JP3611750B2 - Information recording medium and information reproducing method - Google Patents

Description

であればよい。
ここで、数１中のθは焦点ＦＰを通り、コア層１２とクラッド層１４ａ，１４ｂとの境界に垂直な直線と、ホログラム３２内の点Ｐと焦点ＦＰとを通る直線との成す角度であり、ｚはコア層１２中の導波光ＰＷの伝搬方向の位置であり、βはコア層１２中における導波光ＰＷの伝搬定数、λは導波光ＰＷの波長、Ａ，φ，ｆは実定数である。
このホログラムは、前述した第１実施形態及び第２実施形態の特殊な場合と位置づけることができるが、付加的な効果が得られる。第１には、集光することにより光パワーが集中し、回折光信号を大きくとれることである。
【００３３】
また、球面波を導波光ＰＷが伝搬しているコア層検出のために用いる場合、各導波路の位置合わせ用ホログラムが互いに異なる位置に焦点を合わせるような構成とすればよい。図７は、各コア層に形成された位置合わせ用ホログラムが互いに異なる位置に焦点を合わせるような構成とした場合の焦点位置の最も単純な例を説明するための図である。図７では、断面で示した情報記録媒体１０中の各位置合わせ用ホログラム３２ａ〜３２ｃ各々によって形成される焦点ＦＰａ〜ＦＰｃを一直線上に周期的に配置した場合を示している。
【００３４】
そして、この直線上にＮ−ＭＯＳやＣ−ＭＯＳ等のリニアイメージセンサや１次元ＣＣＤなどの１次元アレイ光センサ、又は光スポット位置検出素子（ＰＳＤ）等の光検出器３４を配置すれば導波光がどのコア層を伝搬しているかを検出することができる。このように、回折光を小さな焦点に絞れることで、導波光がどのコア層を伝搬しているかを検出する検出装置の小型化を図ることができるのが第２の効果である。
この実施形態の変形として、点の集合としての線状に集光する形態もあり、この形態でも、上述した第１及び第２の効果が得られるのは全く同様である。線状に集光するホログラムは、点状に集光するホログラムの集合の形態で実現することができる。
【００３５】
第３の効果は、入射光ＩＷと情報記録媒体１０との位置合わせだけでなく、情報記録媒体１０とホログラム画像読み取り用の２次元アレイ光検出器との位置合わせにも利用できることである。
図８は、情報記録媒体１０とホログラム画像読み取り用の２次元アレイ光検出器との位置合わせ方法を説明するための図である。図８では、コア層１２ａにホログラム２２及び位置合わせ用ホログラム３２が形成され、ホログラム２２の回折光が結像面３８で正しくホログラム画像を結合する様子が示され、また、位置合わせ用ホログラム３２から球面回折光ＣＤ１が焦点ＦＰに集光される様子を示している。
【００３６】
ホログラム２２によるホログラム画像は、ＣＣＤ等の２次元アレイ光検出器３６で電気信号に変換して読み出されるが、この光検出器の光検出面が結像面３８からずれていれば、画像のピントがぼけ、正しく信号が読み出せない。
ここで、２次元アレイ光検出器３６と光検出器３４とが互いに固定されており、これらを同時に動かすことでピントを合わせることができる。光検出器３４は、例えば２次元アレイ光検出器３６と同様の２次元アレイ光検出器でもよい。光検出器３４が２次元アレイ光検出器である場合、観測されるのは、球面回折光ＣＤ１の断面である円形のパターンである。この円形のパターンは、球面回折光ＣＤ１の焦点ＦＰに近づくほど小さくなる。従って、円形パターンを観測しながら光検出器３４を動かし、光検出器の受光面を球面回折光ＦＰの焦点に合わせることが可能である。上述のように。光検出器３４と２次元アレイ光検出器３６の光検出面が揃えてある。この場合、やはり図８に示されているとおり、球面回折光ＣＤ１の焦点が結像面３８内に配置されるよう位置合わせ用ホログラム３２を設計しておけば、光検出器３４の受光面と球面回折光ＦＰの焦点の位置合わせをすると、自ずと２次元アレイ光検出器３６の受光面と結像面３８とが合致する、すなわちピントが合うことになる。
【００３７】
以上では、ピント調整、すなわち図８において符号Ｄ２が付された方向の位置合わせ方法について説明したが、同図において符号Ｄ３が付された方向の位置合わせも必要な場合がある。この場合も、前記のように光検出器３４に２次元アレイ光検出器や光スポット位置検出素子（ＰＳＤ）を用いていれば、光検出器３４の受光面のどこに球面回折光ＣＤ１の焦点ＦＰがあるかが検知できるので、予め決められた位置まで平行移動すればよい。もし、結像面３８内での回転の位置合わせも必要な場合は、少なくとも２つの点に焦点を結ぶ２つの球面回折波を用意すればよい。
【００３８】
ところで、前述したように、光検出器３４には２次元アレイ光検出器を用いると、現象が直感的であるために、位置合わせを手動で行うには便利である。しかし、ＣＣＤを始めとした２次元アレイ光検出器は高価であるほか、自動位置合わせを行う場合、２次元アレイ光検出器で受けた球面回折光ＣＤ１の強度パターンから図中符号Ｄ２が付された方向及び符号Ｄ３が付された方向の位置ずれを割り出すには、時として煩雑な画像処理を必要とし、必ずしも位置合わせは高速にならない。２次元アレイ光検出器と比較して安価であり、高速な位置合わせも可能な方法として、ピンホールを用いるものがある。
【００３９】
図９は、ピンホールとアレイではない単体の光検出器を用いた位置合わせ方法を説明する図である。図９に示したように、単体の光検出器４０の光検出面にはピンホール４２が形成されたマスク４１が配置されている。同図で、符号Ｄ３が付された方向に全く位置ずれがないとすると、光強度は焦点ＦＰのごく近傍を除いて、結像面３８とのずれの自乗に反比例する。従って、ピンホールから漏れて光検出器４０で観測される光信号も結像面３８とのずれの自乗に反比例するため、最大の信号が得られるよう、２次元アレイ光検出器３６と結合された光検出器４０を符号Ｄ２が付された方向へ動かせば、ピントが合う。ただし、符号Ｄ３が付された方向に全く位置ずれがないということが保証されない場合がある。この場合は、符号Ｄ２が付された方向に動かしただけでは、球面回折波ＣＤ１を見失う可能性がある。このため、符号Ｄ３が付された方向にも動かし、球面回折波ＣＤ１を探りながら位置合わせを行わなければならない。
【００４０】
なお、２次元アレイ光検出器３６の受光面は、必ずしもホログラム画像の結像面３８と平行とは限らず、あおり角の調整が必要な場含もある。この場合、少なくとも３つの点に焦点を結ぶ３つの球面回折波が必要である。これらの球面回折波を発生させるために、３つの位置合わせ用ホログラムをコア層１２に形成し、これら３つを互いに重ねても重ねなくてもよく、更に、１つの位置合わせ用ホログラムで３つすべてを同時に回折させるようなものでもよいことは、前記と同じである。
【００４１】
【実施例】
〔第１実施例〕
図１０は、本発明の第１実施例による情報記録媒体のコア層の一部を示す上面図である。図１０において、４４は、本発明の第１実施例による情報記録媒体が有するコア層の１つである。本実施例では、図示しない光源からの入射光が端面４５から入射して図示した方向の導波光ＰＷがコア層４４を伝搬する。４６は、画像再生のためのホログラムであり、４８ａ，４８ｂは位置合わせ用ホログラムである。ホログラム４６は、端面４５側であって、コア層４４のほぼ全面に形成されている。位置合わせ用ホログラム４８ａ，４８ｂは図６に示した球面回折波ＣＤ１を形成するホログラムであり、端面４５に対向する端面側に形成されている。図中符号５０ａ，５０ｂは導波光ＰＷが位置合わせ用ホログラム４８ａ，４８ｂに入射した場合に位置合わせ用ホログラム５０ａ，５０ｂによって形成される焦点を示している。図１０は、コア層４４の上面図であるので、焦点５０ａ，５０ｂを位置合わせ用ホログラム４８ａ，４８ｂに重ねて示してある。
【００４２】
本実施例の情報記録媒体は、導波路が５つ、つまり図１０に示したコア層４４が５つと、これらのコア層４４の間に形成されたクラッド層とからなる構造のものを作成した。そして５枚の画像情報を、各々のコア層４４のホログラム４６に重畳させた。本実施形例では各々のコア層４４のホログラムに「ページ１」から「ページ５」までの番号を付した。
【００４３】
図１１は、本実施例による情報記録媒体の断面図である。本実施例では図１６に示した従来技術と同様に、入射光を各コア層に導入するために情報記録媒体４９の一部を４５°にカットして反射面を形成し、情報記録媒体４９の各層に垂直な方向から円筒波面の光ＣＬ１を入射する方式をとっている。全てのコア層に形成された位置合わせ用ホログラム４８ａ，４８ｂから回折される光は、情報記録媒体４９の上面から１ｍｍ上、情報記録媒体４９の表面に平行な面５２内に集光されるように設計した。図１１中Ｐ１〜Ｐ５は、各コア層に付されたページ番号を示している。つまり、符号Ｐ１で示されたコア層にはページ番号として「ページ１」が付されており、符号Ｐ５で示されたコア層にはページ番号として「ページ５」が付されている。また、符号ＦＰ１〜ＦＰ５はそれぞれ、ページ番号Ｐ１〜Ｐ５が付されたコア層に形成された位置合わせ用ホログラム４８ａ，４８ｂによって形成される焦点を示している。また、位置合わせ用ホログラム４８ａ，４８ｂは、焦点ＦＰ１〜ＦＰ５が面５２内において、０．１ｍｍの距離をもって配置されるよう形成されている。
