JP3830770B2 - Hologram recording medium and hologram type information recording / reproducing apparatus - Google Patents

Description

上下の石英ガラス６ａ、６ｂは、ホログラム記録層の上下表面を整形し、ホログラム記録層を保護するためのものであるため、このような目的を果たし、かつ耐熱性がある透明な物質であれば石英以外を用いることは可能である。同様に、スペーサー５も第１の実施の形態においてはフッ素樹脂を用いているが、耐熱性を有し容易に変形しない材質のものであれば、
フッ素樹脂以外の材質をスペーサーとして用いても構わない。
【００２５】
第１の実施の形態にかかるホログラム記録媒体を構成するホログラム記録層には上記のマトリックス材１、光酸発生剤２、色素３が、重量比にして９６：２：２の割合で混在しており、これらの構成要素はホログラム記録層中に均一に分布している。光酸発生剤２及び色素３のマトリックス材１に対する割合は上記以外のものでも構わないが、光酸発生剤２及び色素３の割合が大きくなった場合、記録しようとする領域以外での光の吸収が無視できなくなる。それによりホログラム記録媒体の回折効率が低下するという欠点を生じることから、光酸発生剤２及び色素３の割合は一定の値以下とすることが望ましい。なお、図１及び図２はあくまで模式図であり、ホログラム記録媒体の構造の理解を容易にするためのものであってホログラム記録層４ｂについて、図１によって光酸発生剤２及び色素３の割合及びこれらを構成する粒子の大きさが決定されるのではない。
【００２６】
マトリックス材１はポリメチルメタクリレート以外であっても、透明度が高くて容易に熱変形せず、ホログラム記録層中で発生する酸が熱拡散することが可能であればマトリックス材１として使用が可能である。具体的なマトリックス材１の原料としてポリスチレン、ポリカーボネート等の高分子化合物や、ゾル−ゲル法により作製された無機ガラス等が挙げられる。なお、ホログラム記録層中で発生する酸の熱拡散を容易とする観点からはマトリックス材１は非晶質構造をとることが望ましい。
【００２７】
光酸発生剤２は、ジフェニルヨードニウムヘキサフルオロリン酸以外であっても、特定波長の励起光に対し活性化し、酸を発生するものであれば構わない。具体的にはスルフォニウム塩、ジアゾニウム塩、フォスフォニオウム塩等が光酸発生剤２の原料として挙げられる。
【００２８】
色素３は上記の化学式１に記載した化合物以外であっても、酸と反応して吸光係数が変化するものであれば構わない。具体的には、シアニン、メロシアニン誘導体、クマリン誘導体、カルコン誘導体などが色素３の原料として挙げられる。
【００２９】
次に、第１の実施の形態にかかるホログラム記録媒体の製造方法について説明する。
【００３０】
（イ）マトリックス材１の原料であるポリメチルメタクリレートと、光酸発生剤２の原料であるジフェニルヨードニウムヘキサフルオロリン酸と、色素３の原料である上記の化学式１記載の色素を、重量比が９６：２：２となるよう混合し、これを溶媒である乳酸エチルに溶解させる。
【００３１】
（ロ）乳酸エチルに溶解させた原料を、３時間攪拌する。光酸発生剤２及び色素３とマトリックス材１を乳酸エチル中に均一に分散させるためである。
（ハ）溶解した原料が均一に分散した乳酸エチルを、図３（ａ）に示すように縦と横がそれぞれ３ｃｍ、厚さ0.5mmの大きさの石英ガラス６ａ上にキャストする。
【００３２】
（ニ）石英ガラス６ａの温度をヒーターを使って１２０度に加熱し、１時間その状態を維持する。その結果、溶媒の乳酸エチルは蒸発し、ホログラム記録層４ｂが得られる。
【００３３】
（ホ）石英ガラス６ａ上であって、乳酸エチルがキャストされていない領域上に図３（ｂ）に示すようにスペーサー５を配置する。スペーサー５はフッ素樹脂からなり、スペーサー５の高さは５０μｍである。さらに石英ガラス６ａとは別の石英ガラス６ｂを用意し、この石英ガラス６ｂをスペーサー５及び上記のホログラム記録層４ｂの上部に配置する。
【００３４】
（へ）石英ガラス６ａを１２０度の温度に保ったままで、図３（ｃ）に示すように石英ガラス６ｂの上部からホログラム記録層４ｂに対して均一に圧力を加える。ホログラム記録層４ｂは上からの圧力により横に引き延ばされる。２つのスペーサー５と石英ガラス６ｂが密着することにより、ホログラム記録層４ｂの厚さが均一に５０μｍとなる。
【００３５】
（ト）図３（ｄ）に示すようにホログラム記録層４ｂの厚さが均一になるまで整形された後、全体の温度を室温にまで下げる。全体の温度を下げるためには石英ガラス６ａを低温の金属と接触させる方法や、水や液体窒素の中に投入する等の方法がある。この冷却工程を時間をかけて行ってもホログラム記録媒体は得られるが、急冷する方が望ましい。結果物が非晶質となると光酸発生剤２が熱拡散しやすい構造となり、より良質なホログラム記録媒体が得られるためである。以上で第１の実施の形態にかかるホログラム記録媒体が完成する。
【００３６】
次に、第１の実施の形態にかかる透過型ホログラム情報記録再生装置の構造について図３を用いて説明する。
【００３７】
第１の実施の形態にかかる透過型ホログラム情報記録再生装置は、アルゴンレーザー（λ＝４８８ｎｍ）を用いた光源６と、光源６から生ずる可干渉光を参照光１６と記録光１７に分離する機能を有するビームスプリッター７を含む。また、記録光１７の光路上にはビームスプリッター７の近くから順にミラー９、空間変調器１１、電磁シャッター１２が配置され、参照光１６の光路上にはビームスプリッター７の近くから順にミラー８、ニュートラルデンシティーフィルター１０が配置されている。ホログラム記録媒体４はその下部において銅板１４によって固定され、銅板１４には記録光及び参照光を通過させるための光通過孔１４ａ、１４ｂが設けられている。銅板１４の下部にはヒーター１８ａが配置されている。ヒーター１８ａは温度コントローラー１８ｃと接続され、温度コントローラー１８ｃは熱電対１８ｂを通してホログラム記録媒体４と接続されている。このことによりホログラム記録媒体４は温度コントローラー１８ｃで設定した一定の温度に保たれる。また、記録光１７と参照光１６はホログラム記録媒体４の上面から入射し、ホログラム記録媒体内部の記録領域１３において記録光１７と参照光１６は交差する構造となっている。また、記録光１７がホログラム記録媒体を通過した後の記録光１７の光路上には、光検出器１５が配置されている。
【００３８】
ここで光源６には、可干渉性の光を出射するものであって光酸発生剤２を励起して酸を発生させる波長を出射するものであれば、レーザー以外の光源を用いても構わない。また、レーザーを用いた場合でもアルゴンレーザー以外にＨｅ−Ｎｅレーザー、ＹＡＧレーザー、半導体レーザーなどを用いることが可能である。特に半導体レーザーを用いた場合、光源６を小型化する事が可能でありホログラム情報記録再生装置を小型化する事ができるという利点が生ずる。また、半導体レーザーを光源６に使用した場合に、レーザーを構成する半導体の混晶の比を調整することで多様な発振波長を実現できるため、光酸発生剤に合わせて光源６の波長を変更でき、光酸発生剤２の選択の幅が広がるという利点もある。なお、光源６の発振波長は色素３を直接励起する波長でないことが望ましい。色素３が直接励起された場合、光源６の波長の光に対する吸光係数が変化することになり、回折効率の点で不利が生ずるためである。
【００３９】
銅板１４は、ホログラム記録媒体４を固定する目的で設けられるものであるため、固定できるものであれば銅板に限定する必要はない。銅板に参照光１６及び記録光１７を通すために光通過孔１４ａ、１４ｂを設けた構造以外に、銅板の代わりに透明な物質を用いた構造も望ましい。さらにはホログラム記録媒体４を側面から固定する構造も、光学的なロスが生じないため望ましい。
加熱装置は、ホログラム記録媒体４を加熱するためのものであって、この目的を達成するものである限り、様々な形態が可能である。ヒータをホログラム記録媒体に直接接触させて加熱する構造のものでも、ホログラム記録媒体周辺の環境の温度を上昇させることによる間接加熱構造のものや電磁波照射による輻射加熱でもよい。その他の手段であっても記録光未照射の領域の特性が変化せず、酸が周囲の色素にまで拡散できる方法であれば加熱装置として用いることが可能である。また、図３においては銅板１４の下にヒーターが配置されているが、ヒーターの位置はこれに限定されず、ホログラム記録媒体４の側面部に配置することも可能であり、さらには銅板１４の内部に含めても構わない。参照光１６及び記録光１７の光路を妨げず、効率的にホログラム記録媒体４を加熱できる位置であれば良い。
【００４０】
また、空間変調器１１は、記録光１７の位相や波長などを空間的に変調する装置である。
【００４１】
次に、第１の実施の形態にかかるホログラム記録媒体４及び透過型ホログラム情報記録再生装置を用いた情報の記録方法について図３及び図１を用いて以下に説明する。
【００４２】
光源６から発射された光は、ビームスプリッター７で参照光１６と記録光１７に分離される。参照光１６は、ビームスプリッター７を通過後、ミラー８によって方向が変更され、その後、記録光１７と同一レベルの強度とするため、参照光１６はニュートラルデンシティーフィルター１０で強度の調整を受ける。光源６とニュートラルデンシティーフィルター１０は記録領域１３における参照光１６及び記録光１７の光強度が３ｍＷとなるよう調整されている。その後参照光１６はホログラム記録媒体４に入射する。記録光１７は、ミラー９で方向を変換された後、空間変調器１１で位相が変調され、開いた状態の電磁シャッター１２を通過後、ホログラム記録媒体４に入射する。ここで空間変調器１１で行われる記録光１７の位相変調とは、記録領域１３で記録する情報に応じて行われる。例えば、１の情報を記録する場合は記録領域１３において記録光１７と参照光１６が強め合うように位相を変調し、０の情報を記録する場合は記録領域１３において記録光１７と参照光１６が弱め合うよう位相を変調する。
【００４３】
記録領域１３において、参照光１６と記録光１７は交差する。この際に干渉がおこり、光が強めあった場合、記録領域１３に存在する光酸発生剤２が光と反応して酸を発生する。
【００４４】
記録領域１３において記録しようとする情報に応じて光酸発生剤２より酸が発生した後、加熱装置によってホログラム記録媒体４が加熱される。ヒーター１８ａにより銅板１４が加熱されるが、加熱温度を８０度に保つため、温度コントローラー１８ｃによって温度調整を行う。加熱は１分間行う。ホログラム記録媒体４が加熱されることによって、情報の記録の過程で発生した酸が、熱によって周囲に拡散し、複数の色素３と接触する。色素３は酸と反応して吸光係数が変化する性質を有するため、記録領域１３における参照光１６に対する屈折率が変化する。
【００４５】
光の照射によって記録領域３０における屈折率が変化する具体的なメカニズムは以下の通りである。
図５において、曲線１は第１の実施の形態にかかるホログラム記録媒体４全体の吸収スペクトルを示すグラフである。この曲線１は情報が記録されていない状態での吸収スペクトルを示している。また、曲線２は色素３による吸収スペクトルを示し、曲線３は光酸発生剤２による吸収スペクトルを示している。
【００４６】
一方、図６は、ホログラム記録媒体４に対して波長が４８８ｎｍのアルゴンレーザーを照射して、媒体を加熱する事により情報を記録した後の、ホログラム記録層４ｂにおける吸収スペクトルを示すグラフである。図５と図６を比較すると、光源の波長４８８ｎｍ付近の吸光度が減少するものの、それよりも４８８ｎｍよりも短波長側、４３７ｎｍをピークとする４００〜４６０ｎｍの領域で吸光度が顕著に減少する。これは、光酸発生剤２により発生した酸が、複数の色素３と連鎖的に反応するため、光酸発生剤２による吸光度よりも色素３による吸光度の現象の方が顕著に現れるためである。
【００４７】
この吸収スペクトルとホログラム記録層４ｂの屈折率の間には、次の関係式が成立する。
【００４８】
ｎ_λ ²＝ｎ∞^２＋Ｄλ０^２/（λ^２−λ０^２） ・・・・（１）
ここでｎ∞は波長が無限大の時の屈折率、Ｄは媒体中の光を吸収するサイトの振動子強度により決まる値であり、λ０は吸光度が最大となる波長であり、第１の実施の形態にかかるホログラム記録媒体４では４３７ｎｍである。ここで、情報の記録前と記録後を比較するとホログラム記録層４ｂの吸光係数が減少するため、Ｄの値が減少し、参照光の波長λ＝４８８ｎｍにおいての屈折率が減少する。屈折率が減少することにより、参照光を入射した際に回折が生じて情報の再生が可能となるのである。また、図５，図６及び式（１）から、第１の実施の形態において、ホログラム記録前後での媒体の吸光度の変化が小さく、かつ、効率よく屈折率を減少させてホログラムの記録再生を行うためには、記録光１７と参照光１６の波長λが光酸発生剤２のみを励起し、λ−λ０の絶対値が最小となるような光源６を用いることが望ましい。
【００４９】
次に、記録した情報を再生する方法について説明する。情報の再生は参照光１６のみをホログラム記録媒体４に照射して行う。再生過程においても光源６から出射された光はビームスプリッタ７によって参照光１６と記録光１７に分離されるが、記録光１７はその光路の途中で電磁シャッター１２を閉じておくことで遮断され、ホログラム記録媒体４には入射しない。
【００５０】
入射した参照光１６は記録領域１３において回折し、回折光は情報記録時における記録光１７の光路上を通る。この回折光は記録光１７が有していた空間的な変調情報を再現するため、光検出器１５において、記録光１７が有していた空間的な変調情報を検出することができる。光検出器１５において検出された光情報は電気的信号に変換され、データとして出力される。
【００５１】
