JP2004342165A

JP2004342165A - Optical information recording/reproducing device and method, optical information recording medium, optical information recording device and method, and optical information reproduicing device and method

Info

Publication number: JP2004342165A
Application number: JP2003134699A
Authority: JP
Inventors: Ichiji Ohashi; 一司大橋
Original assignee: Olympus Corp
Current assignee: Olympus Corp
Priority date: 2003-05-13
Filing date: 2003-05-13
Publication date: 2004-12-02

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording/reproducing device which is constituted simply at a low cost while maintaining the characteristics as the holographic recording/reproducing, and can realize highly reliable information reproduction with a high signal-to-noise ratio, and an optical information recording/reproducing method. <P>SOLUTION: The device is provided with a means 6 for generating a luminous flux having a predetermined polarizing direction, a space optical modulator 15, a polarized beam splitter 18, 1/4 wavelength plates 19. 20, and an objective lens 22. The space optical modulator 15 has a plurality of pixels whose transmittance can be modulated in at least one of first and second areas 152 and 153. The half section and the other half section of a luminous flux generated to have a predetermined polarizing direction are arranged to pass through the first and second areas. The two 1/4 wavelength plates are arranged so that the half section and the other half section of the luminous flux reflected by the polarized beam splitter pass and a fast axis and a slow axis are orthogonal to each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、光を用いてディジタルデータ等の情報を媒体に記録する装置、及び方法に関する。また、該媒体に記録された情報を再生する装置、及び方法に関する。とりわけ、記録・再生をホログラフィックに行う装置、及び方法に関する。さらには、光を用いてディジタルデータ等の情報を記録する媒体に関する。
【０００２】
【従来の技術】
現在、光を用いた情報記録媒体としては、コンパクトディスク（ＣＤ）や、ディジタルバーサタイルディスク（ＤＶＤ）や、光磁気（ＭＯ）ディスクなどが使われている。
これらの情報記録媒体では、光を用いて情報が１次元ディジタルデータとして記録され、再生においては光の反射率、或いは反射光の偏光方向の違いがオンオフとして表現される。これらの情報媒体に用いている１次元記録方式では、情報記録密度を上げるために、記録・再生に用いる光源の波長の短波長化、媒体の情報記録層の多層化などが検討されている。
一方、情報を２次元的に記録・再生する方法としてホログラフィック記録・再生方式も従来から提案されている。尚、ここで言う２次元的な記録・再生とは、情報として２次元的に表現されるということであり、ホログラフィック方式の場合、物理的な記録は３次元的になされるとも考えられる。
【０００３】
ホログラフィック方式では、例えば日経サイエンス１９９６年１月号４６から５４ページの、ＤサルティスとＦモックによる記事（原文はＳｃｉｅｎｔｉｆｉｃＡｍｅｒｉｃａｎＮｏｖｅｍｂｅｒ１９９５）に記載されているように、データが２次元情報として媒体に体積的に記録されるため飛躍的な記録密度向上が期待される。
しかし、記録媒体として従来、ニオブ酸リシウム等のバルク状結晶を用いていたため、材料の特殊性という問題や、物体（情報）光に対し角度を持った方向から参照光が照射されるため記録・再生光学系が大型化する、媒体として主流となっているＣＤなどの円盤状ディスク媒体との互換性がないなどの問題があり、実用化されるに到っていない。
そこで、感光材料として感光性ポリマーの普及が近年進んでいることも背景として、これらの問題点を解決する方法が、例えば次の特許文献１〜４に提案されている。
【０００４】
【特許文献１】
特開平１０−１２４８７２号公報
【特許文献２】
特開平１１−３１１９３８号公報
【特許文献３】
特開２００２−１２３９４９号公報
【特許文献４】
特表２００２−５１３９８１号公報
【０００５】
特許文献１，２，３に記載のものは、基本的に同じ考え方に基づいており、ディスク状基板に反射層、ホログラム層（感光層）を設けたものを情報記録媒体とし、情報記録媒体に光を用いて情報をホログラフィック記録する際の、参照光、物体光（情報光）を同軸配置として光学系のコンパクト化を図ると共に、参照光・物体光を共にディスク媒体の片側から照射して、２次元データのホログラフィックな記録を可能としており、従来のディスク媒体との互換性も実現できるようになっている。そして、記録再生光学系には、旋光方向がプラス４５度とマイナス４５度の旋光性光学素子を面状に突き合わせた２分割旋光板が挿入されており、偏光ビームスプリッターと組み合わせることによって、記録時に参照光と物体光（情報光）が同軸的に照射されていても、再生時において、不要となる背景光（０次回折光）と情報光（１次以上の回折光）とを分離することが可能となっている。
【０００６】
具体的には、特許文献１の第１実施形態では、２分割旋光板としてオンオフ制御可能な液晶が用いられている。この液晶は、サーボ時にはオン状態に制御され、旋光性は示さず、記録時及び再生時にはオフ状態に制御され、２分割旋光板の半分はプラス４５度の旋光性、もう半分はマイナス４５度の旋光性を示すようになっている。そして、記録時には、記録されるべき２次元情報は空間光変調器の各画素の旋光性をオンオフ制御することで表現される。また、再生時には、ホログラム記録層に入射する光に対してまず発生する１次再生光を２次的な参照光とし、これによって２次的再生光が発生し、この２次的再生光を電荷結合素子（ＣＣＤ）などの２次元イメージセンサーで検出するようになっている。
【０００７】
また、特許文献１の第２実施形態では、更にビームスプリッターと２次元イメージセンサーを付加し、これにより１次再生光も検出し、１次再生光と２次的再生光の差動検出により信号対雑音比の向上を図っている。
また、特許文献１の第３実施形態では、旋光性光学素子を用いずに、光源を発し記録再生光学系（ピックアップ）に入る光束の半断面を参照光、もう一方の半断面を物体光（情報光）とする方法が示されている。
【０００８】
特許文献２では、３つの実施形態が示されており、いずれも２分割旋光板としてオンオフ制御可能な能動光学素子ではなく、受動光学素子が用いられている。この２分割旋光板の半分はプラス４５度の旋光性、もう半分はマイナス４５度の旋光性を示すようになっている。そして、記録時には、記録領域の半分はＳ偏光に対して右４５度の偏光状態で露光され、もう半分は左４５度の偏光状態で露光される。また、再生時には、この記録領域に再生用参照光を照射することで発生する再生情報光を、ＣＣＤなどの２次元イメージセンサーで検出するようになっている。
【０００９】
特許文献３では、記録再生光学系の構成は特許文献２の第３実施形態のものと概ね同様ながら、特許文献２では参照光と情報光の収束位置が、媒体の厚さ方向でわずかに違えられているのに対し、特許文献３では参照光と情報光の収束位置が同一となっている。そして、記録時には、記録されるべき、ある２次元ページデータについての記録領域は特許文献２同様２つの部分領域からなるものの、いずれの部分領域もＳ偏光に対して右４５度の偏光状態で露光されるとともに、左４５度の偏光状態でも露光される。また、再生時には、この記録領域に再生用参照光を照射することで発生する再生情報光を、ＣＣＤなどの２次元イメージセンサーで検出するようになっている。
【００１０】
また、特許文献４では、偏光ホログラフィーの原理に依拠し、記録媒体に光誘起異方性を持つ材料を用いた方法が開示されている。本方法においても、記録時には、参照光と情報（物体）光は同軸的に、カード状、もしくはディスク状の媒体に、その片側から照射されるようになっている。但し、記録時には、参照光と情報（物体）光は偏光方向が互いに９０度異なる直線偏光とされる。また、再生時には、直線偏光した再生参照光に対し、偏光方向が９０度異なる偏光成分を含んだ情報光が再生され、偏光ビームスプリッターにより不要となる背景光（０次回折光）が情報光（１次以上の回折光）に対して分離されるようになっている。なお、記録用光学系と読み取り（再生）用光学系はそれぞれ別に設けられている。
【００１１】
【発明が解決しようとする課題】
しかし、特許文献１の第１実施形態では、２分割旋光板として液晶を用い、状態に応じてオンオフ制御をするための制御装置を必要とするので、装置全体としての複雑化、高価格化を招く。また、再生において、ホログラム記録層に入射する光に対して最初に発生する１次再生光を２次的な参照光とし、この２次的参照光によって発生する２次的再生光を情報光とするため、最終的な情報光の強度が弱い。従って、信号対雑音比が悪く、信頼性の高い情報再生が困難である。
【００１２】
また、特許文献１の第２実施形態では、１次再生光も検出し、１次再生光と２次的再生光の差動検出により信号対雑音比向上を図っているが、付加的な光学部品、イメージセンサー、及びその駆動電気回路などを必要とし、装置全体としての複雑化、大型化、高価格化を招く。
【００１３】
また、特許文献１の第３実施形態は、２分割旋光板を用いておらず、装置構成が簡単であることは好ましいが、再生の際、発生する不要背景光と情報光の分離ができないので、信号対雑音比が悪く、信頼性の高い情報再生が困難である。
【００１４】
また、特許文献２の第１実施形態、第２実施形態では２分割旋光板を用いているものの、再生の際に発生する不要背景光と情報光との分離ができないので、信号対雑音比が悪く、信頼性の高い情報再生が困難である。
また、特許文献２の第３実施形態では、再生の際に発生する不要背景光と情報光の分離ができるが、Ｓ偏光に対して右（あるいは左）４５度の偏光状態で露光された領域に対し、再生用参照光の偏光方向がそれと直交しているので、再生効率（入射させる再生参照光に対する情報光強度）が低い。従って、この実施形態も信号対雑音比が低く、信頼性の高い情報再生が困難である。
【００１５】
また、特許文献３では、特許文献１、特許文献２において必要とした参照光、情報光の収束位置を違えるための光学素子を必要としないのは好ましいが、以下のような問題がある。
記録されるべきある２次元ページデータについての記録領域は２つに分けて考えることができる。これを部分領域１、部分領域２とする。また、Ｓ偏光に対して右４５度の偏光状態をＢ偏光、左４５度の偏光状態をＡ偏光とする。すると、記録（露光）に際しては、部分領域１と部分領域２は、Ａ偏光状態で露光されると共にＢ偏光状態でも露光される。再生について見ると、再生参照光の半断面の光束部分は２分割旋光板を通過後Ａ偏光になり部分領域１に入射した後、媒体の反射面で反射して部分領域２に入射する。このとき部分領域１ではＡ偏光状態の記録に対応する情報光が再生参照光とは逆向きに発生し、レンズを含む光学系を経て２次元イメージセンサーに入る。またこのとき、部分領域２ではＡ偏光状態の記録に対応する情報光が再生参照光とは逆向きに発生し、媒体の反射面で反射された後、レンズを含む光学系を経て２次元イメージセンサーに入る。しかしながら、部分領域１及び部分領域２はＢ偏光状態でも露光されているため、Ａ偏光に比べれば弱いもののＢ偏光の情報光も再生されてしまう。再生参照光のもう一方の半断面の光束部分についても、Ａ偏光とＢ偏光、部分領域１と部分領域２をそれぞれ入れ替えて、全く同様のことが言える。ところで、記録（露光）に際しては、Ａ偏光状態の情報光とＢ偏光状態の情報光はそれぞれあるページデータの半分ずつを担っている、換言すれば、別の情報を担っている。このため、別の情報が２次元イメージセンサーの同一領域に重なって入ることになる。従って、特許文献３のものも信号対雑音比が悪く、信頼性の高い情報再生が困難である。
【００１６】
また、特許文献４では、原理的に再生時の不要背景光の偏光分離が行い易いものの、記録媒体に光誘起異方性を持つ特殊な材料を用いている。しかし、このような材料はまだ実用的ではない。また、記録光学系と再生光学系を独立して設けているため、装置としての大型化、高価格化を招いている。
【００１７】
本発明は、上記のような状況に鑑みてなされたものであり、ホログラフィック記録再生としての特徴を維持しつつ、装置として簡素で、従って低価格に構成でき、信号対雑音比が良好で信頼性の高い情報再生を実用的に可能とする、光情報記録再生装置及び方法、光情報記録媒体、光情報記録装置及び方法、並びに光情報再生装置及び方法を提供することを目的とする。
【００１８】
【課題を解決するための手段】
上記目的を達成するため、本発明による光情報記録再生装置は、光を用いて媒体に情報を記録し、記録された情報を再生する光情報記録再生装置であって、所定の偏光方向を持つ光束を生成する手段と、空間光変調器と、偏光ビームスプリッターと、２つの４分の１波長板と、対物レンズを有し、前記空間光変調器が、第１の領域と第２の領域を有し、該第１の領域と第２の領域のうち少なくとも一方に各画素の透過率が変調可能な複数の画素を有し、前記光束の半断面ともう一方の半断面がそれぞれ該第１の領域と第２の領域を通過するよう配置され、前記偏光ビームスプリッターが、前記空間光変調器を通過した光束を反射するよう配置され、前記２つの４分の１波長板が、前記偏光ビームスプリッターで反射された光束の半断面ともう一方の半断面がそれぞれを通過するように、かつ、互いにそのファースト軸とスロー軸とが直交するように配置され、前記対物レンズが、前記媒体に対向配置されることを特徴としている。
【００１９】
また、本発明の光情報記録再生装置においては、フォーカス信号、トラッキング信号、及びＲＦ信号を生成する信号検出系を備えたことを特徴としている。
【００２０】
また、本発明の光情報記録再生装置においては、前記媒体に記録された情報を再生する２次元イメージセンサーを備えたことを特徴としている。
【００２１】
また、本発明による光情報記録媒体は、光照射によって屈折率変調を受ける感光層と、周期的に形成されたランド及びグルーブと、該ランド及びグルーブの上面に形成された反射層を有することを特徴としている。
【００２２】
また、本発明による光情報記録再生方法は、請求項１に記載の光情報記録再生装置を用いて、光照射によって屈折率変調を受ける感光層と照射された光を反射するための反射層を有する媒体の、前記感光層に情報を記録、或いは媒体に記録された情報を再生することを特徴としている。
【００２３】
また、本発明の光情報記録方法においては、前記空間光変調器の第１の領域または第２の領域にデータを表示し、該データを表示した領域を通過する光束を情報光とし、もう一方の領域を通過する光束を参照光として、媒体中の感光層にホログラフィックに情報を記録することを特徴としている。
【００２４】
また、本発明による光情報再生方法は、フォーカス信号、トラッキング信号、及びＲＦ信号を生成する信号検出系と前記媒体に記録された情報を再生する２次元イメージセンサーを備えた請求項１に記載の光情報記録再生装置を用いて、請求項４に記載の光情報記録媒体中の感光層を透過する０次回折光を前記信号検出系に導いて、フォーカス信号、及びトラッキング信号を生成し、これらの信号に基づいて前記対物レンズを制御しつつ、前記２次元イメージセンサーの出力から該光情報記録媒体に記録された情報を再生することを特徴としている。
【００２５】
また、本発明による光情報記録装置は、情報光と記録用参照光の各光束を対物レンズで集光して媒体の感光層に情報を記録する光情報記録装置において、前記媒体に照射される光を発する光源と、前記光源から発せられた光を通過させるときに、記録する情報データに対応して変調された情報光として第１通過光束を生成する第１の領域と、前記情報光の光束と干渉する記録用参照光の光束を得るための第２の領域とを有する空間光変調器と、前記空間光変調器で得られる各光束を前記媒体側に向けて導く偏光ビームスプリッターと、前記偏光ビームスプリッターで導かれた各光束のそれぞれが、ファースト軸が互いに直交する２つの４分の１波長板のそれぞれを通過するように配置された２つの４分の１波長板を有し、前記２つの４分の１波長板を通過した前記情報光と記録用参照光の各光束を干渉させて前記媒体の感光層に前記情報データに対応した干渉パターンを記録するようにしたことを特徴としている。
【００２６】
また、本発明による光情報記録方法は、情報光と記録用参照光の各光束を対物レンズで集光して媒体の感光層に情報をホログラフィックに記録する光情報記録方法において、光源から発せられる光を所定の偏光方向を持った光束とし、その光束の一部を、記録する情報データに対応して制御した空間光変調器の第１の領域を通過させることにより該一部の光束を変調させて情報光として第１通過光束を生成するとともに、残りの光束から前記第１通過光束と干渉する記録用参照光となる第２光束を生成し、次いで、前記情報光となる第１通過光束と前記記録用参照光となる第２光束を偏光ビームスプリッターで前記対物レンズ側に導き、その後、前記第１通過光束と前記第２光束のそれぞれを、ファースト軸が互いに直交し、且つ、偏光方向が同じである前記第１通過光束と第２光束の偏光方向に対するファースト軸の角度が４５度となるように配置した２つの４分の１波長板のそれぞれを通過させ、次いで、前記第１通過光束と前記第２光束の各光束を干渉させて前記媒体の感光層に情報をホログラフィックに記録することを特徴としている。
【００２７】
また、本発明による光情報再生装置は、媒体の感光層にホログラフィックに記録された情報を再生する光情報再生装置において、前記媒体に照射される光を発する光源と、前記光源から発せられた光を、再生用参照光として導く偏光ビームスプリッターと、ファースト軸が互いに直交し、かつ、前記偏光ビームスプリッターに導かれた再生用参照光がそれぞれを通過するように配置された２つの４分の１波長板と、前記２つの４分の１波長板を通過して得られる再生用参照光の各光束を前記媒体の感光層に照射したときに、前記媒体の感光層にホログラフィックに記録された情報から得られる反射回折光を、前記偏光ビームスプリッターを経た後に投影するように配置した２次元イメージセンサーと、を有することを特徴としている。
【００２８】
また、本発明による光情報再生方法は、媒体の感光層にホログラフィックに記録された情報を再生する光情報再生方法において、光源から発せられる光を、再生用参照光として偏光ビームスプリッターに導き、前記偏光ビームスプリッターに導かれた再生用参照光が、ファースト軸が互いに直交し、且つ、再生用参照光の偏光方向に対しファースト軸の角度が４５度となるように配置された２つの４分の１波長板のそれぞれを通過させ、前記２つの４分の１波長板を通過して得られる再生用参照光の各光束を前記媒体の感光層に照射させて、前記媒体の感光層にホログラフィックに記録された情報から得られる反射回折光を、前記偏光ビームスプリッターを経た後に２次元イメージセンサーに投影し、２次元イメージセンサーに投影した該反射回折光の検出により前記情報を再生することを特徴としている。
【００２９】
また、本発明による光情報記録再生装置は、情報光と記録用参照光の各光束を対物レンズで集光して媒体の感光層に情報を記録し、この情報を再生用参照光を用いて再生する光情報記録再生装置において、前記媒体に照射される光を発する光源と、記録時に前記光源から発せられた光を通過させるときに、記録する情報データに対応して変調された情報光を生成するための第１の領域と、前記情報光と干渉する記録用参照光を得るための第２の領域とを有し、再生時に前記光源から発せられた光を前記第１の領域及び第２の領域を通過させて再生用参照光を生成する空間光変調器と、前記空間光変調器で得られる記録時の情報光と記録用参照光及び再生時の再生用参照光を前記媒体側に向けて反射するとともに、再生時に前記媒体の感光層から得られる再生光を透過する偏光ビームスプリッターと、前記偏光ビームスプリッターで反射された前記情報光と記録用参照光のそれぞれが、ファースト軸が互いに直交する２つの４分の１波長板のそれぞれを通過するように配置された２つの４分の１波長板と、前記２つの４分の１波長板を通過した前記情報光と記録用参照光を干渉させて前記媒体の感光層に前記情報データに対応した干渉パターンを記録し、且つ再生時に前記２つの４分の１波長板を通過した再生用参照光を前記記録した干渉パターンに照射する対物レンズと、前記２つの４分の１波長板を通過した再生用参照光が前記媒体の感光層に照射されたときに、前記媒体の感光層に記録された情報から得られる反射回折光を、前記２つの４分の１波長板と前記偏光ビームスプリッターを経た後に投影するように配置された２次元イメージセンサーと、を有することを特徴としている。
【００３０】
また、本発明による光情報記録再生方法は、情報光と記録用参照光の各光束を対物レンズで集光して媒体の感光層に情報を記録し、この情報を再生用参照光を用いて再生する光情報記録再生方法において、記録時に、光源から発せられる光を所定の偏光方向を持った光束とし、その光束の一部を、記録する情報データに対応して制御した空間光変調器の第１の領域を通過させることにより情報光を生成するとともに、残りの光束から前記情報光と干渉する記録用参照光を生成し、次いで、前記情報光と前記記録用参照光を偏光ビームスプリッターに導き、次いで、前記偏光ビームスプリッターに導かれた前記情報光と前記記録用参照光のそれぞれを、ファースト軸が互いに直交し、且つ偏光方向が同じである前記情報光と記録用参照光の偏光方向に対しファースト軸の角度が４５度となるように配置された２つの４分の１波長板のそれぞれを通過させ、その後、前記情報光と前記記録用参照光を干渉させて前記媒体の感光層に情報をホログラフィックに記録する工程と、再生時に、前記光源から発せられる光を、前記所定の偏光方向を持った光束として前記空間光変調器を通過させることにより再生用参照光を得て前記偏光ビームスプリッターに導き、次いで前記偏光ビームスプリッターに導かれた再生用参照光を、前記２つの４分の１波長板のそれぞれを通過させ、前記２つの４分の１波長板を通過して得られる再生用参照光を前記媒体の感光層に照射し、前記媒体の感光層から得られる反射回折光を、前記２つの４分の１波長板と前記偏光ビームスプリッターを経た後に２次元イメージセンサーに投影し、２次元イメージセンサーに投影した該反射回折光の検出により前記情報を再生する工程と、を有することを特徴としている。
【００３１】
【発明の実施の形態】
以下、本発明による光情報記録再生装置の好適な実施形態を、図面を用いて説明する。
なお、以下に述べる本実施形態の光情報記録再生装置は、光情報記録用の光情報記録装置として、あるいは光情報再生用の光情報再生装置として、単独でも実施できる装置となっている。
【００３２】
図１は本発明による光情報記録再生装置の一実施形態の要部概略構成図である。
図１において、１は、光情報記録再生装置の主要部をなす光学系である。光学系１は、光情報記録媒体２に情報を記録する、あるいは情報が記録された光情報記録媒体２から情報を再生するための光ピックアップとして、一つのユニットに組み込まれ、光情報記録媒体（以下、媒体という）２と対向して配置されている。
２は、情報が記録されるべき、あるいはそこから情報が再生されるべき媒体である。媒体２は、図１ではその一部を断面として示してある。媒体２の形態としては、ＣＤやＤＶＤのような円盤状ディスク形態とするのが好ましい。この場合、ＣＤやＤＶＤの駆動装置（ドライブ）に於けるのと同様、ディスク媒体２は回転駆動され、光ピックアップは、ディスク媒体２の半径方向に直線駆動される構成となっている。図示はしないが、これらの駆動や制御に必要な機構や電気回路等は従来から知られている方法を使うことができる。
【００３３】
図１で示す光学系１において、部材３は、例えば半導体レーザーなどのコヒーレンスのよい光源である。光源３は、発せられる光が直線偏光していることが望ましく、図１の場合、その偏光方向は紙面に垂直、もしくは平行な方向となっている。また、その波長は、媒体２の感光材料の感度が高い波長が用いられている。
部材４は、光源３から発した光を平行光束に変換するコリメーター光学系である。コリメーター光学系４は、図１では便宜上、１枚レンズ構成のように示されているが、これに限られるものではない。例えば、非点収差を持つ半導体レーザーを光源３に用いた場合は、それを補正するための例えばシリンドリカルレンズなどの光学素子を含めることもできる。また、光束断面内での強度分布の均一化をはかるための光学素子などを含めることもできる。
部材５は、コリメーター光学系４から射出される平行光束の径を所定値に制限する光束絞りである。光束絞り５は、コリメーター光学系４の中、あるいはコリメーター光学系４と光源３との間に配置してもよい。
【００３４】
部材６は、偏光板である。偏光板６は、これを通過した光の偏光方向が、紙面に垂直、もしくは平行な方向となるように回転位置が決められている。但し、光源３から発せられる光が直線偏光している場合は、この偏光板６は不要となる。すなわち、本実施形態では、光源３から発せられる光の偏光の有無に応じて、光源３及び／または偏光板６が、所定の偏光方向を持った光束を生成する偏光生成手段として機能する。
部材７は、ビームスプリッターである。ビームスプリッター７は、光束絞り５を経た入射光に対して、例えば、透過９０％程度、反射１０％程度、などの所定の分岐比を持っている。
【００３５】
ビームスプリッター７の上方側に配置される部材８は信号検出系である。信号検出系８は、主な構成要素として、凸パワーを持つレンズ９と、一方向に凸パワー又は凹パワーを持つシリンドリカルレンズ１０と、４分割フォトディテクター１１を含んでいる。
ビームスプリッター７の下方側に配置される部材１２は、光源モニター系である。光源モニター系１２は、主な構成要素として、凸パワーを持つレンズ１３と、フォトディテクター１４を含んでいる。
【００３６】
ビームスプリッター７の右側に配置される部材１５は、空間光変調器である。空間光変調器１５を正面から、即ち入射光側から光軸１６の方向に見た状態を図２に示す。
図２中、１７は、空間光変調器１５に入射する光束の断面を示している。空間光変調器１５は、各々独立に制御可能な多数の画素１５１を有している。このような空間光変調器１５は、例えば液晶を用いて構成することができる。また、空間光変調器１５は、図１、及び図２で見て上半分の第１の領域１５２と下半分の第２の領域１５３に分けられており、それぞれの領域を光束１７の半断面と、もう一方の半断面が通過するように配置されている。なお、第１の領域１５２と第２の領域１５３を通過するそれぞれの光束は、本発明における第１通過光束および第２通過光束に対応する。