【００４４】
図１２は、図１１に示した本実施例による情報記録媒体４９に記録された情報を読み出す装置の簡略構成を示す図である。図１２において、５４は円筒波面光源であり、半導体レーザ、コリメータ、及びシリンドリカルレンズにより構成され、円筒波を発生する光源である。５６は、回転ステージであり、図中のｙ軸周りに円筒波面光源４９を回転させる。５８は円筒波面光源５４を図中のｙ軸方向へ移動させるＹステージであり、６０は円筒波面光源５４を図中符号Ｄ１又はＤ２が付された方向へ移動させるページ選択用ステージである。これらページ選択用ステージ６０、Ｙステージ５８、及び回転ステージ５６を駆動して円筒波面光源５４から出射される円筒波面光ＣＬ１が情報記録媒体に入射する位置を調整する。主としてページ選択用ステージ６０はページ選択用として用い、Ｙ軸ステージ５８は入射円筒波の焦点位置の調整に用いる。尚、図１２において、６２はアレイ光検出器であり、位置検出用ホログラムから出射される球面回折光を検出する。
【００４５】
はじめに、ページ番号Ｐ１が付された「ページ１」の画像を正確に再生するよう各ステージを調整したところ、ホログラム画像と同時に位置合わせ用ホログラム４８ａ，４８ｂからの回折光により、２つの輝点が観測された。焦点位置での各焦点のスポットサイズは、約φ１０μｍであった。ページ選択用ステージ６０を使って円筒波面光ＣＬ１の焦点を図中Ｄ４方向へ動かしていくと、ページ番号Ｐ１が付された「ページ１」の画像が消え、ページ番号Ｐ２が付された「ページ２」の画像が現れた。さらに続けて動かすと、次々にページ番号Ｐ３が付された「ページ３」、ページ番号Ｐ４が付された「ページ４」、ページ番号Ｐ５が付された「ページ５」へと画像が切り替わった。これと同時に、位置合わせ用ホログラム４８ａ，４８ｂに対応する輝点が図１２中ｘ軸方向へ０．１ｍｍ刻みでずれていくのが観測された。各輝点の輝度が最も強い位置で、ホログラムが正確に像を結んでいることが確認された。
【００４６】
次に、位置合わせ用ホログラム４８ａと位置合わせ用ホログラム４８ｂの真上に、それぞれ１つずつ、アレイ光検出器６２を置いた。これら５つの個別の素子が、位置合わせ用ホログラム４８ａの５つの焦点それぞれの位置に合うよう、アレイ光検出器６２を置いた。尚、本実施例では設計の都合上、焦点を同一直線上にに配置したが、これに限定されるものではない。同様に、位置合わせ用ホログラム４８ｂに合わせてアレイ光検出器６２をもう一つ設置した。その素子を位置合わせ用ホログラム４８ａと位置合わせ用ホログラム４８ｂの焦点に合わせた。アレイ光検出器６２は、それぞれ５つの素子からなり、０．１ｍｍピッチで図１２中のｚ方向に並んでいる。この素子を位置合わせ用ホログラム４８ａ、位置合わせ用ホログラム４８ｂの焦点５つ各々に合うようアレイ光検出器６２を置いた。
【００４７】
ページ選択用ステージ６０を任意の位置まで動かすと、アレイ光検出器６２は２つとも、中央の素子で光が検知された。そこで、その位置の前後にページ選択用ステージ６０を僅かに動かすと、光検知の信号が最大になる位置があった。そこで、ホログラム画像を観測すると、符号Ｐ３が付された「ページ３」が正確に再生されていた。次に、ページ選択用ステージ６０を図中符号Ｄ５が付された方向へ動かしていくと、アレイ光検出器６２で検出される信号は一度かなり弱くなったが、そのまま動かし続けると、今度はアレイ光検出器６２双方で信号が検出され、先ほどの右隣の素子からの信号が強くなった。信号強度が最大になるよう、ページ選択用ステージ６０を調整すると、符号Ｐ２が付された「ページ２」の画像が正確に再生された。同様に、符号Ｐ１が付された「ページ１」、符号Ｐ４が付された「ページ４」、符号Ｐ５が付された「ページ５」も、アレイ光検出器６２からの信号のみを手掛かりに、正確に再生することができた。
【００４８】
〔第２実施例〕
次に、光源と情報記録媒体との位置合わせに関する実施例について説明する。上述した第１実施例において、初めに情報記録媒体４９を装置にセットした状態ではホログラム画像は正確には観測されない。従って、上記の実施例では、最初に１枚のホログラム画像を観測しながら画像が正確に再生されるように、位置調整を行った。しかし、この方法は自動化には不向きである。本実施例では、始めから本発明の位置合わせ用ホログラムのみを用いて位置合わせを行った例を説明する。
【００４９】
図１１に示した情報記録媒体４９を図１２に示した装置にセットした直後、アレイ光検出器６２で検出される信号は弱かった。そこで、その位置の前後でページ選択用ステージ６０を少し動かすと、アレイ光検出器６２で、ページ番号Ｐ１が付された「ページ１」の位置合わせ用ホログラム４８ｂからの回折光が観測された。次に、ページ選択用ステージ６０を図中符号Ｄ４が付された方向へ動かすと、位置合わせ用ホログラム４８ｂからの回折光は、ページ番号Ｐ１が付された「ページ１」、ページ番号Ｐ２が付された「ページ２」、ページ番号Ｐ３が付された「ページ３」へと焦点が順次切り替わっていくのが観測されたが、移動限界点まで位置合わせ用ホログラム４８ａからの回折光は観測されなかった。
【００５０】
そこで、ページ選択用ステージ６０を反対に図中Ｄ５が付された方向へ動かしていった。位置合わせ用ホログラム４８ｂからの回折光は、ページ番号Ｐ５が付された「ページ５」からページ番号Ｐ１が付された「ページ１」まで順次切り替わっていくことが観測されたが、さらに動作を続けると、位置合わせ用ホログラム４８ａからページ番号Ｐ５が付された「ページ５」の信号が現れた。これより、円筒波面光源５４の集光線が、導波光ＰＷの進行方向に向かってコア層に対して反時計回りにずれていることが分かった。このずれを直すように、回転ステージ５６を僅かに回転して、再び、前述のようにページ選択用ステージ６０をスキャンした。しかし、状況は変わらないので、また回転ステージ５６を僅かに回転してページ選択用ステージ６０のスキャンを行った。
【００５１】
同様の動作を何度か繰り返すと、何度目かに位置合わせ用ホログラム４８ａからページ番号Ｐ５が付された「ページ５」の信号が、位置合わせ用ホログラム４８ｂからページ番号Ｐ１が付された「ページ１」の信号が同時に観測され、角度が確実に補正されつつあることが分かった。更に同じことを繰り返すと、今度は位置合わせ用ホログラム４８ａからページ番号Ｐ４が付された「ページ４」の信号が、位置合わせ用ホログラム４８ｂからページ番号Ｐ１が付された「ページ１」の信号が同時に観測された。
【００５２】
この状態からページ選択用ステージ６０を図中符号Ｄ４が付された方向へ動かすと位置合わせ用ホログラム４８ａからページ番号Ｐ５が付された「ページ５」の信号が、位置合わせ用ホログラム４８ｂからページ番号Ｐ２が付された「ページ２」の信号が同時に観測される位置があることが分かった。同じことをさらに何度も繰り返すと、位置合わせ用ホログラム４８ａと位置合わせ用ホログラム４８ｂから同じページの信号が同時に観測される状態になった。
【００５３】
ページ番号Ｐ１が付された「ページ１」にて、これら双方の信号強度が等しく、更に最大になるよう、ページ選択用ステージ６０、回転ステージ５６に加えて、Ｙ軸ステージ５８を微調整したところ、ページ番号Ｐ１が付された「ページ１」の画像が正しく再生されていることが分かった。この状態でページ選択用ステージ６０を動かすと、位置合わせ用ホログラム４８ａと位置合わせ用ホログラム４８ｂとから同時にページ番号Ｐ２が付された「ページ２」の信号をとらえる場所において、ページ番号Ｐ２が付された「ページ２」の画像が正確に再生された。その他のページも同様であった。
【００５４】
〔第３実施例〕
次に、第３実施形態について説明する。この第３実施形態では、２次元アレイ光検出器の情報記録媒体４９に対する位置合わせについて説明する。
これまでは特に必要がなかったために説明しなかったが、情報記録媒体に光を入射するとホログラムによって光は上方に回折されると同時に下方へも回折される。本実施例では、第２実施例と同様に上方に回折される光を観測して光源と媒体との位置合わせを行い、下方に回折されるホログラム画像をＣＣＤにて観測することとした。
【００５５】
本実施例では、図１０に示したホログラム４６及び位置合わせ用ホログラム４８ａ，４８ｂに、図１３に示した３つの位置合わせ用ホログラム６６ａ，６６ｂ，６６ｃ、及び位置合わせを補助するのに必要な情報をまとめた位置合わせ補助情報ホログラム７０を加えた。図１３は、本発明の第２実施例による情報記録媒体のコア層の一部を示す上面図である。位置合わせ用ホログラム６６ａ，６６ｂ，６６ｃは何れも導波光ＰＷを回折したときに球面波の回折光を生ずる。尚、６８ａ，６８ｂ，６８ｃは位置合わせ用ホログラム６６ａ，６６ｂ，６６ｃの回折光により形成される焦点位置を示す。