次に第1の実施の形態にかかる透過型ホログラム情報記録再生装置の性能を測るため、回折効率及び角度多重記録性能について実験した。この実験において回折効率とは、再生時において入力する参照光１６の強度と、光検出器１５において検出する回折光の強度の比を１００倍したもので、％を単位として表される。また、角度多重記録性能は、グラフの参照光１６の入射角度に対するピーク幅で判断される。
【００５２】
透過型ホログラム型情報記録再生装置は図３に示す装置を用い、ホログラム記録媒体４もマトリックス材１、光酸発生剤２及び色素３について第１の実施の形態と同じ物質を用いた。
【００５３】
情報の記録は記録光１７および参照光１６を３ｍWとし、１秒間照射する事によって行った。記録領域はホログラム記録層の表面から３０μｍの深さに設定した。
【００５４】
記録光１７および参照光１６を照射した後、加熱装置によって銅板を80℃に加熱し、1分間発生した酸を拡散させ、周囲の色素３と連鎖的に反応させ、情報を記録した。
【００５５】
情報の再生は、記録光１７を、電磁シャッター１２を閉じる事により遮断し参照光１６のみをホログラム記録媒体４に入射させる事によって行う。通常においては、参照光１６の入射角度を記録時と同じ角度に設定して情報の再生を行うが、本発明では角度多重記録性能についても調べるため、記録時の参照光１６の入射角度を0度として、参照光の角度を変化させて、回折効率を測定した。また、光源６は記録の際と同じものを使用し、参照光１６の強度は0.3mWとした。
【００５６】
再生された情報を検知するための光検出器１５としてはフォトダイオードを採用し、フォトダイオードは記録光１７の光路の延長上に固定して回折光の測定を行った。
【００５７】
以上の条件で測定した結果を図７の曲線1に示す。参照光１６の入射角度が記録時と同じ角度のとき、即ちグラフ中の0度において鋭いピークを示し、回折効率も10％の値を示した。半値幅が狭く、ピーク強度が強いことから、第1の実施の形態にかかる透過型ホログラム型情報記録再生装置において、同一領域に多数の情報を書き込む事が可能であることが明らかとなった。すなわちグラフより、記録する際の参照光の入射角度を約0.5度かえることにより既に書きこんだ情報と区別して新たに情報を書き込む事が可能と考えられ、理論的には同一領域に３６０bitの情報を書き込む事ができる。従来の光記録媒体では同一領域に１bitの情報しか書きこめないため、記録媒体の大きさが同じ場合、第１の実施の形態にかかるホログラム記録媒体４では記録容量が飛躍的に増大すると考えられる。また、この実験において記録領域１３はホログラム記録媒体４の表面から30μmの深さであってこの深さでも記録が可能である事から、ホログラム記録媒体４の表面付近のみならず、内部においても十分記録が可能である事が実証された。従来のホログラム記録媒体では表面近傍でのみ記録が可能であったのに対して、第1の実施の形態にかかるホログラム記録媒体４は大きな利点を有するといえる。また、以下に述べる比較例と比べ回折効率が非常に高い事から、読みこむ際の感度が高くなる事も明らかとなった。
【００５８】
比較のため、従来技術による回折効率及び角度選択性を示すグラフを曲線2に表す。曲線2は第1の実施の形態とは異なり、色素を直接励起する光を照射して色素の吸光係数を変えることにより、記録領域の屈折率を変化させるホログラム記録媒体を用いた結果である。客観性を担保するため、色素、マトリックス材は第1の実施の形態のホログラム記録媒体と同じ物を用い、色素の濃度も第1の実施の形態のホログラム記録媒体と同じ値である。また、光源の波長は、色素を直接励起させるため第1の実施の形態と異なりλ＝457.9nmのアルゴンレーザーを用いたが、それ以外の光源の強度、照射時間などの値は第1の実施の形態についての実験と同じである。
【００５９】
曲線2に示された結果は第1の実施の形態についての結果を示す曲線1と比べ、回折効率においても、角度多重記録性能においても、大きく劣る事が分かる。回折効率が低い事から、読みこむ際には十分な感度を得るために参照光の強度を強めることが必要である。回折効率が低い値となるのは光源の波長と、色素の吸収スペクトルが一致するため、色素の吸光係数が変化する事によってホログラム記録媒体の光透過率が低下するためと思われる。また、ピーク幅が広い事から、同一領域に記録できる情報の数も、第1の実施の形態にかかるホログラム記録媒体に比べて少なくなる。
【００６０】
また、第１の実施の形態に係るホログラム記録媒体４について、情報の記録前後における形状変化を調べた。原子間力顕微鏡により記録領域１３付近の凹凸は１ｎｍ以下であり、ホログラム情報記録によるホログラム記録媒体４の形状変化はほとんど観察されなかった。
【００６１】
以上の実験から、第1の実施の形態にかかる透過方ホログラム情報記録再生装置及びそれに用いたホログラム記録媒体は、従来の技術と比較して優れた性質を示す事が明らかとなった。
【００６２】
第１の実施の形態にかかるホログラム記録媒体を使用することで、以下の利点がある。
【００６３】
第１に光酸発生剤２の光に対する反応によって生じた酸は熱により拡散し、複数の色素３と連鎖的に反応する。従って光子１個が記録領域４に照射されると、領域付近の複数の色素３の吸光係数が変化する。従来の技術では光子１個に対し、１個の分子が反応して屈折率が変化するのみであったため、第１の実施の形態にかかるホログラム記録媒体４を従来の技術と比較すると一定の量の光によって光学特性が変化する物質の量が飛躍的に増加し、ホログラム記録媒体４の書き込み感度が向上する。従って同じ感度ならば光酸発生剤の量を少なくすることが可能で、それにより記録後のホログラム記録媒体４の、光源の波長の光に対する吸光度の変化を低く抑えられ、媒体の透明性を向上させることができる。
【００６４】
第２に、光と反応する役割と、記録領域の吸光係数を変化させる役割を、別々の物質が担っている。このことにより、それぞれの用途に適した物質を個別に選択することが可能となる。従来は記録物質として、光と反応しかつ屈折率を変化させるという２つの条件を一度に満たす物質を選択せねばならず、物質の選択肢が限られていた。
【００６５】
第３に、記録光照射後、加熱装置によってホログラム記録媒体４を加熱するという簡易な方法によって現像が行われる。従って複雑な化学処理によって現像を行う従来の記録媒体に比べ、ホログラム情報記録装置を簡便な構造で実現でき、現像処理工程が単純なため記録媒体にかかる負担も少ない。さらに、現像液のような化学物質を媒体内部に浸透させる必要もないため従来例のようにマトリックス材１にゼラチン層を用いる必要もない。
【００６６】
第４に、記録光１７及び参照光１６と異なる波長の光に対する吸光係数が変化することによって、記録領域１３の屈折率が変化する。そのため記録光１７及び参照光１６は、屈折率の変化による影響は受けるものの、吸光係数の相違による影響が少なく済む。このためホログラム記録媒体中を記録光１７及び参照光１６が通過する過程でホログラム記録媒体４に記録光１７及び参照光１６が吸収されるのを抑制することができる。従って透過度及び回折効率の点で従来よりも優れたホログラム記録媒体が実現できる。
【００６７】
（第２の実施の形態）
本発明の第２の実施の形態について図８を参照して説明する。第２の実施の形態は、ホログラム記録層において光反応促進剤に光ラジカル発生剤１９を用い、色素２０には、光ラジカル発生剤により生じたラジカルと反応して吸光係数が変化し、記録領域において光源に対して屈折率を変化させることにより情報を記録することを特徴とする。
【００６８】
第２の実施の形態において、使用する光ラジカル発生剤１９はヨードニウム塩を用いる。また、色素２０としてポルフィリン誘導体を用いる。
【００６９】
第２の実施の形態にかかるホログラム記録層を用いたホログラム記録媒体は、第１の実施の形態同様、図２に示す構造のものとする。上下の石英ガラス６ａ、６ｂは、ホログラム記録層の上下表面を整形し、ホログラム記録層を保護するためのものであるため、このような目的を果たし、かつ耐熱性がある透明な物質であれば石英以外を用いることは可能である。同様に、スペーサー５も第１の実施の形態においてはフッ素樹脂を用いているが、耐熱性を有し容易に変形しない材質のものであれば、フッ素樹脂以外の材質をスペーサーとして用いても構わない。
【００７０】
第１の実施の形態にかかるホログラム記録媒体を構成するホログラム記録層には上記のマトリックス材１、光ラジカル発生剤１９、色素２０が、重量比にして９６：２：２の割合で混在しており、これらの構成要素はホログラム記録層中に均一に分布している。光ラジカル発生剤１９及び色素２０のマトリックス材１に対する割合は上記以外のものでも構わないが、光ラジカル発生剤１９及び色素２０の割合が大きくなった場合、記録しようとする領域以外での光の吸収が無視できなくなる。それによりホログラム記録媒体の回折効率が低下するという欠点を生じることから、光ラジカル発生剤１９及び色素２０の割合は一定の値以下とすることが望ましい。なお、図１と同様に図８はあくまで模式図であり、ホログラム記録層の構造の理解を容易にするためのものであって、図８によって光ラジカル発生剤１９及び色素２０の割合及びこれらを構成する粒子の大きさが決定されるのではない。
【００７１】
マトリックス材１はポリメチルメタクリレート以外であっても、透明度が高くて容易に熱変形せず、ホログラム記録層中で発生する酸が熱拡散することが可能であればマトリックス材１として使用が可能である。具体的なマトリックス材１の原料としてポリスチレン、ポリカーボネート等の高分子化合物や、ゾル−ゲル法により作製された無機ガラス等が挙げられる。なお、ホログラム記録層中で発生する酸の熱拡散を容易とする観点からはマトリックス材１は非晶質構造をとることが望ましい。
【００７２】
光ラジカル発生剤１９は、ヨードニウム塩以外であっても、特定波長の励起光に対し活性化し、ラジカルを発生するものであれば構わない。具体的にはセレノニウム塩、アルソニウム塩等が光ラジカル発生剤１９の原料として挙げられる。
【００７３】
色素３は、ポルフィリン誘導体以外であっても、ラジカルと反応して吸光係数が変化するものであれば構わない。具体的には、キキサンテン誘導体、チオキサンテン誘導体、アズレニウム誘導体、スクアリリウム誘導体などの有機化合物が色素２０の原料として挙げられる。
【００７４】
次に、第２の実施の形態にかかるホログラム記録媒体の製造方法について説明する。
【００７５】
（イ）マトリックス材１の原料であるポリメチルメタクリレートと、光ラジカル発生剤１９の原料であるヨードニウム塩と、色素２０の原料であるポルフィリン誘導体を、重量比が９６：２：２となるよう混合し、これを溶媒である乳酸エチルに溶解させる。
【００７６】
（ロ）乳酸エチルに溶解させた原料を、３時間攪拌する。光ラジカル発生剤１９及び色素２０とマトリックス材１を乳酸エチル中に均一に分散させるためである。
【００７７】
（ハ）溶解した原料が均一に分散した乳酸エチルを、図１０（ａ）に示すように縦と横がそれぞれ３ｃｍ、厚さ0.5mmの大きさの石英ガラス６ａ上にキャストする。
【００７８】
（ニ）前述の石英ガラス６ａの温度をヒーターを使って１２０度に加熱し、１時間その状態を維持する。その結果、溶媒の乳酸エチルは蒸発し、ホログラム記録層４ｂが得られる。
【００７９】
（ホ）前述の石英ガラス６ａ上であって、乳酸エチルがキャストされていない領域上に図１０（ｂ）に示すようにスペーサー５を配置する。スペーサー５はフッ素樹脂からなり、スペーサー５の高さは５０μｍである。さらに前述の石英ガラス６ａとは別の石英ガラス６ｂを用意し、この石英ガラス６ｂを２つのスペーサー５及び上記のホログラム記録層４ｂの上部に配置する。
【００８０】
（へ）石英ガラス６ａを１２０度の温度に保ったままで、図１０（ｃ）に示すように石英ガラス６ｂの上部からホログラム記録層４ｂに対して均一に圧力を加える。ホログラム記録層４ｂは上からの圧力により横に引き延ばされる。２つのスペーサー５と石英ガラス６ｂが密着することにより、ホログラム記録層４ｂの厚さが均一に５０μｍとなる。
【００８１】
（ト）図１０（ｄ）に示すようにホログラム記録層４ｂの厚さが均一になるまで整形された後、全体のの温度を室温にまで下げる。全体の温度を下げるためには石英ガラス６ａを低温の金属と接触させる手段や、水や液体窒素の中に投入する等の手段がある。この冷却工程を時間をかけて行ってもホログラム記録媒体は得られるが、急冷する方が望ましい。結果物が非晶質となると光酸発生剤２が熱拡散しやすい構造となり、より良質なホログラム記録媒体が得られるためである。以上で第１の実施の形態にかかるホログラム記録媒体が完成する。
【００８２】
なお、第１及び第２の実施の形態にかかるホログラム記録層について、図９のような多層構造をなす構造とすることも有用である。第１及び第２の実施の形態におけるホログラム記録層が光反応促進剤と色素がマトリックス剤中に一様に分散されているのに対し、第３の実施の形態におけるホログラム記録層は、光酸発生剤２を含む光反応層２１と、色素３を含む吸収スペクトル変化層２２が交互に積層した、多層構造を有することを特徴とする。このような構造は、光反応促進剤とマトリックス材を有機溶媒に溶かしたものと、色素とマトリックス材を有機溶媒に溶かしたものを別々に用意し、石英ガラス上に色素を含む有機溶媒をキャスト若しくはスピンコートする事により成膜し、次に光反応促進剤を含む有機溶媒を真空蒸着により成膜する。以上の工程を繰り返すことにより多層構造のホログラム記録媒体を製造することができる。
【００８３】
(第３の実施の形態）
次に、第３の実施の形態にかかる反射型ホログラム型情報記録再生装置について、説明する。第３の実施の形態にかかる装置は図１１に示すように光源２３と、光源からの光を記録光３４と参照光３３の２方向に分ける機能を備えたビームスプリッター２４を有する。また、記録光３４の光路上にはビームスプリッター２４の近くから順に空間変調器２７、電磁シャッター２８が配置され、参照光３３の光路上にはビームスプリッター２４の近くから順にミラー２５、ニュートラルデンシティーフィルター２６、ミラー３１が配置されている。ホログラム記録媒体２９は記録光３４と参照光３３が交差する領域の近辺に配置され、また記録媒体２９はその右側面部において銅板３６によって固定され、記録媒体２９の左側面部には加熱装置３５が配置されている。また、記録光３４はホログラム記録媒体２９の上面から記録媒体に入射し、参照光３３はミラーの位置を調整しておくことによりホログラム記録媒体２９の下面から記録媒体に入射する構造となっている。