【００３７】
部材１８は、偏光ビームスプリッターである。偏光ビームスプリッター１８は、これに入射する光のＳ偏光（紙面に垂直な偏光）成分を媒体２側に向けて反射し、Ｐ偏光（紙面に平行な偏光）成分を透過する。
偏光ビームスプリッター１８の、図１で見て上方の部材１９，２０は共に４分の１波長板である。４分の１波長板１９，２０は、入射する光束２１の半断面部分の光束が４分の１波長板１９に、もう一方の半断面部分の光束が４分の１波長板２０を通過するよう光軸２５を中心にして配置されている。また、４分の１波長板１９，２０は、それらのファースト（Ｆ）軸が互いに直交し、従ってスロー（Ｓ）軸も互いに直交するとともに、偏光ビームスプリッター１８から入射するＳ偏光に対し、Ｆ軸が角度４５°（従って、Ｓ軸も角度４５°）となるように配置されている。なお、図１の実施形態では、２つの４分の１波長板１９，２０は、同一平面を有する平面板を形成するように当接した状態で配置されているが、光軸２５の方向に沿って段違いに配置してもよい。
【００３８】
部材２２は、対物レンズである。対物レンズ２２は、光束２１を媒体２に向けて集光するように媒体２に対向して配置されている。なお、対物レンズ２２は、フォーカシング制御や、トラッキング制御を行うための機構で駆動されるが、光ピックアップにおいて従来から知られている方法を用いることができるので、この機構は単にアクチュエータ２２ａとして示し、詳細な構成の図示はしていない。
偏光ビームスプリッター１８の下方側に配置される部材２３は結像レンズ、部材２４はＣＣＤなどの２次元イメージセンサーである。図１に示すように、対物レンズ２２から２次元イメージセンサー２４までの各構成部材は光軸２５を基準として配置されている。また、対物レンズ２２、結像レンズ２３は、図１では、１枚レンズで構成されているように示してあるが、必要な収差補正の程度に応じて複数枚のレンズ構成としてもよい。
【００３９】
媒体２は、円盤ディスク状など平板状の形態を有しており、対物レンズ２２の側から順に、透明基板層２６と、感光層２７と、透明バッファー層２８と、反射層２９と、保護層３０を有している。
透明基板層２６には、例えば、ＣＤなどで用いられているポリカーボネイトが材料に用いられている。
感光層２７には、光照射によって透過率が大きく変化せず、屈折率が場所的に変調を受けるような材料、例えばフォトポリマーが用いられている。その厚さは、形成されるホログラムがボリュームホログラム、所謂厚いホログラムと見なせる程度、例えば１０μｍ以上、の厚さとなっている。
透明バッファー層２８は、感光層２７の材料が露光によって収縮を生じることがあるのでそれによる影響を低減することを一つの目的として設ける層である。従って用いる材料としては、光弾性の小さいものが好ましい。また、透明基板層２６と感光層２７の間に、あるいは感光層２７を挟んで両側に透明バッファー層を設けてもよい。また、透明バッファー層２８には、トラッキングのガイドとなるランド３１とグルーブ３２が所定の間隔を置いて周期的に形成されている。但し、感光層２７の材料の前記露光による収縮が実用上問題を生じなければ、透明バッファー層２８を省略し、感光層２７に直接、ランド３１とグルーブ３２を形成してもよい。反射層２９はこのランド３１面及びグルーブ３２面上に、例えばアルミニウム蒸着によって形成する。保護層３０は、反射層２９を保護するために設ける層で、ＣＤの保護層に使われているようなプラスティックが材料として用いられている。
【００４０】
次に、このように構成された本実施形態の光情報記録再生装置の動作について説明する。
まず、情報を記録する場合の動作について、図３を用いて説明する。
光源３から発した光は、コリメーター光学系４を経て平行光束とされ、光束絞り５により所定の光束径に制限された後、偏光板６に入射する。このように光束径を制限することで、以降の光学系で不要な迷光やフレアなどが発生することを抑えることができる。偏光板６を通過した光は直線偏光となってビームスプリッター７に入射し、その透過光は空間光変調器１５に到達する。なお、その偏光方向は空間光変調器１５の動作と関連して決められるので後述する。光源３が元々直線偏光の光を発する場合も同様である。
【００４１】
ビームスプリッター７に入射した光は、例えば、透過９０％程度、反射１０％程度の割合で分岐される。反射光は、光源モニター系１２に入射し、光源モニター系１２のレンズ１３よって集光され、フォトディテクター１４で反射光の強度が検出される。これにより、環境温度などにより光源３の出力が変動するのをモニターし、その出力信号に基づいて図示省略した制御手段等を介して光源３を制御し、出力の安定化を図ることができる。
【００４２】
一方、ビームスプリッター７を透過した光は、空間光変調器１５に入射する。空間光変調器１５の第１の領域１５２は、光束１７が通過する領域内の各画素１５１が、情報として記録されるべき２次元ページデータに応じて、そこを通過する光（第１通過光束）に透過率変調を加えるように制御される。但し、ディジタルデータであれば、各画素を明状態か暗状態のいずれかに制御すればよい。この透過率変調を加えられた光束が情報光となる。一般に、液晶素子を用いて透過率変調を行う場合、液晶層に入射する光を直線偏光とし、液晶層の後方に偏光板が設けられた構成となっている。本実施形態においても、空間光変調器１５として液晶素子を用いた場合、液晶層の後方に偏光板が設けられている（詳細な図示は省略する）。このとき、この偏光板を通過する光の偏光方向が偏光ビームスプリッター１８から見てＳ偏光となるように、この液晶層の後方に設けられる偏光板の方向は決められている。
【００４３】
そのような状態で、空間光変調器１５としての液晶素子に入射する光束１７の偏光方向は、用いる液晶層の性質、及び各画素への電界の印加の有無と明暗状態の関係で決められる。例えば、画素に電界を加えないとき（ディジタルデータとしては例えば０）、その画素に入射した光が９０度の旋光を受けるような液晶層であって、そのとき暗状態となり、画素に電界を加えたとき（ディジタルデータとしては例えば１）、その画素に入射した光が旋光を受けないような液晶層であって、そのとき明状態となる関係であれば、液晶素子からなる空間光変調器１５への入射光の偏光方向はＳ偏光（図３の紙面に垂直な偏光）に選ばれる。ディジタルデータの（０、１）と各画素の明暗の関係を逆にとるのであれば、入射光束１７の偏光方向はＰ偏光（図３の紙面に平行な偏光）に選ばれる。
【００４４】
一方、空間光変調器１５の第２の領域１５３は、ホログラフィック記録の際の記録用参照光となる光束（第２通過光束）が通過する領域である。原理的には、記録用参照光には変調を加えなくともホログラフィック記録が可能であるため、この部分は空白とする、即ち、空間光変調器１５を第１の領域１５２のみで構成することも可能である。
【００４５】
しかし、空間光変調器１５の第２の領域１５３に光束が通過する複数の画素１５１を設けると次のような利点がある。
例えば、第１の領域１５２を通過した光の全体的な明るさに応じて、第２の領域１５３の透過率を制御すれば、情報を記録する際のホログラフィック露光により感光層に形成される干渉縞のコントラストを向上させることができるので好ましい。この場合、第２の領域１５３は画素毎に制御する必要はなく全画素を一様に制御すればよいので、第２の領域１５３は必ずしも多画素を有する空間光変調器である必要はない。但し、第１の領域１５２と第２の領域１５３を一体の素子として構成すれば、コスト面で有利であるとともに、別体としたときに両者の繋ぎ部分で発生する光束のけられ（ケラレ）がなくなるので更に有利となる。また、第２の領域１５３を複数画素を有する位相変調型の空間光変調器として構成すると、記録の際、この位相変調型の第２の領域１５３を通過する記録用参照光に所定の位相変調パターンを持たせて記録（露光）することができ、この位相変調パターンを鍵として持っている者だけが記録されたデータを読み出せるようになるといった使い方（あるいは再生方法）が可能になる。但し、何れの場合も、第２の領域１５３を通過した光はＳ偏光となるよう構成する。従って、空間光変調器１５を通過する光束に対し、透過率変調をするための、あるいは位相変調するための第２の領域１５３を設けないような、すなわち第２の領域を空白とする場合は、空間光変調器１５に入射する光１７の偏光はＳ偏光となるように偏光板６あるいは光源３を構成する。
【００４６】
なお、空間光変調器１５を第１の領域１５２のみで構成することも可能であるが、本発明では、空間光変調器１５の第１の領域１５２に対応する第２の領域１５３が空白であっても、この空白部分を通過する光束は第２通過光束という。
【００４７】
空間光変調器１５の第１の領域１５２を通過した光束１７１、第２の領域１５３を通過した光束１７２は、共にＳ偏光状態で偏光ビームスプリッター１８に入射して反射される。その後、光束１７２は４分の１波長板１９に、光束１７１は４分の１波長板２０に、それぞれ入射する。
４分の１波長板１９，２０にＳ偏光の光束１７１，１７２がそれぞれ入射すると、それぞれの入射光は、４分の１波長板１９，２０についてそれぞれ逆回りの円偏光となって射出される。ここでは説明の便宜上、４分の１波長板１９を左回り４分の１波長板、４分の１波長板２０を右回り４分の１波長板とし、それぞれから射出される円偏光を左回り円偏光、右回り円偏光とする（なお、左右を逆にとることも可能である）。
【００４８】
光束１７２は、左回り４分の１波長板１９を経て左回り円偏光となって対物レンズ２２に入射し、感光層２７を経て、反射層２９で最小集光スポットになると同時に反射される。反射後、再び感光層２７を通って対物レンズ２２に入射し、平行光束となって右回り４分の１波長板２０に入射する。この光束は右回り４分の１波長板２０を通過することで再びＳ偏光となり、偏光ビームスプリッター１８で反射される。
一方、光束１７１は、光束１７２と逆の経路をたどり、右回り４分の１波長板２０を経て右回り円偏光となって対物レンズ２２に入射し、感光層２７を経て反射層２９で最小集光スポットになると同時に反射される。反射後、再び感光層２７を通って対物レンズ２２に入射し、平行光束となって左回り４分の１波長板１９に入射する。この光束は左回り４分の１波長板１９を通過することで再びＳ偏光となり、偏光ビームスプリッター１８で反射される。
【００４９】
なお、光が媒体２の透明基板層２６に入射する際、およびそこから射出する際、光は透明基板層２６の屈折率に応じた屈折を受けるが、本発明の本質に関わる事柄ではないので、図では、屈折状態を省略して図示している。
【００５０】
ここで、光束１７２が感光層２７を最初に通過する領域を露光領域（第１露光領域）２７１、反射層２９で反射してから通過する領域を露光領域（第２露光領域）２７２とすると、いずれの露光領域でも情報光（物体光）たる光束１７１は右回り円偏光として進行し、いずれの露光領域でも記録用参照光たる光束１７２は、これとは逆向きに、左回り円偏光として進行するから、両者による干渉の結果、空間光変調器１５の第１の領域１５２に表現された２次元ページデータが、感光層２７の露光領域２７１、露光領域２７２それぞれに干渉パターンとして、即ちホログラフィックに記録される。より正確には、感光層２７の露光領域２７１と露光領域２７２で干渉するのは、空間光変調器１５の第１の領域１５２の、対物レンズ２２などを経たフレネル回折パターンと、第２の領域１５３の、対物レンズ２２などを経たフレネル回折パターンと考えることができる。感光層２７の露光領域２７１、２７２に形成されるホログラムは反射型ホログラムである。
【００５１】
この記録の際には、フォーカシング制御とトラッキング制御等も同時に次のようにして行われる。
感光層２７等を通過し、再びＳ偏光として偏光ビームスプリッター１８で反射された戻りの光束１７１、１７２は、再度、空間光変調器１５を通過する。記録時、空間光変調器１５の第１の領域１５２は、記録すべき２次元ページデータの情報を明暗パターンとして表現しているが、光束１７１、１７２はいずれも１度ずつ、空間光変調器１５の第１の領域１５２、第２の領域１５３を平行光束として通過するので、ビームスプリッター７に入射する戻りの光束の断面は、概ね、光軸１６に関して対称な明暗パターンを有する。このような光軸１６に関して対称な明暗パターンを有する戻りの光束の一部がビームスプリッター７で反射されて、信号検出系８に入るので、信号検出系８は構成的にも動作的にもＣＤなどの駆動装置における信号検出系と同様とすることができ、フォーカス信号を周知の非点収差法で、トラッキング信号を周知のプッシュプル法で生成できるとともに、ＲＦ信号も周知の方法で生成することができる。但し、ＲＦ信号を生成するのは、主にＣＤなどの従来型光ディスクを再生する場合である。このようにして、本実施形態の光情報記録再生装置によれば、媒体２への記録と、フォーカシング信号及びトラッキング信号の生成に基いたフォーカシング制御及びトラッキング制御を同時に行うこともできる。
【００５２】
なお、空間光変調器１５の第１の領域１５２の画素の大半が暗状態になると、信号検出系８に入る光が弱すぎて所定の信号を生成できないので、第１の領域１５２の画素の一部は必ず明状態にしておくとよい。或いは、２画素で１組１ビットとし、どちらか一方の画素は必ず明、もう一方は暗とする方法を用いることもできる。但しこの場合は、１ページで表現できる情報量が半減してしまうので注意を要する。或いは、媒体２への露光による記録と、フォーカシング信号及びトラッキング信号の生成に基いたフォーカシング制御及びトラッキング制御を同時に行うのではなく交互に行うようにすれば、フォーカシング信号及びトラッキング信号の生成を行う瞬間は、空間光変調器１５の第１の領域１５２の画素は全て明状態とすることができる。但し、フォーカシング信号及びトラッキング信号の生成に基いたフォーカシング制御及びトラッキング制御は、媒体２への記録のために感光層２７におけるある露光領域と次の露光領域の中間に集光スポットがあるときには、タイミングを合わせて光源３の出力を下げた状態で行う。
【００５３】
媒体２に設けられたランド３１及びグルーブ３２は、従来の追記型光ディスクに於けるのと同様、記録（書き込み）の際、ラジアル方向（ディスクの半径方向）の位置の基準となる。従ってラジアル方向に関しては、記録する感光層２７の、ランド３１或いはグルーブ３２に対応する位置で記録（露光）が行われる。タンジェンシャル方向（トラックの接線方向）の記録位置制御はタイミング制御によりなされる。
以上の説明から分かるとおり、本実施形態の光情報記録再生装置によれば、従来の追記型光ディスクを媒体として用いて従来の記録方式で記録することも可能である。
【００５４】
次に、記録された情報を再生する場合の動作について、図４、図５、図６を用いて説明する。図５、図６は、媒体２の露光領域２７１，２７２の近辺を拡大した図である。図４に示すように、光源３からの光を光源モニター１２に導いて光源３の出力を制御するまでの動作は図３に示した記録時と同様である。但し、光源３の出力は、露光領域２７１、２７２に形成された干渉縞のコントラストが再生時の再露光によって低下させられることのない程度まで低く制御される。各々独立に制御可能な多数の画素１５１を有する空間光変調器１５の全画素は明状態に制御され、第１の領域１５２、第２の領域１５３とも光が通過する。このとき、第１の領域１５２を通過した光束１７３、第２の領域１５３を通過した光束１７４は、何れもＳ偏光となっている。
【００５５】
まず、光束１７４について見ると、光束１７４は、偏光ビームスプリッター１８で反射された後、左回り４分の１波長板１９を経て左回り円偏光となり、対物レンズ２２を経て、再生用参照光として露光領域２７１を照射する。これによって、図５に示すように、反射回折光３３を生じると共に、そのまま透過する０次回折光３４を生じる。反射回折光３３は、記録時の右回り円偏光した情報光に対応する再生光であるが、実際的には楕円偏光となる。従って、左回り４分の１波長板１９を通過後も楕円偏光となるが、Ｐ偏光成分を強く含んでおり、このＰ偏光成分は偏光ビームスプリッター１８を通過し結像レンズ２３を経て、再生すべき２次元ページデータが２次元イメージセンサー２４の一部（図４では光軸２５を中心にして左右対称にしたセンサー面の右半分側）に投影される。
【００５６】
一方、露光領域２７１を透過した０次回折光３４は反射層２９で反射され、露光領域２７２を照射する。これによって、反射回折光３５を生じると共に、そのまま透過する０次回折光３６を生じる。反射回折光３５も、反射回折光３３同様、記録時の右回り円偏光した情報光に対応する再生光であり、反射面２９で反射した後、反射回折光３３と同様の作用を受け、２次元イメージセンサー２４の一部（図４では前記センサー面の右半分側）に投影される。このとき、反射回折光３３による２次元イメージセンサー２４上の再生パターンと、反射回折光３５による２次元イメージセンサー２４上の再生パターンは殆ど同一である。なお、反射回折光３３と反射回折光３５は何れも、一般のホログラフィーでいう直接像に相当する。
【００５７】
更に一方、露光領域２７２を透過した０次回折光３６は、左回り円偏光であり、右回り４分の１波長板２０を通過するとＳ偏光となって偏光ビームスプリッター１８で反射され、２次元イメージセンサー２４には入らない。従って、再生時に信号対雑音比を劣化させる要因となる不要背景光（０次回折光）が、２次元イメージセンサー２４に入る情報信号光から分離される。同時に、偏光ビームスプリッター１８で反射されることにより２次元イメージセンサー２４に入る情報信号光から分離された０次回折光３６は、ビームスプリッター１７により一部が反射されて信号検出系８に入る。
【００５８】
次に、光束１７３について見ると、光束１７３は、偏光ビームスプリッター１８で反射された後、右回り４分の１波長板２０を経て右回り円偏光となり、対物レンズ２２を経て、再生用参照光として露光領域２７２を照射する。これによって、図６に示すように、反射回折光３７を生じると共に、そのまま透過する０次回折光３８を生じる。反射回折光３７は、一般のホログラフィーでいう共役像に対応する光である。反射回折光３７は、右回り４分の１波長板２０を通過後、楕円偏光となり、そのＰ偏光成分は偏光ビームスプリッター１８を通過し結像レンズ２３を経て、再生すべき２次元ページデータが２次元イメージセンサー２４の一部（図４では光軸２４を中心にして左右対称にしたセンサー面の左半分側）に投影される。
【００５９】
一方、露光領域２７２を透過した０次回折光３８は反射層２９で反射され、露光領域２７１を照射する。これによって、反射回折光３９を生じると共に、そのまま透過する０次回折光４０を生じる。反射回折光３９も、反射回折光３７同様、一般のホログラフィーでいう共役像に対応する光であり、反射面２９で反射した後、反射回折光３７と同様の作用を受け、２次元イメージセンサー２４の一部（図４では前記センサー面の左半分側）に投影される。この時、反射回折光３７による２次元イメージセンサー２４上の再生パターンと、反射回折光３９による２次元イメージセンサー２４上の再生パターンは殆ど同一である。
【００６０】
他方、露光領域２７１を透過した０次回折光４０は、右回り円偏光であり、左回り４分の１波長板１９を通過するとＳ偏光となって偏光ビームスプリッター１８で反射され、２次元イメージセンサー２４には入らない。従ってこの場合も、再生時に信号対雑音比を劣化させる要因となる不要背景光（０次回折光）が、２次元イメージセンサー２４に入る情報信号光から分離される。同時に、偏光ビームスプリッター１８で反射されることにより２次元イメージセンサー２４に入る情報信号光から分離された０次回折光４０は、ビームスプリッター１７により一部が反射されて信号検出系８に入り、光束１７４から分離された０次回折光３６と共に、フォーカス信号、トラッキング信号、及びＲＦ信号を生成し、これに基づいた対物レンズのフォーカス制御、トラッキング制御がなされる。
【００６１】
以上のように、２次元イメージセンサー２４には、同じページデータが２箇所に投影されるので、一方の個所からのデータ再生において何らかのエラーが生じた場合でも、もう一方の個所からの再生データでエラーを補正することができ、極めて信頼性の高い情報再生が可能になる。
なお、元々空間光変調器１５の第１の領域１５２に表示する２次元ページデータそのものにエラー訂正の仕組みを組み込むのであれば、記録用の情報光に対応する再生光としては反射回折光３３と反射回折光３５のみを使うことも勿論可能である。この場合、２次元イメージセンサー２４は半分の領域（図４ではセンサー面の右半分側の領域）で足り、従って画素数も半分でよい。
【００６２】
また、ＣＤなどの従来型光ディスクを媒体２の位置に置き、空間光変調器１５の第１の領域１５２及び第２の領域１５３の全画素を明状態にすれば、このディスクに入射する再生用参照光によって得られる再生光は上記の説明の透過０次回折光と同じ経路をたどるので、フォーカス信号、トラッキング信号、及びＲＦ信号が得られる。即ち、本実施形態の光情報記録再生装置によれば、従来型光ディスクの再生も可能である。
【００６３】
以上のように本実施形態の光情報記録再生装置によれば、ホログラフィック記録再生装置として簡素で、従って低価格に構成でき、再生時には、信号対雑音比が良好で信頼性の高い情報記録再生が可能となる。また従来型光ディスクとの互換性も確保される。
【００６４】
なお、上記の実施形態では、感光層を有する媒体に対してのホログラフィック記録再生装置として説明したが、これに限らず、ホログラフィック記録装置として、あるいはホログラフィック再生装置として単独で用いることができる。
【００６５】
【発明の効果】
以上のように本発明の光情報記録再生装置及び方法、光情報記録媒体、光情報記録装置及び方法、並びに光情報再生装置及び方法に依れば、ホログラフィック記録再生装置として簡素で、従って低価格に構成でき、信号対雑音比が良好で信頼性の高い情報記録再生が可能となる。また従来型光ディスクとの互換性も確保される。
【図面の簡単な説明】
【図１】本発明による光情報記録再生装置の一実施形態の要部概略構成図である。
【図２】本実施形態に用いる空間光変調器の平面図である。
【図３】本実施形態の光情報記録再生装置における情報を記録する場合の動作を示す説明図である。
【図４】本実施形態の光情報記録再生装置における情報を記録する場合の動作を示す説明図である。
【図５】本実施形態の光情報記録再生装置における情報を再生する場合の光束１７４の状態を媒体２の露光領域２７１，２７２の近辺を拡大して示す説明図である。
【図６】本実施形態の光情報記録再生装置における情報を再生する場合の光束１７３の状態を媒体２の露光領域２７１，２７２の近辺を拡大して示す説明図である。
【符号の説明】
１光情報記録再生装置の主要部をなす光学系
２光情報記録媒体
３光源
４コリメーター光学系
５光束絞り
６偏光板
７ビームスプリッター
８信号検出系
９凸パワーを持つレンズ
１０一方向に凸パワー又は凹パワーを持つシリンドリカルレンズ
１１４分割フォトディテクター
１２光源モニター系
１３凸パワーを持つレンズ
１４フォトディテクター
１５空間光変調器
１５１各々独立に制御可能な多数の画素
１５２第１の領域
１５３第２の領域
１６光軸
１７空間変調器１５に入射する光束の断面
１８偏光ビームスプリッター
１９，２０４分の１波長板
２１４分の１波長板１９，２０に入射する光束
２２対物レンズ
２２ａアクチュエータ
２３結像レンズ
２４２次元イメージセンサー
２５光軸
２６透明基板層
２７感光層
２８透明バッファー層
２９反射層
３０保護層
３１ランド
３２グルーブ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for recording information such as digital data on a medium using light. Further, the present invention relates to an apparatus and a method for reproducing information recorded on the medium. In particular, it relates to an apparatus and a method for performing holographic recording and reproduction. Further, the present invention relates to a medium for recording information such as digital data using light.
[0002]
[Prior art]
At present, compact discs (CD), digital versatile discs (DVD), magneto-optical (MO) discs and the like are used as information recording media using light.
In these information recording media, information is recorded as one-dimensional digital data using light, and in reproduction, a difference in light reflectance or a polarization direction of reflected light is expressed as on / off. In the one-dimensional recording method used for these information media, shortening the wavelength of a light source used for recording / reproduction and increasing the number of information recording layers of the medium have been studied in order to increase the information recording density.
On the other hand, a holographic recording / reproducing method has been conventionally proposed as a method for two-dimensionally recording / reproducing information. Here, the two-dimensional recording / reproduction means that the information is expressed two-dimensionally as information, and in the case of the holographic method, it is considered that the physical recording is performed three-dimensionally.
[0003]
In the holographic method, data is written as two-dimensional information on a medium as described in an article by D-Saltis and F. Mock (originally Scientific American November 1995), for example, pages 46 to 54 of Nikkei Science January 1996 issue. Since recording is performed volumetrically, a dramatic improvement in recording density is expected.