【００５６】
本実施例で用いる情報記録媒体４９も、上述した第１、第２実施例と同様の５ページからなる媒体で、５ページ全てにつき、画像再生のためのホログラム４６から下方へ回折される光の結像面をそろえ、情報記録媒体底面から下１ｍｍ、媒体下面と平行な面とした。また、位置合わせ用ホログラム６６ａについては、５つのページ全てについて上記結像面内の同じ点に集光するように設計した。位置合わせ用ホログラム６６ｂ，６６ｃについても同様である。位置合わせ用ホログラム６６ａ，６６ｂ，６６ｃからの回折光のスポットサイズは、結像面上すなわち焦点において、約φ１０μｍであった。なお、位置合わせ補助情報ホログラム７０には、ページアドレス情報、符号方式情報の情報を重畳させた。
【００５７】
ここで、ページアドレス情報とは、ページを区別するための識別子であり、第２実施例で用いたページ番号とは独立に各画像に異なる番号または名前を割り当てられる。本実施例の情報記録媒体は５枚のページを有するが、このような情報記録媒体複数からなる規模の大きな媒体では重要である。ページ番号Ｐ１が付された「ページ１」に“０１”を、ページ番号Ｐ２が付された「ページ２」に“０２”を、以下同様に“０５”までの番号を割り当てた。符号方式は、デジタル情報処理機器の外部記憶装置として用いる場合の、デジタルデータとホログラム画像との相互変換の方式である。本実施例では、デジタルデータヘの変換は行わず、番号“００”とした。
【００５８】
本実施形態では、図１４に示す光検出面を有する光検出器７２を用意した。図１４は、第３実施例で用いられる光検出器の光検出面の構成を示す図である。図１４に示したように、光検出器７２は、支持台７４の上にホログラム画像を読み取るＣＣＤ７６を固定し、その周りに位置合わせ用光検出器７８ａ〜７８ｃを配置し、更に、位置合わせ補助情報検出器８０を配置した。図１３と図１４とを比較すれば分かるように、位置合わせ用ホログラム６６ａには位置合わせ用光検出器７８ａが、位置合わせ用ホログラム６６ｂには位置合わせ用光検出器７８ｂが、位置合わせ用ホログラム６６ｃには位置合わせ用光検出器７８ｃがそれぞれ対応している。
【００５９】
位置合わせ用光検出器７８ａ、位置合わせ用光検出器７８ｂ、位置合わせ用光検出器７８ｃ共に、有効受光面はφ１０μｍの円形とした。更に、位置合わせ補助情報検出器６２は、位置合わせ補助情報ホログラム７０に対応して配置され、０．５ｍｍ四方のデ検出器１０個からなる。また、ＣＣＤ７６を含む全ての検出器の受光面は１平面内にそろえた。
【００６０】
図１５に示すように、図１４に示した光検出器７２をＸＹＺの３軸の平行移動と回転、あおりの調整ができる６軸ステージの上に固定し、図１２の装置に配置された情報記録媒体４９に対して−ｙ軸方向に位置するよう配置した。図１５は、第３実施例における情報記録媒体４９と光検出器７２との位置関係を示す図である。尚、６軸ステージにおける回転、あおりの回転中心は、全て位置合わせ用光検出器７８ｂの中心に精密に合わせた。以上で、読み取り装置の準備を完了し、次に実際にホログラム画像の読み取り操作を行った。
【００６１】
初めに情報記録媒体４９をセットし、引き続き第２実施例に記述した方法で、光源円筒波面光源５４と情報記録媒体４９との位置合わせを行い、５つのうちの１ページが正確に再生される状態にした。この状態では、ホログラム画像はＣＣＤ７６に対して図中ｘｙ軸方向に多少のズレがあり、またピントも合っていない。そこで、光検出器７２をＸＹ面内の２方向にスキャンした。この操作において、位置合わせ用光検出器７８ｂにて微弱な光が観測される領域があった。位置合わせ用光検出器７８ｂから得られる光信号が最大になる位置での光強度の１／１０以上の強度が観測される領域を称して領域Ａ１とした。
【００６２】
次に、位置合わせ用光検出器７８ｂが、領域Ａ１の概ね中心部に位置するよう、ＸＹ面内において移動させた。ここで、図１５のφ方向に光検出器７２を回転させると、位置合わせ用光検出器７８ｃで光信号が検出される領域があり、検出される信号が最大になる点で止めた。続いて、Ｚ軸方向に光検出器７２を僅かに移動させ情報記録媒体４９に近づけると、位置合わせ用光検出器検出器７８ｂで観測される光が強くなった。
【００６３】
ここで、再びＸＹ面内のスキャンを領域Ａ１内で行い、光信号が最大になる位置での光強度の１／１０以上の強度が観測される領域を称して領域Ａ２とした（このとき、Ａ２はＡ１に含まれる）。位置合わせ用光検出器７８ｂが、領域Ａ２の概ね中心部に位置するよう、光検出器７２をＸＹ面内において動かした。ここで、再び位置合わせ用光検出器７８ｃで検出される信号が最大になる点まで、φ方向に回転した。続いて、光検出器４９をｚ軸方向へ移動させて情報記録媒体４９に近づけた。同じ操作を繰り返し、スキャン領域を狭めていったところ、ｎ回目に、Ｚ軸ステージによって光検出器を媒体に近づけると、それまでとは逆に光信号が弱くなり、領域Ａｎ内でスキャンを行っても前回よりも強い光信号が得られなかった。ここで、ｎは自然数である。
【００６４】
これは、焦点を通り過ぎたかまたは焦点に非常に近いことを意味するので、情報記録媒体の位置をｎ−２回目の位置に戻し、媒体への近づけ方を遅く設定して、再び操作を繰り返した。Ｚ軸ステージの精度ではスキャン領域を狭められなくなったところで操作を止めた。最後に、ψ、θ方向のあおりを調整して、位置合わせ用光検出器７８ｃでも最大の光信号が得られるようにした。このとき、ＣＣＤ７６で検出される画像信号は、ホログラム画像に忠実であり、ピントが正しく含わせられていることが、確認された。また、位置合わせ補助情報ホログラム７０領域に載せられたページアドレス情報（“０１”〜“０５”）、符号方式情報（“００”）も正しく読み取ることができた。
【００６５】
【発明の効果】
以上説明したように、本発明によれば、ホログラムによって情報を記憶する情報記録媒体において、情報再生用の光源と情報記録媒体との間、光検出器と媒体との間で位置合わせを容易に行うことができ、その結果誤り発生率を抑制することができるという効果がある。
【図面の簡単な説明】
【図１】本発明の実施形態が適用される情報記録媒体の概略を示す斜視図である。
【図２】本発明の第１実施形態による情報記録媒体の構成の一部を示す模式図である。
【図３】図２に示した構造のコア層１２を複数有する情報記録媒体１０の断面図である。
【図４】本発明の第２実施形態による情報記録媒体の構成の一部を示す模式図である。
【図５】図４に示したコア層１２を複数を備える情報記録媒体１０への光入射の様子を説明する図である。
【図６】本発明の第３実施形態による情報記録媒体の構成の一部を示す断面図である。
【図７】各コア層に形成された位置合わせ用ホログラムが互いに異なる位置に焦点を合わせるような構成とした場合の焦点位置の最も単純な例を説明するための図である。
【図８】情報記録媒体１０とホログラム画像読み取り用の２次元アレイ光検出器との位置合わせ方法を説明するための図である。
【図９】ピンホールとアレイではない単体の光検出器を用いた位置合わせ方法を説明する図である。
【図１０】本発明の第１実施例による情報記録媒体のコア層の一部を示す上面図である。
【図１１】本実施例による情報記録媒体の断面図である。
【図１２】図１１に示した本実施例による情報記録媒体４９に記録された情報を読み出す装置の簡略構成を示す図である。
【図１３】本発明の第２実施例による情報記録媒体のコア層の一部を示す上面図である。
【図１４】第３実施例で用いられる光検出器の光検出面の構成を示す図である。
【図１５】第３実施例における情報記録媒体４９と光検出器７２との位置関係を示す図である。
【図１６】再生専用多重ホログラムカードの原理を示す図である。
【符号の説明】
１０…情報記録媒体、１２ａ，１２ｂ，１２ｃ，１２ｄ，１２ｅ，３０ａ〜３０ｇ…コア層（光導波路）、１４ａ，１４ｂ，１４ｃ，１４ｄ，１４ｅ，１４ｆ…クラッド層（光導波路）、１６ｃ，２２，２６…ホログラム、２４，２４ｂ，２４ｃ，２４ｄ，２８ａ，２８ｂ，３２，３２ａ…位置合わせ用ホログラム（位置合わせ構造）、ＦＰ，ＦＰａ．ＦＰｂ．ＦＰｃ…焦点（所定の点）。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information recording medium and an information reproducing method, and more particularly to an information recording medium suitable for use as a portable memory card such as a magnetic card and an IC card and a reproducing method thereof.