【００８４】
第３の実施の形態にかかる反射型ホログラム型情報記録再生装置に用いるホログラム記録媒体２９は、第１の実施の形態で用いられている光酸発生剤と色素の組み合わせでも、第２の実施の形態にかかる光ラジカル発生剤と色素の組み合わせでも構わない。また、ホログラム記録媒体中に光反応促進剤と色素が一様に分布した構造でも、第３の実施の形態にかかる光反応層と吸収スペクトル変化層からなる多層構造からなるものでも構わない。また、反射型ホログラム型の情報記録はホログラム記録媒体２９に対し上面から記録光３４が照射され、下面から参照光が照射される構造であれば可能であるため、反射型ホログラム型情報記録再生装置の形態に合わせ適宜ミラーの数を調整することが可能である。ただし、記録光及び参照光の強度の低下を抑制する観点からはミラーの数は少ない方が望ましい。また、第５の実施の形態にかかるホログラム型情報記録再生装置は１つの光源２３をビームスプリッター２４によって２つに分離する構造としているが、記録光用と、参照光用に別途２つの光源を用いても構わない。ただし、その場合波長及び位相の同期をとるための装置が別途必要となる。また、加熱装置３５を銅板３６中に組み込んだ構造とすると、ホログラム型情報記録再生装置のさらなる小型化が可能となる。なお、加熱装置３５はヒータをホログラム記録媒体に直接接触させて加熱する構造のものでも、ホログラム記録媒体周辺の環境の温度を上昇させることによる間接加熱構造のものや電磁波照射による輻射加熱でもよい。その他の手段であっても記録光未照射の領域の特性が変化せず、酸が周囲の色素にまで拡散できる手段であれば加熱装置として用いることが可能である。
【００８５】
次に、第３の実施の形態にかかるホログラム記録媒体４及び透過型ホログラム情報記録再生装置を用いた情報の記録方法について図１１を用いて以下に説明する。
【００８６】
光源２３から発射された光は、ビームスプリッター２４で参照光３３と、記録光３４に分離される。参照光３３は、ビームスプリッター２４を通過後、ミラー２５によって方向が変更され、その後、記録光３４と同一レベルの強度とするため、参照光３３はニュートラルデンシティーフィルター２６で強度の調整を受ける。その後ミラー３１によって再度方向が変更され、ホログラム記録媒体２９に下の面から入射する。記録光３４は、空間変調器２７で位相が変調され、開いた状態の電磁シャッター２８を通過後、ホログラム記録媒体２９に入射する。ここで空間変調器２７で行われる記録光３４の位相変調とは、記録領域３０で記録する情報の内容に対応して行われる。例えば、１の情報を記録する場合は記録領域３０において記録光３４と参照光３３が強め合うように位相を変調し、０の情報を記録する場合は記録領域３０において記録光３４と参照光３３が弱め合うよう位相を変調する。
【００８７】
記録領域３０において、参照光３３と記録光３４は交差する。この際に干渉がおこり、光が強めあった場合、記録領域３０に存在する光酸発生剤２が光と反応して酸を発生する。
【００８８】
次に、記録の現像の方法について説明する。記録領域３０において情報に応じて光酸発生剤２より酸が発生した後、加熱装置３５によってホログラム記録媒体２９が加熱される。従って情報の記録の過程で発生した酸が、熱によって周囲に拡散し、複数の色素３と接触する。色素３は酸と反応して吸光係数が変化する性質を有するため、記録領域１３における参照光１６に対する屈折率が変化する。
【００８９】
次に、記録した情報を再生する方法について説明する。情報の再生は参照光１６のみをホログラム記録媒体４に照射して行う。光源６から出射された光はビームスプリッタ７によって分離されるが、記録光１７はその後電磁シャッター１２を閉じることで遮断され、ホログラム記録媒体４には入射しない。
【００９０】
入射した参照光３３は記録領域３０において回折し、回折光は情報記録時における記録光３２の光路上を通る。この回折光は記録光３２が有していた空間的な変調情報を再現するため、光検出器３２において、記録光３４が有していた空間的な変調情報を検出することができる。光検出器３２において検出された光情報は電気的信号に変換され、データとして出力される。
【００９１】
(その他の実施の形態)
上述のように、本発明は第１から第３の実施の形態によって記載したが、この開示の一部をなす論述及び図面はこの発明を限定するものであると理解するべきではない。この開示から当業者には様々な代替実施の形態、実施例及び運用技術が明らかになると思われる。
【００９２】
例えば、第１から第３の実施の形態にかかるホログラム記録媒体に使用される光反応促進剤について、光酸発生剤もしくは光ラジカル発生剤に限定して解釈する必要はなく、例えば光と反応して強いアルカリやイオンを発生する物質でも光反応促進剤としての適用が可能である。その他でも光に対して不活性なマトリックス材と、それ以外の複数の物質であって光を触媒として反応し、その結果物により吸光係数が変化するような物質を組み合わせたホログラム記録媒体も可能である。
【００９３】
また、第３の実施の形態にかかる反射型ホログラム型情報記録再生装置の構造から、ホログラム型情報再生専用装置を考案することが可能である。再生専用とした場合、記録光を入射する必要がないため、ビームスプリッターやミラーなどを用いた複雑な構造は必要なく、参照光用に光源及びニュートラルデンシティーフィルタを配置すれば足りる。また、第３の実施の形態にかかる装置は、参照光３３が照射されるのがホログラム記録媒体２９に対して光検出器３２と同じ側にある。また、参照光３３及び記録光３４のホログラム記録媒体２９に対する入射角度は、干渉が生ずる限り任意に設定が可能であるため、記録光の入射角度をホログラム記録媒体２９の表面に対してほぼ垂直とした場合、近接した位置に光検出器光源を配置することが可能である。また、前述のように光源には小型の半導体レーザーを使用することが可能であり、光検出器にフォトダイオードを用いることもできる。従って、再生機構を非常に小型化することが可能で、現在のポータブルＣＤプレイヤー程度の大きさで、かつＤＶＤよりも記録容量の大きい携帯型ホログラム型情報再生専用装置が実現できる。
【００９４】
また、第１及び第３の実施の形態にかかるホログラム型情報記録再生装置の光源から出射する光の幅を広くすることも有効である。この場合、記録光に２次元的な情報を載せることが可能であるため、１度の書き込みにおいて複数の情報を記録できる。また、読み込みに際しても光検出器に例えばＣＣＤのような２次元的に光情報を読みとることが可能な装置を用いることにより１度に複数の情報を読みとることができる。従って１度に単数の情報のみ書き込み及び読みとり可能な従来の情報記録装置と比較して高速の動作が実現できる。
【００９５】
このように、本発明はここでは記載していない様々な実施の形態等を包含するということを理解すべきである。したがって、本発明はこの開示から妥当な特許請求の範囲に係る発明特定事項によってのみ限定されるものである。
【００９６】
【発明の効果】
以上説明したように本発明によれば、高い感度を有するホログラム記録媒体及びホログラム型情報記録再生装置を提供することができる。
【００９７】
また本発明によれば、高い回折効率を有するホログラム記録媒体及びホログラム型情報記録再生装置を提供することができる。
【００９８】
さらに本発明によれば、角度多重記録性能に優れたホログラム記録媒体及びホログラム型情報記録再生装置を提供することができる。
【図面の簡単な説明】
【図１】第１の実施の形態にかかるホログラム記録媒体における、ホログラム記録層を示す断面図である。
【図２】第１の実施の形態にかかるホログラム記録媒体を示す断面図である。
【図３】第１の実施の形態に係るホログラム記録媒体の製造工程を示す図である。
【図４】第１の実施の形態にかかる透過型ホログラム型情報記録再生装置を示す模式図である。
【図５】記録光照射前の、ホログラム記録媒体の吸収スペクトルを示すグラフである。
【図６】記録光照射後の、ホログラム記録媒体の吸収スペクトルを示すグラフである。
【図７】第１の実施の形態にかかるホログラム記録媒体及び従来技術にかかるホログラム記録媒体の参照光入射角度に対する回折効率を示すグラフである。
【図８】第２の実施の形態にかかるホログラム記録媒体における、ホログラム記録層を示す断面図である。
【図９】多層構造をなすホログラム記録層を示す断面図である。
【図１０】第２の実施の形態に係るホログラム記録媒体の製造工程を示す図である。
【図１１】第３の実施の形態にかかる、反射型ホログラム型情報記録再生装置を示す模式図である。
【図１２】従来例にかかる、透過型ホログラム型情報記録再生装置を示す模式図である。
【符号の説明】
１ マトリックス材
２ 光酸発生剤
３ 色素
４ ホログラム記録媒体
４ｂ ホログラム記録層
５ スペーサー
６ 光源
６ａ、６ｂ 石英ガラス
７ ビームスプリッター
８ ミラー
９ ミラー
１０ ニュートラルデンシティーフィルター
１１ 空間変調器
１２ 電磁シャッター
１３ 記録領域
１４ 銅板
１４ａ、１４ｂ 光通過孔
１５ 光検出器
１６ 参照光
１７ 記録光
１８ａ ヒーター
１８ｂ 熱電対
１８ｃ 温度コントローラー
１９ 光ラジカル発生剤
２０ 色素
２１ 光反応層
２２ 吸収スペクトル変化層
２３ 光源
２４ ビームスプリッター
２５ ミラー
２６ ニュートラルデンシティーフィルター
２７ 空間変調器
２８ 電磁シャッター
２９ ホログラム記録媒体
３０ 記録領域
３１ ミラー
３２ 光検出器
３３ 参照光
３４ 記録光
３５ 加熱装置
１１０ 光源
１１１ ビームスプリッター
１１２ ミラー
１１３ ミラー
１１４ ニュートラルデンシティーフィルター
１１５ 空間変調器
１１６ 電磁シャッター
１１７ ホログラム記録媒体
１１８ 記録領域
１１９ 銅板
１２０ 光検出器
１２１ 参照光
１２２ 記録光[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hologram recording medium and a hologram type information recording / reproducing apparatus, and more particularly to a volume hologram recording medium and a hologram type information recording / reproducing apparatus for recording interference fringes with a refractive index difference inside a recording layer.
[0002]
[Prior art]
In recent years, hologram technology has attracted attention as an information recording system that can handle a large amount of data. When the hologram technology is used, multiple writing can be performed on the same region by irradiating the reference light at different angles, and three-dimensional recording can be performed by using a volume hologram recording medium.
The mechanism of the apparatus will be described with reference to the schematic diagram of the transmission hologram type information recording / reproducing apparatus shown in FIG. The hologram type information recording / reproducing apparatus records information by irradiating the recording light 118 and the reference light 121 which are coherent light from two directions onto the recording area 118 in the hologram recording medium 117. The recording light 122 is modulated in wavelength or phase by the spatial modulator 115 corresponding to the information to be recorded, and the recording light 122 and the reference light 121 interfere in the recording area 118. Since the hologram recording medium 117 has the property that the refractive index changes according to the interference pattern, the refractive index change according to the information content is recorded in the recording area 118.
