JP3864584B2

JP3864584B2 - Optical information recording / reproducing device

Info

Publication number: JP3864584B2
Application number: JP30486698A
Authority: JP
Inventors: 青児西脇; 慶明金馬
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-10-27
Filing date: 1998-10-27
Publication date: 2007-01-10
Anticipated expiration: 2018-10-27
Also published as: JP2000132848A

Description

【０００１】
【発明の属する技術分野】
本発明は光ディスク等の情報記録媒体に信号を記録、または情報記録媒体の信号を再生するために使われる光学式情報記録再生装置に関するものである。
【０００２】
【従来の技術】
従来の技術を、図１４から図１８に基づいて説明する。図１４は従来例における光学式情報記録再生装置としての光ディスク装置の断面構成を示している。図１４に於いて半導体レーザー等の放射光源１’を出射するレーザー光はビームスプリッタ−２に入射し、スプリット面２ａを反射してコリメートレンズ３により平行光に変換され、１／４波長板４’により直線偏光（Ｓ波）から円偏光に変換され、対物レンズ５により集光されて情報記録媒体としての光ディスク基材６の信号面６ａ上に収束する。信号面６ａを反射する光は対物レンズ５を経て１／４波長板４’により直線偏光（Ｐ波）に変換され、コリメートレンズ３により収束性の光となり、ビームスプリッタ−２のスプリット面２ａを透過し、ホログラム基板７’上のホログラム面７’ａに入射し、これを透過して入射光軸８’を対称軸とする＋１次回折光８’ａ、−１次回折光８’ｂに分岐し、検出器９’上の検出面９’ａに入射する。
【０００３】
図１５は従来例における光ディスク装置のホログラム面と検出面の構成を示している。ホログラム面７’ａと入射光１０の光軸８’との交点をＯとして、ホログラム面７’ａは点Ｏで直交する２直線（Ｘ軸、Ｙ軸）で４分割され、さらにそれぞれの象限でＸ軸に沿った短冊に分割される。ホログラム面７’ａの第１象限に入射する光１０は１次回折側で検出面９’ａ上の点Ａを原点としてみた場合の第１象限位置に入射し、第２象限では点Ａに対する第２象限位置に、第３象限では点Ａに対する第４象限位置に、第４象限では点Ａに対する第３象限位置に入射する。検出面９’ａと入射光軸８’との交点をＯ’、点Ｏ’で直交する２直線をｘ軸及びｙ軸、点Ａの点Ｏ’に関する対称点をＡ’とすると、−１次回折側では検出面上での入射位置が点Ｏ’に対し対称に現れ、ホログラム面７’ａの第１象限に入射する光１０は検出面上の点Ａ’を原点とする第３象限位置に、第２象限では点Ａ’に対する第４象限位置に、第３象限では点Ａ’に対する第２象限位置に、第４象限では点Ａ’に対する第１象限位置に入射する。またホログラム面７’ａの各象限で白地で表示した一つ置きの短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂではホログラム側から見て１次回折光が検出面９’ａよりも奥側で収束し、検出面上でそれぞれ１ｂ、２ｂ、３ｂ、４ｂの光スポットとなり、斜線で示したその他の短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９’ａよりも手前側で収束し、検出面上でそれぞれ１ｆ、２ｆ、３ｆ、４ｆの光スポットとなる。これとは反対に、−１次回折光では短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂは検出面９’ａよりも手前側で収束し、検出面上でそれぞれ１ｂ’、２ｂ’、３ｂ’、４ｂ’の光スポットとなり、短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９’ａよりも奥側で収束し、検出面上でそれぞれ１ｆ’、２ｆ’、３ｆ’、４ｆ’の光スポットとなる。１次回折側に於ける光検出器の形状はｙ軸に沿った短冊形状の組み合わせであり、一つ飛ばしごとに導通されて検出光が信号Ｆ１、Ｆ２として出力される。光スポット１ｂと１ｆ、２ｂと２ｆ、３ｂと３ｆ、４ｂと４ｆは、それぞれのビームの中心（１ｂＯと１ｆＯ、２ｂＯと２ｆＯ、３ｂＯと３ｆＯ、４ｂＯと４ｆＯ）が互いに境界線を挟んで隣同士の光検出器に入射している。−１次回折側に於ける光検出器の形状は点Ａ’を中心として４分割されており、光スポット１ｂ’と１ｆ’、２ｂ’と２ｆ’、３ｂ’と３ｆ’、４ｂ’と４ｆ’がそれぞれの分割検出器（ｔ３、ｔ４、ｔ２、ｔ１）の中心に入射している。検出器からの信号は加算器、減算器で処理され、制御信号や再生信号が生成される。例えば、信号Ｆ１、Ｆ２を減算器１１ａにより差分することで、光ディスク信号面６ａのフォーカスエラー信号１２ａが得られる。また、検出器ｔ１、ｔ４の導通信号と検出器ｔ２、ｔ３の導通信号を減算器１１ｃにより差分することで、光ディスク信号面６ａの位相差トラッキングエラー信号１２ｃが得られ、検出器ｔ１、ｔ２の導通信号と検出器ｔ３、ｔ４の導通信号を減算器１１ｄにより差分することで、光ディスク信号面６ａのプッシュプルトラッキングエラー信号１２ｄが得られる。さらに、信号Ｆ１、Ｆ２を加算器１１ｂで加算した信号１２ｂに、検出器ｔ１、ｔ２の導通信号と検出器ｔ３、ｔ４の導通信号を加算器１１ｅで加算した信号１２ｅに加えることで、光ディスク信号面６ａの再生信号が得られる。
【０００４】
図１６、図１７は従来例における光ディスク装置のフォーカスエラー検出原理を示すために、ディフォーカス発生時の検出面上での光分布を示している。図１６は光ディスク６が対物レンズ５から遠ざかる場合で、図１７は近づく場合である。図１６の場合、ディフォーカスによって光スポットが矢印の方向に延び、Ｆ１の出力が増大し、Ｆ２の出力が減少し、フォーカスエラー信号（以下ＦＥ信号と呼ぶ）＝Ｆ２−Ｆ１＜０となる。一方、図１７の場合、ディフォーカスによって光スポットが矢印の方向に延び、Ｆ２の出力が増大し、Ｆ１の出力が減少し、ＦＥ＝Ｆ２−Ｆ１＞０となる。よって、減算器１１ａにより光ディスク信号面６ａのフォーカスエラー信号１２ａが得られることが分かる。
【０００５】
図１８は従来例における光ディスク装置のＦＥ信号ディフォーカス特性を示している。図１８において縦軸はＦＥ信号の出力値、横軸は光ディスク信号面６ａのディフォーカス量で、プラス側が光ディスク６が対物レンズ５から遠ざかる側である。従来例におけるＦＥ特性は曲線１３’である。ジャストフォーカス近傍でｓ字を描き、ＦＥ→０となるように制御すれば、光ディスク信号面６ａにフォーカスがかけられる。
【０００６】
【発明が解決しようとする課題】
このような従来の光ディスク装置において以下の問題があった。すなわち、図１６において矢印３ａ、４ａの方向に光スポットが延びることで、あるディフォーカス量で光スポットが重なり互いに干渉し合って、ＦＥ信号に影響を与える。図１８の曲線１３’におけるディフォーカス２０μｍ〜４０μｍの領域で発生するうねりは、これが原因である。また、図１７において矢印１ａ、２ａの方向に光スポットが延びることで、あるディフォーカス量で光スポットが重なり互いに干渉し合ううえ、矢印１ａ、２ａの方向には長く検出器が横たわっているので、大きなディフォーカスで光スポットが拡がっても検出器上には大きな光エネルギーが残り、これらがＦＥ信号に影響を与える。図１８の曲線１３’におけるディフォーカス−２０μｍ〜−４０μｍの領域で発生する大きなオフセットε１は、これが原因である。一般に、光ディスクの信号面が単一面の場合は、±１０μｍを越える大きなディフォーカス量でのＦＥ信号特性にオフセットやうねりがあっても問題がないが、ＤＶＤの２層ディスクのように、第１の信号面から４０μｍ〜７０μｍ（光学的には屈折率で割って２５μｍ〜５０μｍに相当）だけ離れた位置に第２の信号面がある場合には、２５μｍ〜５０μｍまたは−２５μｍ〜−５０μｍのディフォーカス領域で発生するオフセットやうねりがフォーカス制御の外乱となる。例えば、図１８の曲線１３’の場合、ディフォーカス−３０μｍ位置でのオフセットはε１＝−０．０４の大きさであり、多層ディスクにおいて対物レンズから見て奥側の信号面にフォーカス制御がかかっている場合、手前側（光学的に３０μｍだけ対物レンズ側にあるとして）の信号面から−０．０４のオフセットが外乱として加わり、これが０．５μｍ程度のディフォーカスを発生させ、信号の再生特性を大きく劣化させる。このように、従来の光ディスク装置において、２５μｍ〜５０μｍまたは−２５μｍ〜−５０μｍのディフォーカス領域で発生するＦＥ信号の大きなオフセットやうねりが２層以上の多層ディスクの再生性能を大きく損なうことになるという問題点があった。本発明はかかる問題点に鑑み、ＦＥ信号の大きなオフセットやうねりを押さえ、多層ディスクの良好な再生や記録を安定して行える光ディスク装置を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は上記問題点を解決するため、以下の手段を用いる。すなわち、放射光源と、対物レンズと、ホログラム等の光分配手段と、光検出器からなり、放射光源を出た光は対物レンズにより光ディスクの信号面に集光し、その反射光は対物レンズを経て光分配手段に入射し、光分配手段により光は２方向に回折し、一方の回折光が光分配手段上の点Ｏで直交する２直線（ｘ軸、ｙ軸）により少なくとも４つの領域に分配され、それぞれ直線ＯＡの周りを一象限分だけ回転して光検出器上の点Ａの周りに入射し、もう一方の回折光もｘ軸、ｙ軸により少なくとも４つの領域に分配され、それぞれ直線ＯＡ’の周りを一象限分だけ回転して光検出器上の点Ａ’の周りに入射することを特徴とする光ディスク装置であり、ｙ軸は線分ＡＡ’に一致し、光分配手段はその各象限がｘ軸方向に沿った分割線で短冊状のセルに分割され、一つ置きの短冊セルを回折する光は検出面の手前で収束し（収束光Ｆ）、その他の短冊セルを回折する光は検出面の奥で収束し（収束光Ｂ）、点Ａを原点とした座標の各象限で少なくとも２つの光検出器がｙ軸に沿って隣接して構成され、該光検出器にそれぞれ収束光Ｆと収束光Ｂが入射することを特徴とする。
【０００８】
また、点Ａを原点とした座標の各象限で、４つの光検出器Ｄ１、Ｄ２、Ｄ３、Ｄ４がｙ軸に沿ってこの順に隣接して構成され、１つ飛びの検出器Ｄ１とＤ３、Ｄ２とＤ４が互いに導通することを特徴としており、第１象限位置の光検出器Ｄ１、Ｄ２、Ｄ３が第４象限位置の光検出器Ｄ２、Ｄ３、Ｄ４と導通し、第２象限位置の光検出器Ｄ２、Ｄ３、Ｄ４が第３象限位置の光検出器Ｄ１、Ｄ２、Ｄ３と導通し、第１象限位置の光検出器Ｄ１が第２象限位置の光検出器Ｄ１と導通し、第１象限位置の光検出器Ｄ１及びこれに導通する検出器からの信号をＦ１とし、第１象限位置の光検出器Ｄ２及びこれに導通する検出器からの信号をＦ２とし、Ｆ１とＦ２との差分から光ディスク信号面のフォーカスエラー信号を得ることを特徴とする。
【０００９】
さらに、点Ａを原点とした座標での第１象限位置の光検出器Ｄ１、Ｄ２、Ｄ３がそれぞれ第４象限位置の光検出器Ｄ２、Ｄ３、Ｄ４とほぼｙ軸に沿った直線上に形成され、第２象限位置の光検出器Ｄ２、Ｄ３、Ｄ４がそれぞれ第３象限位置の光検出器Ｄ１、Ｄ２、Ｄ３とほぼｙ軸に沿った直線上に形成されており、第４象限位置の光検出器Ｄ１及び第３象限位置の光検出器Ｄ４が省かれてもよく、第１象限位置の光検出器Ｄ４及び第２象限位置の光検出器Ｄ１が省かれてもよい。
【００１０】
さらに、光分割手段の各象限において、点Ｏから離れた領域Ｃを回折し光検出器上に入射する位置は、その象限内の他領域Ｂを回折し光検出器上の点Ａの周りに入射する位置よりも点Ａから見て外側にあり、領域Ｂとは独立した光検出器で検出されることを特徴とする。この時、光分割手段の領域Ｃを回折する光の収束点がほぼ光検出面上にあることを特徴とし、光分割手段の領域Ｃが点Ｏを中心とする円の外の領域、又はその一部であり、領域Ｃが点Ｏを中心とする円の外にあって、ｘ軸及びこれに平行な直線に挟まれた領域であってもよく、領域Ｃが点Ｏを中心とする輪帯状の領域であってもよい。
【００１１】
一方、光分割手段の領域Ｂは点Ｏを取り巻く内周領域Ｂ１とそれ以外の領域Ｂ２に分けられ、領域Ｂ１及び領域Ｂ２を回折し検出器に入射する光スポットの位置がｘ軸に沿ってずれることを特徴とし、光分割手段の領域Ｂ１がｘ軸、ｙ軸及びこれらと平行な直線に囲まれた領域であってもよく、領域Ｂ１が点Ｏを中心とする円内の領域であり、領域Ｂ２が点Ｏを中心とする輪帯状の領域であってもよい。
【００１２】
さらに、点Ａ’の周りに回折する側の各分配光は点Ａを原点とした座標での第１象限位置に構成された光検出器ＤＴ１と、第２象限位置に構成された光検出器ＤＴ２と、第３象限位置に構成された光検出器ＤＴ３と、第４象限位置に構成された光検出器ＤＴ４とによりそれぞれ検出され、各検出器からの検出信号をＴ１、Ｔ２、Ｔ３、Ｔ４とすると、（Ｔ１＋Ｔ４）−（Ｔ２＋Ｔ３）または（Ｔ１＋Ｔ２）−（Ｔ３＋Ｔ４）または（Ｔ１＋Ｔ３）−（Ｔ２＋Ｔ４）から光ディスク信号面のトラッキングエラー信号を得ることを特徴とする。
【００１３】
上記の様な構成により、検出器上の各象限に配置されたビームスポットが光ディスクのディフォーカスによって互いに逃げ合って重なることがなく、検出器上に光エネルギーが残りにくいので、２５μｍ〜５０μｍまたは−２５μｍ〜−５０μｍのディフォーカス領域におけるＦＥ信号の大きなオフセットやうねりを大幅に抑えることができる。
【００１４】
【発明の実施の形態】
以下本発明の第１の実施の形態を図１から図４、及び図１８に基づいて説明する。なお従来例と共通の要素については、同一の番号を振って説明する。図１は本発明の第１の実施の形態における光ディスク装置の断面構成を示しており、放射光源１とその周辺に関する側面図も下に付け加えている。図１に於いて光検出基板９上に取り付けられた半導体レーザー等の放射光源１を出射するレーザー光は、光検出基板９上に取り付けられた反射ミラー１４を反射して偏光性ホログラム基板７を透過し、１／４波長板４により直線偏光（Ｓ波）から円偏光に変換され、コリメートレンズ３により平行光に変換され、対物レンズ５により集光されて光ディスク基材６の信号面６ａ上に収束する。信号面６ａを反射する光は対物レンズ５、コリメートレンズ３を経て収束性の光となり、１／４波長板４により直線偏光（Ｐ波）に変換され、偏光性ホログラム基板７上のホログラム面７ａに入射し、これを透過して入射光軸８を対称軸とする１回折光８ａ、−１次回折光８ｂに分岐し、検出器９上の検出面９ａに入射する。
【００１５】
図２は本発明の第１の実施の形態における光ディスク装置のホログラム面と検出面の構成を示している。ホログラム面７ａと入射光１０の光軸８との交点をＯとして、ホログラム面７ａは点Ｏで直交する２直線（Ｘ軸、Ｙ軸）で４分割され、さらにそれぞれの象限でＸ軸に沿った短冊に分割される。ホログラム面７ａの第１象限に入射する光１０は１次回折側で検出面９ａ上の点Ａを原点としてみた場合の第２象限位置に入射し、第２象限では点Ａに対する第３象限位置に、第３象限では点Ａに対する第４象限位置に、第４象限では点Ａに対する第１象限位置に入射する。すなわちホログラム面７ａ上での光１０が各象限ごとにＯＡを結ぶ直線の周りで１象限分だけ回転して検出面上９ａに入射する。検出面９ａと入射光軸８との交点をＯ’、点Ｏ’で直交する２直線をｘ軸及びｙ軸、点Ａの点Ｏ’に関する対称点をＡ’とすると、−１次回折側では検出面上での入射位置が点Ｏ’に対し対称に現れ、ホログラム面７ａの第１象限に入射する光１０は検出面上の点Ａ’を原点とする第４象限位置に、第２象限では点Ａ’に対する第１象限位置に、第３象限では点Ａ’に対する第２象限位置に、第４象限では点Ａ’に対する第３象限位置に入射する。またホログラム面７ａの各象限で白地で表示した一つ置きの短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂではホログラム側から見て１次回折光が検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｂ、２ｂ、３ｂ、４ｂの光スポットとなり、斜線で示したその他の短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｆ、２ｆ、３ｆ、４ｆの光スポットとなる。これとは反対に、−１次回折光では短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｂ’、２ｂ’、３ｂ’、４ｂ’の光スポットとなり、短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｆ’、２ｆ’、３ｆ’、４ｆ’の光スポットとなる。１次回折側に於ける光検出器の形状はｙ軸に沿った短冊形状の組み合わせであり、一つ飛ばしごとに導通されて検出光が信号Ｆ１、Ｆ２として出力される。光スポット１ｂと１ｆ、２ｂと２ｆ、３ｂと３ｆ、４ｂと４ｆは、それぞれのビームの中心（１ｂＯと１ｆＯ、２ｂＯと２ｆＯ、３ｂＯと３ｆＯ、４ｂＯと４ｆＯ）が互いに境界線を挟んで隣同士の光検出器に入射している。−１次回折側に於ける光検出器の形状は点Ａ’を中心として４分割されており、光スポット１ｂ’と１ｆ’、２ｂ’と２ｆ’、３ｂ’と３ｆ’、４ｂ’と４ｆ’がそれぞれの分割検出器（Ｔ４、Ｔ１、Ｔ２、Ｔ３）の中心に入射している。検出器からの信号は加算器、減算器で処理され、制御信号や再生信号が生成される。例えば、信号Ｆ１、Ｆ２を減算器１１ａにより差分することで、光ディスク信号面６ａのフォーカスエラー信号１２ａが得られる。また、検出器Ｔ１、Ｔ３の導通信号と検出器Ｔ２、Ｔ４の導通信号を減算器１１ｃにより差分することで、光ディスク信号面６ａの位相差トラッキングエラー信号１２ｃが得られ、検出器Ｔ１、Ｔ４の導通信号と検出器Ｔ２、Ｔ３の導通信号を減算器１１ｄにより差分することで、光ディスク信号面６ａのプッシュプルトラッキングエラー信号１２ｄが得られる。さらに、信号Ｆ１、Ｆ２を加算器１１ｂで加算した信号１２ｂに、検出器Ｔ１、Ｔ４の導通信号と検出器Ｔ２、Ｔ３の導通信号を加算器１１ｅで加算した信号１２ｅに加えることで、光ディスク信号面６ａの再生信号が得られる。
【００１６】
図３、図４は本発明の第１の実施の形態における光ディスク装置のフォーカスエラー検出原理を示すために、ディフォーカス発生時の検出面上での光分布を示している。図３は光ディスク６が対物レンズ５から遠ざかる場合で、図４は近づく場合である。図３の場合、ディフォーカスによって光スポットが矢印の方向に延び、Ｆ１の出力が増大し、Ｆ２の出力が減少し、ＦＥ＝Ｆ２−Ｆ１＜０となる。一方、図４の場合、ディフォーカスによって光スポットが矢印の方向に延び、Ｆ２の出力が増大し、Ｆ１の出力が減少し、ＦＥ＝Ｆ２−Ｆ１＞０となる。よって、減算器１１ａにより光ディスク信号面６ａのフォーカスエラー信号１２ａが得られることが分かる。
【００１７】
図１８には本発明の第１の実施の形態における光ディスク装置のフォーカスエラー信号ディフォーカス特性を付記しており、第１の実施の形態におけるＦＥ特性は曲線１３である。ジャストフォーカス近傍でｓ字を描き、ＦＥ→０となるように制御すれば、光ディスク信号面６ａにフォーカスがかけられる。
【００１８】
なお、本の実施の形態では図３、図４の矢印１ａ、２ａ、３ａ、４ａで示すように、点Ａの周りに配置されたビームスポットが光ディスクのディフォーカスによって互いに逃げ合って重なることがなく、しかも検出器上に光エネルギーが残りにくい。その結果、図１８の曲線１３では、従来例において見られた２０μｍ〜４０μｍの領域のうねりが現れず、−２０μｍ〜−５０μｍの領域でもオフセットがほとんど発生していない。例えば、曲線１３の場合、ディフォーカス−３２μｍ位置でのオフセットはε２＝０．０１の大きさであり、対物レンズから見て奥側の信号面にフォーカス制御がかかっている場合、手前側（光学的に３２μｍだけ対物レンズ側にあるとして）の信号面から０．０１のオフセットが外乱として加わるが、これは０．１５μｍ程度の小さなディフォーカスに相当し、信号の再生特性をほとんど劣化させることはない。従って、２層ディスクの良好な再生や記録を安定して行うことができる。
【００１９】
次に本発明の第２の実施の形態を図５に基づいて説明する。第２の実施の形態はホログラム面と検出面の構成を除いてその他の構成は全て第１の実施の形態と同じであり、同一部の説明を省略する。図５は本発明の第２の実施の形態における光ディスク装置のホログラム面と検出面の構成を示している。ホログラム面７ａと入射光１０の光軸８との交点をＯとして、ホログラム面７ａは点Ｏで直交する２直線（Ｘ軸、Ｙ軸）で４分割され、さらに点Ｏを中心とした円１５内の領域がそれぞれの象限でＸ軸に沿った短冊に分割される。ホログラム面７ａの第１象限に入射する光１０は１次回折側で検出面９ａ上の点Ａを原点としてみた場合の第２象限位置に入射し、第２象限では点Ａに対する第３象限位置に、第３象限では点Ａに対する第４象限位置に、第４象限では点Ａに対する第１象限位置に入射する。すなわちホログラム面７ａ上での光１０が各象限ごとにＯＡを結ぶ直線の周りで１象限分だけ回転して検出面上９ａに入射する。検出面９ａと入射光軸８との交点をＯ’、点Ｏ’で直交する２直線をｘ軸及びｙ軸、点Ａの点Ｏ’に関する対称点をＡ’とすると、−１次回折側では検出面上での入射位置が点Ｏ’に対し対称に現れ、ホログラム面７ａの第１象限に入射する光１０は検出面上の点Ａ’を原点とする第４象限位置に、第２象限では点Ａ’に対する第１象限位置に、第３象限では点Ａ’に対する第２象限位置に、第４象限では点Ａ’に対する第３象限位置に入射する。またホログラム面７ａの各象限で白地で表示した一つ置きの短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂではホログラム側から見て１次回折光が検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｂ、２ｂ、３ｂ、４ｂの光スポットとなり、斜線で示したその他の短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｆ、２ｆ、３ｆ、４ｆの光スポットとなり、ホログラム面７ａの各象限で円１５の外の領域１Ｇ、２Ｇ、３Ｇ、４Ｇではホログラム側から見て１次回折光がほぼ検出面９ａ上で収束し、検出面上でそれぞれ１ｇ、２ｇ、３ｇ、４ｇの光スポットとなる。これとは反対に、−１次回折光では短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｂ’、２ｂ’、３ｂ’、４ｂ’の光スポットとなり、短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｆ’、２ｆ’、３ｆ’、４ｆ’の光スポットとなり、円１５の外の領域１Ｇ、２Ｇ、３Ｇ、４Ｇではほぼ検出面９ａ上で収束し、検出面上でそれぞれ１ｇ’、２ｇ’、３ｇ’、４ｇ’の光スポットとなる。光スポット１ｇ、２ｇ、３ｇ、４ｇの位置は点Ａからみて、光スポット１ｂと１ｆ、２ｂと２ｆ、３ｂと３ｆ、４ｂと４ｆの位置より外側にあり、光スポット１ｇ’、２ｇ’、３ｇ’、４ｇ’の位置は点Ａ’からみて、光スポット１ｂ’と１ｆ’、２ｂ’と２ｆ’、３ｂ’と３ｆ’、４ｂ’と４ｆ’の位置より外側にある。１次回折側に於ける光検出器の形状は、光スポット１ｂ、１ｆ、２ｂ、２ｆ、３ｂ、３ｆ、４ｂ、４ｆを検出するものがｙ軸に沿った短冊形状の組み合わせであり、第１の実施の形態と同様に一つ飛ばしごとに導通されて検出光が信号Ｆ１、Ｆ２として出力される。また、光スポット１ｇ、２ｇ、３ｇ、４ｇに関しては導通された光検出器Ｆ３により検出される。光スポット１ｂと１ｆ、２ｂと２ｆ、３ｂと３ｆ、４ｂと４ｆの位置関係、及びこれらのスポットと信号Ｆ１、Ｆ２を生成する短冊形状の検出器との位置関係については第１の実施の形態と同様であり、説明を省略する。−１次回折側に於ける光検出器の形状は点Ａ’を中心として４分割されており、光スポット１ｂ’と１ｆ’、２ｂ’と２ｆ’、３ｂ’と３ｆ’、４ｂ’と４ｆ’がそれぞれの分割検出器（Ｔ４、Ｔ１、Ｔ２、Ｔ３）の領域に入射している。また、光スポット１ｇ’、２ｇ’、３ｇ’、４ｇ’はそれぞれ分割検出器Ｔ４、Ｔ１、Ｔ２、Ｔ３から伸びた検出領域に入射している。検出器からの信号は加算器、減算器で処理され、制御信号や再生信号が生成される。例えば、信号Ｆ１、Ｆ２を減算器１１ａにより差分することで、光ディスク信号面６ａのフォーカスエラー信号１２ａが得られる。また、検出器Ｔ１、Ｔ３の導通信号と検出器Ｔ２、Ｔ４の導通信号を減算器１１ｃにより差分することで、光ディスク信号面６ａの位相差トラッキングエラー信号１２ｃが得られ、検出器Ｔ１、Ｔ４の導通信号と検出器Ｔ２、Ｔ３の導通信号を減算器１１ｄにより差分することで、光ディスク信号面６ａのプッシュプルトラッキングエラー信号１２ｄが得られる。さらに、信号Ｆ１、Ｆ２を加算器１１ｂで加算した信号１２ｂに検出器Ｆ３の検出信号を加え、検出器Ｔ１、Ｔ４の導通信号と検出器Ｔ２、Ｔ３の導通信号を加算器１１ｅで加算した信号１２ｅに加えることで、光ディスク信号面６ａの再生信号が得られる。
【００２０】
第２の実施の形態のフォーカスエラー検出原理は第１の実施の形態と同じであり、ディフォーカス発生時の検出面上での光分布の動きも同様である。光スポット１ｇ、２ｇ、３ｇ、４ｇに関してはディフォーカスによってそれぞれ矢印１ｈ、２ｈ、３ｈ、４ｈの方位に延びるが、この方位にはＦＥ検出に関わる検出器が存在しないので、ＦＥ特性に影響しない。従って第１の実施の形態と同じく、ディフォーカス時でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。さらに第２の実施の形態では信号Ｆ１、Ｆ２を加算器１１ｂで加えて再生信号とすることもでき、Ｆ１、Ｆ２が開口の小さい領域（円１５内の領域）の検出信号であることから、基材６の厚さが異なった光ディスクの再生を行っても開口の小さい領域では収差が小さいことから、再生特性の劣化を小さくすることができる。例えば、基材厚０．６ｍｍのＤＶＤの再生を全検出器の信号総和（Ｆ１＋Ｆ２＋Ｔ１＋Ｔ２＋Ｔ３＋Ｔ４）で行い、同一の対物レンズ５を用いて基材厚１．２ｍｍのＣＤの再生をＦ１＋Ｆ２で行うことができ、一つの光ディスク装置でありながら、多種の光ディスクの再生に対応できる。