[0002]
[Prior art]
Conventionally, a magnetic card such as a telephone card is used as a general information card that can be carried in a pocket. In recent years, IC cards have appeared and are considered to be applied to electronic commerce. Although magnetic cards are inexpensive, there is a risk of counterfeiting, and there are drawbacks that IC card counterfeiting is difficult but the bit unit price becomes expensive.
[0003]
In order to make up for this drawback, a read-only multiplex hologram card made by stacking planar single mode optical waveguides including diffraction gratings in a multilayer manner so as to generate a hologram image has been devised. Details of this card are described in Japanese Patent Application No. 11-036540, and will be briefly introduced here.
A so-called slab optical waveguide with a structure in which a plate-like transparent medium such as quartz or plastic is used as a core layer and is sandwiched by a medium having a lower refractive index than that is used to confine light in the core layer and propagate in the in-plane direction. It can be applied to optical communication parts such as semiconductor lasers. The reproduction-only multiplex hologram card is characterized in that the waveguides are stacked in layers, and each waveguide layer includes a hologram.
[0004]
FIG. 16 is a diagram showing the principle of a reproduction-only multiplex hologram card. In FIG. 16, a cross section of the hologram card is shown.
The reproduction-only multiplex hologram card 100 shown in FIG. 16 has a structure in which a clad layer 102a, a core layer 104a, a clad layer 102b, a core layer 104b, a clad layer 102c, a core layer 104c,. is there.
[0005]
The core layers 104a, 104b, 104c,... Having a higher refractive index than the clad layers 102a, 10b, 102c,... Constitute a waveguide layer, and the core layers 104a, 104b, 104c,. A scattering factor (hologram) 106 on which information is previously superimposed by the method is formed. In addition, a part denoted by reference numeral 108 in the figure is cut at 45 °, and a reflective surface 110 is formed at this part. In FIG. 16, reference numeral LB denotes laser light emitted from a light source (not shown) such as a semiconductor laser, and 114 denotes a convex lens for condensing the laser light LB.
[0006]
A laser beam LB emitted from a laser light source (not shown) is collected by a convex lens 114, is incident from the surface 101 of the reproduction-only multiplex hologram card 100, and is incident on a coupling point 116 in the example shown in FIG. The laser beam LB incident on the coupling point 116 is reflected by the reflecting surface 110, couples to the core layer 104b, and propagates in the core layer 104b as guided light PB in a direction parallel to the layer. The guided light PB is scattered by the hologram 106 formed on the core layer 104b, and is emitted as a diffracted light DB from the surface 101 of the reproduction-only multiplex hologram card 100, and a hologram image Im is formed by the diffracted light DB. By reading this hologram image Im with a two-dimensional photodetector such as a CCD, it is possible to read information superimposed as a hologram 106 on the core layer 104b. Also, the core layer to which the laser beam LB light is coupled is changed by moving the convex lens 114 in FIG. 16 in the direction indicated by reference sign D100 in the figure, and the core layer 104a, the core layer 104b, the core layer 104c,. The recorded information can be read out separately.
[0007]
[Problems to be solved by the invention]
By the way, the performance index of the reproduction-only multiplex hologram card includes a recording capacity, an information reproduction speed, an error occurrence rate, and the like. These are not independent but closely related to each other. The recording capacity of one medium can be improved by improving the information capacity of the hologram associated with one core layer, that is, placing more information on the hologram image. However, if an attempt is made to increase the amount of information while maintaining the image quality of the hologram image, the error rate increases. For this reason, in order to perform error correction, it is necessary to increase the redundancy of information to be recorded in advance, and there is a problem that the net information capacity cannot be increased after all.
[0008]
Originally, hologram images are sequentially read out one by one, and the laser beam LB is coupled to only one of the plurality of core layers at a time, but the method of introducing light into the medium is poor. Then, the laser beam LB is coupled to a plurality of core layers at a time, and as a result, a plurality of hologram images are overlapped, and the image quality is deteriorated. This is referred to as crosstalk. If the interval between adjacent core layers is increased (in other words, the thickness of the cladding layer is increased), the crosstalk is improved. However, this reduces the number of cores of one medium. Therefore, in order to correctly introduce light into the medium, precise alignment between the light source and the medium is important.
[0009]
On the other hand, the diffracted light DB diffracted by the hologram 106 forms an image at a position separated by a predetermined distance and becomes a hologram image Im. At this position, an image is detected by a two-dimensional photodetector. As a matter of fact, when the position of the two-dimensional photodetector is shifted, the focus is lost. As a result, the image quality deteriorates and the error occurrence rate increases. For this reason, the alignment between the medium and the two-dimensional detector is also important.
[0010]
The present invention has been made in view of the above circumstances, and can accurately perform the relative alignment between the light source and the medium and the relative alignment between the medium and the two-dimensional photodetector, and as a result. An object of the present invention is to provide an information recording medium and an information reproducing method capable of suppressing an error occurrence rate.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, an information recording medium of the present invention has a single-mode planar optical waveguide, and the information recording medium records information by a hologram. Diffracted light that is confined near the core layer of the optical waveguide and propagates in the optical waveguide An alignment structure is provided. It is preferable that a plurality of each optical waveguide is provided. Here, the alignment structure is , One pair is preferably provided for each of the optical waveguides. More specifically, the alignment structure selectively diffracts the light propagating through the optical waveguide in a direction substantially perpendicular to the surface of the optical waveguide or the light propagating through the optical waveguide in a specific direction. It is a hologram that is selectively diffracted. this Used in alignment structure The hologram is preferably one that diffracts light propagating in different waveguides in different directions.
Another aspect of the alignment structure is a hologram that collects diffracted light in the vicinity of a specific point inside the surface of the information recording medium or outside the information recording medium. this Used in alignment structure The hologram is preferably a hologram that condenses light diffracted from light propagating through different waveguides in the vicinity of different predetermined points.
Furthermore, another aspect of the alignment structure has three or more points on which the diffracted light is collected.
The information reproducing method of the present invention is an information reproducing method for reproducing information recorded on an information recording medium, wherein light is incident on the information recording medium according to claim 6 by a predetermined method, and the information recording medium is reproduced. A direction in which light is diffracted by the formed hologram is detected, and which core layer is coupled with the light having the highest intensity is measured according to the detection result.
The information reproducing method of the present invention is an information reproducing method for reproducing information recorded on an information recording medium, wherein light is incident on the information recording medium according to claim 9 in a predetermined direction, and the information recording medium is A condensing position of light diffracted by the formed hologram is detected, and the core layer is measured to which light having the highest intensity is coupled according to the detection result.
According to the present invention having the above configuration, the alignment structure is configured by a hologram, and as a result, the energy of the diffracted light can be concentrated, which is not only convenient for observation but also diffracted for each individual waveguide. If the directions are different, the direction of the diffracted light can be observed to determine which waveguide is currently guiding the light, which is effective for alignment.
Such an information recording medium according to the present invention is difficult to forge or duplicate, so it can be used as an electronic commerce quote authentication card, and can be produced at a low cost with a large storage capacity, so a CD, CD-ROM, DVD, etc. Thus, it is suitable for uses such as distribution of music, video software or computer software.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an information recording medium and an information reproducing method according to an embodiment of the present invention will be described in detail with reference to the drawings.
Before describing the present embodiment in detail, an outline of an information recording medium and an information reproducing method to which the present embodiment is applied will be described.
FIG. 1 is a perspective view schematically showing an information recording medium to which an embodiment of the present invention is applied. The information recording medium 10 shown in FIG. 1 has a cladding layer 14a, a core layer 12a, a cladding layer 14b, a core layer 12b, a cladding layer 14c, a core layer 12c, a cladding layer 14d, a core layer 12d, and a cladding layer in order from the surface 11a. 14e, the core layer 12e, and the clad layer 14f are laminated in this order. The core layers 12a to 12e are formed using a material having a refractive index higher than that of the cladding layers 14a to 14f. The core layers 12a to 12f form a planar single mode optical waveguide. The core layers 12a to 12e preferably have a higher refractive index than all the cladding layers 14a to 14f, but the structure is not limited to this. For example, each core layer 12a must be higher in refractive index than the adjacent cladding layers 14a and 14b, but may have a lower refractive index than the cladding layer 14f.
[0013]
In each of the core layers 12a to 12e, holograms (scattering factors) on which information is preliminarily superimposed are formed by a method such as modulating the refractive index. In FIG. 1, only the hologram 16c formed on the core layer 12c is conceptually shown in a planar shape. The information recording medium 10 according to the present embodiment has a substantially rectangular parallelepiped shape, and has a structure in which the core layers 12a to 12e and the cladding layers 14a to 14f are exposed to the outside on the end surface 11b.
[0014]
A cylindrical lens 18 condenses a plane light wave PL from a light source (not shown) in the direction indicated by the symbol D1, but does not collect light in a direction orthogonal to the direction indicated by the symbol D1. It is. That is, the cylindrical lens 18 is for converting the plane light wave PL into a light wave CL having a cylindrical wavefront and coupling it to any one of the core layers 12 a to 12 e of the information recording medium 10.