[0003]
Next, a method for reproducing hologram information will be described. Information reproduction is performed using only the reference beam 121. The recording light is blocked by closing the electromagnetic shutter 116, and only the reference light 121 enters the hologram recording medium 117. Since the reference light 121 is diffracted in the recording region 118 whose refractive index has been changed in advance during recording, the diffracted light having the same information as the recording light 122 irradiated during recording is detected even though the recording light is not incident. The device 120 is reached and the information is reproduced.
[0004]
[Problems to be solved by the invention]
As described above, the hologram type information recording / reproducing apparatus is configured, and research on the hologram type information recording / reproducing apparatus, particularly the hologram recording medium, has been actively conducted, and silver salt emulsion, dichromated gelatin, photopolymer, etc. are used. Recording media that have been proposed have been proposed. However, there are various drawbacks in the prior art. The features and drawbacks of the hologram recording medium according to the prior art will be described below.
[0005]
(A) Silver salt emulsion: A silver salt emulsion records a hologram by exposing silver halide dispersed in a gelatin layer to deposit silver. When a silver salt emulsion is used as a hologram type information recording medium, high sensitivity can be realized, but on the other hand, chemical processing such as development, washing, and bleaching is required after exposure, and there is a drawback that these processes are complicated. In addition, there is a drawback that the gelatin layer is deformed by chemical treatment or drying, and the recorded information is not accurately reproduced.
[0006]
(B) Bichromate gelatin: Dichromate gelatin records a hologram by exposing a gelatin layer to a photosensitized material by immersing the gelatin layer in an ammonium dichromate solution and hardening the gelatin. When dichromated gelatin is used as a hologram type information recording medium, there is a drawback that washing after exposure and dehydration treatment with isopropyl alcohol are required, and the processing is complicated, and the gelatin layer is deformed by these treatments, There are drawbacks such as the gelatin layer being vulnerable to moisture.
[0007]
(C) Photopolymer: The photopolymer records a hologram by polymerizing monomers by exposure to change the refractive index. When a photopolymer is used as a hologram type information recording medium, since information recording is performed by polymerization of monomers, there is a drawback that volume change due to polymerization reaction is essentially inevitable.
[0008]
(D) Photorefractive crystal: As the photorefractive crystal, iron niobium-doped lithium niobate or barium titanate is generally used, and the charge is spatially separated in the crystal by exposure, and the charge is redistributed. A hologram is recorded by changing the refractive index by the generated internal electric field. When a photorefractive crystal is used as a hologram type information recording medium, there are drawbacks that it is difficult and expensive to produce a large crystal, and that characteristics vary depending on the individual.
[0009]
(E) Photorefractive polymer: The photorefractive polymer is a material having performances such as charge generation by exposure, charge transport, and electro-optic effect, and similarly to the photorefractive crystal, the charge is spatially separated by exposure, Holograms are recorded by changing the refractive index with an internal electric field generated by charge redistribution. When a photorefractive polymer is used as a hologram type information recording medium, since the internal electric field formed by exposure is small, it is necessary to provide an electrode on the surface of the medium and apply an electric field from the outside, and there is a drawback that the apparatus becomes complicated.
[0010]
(F) Photoresist: Photoresist changes the solubility in a solvent by exposure, and records a hologram as unevenness by a phenomenon. When a photoresist is used as a hologram type information recording medium, a development processing step is required in addition to light irradiation, and information is recorded as holograms on the surface as irregularities. There are drawbacks such as difficulty in multiple writing.
[0011]
In addition to the drawbacks of the individual hologram recording media described above, the following problems can be raised when used as a hologram type information recording medium common to the hologram recording material. That is, the hologram recording material uses a substance having a large extinction coefficient at the wavelength of recording light in order to obtain writing sensitivity. In general, since the recording light intensity in the recording medium is exponentially attenuated, in the conventional hologram recording medium, the hologram is mainly recorded only near the surface on the recording light incident side in the recording layer of the recording medium. It will be. Therefore, the angle selectivity at the time of hologram reproduction is inferior, and angle multiplex recording is difficult. Further, since it has a large extinction coefficient, the diffraction efficiency is also inferior and sufficient sensitivity cannot be obtained.
[0012]
Accordingly, an object of the present invention is to provide a hologram recording medium and a hologram type information recording / reproducing apparatus having high sensitivity.
[0013]
Another object of the present invention is to provide a hologram recording medium and a hologram type information recording / reproducing apparatus having high diffraction efficiency.
[0014]
Another object of the present invention is to provide a hologram recording medium and a hologram type information recording / reproducing apparatus excellent in angle multiplex recording performance.
