で支持する平面部が形成された参照面基板とを備え、該可撓性部材を該曲面部の表面に吸着させて変形させる変形可能ミラーであって、
該曲面部の該参照面基板の中心部に対する片側断面における表面形状は、
該参照面基板の中心部から半径ｒ１までの部分が、該可撓性部材が吸着することにより、該可撓性部材の反射面にて反射される光ビームに、必ず特定の収差を与える状態に該可撓性部材を変形させるように設定されており、半径ｒ１から半径ｒ２（ｒ１＜ｒ２）までの部分が該曲面部分においても前記特定の収差を発生させるべく設定されており、該中心部から半径ｒ３（ｒ２＜ｒ３）の部分に該曲面部の最深部が設けられ、中心部から半径ｒ４（ｒ３＜ｒ４）の部分に、該曲面部から該周縁部の該平面部へ遷移する部分が設けられて構成されており、
該曲面部における半径ｒ１から半径ｒ３までの表面部分が、半径ｒにおける深さを示す関数ｆ（ｒ）で表される曲線で形成されており、該関数ｆ（ｒ）は、半径ｒ１から半径ｒ３までの間に変曲点が１つ存在し、該変曲点から半径ｒ３までの部分がｆ”（ｒ）＞０となっている、変形可能ミラー。An elastically deformable flexible member having a reflection surface for reflecting incident light on the surface; and a back surface side of the flexible member, which is installed facing the back surface to allow the deformation of the flexible member. A curved surface portion whose central portion protrudes toward the flexible member so as to form a space, and a flat portion for supporting the flexible member in a state where the planarity is maintained is formed on a peripheral portion of the curved surface portion. A deformable mirror comprising a surface substrate and deforming the flexible member by adsorbing the flexible member on the surface of the curved surface portion,
The surface shape of the curved surface portion in one-side cross section with respect to the center portion of the reference surface substrate,
A state in which a part from the center of the reference surface substrate to a radius r1 always gives a specific aberration to the light beam reflected on the reflection surface of the flexible member due to the adsorption of the flexible member. The portion from the radius r1 to the radius r2 (r1 <r2) is set so as to generate the specific aberration even in the curved surface portion. The deepest portion of the curved surface portion is provided at a portion of radius r3 (r2 <r3) from the portion, and the transition from the curved surface portion to the flat portion of the peripheral portion is provided at a portion of radius r4 (r3 <r4) from the center portion. Parts are provided and configured,
Surface portion from a radius r1 to a radius r3 in the curved surface portion is formed by the curve you express the function f (r) indicating the depth at radius r, The function f (r) is the radius from the radius r1 there inflection point is one until r3, a portion from the inflection point to a radius r3 is in the f "(r)> 0, the deformable mirror. 前記平面部の最外側が中心部から半径ｒ５（ｒ４＜ｒ５）の部分に設けられており、
前記参照面基板の前記平面部における水平部分の距離に相当するｒ５−ｒ４が、下記（１）式の条件
ｒ５−ｒ４≦０．２ｍｍ …（１）
を満足する請求項１記載の変形可能ミラー。The outermost surface of the plane portion is provided at a portion having a radius r5 (r4 <r5) from the center portion,
R5-r4 corresponding to the distance of the horizontal portion in the plane portion of the reference surface substrate is a condition of the following formula (1): r5-r4 ≦ 0.2 mm (1)
The deformable mirror according to claim 1, which satisfies the following. 前記参照面基板の半径ｒ３から半径ｒ４までの部分が、半径ｒにおける深さを示す関数ｇ（ｒ）で表される曲線で形成されており、該関数ｇ（ｒ）は、半径ｒ３から半径ｒ４までの間に変曲点が１つ存在し、該変曲点から半径ｒ４までの部分がｇ”（ｒ）＜０となっている請求項１又は請求項２記載の変形可能ミラー。A portion from the radius r3 to the radius r4 of the reference surface substrate is formed by a curve represented by a function g (r) indicating a depth at the radius r , and the function g (r) is a radius from the radius r3 to the radius r3. there inflection point is one until r4, deformable mirror portion from the inflection point to a radius r4 is g "(r) <0 and going on claim 1 or claim 2, wherein. 前記参照面基板の前記中心部から前記平面部の最外側までの部分が全て微分可能な断面曲線である、請求項１〜３のいずれかに記載の変形可能ミラー。The deformable mirror according to any one of claims 1 to 3, wherein a portion from the central portion of the reference surface substrate to an outermost portion of the plane portion is a differentiable cross-sectional curve. 前記参照面基板の前記中心部から半径ｒ４までの部分が、下記（２）式の条件を満足し、
ｒ４≧２×ｒ２ …（２）
かつ、ｒ３がその中間点、若しくは、該中間点より該中心部寄りに位置する請求項１〜請求項４のいずれかに記載の変形可能ミラー。A portion of the reference surface substrate from the center to a radius r4 satisfies the condition of the following expression (2);
r4 ≧ 2 × r2 (2)
The deformable mirror according to any one of claims 1 to 4, wherein r3 is located at an intermediate point thereof or closer to the center than the intermediate point. 前記参照面基板の半径ｒ１の部分の深さｄ１と、最深部に相当する半径ｒ３の部分の深さｄ３との差ｄ３−ｄ１が、下記（３）式の条件
０．５μｍ≦ｄ３−ｄ１≦１．５μｍ …（３）
を満足する請求項１〜請求項５のいずれかに記載の変形可能ミラー。The difference d3-d1 between the depth d1 of the radius r1 portion of the reference surface substrate and the depth d3 of the radius r3 portion corresponding to the deepest portion is 0.5 μm ≦ d3-d1 in the following expression (3). ≦ 1.5 μm (3)
The deformable mirror according to any one of claims 1 to 5, which satisfies the following.
JP06519697A 1997-03-18 1997-03-18 Deformable mirror Expired - Fee Related JP3552873B2 (en)

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