[0015]
In the example shown in FIG. 1, an example in which light collected on a line parallel to the boundary between the core layer and the clad layer on the end face of the information recording medium 10 is incident from the coupling position 19 using the cylindrical lens 18. However, the present invention is not limited to this. For example, the reflective surface 110 shown in FIG. 16 is formed on a part of the information recording medium 10 and the plane light wave PL is incident from the surface of the information recording medium 10. You may do it. Reference numeral 20 denotes an imaging surface on which a hologram image Im generated by the diffracted light DW generated by diffracting the guided light PW propagating through any of the core layers 12a to 12e by the hologram is formed. Note that the hologram image Im can be converted into an electrical signal by aligning the light detection surface of a two-dimensional photodetector such as a CCD with the imaging surface 20.
[0016]
The light source (not shown), the cylindrical lens 18, and the two-dimensional photodetector are provided in a reproducing device (not shown) that reproduces and reads the hologram image Im from the information recording medium 10, and the information recording medium 10 is removed from the reproducing device. It is portable (removable medium).
[0017]
In the above configuration, the planar light wave PL emitted from a light source (not shown) is condensed by the cylindrical lens 18 into a light wave CL having a cylindrical wavefront, and enters the core layer 12c from the coupling position 19 of the end surface 11b of the information recording medium 10. To do. The light incident on the core layer 12c propagates in the core layer 12c as guided light PW in a direction parallel to the layer. The guided light PW is scattered by the hologram 16c formed on the core layer 12c, and is emitted from the surface 11a of the information recording medium 10 as diffracted light DW. A hologram image Im is formed on the imaging surface 20 by the diffracted light DW. . By reading this hologram image Im with a two-dimensional photodetector such as a CCD, it is possible to read information superimposed as a hologram 16c on the core layer 12c. In addition, by changing the position of the cylindrical lens 18 and setting the coupling position 19 in another core layer, information recorded in the other core layer can be read out separately.
[0018]
At this time, if the coupling method between the light collected on the straight line by the cylindrical lens 18 and the core layer is appropriate, the light energy is concentrated on only one core layer, and the light coupled to the other core layers has an intensity. Can be ignored. Therefore, the hologram images respectively formed in different core layers are not observed overlapping each other. However, if the coupling method is not appropriate, the guided light propagates simultaneously to the plurality of core layers, and as a result, the plurality of hologram images are overlapped and observed. In addition, since a laser is usually used as the light source, the plurality of hologram images do not simply overlap but interfere with each other. In the present embodiment, the final goal is to eliminate such inconvenience and suppress the error occurrence rate. For this purpose, the image quality of the hologram image Im must be good. In addition, a target hologram image must be accurately selected from a plurality of hologram images and reproduced.
[0019]
[First Embodiment]
Next, a first embodiment of the present invention will be described.
FIG. 2 is a schematic diagram showing a part of the configuration of the information recording medium according to the first embodiment of the present invention.
In the present embodiment, there is provided an information recording medium and an information reproducing method capable of examining “which core layer is currently guiding light” in order to select a target hologram image from a plurality of hologram images. provide.
In this embodiment, in addition to forming a hologram in the core layer of the information recording medium 10 shown in FIG. 1, a positioning hologram for examining “which core layer is currently guiding light” is formed. doing.
[0020]
FIG. 2 shows the structure of the core layers 12a to 12e in FIG. 1, and a hologram 22 for information recording and a hologram 24 for alignment are formed on the core layer 12. The guided light PW propagating through the core layer 12 is diffracted by the hologram 22 and the alignment hologram 24. As a result, the hologram 22 generates the diffracted light DW1 and the alignment hologram 24 generates the diffracted light DW2.
[0021]
Here, the alignment hologram 24 is designed so as to selectively diffract light in one direction. For example, as shown in FIG. 2, the alignment hologram 24 has a straight line that is perpendicular to the traveling direction of the guided light PW and has a longitudinal direction in a direction parallel to the core layer 12. The pattern is such that the interval is 2π / β (β is the propagation constant of the waveguide). At this time, if the area of the alignment hologram 24 is sufficiently large, the diffracted light DW2 travels in a direction perpendicular to the core layer 12.
[0022]
FIG. 3 is a cross-sectional view of the information recording medium 10 having a plurality of core layers 12 having the structure shown in FIG. FIG. 3 is a diagram when the core layer 12 having the structure shown in FIG. 2 is applied to the information recording medium 10 shown in FIG. As shown in FIG. 3, alignment holograms 24b to 24d are formed in the core layers 12b to 12d, respectively. The alignment holograms 24b to 24d formed on the core layers 12b to 12d are different in the following points. That is, as shown in the drawing, the light wave CL is incident from the end surface 11b of the information recording medium 10, but the alignment hologram 24c diffracts the incident light wave CL in a direction perpendicular to the core layer 12c and diffracted light DW4. The alignment hologram 24b is diffracted in the diagonally upward right direction in the drawing to be diffracted light DW3, and the alignment hologram 24d is diffracted in the diagonally upward left direction in the drawing to be diffracted light DW5. This is the structure. As described above, the alignment hologram formed for each core layer has a structure that generates diffracted light traveling in different directions, so which core layer the incident light wave CL is incident on and guided to. This can be understood by observing the traveling direction of the diffracted light.
[0023]
The hologram 22 and the alignment hologram 24 only need to be able to diffract the guided light propagating through the core layer, and are not limited to their formation positions. For example, the hologram 22 and the alignment hologram 24 may be formed inside the core layer or at the interface between the core layer and the adjacent cladding layer. In addition, as is well known, the waveguide mode propagating through the core layer oozes out to the cladding layer as well, so even within the cladding layer, the hologram 22 and alignment can be achieved if it is made sufficiently close to the core layer. The hologram 24 can perform its function.
[0024]
In the example shown in FIG. 2, the structure is shown in which the alignment hologram 24 is arranged beside the hologram 22 inside the core layer 12, but this position is not limited. In FIG. 2, any of the front side, back side, right side, and left side of the hologram 22 is natural, and the hologram 22 may be partially or entirely overlapped.
[0025]
Further, there is a method of designing a hologram that simultaneously generates both the diffracted light DW1 forming the hologram image Im and the diffracted light DW2 used for alignment. In this case, the hologram 22 and the alignment hologram are used. 24 are grouped together. Such a hologram generates a light wave field expressed by superposition of the diffracted light DW1 forming the hologram image Im and the diffracted light DW2 for alignment.
[0026]
As described above, the image quality of the hologram image Im deteriorates if the coupling method between the light wave incident on the information recording medium 10 and the core layer is not appropriate. The coupling method here includes a method of aligning the focal position of the light wave CL and the core layer shown in FIG. 1 as the incident light wave. Next, the relationship between the focal position of the cylindrical wavefront CL and the coupling position 19 will be described.
[0027]
[Second Embodiment]
FIG. 4 is a schematic diagram showing a part of the configuration of the information recording medium according to the second embodiment of the present invention. In the second embodiment shown in FIG. 4, a hologram 26 and two alignment holograms 28 a and 28 b are formed on the core layer 12. The alignment holograms 28a and 28b are formed in a pair of left and right with respect to the traveling direction of the guided light PW. Further, the core layer 12 shown in FIG. 4 is formed as each of the core layers 12a to 12e in FIG. 1, but light is actually transmitted in the directions of the diffracted lights DW7a and DW7b as shown in FIG. It is designed so that the core layer being guided can be detected.
[0028]
FIG. 5 is a diagram illustrating a state of light incidence on the information recording medium 10 including a plurality of core layers 12 illustrated in FIG. Each core layer is numbered 30a-30g in order from the bottom. FIG. 5 is a cross-sectional view of the information recording medium 10 having a plurality of core layers 12 shown in FIG. 4. However, the illustration is simplified for easy understanding, and FIG. A cross section when the information recording medium 10 is cut along a plane perpendicular to the traveling direction of the wave light PW is shown.
[0029]
As described above, the information recording medium 10 can be removed from a reproducing device (not shown) and can be carried. In FIG. 5, the information recording medium 10 is purely used without electricity immediately after the information recording medium 10 is loaded into the reproducing device. In addition, it is assumed that only mechanical and rough positioning on the order of 0.1 mm has been completed.
In this state, as shown in the figure, the incident light IW obtained by condensing the wavefront CL on a straight line is inclined with respect to the core layers 30 a to 30 g of the information recording medium 10. In the figure, the regions labeled Z1 and Z2 are regions where the alignment holograms 28a and 28b formed in the core layers 30a to 30g are respectively arranged. At this time, only the core layer 30b receives incident light on the alignment hologram in the region Z1. Accordingly, in the region Z1, the incident light IW is incident on the core layer 30b to generate the diffracted light DW8. As a result, it is detected that the guided light PW is propagating through the core layer 30b.