[0015]
[Means for Solving the Problems]
A first feature of the present invention is a photoreaction accelerator by irradiating a transparent substrate and light having a wavelength that excites the photoreaction accelerator and the photoreaction accelerator disposed at a specific position on the transparent substrate. A hologram recording layer, a transparent substrate disposed on the hologram recording layer, the transparent substrate and the hologram recording This is a hologram recording medium composed of a spacer that joins the transparent substrates disposed in a region other than the hologram recording layer between the transparent substrates on the layers with a predetermined distance. Here, the photoreaction accelerator is a substance that is activated by irradiation with light having a specific wavelength and reacts with a dye contained in the hologram recording layer. The dye means a substance that reacts with a photoreaction accelerator irradiated with light of a specific wavelength, and as a result, changes its extinction coefficient with respect to the specific wavelength described above and another wavelength. For example, the photoreaction accelerator is a photoacid. When it is a generating agent, it is a dye that reacts with the generated acid to change its extinction coefficient for another wavelength. A transparent substrate should just be a transparent substrate and is a concept containing an inorganic material and an organic material.
[0016]
According to the first feature of the present invention, the wavelength of the light applied to the hologram recording medium is different from the wavelength of the light whose absorption coefficient changes in the hologram recording medium. Therefore, when the recorded information is read, the absorption coefficient of the hologram recording medium with respect to the reference light does not change, so that high diffraction efficiency can be obtained. In addition, information is recorded by two substances: a photoreaction accelerator that plays a role in reacting to light emitted from a light source, and a dye that plays a role in changing an extinction coefficient for light of a specific wavelength different from the wavelength of the light source. Therefore, it is possible to separately select substances suitable for each role. That is, the range of selection of a substance is wider than when one substance plays these two roles, and a higher quality hologram recording medium can be obtained.
[0017]
The photoreaction accelerator is preferably a photoacid generator or a photoradical generator. Here, the photoacid generator refers to a substance that generates an acid when irradiated with light of a specific wavelength, and the photoradical generator refers to a substance that generates a radical when irradiated with light of a specific wavelength. Say. When a photoacid generator or a photoradical generator is used as the photoreaction accelerator, the acid or radical generated by the photoacid generator reacts with a plurality of dyes in a chain, so that one photon is incident. The light absorption coefficient of light of a specific wavelength of a plurality of substances changes. That is, it is possible to realize a highly sensitive hologram recording medium.
[0018]
The second feature of the present invention is that it reacts with the photoreaction accelerator by being irradiated with light having a wavelength that excites the photoreaction accelerator and the photoreaction accelerator disposed on the transparent substrate. A hologram recording layer comprising: a dye that changes an absorption coefficient for light having a wavelength different from the wavelength; a transparent substrate disposed on the hologram recording layer; the transparent substrate; and the hologram recording layer. A hologram recording medium, comprising: a hologram recording medium, comprising: a transparent substrate disposed between regions of the transparent substrate and disposed in a region other than the hologram recording layer; A support to be fixed, a light source having a wavelength for exciting the photoreaction accelerator, a spatial modulator disposed on an optical path of recording light obtained from the light source, and reference light obtained from the light source. An optical system for intersecting the light by the hologram recording layer lies in a hologram information recording and reproducing apparatus characterized in that it comprises a light detector arranged on the optical path of the recording light which has passed through the hologram recording medium. Here, the photoreaction accelerator, the dye, and the transparent substrate have the same concept as in the first feature of the present invention, and the spatial modulator spatially changes the phase or wavelength of the recording light obtained from the light source. A device for modulation.
[0019]
The hologram type information recording / reproducing apparatus according to the second feature preferably has a heating device for heating the hologram recording medium around a hologram recording medium or a support for fixing the hologram recording medium. By having the heating device, the acid generated by irradiating with light of a specific wavelength can be efficiently diffused to the surroundings by heat. Accordingly, it is possible to provide a hologram type information recording / reproducing apparatus that reacts in a chain manner with a plurality of dyes present in the vicinity and has high sensitivity in recording.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and width of the hologram recording medium, the ratio of the sizes of the components of the recording apparatus, and the like are different from the actual ones. In addition, it goes without saying that portions with different dimensional relationships and ratios are also included in the drawings.
[0021]
(First embodiment)
The structure of a hologram recording medium used in the transmission hologram information recording / reproducing apparatus according to the first embodiment of the present invention will be described below with reference to FIGS.
[0022]
The hologram recording medium according to the first embodiment includes a transparent substrate 6a, a hologram recording layer 4b disposed on the transparent substrate 6a, a transparent substrate 6b disposed on the hologram recording layer 4b, and a transparent substrate 6a. , 6b. The hologram recording layer 4b is composed of a matrix material 1, a photoacid generator 2, and a dye 3 that reacts with an acid generated from the photoacid generator 2 by light irradiation to change an absorption coefficient for light having a wavelength different from that of the light. It is configured.
[0023]
The matrix material 1 is a transparent substance that constitutes the entire hologram recording layer. As the material of the matrix material 1, polymethyl methacrylate is used in the first embodiment. The photoacid generator 2 is a substance having a characteristic of generating an acid and generating an acid when irradiated with excitation light. In the first embodiment, diphenyliodonium hexafluorophosphoric acid is used as the photoacid generator 2. The dye 3 is a substance having a characteristic of reacting with an acid generated from the photoacid generator 2 by irradiation with excitation light. In the first embodiment, a dye represented by Chemical Formula 1 is used as the dye 3.
[0024]
[Chemical 1]

Since the upper and lower quartz glasses 6a and 6b are intended to shape the upper and lower surfaces of the hologram recording layer and protect the hologram recording layer, any transparent material having such a purpose and heat resistance can be used. It is possible to use materials other than quartz. Similarly, the spacer 5 also uses a fluororesin in the first embodiment, but if it is made of a material that has heat resistance and does not easily deform,
You may use materials other than a fluororesin as a spacer.
[0025]
In the hologram recording layer constituting the hologram recording medium according to the first embodiment, the matrix material 1, the photoacid generator 2, and the dye 3 are mixed at a weight ratio of 96: 2: 2. These constituent elements are uniformly distributed in the hologram recording layer. The ratio of the photoacid generator 2 and the dye 3 to the matrix material 1 may be other than the above. However, when the ratio of the photoacid generator 2 and the dye 3 is increased, the ratio of the light outside the region to be recorded is increased. Absorption cannot be ignored. This causes a disadvantage that the diffraction efficiency of the hologram recording medium is lowered. Therefore, the ratio of the photoacid generator 2 and the dye 3 is preferably set to a certain value or less. FIGS. 1 and 2 are schematic views only, and are for facilitating understanding of the structure of the hologram recording medium. The ratio of the photoacid generator 2 and the dye 3 is shown in FIG. And the size of the particles constituting them is not determined.
[0026]
Even if the matrix material 1 is other than polymethylmethacrylate, it can be used as the matrix material 1 as long as it has high transparency and does not easily thermally deform, and the acid generated in the hologram recording layer can be thermally diffused. is there. Specific examples of the raw material for the matrix material 1 include polymer compounds such as polystyrene and polycarbonate, inorganic glass produced by a sol-gel method, and the like. From the viewpoint of facilitating thermal diffusion of the acid generated in the hologram recording layer, the matrix material 1 preferably has an amorphous structure.
[0027]
Even if the photoacid generator 2 is other than diphenyliodonium hexafluorophosphoric acid, it may be anything as long as it is activated with respect to excitation light having a specific wavelength and generates an acid. Specifically, sulfonium salts, diazonium salts, phosphonium salts, and the like are listed as raw materials for the photoacid generator 2.
[0028]
The dye 3 may be a compound other than the compound described in Chemical Formula 1 as long as it can react with an acid and change its extinction coefficient. Specifically, cyanine, a merocyanine derivative, a coumarin derivative, a chalcone derivative, and the like can be used as the raw material of the dye 3.
[0029]
Next, a method for manufacturing the hologram recording medium according to the first embodiment will be described.
[0030]
(A) Polymethyl methacrylate, which is a raw material of the matrix material 1, diphenyliodonium hexafluorophosphoric acid, which is a raw material of the photoacid generator 2, and a dye described in the above chemical formula 1, which is a raw material of the dye 3, have a weight ratio of It mixes so that it may become 96: 2: 2, and this is dissolved in the ethyl lactate which is a solvent.
[0031]
(B) The raw material dissolved in ethyl lactate is stirred for 3 hours. This is because the photoacid generator 2, the dye 3 and the matrix material 1 are uniformly dispersed in ethyl lactate.
(C) As shown in FIG. 3 (a), ethyl lactate in which the dissolved raw material is uniformly dispersed is cast on quartz glass 6a having a length and width of 3 cm and a thickness of 0.5 mm.
[0032]
(D) The temperature of the quartz glass 6a is heated to 120 degrees using a heater, and the state is maintained for 1 hour. As a result, the solvent ethyl lactate evaporates, and the hologram recording layer 4b is obtained.
[0033]
(E) As shown in FIG. 3B, the spacer 5 is disposed on the area on the quartz glass 6a where ethyl lactate is not cast. The spacer 5 is made of a fluororesin, and the height of the spacer 5 is 50 μm. Further, a quartz glass 6b different from the quartz glass 6a is prepared, and this quartz glass 6b is disposed on the spacer 5 and the hologram recording layer 4b.
[0034]
(F) With the quartz glass 6a kept at a temperature of 120 ° C., a uniform pressure is applied to the hologram recording layer 4b from the top of the quartz glass 6b as shown in FIG. 3C. The hologram recording layer 4b is stretched horizontally by pressure from above. When the two spacers 5 and the quartz glass 6b are in close contact with each other, the thickness of the hologram recording layer 4b is uniformly 50 μm.
[0035]
(G) After the hologram recording layer 4b is shaped to be uniform as shown in FIG. 3D, the entire temperature is lowered to room temperature. In order to lower the overall temperature, there are a method of bringing the quartz glass 6a into contact with a low-temperature metal, a method of putting it in water or liquid nitrogen, and the like. Although the hologram recording medium can be obtained even if this cooling step is performed over time, it is preferable to cool it rapidly. This is because, when the resultant product is amorphous, the photoacid generator 2 has a structure in which heat diffusion is easy, and a higher quality hologram recording medium can be obtained. The hologram recording medium according to the first embodiment is thus completed.
[0036]
Next, the structure of the transmission hologram information recording / reproducing apparatus according to the first embodiment will be described with reference to FIG.
[0037]
The transmission hologram information recording / reproducing apparatus according to the first embodiment has a light source 6 using an argon laser (λ = 488 nm) and a function of separating coherent light generated from the light source 6 into reference light 16 and recording light 17. Includes a beam splitter 7. A mirror 9, a spatial modulator 11, and an electromagnetic shutter 12 are arranged in order from the vicinity of the beam splitter 7 on the optical path of the recording light 17, and the mirror 8, in order from the vicinity of the beam splitter 7, on the optical path of the reference light 16. A neutral density filter 10 is disposed. The hologram recording medium 4 is fixed at its lower part by a copper plate 14, and the copper plate 14 is provided with light passage holes 14a and 14b for allowing recording light and reference light to pass therethrough. A heater 18 a is disposed below the copper plate 14. The heater 18a is connected to a temperature controller 18c, and the temperature controller 18c is connected to the hologram recording medium 4 through a thermocouple 18b. As a result, the hologram recording medium 4 is kept at a constant temperature set by the temperature controller 18c. Further, the recording light 17 and the reference light 16 are incident from the upper surface of the hologram recording medium 4, and the recording light 17 and the reference light 16 intersect each other in the recording area 13 inside the hologram recording medium. A photodetector 15 is disposed on the optical path of the recording light 17 after the recording light 17 has passed through the hologram recording medium.