【００２１】
次に本発明の第３の実施の形態を図６に基づいて説明する。第３の実施の形態はホログラム面の構成を除いてその他の構成は全て第２の実施の形態と同じであり、同一部の説明を省略する。図６は本発明の第３の実施の形態における光ディスク装置のホログラム面と検出面の構成を示している。ホログラム面７ａと入射光１０の光軸８との交点をＯとして、ホログラム面７ａは点Ｏで直交する２直線（Ｘ軸、Ｙ軸）で４分割され、さらに点Ｏを中心とした円１５内又は直線１６、１７の外側の領域がそれぞれの象限でＸ軸に沿った短冊に分割される。ホログラム面７ａの第１象限に入射する光１０は１次回折側で検出面９ａ上の点Ａを原点としてみた場合の第２象限位置に入射し、第２象限では点Ａに対する第３象限位置に、第３象限では点Ａに対する第４象限位置に、第４象限では点Ａに対する第１象限位置に入射する。すなわちホログラム面７ａ上での光１０が各象限ごとにＯＡを結ぶ直線の周りで１象限分だけ回転して検出面上９ａに入射する。検出面９ａと入射光軸８との交点をＯ’、点Ｏ’で直交する２直線をｘ軸及びｙ軸、点Ａの点Ｏ’に関する対称点をＡ’とすると、−１次回折側では検出面上での入射位置が点Ｏ’に対し対称に現れ、ホログラム面７ａの第１象限に入射する光１０は検出面上の点Ａ’を原点とする第４象限位置に、第２象限では点Ａ’に対する第１象限位置に、第３象限では点Ａ’に対する第２象限位置に、第４象限では点Ａ’に対する第３象限位置に入射する。またホログラム面７ａの各象限で白地で表示した一つ置きの短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂではホログラム側から見て１次回折光が検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｂ、２ｂ、３ｂ、４ｂの光スポットとなり、斜線で示したその他の短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｆ、２ｆ、３ｆ、４ｆの光スポットとなり、ホログラム面７ａの各象限で円１５の外かつ直線１６、１７の間の領域１Ｇ、２Ｇ、３Ｇ、４Ｇではほぼ検出面９ａ上で収束し、検出面上でそれぞれ１ｇ、２ｇ、３ｇ、４ｇの光スポットとなる。これとは反対に、−１次回折光では短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｂ’、２ｂ’、３ｂ’、４ｂ’の光スポットとなり、短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆでは検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｆ’、２ｆ’、３ｆ’、４ｆ’の光スポットとなり、円１５の外かつ直線１６、１７の間の領域１Ｇ、２Ｇ、３Ｇ、４Ｇではほぼ検出面９ａ上で収束し、検出面上でそれぞれ１ｇ’、２ｇ’、３ｇ’、４ｇ’の光スポットとなる。光スポット１ｇ、２ｇ、３ｇ、４ｇの位置は点Ａからみて、光スポット１ｂと１ｆ、２ｂと２ｆ、３ｂと３ｆ、４ｂと４ｆの位置より外側にあり、光スポット１ｇ’、２ｇ’、３ｇ’、４ｇ’の位置は点Ａ’からみて、光スポット１ｂ’と１ｆ’、２ｂ’と２ｆ’、３ｂ’と３ｆ’、４ｂ’と４ｆ’の位置より外側にある。第３の実施の形態はホログラム面７ａの分割の仕方が違うだけで、光検出器の形状や配線、信号検出原理は第２の実施の形態と全く同じであり、第２の実施の形態と同じく、ディフォーカス時でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。また第２の実施の形態と同じく、基材厚０．６ｍｍのＤＶＤの再生を全検出器の信号総和（Ｆ１＋Ｆ２＋Ｔ１＋Ｔ２＋Ｔ３＋Ｔ４）で行い、同一対物レンズ５を用いて基材厚１．２ｍｍのＣＤの再生をＦ１＋Ｆ２で行うことができ、一つの光ディスク装置でありながら、多種の光ディスクの再生に対応できる。さらに第２の実施の形態に比べて開口の大きい領域を一部Ｆ１、Ｆ２に取り込んでいるので、基材６の厚さにむらがある光ディスクであっても、ジャストフォーカス近傍でのＦＥ特性が乱されず、正確な焦点制御が維持できる（基材６の厚さにむらがあると、開口の小さい領域での収差と開口の大きい領域での収差が乖離するため、第２の実施の形態のような開口の小さい領域だけを使ったＦＥ検出はジャストフォーカス近傍でＦＥ特性が乱される可能性があった）。
【００２２】
次に本発明の第４の実施の形態を図７に基づいて説明する。第４の実施の形態はホログラム面の一部の構成を除いてその他の構成は全て第３の実施の形態と同じであり、同一部の説明を省略する。図７は本発明の第４の実施の形態における光ディスク装置のホログラム面と検出面の構成を示している。第３の実施の形態との違いは、点Ｏを中心とした方形１８内の短冊領域で、他の短冊領域に比べ検出面上での入射位置をｘ軸方向に若干変えた点である。方形１８内の短冊領域で白地で表示した一つ置きの短冊領域１’Ｂ、２’Ｂ、３’Ｂ、４’Ｂはホログラム側から見て１次回折光が検出面９ａよりも奥側で収束し、検出面上でそれぞれ１’ｂ、２’ｂ、３’ｂ、４’ｂの光スポットとなり、斜線で示したその他の短冊領域１’Ｆ、２’Ｆ、３’Ｆ、４’Ｆでは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１’ｆ、２’ｆ、３’ｆ、４’ｆの光スポットとなる。光スポット１’ｂ、２’ｂ、３’ｂ、４’ｂは光スポット１ｂ、２ｂ、３ｂ、４ｂに比べ検出器の境界線から離れる側にシフトしている。また、−１次回折光では短冊領域１’Ｂ、２’Ｂ、３’Ｂ、４’Ｂは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１’ｂ’、２’ｂ’、３’ｂ’、４’ｂ’の光スポットとなり、短冊領域１’Ｆ、２’Ｆ、３’Ｆ、４’Ｆでは検出面９ａよりも奥側で収束し、検出面上でそれぞれ１’ｆ’、２’ｆ’、３’ｆ’、４’ｆ’の光スポットとなる。第４の実施の形態はホログラム面７ａの分割の仕方が違うだけで、光検出器の形状や配線、信号検出原理は第３の実施の形態と全く同じであり、第３の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。また第３の実施の形態と同じく、基材厚０．６ｍｍのＤＶＤの再生を全検出器の信号総和（Ｆ１＋Ｆ２＋Ｔ１＋Ｔ２＋Ｔ３＋Ｔ４）で行い、同一の対物レンズ５を用いて基材厚１．２ｍｍのＣＤの再生をＦ１＋Ｆ２で行うことができ、一つの光ディスク装置でありながら、多種の光ディスクの再生に対応できる。さらに方形１８内の開口の小さい領域を検出器の境界線から遠ざけることで、開口の小さい領域での収差がＦＥに与える影響と開口の大きい領域での収差がＦＥに与える影響のバランスをとることができ、第３の実施の形態と比べても、基材６の厚さにむらがある光ディスクであってもジャストフォーカス近傍のＦＥ特性が乱されず、より正確な焦点制御が維持できる。
【００２３】
次に本発明の第５の実施の形態を図８に基づいて説明する。第５の実施の形態はホログラム面の構成を除いてその他の構成は全て第２の実施の形態と同じであり、同一部の説明を省略する。図８は本発明の第５の実施の形態における光ディスク装置のホログラム面と検出面の構成を示している。ホログラム面７ａと入射光１０の光軸８との交点をＯとして、ホログラム面７ａは点Ｏで直交する２直線（Ｘ軸、Ｙ軸）で４分割され、さらに点Ｏを中心とした円１５内又は円１９外の領域がそれぞれの象限でＸ軸に沿った短冊に分割される。ホログラム面７ａの第１象限に入射する光１０は１次回折側で検出面９ａ上の点Ａを原点としてみた場合の第２象限位置に入射し、第２象限では点Ａに対する第３象限位置に、第３象限では点Ａに対する第４象限位置に、第４象限では点Ａに対する第１象限位置に入射する。すなわちホログラム面７ａ上での光１０が各象限ごとにＯＡを結ぶ直線の周りで１象限分だけ回転して検出面上９ａに入射する。検出面９ａと入射光軸８との交点をＯ’、点Ｏ’で直交する２直線をｘ軸及びｙ軸、点Ａの点Ｏ’に関する対称点をＡ’とすると、−１次回折側では検出面上での入射位置が点Ｏ’に対し対称に現れ、ホログラム面７ａの第１象限に入射する光１０は検出面上の点Ａ’を原点とする第４象限位置に、第２象限では点Ａ’に対する第１象限位置に、第３象限では点Ａ’に対する第２象限位置に、第４象限では点Ａ’に対する第３象限位置に入射する。またホログラム面７ａの各象限で白地で表示した一つ置きの短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂ、及び１’Ｂ、２’Ｂ、３’Ｂ、４’Ｂではホログラム側から見て１次回折光が検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｂ、２ｂ、３ｂ、４ｂ、及び１’ｂ、２’ｂ、３’ｂ、４’ｂの光スポットとなり、斜線で示したその他の短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆ、及び１’Ｆ、２’Ｆ、３’Ｆ、４’Ｆでは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｆ、２ｆ、３ｆ、４ｆ及び１’ｆ、２’ｆ、３’ｆ、４’ｆの光スポットとなり、ホログラム面７ａの各象限で円１５の外かつ円１９の内の領域１Ｇ、２Ｇ、３Ｇ、４Ｇではほぼ検出面９ａ上で収束し、検出面上でそれぞれ１ｇ、２ｇ、３ｇ、４ｇの光スポットとなる。これとは反対に、−１次回折光では短冊領域１Ｂ、２Ｂ、３Ｂ、４Ｂ、及び１’Ｂ、２’Ｂ、３’Ｂ、４’Ｂは検出面９ａよりも手前側で収束し、検出面上でそれぞれ１ｂ’、２ｂ’、３ｂ’、４ｂ’及び１’ｂ’、２’ｂ’、３’ｂ’、４’ｂ’の光スポットとなり、短冊領域１Ｆ、２Ｆ、３Ｆ、４Ｆ、及び１’Ｆ、２’Ｆ、３’Ｆ、４’Ｆでは検出面９ａよりも奥側で収束し、検出面上でそれぞれ１ｆ’、２ｆ’、３ｆ’、４ｆ’、及び１’ｆ’、２’ｆ’、３’ｆ’、４’ｆ’の光スポットとなり、円１５の外かつ円１９の内の領域１Ｇ、２Ｇ、３Ｇ、４Ｇではほぼ検出面９ａ上で収束し、検出面上でそれぞれ１ｇ’、２ｇ’、３ｇ’、４ｇ’の光スポットとなる。光スポット１ｇ、２ｇ、３ｇ、４ｇの位置は点Ａからみて、光スポット１ｂと１ｆ、２ｂと２ｆ、３ｂと３ｆ、４ｂと４ｆの位置より外側にあり、光スポット１ｇ’、２ｇ’、３ｇ’、４ｇ’の位置は点Ａ’からみて、光スポット１ｂ’と１ｆ’、２ｂ’と２ｆ’、３ｂ’と３ｆ’、４ｂ’と４ｆ’の位置より外側にある。第５の実施の形態はホログラム面７ａの分割の仕方が違うだけで、光検出器の形状や配線、信号検出原理は第２の実施の形態と全く同じであり、第２の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。また基材厚の大きく異なる光ディスクを再生する場合、開口の大きい領域の光に対応する１’ｂ、２’ｂ、３’ｂ、４’ｂや１’ｆ、２’ｆ、３’ｆ、４’ｆの光スポットは大きく拡がって検出器上に残りにくいので、第２の実施の形態と同じく、基材厚０．６ｍｍのＤＶＤの再生を全検出器の信号総和（Ｆ１＋Ｆ２＋Ｔ１＋Ｔ２＋Ｔ３＋Ｔ４）で行い、同じ対物レンズ５を使って基材厚１．２ｍｍのＣＤの再生をＦ１＋Ｆ２で行うことができ、一つの光ディスク装置でありながら、多種の光ディスクの再生に対応できる。さらに第２の実施の形態に比べて開口の大きい領域（円１９外の領域）を一部Ｆ１、Ｆ２に取り込んでいるので、基材６の厚さにむらがある光ディスクであっても、ジャストフォーカス近傍でのＦＥ特性が乱されず、正確な焦点制御が維持できる。
【００２４】
次に本発明の第６の実施の形態を図９に基づいて説明する。第６の実施の形態は光スポットの検出面上での入射位置を若干変えた点以外、その構成は第５の実施の形態と全く同じであり、同一部の説明を省略する。図９は本発明の第６の実施の形態における光ディスク装置の検出面の構成を示している。第５の実施の形態との違いは、光スポット１ｂ、２ｂ、３ｂ、４ｂ、及び１ｆ、２ｆ、３ｆ、４ｆの入射位置がスポット１’ｂ、２’ｂ、３’ｂ、４’ｂ、及び１’ｆ、２’ｆ、３’ｆ、４’ｆに比べ検出器の境界線から離れる側にシフトしている。第６の実施の形態はホログラム面７ａの仕様が違うだけで、光検出器の形状や配線、信号検出原理は第５の実施の形態と全く同じであり、第５の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。また第５の実施の形態と同じく、基材厚０．６ｍｍのＤＶＤの再生を全検出器の信号総和（Ｆ１＋Ｆ２＋Ｔ１＋Ｔ２＋Ｔ３＋Ｔ４）で行い、同じ対物レンズ５を使って基材厚１．２ｍｍのＣＤの再生をＦ１＋Ｆ２で行うことができ、一つの光ディスク装置でありながら、多種の光ディスクの再生に対応できる。さらに第５の実施の形態と同じく、基材６の厚さにむらがある光ディスクであってもジャストフォーカス近傍のＦＥ特性が乱されず、正確な焦点制御が維持できる。
【００２５】
次に本発明の第７の実施の形態を図１０に基づいて説明する。第７の実施の形態は検出器の形状が若干異なる以外は、その構成は第１の実施の形態と全く同じであり、同一部の説明を省略する。図１０は本発明の第７の実施の形態における光ディスク装置の検出面の構成を示している。第１の実施の形態との違いは、検出器Ｆ２ｂ、Ｆ２ｄ、Ｆ１ｂ、Ｆ１ｄの形状で、第１の実施の形態では短冊状であったのが第７の実施の形態では下半分、または上半分での幅を変化させている。以上の変化を加えることで、図１８で示したＦＥ信号の特性曲線１３の形状を微調整できる。第７の実施の形態は光検出器の形状が違うだけで、信号検出原理は第１の実施の形態と全く同じであり、第１の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。
【００２６】
次に本発明の第８の実施の形態を図１１に基づいて説明する。第８の実施の形態は検出器の形状が若干異なる以外は、その構成は第７の実施の形態と全く同じであり、同一部の説明を省略する。図１１は本発明の第８の実施の形態における光ディスク装置の検出面の構成を示している。第７の実施の形態との違いは、検出器Ｆ１ｅ、Ｆ２ｅが省略されている点である。以上の変化を加えることで、図１８で示したＦＥ信号の特性曲線１３の形状を微調整できる。第８の実施の形態は光検出器の形状が違うだけで、信号検出原理は第７の実施の形態や第１の実施の形態と全く同じであり、第７の実施の形態や第１の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。
【００２７】
次に本発明の第９の実施の形態を図１２に基づいて説明する。第９の実施の形態は検出器の形状が若干異なる以外は、その構成は第８の実施の形態と全く同じであり、同一部の説明を省略する。図１２は本発明の第９の実施の形態における光ディスク装置の検出面の構成を示している。第８の実施の形態との違いは、検出器Ｆ１ａ、Ｆ２ａが省略されている点である。以上の変化を加えることで、図１８で示したＦＥ信号の特性曲線１３の形状を微調整できる。第９の実施の形態は光検出器の形状が違うだけで、信号検出原理は第８の実施の形態や第１の実施の形態と全く同じであり、第８の実施の形態や第１の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。
【００２８】
次に本発明の第１０の実施の形態を図１３に基づいて説明する。第１０の実施の形態はコリメートレンズ３、偏光性ホログラム基板７と１／４波長板の位置が変わった以外は、その構成は第１の実施の形態と全く同じであり、同一部の説明を省略する。図１３は本発明の第１０の実施の形態における光ディスク装置の断面構成を示しており、放射光源１とその周辺に関する側面図も下に付け加えている。図１３に於いて光検出基板９上に取り付けられた半導体レーザー等の放射光源１を出射するレーザー光は、光検出基板９上に取り付けられた反射ミラー１４を反射してコリメートレンズ３により平行光に変換され、偏光性ホログラム基板７を透過し、１／４波長板４により直線偏光（Ｓ波）から円偏光に変換され、対物レンズ５により集光されて光ディスク基材６の信号面６ａ上に収束する。信号面６ａを反射する光は対物レンズ５を経て１／４波長板４により直線偏光（Ｐ波）に変換され、偏光性ホログラム基板７上のホログラム面７ａに入射し、これを透過して光軸８を対称軸とする１回折光８ａ、−１次回折光８ｂに分岐し、これらの回折光がコリメートレンズ３を経て収束性の光となり、検出器９上の検出面９ａに入射する。第１０の実施の形態の第１の実施の形態との違いは、偏光性ホログラム基板７と１／４波長板の位置が対物レンズ５の前に来た点であり、偏光性ホログラム基板７と１／４波長板を対物レンズ５と一体にすることができるので、光ディスク基板６に追従する対物レンズ５に変位があっても偏光性ホログラム基板７も同じように移動するので、戻り光とホログラムパターンの相対的な位置変化による再生特性や制御特性の性能劣化が少ない。また、第１０の実施の形態は制御信号の検出原理は第１の実施の形態と全く同じであり、第１の実施の形態と同じく、ディフォーカス位置でのオフセットやうねりの発生が回避でき、２層ディスクの良好な再生や記録を安定して行うことができる。
【００２９】
以上、１０種類の実施の形態について説明を加えたが、これらを組み合わせたものも同様の効果を持つ。例えば、第２の実施の形態から第９の実施の形態は光学系として第１０の実施の形態のものを用いてもよく、図１４に示した従来例の光学系であってもよい。また、第７の実施の形態から第９の実施の形態の説明では第２の実施の形態から第６の実施の形態で現れた光スポット１ｇ、２ｇ、３ｇ、４ｇを描いてないが、当然これらの光スポットを生成するための第２の実施の形態から第６の実施の形態で使われたホログラムの分割方式を採用してもよい。また、反対に第１の実施の形態から第９の実施の形態では、ホログラム面７ａ上での光１０が各象限ごとにＯＡを結ぶ直線の周りで１象限分だけ反時計回りに回転して検出面上９ａに入射する例をとって説明したが、時計回りであっても同様の効果を持つ。さらに、上記の実施の形態ではホログラムを偏光性のもので説明したが無偏光性のものでもよく、この時１／４波長板４はなくてよい。さらに上記の実施の形態では検出器Ｔ１、Ｔ４の導通信号と検出器Ｔ２、Ｔ３の導通信号を減算器１１ｄにより差分することで、光ディスク信号面６ａのプッシュプルトラッキングエラー信号１２ｄが得たが、光ディスク装置に対するトラックの方向により、検出器Ｔ１、Ｔ２の導通信号と検出器Ｔ３、Ｔ４の導通信号の差分がプッシュプルトラッキングエラー信号になる場合もある。
【００３０】
また、上記は光ディスクを用いて説明したが、本願発明を、テープ状、カード状、ドラム状等の別の媒体形状の同様の装置に応用することは本願発明の範囲である。
【００３１】
【発明の効果】
以上の本発明により、検出器上の各象限に配置されたビームスポットが光ディスクのディフォーカスによって互いに逃げ合って重なることがなく、その上検出器上に光エネルギーが残りにくいので、２５μｍ〜５０μｍまたは−２５μｍ〜−５０μｍのディフォーカス領域におけるＦＥ信号の大きなオフセットやうねりを大幅に抑えることができ、２層ディスクの良好な再生や記録を安定して行うことができる。また、基材厚が大きく異なった光ディスクの再生を行っても、開口の小さい領域の戻り光を利用して再生信号を得ることができるので再生特性の劣化を小さくすることができ、一つの対物レンズを用いた光ディスク装置でありながら、ＤＶＤやＣＤ等の多種の光ディスクの再生に対応できる。さらに、開口の大きい領域の一部をフォーカス制御信号に取り込んでいるので、基材の厚さにむらがある光ディスクであっても、ジャストフォーカス近傍でのＦＥ特性が乱されず、正確な焦点制御が維持できる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態における光ディスク装置の断面構成図
【図２】本発明の第１の実施の形態における光ディスク装置のホログラム面と検出面の構成図
【図３】本発明の第１の実施の形態における光ディスク装置のディフォーカス発生時の検出面上での光分布図
【図４】本発明の第１の実施の形態における光ディスク装置のディフォーカス発生時の検出面上での光分布図
【図５】本発明の第２の実施の形態における光ディスク装置のホログラム面と検出面の構成図
【図６】本発明の第３の実施の形態における光ディスク装置のホログラム面と検出面の構成図
【図７】本発明の第４の実施の形態における光ディスク装置のホログラム面と検出面の構成図
【図８】本発明の第５の実施の形態における光ディスク装置のホログラム面と検出面の構成図
【図９】本発明の第６の実施の形態における光ディスク装置の検出面構成図
【図１０】本発明の第７の実施の形態における光ディスク装置の検出面構成図
【図１１】本発明の第８の実施の形態における光ディスク装置の検出面構成図
【図１２】本発明の第９の実施の形態における光ディスク装置の検出面構成図
【図１３】本発明の第１０の実施の形態における光ディスク装置の断面構成図
【図１４】従来例における光ディスク装置の断面構成図
【図１５】従来例における光ディスク装置のホログラム面と検出面の構成図
【図１６】従来例における光ディスク装置のディフォーカス発生時の検出面上での光分布図
【図１７】従来例における光ディスク装置のディフォーカス発生時の検出面上での光分布図
【図１８】本願発明および従来例における光ディスク装置のフォーカスエラー信号ディフォーカス特性図
【符号の説明】
１放射光源
３コリメートレンズ
４１／４波長板
５対物レンズ
６ａ光ディスク信号面
７ａホログラム面
９ａ光検出面
１０戻り光
１Ｂ，１Ｆ，２Ｂ，２Ｆ，３Ｂ，３Ｆ，４Ｂ，４Ｆホログラム領域
１ｂ，１ｆ，２ｂ，２ｆ，３ｂ，３ｆ，４ｂ，４ｆ検出面上光スポット
Ｆ１，Ｆ２，１２ａ，１２ｂ，１２ｃ，１２ｄ，１２ｅ検出信号
Ｔ１，Ｔ２，Ｔ３，Ｔ４光検出器
１１ａ，１１ｃ，１１ｄ減算器
１１ｂ，１１ｅ加算器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording / reproducing apparatus used for recording a signal on an information recording medium such as an optical disk or reproducing a signal of the information recording medium.
[0002]
[Prior art]
Conventional techniques will be described with reference to FIGS. FIG. 14 shows a cross-sectional configuration of an optical disc apparatus as an optical information recording / reproducing apparatus in a conventional example. In FIG. 14, a laser beam emitted from a radiation light source 1 ′ such as a semiconductor laser is incident on a beam splitter-2, is reflected by a split surface 2a, is converted into parallel light by a collimator lens 3, and a quarter-wave plate 4 'Is converted from linearly polarized light (S wave) to circularly polarized light, condensed by the objective lens 5, and converged on the signal surface 6a of the optical disk substrate 6 as an information recording medium. The light reflected from the signal surface 6a passes through the objective lens 5 and is converted into linearly polarized light (P wave) by the quarter-wave plate 4 ′, and becomes convergent light by the collimating lens 3, and passes through the split surface 2a of the beam splitter-2. Transmits and enters the hologram surface 7'a on the hologram substrate 7 ', passes through it, and branches into + 1st order diffracted light 8'a and -1st order diffracted light 8'b with the incident optical axis 8' as the axis of symmetry. , Enters the detection surface 9′a on the detector 9 ′.
[0003]