However, since a bulk crystal such as lithium niobate has been used as a recording medium, there is a problem of specialty of a material, and a reference light is irradiated from a direction having an angle to object (information) light. There are problems such as an increase in the size of a reproduction optical system and incompatibility with a disc-shaped disk medium such as a CD which has become a mainstream medium, and it has not been put to practical use.
In view of the recent spread of photosensitive polymers as photosensitive materials, methods for solving these problems have been proposed in, for example, the following Patent Documents 1 to 4.
[0004]
[Patent Document 1]
JP-A-10-124872
[Patent Document 2]
JP-A-11-31938
[Patent Document 3]
JP-A-2002-123949
[Patent Document 4]
JP-T-2002-53981
[0005]
The ones described in Patent Documents 1, 2, and 3 are basically based on the same concept. A disk-shaped substrate provided with a reflection layer and a hologram layer (photosensitive layer) is used as an information recording medium. When holographic recording of information using light, the reference light and object light (information light) are coaxially arranged to reduce the size of the optical system, and both the reference light and object light are irradiated from one side of the disk medium. Holographic recording of two-dimensional data is possible, and compatibility with conventional disk media can be realized. The recording / reproducing optical system is provided with a two-part optical rotation plate in which optical rotation optical elements having optical rotation directions of plus 45 degrees and minus 45 degrees are abutted in a plane, and combined with a polarizing beam splitter to perform recording at the time of recording. Even when the reference light and the object light (information light) are irradiated coaxially, it is possible to separate unnecessary background light (0th-order diffracted light) and information light (first-order or higher-order diffracted light) during reproduction. It is possible.
[0006]
Specifically, in the first embodiment of Patent Literature 1, a liquid crystal that can be turned on and off is used as the two-part optical rotation plate. This liquid crystal is controlled to be in an on state at the time of servo and does not show optical rotation, but is controlled to be in an off state at the time of recording and reproduction. It shows optical rotation. Then, at the time of recording, the two-dimensional information to be recorded is expressed by controlling the optical rotation of each pixel of the spatial light modulator on / off. At the time of reproduction, the primary reproduction light generated first with respect to the light incident on the hologram recording layer is used as a secondary reference light, thereby generating a secondary reproduction light. Detection is performed by a two-dimensional image sensor such as a coupling element (CCD).
[0007]
Further, in the second embodiment of Patent Document 1, a beam splitter and a two-dimensional image sensor are further added to detect a primary reproduction light, and a signal is detected by differential detection of the primary reproduction light and the secondary reproduction light. The noise to noise ratio is improved.
In the third embodiment of Patent Document 1, a half section of a light beam emitted from a light source and entering a recording / reproducing optical system (pickup) is referred to as reference light, and the other half section is referred to as object light (without using an optical rotatory optical element). (Information light).
[0008]
Patent Literature 2 discloses three embodiments, each of which uses a passive optical element instead of an active optical element capable of on / off control as a two-part optical rotation plate. Half of the two-part optical rotation plate has an optical rotation of plus 45 degrees, and the other half has an optical rotation of minus 45 degrees. At the time of recording, half of the recording area is exposed to the right 45 degree polarization state with respect to the S polarized light, and the other half is exposed to the left 45 degree polarization state. During reproduction, reproduction information light generated by irradiating the recording area with reproduction reference light is detected by a two-dimensional image sensor such as a CCD.
[0009]
In Patent Literature 3, the configuration of the recording / reproducing optical system is almost the same as that of the third embodiment of Patent Literature 2, but in Patent Literature 2, the convergence positions of the reference light and the information light are slightly different in the thickness direction of the medium. On the other hand, in Patent Document 3, the convergence positions of the reference light and the information light are the same. Then, at the time of recording, the recording area for certain two-dimensional page data to be recorded is composed of two partial areas as in Patent Document 2, but each of the partial areas is exposed in a polarization state of 45 degrees to the right with respect to S-polarized light. At the same time, the light is exposed even in the polarization state of 45 degrees to the left. During reproduction, reproduction information light generated by irradiating the recording area with reproduction reference light is detected by a two-dimensional image sensor such as a CCD.
[0010]
Patent Document 4 discloses a method based on the principle of polarization holography and using a material having photoinduced anisotropy for a recording medium. Also in this method, at the time of recording, the reference light and the information (object) light are irradiated coaxially onto a card-shaped or disk-shaped medium from one side thereof. However, at the time of recording, the reference light and the information (object) light are linearly polarized light having polarization directions different from each other by 90 degrees. At the time of reproduction, information light including a polarization component having a polarization direction different from that of the linearly polarized reproduction reference light by 90 degrees is reproduced, and unnecessary background light (0th-order diffracted light) becomes unnecessary by the polarization beam splitter. (Diffraction light of the next order or more). Note that the recording optical system and the reading (reproducing) optical system are provided separately.
[0011]
[Problems to be solved by the invention]
However, in the first embodiment of Patent Document 1, a liquid crystal is used as a two-segment optical rotation plate, and a control device for performing on / off control according to the state is required. Therefore, the overall device becomes complicated and expensive. Invite. In the reproduction, the primary reproduction light generated first with respect to the light incident on the hologram recording layer is used as the secondary reference light, and the secondary reproduction light generated by the secondary reference light is referred to as the information light. Therefore, the intensity of the final information light is weak. Therefore, the signal-to-noise ratio is poor, and it is difficult to reproduce information with high reliability.
[0012]
In the second embodiment of Patent Document 1, the primary reproduction light is also detected, and the signal-to-noise ratio is improved by detecting the differential between the primary reproduction light and the secondary reproduction light. This requires components, an image sensor, and an electric circuit for driving the components, which leads to an increase in complexity, size, and cost of the entire device.
[0013]
The third embodiment of Patent Document 1 does not use a two-segment optical rotation plate and preferably has a simple device configuration. However, during reproduction, unnecessary background light and information light generated cannot be separated. And the signal-to-noise ratio is poor, making it difficult to reproduce information with high reliability.
[0014]
In the first and second embodiments of Patent Literature 2, although the two-split optical rotation plate is used, since the unnecessary background light and the information light generated at the time of reproduction cannot be separated, the signal-to-noise ratio is low. Bad and difficult to reproduce information with high reliability.
Further, in the third embodiment of Patent Document 2, unnecessary background light and information light generated at the time of reproduction can be separated, but the region exposed to the right (or left) 45-degree polarization state with respect to the S-polarized light can be separated. On the other hand, since the polarization direction of the reproduction reference light is orthogonal to that, the reproduction efficiency (information light intensity with respect to the input reproduction reference light) is low. Therefore, this embodiment also has a low signal-to-noise ratio, making it difficult to reproduce information with high reliability.
[0015]
In Patent Document 3, it is preferable that an optical element for changing the convergence position of the reference light and the information light required in Patent Documents 1 and 2 is not required, but the following problem arises.
The recording area for certain two-dimensional page data to be recorded can be divided into two. These are referred to as partial area 1 and partial area 2. The polarization state at the right 45 degrees with respect to the S polarization is B polarization, and the polarization state at the left 45 degrees is A polarization. Then, upon recording (exposure), the partial area 1 and the partial area 2 are exposed in the A-polarized state and also in the B-polarized state. Regarding the reproduction, the light beam portion of the half cross section of the reproduction reference light becomes A-polarized light after passing through the two-part optical rotation plate, enters the partial area 1, reflects on the reflection surface of the medium, and enters the partial area 2. At this time, in the partial area 1, the information light corresponding to the recording in the A polarization state is generated in the direction opposite to the reproduction reference light, and enters the two-dimensional image sensor via the optical system including the lens. At this time, in the partial region 2, the information light corresponding to the recording in the A-polarized state is generated in the direction opposite to the reproduction reference light, and is reflected on the reflection surface of the medium. Enter the sensor. However, since the partial region 1 and the partial region 2 are also exposed in the B-polarized state, the B-polarized information light is reproduced though it is weaker than the A-polarized light. The same can be said for the light flux portion of the other half cross section of the reproduction reference light, except that the A-polarized light and the B-polarized light, and the partial regions 1 and 2 are interchanged. By the way, at the time of recording (exposure), the information light in the A polarization state and the information light in the B polarization state each carry half of certain page data, in other words, carry other information. For this reason, different information overlaps and enters the same area of the two-dimensional image sensor. Therefore, the signal disclosed in Patent Document 3 also has a poor signal-to-noise ratio, and it is difficult to reproduce information with high reliability.
[0016]
Further, in Patent Document 4, although a polarization separation of unnecessary background light during reproduction is easily performed in principle, a special material having light-induced anisotropy is used for a recording medium. However, such materials are not yet practical. Further, since the recording optical system and the reproduction optical system are provided independently, the size and cost of the apparatus are increased.
[0017]
SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and has a simple and low-cost apparatus as a device while maintaining the characteristics of holographic recording and reproduction, and has a good signal-to-noise ratio and high reliability. It is an object of the present invention to provide an optical information recording / reproducing apparatus and method, an optical information recording medium, an optical information recording apparatus and method, and an optical information reproducing apparatus and method that enable highly-reproducible information reproduction to be practically performed.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, an optical information recording / reproducing apparatus according to the present invention is an optical information recording / reproducing apparatus that records information on a medium using light and reproduces the recorded information, and has a predetermined polarization direction. Means for generating a light beam, a spatial light modulator, a polarizing beam splitter, two quarter-wave plates, and an objective lens, wherein the spatial light modulator comprises a first region and a second region. Having a plurality of pixels in each of which the transmittance of each pixel can be modulated in at least one of the first region and the second region, wherein a half cross section and the other half cross section of the light beam are And the polarizing beam splitter is arranged to reflect the light beam passing through the spatial light modulator, and the two quarter-wave plates are arranged to pass through the first and second regions. The half cross section of the light beam reflected by the beam splitter and the As square half-section of the pass, respectively, and are arranged such that its fast axis and slow axis orthogonal to each other, the objective lens is characterized in that disposed opposite to said medium.
[0019]
Further, the optical information recording / reproducing apparatus of the present invention is characterized by including a signal detection system for generating a focus signal, a tracking signal, and an RF signal.
[0020]
Further, the optical information recording / reproducing apparatus according to the present invention is characterized by including a two-dimensional image sensor for reproducing information recorded on the medium.
[0021]
Further, the optical information recording medium according to the present invention has a photosensitive layer that undergoes a refractive index modulation by light irradiation, lands and grooves formed periodically, and a reflective layer formed on the top surfaces of the lands and grooves. Features.
[0022]
Further, an optical information recording / reproducing method according to the present invention uses the optical information recording / reproducing apparatus according to claim 1 to form a photosensitive layer that undergoes refractive index modulation by light irradiation and a reflective layer for reflecting the irradiated light. It is characterized in that information is recorded on the photosensitive layer or information recorded on the medium is reproduced.
[0023]
Further, in the optical information recording method of the present invention, data is displayed on the first area or the second area of the spatial light modulator, a light beam passing through the area displaying the data is used as information light, and Is characterized in that information is holographically recorded on a photosensitive layer in a medium by using a light beam passing through the area as reference light.
[0024]
2. The optical information reproducing method according to claim 1, further comprising a signal detection system that generates a focus signal, a tracking signal, and an RF signal, and a two-dimensional image sensor that reproduces information recorded on the medium. An optical information recording / reproducing device is used to guide the 0th-order diffracted light transmitted through the photosensitive layer in the optical information recording medium according to claim 4 to the signal detection system to generate a focus signal and a tracking signal. The information recorded on the optical information recording medium is reproduced from the output of the two-dimensional image sensor while controlling the objective lens based on a signal.
[0025]
In the optical information recording apparatus according to the present invention, in the optical information recording apparatus for recording information on a photosensitive layer of a medium by condensing each light beam of information light and recording reference light with an objective lens, the medium is irradiated with the medium. A light source that emits light, a first region that, when passing light emitted from the light source, generates a first passing light flux as information light modulated in accordance with information data to be recorded; A spatial light modulator having a second region for obtaining a light beam of the recording reference light that interferes with the light beam, and a polarizing beam splitter that guides each light beam obtained by the spatial light modulator toward the medium side, Each of the light beams guided by the polarizing beam splitter has two quarter-wave plates arranged so as to pass through each of two quarter-wave plates whose first axes are orthogonal to each other, The two quarters It is characterized in that so as to record an interference pattern corresponding to the information data in the photosensitive layer of the information beam and the respective light beams of the recording-specific reference light to interfere with the medium that has passed through the elongated plate.
[0026]
Further, the optical information recording method according to the present invention is an optical information recording method in which each light beam of an information light and a recording reference light is condensed by an objective lens and information is holographically recorded on a photosensitive layer of a medium. The received light is converted into a light beam having a predetermined polarization direction, and a part of the light beam is passed through a first area of a spatial light modulator controlled in accordance with information data to be recorded, thereby converting the light beam. The first light beam is modulated to generate a first light beam as information light, and the second light beam is generated from the remaining light beam as a recording reference light that interferes with the first light beam, and then the first light beam becomes the information light. A light beam and a second light beam serving as the recording reference light are guided to the objective lens side by a polarizing beam splitter, and then the first passing light beam and the second light beam are first polarized perpendicular to each other and polarized. direction Passing through each of the two quarter-wave plates arranged so that the angle of the first axis with respect to the polarization direction of the first light beam and the second light beam which are the same is 45 degrees, and then the first light beam And holographically recording information on the photosensitive layer of the medium by causing the respective light beams of the first and second light beams to interfere with each other.
[0027]
Further, an optical information reproducing apparatus according to the present invention is an optical information reproducing apparatus for reproducing information holographically recorded on a photosensitive layer of a medium, wherein the light source emits light applied to the medium, and the light source emits light. A polarization beam splitter that guides light as reproduction reference light, and two quarters, where the first axes are orthogonal to each other, and the reproduction reference light guided to the polarization beam splitter is arranged to pass through each. When each light beam of the reference light for reproduction obtained by passing through the one-wave plate and the two quarter-wave plates is irradiated on the photosensitive layer of the medium, it is holographically recorded on the photosensitive layer of the medium. And a two-dimensional image sensor arranged to project reflected diffracted light obtained from the obtained information after passing through the polarizing beam splitter.
[0028]
Further, the optical information reproducing method according to the present invention is an optical information reproducing method for reproducing information holographically recorded on a photosensitive layer of a medium, wherein light emitted from a light source is guided to a polarizing beam splitter as reproduction reference light, The reproduction reference light guided to the polarization beam splitter is composed of two quadrants arranged such that the first axes are orthogonal to each other and the angle of the first axis is 45 degrees with respect to the polarization direction of the reproduction reference light. Of the reference light for reproduction obtained by passing through the two quarter-wave plates, and irradiating the photosensitive layer of the medium with the luminous flux of the reference light for reproduction. The reflected and diffracted light obtained from the information recorded in the graphic is projected on a two-dimensional image sensor after passing through the polarizing beam splitter, and is projected on the two-dimensional image sensor. It is characterized by reproducing the information by detecting the diffracted light.
[0029]
Further, the optical information recording / reproducing apparatus according to the present invention condenses each light beam of the information light and the recording reference light with an objective lens, records information on a photosensitive layer of a medium, and uses the reproduction reference light for the information. In an optical information recording / reproducing apparatus for reproducing, a light source that emits light applied to the medium, and when passing light emitted from the light source during recording, an information light modulated corresponding to information data to be recorded is transmitted. A first area for generating, and a second area for obtaining a recording reference light that interferes with the information light, and emits light emitted from the light source during reproduction to the first area and the second area. 2, a spatial light modulator that generates a reference light for reproduction by passing through the area 2, a recording-side information light, a recording reference light, and a reproduction-specific reference light obtained during reproduction obtained by the spatial light modulator. To the light-sensitive layer of the medium during reproduction. A polarization beam splitter that transmits the obtained reproduction light, and the information light and the recording reference light reflected by the polarization beam splitter pass through each of two quarter-wave plates whose first axes are orthogonal to each other. Two quarter-wave plates arranged so that the information light and the recording reference light that have passed through the two quarter-wave plates interfere with the information data on the photosensitive layer of the medium. An objective lens that records a corresponding interference pattern and irradiates the recorded interference pattern with a reproduction reference beam that has passed through the two quarter-wave plates during reproduction, and the two quarter-wave plates. When the passed reference light for reproduction is applied to the photosensitive layer of the medium, the reflected diffracted light obtained from the information recorded on the photosensitive layer of the medium is reflected by the two quarter-wave plates and the polarizing beams. Pre It is characterized by having a two-dimensional image sensor disposed to project in after a terpolymer.
[0030]