[0038]
Here, the light source 6 may be a light source other than a laser as long as it emits coherent light and emits a wavelength that excites the photoacid generator 2 to generate an acid. Absent. Even when a laser is used, a He—Ne laser, a YAG laser, a semiconductor laser, or the like can be used in addition to the argon laser. In particular, when a semiconductor laser is used, there is an advantage that the light source 6 can be miniaturized and the hologram information recording / reproducing apparatus can be miniaturized. In addition, when a semiconductor laser is used as the light source 6, various oscillation wavelengths can be realized by adjusting the ratio of the mixed crystal of the semiconductor constituting the laser, so the wavelength of the light source 6 is changed according to the photoacid generator. In addition, there is an advantage that the range of selection of the photoacid generator 2 is widened. The oscillation wavelength of the light source 6 is preferably not a wavelength that directly excites the dye 3. This is because when the dye 3 is directly excited, the extinction coefficient with respect to the light of the wavelength of the light source 6 changes, which is disadvantageous in terms of diffraction efficiency.
[0039]
Since the copper plate 14 is provided for the purpose of fixing the hologram recording medium 4, it need not be limited to the copper plate as long as it can be fixed. In addition to the structure in which the light passage holes 14a and 14b are provided to allow the reference light 16 and the recording light 17 to pass through the copper plate, a structure using a transparent material instead of the copper plate is also desirable. Furthermore, a structure in which the hologram recording medium 4 is fixed from the side is also desirable because no optical loss occurs.
The heating device is for heating the hologram recording medium 4, and various forms are possible as long as the object is achieved. A structure in which a heater is directly brought into contact with the hologram recording medium for heating, an indirect heating structure by raising the temperature of the environment around the hologram recording medium, or radiation heating by electromagnetic wave irradiation may be used. Any other means can be used as a heating device as long as it does not change the characteristics of the region not irradiated with the recording light and can diffuse the acid to the surrounding dye. In FIG. 3, the heater is disposed below the copper plate 14, but the position of the heater is not limited to this, and can be disposed on the side surface of the hologram recording medium 4. It may be included inside. Any position where the hologram recording medium 4 can be efficiently heated without obstructing the optical paths of the reference beam 16 and the recording beam 17 may be used.
[0040]
The spatial modulator 11 is a device that spatially modulates the phase and wavelength of the recording light 17.
[0041]
Next, an information recording method using the hologram recording medium 4 and the transmissive hologram information recording / reproducing apparatus according to the first embodiment will be described below with reference to FIGS.
[0042]
The light emitted from the light source 6 is separated into the reference light 16 and the recording light 17 by the beam splitter 7. The direction of the reference light 16 is changed by the mirror 8 after passing through the beam splitter 7, and then the intensity of the reference light 16 is adjusted by the neutral density filter 10 so as to have the same intensity as that of the recording light 17. The light source 6 and the neutral density filter 10 are adjusted so that the light intensities of the reference light 16 and the recording light 17 in the recording area 13 are 3 mW. Thereafter, the reference beam 16 enters the hologram recording medium 4. The direction of the recording light 17 is changed by the mirror 9, the phase of the recording light 17 is modulated by the spatial modulator 11, and after passing through the open electromagnetic shutter 12, the recording light 17 enters the hologram recording medium 4. Here, the phase modulation of the recording light 17 performed by the spatial modulator 11 is performed according to information recorded in the recording area 13. For example, when recording 1 information, the phase is modulated so that the recording light 17 and the reference light 16 are intensified in the recording area 13, and when recording 0 information, the recording light 17 and the reference light 16 are recorded in the recording area 13. Modulates the phase so that
[0043]
In the recording area 13, the reference beam 16 and the recording beam 17 intersect each other. At this time, when interference occurs and light is strengthened, the photoacid generator 2 present in the recording area 13 reacts with light to generate acid.
[0044]
After acid is generated from the photoacid generator 2 in accordance with information to be recorded in the recording area 13, the hologram recording medium 4 is heated by a heating device. The copper plate 14 is heated by the heater 18a. In order to keep the heating temperature at 80 degrees, the temperature is adjusted by the temperature controller 18c. Heat for 1 minute. When the hologram recording medium 4 is heated, the acid generated in the information recording process diffuses to the surroundings by heat and comes into contact with the plurality of dyes 3. Since the dye 3 has a property that the extinction coefficient changes by reacting with an acid, the refractive index with respect to the reference light 16 in the recording region 13 changes.
[0045]
The specific mechanism by which the refractive index in the recording area 30 changes due to light irradiation is as follows.
In FIG. 5, curve 1 is a graph showing the absorption spectrum of the entire hologram recording medium 4 according to the first embodiment. This curve 1 shows an absorption spectrum in a state where no information is recorded. Curve 2 shows an absorption spectrum by the dye 3, and curve 3 shows an absorption spectrum by the photoacid generator 2.
[0046]
On the other hand, FIG. 6 is a graph showing an absorption spectrum in the hologram recording layer 4b after recording information by irradiating the hologram recording medium 4 with an argon laser having a wavelength of 488 nm and heating the medium. Comparing FIG. 5 and FIG. 6, although the absorbance near the wavelength of 488 nm of the light source is decreased, the absorbance is remarkably decreased in the region of 400 to 460 nm having a peak at 437 nm shorter than 488 nm. This is because the acid generated by the photoacid generator 2 reacts with the plurality of dyes 3 in a chain manner, so that the phenomenon of absorbance due to the dye 3 appears more remarkably than the absorbance due to the photoacid generator 2. .
[0047]
The following relational expression is established between this absorption spectrum and the refractive index of the hologram recording layer 4b.
[0048]
n_λ ²= N∞²+ Dλ0²/ (Λ²-Λ0²(1)
Here, n∞ is a refractive index when the wavelength is infinite, D is a value determined by the vibrator strength of the site that absorbs light in the medium, and λ0 is a wavelength at which the absorbance is maximized. In the hologram recording medium 4 according to the embodiment, the wavelength is 437 nm. Here, comparing the information before and after recording, the extinction coefficient of the hologram recording layer 4b decreases, so the value of D decreases and the refractive index of the reference light at the wavelength λ = 488 nm decreases. By reducing the refractive index, diffraction occurs when the reference light is incident, and information can be reproduced. Further, from FIG. 5, FIG. 6 and equation (1), in the first embodiment, the change in the absorbance of the medium before and after hologram recording is small, and the refractive index is efficiently reduced to record and reproduce the hologram. For this purpose, it is desirable to use a light source 6 in which the wavelength λ of the recording light 17 and the reference light 16 excites only the photoacid generator 2 and the absolute value of λ−λ0 is minimized.
[0049]
Next, a method for reproducing the recorded information will be described. Information reproduction is performed by irradiating the hologram recording medium 4 with only the reference beam 16. Even in the reproduction process, the light emitted from the light source 6 is separated into the reference light 16 and the recording light 17 by the beam splitter 7, but the recording light 17 is blocked by closing the electromagnetic shutter 12 in the middle of the optical path, It does not enter the hologram recording medium 4.
[0050]
The incident reference light 16 is diffracted in the recording area 13, and the diffracted light passes through the optical path of the recording light 17 during information recording. Since this diffracted light reproduces the spatial modulation information that the recording light 17 has, the photodetector 15 can detect the spatial modulation information that the recording light 17 has. The optical information detected by the photodetector 15 is converted into an electrical signal and output as data.
[0051]
Next, in order to measure the performance of the transmission type hologram information recording / reproducing apparatus according to the first embodiment, experiments were conducted on diffraction efficiency and angle multiplexing recording performance. In this experiment, the diffraction efficiency is 100 times the ratio of the intensity of the reference light 16 input at the time of reproduction and the intensity of the diffracted light detected by the photodetector 15, and is expressed in units of%. The angle multiplexing recording performance is determined by the peak width with respect to the incident angle of the reference light 16 in the graph.
[0052]
The transmission hologram type information recording / reproducing apparatus uses the apparatus shown in FIG. 3, and the hologram recording medium 4 also uses the same materials as in the first embodiment for the matrix material 1, the photoacid generator 2 and the dye 3.
[0053]
Information was recorded by irradiating recording light 17 and reference light 16 at 3 mW for 1 second. The recording area was set to a depth of 30 μm from the surface of the hologram recording layer.
[0054]
After irradiating the recording light 17 and the reference light 16, the copper plate was heated to 80 ° C. by a heating device, and the acid generated for 1 minute was diffused and reacted with the surrounding dye 3 to record information.
[0055]
Information reproduction is performed by blocking the recording light 17 by closing the electromagnetic shutter 12 and allowing only the reference light 16 to enter the hologram recording medium 4. Normally, the information is reproduced by setting the incident angle of the reference beam 16 to the same angle as at the time of recording. However, in the present invention, the angle of incidence of the reference beam 16 at the time of recording is set to 0 in order to investigate the angle multiplexing recording performance. The diffraction efficiency was measured by changing the angle of the reference beam as degrees. The light source 6 was the same as that used for recording, and the intensity of the reference light 16 was 0.3 mW.
[0056]
A photodiode was adopted as the photodetector 15 for detecting the reproduced information, and the photodiode was fixed on the extension of the optical path of the recording light 17 to measure the diffracted light.
[0057]
The result of measurement under the above conditions is shown by curve 1 in FIG. When the incident angle of the reference beam 16 was the same as that at the time of recording, that is, at 0 degree in the graph, a sharp peak was shown, and the diffraction efficiency was also 10%. Since the full width at half maximum is narrow and the peak intensity is strong, it has been clarified that the transmission hologram type information recording / reproducing apparatus according to the first embodiment can write a large amount of information in the same area. That is, from the graph, it is considered that it is possible to write new information separately from the previously written information by changing the incident angle of the reference light at the time of recording by about 0.5 degrees. Theoretically, 360-bit information can be written in the same area. Can be written. Since the conventional optical recording medium can write only 1-bit information in the same area, it is considered that the recording capacity of the hologram recording medium 4 according to the first embodiment increases dramatically when the size of the recording medium is the same. . In this experiment, the recording area 13 has a depth of 30 μm from the surface of the hologram recording medium 4 and recording is possible at this depth, so that not only the vicinity of the surface of the hologram recording medium 4 but also the inside is sufficient. It was demonstrated that recording was possible. While the conventional hologram recording medium can record only near the surface, it can be said that the hologram recording medium 4 according to the first embodiment has a great advantage. Further, since the diffraction efficiency is very high as compared with the comparative example described below, it has been clarified that the sensitivity when reading is increased.
[0058]
For comparison, a graph showing diffraction efficiency and angle selectivity according to the prior art is shown in Curve 2. Curve 2 is the result of using a hologram recording medium in which the refractive index of the recording area is changed by irradiating light that directly excites the dye and changing the absorption coefficient of the dye, unlike the first embodiment. In order to ensure objectivity, the same dye and matrix material as the hologram recording medium of the first embodiment are used, and the concentration of the dye is the same value as that of the hologram recording medium of the first embodiment. In addition, the wavelength of the light source used an argon laser of λ = 457.9 nm unlike the first embodiment in order to directly excite the dye. It is the same as the experiment on the form of.