[0030]
In addition, only the core layer 30f is incident on the alignment hologram in the region Z2 in the figure. Accordingly, in the region Z2, the incident light IW is incident on the core layer 30f to generate the diffracted light DW9. As a result, it is detected that the guided light PW is propagating through the core layer 30f. By comparing the detection signals in the areas Z1 and Z2, it can be seen how much the information recording medium 10 is inclined in either direction with respect to the incident light IW. From this state, when the angle is shifted in the direction in which the information recording medium 10 and the incident light Iw are aligned, the core layers detected in the areas Z1 and Z2 become closer, and conversely, the inclination is increased. The core layer to be done becomes more separated. Thereby, the inclination of the information recording medium 10 with respect to the incident light IW can be corrected. At the same time, when the positions of the information recording medium 10 and the incident light IW are vibrated in the vertical direction in FIG. 5, the core layers detected in the regions Z1 and Z are the same core layer and are used for alignment. Appropriate light incidence can be realized at an angle and position with respect to the incident light IW of the information recording medium 10 at which the intensities of the diffracted light by the holograms 28a and 28b are equal and the intensities of these diffracted lights are both maximum.
[0031]
[Third Embodiment]
FIG. 6 is a sectional view showing a part of the configuration of the information recording medium according to the third embodiment of the present invention. A hologram has a degree of freedom in generating an optical wavefront, and can generate a so-called spherical wave optical wavefront that collects incident light at a single point like a general lens. In the present embodiment, a hologram that diffracts the guided light PW and focuses it on a point outside the information recording medium 10 is used as the alignment hologram. There are various forms of holograms having this function, and the present embodiment is not limited to specific forms of holograms.
[0032]
For example, a hologram that generates diffracted light that is focused on the focal point FP in FIG.
[Expression 1]

If it is.
Here, θ in Equation 1 is an angle formed by a straight line passing through the focal point FP and perpendicular to the boundary between the core layer 12 and the cladding layers 14a and 14b and a straight line passing through the point P in the hologram 32 and the focal point FP. Z is the position in the propagation direction of the guided light PW in the core layer 12, β is the propagation constant of the guided light PW in the core layer 12, λ is the wavelength of the guided light PW, and A, φ, and f are real constants. It is.
Although this hologram can be positioned as a special case of the first embodiment and the second embodiment described above, an additional effect can be obtained. First, the light power is concentrated by condensing, and a diffracted light signal can be taken large.
[0033]
Further, when the spherical wave is used for detecting the core layer in which the guided light PW is propagating, the configuration may be such that the alignment holograms of the respective waveguides are focused on different positions. FIG. 7 is a diagram for explaining the simplest example of the focal position when the alignment holograms formed on the core layers are configured to focus on different positions. FIG. 7 shows a case where the focal points FPa to FPc formed by the respective alignment holograms 32a to 32c in the information recording medium 10 shown in cross section are periodically arranged on a straight line.
[0034]
A linear image sensor such as an N-MOS or C-MOS, a one-dimensional array photosensor such as a one-dimensional CCD, or a photodetector 34 such as a light spot position detecting element (PSD) is arranged on this straight line. It is possible to detect which core layer the wave light propagates through. As described above, the second effect is that the detection device that detects which core layer the guided light propagates can be reduced in size by narrowing the diffracted light to a small focal point.
As a modification of this embodiment, there is a form in which light is condensed into a line as a set of points. In this form as well, the first and second effects described above can be obtained in exactly the same way. Holograms that converge linearly can be realized in the form of a collection of holograms that converge in a dotted manner.
[0035]
The third effect is that it can be used not only for alignment of the incident light IW and the information recording medium 10 but also for alignment of the information recording medium 10 and the two-dimensional array photodetector for reading the hologram image.
FIG. 8 is a diagram for explaining an alignment method between the information recording medium 10 and the two-dimensional array photodetector for reading a hologram image. In FIG. 8, the hologram 22 and the alignment hologram 32 are formed on the core layer 12 a, and a state in which the diffracted light of the hologram 22 correctly combines the hologram images on the imaging surface 38 is shown. The spherical diffracted light CD1 is shown focused on the focal point FP.
[0036]
A hologram image obtained by the hologram 22 is read by being converted into an electrical signal by a two-dimensional array photodetector 36 such as a CCD. If the light detection surface of the photodetector is shifted from the image plane 38, the image is focused. Blurred and the signal cannot be read correctly.
Here, the two-dimensional array photodetector 36 and the photodetector 34 are fixed to each other, and can be brought into focus by moving them simultaneously. The photodetector 34 may be a two-dimensional array photodetector similar to the two-dimensional array photodetector 36, for example. When the photodetector 34 is a two-dimensional array photodetector, what is observed is a circular pattern that is a cross section of the spherical diffracted light CD1. This circular pattern becomes smaller as it approaches the focal point FP of the spherical diffracted light CD1. Therefore, it is possible to move the photodetector 34 while observing the circular pattern, and to adjust the light receiving surface of the photodetector to the focal point of the spherical diffracted light FP. As mentioned above. The light detection surfaces of the light detector 34 and the two-dimensional array light detector 36 are aligned. In this case, as shown in FIG. 8, if the alignment hologram 32 is designed so that the focal point of the spherical diffracted light CD1 is located in the imaging plane 38, the light receiving surface of the photodetector 34 and When the focal point of the spherical diffracted light FP is aligned, the light receiving surface of the two-dimensional array photodetector 36 and the imaging surface 38 naturally match, that is, focus.
[0037]
The focus adjustment, that is, the alignment method in the direction indicated by the symbol D2 in FIG. 8 has been described above, but the alignment in the direction indicated by the symbol D3 in FIG. Also in this case, if a two-dimensional array photodetector or a light spot position detection element (PSD) is used for the photodetector 34 as described above, the focal point FP of the spherical diffracted light CD1 is located anywhere on the light receiving surface of the photodetector 34. Since it can be detected whether or not there is, it is only necessary to translate to a predetermined position. If rotational alignment within the image plane 38 is also required, two spherical diffracted waves that focus on at least two points may be prepared.
[0038]
By the way, as described above, when a two-dimensional array photodetector is used as the photodetector 34, the phenomenon is intuitive, which is convenient for performing alignment manually. However, a two-dimensional array photodetector such as a CCD is expensive, and in the case of performing automatic alignment, the reference symbol D2 is given from the intensity pattern of the spherical diffracted light CD1 received by the two-dimensional array photodetector. In order to determine the positional deviation in the direction indicated by the direction D3 and the direction D3, sometimes complicated image processing is required, and the alignment is not necessarily performed at high speed. As a method that is cheaper than a two-dimensional array photodetector and can be aligned at high speed, there is a method using a pinhole.
[0039]
FIG. 9 is a diagram for explaining an alignment method using a single photodetector that is not a pinhole and an array. As shown in FIG. 9, a mask 41 having a pinhole 42 is disposed on the light detection surface of a single photodetector 40. In the same figure, if there is no position shift in the direction indicated by the symbol D3, the light intensity is inversely proportional to the square of the shift from the image plane 38 except in the very vicinity of the focal point FP. Therefore, since the optical signal leaked from the pinhole and observed by the photodetector 40 is also inversely proportional to the square of the deviation from the imaging plane 38, it is combined with the two-dimensional array photodetector 36 so as to obtain the maximum signal. If the photo detector 40 is moved in the direction indicated by the symbol D2, the camera is focused. However, it may not be guaranteed that there is no positional deviation in the direction to which the symbol D3 is attached. In this case, there is a possibility that the spherical diffracted wave CD1 may be lost simply by moving in the direction indicated by the symbol D2. For this reason, it is necessary to move in the direction to which the symbol D3 is attached and to perform alignment while searching for the spherical diffraction wave CD1.
[0040]
Note that the light receiving surface of the two-dimensional array photodetector 36 is not necessarily parallel to the image plane 38 of the hologram image, and there is a case where the tilt angle needs to be adjusted. In this case, three spherical diffraction waves that focus on at least three points are required. In order to generate these spherical diffracted waves, three alignment holograms are formed on the core layer 12, and these three may or may not overlap each other. It is the same as described above that all may be diffracted simultaneously.
[0041]
【Example】
[First embodiment]
FIG. 10 is a top view showing a part of the core layer of the information recording medium according to the first embodiment of the present invention. In FIG. 10, 44 is one of the core layers of the information recording medium according to the first embodiment of the present invention. In the present embodiment, incident light from a light source (not shown) enters from the end face 45, and guided light PW in the direction shown in the figure propagates through the core layer 44. 46 is a hologram for image reproduction, and 48a and 48b are alignment holograms. The hologram 46 is formed on almost the entire surface of the core layer 44 on the end face 45 side. The alignment holograms 48a and 48b are holograms for forming the spherical diffracted wave CD1 shown in FIG. 6 and are formed on the end face side facing the end face 45. Reference numerals 50a and 50b in the figure indicate focal points formed by the alignment holograms 50a and 50b when the guided light PW is incident on the alignment holograms 48a and 48b. Since FIG. 10 is a top view of the core layer 44, the focal points 50a and 50b are superimposed on the alignment holograms 48a and 48b.
[0042]
The information recording medium of this example was prepared with a structure comprising five waveguides, that is, five core layers 44 shown in FIG. 10 and a clad layer formed between these core layers 44. . Then, the five pieces of image information were superimposed on the holograms 46 of the respective core layers 44. In this embodiment, the numbers from “page 1” to “page 5” are given to the holograms of the respective core layers 44.