In the optical information recording / reproducing method according to the present invention, the information light and the recording reference light are condensed by an objective lens to record information on a photosensitive layer of a medium, and the information is reproduced using the reproduction reference light. In the optical information recording / reproducing method for reproducing, at the time of recording, light emitted from a light source is converted into a light beam having a predetermined polarization direction, and a part of the light beam is controlled by a spatial light modulator controlled according to information data to be recorded. The information light is generated by passing through the first area, and the recording reference light that interferes with the information light is generated from the remaining light flux, and then the information light and the recording reference light are transmitted to a polarizing beam splitter. Then, the information light and the recording reference light guided to the polarization beam splitter are respectively polarized by the information light and the recording reference light whose first axes are orthogonal to each other and whose polarization directions are the same. Light passing through each of the two quarter-wave plates arranged so that the angle of the first axis is 45 degrees with respect to the direction, and thereafter, the information light and the recording reference light interfere with each other to expose the medium. A step of holographically recording information on the layer, and at the time of reproduction, a light emitted from the light source is obtained as a reference light for reproduction by passing through the spatial light modulator as a light beam having the predetermined polarization direction. The reproduction reference light guided to the polarization beam splitter and then guided to the polarization beam splitter is passed through each of the two quarter-wave plates, and passed through the two quarter-wave plates. The obtained reference light for reproduction is applied to the photosensitive layer of the medium, and the reflected diffracted light obtained from the photosensitive layer of the medium is two-dimensionally reflected after passing through the two quarter-wave plates and the polarizing beam splitter. Projected onto the image sensor is characterized by comprising the steps of: Detection of the reflected diffracted light projected onto the two-dimensional image sensor to reproduce the information.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an optical information recording / reproducing apparatus according to the present invention will be described with reference to the drawings.
The optical information recording / reproducing device of the present embodiment described below is a device that can be implemented alone as an optical information recording device for recording optical information or as an optical information reproducing device for reproducing optical information.
[0032]
FIG. 1 is a schematic diagram of a main part of an embodiment of an optical information recording / reproducing apparatus according to the present invention.
In FIG. 1, reference numeral 1 denotes an optical system which is a main part of the optical information recording / reproducing apparatus. The optical system 1 is incorporated in one unit as an optical pickup for recording information on the optical information recording medium 2 or reproducing information from the optical information recording medium 2 on which information is recorded. (Hereinafter, referred to as a medium) 2.
Reference numeral 2 denotes a medium on which information is to be recorded or from which information is to be reproduced. The medium 2 is partially shown in cross section in FIG. The medium 2 is preferably in the form of a disc such as a CD or DVD. In this case, the disk medium 2 is driven to rotate, and the optical pickup is driven linearly in the radial direction of the disk medium 2, as in a CD or DVD drive device (drive). Although not shown, a conventionally known method can be used for a mechanism, an electric circuit, and the like necessary for these driving and control.
[0033]
In the optical system 1 shown in FIG. 1, the member 3 is a light source having good coherence, such as a semiconductor laser. It is desirable that the light emitted from the light source 3 is linearly polarized. In the case of FIG. 1, the polarization direction is perpendicular or parallel to the plane of the drawing. As the wavelength, a wavelength at which the sensitivity of the photosensitive material of the medium 2 is high is used.
The member 4 is a collimator optical system that converts light emitted from the light source 3 into a parallel light beam. Although the collimator optical system 4 is shown in FIG. 1 as a single-lens configuration for convenience, it is not limited to this. For example, when a semiconductor laser having astigmatism is used as the light source 3, an optical element such as a cylindrical lens for correcting the astigmatism may be included. Further, an optical element for uniformizing the intensity distribution in the light beam cross section can be included.
The member 5 is a light beam stop that limits the diameter of the parallel light beam emitted from the collimator optical system 4 to a predetermined value. The beam stop 5 may be arranged in the collimator optical system 4 or between the collimator optical system 4 and the light source 3.
[0034]
The member 6 is a polarizing plate. The rotation position of the polarizing plate 6 is determined such that the polarization direction of the light passing therethrough is perpendicular or parallel to the paper. However, when the light emitted from the light source 3 is linearly polarized, the polarizing plate 6 becomes unnecessary. That is, in the present embodiment, the light source 3 and / or the polarizing plate 6 function as a polarization generation unit that generates a light beam having a predetermined polarization direction depending on whether or not the light emitted from the light source 3 is polarized.
The member 7 is a beam splitter. The beam splitter 7 has a predetermined branching ratio, for example, about 90% transmission and about 10% reflection with respect to the incident light passing through the light beam stop 5.
[0035]
The member 8 disposed above the beam splitter 7 is a signal detection system. The signal detection system 8 includes a lens 9 having a convex power, a cylindrical lens 10 having a convex power or a concave power in one direction, and a quadrant photodetector 11 as main components.
The member 12 disposed below the beam splitter 7 is a light source monitoring system. The light source monitoring system 12 includes a lens 13 having a convex power and a photodetector 14 as main components.
[0036]
The member 15 disposed on the right side of the beam splitter 7 is a spatial light modulator. FIG. 2 shows a state in which the spatial light modulator 15 is viewed from the front, that is, in the direction of the optical axis 16 from the incident light side.
In FIG. 2, reference numeral 17 denotes a cross section of a light beam incident on the spatial light modulator 15. The spatial light modulator 15 has a number of pixels 151 that can be controlled independently. Such a spatial light modulator 15 can be configured using, for example, liquid crystal. The spatial light modulator 15 is divided into an upper half first region 152 and a lower half second region 153 in FIGS. 1 and 2. And the other half section is arranged to pass. Each light beam passing through the first region 152 and the second region 153 corresponds to the first light beam and the second light beam in the present invention.
[0037]
The member 18 is a polarization beam splitter. The polarization beam splitter 18 reflects the S-polarized (polarized light perpendicular to the paper surface) component of the light incident thereon toward the medium 2 and transmits the P-polarized light (polarized light parallel to the paper surface) component.
The upper members 19 and 20 of the polarizing beam splitter 18 as viewed in FIG. 1 are both quarter-wave plates. The quarter-wave plates 19 and 20 are such that the half-section light beam of the incident light beam 21 passes through the quarter-wave plate 19 and the other half-section light beam passes through the quarter-wave plate 20. The optical axis 25 is arranged as a center. The quarter-wave plates 19 and 20 have their fast (F) axes orthogonal to each other, and therefore their slow (S) axes orthogonal to each other. The axes are arranged at an angle of 45 ° (therefore, the S axis is also at an angle of 45 °). In the embodiment of FIG. 1, the two quarter-wave plates 19 and 20 are arranged in contact with each other to form a plane plate having the same plane. It may be arranged along the steps.
[0038]
The member 22 is an objective lens. The objective lens 22 is disposed to face the medium 2 so as to focus the light beam 21 toward the medium 2. The objective lens 22 is driven by a mechanism for performing focusing control and tracking control. However, since a conventionally known method for an optical pickup can be used, this mechanism is simply shown as an actuator 22a, The detailed configuration is not shown.
A member 23 disposed below the polarization beam splitter 18 is an imaging lens, and a member 24 is a two-dimensional image sensor such as a CCD. As shown in FIG. 1, each component from the objective lens 22 to the two-dimensional image sensor 24 is arranged with the optical axis 25 as a reference. Further, although the objective lens 22 and the imaging lens 23 are shown as being constituted by a single lens in FIG. 1, a plurality of lenses may be constituted according to the required degree of aberration correction.
[0039]
The medium 2 has a plate-like form such as a disk shape, and in order from the objective lens 22 side, a transparent substrate layer 26, a photosensitive layer 27, a transparent buffer layer 28, a reflective layer 29, and a protective layer. 30.
For the transparent substrate layer 26, for example, polycarbonate used for a CD or the like is used as a material.
The photosensitive layer 27 is made of a material whose transmittance does not change significantly by light irradiation and whose refractive index is locally modulated, for example, a photopolymer. The thickness is such that the formed hologram can be regarded as a volume hologram, a so-called thick hologram, for example, 10 μm or more.
The transparent buffer layer 28 is a layer provided for one purpose to reduce the influence of the material of the photosensitive layer 27, which may be contracted by exposure to light. Therefore, a material having a small photoelasticity is preferably used. Further, a transparent buffer layer may be provided between the transparent substrate layer 26 and the photosensitive layer 27 or on both sides of the photosensitive layer 27. In the transparent buffer layer 28, lands 31 and grooves 32 serving as tracking guides are periodically formed at predetermined intervals. However, if shrinkage of the material of the photosensitive layer 27 by the exposure does not cause a practical problem, the transparent buffer layer 28 may be omitted and the lands 31 and the grooves 32 may be formed directly on the photosensitive layer 27. The reflection layer 29 is formed on the surface of the land 31 and the surface of the groove 32 by, for example, aluminum evaporation. The protective layer 30 is a layer provided for protecting the reflective layer 29, and is made of a plastic material used for a protective layer of a CD.
[0040]
Next, the operation of the thus configured optical information recording / reproducing apparatus of the present embodiment will be described.
First, an operation for recording information will be described with reference to FIG.
The light emitted from the light source 3 is converted into a parallel light beam through a collimator optical system 4, is restricted to a predetermined light beam diameter by a light beam stop 5, and then enters a polarizing plate 6. By limiting the luminous flux diameter in this way, it is possible to suppress the occurrence of unnecessary stray light and flare in the subsequent optical system. The light passing through the polarizing plate 6 becomes linearly polarized light and enters the beam splitter 7, and the transmitted light reaches the spatial light modulator 15. The polarization direction is determined in relation to the operation of the spatial light modulator 15, and will be described later. The same applies to the case where the light source 3 originally emits linearly polarized light.
[0041]
The light incident on the beam splitter 7 is branched at a rate of, for example, about 90% of transmission and about 10% of reflection. The reflected light enters the light source monitor system 12, is collected by the lens 13 of the light source monitor system 12, and the photodetector 14 detects the intensity of the reflected light. As a result, it is possible to monitor the fluctuation of the output of the light source 3 due to the environmental temperature and the like, and control the light source 3 based on the output signal via control means (not shown) to stabilize the output.
[0042]