FIG. 15 shows a configuration of a hologram surface and a detection surface of an optical disk device in a conventional example. The intersection of the hologram surface 7'a and the optical axis 8 'of the incident light 10 is defined as O, and the hologram surface 7'a is divided into four by two straight lines (X axis and Y axis) orthogonal to the point O, and each quadrant is further divided. Is divided into strips along the X axis. The light 10 incident on the first quadrant of the hologram surface 7'a is incident on the first quadrant position when the point A on the detection surface 9'a is regarded as the origin on the first-order diffraction side, and is incident on the point A in the second quadrant. The light enters the second quadrant position, the fourth quadrant position with respect to point A in the third quadrant, and the third quadrant position with respect to point A in the fourth quadrant. Assuming that the intersection of the detection surface 9′a and the incident optical axis 8 ′ is O ′, the two straight lines orthogonal to the point O ′ are the x axis and the y axis, and the symmetry point of the point A ′ of the point A is A ′, −1 On the next diffraction side, the incident position on the detection surface appears symmetrically with respect to the point O ′, and the light 10 incident on the first quadrant of the hologram surface 7′a is in the third quadrant with the point A ′ on the detection surface as the origin. In the second quadrant, the light enters the fourth quadrant position with respect to the point A ′, in the third quadrant, the second quadrant position with respect to the point A ′, and in the fourth quadrant with respect to the first quadrant position with respect to the point A ′. Further, in every other strip area 1B, 2B, 3B, 4B displayed in a white background in each quadrant of the hologram surface 7'a, the first-order diffracted light converges behind the detection surface 9'a when viewed from the hologram side, The light spots of 1b, 2b, 3b, and 4b are respectively detected on the detection surface, and the other strip regions 1F, 2F, 3F, and 4F indicated by hatching converge on the front side of the detection surface 9'a, and are converged on the detection surface. The light spots are 1f, 2f, 3f, and 4f, respectively. On the other hand, the strip regions 1B, 2B, 3B, and 4B converge on the near side of the detection surface 9′a in the −1st order diffracted light, and 1b ′, 2b ′, 3b ′, and 4b ′ respectively on the detection surface. In the strip regions 1F, 2F, 3F, and 4F, the light spots converge on the back side of the detection surface 9′a, and become light spots 1f ′, 2f ′, 3f ′, and 4f ′, respectively, on the detection surface. The shape of the photodetector on the first-order diffraction side is a combination of strips along the y-axis. Each detector is turned on to output detection light as signals F1 and F2. The light spots 1b and 1f, 2b and 2f, 3b and 3f, 4b and 4f are adjacent to each other with their respective beam centers (1bO and 1fO, 2bO and 2fO, 3bO and 3fO, 4bO and 4fO) across the boundary. Is incident on the photodetector. The shape of the photodetector on the −1st order diffraction side is divided into four with the point A ′ as the center, and the light spots 1b ′ and 1f ′, 2b ′ and 2f ′, 3b ′ and 3f ′, 4b ′ and 4f. 'Is incident on the center of each split detector (t3, t4, t2, t1). The signal from the detector is processed by an adder and a subtracter to generate a control signal and a reproduction signal. For example, the focus error signal 12a of the optical disc signal surface 6a is obtained by subtracting the signals F1 and F2 by the subtractor 11a. Also, the phase difference tracking error signal 12c of the optical disc signal surface 6a is obtained by subtracting the conduction signals of the detectors t1 and t4 and the conduction signals of the detectors t2 and t3 by the subtractor 11c, and the detectors t1 and t2 The push-pull tracking error signal 12d of the optical disc signal surface 6a is obtained by subtracting the conduction signal and the conduction signals of the detectors t3 and t4 by the subtractor 11d. Further, an optical disc signal is obtained by adding the signals F1 and F2 added by the adder 11b to the signal 12e obtained by adding the conduction signals of the detectors t1 and t2 and the conduction signals of the detectors t3 and t4 by the adder 11e. A reproduction signal of the surface 6a is obtained.
[0004]
FIGS. 16 and 17 show the light distribution on the detection surface when defocusing occurs in order to show the focus error detection principle of the optical disc apparatus in the conventional example. FIG. 16 shows the case where the optical disk 6 is moved away from the objective lens 5, and FIG. In the case of FIG. 16, the light spot extends in the direction of the arrow due to defocus, the output of F1 increases, the output of F2 decreases, and the focus error signal (hereinafter referred to as FE signal) = F2−F1 <0. On the other hand, in the case of FIG. 17, the light spot extends in the direction of the arrow due to defocus, the output of F2 increases, the output of F1 decreases, and FE = F2−F1> 0. Therefore, it can be seen that the focus error signal 12a of the optical disc signal surface 6a can be obtained by the subtractor 11a.
[0005]
FIG. 18 shows the FE signal defocus characteristics of the optical disc apparatus in the conventional example. In FIG. 18, the vertical axis represents the output value of the FE signal, the horizontal axis represents the defocus amount of the optical disc signal surface 6 a, and the plus side is the side where the optical disc 6 moves away from the objective lens 5. The FE characteristic in the conventional example is a curve 13 ′. If an s-shape is drawn in the vicinity of the just focus, and control is performed so that FE → 0, the optical disc signal surface 6a is focused.
[0006]
[Problems to be solved by the invention]
Such a conventional optical disk apparatus has the following problems. That is, in FIG. 16, the light spots extend in the directions of arrows 3a and 4a, so that the light spots overlap with each other with a certain defocus amount and interfere with each other, thereby affecting the FE signal. This is the cause of the undulation that occurs in the defocus region of 20 μm to 40 μm in the curve 13 ′ in FIG. 18. Further, in FIG. 17, the light spots extend in the directions of arrows 1a and 2a, so that the light spots overlap and interfere with each other with a certain defocus amount, and the detector lies long in the directions of arrows 1a and 2a. Even if the light spot expands with a large defocus, a large amount of light energy remains on the detector, which affects the FE signal. This is caused by the large offset ε1 generated in the region of defocus −20 μm to −40 μm in the curve 13 ′ in FIG. In general, when the signal surface of the optical disk is a single surface, there is no problem even if there is an offset or waviness in the FE signal characteristics with a large defocus amount exceeding ± 10 μm. When the second signal surface is located 40 μm to 70 μm away from the signal surface (optically equivalent to 25 μm to 50 μm when divided by the refractive index), a dimming of 25 μm to 50 μm or −25 μm to −50 μm An offset or waviness that occurs in the focus area becomes a disturbance in focus control. For example, in the case of the curve 13 ′ in FIG. 18, the offset at the defocus position of −30 μm is ε1 = −0.04, and focus control is applied to the signal surface on the back side when viewed from the objective lens in the multilayer disk. In this case, an offset of −0.04 is added as a disturbance from the signal surface on the front side (assuming that it is optically 30 μm away from the objective lens side), which generates a defocus of about 0.5 μm, and the signal reproduction characteristics. Is greatly deteriorated. As described above, in the conventional optical disc apparatus, a large offset or waviness of the FE signal generated in the defocus region of 25 μm to 50 μm or −25 μm to −50 μm greatly impairs the reproduction performance of the multilayer disc having two or more layers. There was a problem. In view of such problems, an object of the present invention is to provide an optical disc apparatus that can stably perform a good reproduction and recording of a multi-layer disc by suppressing a large offset and undulation of an FE signal.
[0007]
[Means for Solving the Problems]
The present invention uses the following means in order to solve the above problems. That is, it consists of a radiation light source, an objective lens, a light distribution means such as a hologram, and a photodetector. The light emitted from the radiation light source is condensed on the signal surface of the optical disk by the objective lens, and the reflected light passes through the objective lens. Then, the light is incident on the light distribution means, and the light is diffracted in two directions by the light distribution means, and one diffracted light is divided into at least four regions by two straight lines (x-axis and y-axis) perpendicular to the point O on the light distribution means. Each of which is distributed around the straight line OA by one quadrant and incident around the point A on the photodetector, and the other diffracted light is also distributed into at least four regions by the x-axis and y-axis, An optical disc apparatus characterized by rotating around a straight line OA ′ by one quadrant and entering around a point A ′ on the photodetector, and the y-axis coincides with the line segment AA ′, and the light distribution means Each quadrant is a dividing line along the x-axis. The light that is diffracted into every other strip cell and converges in front of the detection surface (convergent light F), and the light that diffracts other strip cells converges behind the detection surface (convergent light B). , At least two photodetectors are adjacently arranged along the y-axis in each quadrant of coordinates with the point A as the origin, and convergent light F and convergent light B are incident on the photodetectors, respectively. To do.
[0008]
Also, in each quadrant of coordinates with the point A as the origin, four photodetectors D1, D2, D3, D4 are arranged adjacent to each other in this order along the y-axis, and one skip detector D1, D3, D2 and D4 are electrically connected to each other, and the photodetectors D1, D2, and D3 in the first quadrant position are electrically connected to the photodetectors D2, D3, and D4 in the fourth quadrant position, and light in the second quadrant position. The detectors D2, D3, D4 are electrically connected to the photodetectors D1, D2, D3 in the third quadrant position, the photodetector D1 in the first quadrant position is electrically connected to the photodetector D1 in the second quadrant position, and the first The signal from the photodetector D1 in the quadrant position and the detector conducting to it is F1, the signal from the photodetector D2 in the first quadrant position and the detector conducting to this is F2, and the difference between F1 and F2 The focus error signal of the optical disc signal surface is obtained from the above.
[0009]
Further, the photodetectors D1, D2, and D3 in the first quadrant position at the coordinates with the point A as the origin are formed on a straight line substantially along the y axis with the photodetectors D2, D3, and D4 in the fourth quadrant position, respectively. The second quadrant position photodetectors D2, D3, D4 are formed on a straight line substantially along the y axis with the third quadrant position photodetectors D1, D2, D3, respectively. The photodetector D1 and the photodetector D4 in the third quadrant position may be omitted, and the photodetector D4 in the first quadrant position and the photodetector D1 in the second quadrant position may be omitted.
[0010]