[0059]
It can be seen that the result shown in the curve 2 is greatly inferior in diffraction efficiency and angle multiplex recording performance as compared with the curve 1 showing the result of the first embodiment. Since the diffraction efficiency is low, it is necessary to increase the intensity of the reference light in order to obtain sufficient sensitivity when reading. The reason why the diffraction efficiency is low is that the wavelength of the light source and the absorption spectrum of the dye coincide with each other, so that the light transmittance of the hologram recording medium is lowered by the change of the absorption coefficient of the dye. Further, since the peak width is wide, the number of information that can be recorded in the same area is smaller than that of the hologram recording medium according to the first embodiment.
[0060]
Further, the change in shape of the hologram recording medium 4 according to the first embodiment before and after information recording was examined. The unevenness in the vicinity of the recording region 13 was 1 nm or less by an atomic force microscope, and almost no change in the shape of the hologram recording medium 4 due to hologram information recording was observed.
[0061]
From the above experiments, it has been clarified that the transmission hologram information recording / reproducing apparatus according to the first embodiment and the hologram recording medium used therefor exhibit superior properties as compared with the prior art.
[0062]
Use of the hologram recording medium according to the first embodiment has the following advantages.
[0063]
First, the acid generated by the reaction of the photoacid generator 2 with light diffuses by heat and reacts with the plurality of dyes 3 in a chain manner. Therefore, when one photon is irradiated onto the recording area 4, the extinction coefficients of the plurality of dyes 3 near the area change. In the conventional technique, only one molecule reacts with one photon and the refractive index changes, so that the hologram recording medium 4 according to the first embodiment has a certain amount compared to the conventional technique. The amount of the substance whose optical characteristics change due to the light increases dramatically, and the writing sensitivity of the hologram recording medium 4 is improved. Therefore, if the sensitivity is the same, the amount of the photoacid generator can be reduced, whereby the change in the absorbance of the hologram recording medium 4 after recording with respect to the light of the wavelength of the light source can be kept low, and the transparency of the medium is improved. Can be made.
[0064]
Secondly, different substances have the role of reacting with light and the role of changing the extinction coefficient of the recording area. This makes it possible to individually select substances suitable for each application. Conventionally, as a recording material, a material that satisfies the two conditions of reacting with light and changing the refractive index at a time must be selected, and the choice of materials has been limited.
[0065]
Thirdly, after the recording light irradiation, development is performed by a simple method in which the hologram recording medium 4 is heated by a heating device. Therefore, the hologram information recording apparatus can be realized with a simple structure as compared with the conventional recording medium that performs development by complicated chemical processing, and the development processing process is simple, so the burden on the recording medium is small. Furthermore, since it is not necessary for a chemical substance such as a developer to penetrate into the medium, it is not necessary to use a gelatin layer for the matrix material 1 as in the conventional example.
[0066]
Fourth, the refractive index of the recording region 13 changes as the absorption coefficient for light having a wavelength different from that of the recording light 17 and the reference light 16 changes. Therefore, although the recording light 17 and the reference light 16 are affected by the change in the refractive index, the influence due to the difference in the absorption coefficient is small. Therefore, it is possible to suppress the recording light 17 and the reference light 16 from being absorbed by the hologram recording medium 4 in the process in which the recording light 17 and the reference light 16 pass through the hologram recording medium. Accordingly, it is possible to realize a hologram recording medium superior to the conventional one in terms of transmittance and diffraction efficiency.
[0067]
(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. In the second embodiment, a photoradical generator 19 is used as a photoreaction accelerator in the hologram recording layer, and the dye 20 reacts with radicals generated by the photoradical generator to change the extinction coefficient, so that the recording area The information is recorded by changing the refractive index with respect to the light source.
[0068]
In the second embodiment, the photoradical generator 19 used is an iodonium salt. Further, a porphyrin derivative is used as the dye 20.
[0069]
The hologram recording medium using the hologram recording layer according to the second embodiment is assumed to have the structure shown in FIG. 2, as in the first embodiment. Since the upper and lower quartz glasses 6a and 6b are intended to shape the upper and lower surfaces of the hologram recording layer and protect the hologram recording layer, any transparent material having such a purpose and heat resistance can be used. It is possible to use materials other than quartz. Similarly, although the fluororesin is used for the spacer 5 in the first embodiment, a material other than the fluororesin may be used as the spacer as long as it is heat resistant and does not easily deform. Absent.
[0070]
In the hologram recording layer constituting the hologram recording medium according to the first embodiment, the matrix material 1, the photo radical generator 19, and the dye 20 are mixed at a weight ratio of 96: 2: 2. These constituent elements are uniformly distributed in the hologram recording layer. The ratio of the photo radical generator 19 and the dye 20 to the matrix material 1 may be other than those described above. However, when the ratio of the photo radical generator 19 and the dye 20 is increased, the ratio of the light outside the region to be recorded is increased. Absorption cannot be ignored. This causes a disadvantage that the diffraction efficiency of the hologram recording medium is lowered. Therefore, the ratio of the photo radical generator 19 and the dye 20 is preferably set to a certain value or less. 8 is merely a schematic diagram as in FIG. 1, and is for facilitating understanding of the structure of the hologram recording layer. FIG. 8 shows the ratio of the photo radical generator 19 and the dye 20 and the ratios thereof. The size of the constituent particles is not determined.
[0071]
Even if the matrix material 1 is other than polymethylmethacrylate, it can be used as the matrix material 1 as long as it has high transparency and does not easily thermally deform, and the acid generated in the hologram recording layer can be thermally diffused. is there. Specific examples of the raw material for the matrix material 1 include polymer compounds such as polystyrene and polycarbonate, inorganic glass produced by a sol-gel method, and the like. From the viewpoint of facilitating thermal diffusion of the acid generated in the hologram recording layer, the matrix material 1 preferably has an amorphous structure.
[0072]
The photoradical generator 19 may be other than an iodonium salt as long as it is activated by excitation light having a specific wavelength and generates a radical. Specifically, selenonium salts, arsonium salts, and the like are listed as raw materials for the photo radical generator 19.
[0073]
The dye 3 may be a substance other than the porphyrin derivative as long as it has an extinction coefficient that reacts with a radical. Specifically, an organic compound such as a xanthene derivative, a thioxanthene derivative, an azurenium derivative, a squarylium derivative, or the like can be used as a raw material of the dye 20.
[0074]
Next, a method for manufacturing a hologram recording medium according to the second embodiment will be described.
[0075]
(A) Mixing polymethyl methacrylate, which is a raw material of the matrix material 1, iodonium salt, which is a raw material of the photoradical generator 19, and a porphyrin derivative, which is a raw material of the dye 20, so that the weight ratio is 96: 2: 2. This is dissolved in ethyl lactate as a solvent.
[0076]
(B) The raw material dissolved in ethyl lactate is stirred for 3 hours. This is because the photoradical generator 19 and the dye 20 and the matrix material 1 are uniformly dispersed in ethyl lactate.
[0077]
(C) As shown in FIG. 10 (a), ethyl lactate in which the dissolved raw material is uniformly dispersed is cast on a quartz glass 6a having a length and width of 3 cm and a thickness of 0.5 mm.
[0078]
(D) The temperature of the quartz glass 6a described above is heated to 120 degrees using a heater, and the state is maintained for 1 hour. As a result, the solvent ethyl lactate evaporates, and the hologram recording layer 4b is obtained.
[0079]
(E) The spacer 5 is arranged on the above-described quartz glass 6a on the region where ethyl lactate is not cast as shown in FIG. The spacer 5 is made of a fluororesin, and the height of the spacer 5 is 50 μm. Further, a quartz glass 6b different from the above-described quartz glass 6a is prepared, and this quartz glass 6b is disposed on the two spacers 5 and the hologram recording layer 4b.
[0080]
(F) With the quartz glass 6a kept at a temperature of 120 ° C., a uniform pressure is applied to the hologram recording layer 4b from the top of the quartz glass 6b as shown in FIG. 10C. The hologram recording layer 4b is stretched horizontally by pressure from above. When the two spacers 5 and the quartz glass 6b are in close contact with each other, the thickness of the hologram recording layer 4b is uniformly 50 μm.
[0081]
(G) After the hologram recording layer 4b is shaped to be uniform as shown in FIG. 10D, the entire temperature is lowered to room temperature. In order to lower the overall temperature, there are means for bringing the quartz glass 6a into contact with a low-temperature metal and means for putting it in water or liquid nitrogen. Although the hologram recording medium can be obtained even if this cooling step is performed over time, it is preferable to cool it rapidly. This is because, when the resultant product is amorphous, the photoacid generator 2 has a structure in which heat diffusion is easy, and a higher quality hologram recording medium can be obtained. The hologram recording medium according to the first embodiment is thus completed.
[0082]
Note that it is also useful to make the hologram recording layer according to the first and second embodiments have a multilayer structure as shown in FIG. The hologram recording layer in the first and second embodiments has the photoreaction accelerator and the dye uniformly dispersed in the matrix agent, whereas the hologram recording layer in the third embodiment has a photoacid It has a multilayer structure in which the photoreactive layer 21 containing the generator 2 and the absorption spectrum changing layer 22 containing the dye 3 are alternately laminated. Such a structure is prepared by separately preparing a photoreaction accelerator and matrix material dissolved in an organic solvent, and a pigment and matrix material dissolved in an organic solvent, and casting the organic solvent containing the pigment on quartz glass. Alternatively, a film is formed by spin coating, and then an organic solvent containing a photoreaction accelerator is formed by vacuum deposition. By repeating the above steps, a hologram recording medium having a multilayer structure can be manufactured.
[0083]
(Third embodiment)
Next, a reflective hologram information recording / reproducing apparatus according to a third embodiment will be described. As shown in FIG. 11, the apparatus according to the third embodiment includes a light source 23 and a beam splitter 24 having a function of dividing light from the light source into two directions of recording light 34 and reference light 33. Further, a spatial modulator 27 and an electromagnetic shutter 28 are arranged in order from the vicinity of the beam splitter 24 on the optical path of the recording light 34, and a mirror 25 and a neutral density on the optical path of the reference light 33 in order from the vicinity of the beam splitter 24. A filter 26 and a mirror 31 are arranged. The hologram recording medium 29 is disposed in the vicinity of a region where the recording light 34 and the reference light 33 intersect. The recording medium 29 is fixed by a copper plate 36 on the right side surface thereof, and a heating device 35 is disposed on the left side surface portion of the recording medium 29. Has been. The recording light 34 is incident on the recording medium from the upper surface of the hologram recording medium 29, and the reference light 33 is incident on the recording medium from the lower surface of the hologram recording medium 29 by adjusting the position of the mirror. .