On the other hand, the light transmitted through the beam splitter 7 enters the spatial light modulator 15. The first region 152 of the spatial light modulator 15 is a device in which each pixel 151 in the region through which the light beam 17 passes passes light (the first passing light beam) according to the two-dimensional page data to be recorded as information. ) Is controlled to add transmittance modulation. However, in the case of digital data, each pixel may be controlled to either a bright state or a dark state. The light beam subjected to the transmittance modulation becomes information light. Generally, when transmittance modulation is performed using a liquid crystal element, light incident on the liquid crystal layer is linearly polarized, and a polarizing plate is provided behind the liquid crystal layer. Also in the present embodiment, when a liquid crystal element is used as the spatial light modulator 15, a polarizing plate is provided behind the liquid crystal layer (detailed illustration is omitted). At this time, the direction of the polarizing plate provided behind the liquid crystal layer is determined so that the polarization direction of the light passing through the polarizing plate is S-polarized when viewed from the polarizing beam splitter 18.
[0043]
In such a state, the polarization direction of the light beam 17 incident on the liquid crystal element as the spatial light modulator 15 is determined by the properties of the liquid crystal layer used, and whether or not an electric field is applied to each pixel and the relationship between the light and dark states. For example, when an electric field is not applied to a pixel (for example, 0 as digital data), the liquid crystal layer is such that light incident on the pixel receives a 90-degree optical rotation, and then becomes a dark state, and an electric field is applied to the pixel. (For example, 1 as digital data), the liquid crystal layer is such that the light incident on the pixel is not subjected to optical rotation, and if it is in a bright state at that time, the spatial light modulator 15 composed of a liquid crystal element is used. The polarization direction of the incident light is selected as S-polarized light (polarized light perpendicular to the paper surface of FIG. 3). If the relationship between the digital data (0, 1) and the brightness of each pixel is reversed, the polarization direction of the incident light beam 17 is selected to be P-polarized light (polarized light parallel to the plane of FIG. 3).
[0044]
On the other hand, the second area 153 of the spatial light modulator 15 is an area through which a light beam (second passing light beam) serving as recording reference light in holographic recording passes. In principle, holographic recording can be performed without applying any modulation to the recording reference light. Therefore, this portion should be left blank, that is, the spatial light modulator 15 should be composed of only the first region 152. Is also possible.
[0045]
However, providing a plurality of pixels 151 through which a light beam passes in the second region 153 of the spatial light modulator 15 has the following advantages.
For example, if the transmittance of the second area 153 is controlled according to the overall brightness of the light passing through the first area 152, the information is formed on the photosensitive layer by holographic exposure when recording information. This is preferable because the contrast of interference fringes can be improved. In this case, it is not necessary to control the second area 153 for each pixel, and it is sufficient to uniformly control all pixels. Therefore, the second area 153 does not necessarily need to be a spatial light modulator having a large number of pixels. However, if the first region 152 and the second region 153 are configured as an integrated element, it is advantageous in terms of cost, and when separated, the luminous flux generated at the joint between the two is vignetted (vignetting). Is even more advantageous because of the elimination of When the second area 153 is configured as a phase modulation type spatial light modulator having a plurality of pixels, a predetermined phase modulation is applied to the recording reference light passing through the phase modulation type second area 153 at the time of recording. Recording (exposure) can be performed with a pattern, and a use (or reproduction method) in which only a person having the phase modulation pattern as a key can read recorded data can be performed. However, in any case, the light passing through the second region 153 is configured to be S-polarized light. Therefore, when the second region 153 for transmittance modulation or phase modulation is not provided for the light beam passing through the spatial light modulator 15, that is, when the second region is blank, The polarization plate 6 or the light source 3 is configured so that the polarization of the light 17 incident on the spatial light modulator 15 is S-polarization.
[0046]
Although the spatial light modulator 15 can be configured only with the first region 152, in the present invention, the second region 153 corresponding to the first region 152 of the spatial light modulator 15 is blank. Even if there is, the light beam passing through this blank portion is referred to as a second light beam.
[0047]
The light beam 171 that has passed through the first region 152 and the light beam 172 that has passed through the second region 153 of the spatial light modulator 15 both enter the polarization beam splitter 18 in the S-polarized state and are reflected. Thereafter, the light beam 172 enters the quarter-wave plate 19 and the light beam 171 enters the quarter-wave plate 20.
When the s-polarized light beams 171 and 172 enter the quarter-wave plates 19 and 20, respectively, the respective incident lights are emitted as the oppositely-circularly-polarized light with respect to the quarter-wave plates 19 and 20, respectively. . Here, for convenience of explanation, the quarter-wave plate 19 is a counterclockwise quarter-wave plate, and the quarter-wave plate 20 is a clockwise quarter-wave plate. Circularly polarized light and clockwise circularly polarized light (the left and right sides can be reversed).
[0048]
The light flux 172 passes through the counterclockwise quarter-wave plate 19, becomes counterclockwise circularly polarized light, enters the objective lens 22, passes through the photosensitive layer 27, and is reflected at the same time as a minimum condensed spot on the reflection layer 29. After the reflection, the light again enters the objective lens 22 through the photosensitive layer 27, and becomes a parallel light flux and enters the clockwise quarter-wave plate 20. This light beam passes through the clockwise quarter-wave plate 20 to become S-polarized light again, and is reflected by the polarization beam splitter 18.
On the other hand, the light beam 171 follows the reverse path of the light beam 172, passes through the clockwise quarter-wave plate 20, becomes right-handed circularly polarized light, enters the objective lens 22, passes through the photosensitive layer 27, and is minimized by the reflection layer 29. It is reflected at the same time as the light spot. After the reflection, the light again enters the objective lens 22 through the photosensitive layer 27, and becomes a parallel light beam and enters the counterclockwise quarter-wave plate 19. This light beam passes through the counterclockwise quarter-wave plate 19, becomes S-polarized light again, and is reflected by the polarization beam splitter 18.
[0049]
When light enters and exits the transparent substrate layer 26 of the medium 2, the light is refracted according to the refractive index of the transparent substrate layer 26, but is not a matter related to the essence of the present invention. In the drawings, the refraction state is omitted.
[0050]
Here, an area where the light beam 172 first passes through the photosensitive layer 27 is an exposure area (first exposure area) 271, and an area where the light flux 172 passes after being reflected by the reflection layer 29 is an exposure area (second exposure area) 272. The light beam 171 as the information light (object light) travels as clockwise circularly polarized light in any exposure region, and the light beam 172 as the recording reference light travels as counterclockwise circularly polarized light in any exposure region in the opposite direction. Therefore, as a result of the interference between the two, the two-dimensional page data expressed in the first area 152 of the spatial light modulator 15 is applied to each of the exposure area 271 and the exposure area 272 of the photosensitive layer 27 as an interference pattern, ie, holographically. Recorded in. More precisely, the interference between the exposure area 271 and the exposure area 272 of the photosensitive layer 27 is caused by the fact that the first area 152 of the spatial light modulator 15 has a Fresnel diffraction pattern passing through the objective lens 22 and the like, 153 can be considered as a Fresnel diffraction pattern passing through the objective lens 22 and the like. The holograms formed in the exposure regions 271 and 272 of the photosensitive layer 27 are reflection holograms.
[0051]
At the time of this recording, focusing control, tracking control, and the like are simultaneously performed as follows.
The returning light beams 171 and 172 that have passed through the photosensitive layer 27 and the like and are reflected again by the polarization beam splitter 18 as S-polarized light pass through the spatial light modulator 15 again. At the time of recording, the first area 152 of the spatial light modulator 15 expresses the information of the two-dimensional page data to be recorded as a light-dark pattern. Since the light beam passes through the 15 first regions 152 and the second regions 153 as parallel light beams, the cross section of the returning light beam incident on the beam splitter 7 has a generally bright and dark pattern symmetrical with respect to the optical axis 16. A part of the returning light beam having a light-dark pattern symmetrical with respect to the optical axis 16 is reflected by the beam splitter 7 and enters the signal detection system 8, so that the signal detection system 8 has a CD structure and operation. The focus signal can be generated by a known astigmatism method, the tracking signal can be generated by a known push-pull method, and the RF signal can be generated by a known method. Can be. However, an RF signal is generated mainly when a conventional optical disc such as a CD is reproduced. In this manner, according to the optical information recording / reproducing apparatus of the present embodiment, it is possible to simultaneously perform recording on the medium 2 and focusing control and tracking control based on generation of the focusing signal and the tracking signal.
[0052]
When most of the pixels in the first area 152 of the spatial light modulator 15 are in a dark state, the light entering the signal detection system 8 is too weak to generate a predetermined signal, so that the pixels in the first area 152 Some should always be in the bright state. Alternatively, it is also possible to use a method in which two pixels are set to one bit, and one of the pixels is always bright and the other is dark. However, in this case, care must be taken because the amount of information that can be expressed on one page is reduced by half. Alternatively, if the recording by exposure to the medium 2 and the focusing control and the tracking control based on the generation of the focusing signal and the tracking signal are performed not alternately but alternately, the moment when the focusing signal and the tracking signal are generated is performed. , All pixels in the first region 152 of the spatial light modulator 15 can be in a bright state. However, the focusing control and the tracking control based on the generation of the focusing signal and the tracking signal are performed when the light-condensing spot is located between a certain exposure area and the next exposure area in the photosensitive layer 27 for recording on the medium 2. And the output of the light source 3 is lowered.
[0053]
The land 31 and the groove 32 provided on the medium 2 serve as a reference for the position in the radial direction (radial direction of the disc) at the time of recording (writing), as in the conventional write-once optical disc. Therefore, in the radial direction, recording (exposure) is performed at a position corresponding to the land 31 or the groove 32 of the photosensitive layer 27 to be recorded. The recording position control in the tangential direction (tangential direction of the track) is performed by timing control.