Further, in each quadrant of the light splitting means, the position where the region C away from the point O is diffracted and incident on the photodetector is diffracted in the other region B within the quadrant and around the point A on the photodetector. It is characterized in that it is detected by a photodetector that is outside of the incident position from the point A and independent of the region B. At this time, the convergence point of the light diffracting the region C of the light splitting means is substantially on the light detection surface, and the region C of the light splitting means is a region outside the circle centered on the point O, or It may be a part of the region C outside the circle centered at the point O and sandwiched between the x axis and a straight line parallel to the x axis. It may be a band-like region.
[0011]
On the other hand, the region B of the light splitting means is divided into an inner peripheral region B1 surrounding the point O and the other region B2, and the position of the light spot that diffracts the regions B1 and B2 and enters the detector is along the x-axis. The region B1 of the light splitting means may be a region surrounded by the x axis, the y axis, and a straight line parallel thereto, and the region B1 is a region within a circle centered on the point O. The region B2 may be a ring-shaped region centered on the point O.
[0012]
Further, each of the distributed lights on the side diffracted around the point A ′ has a photodetector DT1 configured in the first quadrant position in coordinates with the point A as the origin, and a photodetector configured in the second quadrant position. Detected by DT2, the photodetector DT3 configured in the third quadrant position, and the photodetector DT4 configured in the fourth quadrant position, detection signals from the detectors are T1, T2, T3, T4, respectively. Then, a tracking error signal on the optical disc signal surface is obtained from (T1 + T4)-(T2 + T3) or (T1 + T2)-(T3 + T4) or (T1 + T3)-(T2 + T4).
[0013]
With the configuration as described above, the beam spots arranged in each quadrant on the detector do not escape and overlap each other due to the defocusing of the optical disk, and light energy hardly remains on the detector, so that 25 μm to 50 μm or − A large offset and waviness of the FE signal in the defocus region of 25 μm to −50 μm can be greatly suppressed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 4 and FIG. Elements common to the conventional example will be described with the same numbers. FIG. 1 shows a cross-sectional configuration of the optical disk apparatus according to the first embodiment of the present invention, and a side view relating to the radiation light source 1 and its periphery is also added below. In FIG. 1, the laser light emitted from the radiation light source 1 such as a semiconductor laser mounted on the light detection substrate 9 is reflected by the reflection mirror 14 mounted on the light detection substrate 9 to cause the polarization hologram substrate 7 to pass. The light is transmitted, converted from linearly polarized light (S wave) into circularly polarized light by the quarter wavelength plate 4, converted to parallel light by the collimating lens 3, condensed by the objective lens 5, and on the signal surface 6 a of the optical disk substrate 6. Converge to. The light reflected from the signal surface 6 a becomes convergent light through the objective lens 5 and the collimating lens 3, converted into linearly polarized light (P wave) by the quarter wavelength plate 4, and the hologram surface 7 a on the polarizing hologram substrate 7. Is incident on the detection surface 9a on the detector 9, and is branched into a first diffracted light 8a and a −1st order diffracted light 8b having the incident optical axis 8 as a symmetry axis.
[0015]
FIG. 2 shows the configuration of the hologram surface and the detection surface of the optical disk device according to the first embodiment of the present invention. The intersection of the hologram surface 7a and the optical axis 8 of the incident light 10 is defined as O, and the hologram surface 7a is divided into four by two straight lines (X axis and Y axis) orthogonal to the point O, and further along the X axis in each quadrant. Divided into strips. The light 10 incident on the first quadrant of the hologram surface 7a enters the second quadrant position when the point A on the detection surface 9a is regarded as the origin on the first-order diffraction side, and the third quadrant position relative to the point A in the second quadrant. In addition, the light enters the fourth quadrant position with respect to the point A in the third quadrant and the first quadrant position with respect to the point A in the fourth quadrant. That is, the light 10 on the hologram surface 7a is rotated by one quadrant around the straight line connecting OA in each quadrant and is incident on the detection surface 9a. Assuming that the intersection of the detection surface 9a and the incident optical axis 8 is O ′, the two straight lines orthogonal to the point O ′ are the x-axis and the y-axis, and the symmetry point with respect to the point O ′ of the point A is A ′, the −1st order diffraction side Then, the incident position on the detection surface appears symmetrically with respect to the point O ′, and the light 10 incident on the first quadrant of the hologram surface 7a is in the fourth quadrant position with the point A ′ on the detection surface as the origin, in the second quadrant position. In the quadrant, the light enters the first quadrant position with respect to the point A ′, in the third quadrant the second quadrant position with respect to the point A ′, and in the fourth quadrant with respect to the third quadrant position with respect to the point A ′. Further, in every other strip area 1B, 2B, 3B, 4B displayed in white in each quadrant of the hologram surface 7a, the first-order diffracted light converges behind the detection surface 9a when viewed from the hologram side, and on the detection surface. The light spots are 1b, 2b, 3b, and 4b, respectively, and the other strip regions 1F, 2F, 3F, and 4F indicated by hatching converge on the front side of the detection surface 9a, and 1f, 2f, and 3f on the detection surface, respectively. 4f light spot. On the other hand, the strip regions 1B, 2B, 3B, and 4B converge on the near side of the detection surface 9a in the −1st-order diffracted light, and light of 1b ′, 2b ′, 3b ′, and 4b ′ respectively on the detection surface. In the strip regions 1F, 2F, 3F, and 4F, the light beams converge on the back side of the detection surface 9a and become light spots 1f ′, 2f ′, 3f ′, and 4f ′, respectively, on the detection surface. The shape of the photodetector on the first-order diffraction side is a combination of strips along the y-axis. Each detector is turned on to output detection light as signals F1 and F2. The light spots 1b and 1f, 2b and 2f, 3b and 3f, 4b and 4f are adjacent to each other with their respective beam centers (1bO and 1fO, 2bO and 2fO, 3bO and 3fO, 4bO and 4fO) across the boundary. Is incident on the photodetector. The shape of the photodetector on the −1st order diffraction side is divided into four with the point A ′ as the center, and the light spots 1b ′ and 1f ′, 2b ′ and 2f ′, 3b ′ and 3f ′, 4b ′ and 4f. 'Is incident on the center of each split detector (T4, T1, T2, T3). The signal from the detector is processed by an adder and a subtracter to generate a control signal and a reproduction signal. For example, the focus error signal 12a of the optical disc signal surface 6a is obtained by subtracting the signals F1 and F2 by the subtractor 11a. Also, the phase difference tracking error signal 12c of the optical disc signal surface 6a is obtained by subtracting the conduction signals of the detectors T1 and T3 and the conduction signals of the detectors T2 and T4 by the subtractor 11c, and the detectors T1 and T4 The push-pull tracking error signal 12d of the optical disc signal surface 6a is obtained by subtracting the conduction signal and the conduction signals of the detectors T2 and T3 by the subtractor 11d. Further, an optical disc signal is obtained by adding the signals F1 and F2 added by the adder 11b to the signal 12e obtained by adding the conduction signals of the detectors T1 and T4 and the conduction signals of the detectors T2 and T3 by the adder 11e. A reproduction signal of the surface 6a is obtained.
[0016]
FIGS. 3 and 4 show the light distribution on the detection surface when defocusing occurs in order to show the focus error detection principle of the optical disc apparatus according to the first embodiment of the present invention. FIG. 3 shows a case where the optical disk 6 is moved away from the objective lens 5, and FIG. In the case of FIG. 3, the light spot extends in the direction of the arrow due to defocus, the output of F1 increases, the output of F2 decreases, and FE = F2−F1 <0. On the other hand, in the case of FIG. 4, the light spot extends in the direction of the arrow due to defocus, the output of F2 increases, the output of F1 decreases, and FE = F2-F1> 0. Therefore, it can be seen that the focus error signal 12a of the optical disc signal surface 6a can be obtained by the subtractor 11a.
[0017]
FIG. 18 additionally shows the focus error signal defocus characteristic of the optical disc apparatus according to the first embodiment of the present invention. The FE characteristic according to the first embodiment is a curve 13. If an s-shape is drawn in the vicinity of the just focus, and control is performed so that FE → 0, the optical disc signal surface 6a is focused.
[0018]
In the present embodiment, as indicated by arrows 1a, 2a, 3a, and 4a in FIGS. 3 and 4, the beam spots arranged around the point A may escape and overlap each other due to defocusing of the optical disk. In addition, light energy hardly remains on the detector. As a result, in the curve 13 of FIG. 18, the undulation in the region of 20 μm to 40 μm, which is seen in the conventional example, does not appear, and almost no offset occurs in the region of −20 μm to −50 μm. For example, in the case of the curve 13, the offset at the defocus −32 μm position is ε2 = 0.01, and when focus control is applied to the signal surface on the back side when viewed from the objective lens, the front side (optical Although an offset of 0.01 is added as a disturbance from the signal surface (assuming that only 32 μm is on the objective lens side), this corresponds to a small defocus of about 0.15 μm, and the signal reproduction characteristics are almost deteriorated. Absent. Therefore, good reproduction and recording of the dual-layer disc can be performed stably.
[0019]
Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is the same as the first embodiment except for the configuration of the hologram surface and the detection surface, and the description of the same parts is omitted. FIG. 5 shows the configuration of the hologram surface and the detection surface of the optical disk device according to the second embodiment of the present invention. The intersection of the hologram surface 7a and the optical axis 8 of the incident light 10 is defined as O. The hologram surface 7a is divided into four by two straight lines (X axis and Y axis) orthogonal to the point O, and a circle 15 centered on the point O is obtained. The inner area is divided into strips along the X axis in each quadrant. The light 10 incident on the first quadrant of the hologram surface 7a enters the second quadrant position when the point A on the detection surface 9a is regarded as the origin on the first-order diffraction side, and the third quadrant position with respect to the point A in the second quadrant. In addition, the light enters the fourth quadrant position with respect to the point A in the third quadrant and the first quadrant position with respect to the point A in the fourth quadrant. That is, the light 10 on the hologram surface 7a is rotated by one quadrant around the straight line connecting OA in each quadrant and is incident on the detection surface 9a. Assuming that the intersection of the detection surface 9a and the incident optical axis 8 is O ′, the two straight lines orthogonal to the point O ′ are the x-axis and the y-axis, and the symmetry point with respect to the point O ′ of the point A is A ′, the −1st order diffraction side Then, the incident position on the detection surface appears symmetrically with respect to the point O ′, and the light 10 incident on the first quadrant of the hologram surface 7a is in the fourth quadrant position with the point A ′ on the detection surface as the origin, in the second quadrant position. In the quadrant, the light enters the first quadrant position with respect to the point A ′, in the third quadrant the second quadrant position with respect to the point A ′, and in the fourth quadrant with respect to the third quadrant position with respect to the point A ′. Further, in every other strip area 1B, 2B, 3B, 4B displayed in white in each quadrant of the hologram surface 7a, the first-order diffracted light converges behind the detection surface 9a when viewed from the hologram side, and on the detection surface. The light spots are 1b, 2b, 3b, and 4b, respectively, and the other strip regions 1F, 2F, 3F, and 4F indicated by hatching converge on the front side of the detection surface 9a, and 1f, 2f, and 3f on the detection surface, respectively. 4f light spots, and in each quadrant of the hologram surface 7a, in the regions 1G, 2G, 3G, and 4G outside the circle 15, the first-order diffracted light converges on the detection surface 9a as viewed from the hologram side. The light spots are 1 g, 2 g, 3 g, and 4 g, respectively. On the other hand, the strip regions 1B, 2B, 3B, and 4B converge on the near side of the detection surface 9a in the −1st-order diffracted light, and light of 1b ′, 2b ′, 3b ′, and 4b ′ respectively on the detection surface. In the strip regions 1F, 2F, 3F, and 4F, the light beams converge on the back side of the detection surface 9a, become light spots of 1f ′, 2f ′, 3f ′, and 4f ′ on the detection surface, respectively. In the regions 1G, 2G, 3G, and 4G, the light converges substantially on the detection surface 9a, and becomes light spots of 1g ′, 2g ′, 3g ′, and 4g ′, respectively. The positions of the light spots 1g, 2g, 3g, and 4g are seen from the point A and are outside the positions of the light spots 1b and 1f, 2b and 2f, 3b and 3f, 4b and 4f, and the light spots 1g ′, 2g ′, and 3g. The positions of '4g' are outside the positions of the light spots 1b 'and 1f', 2b 'and 2f', 3b 'and 3f', 4b 'and 4f', as viewed from the point A '. The shape of the photodetector on the first-order diffraction side is a combination of strip shapes along the y-axis that detect the light spots 1b, 1f, 2b, 2f, 3b, 3f, 4b, and 4f. In the same manner as in the first embodiment, the detection light is output as the signals F1 and F2 by turning on one by one. Further, the light spots 1g, 2g, 3g, and 4g are detected by the conducted photodetector F3. The positional relationship between the light spots 1b and 1f, 2b and 2f, 3b and 3f, 4b and 4f, and the positional relationship between these spots and the strip-shaped detectors that generate the signals F1 and F2 are described in the first embodiment. The description is omitted. The shape of the photodetector on the −1st order diffraction side is divided into four with the point A ′ as the center, and the light spots 1b ′ and 1f ′, 2b ′ and 2f ′, 3b ′ and 3f ′, 4b ′ and 4f. 'Is incident on the area of each split detector (T4, T1, T2, T3). The light spots 1g ', 2g', 3g ', 4g' are incident on detection areas extending from the divided detectors T4, T1, T2, T3, respectively. The signal from the detector is processed by an adder and a subtracter to generate a control signal and a reproduction signal. For example, the focus error signal 12a of the optical disc signal surface 6a is obtained by subtracting the signals F1 and F2 by the subtractor 11a. Also, the phase difference tracking error signal 12c of the optical disc signal surface 6a is obtained by subtracting the conduction signals of the detectors T1 and T3 and the conduction signals of the detectors T2 and T4 by the subtractor 11c, and the detectors T1 and T4 The push-pull tracking error signal 12d of the optical disc signal surface 6a is obtained by subtracting the conduction signal and the conduction signals of the detectors T2 and T3 by the subtractor 11d. Further, a signal obtained by adding the detection signal of the detector F3 to the signal 12b obtained by adding the signals F1 and F2 by the adder 11b, and adding the conduction signals of the detectors T1 and T4 and the conduction signals of the detectors T2 and T3 by the adder 11e. By adding to 12e, a reproduction signal of the optical disc signal surface 6a is obtained.
[0020]
The focus error detection principle of the second embodiment is the same as that of the first embodiment, and the movement of the light distribution on the detection surface when defocus occurs is the same. The light spots 1g, 2g, 3g, and 4g extend in the directions indicated by arrows 1h, 2h, 3h, and 4h, respectively, by defocusing. However, since there is no detector related to FE detection in these directions, the FE characteristics are not affected. Accordingly, as in the first embodiment, the occurrence of offset and waviness during defocusing can be avoided, and good reproduction and recording of a dual-layer disc can be performed stably. Further, in the second embodiment, the signals F1 and F2 can be added by the adder 11b to be a reproduction signal, and F1 and F2 are detection signals in a region having a small opening (region in the circle 15). Even when optical discs having different thicknesses of the base material 6 are reproduced, the aberration is small in the region where the aperture is small, so that the degradation of the reproduction characteristics can be reduced. For example, a DVD with a substrate thickness of 0.6 mm can be reproduced with the signal sum of all detectors (F1 + F2 + T1 + T2 + T3 + T4), and a CD with a substrate thickness of 1.2 mm can be reproduced with F1 + F2 using the same objective lens 5. Even with a single optical disk device, it is possible to support reproduction of various types of optical disks.
[0021]
Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is the same as the second embodiment except for the configuration of the hologram surface, and the description of the same parts is omitted. FIG. 6 shows the configuration of the hologram surface and the detection surface of the optical disk device according to the third embodiment of the present invention. The intersection of the hologram surface 7a and the optical axis 8 of the incident light 10 is defined as O. The hologram surface 7a is divided into four by two straight lines (X axis and Y axis) orthogonal to the point O, and a circle 15 centered on the point O is obtained. The area inside or outside the straight lines 16 and 17 is divided into strips along the X axis in each quadrant. The light 10 incident on the first quadrant of the hologram surface 7a enters the second quadrant position when the point A on the detection surface 9a is regarded as the origin on the first-order diffraction side, and the third quadrant position relative to the point A in the second quadrant. In addition, the light enters the fourth quadrant position with respect to the point A in the third quadrant and the first quadrant position with respect to the point A in the fourth quadrant. That is, the light 10 on the hologram surface 7a is rotated by one quadrant around the straight line connecting OA in each quadrant and is incident on the detection surface 9a. Assuming that the intersection of the detection surface 9a and the incident optical axis 8 is O ′, the two straight lines orthogonal to the point O ′ are the x-axis and the y-axis, and the symmetry point with respect to the point O ′ of the point A is A ′, the −1st order diffraction side Then, the incident position on the detection surface appears symmetrically with respect to the point O ′, and the light 10 incident on the first quadrant of the hologram surface 7a is in the fourth quadrant position with the point A ′ on the detection surface as the origin, in the second quadrant position. In the quadrant, the light enters the first quadrant position with respect to the point A ′, in the third quadrant the second quadrant position with respect to the point A ′, and in the fourth quadrant with respect to the third quadrant position with respect to the point A ′. Further, in every other strip area 1B, 2B, 3B, 4B displayed in white in each quadrant of the hologram surface 7a, the first-order diffracted light converges behind the detection surface 9a when viewed from the hologram side, and on the detection surface. The light spots are 1b, 2b, 3b, and 4b, respectively, and the other strip regions 1F, 2F, 3F, and 4F indicated by hatching converge on the front side of the detection surface 9a, and 1f, 2f, and 3f on the detection surface, respectively. 4f becomes a light spot, and in each quadrant of the hologram surface 7a, in the regions 1G, 2G, 3G, and 4G outside the circle 15 and between the straight lines 16 and 17, almost converge on the detection surface 9a, and 1 g on the detection surface. 2g, 3g, 4g light spots. On the other hand, the strip regions 1B, 2B, 3B, and 4B converge on the near side of the detection surface 9a in the −1st-order diffracted light, and light of 1b ′, 2b ′, 3b ′, and 4b ′ respectively on the detection surface. In the strip regions 1F, 2F, 3F, and 4F, the light beams converge on the back side of the detection surface 9a, become light spots of 1f ′, 2f ′, 3f ′, and 4f ′ on the detection surface, In the regions 1G, 2G, 3G, and 4G between the straight lines 16 and 17, the light converges substantially on the detection surface 9a and becomes light spots of 1g ′, 2g ′, 3g ′, and 4g ′, respectively. The positions of the light spots 1g, 2g, 3g, and 4g are seen from the point A and are outside the positions of the light spots 1b and 1f, 2b and 2f, 3b and 3f, 4b and 4f, and the light spots 1g ′, 2g ′, and 3g. The positions of '4g' are outside the positions of the light spots 1b 'and 1f', 2b 'and 2f', 3b 'and 3f', 4b 'and 4f', as viewed from the point A '. In the third embodiment, only the way of dividing the hologram surface 7a is different, and the shape, wiring, and signal detection principle of the photodetector are exactly the same as those of the second embodiment. Similarly, the occurrence of offset and waviness during defocusing can be avoided, and good reproduction and recording of a dual-layer disc can be performed stably. Similarly to the second embodiment, a DVD with a substrate thickness of 0.6 mm is reproduced with the signal sum of all detectors (F1 + F2 + T1 + T2 + T3 + T4), and a CD with a substrate thickness of 1.2 mm is reproduced using the same objective lens 5. F1 + F2 can be performed, and various optical discs can be played back even though the optical disc apparatus is one. Further, since the areas having larger openings than the second embodiment are partially taken into F1 and F2, even if the optical disk has uneven thickness of the base material 6, the FE characteristics near the just focus are obtained. Accurate focus control can be maintained without being disturbed (if the thickness of the substrate 6 is uneven, the aberration in the region with a small aperture and the aberration in the region with a large aperture are separated from each other. In the case of FE detection using only a region with a small aperture such as FE characteristics may be disturbed near the just focus).