[0043]
FIG. 11 is a cross-sectional view of the information recording medium according to this embodiment. In the present embodiment, as in the prior art shown in FIG. 16, in order to introduce incident light into each core layer, a part of the information recording medium 49 is cut at 45 ° to form a reflective surface. The light CL1 having a cylindrical wavefront is incident from a direction perpendicular to each layer. The light diffracted from the alignment holograms 48 a and 48 b formed in all the core layers is condensed in a plane 52 that is 1 mm above the upper surface of the information recording medium 49 and parallel to the surface of the information recording medium 49. Designed. In FIG. 11, P1 to P5 indicate page numbers assigned to the core layers. That is, “page 1” is assigned as the page number to the core layer indicated by reference numeral P1, and “page 5” is assigned as the page number to the core layer indicated by reference numeral P5. Reference numerals FP1 to FP5 indicate focal points formed by the alignment holograms 48a and 48b formed in the core layers assigned the page numbers P1 to P5, respectively. The alignment holograms 48a and 48b are formed such that the focal points FP1 to FP5 are arranged with a distance of 0.1 mm in the plane 52.
[0044]
FIG. 12 is a diagram showing a simplified configuration of an apparatus for reading information recorded on the information recording medium 49 according to the present embodiment shown in FIG. In FIG. 12, reference numeral 54 denotes a cylindrical wavefront light source, which includes a semiconductor laser, a collimator, and a cylindrical lens, and is a light source that generates a cylindrical wave. Reference numeral 56 denotes a rotation stage that rotates the cylindrical wavefront light source 49 around the y-axis in the drawing. Reference numeral 58 denotes a Y stage that moves the cylindrical wavefront light source 54 in the y-axis direction in the figure, and reference numeral 60 denotes a page selection stage that moves the cylindrical wavefront light source 54 in the direction labeled D1 or D2 in the figure. The page selection stage 60, the Y stage 58, and the rotary stage 56 are driven to adjust the position at which the cylindrical wavefront light CL1 emitted from the cylindrical wavefront light source 54 enters the information recording medium. The page selection stage 60 is mainly used for page selection, and the Y-axis stage 58 is used for adjusting the focal position of the incident cylindrical wave. In FIG. 12, reference numeral 62 denotes an array photodetector that detects spherical diffracted light emitted from the position detection hologram.
[0045]
First, when each stage was adjusted so that the image of “page 1” with the page number P1 was accurately reproduced, two bright spots were generated by the diffracted light from the alignment holograms 48a and 48b simultaneously with the hologram image. Observed. The spot size of each focus at the focus position was about φ10 μm. When the focus of the cylindrical wavefront light CL1 is moved in the direction D4 in the figure using the page selection stage 60, the image of “page 1” with the page number P1 disappears and “page with the page number P2” 2 "image appeared. When the image was moved further, the images were switched to “page 3” with page number P3, “page 4” with page number P4, and “page 5” with page number P5. At the same time, it was observed that the bright spots corresponding to the alignment holograms 48a and 48b were shifted by 0.1 mm in the x-axis direction in FIG. It was confirmed that the hologram formed an image accurately at the position where the brightness of each bright spot was the strongest.
[0046]
Next, one array photodetector 62 was placed right above the alignment hologram 48a and the alignment hologram 48b. The array photodetector 62 was placed so that these five individual elements were aligned with the positions of the five focal points of the alignment hologram 48a. In this embodiment, the focal points are arranged on the same straight line for the sake of design, but the present invention is not limited to this. Similarly, another array photodetector 62 was installed in accordance with the alignment hologram 48b. The element was adjusted to the focus of the alignment hologram 48a and the alignment hologram 48b. Each of the array photodetectors 62 includes five elements, and is arranged in the z direction in FIG. 12 at a pitch of 0.1 mm. The array photodetector 62 is placed so that this element is aligned with each of the five focal points of the alignment hologram 48a and the alignment hologram 48b.
[0047]
When the page selection stage 60 was moved to an arbitrary position, light was detected by the central element in both of the array photodetectors 62. Therefore, when the page selection stage 60 is slightly moved before and after the position, there is a position where the light detection signal becomes maximum. Therefore, when observing the hologram image, “page 3” to which the reference symbol P3 is attached was accurately reproduced. Next, when the page selection stage 60 is moved in the direction indicated by the symbol D5 in the figure, the signal detected by the array photodetector 62 becomes considerably weak once. A signal was detected by both the photodetectors 62, and the signal from the element on the right side just became stronger. When the page selection stage 60 was adjusted so that the signal intensity was maximized, the image of “page 2” denoted by reference symbol P2 was accurately reproduced. Similarly, “page 1” to which reference symbol P1 is attached, “page 4” to which reference symbol P4 is attached, and “page 5” to which reference symbol P5 is attached are also based on only signals from the array photodetector 62. I was able to play it accurately.
[0048]
[Second Embodiment]
Next, an embodiment relating to alignment between the light source and the information recording medium will be described. In the first embodiment described above, the hologram image is not accurately observed when the information recording medium 49 is initially set in the apparatus. Therefore, in the above embodiment, the position adjustment is performed so that the image is accurately reproduced while observing one hologram image first. However, this method is not suitable for automation. In this embodiment, an example will be described in which alignment is performed using only the alignment hologram of the present invention from the beginning.
[0049]
Immediately after the information recording medium 49 shown in FIG. 11 was set in the apparatus shown in FIG. 12, the signal detected by the array photodetector 62 was weak. Therefore, when the page selection stage 60 was slightly moved before and after that position, the array light detector 62 observed the diffracted light from the alignment hologram 48b of “page 1” assigned the page number P1. Next, when the page selection stage 60 is moved in the direction labeled D4 in the figure, the diffracted light from the alignment hologram 48b is labeled "page 1" with page number P1 and page number P2. It was observed that the focal point was sequentially switched to “Page 2” and “Page 3” with page number P3, but no diffracted light from the alignment hologram 48a was observed until the movement limit point. It was.
[0050]
Therefore, the page selection stage 60 was moved in the direction opposite to D5 in the figure. It has been observed that the diffracted light from the alignment hologram 48b is sequentially switched from “page 5” with the page number P5 to “page 1” with the page number P1, but continues to operate. Then, a signal “page 5” with the page number P5 appears from the alignment hologram 48a. From this, it was found that the condensing line of the cylindrical wavefront light source 54 is shifted counterclockwise with respect to the core layer in the traveling direction of the guided light PW. The rotation stage 56 was slightly rotated to correct this shift, and the page selection stage 60 was scanned again as described above. However, the situation does not change, and the page selection stage 60 is scanned by slightly rotating the rotary stage 56.
[0051]
When the same operation is repeated several times, the signal of “page 5” with the page number P5 added from the alignment hologram 48a is displayed several times, and the “page with the page number P1 added from the alignment hologram 48b” 1 "signal was observed at the same time, and it was found that the angle was being corrected. If the same thing is further repeated, the signal of “page 4” with the page number P4 added from the alignment hologram 48a and the signal of “page 1” with the page number P1 added from the alignment hologram 48b will be displayed. Observed at the same time.
[0052]
When the page selection stage 60 is moved in this direction in the direction labeled D4 in the figure, the signal “page 5” with the page number P5 from the alignment hologram 48a becomes the page number from the alignment hologram 48b. It was found that there is a position where the signal of “page 2” with P2 is observed at the same time. When the same thing was repeated many more times, signals of the same page were observed simultaneously from the alignment hologram 48a and the alignment hologram 48b.
[0053]
In “Page 1” with the page number P1, the Y-axis stage 58 is finely adjusted in addition to the page selection stage 60 and the rotary stage 56 so that the signal intensities of both of them are equal and further maximized. It was found that the image of “page 1” with page number P1 was correctly reproduced. When the page selection stage 60 is moved in this state, the page number P2 is added at the place where the signal of “page 2” to which the page number P2 is added simultaneously from the alignment hologram 48a and the alignment hologram 48b is captured. The image of “Page 2” was reproduced accurately. The other pages were the same.
[0054]
[Third embodiment]
Next, a third embodiment will be described. In the third embodiment, alignment of the two-dimensional array photodetector with respect to the information recording medium 49 will be described.
Although not described here because it was not particularly necessary, when light is incident on the information recording medium, the light is diffracted upward by the hologram and simultaneously diffracted downward. In the present embodiment, similarly to the second embodiment, the light diffracted upward is observed to align the light source and the medium, and the hologram image diffracted downward is observed by the CCD.
[0055]
In this embodiment, the hologram 46 and alignment holograms 48a and 48b shown in FIG. 10 are added to the three alignment holograms 66a, 66b and 66c shown in FIG. 13 and information necessary for assisting the alignment. A positioning auxiliary information hologram 70 was added. FIG. 13 is a top view showing a part of the core layer of the information recording medium according to the second embodiment of the present invention. The alignment holograms 66a, 66b, and 66c all generate spherical wave diffracted light when the guided light PW is diffracted. Reference numerals 68a, 68b, and 68c denote focal positions formed by the diffracted light of the alignment holograms 66a, 66b, and 66c.
[0056]
The information recording medium 49 used in this embodiment is also a five-page medium similar to the first and second embodiments described above, and the light diffracted downward from the hologram 46 for image reproduction is reproduced for all five pages. The imaging surfaces were aligned, and the surface was 1 mm below the bottom surface of the information recording medium and parallel to the bottom surface of the medium. Further, the alignment hologram 66a is designed so that all five pages are focused on the same point in the image plane. The same applies to the alignment holograms 66b and 66c. The spot size of the diffracted light from the alignment holograms 66a, 66b, and 66c was about φ10 μm on the image plane, that is, at the focal point. In addition, information on page address information and coding method information is superimposed on the alignment auxiliary information hologram 70.