[0084]
The hologram recording medium 29 used in the reflection-type hologram information recording / reproducing apparatus according to the third embodiment may be a combination of the photoacid generator and the dye used in the first embodiment, or the second embodiment. It may be a combination of a photo radical generator and a pigment according to the form. Further, a structure in which the photoreaction accelerator and the dye are uniformly distributed in the hologram recording medium or a multilayer structure including the photoreaction layer and the absorption spectrum changing layer according to the third embodiment may be used. Reflective hologram information recording is possible as long as the hologram recording medium 29 has a structure in which the recording light 34 is irradiated from the upper surface and the reference light is irradiated from the lower surface. The number of mirrors can be adjusted as appropriate according to the form. However, it is desirable that the number of mirrors is small from the viewpoint of suppressing a decrease in the intensity of the recording light and the reference light. The hologram information recording / reproducing apparatus according to the fifth embodiment has a structure in which one light source 23 is separated into two by a beam splitter 24. However, two separate light sources are used for recording light and reference light. You may use. In this case, however, a device for synchronizing the wavelength and phase is required separately. If the heating device 35 is incorporated in the copper plate 36, the hologram type information recording / reproducing device can be further downsized. Note that the heating device 35 may have a structure in which a heater is directly brought into contact with the hologram recording medium for heating, an indirect heating structure by raising the temperature of the environment around the hologram recording medium, or radiation heating by electromagnetic wave irradiation. Any other means can be used as a heating device as long as it does not change the characteristics of the region not irradiated with the recording light and can diffuse the acid to the surrounding dye.
[0085]
Next, an information recording method using the hologram recording medium 4 and transmission hologram information recording / reproducing apparatus according to the third embodiment will be described with reference to FIG.
[0086]
The light emitted from the light source 23 is separated into the reference light 33 and the recording light 34 by the beam splitter 24. The direction of the reference light 33 is changed by the mirror 25 after passing through the beam splitter 24, and then the intensity of the reference light 33 is adjusted by the neutral density filter 26 in order to obtain the same intensity as that of the recording light 34. Thereafter, the direction is changed again by the mirror 31 and enters the hologram recording medium 29 from the lower surface. The recording light 34 is phase-modulated by the spatial modulator 27, passes through the open electromagnetic shutter 28, and then enters the hologram recording medium 29. Here, the phase modulation of the recording light 34 performed by the spatial modulator 27 is performed in accordance with the content of information recorded in the recording area 30. For example, when recording one information, the phase is modulated so that the recording light 34 and the reference light 33 are intensified in the recording area 30, and when recording zero information, the recording light 34 and the reference light 33 are recorded in the recording area 30. Modulates the phase so that
[0087]
In the recording area 30, the reference beam 33 and the recording beam 34 intersect. At this time, when interference occurs and light is strengthened, the photoacid generator 2 present in the recording area 30 reacts with light to generate acid.
[0088]
Next, a recording development method will be described. After the acid is generated from the photoacid generator 2 according to information in the recording area 30, the hologram recording medium 29 is heated by the heating device 35. Therefore, the acid generated in the information recording process diffuses to the surroundings by heat and comes into contact with the plurality of dyes 3. Since the dye 3 has a property that the extinction coefficient changes by reacting with an acid, the refractive index with respect to the reference light 16 in the recording region 13 changes.
[0089]
Next, a method for reproducing the recorded information will be described. Information reproduction is performed by irradiating the hologram recording medium 4 with only the reference beam 16. The light emitted from the light source 6 is separated by the beam splitter 7, but the recording light 17 is then blocked by closing the electromagnetic shutter 12 and does not enter the hologram recording medium 4.
[0090]
The incident reference light 33 is diffracted in the recording region 30, and the diffracted light passes on the optical path of the recording light 32 during information recording. Since the diffracted light reproduces the spatial modulation information that the recording light 32 has, the photodetector 32 can detect the spatial modulation information that the recording light 34 has. The optical information detected by the photodetector 32 is converted into an electrical signal and output as data.
[0091]
(Other embodiments)
As described above, the present invention has been described according to the first to third embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.
[0092]
For example, the photoreaction accelerator used in the hologram recording media according to the first to third embodiments need not be interpreted as being limited to a photoacid generator or a photoradical generator. For example, it reacts with light. Even substances that generate strong alkalis or ions can be applied as photoreaction accelerators. In addition, a hologram recording medium is also possible that combines a matrix material that is inactive to light and a plurality of other substances that react with light as a catalyst and whose absorption coefficient changes as a result. is there.
[0093]
Further, it is possible to devise a hologram type information reproducing apparatus from the structure of the reflection type hologram information recording / reproducing apparatus according to the third embodiment. In the case of the reproduction only, since it is not necessary to enter the recording light, a complicated structure using a beam splitter or a mirror is not necessary, and it is sufficient to arrange a light source and a neutral density filter for the reference light. In the apparatus according to the third embodiment, the reference beam 33 is irradiated on the same side as the photodetector 32 with respect to the hologram recording medium 29. Further, the incident angles of the reference beam 33 and the recording beam 34 with respect to the hologram recording medium 29 can be arbitrarily set as long as interference occurs, so that the incident angle of the recording beam is substantially perpendicular to the surface of the hologram recording medium 29. In this case, it is possible to arrange the light source of the photodetector at a position close to it. As described above, a small semiconductor laser can be used as the light source, and a photodiode can be used as the photodetector. Therefore, the reproduction mechanism can be made very small, and a portable hologram type information reproduction-dedicated apparatus that is about the size of a current portable CD player and has a recording capacity larger than that of a DVD can be realized.
[0094]
It is also effective to increase the width of light emitted from the light source of the hologram information recording / reproducing apparatus according to the first and third embodiments. In this case, since two-dimensional information can be put on the recording light, a plurality of information can be recorded in one writing. In reading, a plurality of pieces of information can be read at a time by using a device capable of reading light information in a two-dimensional manner, such as a CCD, as the photodetector. Therefore, a high-speed operation can be realized as compared with a conventional information recording apparatus capable of writing and reading only a single piece of information at a time.
[0095]
Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters according to the scope of claims reasonable from this disclosure.
[0096]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a hologram recording medium and a hologram type information recording / reproducing apparatus having high sensitivity.
[0097]
Further, according to the present invention, it is possible to provide a hologram recording medium and a hologram type information recording / reproducing apparatus having high diffraction efficiency.
[0098]
Furthermore, according to the present invention, it is possible to provide a hologram recording medium and a hologram type information recording / reproducing apparatus excellent in angle multiplexing recording performance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a hologram recording layer in a hologram recording medium according to a first embodiment.
FIG. 2 is a sectional view showing a hologram recording medium according to the first embodiment.
FIG. 3 is a diagram showing manufacturing steps of the hologram recording medium according to the first embodiment.
FIG. 4 is a schematic diagram showing a transmission hologram type information recording / reproducing apparatus according to the first embodiment.
FIG. 5 is a graph showing an absorption spectrum of a hologram recording medium before irradiation with recording light.
FIG. 6 is a graph showing an absorption spectrum of a hologram recording medium after irradiation with recording light.
7 is a graph showing diffraction efficiency with respect to a reference light incident angle of the hologram recording medium according to the first embodiment and the hologram recording medium according to the related art. FIG.
FIG. 8 is a cross-sectional view showing a hologram recording layer in a hologram recording medium according to a second embodiment.
FIG. 9 is a cross-sectional view showing a hologram recording layer having a multilayer structure.
FIG. 10 is a diagram showing a manufacturing process of the hologram recording medium according to the second embodiment.
FIG. 11 is a schematic diagram showing a reflective hologram information recording / reproducing apparatus according to a third embodiment.
FIG. 12 is a schematic diagram showing a transmission hologram type information recording / reproducing apparatus according to a conventional example.
[Explanation of symbols]
1 Matrix material
2 Photoacid generator
3 Dye
4 Hologram recording medium
4b Hologram recording layer
5 Spacer
6 Light source
6a, 6b quartz glass
7 Beam splitter
8 Mirror
9 Mirror
10 Neutral density filter
11 Spatial modulator
12 Electromagnetic shutter
13 Recording area
14 Copper plate
14a, 14b Light passage hole
15 Photodetector
16 Reference beam
17 Recording light
18a heater
18b thermocouple
18c temperature controller
19 Photoradical generator
20 Dye
21 Photoreactive layer
22 Absorption spectrum changing layer
23 Light source
24 Beam splitter
25 mirror
26 Neutral density filter
27 Spatial modulator
28 Electromagnetic shutter
29 Hologram recording medium
30 recording area
31 mirror
32 photodetectors
33 Reference beam
34 Recording light
35 Heating device
110 Light source
111 Beam splitter
112 mirror
113 Mirror
114 Neutral Density Filter
115 Spatial modulator
116 Electromagnetic shutter
117 Hologram recording medium
118 Recording area
119 Copper plate
120 photodetectors
121 Reference beam
122 Recording light

Claims (6)

A transparent substrate;
A photoreaction accelerator that reacts with light of a first wavelength provided on the transparent substrate; and a dye whose absorption coefficient changes with respect to light of a second wavelength different from the first wavelength by the action of the photoreaction accelerator; A hologram recording medium comprising: a hologram recording layer comprising: A first transparent substrate;
A photoreaction accelerator that reacts with light of the first wavelength provided on the first transparent substrate, and an absorption coefficient for light of a second wavelength different from the first wavelength is changed by the action of the photoreaction accelerator. A hologram recording layer containing a dye to be
A second transparent substrate provided on the hologram recording layer;
A hologram recording medium comprising: a spacer disposed between the first and second transparent substrates and in a region other than the hologram recording layer .   The hologram recording medium according to claim 1, wherein the photoreaction accelerator is a photoacid generator or a photoradical generator. A transparent substrate;
A photoreaction accelerator that reacts with light of a first wavelength provided on the transparent substrate; and a dye whose absorption coefficient changes with respect to light of a second wavelength different from the first wavelength by the action of the photoreaction accelerator; A hologram recording medium comprising a hologram recording layer comprising:
A support for supporting the hologram recording medium;
A light source having a wavelength for exciting the photoreaction accelerator;
A spatial modulator disposed on an optical path of recording light obtained from the light source;
An optical system for causing the hologram recording layer to interfere with the reference light obtained from the light source and the recording light;
A hologram type information recording / reproducing apparatus comprising: a photodetector disposed on an optical path of the recording light that has passed through the hologram recording medium. A first transparent substrate;
A photoreaction accelerator that reacts with light of the first wavelength provided on the first transparent substrate, and an absorption coefficient for light of a second wavelength different from the first wavelength is changed by the action of the photoreaction accelerator. A hologram recording layer containing a dye to be
A second transparent substrate provided on the hologram recording layer;
A hologram recording medium comprising a spacer disposed between the first and second transparent substrates and in a region other than the hologram recording layer;
A support for supporting the hologram recording medium;
A light source having a wavelength for exciting the photoreaction accelerator;
A spatial modulator disposed on an optical path of recording light obtained from the light source;
An optical system for causing the hologram recording layer to interfere with the reference light obtained from the light source and the recording light;
A hologram type information recording / reproducing apparatus comprising: a photodetector disposed on an optical path of the recording light that has passed through the hologram recording medium.   6. The hologram type information recording / reproducing apparatus according to claim 4, further comprising a hologram recording medium heating device around the hologram recording medium or a support that supports the hologram recording medium.

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