[0022]
Next, a fourth embodiment of the present invention will be described with reference to FIG. The fourth embodiment is the same as the third embodiment except for a part of the configuration of the hologram surface, and the description of the same parts is omitted. FIG. 7 shows a configuration of a hologram surface and a detection surface of an optical disk device according to the fourth embodiment of the present invention. The difference from the third embodiment is that the incident position on the detection surface is slightly changed in the x-axis direction in the rectangular region in the rectangle 18 with the point O as the center compared to the other rectangular regions. The alternate strip regions 1′B, 2′B, 3′B, and 4′B, which are displayed in white in the strip region in the rectangular shape 18, show the first-order diffracted light behind the detection surface 9a when viewed from the hologram side. The light beams converge to become light spots of 1′b, 2′b, 3′b, and 4′b on the detection surface, respectively, and the other strip regions 1′F, 2′F, 3′F, and 4 ′ indicated by hatching. In F, the light converges on the near side of the detection surface 9a, and becomes a light spot of 1′f, 2′f, 3′f, and 4′f on the detection surface, respectively. The light spots 1′b, 2′b, 3′b, and 4′b are shifted to the side farther from the boundary line of the detector than the light spots 1b, 2b, 3b, and 4b. Further, in the −1st order diffracted light, the strip regions 1′B, 2′B, 3′B, 4′B converge on the near side of the detection surface 9a, and 1′b ′, 2′b ′ on the detection surface, respectively. 3′b ′ and 4′b ′, and in the strip regions 1′F, 2′F, 3′F, and 4′F, the light spots converge on the back side of the detection surface 9a, and 1 on the detection surface. The light spots are 'f', 2'f ', 3'f', 4'f '. The fourth embodiment is different from the third embodiment only in the way of dividing the hologram surface 7a, and the shape, wiring, and signal detection principle of the photodetector are exactly the same as those in the third embodiment. Similarly, the occurrence of offset and waviness at the defocus position can be avoided, and good reproduction and recording of a two-layer disc can be performed stably. Similarly to the third embodiment, reproduction of a DVD with a substrate thickness of 0.6 mm is performed with the signal sum of all detectors (F1 + F2 + T1 + T2 + T3 + T4), and the same objective lens 5 is used to reproduce a DVD with a substrate thickness of 1.2 mm. Reproduction can be performed by F1 + F2, and it is possible to cope with reproduction of various types of optical discs even though it is a single optical disc apparatus. Further, by keeping the small aperture area in the square 18 away from the boundary line of the detector, the influence of the aberration in the small aperture area on the FE and the influence of the aberration in the large aperture area on the FE are balanced. Compared to the third embodiment, even in the case of an optical disc with uneven thickness of the base material 6, the FE characteristics in the vicinity of the just focus are not disturbed, and more accurate focus control can be maintained.
[0023]
Next, a fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment is the same as the second embodiment except for the configuration of the hologram surface, and the description of the same parts is omitted. FIG. 8 shows the configuration of the hologram surface and the detection surface of the optical disk device according to the fifth embodiment of the present invention. The intersection of the hologram surface 7a and the optical axis 8 of the incident light 10 is defined as O. The hologram surface 7a is divided into four by two straight lines (X axis and Y axis) orthogonal to the point O, and a circle 15 centered on the point O is obtained. The area inside or outside the circle 19 is divided into strips along the X axis in each quadrant. The light 10 incident on the first quadrant of the hologram surface 7a enters the second quadrant position when the point A on the detection surface 9a is regarded as the origin on the first-order diffraction side, and the third quadrant position relative to the point A in the second quadrant. In addition, the light enters the fourth quadrant position with respect to the point A in the third quadrant and the first quadrant position with respect to the point A in the fourth quadrant. That is, the light 10 on the hologram surface 7a is rotated by one quadrant around the straight line connecting OA in each quadrant and is incident on the detection surface 9a. Assuming that the intersection of the detection surface 9a and the incident optical axis 8 is O ′, the two straight lines orthogonal to the point O ′ are the x-axis and the y-axis, and the symmetry point with respect to the point O ′ of the point A is A ′, the −1st order diffraction side Then, the incident position on the detection surface appears symmetrically with respect to the point O ′, and the light 10 incident on the first quadrant of the hologram surface 7a is in the fourth quadrant position with the point A ′ on the detection surface as the origin, in the second quadrant position. In the quadrant, the light enters the first quadrant position with respect to the point A ′, in the third quadrant the second quadrant position with respect to the point A ′, and in the fourth quadrant with respect to the third quadrant position with respect to the point A ′. Also, every other strip area 1B, 2B, 3B, 4B and 1'B, 2'B, 3'B, 4'B displayed in white in each quadrant of the hologram surface 7a is viewed from the hologram side for the next time. The folded light converges on the back side of the detection surface 9a, and becomes 1b, 2b, 3b, 4b and 1'b, 2'b, 3'b, 4'b light spots on the detection surface, respectively, indicated by hatching The other strip regions 1F, 2F, 3F, 4F, and 1′F, 2′F, 3′F, 4′F converge on the front side of the detection surface 9a, and 1f, 2f, 3f, 4f, and 1'f, 2'f, 3'f, and 4'f become light spots. In each quadrant of the hologram surface 7a, in the regions 1G, 2G, 3G, and 4G outside the circle 15 and within the circle 19 It almost converges on the detection surface 9a, and becomes a 1g, 2g, 3g, 4g light spot on the detection surface, respectively. On the contrary, the strip regions 1B, 2B, 3B, 4B and 1′B, 2′B, 3′B, 4′B converge on the near side of the detection surface 9a and are detected by the −1st order diffracted light. On the surface, light spots of 1b ', 2b', 3b ', 4b' and 1'b ', 2'b', 3'b ', 4'b' respectively become strip regions 1F, 2F, 3F, 4F, And 1′F, 2′F, 3′F and 4′F converge on the back side of the detection surface 9a, and 1f ′, 2f ′, 3f ′, 4f ′ and 1′f ′ on the detection surface, respectively. 2'f ', 3'f', and 4'f 'become light spots, and converge on the detection surface 9a in the regions 1G, 2G, 3G, and 4G outside the circle 15 and within the circle 19, and are detected on the detection surface 9a. The light spots are 1 g ′, 2 g ′, 3 g ′, and 4 g ′, respectively. The positions of the light spots 1g, 2g, 3g, and 4g are seen from the point A and are outside the positions of the light spots 1b and 1f, 2b and 2f, 3b and 3f, 4b and 4f, and the light spots 1g ′, 2g ′, and 3g. The positions of '4g' are outside the positions of the light spots 1b 'and 1f', 2b 'and 2f', 3b 'and 3f', 4b 'and 4f', as viewed from the point A '. The fifth embodiment is different from the second embodiment only in the way of dividing the hologram surface 7a. The shape, wiring, and signal detection principle of the photodetector are exactly the same as those in the second embodiment. Similarly, the occurrence of offset and waviness at the defocus position can be avoided, and good reproduction and recording of a two-layer disc can be performed stably. Further, when reproducing optical disks having greatly different substrate thicknesses, 1′b, 2′b, 3′b, 4′b, 1′f, 2′f, 3′f, Since the light spot of 4′f is greatly expanded and hardly remains on the detector, the reproduction of the DVD with the substrate thickness of 0.6 mm is performed with the signal sum of all detectors (F1 + F2 + T1 + T2 + T3 + T4) as in the second embodiment. The same objective lens 5 can be used to reproduce a CD having a substrate thickness of 1.2 mm with F1 + F2, and it is possible to cope with the reproduction of various types of optical discs even though it is a single optical disc apparatus. Further, since the area having a large opening (area outside the circle 19) is partially taken into F1 and F2 compared to the second embodiment, even if the optical disk has uneven thickness of the base material 6, FE characteristics near the focus are not disturbed, and accurate focus control can be maintained.
[0024]
Next, a sixth embodiment of the present invention will be described with reference to FIG. The configuration of the sixth embodiment is the same as that of the fifth embodiment except that the incident position of the light spot on the detection surface is slightly changed, and the description of the same parts is omitted. FIG. 9 shows the configuration of the detection surface of the optical disc apparatus according to the sixth embodiment of the present invention. The difference from the fifth embodiment is that the incident positions of the light spots 1b, 2b, 3b, 4b and 1f, 2f, 3f, 4f are the spots 1′b, 2′b, 3′b, 4′b, And 1′f, 2′f, 3′f, and 4′f, the shift is away from the detector boundary. In the sixth embodiment, only the specification of the hologram surface 7a is different, and the shape, wiring, and signal detection principle of the photodetector are exactly the same as those in the fifth embodiment. As in the fifth embodiment, Occurrence of offset and waviness at the defocus position can be avoided, and good reproduction and recording of a two-layer disc can be performed stably. Similarly to the fifth embodiment, reproduction of a DVD with a substrate thickness of 0.6 mm is performed with the signal sum of all detectors (F1 + F2 + T1 + T2 + T3 + T4), and reproduction of a CD with a substrate thickness of 1.2 mm using the same objective lens 5. F1 + F2 can be performed, and various optical discs can be played back even though the optical disc apparatus is one. Further, as in the fifth embodiment, even if the thickness of the substrate 6 is uneven, the FE characteristics in the vicinity of the just focus are not disturbed, and accurate focus control can be maintained.
[0025]
Next, a seventh embodiment of the present invention will be described with reference to FIG. The configuration of the seventh embodiment is exactly the same as that of the first embodiment except that the shape of the detector is slightly different, and the description of the same parts is omitted. FIG. 10 shows the configuration of the detection surface of the optical disc apparatus according to the seventh embodiment of the present invention. The difference from the first embodiment is the shape of the detectors F2b, F2d, F1b, and F1d. In the first embodiment, the shape is a strip, but in the seventh embodiment, the lower half or the top. The width in half is changed. By adding the above changes, the shape of the characteristic curve 13 of the FE signal shown in FIG. 18 can be finely adjusted. The seventh embodiment is different from the first embodiment only in the shape of the photodetector, and the signal detection principle is exactly the same as in the first embodiment. As in the first embodiment, the offset and waviness at the defocus position are the same. Can be prevented, and good reproduction and recording of a dual-layer disc can be performed stably.
[0026]
Next, an eighth embodiment of the present invention will be described with reference to FIG. The configuration of the eighth embodiment is exactly the same as that of the seventh embodiment except that the shape of the detector is slightly different, and the description of the same parts is omitted. FIG. 11 shows the configuration of the detection surface of the optical disc apparatus according to the eighth embodiment of the present invention. The difference from the seventh embodiment is that the detectors F1e and F2e are omitted. By adding the above changes, the shape of the characteristic curve 13 of the FE signal shown in FIG. 18 can be finely adjusted. In the eighth embodiment, only the shape of the photodetector is different, and the principle of signal detection is exactly the same as in the seventh embodiment and the first embodiment. As in the embodiment, the occurrence of offset and waviness at the defocus position can be avoided, and good reproduction and recording of a dual-layer disc can be performed stably.
[0027]
Next, a ninth embodiment of the present invention will be described with reference to FIG. The configuration of the ninth embodiment is exactly the same as that of the eighth embodiment except that the shape of the detector is slightly different, and the description of the same parts is omitted. FIG. 12 shows the configuration of the detection surface of the optical disc apparatus according to the ninth embodiment of the present invention. The difference from the eighth embodiment is that the detectors F1a and F2a are omitted. By adding the above changes, the shape of the characteristic curve 13 of the FE signal shown in FIG. 18 can be finely adjusted. The ninth embodiment differs from the eighth embodiment only in the shape of the photodetector, and the signal detection principle is exactly the same as in the eighth embodiment and the first embodiment. As in the embodiment, the occurrence of offset and waviness at the defocus position can be avoided, and good reproduction and recording of a dual-layer disc can be performed stably.
[0028]
Next, a tenth embodiment of the present invention will be described with reference to FIG. The configuration of the tenth embodiment is exactly the same as that of the first embodiment except that the positions of the collimating lens 3, the polarizing hologram substrate 7 and the quarter wavelength plate are changed. Omitted. FIG. 13 shows a cross-sectional configuration of the optical disc apparatus according to the tenth embodiment of the present invention, and a side view relating to the radiation light source 1 and its periphery is also added below. In FIG. 13, the laser light emitted from the radiation light source 1 such as a semiconductor laser attached on the light detection substrate 9 is reflected by the reflection mirror 14 attached on the light detection substrate 9 and is collimated by the collimating lens 3. And is transmitted through the polarizing hologram substrate 7, converted from linearly polarized light (S wave) to circularly polarized light by the quarter wavelength plate 4, condensed by the objective lens 5, and on the signal surface 6 a of the optical disk substrate 6. Converge to. The light reflected from the signal surface 6a passes through the objective lens 5 and is converted into linearly polarized light (P wave) by the quarter wavelength plate 4, and enters the hologram surface 7a on the polarizing hologram substrate 7, and is transmitted through the light. The diffracted light splits into a 1st-order diffracted light 8a and a −1st-order diffracted light 8b with the axis 8 as a symmetric axis, and the diffracted light becomes convergent light through the collimating lens 3 and enters the detection surface 9a on the detector 9. The difference between the tenth embodiment and the first embodiment is that the positions of the polarizing hologram substrate 7 and the quarter-wave plate are in front of the objective lens 5. Since the quarter-wave plate can be integrated with the objective lens 5, even if the objective lens 5 following the optical disk substrate 6 is displaced, the polarizing hologram substrate 7 moves in the same manner, so that the return light and the hologram There is little performance degradation of reproduction characteristics and control characteristics due to relative position changes of the pattern. In the tenth embodiment, the detection principle of the control signal is exactly the same as in the first embodiment, and as in the first embodiment, the occurrence of offset and waviness at the defocus position can be avoided. Good reproduction and recording of a dual-layer disc can be performed stably.
[0029]
As mentioned above, although description was added about ten types of embodiment, what combined these has the same effect. For example, in the second to ninth embodiments, the optical system of the tenth embodiment may be used as the optical system, or the conventional optical system shown in FIG. In the description of the seventh to ninth embodiments, the light spots 1g, 2g, 3g, and 4g that appear in the second to sixth embodiments are not drawn. The hologram dividing method used in the second to sixth embodiments for generating these light spots may be employed. On the other hand, in the first to ninth embodiments, the light 10 on the hologram surface 7a rotates counterclockwise by one quadrant around the straight line connecting OA for each quadrant. Although an example in which the light is incident on the detection surface 9a has been described, the same effect can be obtained even in the clockwise direction. Furthermore, in the above embodiment, the hologram has been described as having a polarizing property. However, a non-polarizing material may be used, and at this time, the quarter wavelength plate 4 may be omitted. Further, in the above embodiment, the push-pull tracking error signal 12d of the optical disc signal surface 6a is obtained by subtracting the conduction signals of the detectors T1 and T4 and the conduction signals of the detectors T2 and T3 by the subtractor 11d. Depending on the track direction with respect to the optical disc apparatus, the difference between the conduction signals of the detectors T1 and T2 and the conduction signals of the detectors T3 and T4 may be a push-pull tracking error signal.
[0030]
Although the above has been described using an optical disk, it is within the scope of the present invention to apply the present invention to a similar apparatus having another medium shape such as a tape shape, a card shape, or a drum shape.
[0031]
【The invention's effect】
According to the present invention described above, the beam spots arranged in each quadrant on the detector do not escape and overlap each other due to the defocusing of the optical disc, and the light energy hardly remains on the detector, so that 25 μm to 50 μm or A large offset and waviness of the FE signal in the defocus region of −25 μm to −50 μm can be greatly suppressed, and good reproduction and recording of the dual-layer disc can be performed stably. In addition, even when optical discs with significantly different substrate thicknesses are reproduced, a reproduction signal can be obtained using the return light in a region with a small aperture, so that the deterioration of reproduction characteristics can be reduced, and one objective can be obtained. Although it is an optical disk device using a lens, it can cope with reproduction of various optical disks such as DVD and CD. In addition, since a part of the area with a large aperture is included in the focus control signal, the FE characteristics in the vicinity of the just focus are not disturbed, and accurate focus control is possible even with an optical disk with uneven substrate thickness. Can be maintained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an optical disc apparatus according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of a hologram surface and a detection surface of the optical disc device according to the first embodiment of the present invention.
FIG. 3 is a light distribution diagram on a detection surface when defocusing occurs in the optical disc apparatus according to the first embodiment of the present invention;
FIG. 4 is a light distribution diagram on a detection surface when defocusing occurs in the optical disc apparatus according to the first embodiment of the present invention.
FIG. 5 is a configuration diagram of a hologram surface and a detection surface of an optical disc device according to a second embodiment of the present invention.
FIG. 6 is a configuration diagram of a hologram surface and a detection surface of an optical disc device according to a third embodiment of the present invention.
FIG. 7 is a configuration diagram of a hologram surface and a detection surface of an optical disc device according to a fourth embodiment of the present invention.
FIG. 8 is a configuration diagram of a hologram surface and a detection surface of an optical disc device according to a fifth embodiment of the present invention.
FIG. 9 is a configuration diagram of a detection surface of an optical disc device according to a sixth embodiment of the present invention.
FIG. 10 is a configuration diagram of a detection surface of an optical disc device according to a seventh embodiment of the present invention.
FIG. 11 is a configuration diagram of a detection surface of an optical disc device according to an eighth embodiment of the present invention.
FIG. 12 is a configuration diagram of a detection surface of an optical disc device according to a ninth embodiment of the present invention.
FIG. 13 is a sectional configuration diagram of an optical disc device according to a tenth embodiment of the present invention.
FIG. 14 is a cross-sectional configuration diagram of an optical disc apparatus in a conventional example.
FIG. 15 is a configuration diagram of a hologram surface and a detection surface of an optical disc apparatus in a conventional example.
FIG. 16 is a light distribution diagram on a detection surface when defocusing occurs in an optical disc apparatus in a conventional example.
FIG. 17 is a light distribution diagram on a detection surface when defocusing occurs in an optical disc apparatus in a conventional example.
FIG. 18 is a focus error signal defocus characteristic diagram of an optical disc apparatus according to the present invention and a conventional example.
[Explanation of symbols]
1 Radiation light source
3 Collimating lens
4 1/4 wave plate
5 Objective lens
6a Optical disc signal surface
7a Hologram surface
9a Light detection surface
10 Return light
1B, 1F, 2B, 2F, 3B, 3F, 4B, 4F Hologram area
1b, 1f, 2b, 2f, 3b, 3f, 4b, 4f Light spot on the detection surface
F1, F2, 12a, 12b, 12c, 12d, 12e Detection signal
T1, T2, T3, T4 photodetector
11a, 11c, 11d subtractor
11b, 11e Adder