As can be understood from the above description, according to the optical information recording / reproducing apparatus of the present embodiment, it is also possible to perform recording by a conventional recording method using a conventional write-once optical disc as a medium.
[0054]
Next, an operation for reproducing recorded information will be described with reference to FIGS. 4, 5, and 6. FIG. FIGS. 5 and 6 are enlarged views of the vicinity of the exposure areas 271 and 272 of the medium 2. As shown in FIG. 4, the operation until the light from the light source 3 is guided to the light source monitor 12 and the output of the light source 3 is controlled is the same as that in the recording shown in FIG. However, the output of the light source 3 is controlled so low that the contrast of the interference fringes formed in the exposure regions 271 and 272 is not reduced by re-exposure during reproduction. All the pixels of the spatial light modulator 15 having a large number of pixels 151 that can be controlled independently are controlled to be in a bright state, and light passes through the first region 152 and the second region 153. At this time, the light beam 173 that has passed through the first region 152 and the light beam 174 that has passed through the second region 153 are both S-polarized.
[0055]
First, regarding the light beam 174, the light beam 174 is reflected by the polarization beam splitter 18, becomes a left-handed circularly polarized light through a left-handed quarter-wave plate 19, passes through the objective lens 22, and serves as reference light for reproduction. The exposure area 271 is irradiated. As a result, as shown in FIG. 5, a reflected diffracted light 33 is generated, and a zero-order diffracted light 34 that is transmitted as it is is generated. The reflected diffracted light 33 is reproduction light corresponding to the clockwise circularly polarized information light during recording, but is actually elliptically polarized light. Therefore, although the light becomes elliptically polarized light even after passing through the counterclockwise quarter-wave plate 19, it contains a strong P-polarized component, and this P-polarized component passes through the polarizing beam splitter 18, passes through the imaging lens 23, and is reproduced. The two-dimensional page data to be projected is projected on a part of the two-dimensional image sensor 24 (in FIG. 4, the right half of the sensor surface symmetrical about the optical axis 25).
[0056]
On the other hand, the zero-order diffracted light 34 transmitted through the exposure region 271 is reflected by the reflection layer 29 and irradiates the exposure region 272. As a result, the reflected diffracted light 35 is generated, and the zero-order diffracted light 36 that is transmitted as it is is generated. Like the reflected diffracted light 33, the reflected diffracted light 35 is also reproduction light corresponding to the clockwise circularly polarized information light at the time of recording. After being reflected by the reflecting surface 29, it undergoes the same operation as the reflected diffracted light 33. The image is projected on a part of the dimensional image sensor 24 (in FIG. 4, the right half of the sensor surface). At this time, the reproduction pattern on the two-dimensional image sensor 24 by the reflected diffraction light 33 and the reproduction pattern on the two-dimensional image sensor 24 by the reflection diffraction light 35 are almost the same. Both the reflected and diffracted light 33 and the reflected and diffracted light 35 correspond to a direct image in general holography.
[0057]
On the other hand, the 0th-order diffracted light 36 transmitted through the exposure area 272 is left-handed circularly polarized light. When passing through the right-handed quarter-wave plate 20, the light becomes S-polarized light and is reflected by the polarization beam splitter 18 to be two-dimensionally imaged. It does not enter the sensor 24. Therefore, unnecessary background light (0th-order diffracted light), which is a factor of deteriorating the signal-to-noise ratio during reproduction, is separated from the information signal light entering the two-dimensional image sensor 24. At the same time, the 0th-order diffracted light 36 separated from the information signal light entering the two-dimensional image sensor 24 by being reflected by the polarization beam splitter 18 is partially reflected by the beam splitter 17 and enters the signal detection system 8.
[0058]
Next, regarding the light beam 173, the light beam 173 is reflected by the polarization beam splitter 18, passes through the clockwise quarter-wave plate 20, becomes right-handed circularly polarized light, passes through the objective lens 22, and passes through the reference lens for reproduction. The exposure area 272 is irradiated. As a result, as shown in FIG. 6, a reflected diffracted light 37 is generated, and a zero-order diffracted light 38 that is transmitted as it is is generated. The reflected diffracted light 37 is light corresponding to a conjugate image in general holography. The reflected diffracted light 37 becomes elliptically polarized light after passing through the clockwise quarter-wave plate 20, and its P-polarized light component passes through the polarizing beam splitter 18, passes through the imaging lens 23, and is converted into two-dimensional page data to be reproduced. The image is projected on a part of the two-dimensional image sensor 24 (in FIG. 4, the left half side of the sensor surface symmetrical about the optical axis 24).
[0059]
On the other hand, the zero-order diffracted light 38 transmitted through the exposure region 272 is reflected by the reflection layer 29 and irradiates the exposure region 271. As a result, the reflected diffracted light 39 is generated, and the zero-order diffracted light 40 that is transmitted as it is is generated. Like the reflected diffracted light 37, the reflected diffracted light 39 is also light corresponding to a conjugate image in general holography. (In FIG. 4, the left half of the sensor surface). At this time, the reproduction pattern on the two-dimensional image sensor 24 by the reflected diffraction light 37 and the reproduction pattern on the two-dimensional image sensor 24 by the reflection diffraction light 39 are almost the same.
[0060]
On the other hand, the 0th-order diffracted light 40 transmitted through the exposure region 271 is clockwise circularly polarized light. When passing through the counterclockwise quarter-wave plate 19, it becomes S-polarized light and is reflected by the polarization beam splitter 18. Does not enter 24. Therefore, also in this case, unnecessary background light (0th-order diffracted light) which causes a deterioration in the signal-to-noise ratio during reproduction is separated from the information signal light entering the two-dimensional image sensor 24. At the same time, the 0th-order diffracted light 40 separated from the information signal light entering the two-dimensional image sensor 24 by being reflected by the polarization beam splitter 18 is partially reflected by the beam splitter 17 and enters the signal detection system 8 to generate a light flux. A focus signal, a tracking signal, and an RF signal are generated together with the 0th-order diffracted light 36 separated from 174, and focus control and tracking control of the objective lens are performed based on the focus signal, the tracking signal, and the RF signal.
[0061]
As described above, since the same page data is projected onto two places on the two-dimensional image sensor 24, even if an error occurs in data reproduction from one place, the reproduced data from the other place is used. An error can be corrected, and information can be reproduced with extremely high reliability.
If the error correction mechanism is incorporated in the two-dimensional page data itself displayed in the first area 152 of the spatial light modulator 15, the reflected diffracted light 33 is used as the reproduction light corresponding to the recording information light. Of course, it is also possible to use only the reflected diffraction light 35. In this case, the two-dimensional image sensor 24 suffices in a half area (the area on the right half side of the sensor surface in FIG. 4), and therefore the number of pixels may be half.
[0062]
Also, if a conventional optical disk such as a CD is placed at the position of the medium 2 and all the pixels of the first area 152 and the second area 153 of the spatial light modulator 15 are in a bright state, the light incident on the disk can be reproduced. Since the reproduction light obtained by the reference light follows the same path as the transmitted zero-order diffracted light described above, a focus signal, a tracking signal, and an RF signal are obtained. That is, according to the optical information recording / reproducing apparatus of the present embodiment, it is possible to reproduce a conventional optical disc.
[0063]
As described above, according to the optical information recording / reproducing apparatus of the present embodiment, the holographic recording / reproducing apparatus is simple, and therefore can be configured at a low cost. Becomes possible. Also, compatibility with the conventional optical disk is ensured.
[0064]
In the above embodiment, a holographic recording / reproducing apparatus for a medium having a photosensitive layer has been described. However, the present invention is not limited to this, and can be used alone as a holographic recording apparatus or a holographic reproducing apparatus. .
[0065]
【The invention's effect】
As described above, according to the optical information recording / reproducing apparatus and method, the optical information recording medium, the optical information recording apparatus and method, and the optical information reproducing apparatus and method of the present invention, the holographic recording / reproducing apparatus is simple, and therefore has a low It can be constructed at a low price, and has a good signal-to-noise ratio and enables highly reliable information recording and reproduction. Also, compatibility with the conventional optical disk is ensured.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a main part of an embodiment of an optical information recording / reproducing apparatus according to the present invention.
FIG. 2 is a plan view of a spatial light modulator used in the present embodiment.
FIG. 3 is an explanatory diagram showing an operation when recording information in the optical information recording / reproducing apparatus of the embodiment.
FIG. 4 is an explanatory diagram showing an operation when recording information in the optical information recording / reproducing apparatus of the embodiment.
FIG. 5 is an explanatory diagram showing a state of a light beam 174 when reproducing information in the optical information recording / reproducing apparatus of the present embodiment by enlarging the vicinity of exposure areas 271 and 272 of a medium 2;
FIG. 6 is an explanatory diagram showing a state of a light beam 173 when reproducing information in the optical information recording / reproducing apparatus of the present embodiment, by enlarging the vicinity of exposure areas 271 and 272 of the medium 2;
[Explanation of symbols]
1. Optical system which is a main part of optical information recording / reproducing device
2 Optical information recording medium
3 light source
4 Collimator optical system
5 Beam stop
6 Polarizing plate
7 Beam splitter
8 Signal detection system
9 Lens with convex power
10. Cylindrical lens with convex power or concave power in one direction
11 4-part photodetector
12. Light source monitor system
13 Lens with convex power
14 Photo Detector
15 Spatial light modulator
151 Many independently controllable pixels
152 First Area
153 Second Area
16 Optical axis
17 Cross section of light beam incident on spatial modulator 15
18 Polarizing beam splitter
19,20 quarter-wave plate
21. Light flux incident on quarter-wave plates 19 and 20
22 Objective lens
22a Actuator
23 Imaging lens
24 2D image sensor
25 Optical axis
26 Transparent substrate layer
27 Photosensitive layer
28 Transparent buffer layer
29 Reflective layer
30 Protective layer
31 Land
32 grooves