[0057]
Here, the page address information is an identifier for distinguishing pages, and a different number or name is assigned to each image independently of the page number used in the second embodiment. The information recording medium of this embodiment has five pages, which is important for a large-scale medium composed of a plurality of such information recording media. "01" is assigned to "Page 1" with page number P1, "02" is assigned to "Page 2" with page number P2, and so on. The encoding method is a method of mutual conversion between digital data and a hologram image when used as an external storage device of a digital information processing device. In this embodiment, conversion to digital data is not performed and the number is “00”.
[0058]
In the present embodiment, a photodetector 72 having a light detection surface shown in FIG. 14 is prepared. FIG. 14 is a diagram showing the configuration of the light detection surface of the photodetector used in the third embodiment. As shown in FIG. 14, the photodetector 72 fixes a CCD 76 that reads a hologram image on a support stand 74, arranges photodetectors 78 a to 78 c for alignment around it, and further assists in alignment. An information detector 80 is arranged. As can be seen from a comparison between FIGS. 13 and 14, the alignment hologram 66a includes the alignment photodetector 78a, the alignment hologram 66b includes the alignment photodetector 78b, and the alignment hologram. 66c corresponds to the alignment photodetector 78c.
[0059]
The effective light receiving surface of each of the alignment light detector 78a, the alignment light detector 78b, and the alignment light detector 78c has a circular shape of φ10 μm. Further, the alignment auxiliary information detector 62 is arranged corresponding to the alignment auxiliary information hologram 70, and is composed of ten 0.5 mm square detectors. In addition, the light receiving surfaces of all the detectors including the CCD 76 were aligned in one plane.
[0060]
As shown in FIG. 15, the photodetector 72 shown in FIG. 14 is fixed on a 6-axis stage that can adjust XYZ three-axis translation, rotation, and tilt, and information arranged in the apparatus shown in FIG. The recording medium 49 is disposed so as to be positioned in the −y axis direction. FIG. 15 is a diagram showing the positional relationship between the information recording medium 49 and the photodetector 72 in the third embodiment. Note that the rotation and tilting centers of the 6-axis stage were precisely aligned with the center of the alignment photodetector 78b. Thus, the preparation of the reading device was completed, and then the hologram image reading operation was actually performed.
[0061]
First, the information recording medium 49 is set, and then the light source cylindrical wavefront light source 54 and the information recording medium 49 are aligned by the method described in the second embodiment, and one of the five pages is accurately reproduced. It was in a state. In this state, the hologram image is slightly shifted in the xy-axis direction in the figure with respect to the CCD 76, and is not in focus. Therefore, the photodetector 72 was scanned in two directions in the XY plane. In this operation, there was an area where weak light was observed by the alignment photodetector 78b. A region where an intensity of 1/10 or more of the light intensity at the position where the optical signal obtained from the alignment photodetector 78b is maximum is observed is referred to as an area A1.
[0062]
Next, the alignment photodetector 78b was moved in the XY plane so as to be positioned substantially at the center of the region A1. Here, when the photodetector 72 is rotated in the φ direction in FIG. 15, there is an area where the optical signal is detected by the alignment photodetector 78 c, and the detection is stopped at the point where the detected signal becomes maximum. Subsequently, when the photodetector 72 was slightly moved in the Z-axis direction and brought close to the information recording medium 49, the light observed by the alignment photodetector detector 78b became stronger.
[0063]
Here, scanning in the XY plane is performed again in the region A1, and a region where an intensity of 1/10 or more of the light intensity at the position where the optical signal is maximum is observed is referred to as a region A2 (at this time, A2 is included in A1). The photodetector 72 was moved in the XY plane so that the alignment photodetector 78b was positioned approximately at the center of the region A2. Here, the rotation was performed in the φ direction until the signal detected by the alignment photodetector 78c was maximized. Subsequently, the photodetector 49 was moved in the z-axis direction so as to approach the information recording medium 49. Repeating the same operation and narrowing the scan area, the n-th time, when the photo detector is brought closer to the medium by the Z-axis stage, the optical signal becomes weaker and the scan is performed in the area An. However, I could not get a stronger optical signal than the previous time. Here, n is a natural number.
[0064]
This means that the focus has passed or is very close to the focus, so the position of the information recording medium is returned to the n-2th position, the approach to the medium is set slower, and the operation is repeated again. . The operation was stopped when the scan area could not be narrowed with the accuracy of the Z-axis stage. Finally, the tilts in the ψ and θ directions are adjusted so that the maximum optical signal can be obtained by the alignment photodetector 78c. At this time, it was confirmed that the image signal detected by the CCD 76 is faithful to the hologram image and correctly includes the focus. Further, the page address information (“01” to “05”) and the coding method information (“00”) placed in the alignment auxiliary information hologram 70 region could be read correctly.
[0065]
【The invention's effect】
As described above, according to the present invention, in an information recording medium for storing information by hologram, alignment between the light source for information reproduction and the information recording medium and between the photodetector and the medium can be easily performed. As a result, the error rate can be suppressed.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing an information recording medium to which an embodiment of the present invention is applied.
FIG. 2 is a schematic diagram showing a part of the configuration of the information recording medium according to the first embodiment of the present invention.
3 is a cross-sectional view of an information recording medium 10 having a plurality of core layers 12 having the structure shown in FIG.
FIG. 4 is a schematic diagram showing a part of the configuration of an information recording medium according to a second embodiment of the present invention.
5 is a diagram illustrating a state of light incidence on an information recording medium 10 including a plurality of core layers 12 illustrated in FIG.
FIG. 6 is a cross-sectional view showing a part of the configuration of an information recording medium according to a third embodiment of the present invention.
FIG. 7 is a diagram for explaining the simplest example of the focal position when the alignment holograms formed on each core layer are configured to focus on different positions.
FIG. 8 is a diagram for explaining a method of aligning the information recording medium and a two-dimensional array photodetector for reading a hologram image.
FIG. 9 is a diagram for explaining an alignment method using a single photodetector that is not a pinhole and an array;
FIG. 10 is a top view showing a part of the core layer of the information recording medium according to the first embodiment of the present invention.
FIG. 11 is a sectional view of an information recording medium according to the present embodiment.
12 is a diagram showing a simplified configuration of an apparatus for reading information recorded on the information recording medium 49 according to the present embodiment shown in FIG.
FIG. 13 is a top view showing a part of a core layer of an information recording medium according to a second embodiment of the present invention.
FIG. 14 is a diagram showing a configuration of a light detection surface of a photodetector used in the third embodiment.
15 is a diagram showing a positional relationship between an information recording medium 49 and a photodetector 72 in the third embodiment. FIG.
FIG. 16 is a diagram showing the principle of a reproduction-only multiplex hologram card.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Information recording medium, 12a, 12b, 12c, 12d, 12e, 30a-30g ... Core layer (optical waveguide), 14a, 14b, 14c, 14d, 14e, 14f ... Cladding layer (optical waveguide), 16c, 22, 26 ... Hologram, 24, 24b, 24c, 24d, 28a, 28b, 32, 32a ... Alignment hologram (alignment structure), FP, FPa. FPb. FPc: Focus (predetermined point).

Claims (11)

Has a single-mode planar optical waveguide, in the information recording medium for recording information by the hologram, aligned to diffract light the optical waveguide propagates the optical waveguide is a constrained in the vicinity of the core layer in the optical waveguide An information recording medium comprising a structure. The information recording medium according to claim 1, comprising a plurality of the optical waveguides. 3. The information recording medium according to claim 1, wherein a pair of the alignment structures are provided for each of the optical waveguides. The information recording medium according to claim 1, wherein the alignment structure selectively diffracts light propagating through the optical waveguide in a direction substantially perpendicular to a surface of the optical waveguide. 4. The information recording medium according to claim 1, wherein the alignment structure is a hologram, and selectively propagates light propagating through the optical waveguide in a specific direction. 6. The information recording medium according to claim 5, wherein the hologram used in the alignment structure diffracts light propagating through different waveguides in different directions. 5. The information recording according to claim 4, wherein the alignment structure is a hologram that condenses diffracted light on a surface of the information recording medium or in the vicinity of a specific point outside the information recording medium. Medium. 8. The information recording according to claim 7, wherein the hologram used in the alignment structure is a hologram for condensing light diffracted from light propagating in different waveguides in the vicinity of different predetermined points. Medium. 9. The information recording medium according to claim 7, wherein the alignment structure has three or more points on which the diffracted light is collected. In an information reproduction method for reproducing information recorded on an information recording medium,
  Light is incident on the information recording medium according to claim 5 by a predetermined method,
  Detecting the direction in which light is diffracted by the hologram formed on the information recording medium,
  Measure which core layer has the highest intensity light coupled according to the detection result
  An information reproduction method characterized by the above. In an information reproduction method for reproducing information recorded on an information recording medium,
  Light is incident on the information recording medium according to claim 8 in a predetermined direction,
  Detecting the condensing position of the light diffracted by the hologram formed on the information recording medium,
  Measure which core layer is coupled with the highest intensity light according to the detection result
  An information reproduction method characterized by the above.

Images