Claims

The light source includes an emission light source, an objective lens, a light distribution means such as a hologram, and a photodetector. The light emitted from the emission light source is condensed on the signal surface of the optical disk by the objective lens, and the reflected light is the objective lens. Through the light distribution means, the light is diffracted in two directions by the light distribution means, and one diffracted light is at least by two straight lines (x axis, y axis) perpendicular to the point O on the light distribution means. It is distributed into four regions, each rotated around a straight line OA by one quadrant, and incident around a point A on the photodetector, and the other diffracted light is also at least four by the x-axis and y-axis. An optical information recording / reproducing apparatus, wherein the optical information recording / reproducing apparatus is divided into regions and rotated around a straight line OA ′ by one quadrant and incident around a point A ′ on the photodetector.

The y-axis coincides with the line segment AA ′, and the light distributing means is divided into strip-shaped cells with dividing lines along the x-axis direction, and the light diffracting every other strip cell converges. Light that converges in front of the detection surface as light F, diffracts other strip cells, converges in the back of the detection surface as convergent light B, and has at least two photodetectors in each quadrant of the coordinates with point A as the origin The optical information recording / reproducing apparatus according to claim 1, wherein the converging light F and the converging light B are incident on the photodetector, respectively.

In each quadrant of coordinates with the point A as the origin, four photodetectors D1, D2, D3, and D4 are arranged adjacent to each other in this order along the y-axis, and one skip detector D1, D3, and D2 are arranged. 3. The optical information recording / reproducing apparatus according to claim 2, wherein D4 and D4 are electrically connected to each other.

The photodetectors D1, D2, D3 in the first quadrant position at the coordinates with the point A as the origin are electrically connected to the photodetectors D2, D3, D4 in the fourth quadrant position, and the photodetector D2, in the second quadrant position, D3 and D4 conduct with the photodetectors D1, D2 and D3 in the third quadrant position, the photodetector D1 in the first quadrant position conducts with the photodetector D1 in the second quadrant position, and light in the first quadrant position The signal from the detector D1 and the detector conducting to this is F1, and the signal from the photodetector D2 in the first quadrant position and the detector conducting to this is F2, and the optical disc signal is calculated from the difference between F1 and F2. 4. The optical information recording / reproducing apparatus according to claim 3, wherein a surface focus error signal is obtained.

The photodetectors D1, D2, D3 in the first quadrant position at the coordinates with the point A as the origin are formed on a straight line substantially along the y axis with the photodetectors D2, D3, D4 in the fourth quadrant position, respectively. 5. The photodetectors D2, D3, D4 in the second quadrant position are respectively formed on a straight line substantially along the y axis with the photodetectors D1, D2, D3 in the third quadrant position. Optical information recording / reproducing apparatus.

6. The optical information recording / reproducing apparatus according to claim 4, wherein the photodetector D1 in the fourth quadrant position and the photodetector D4 in the third quadrant position at the coordinates with the point A as the origin are omitted. apparatus.

7. The light detector D4 in the first quadrant position and the light detector D1 in the second quadrant position at the coordinates with the point A as the origin are omitted. Optical information recording / reproducing apparatus.

In each quadrant of the light splitting means, the position where the region C away from the point O is diffracted and incident on the photodetector is diffracted in the other region B in the quadrant and the position of the point A on the photodetector is 2. The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus is detected by a photodetector which is located outside of the point A and is independent of the region B with respect to the incident position.

9. The optical information recording / reproducing apparatus according to claim 8, wherein a convergence point of light diffracting the region C of the light dividing means is substantially on the light detection surface.

9. The optical information recording / reproducing apparatus according to claim 8, wherein the area C of the light dividing means is an area outside a circle centered on the point O, or a part thereof.

11. The optical system according to claim 10, wherein the region C of the light dividing means is outside a circle centered on the point O and is sandwiched between the x axis and a straight line parallel to the x axis. Information recording / reproducing apparatus.

11. The optical information recording / reproducing apparatus according to claim 10, wherein the region C of the light dividing means is a ring-shaped region centered on the point O.

The region B of the light dividing means is divided into an inner peripheral region B1 surrounding the point O and the other region B2, and the position of the light spot that diffracts the regions B1 and B2 and enters the detector is on the x-axis. 9. The optical information recording / reproducing apparatus according to claim 8, wherein the optical information recording / reproducing apparatus is displaced along the optical information recording / reproducing apparatus.

14. The optical information recording / reproducing apparatus according to claim 13, wherein the area B1 of the light dividing means is an area surrounded by an x axis, a y axis, and a straight line parallel thereto.

14. The optical system according to claim 13, wherein the region B1 of the light splitting means is a region in a circle centered on the point O, and the region B2 is a ring-shaped region centered on the point O. Information recording / reproducing apparatus.

Each distributed light on the side diffracted around the point A ′ has a photodetector DT1 configured in the first quadrant position in coordinates with the point A as the origin, and a photodetector DT2 configured in the second quadrant position. Detected by the photodetector DT3 configured in the third quadrant position and the photodetector DT4 configured in the fourth quadrant position, and detection signals from the detectors are T1, T2, T3, and T4, respectively. 2. The optical information recording / reproducing method according to claim 1, wherein a tracking error signal of the optical disc signal surface is obtained from (T1 + T4)-(T2 + T3) or (T1 + T2)-(T3 + T4) or (T1 + T3)-(T2 + T4). apparatus.