Claims

An optical information recording and reproducing apparatus for recording information on a medium using light and reproducing the recorded information,
Means for generating a light beam having a predetermined polarization direction, a spatial light modulator, a polarization beam splitter, two quarter-wave plates, and an objective lens;
The spatial light modulator has a first region and a second region, and at least one of the first region and the second region has a plurality of pixels whose transmittance of each pixel can be modulated. , A half section of the light beam and the other half section are arranged to pass through the first region and the second region, respectively,
The polarizing beam splitter is arranged to reflect a light beam that has passed through the spatial light modulator,
The two quarter-wave plates are arranged such that a half cross section and another half cross section of the light beam reflected by the polarizing beam splitter pass through each other, and that the first axis and the slow axis are orthogonal to each other. Are arranged as
The optical information recording / reproducing apparatus, wherein the objective lens is arranged to face the medium.

The optical information recording / reproducing apparatus according to claim 1, further comprising a signal detection system that generates a focus signal, a tracking signal, and an RF signal.

3. The optical information recording / reproducing apparatus according to claim 1, further comprising a two-dimensional image sensor for reproducing information recorded on the medium.

An optical information recording medium comprising: a photosensitive layer that undergoes a refractive index modulation by light irradiation; lands and grooves formed periodically; and a reflective layer formed on the lands and grooves.

Using the optical information recording / reproducing device according to claim 1, information is recorded on the photosensitive layer of a medium having a photosensitive layer that undergoes refractive index modulation by light irradiation and a reflective layer for reflecting the irradiated light. Alternatively, an optical information recording / reproducing method comprising reproducing information recorded on the medium.

Data is displayed on a first area or a second area of the spatial light modulator, a light beam passing through the area displaying the data is used as information light, and a light beam passing through the other area is used as reference light, and 6. The optical information recording method according to claim 5, wherein information is holographically recorded on the inner photosensitive layer.

The optical information recording / reproducing apparatus according to claim 1, further comprising a signal detection system that generates a focus signal, a tracking signal, and an RF signal, and a two-dimensional image sensor that reproduces information recorded on the medium. 4. The zero-order diffracted light transmitted through the photosensitive layer in the optical information recording medium according to 4 is guided to the signal detection system to generate a focus signal and a tracking signal, and control the objective lens based on these signals. And reproducing information recorded on the optical information recording medium from an output of the two-dimensional image sensor.

In an optical information recording apparatus for recording information on a photosensitive layer of a medium by condensing each light beam of information light and recording reference light with an objective lens,
A light source that emits light applied to the medium,
A first region for generating a first passing light beam as information light modulated in accordance with information data to be recorded when passing the light emitted from the light source; and a recording area for interfering with the light beam of the information light. A spatial light modulator having a second region for obtaining a beam of reference light;
A polarizing beam splitter that guides each light beam obtained by the spatial light modulator toward the medium side,
Each of the light beams guided by the polarizing beam splitter has two quarter-wave plates arranged so as to pass through each of two quarter-wave plates whose first axes are orthogonal to each other,
An interference pattern corresponding to the information data is recorded on a photosensitive layer of the medium by causing the light beams of the information light and the recording reference light that have passed through the two quarter-wave plates to interfere with each other. Optical information recording device.

In an optical information recording method for condensing each light flux of information light and recording reference light with an objective lens and holographically recording information on a photosensitive layer of a medium,
The light emitted from the light source is converted into a light beam having a predetermined polarization direction, and a part of the light beam is passed through a first region of a spatial light modulator controlled according to information data to be recorded. The first light beam is generated as information light by modulating the light beam of the first light beam, and the second light beam serving as the recording reference light that interferes with the first light beam is generated from the remaining light beams,
Next, a first light beam that becomes the information light and a second light beam that becomes the reference light for recording are guided to the objective lens side via a polarizing beam splitter,
Thereafter, each of the first passing light beam and the second light beam has a fast axis orthogonal to each other, and the angle of the first axis with respect to the polarizing direction of the first passing light beam and the second light beam having the same polarization direction is 45 degrees. Through each of the two quarter-wave plates arranged so that
Then, information is holographically recorded on a photosensitive layer of the medium by causing each of the first light beam and the second light beam to interfere with each other.

In an optical information reproducing apparatus for reproducing information holographically recorded on a photosensitive layer of a medium,
A light source that emits light applied to the medium,
A polarizing beam splitter that guides light emitted from the light source as reproduction reference light,
Two quarter-wave plates whose first axes are orthogonal to each other and arranged so that the reproduction reference light guided to the polarizing beam splitter passes through each of them;
When each light beam of the reference light for reproduction obtained by passing through the two quarter-wave plates is irradiated on the photosensitive layer of the medium, it is obtained from information holographically recorded on the photosensitive layer of the medium. A two-dimensional image sensor arranged to project reflected diffracted light after passing through the polarizing beam splitter;
An optical information reproducing apparatus comprising:

An optical information reproducing method for reproducing information holographically recorded on a photosensitive layer of a medium,
The light emitted from the light source is guided to the polarizing beam splitter as reference light for reproduction,
The reproduction reference light guided to the polarization beam splitter has two first quarters arranged such that the first axes are orthogonal to each other and the angle of the first axis to the polarization direction of the reproduction reference light is 45 degrees. Pass through each of the one wave plates,
Each light beam of the reproduction reference light obtained by passing through the two quarter-wave plates is irradiated on the photosensitive layer of the medium, and the reflection obtained from information holographically recorded on the photosensitive layer of the medium is obtained. The diffracted light is projected on a two-dimensional image sensor after passing through the polarizing beam splitter,
An optical information reproducing method, wherein the information is reproduced by detecting the reflected diffracted light projected on a two-dimensional image sensor.

In an optical information recording / reproducing apparatus which condenses each light beam of information light and recording reference light with an objective lens to record information on a photosensitive layer of a medium, and reproduces this information using reproduction reference light,
A light source that emits light applied to the medium,
When passing light emitted from the light source at the time of recording, a first area for generating an information light modulated in accordance with information data to be recorded, and a recording reference light that interferes with the information light. A spatial light modulator having a second region for obtaining, and generating a reference light for reproduction by passing light emitted from the light source during reproduction through the first region and the second region;
The information light at the time of recording and the reference light for recording and the reference light for recording obtained at the time of reproduction obtained by the spatial light modulator are reflected toward the medium side, and the reproduction light obtained from the photosensitive layer of the medium at the time of reproduction is reproduced. A transmitting polarizing beam splitter,
The two quarters are arranged such that the information light and the recording reference light reflected by the polarization beam splitter pass through each of two quarter-wave plates whose first axes are orthogonal to each other. A wave plate,
The information light having passed through the two quarter-wave plates and the recording reference light interfere with each other to record an interference pattern corresponding to the information data on a photosensitive layer of the medium, and the two four-wavelength plates are reproduced during reproduction. An objective lens for irradiating the recorded reference pattern with the reproduction reference light that has passed through the half-wave plate,
When the reproduction reference light that has passed through the two quarter-wave plates is irradiated on the photosensitive layer of the medium, the reflected diffraction light obtained from the information recorded on the photosensitive layer of the medium is converted into the two diffracted lights. A two-dimensional image sensor arranged to project after passing through a quarter-wave plate and the polarizing beam splitter;
An optical information recording / reproducing device comprising:

An optical information recording / reproducing method in which each light flux of the information light and the recording reference light is condensed by an objective lens to record information on a photosensitive layer of a medium, and the information is reproduced using a reproduction reference light,
At the time of recording, light emitted from a light source is converted into a light beam having a predetermined polarization direction, and a part of the light beam is passed through a first area of a spatial light modulator controlled according to information data to be recorded. While generating light, generating a recording reference light that interferes with the information light from the remaining light flux,
Next, the information light and the recording reference light are guided to a polarizing beam splitter,
Next, each of the information light and the recording reference light guided to the polarization beam splitter is firstly orthogonal to each other, and the first direction with respect to the polarization direction of the information light and the recording reference light having the same polarization direction. Passing through each of the two quarter-wave plates arranged such that the angle of the axis is 45 degrees,
Thereafter, a step of holographically recording information on the photosensitive layer of the medium by causing the information light and the recording reference light to interfere with each other,
At the time of reproduction, light emitted from the light source is guided to the polarization beam splitter by obtaining a reproduction reference light by passing through the spatial light modulator as a light beam having the predetermined polarization direction,
Next, the reference light for reproduction guided to the polarization beam splitter is passed through each of the two quarter-wave plates,
The reproduction reference light obtained by passing through the two quarter-wave plates is irradiated on the photosensitive layer of the medium, and the reflected diffracted light obtained from the photosensitive layer of the medium is reflected by the two quarter-wavelength plates. After passing through the plate and the polarizing beam splitter, it is projected on a two-dimensional image sensor,
Reproducing the information by detecting the reflected diffracted light projected on the two-dimensional image sensor;
An optical information recording / reproducing method, comprising: