JP4290304B2 - Optical recording medium reproducing method and reproducing apparatus - Google Patents

Optical recording medium reproducing method and reproducing apparatus Download PDF

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Publication number
JP4290304B2
JP4290304B2 JP2000032412A JP2000032412A JP4290304B2 JP 4290304 B2 JP4290304 B2 JP 4290304B2 JP 2000032412 A JP2000032412 A JP 2000032412A JP 2000032412 A JP2000032412 A JP 2000032412A JP 4290304 B2 JP4290304 B2 JP 4290304B2
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light
recording medium
refractive index
optical recording
region
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JP2001229543A (en
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淳二 富永
隆志 中野
伸史 阿刀田
寛 藤
博之 片山
賢司 太田
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National Institute of Advanced Industrial Science and Technology AIST
Sharp Corp
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National Institute of Advanced Industrial Science and Technology AIST
Sharp Corp
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Description

【0001】
【発明の属する技術分野】
本発明は、近接場光を使用することにより、光の回折限界を越えた光記録媒体の再生方法および再生装置に関するものである。
【0002】
【従来の技術】
従来、光記録の高密度化のために種々の方式が開発されている。たとえば、雑誌「エレクトロニクス」(オーム社発行)の1998年10月号の100〜102頁、あるいは論文誌 Applied Physics Letters, Vol.73, No.15, 12 October 1998, pp2078-2080 には、近接場光を用いた記録再生方式が開示されている。近接場光とは、媒質中の光が作る電磁場が媒質表面にごくわずかしみ出してきたもので、媒質表面のごく近傍にまとわりつくように局在しているものである。
【0003】
図5を用いて、この近接場光を用いた従来の再生方式について説明する。
この方式に用いられる光ディスク102は、同図に示すように、基板111上に、保護層112、マスク層113、保護層114、記録層115、保護層116が順に成膜された構造である。ここで、記録膜115には、相変化材料であるGe2 Sb2 Te5 が使用されており、情報は記録マークmで記録される。また、マスク層113には、照射されたレーザスポット101aの中心の高温部分のみが不透明から透明に可逆的に変化するといった性質をもつ物質、アンチモン膜が使用されている。
【0004】
このような光ディスク102に、レーザビーム101を対物レンズ105を介して照射すると、上記マスク層113を成すアンチモン膜のレーザスポット101a中心の高温部分で屈折率が変化し、不透明から透明に変化し、マスク層113にスポット径よりも小さなアパーチャ103が形成される。アパーチャ103は、数nm〜数百nmの微細な開口である。
【0005】
このアパーチャ103(アパーチャ周囲も含む)では近接場光104が発生し、発生した近接場光104がアパーチャ103から記録層115に到達し、記録層115との相互作用で散乱されて記録層115に記録された記録マークmの情報を含む散乱光となる。そして、この散乱光をアパーチャ103を通して受光して、記録層115の記録マークmの情報を再生する。これにより、レーザ波長より小さい100nm以下の記録マークmの再生が可能となる。
【0006】
また、このような再生を可能とするために、上記光ディスク102における記録層115とマスク層113との間の保護層114の厚みは、アパーチャ103によって発生した近接場光104が記録層115に到達する距離に設定されている。
【0007】
【発明が解決しようとする課題】
しかしながら、上述の再生方式では、マスク層113におけるアパーチャ103以外の領域では光を遮り、微細な開口であるアパーチャ103を通して散乱光を受光するようになっているため、記録マークmの情報を含んだ散乱光の光量が小さい。したがって、再生信号のSN比が低下し、情報の再生が難しくなるという問題点がある。
【0008】
なお、アパーチャ103を大きくすることで、アパーチャ103を透過する散乱光の光量を大きくできるが、アパーチャ103を大きくすると分解能が低下するため、記録密度を上げるといった目的と逆行し、そのため、アパーチャ103を大きくすることで再生信号のSN比を高めることは好ましくない。
【0009】
本発明は、上記問題点に鑑みなされたもので、情報の再生に用いられる、記録マークの情報を含んだ散乱光の光量を増大させてSN比の高い再生を行うことができる光記録媒体の再生方法および再生装置を提供することを目的としている。
【0010】
【課題を解決するための手段】
本発明の光記録媒体の再生方法は、上記の課題を解決するために、光学情報を記録する記録層と、光照射または加熱により屈折率が変化し、この変化が可逆的に生じる機能層とを備えた光記録媒体を使用し、光記録媒体に光束を入射することにより機能層に局所的な屈折率変化領域を生じさせ、屈折率変化領域で発生した近接場光と記録層との相互作用によって散乱した散乱光であり、屈折率変化領域以外の領域を透過する散乱光から記録層の光学情報を読み出すことを特徴としている。
【0011】
機能層の屈折率変化領域で発生した近接場光と記録層との相互作用で散乱した散乱光であり、記録層に記録されている光学情報を含む散乱光は、機能層における屈折率変化領域を透過するものと、屈折率変化領域以外の広い面積を透過するものとに分かれる。
【0012】
このうち、屈折率変化領域を透過する散乱光は、透過率が高いため強度こそ大きいが、屈折率変化領域の面積が小さいため、屈折率変化領域の面積を大きくできない場合、散乱光の光量はトータル的に見ると、屈折率変化領域以外を透過する散乱光に比べて小さくなる。これに対し、屈折率変化領域以外を透過する散乱光は、透過率が低いため強度こそ小さいが、屈折率変化領域の面積が小さいほどその面積が広くなるため、その光量はトータル的に見ると大きくなる。
【0013】
そこで、本発明では、上述したように、従来では遮られていた、屈折率変化領域以外の領域を透過する散乱光から記録層の光学情報を読み出すようにした。これにより、屈折率変化領域を大きくすることなく、記録層の光学情報を含んだ散乱光の光量を上げることができるので、再生信号のSN比を高くでき、記録情報の再生が容易になる。
【0014】
また、上記した本発明の光記録媒体の再生方法では、光記録媒体に照射する光束の光量、あるいは上記光記録媒体と照射する光束との相対線速度を制御して、屈折率変化領域以外の領域を透過する散乱光の強度を屈折率変化領域を透過する散乱光の強度より大きくすることが望ましい。
【0015】
機能層に形成される屈折率変化領域の大きさは、機能層における温度分布で決まる。したがって、光記録媒体に照射される光束の光量、あるいは光記録媒体と照射する光束との相対線速度を制御して、上述のように、屈折率変化領域以外の領域を透過する散乱光の強度を、屈折率変化領域を透過する散乱光の強度より大きくすることで、屈折率変化領域の大きさが適切に制御されることとなり、再生に寄与する屈折率変化領域以外の領域を透過する散乱光を増大させて、より効率よく、再生信号のSN比を高くして、記録情報の再生を容易にできる。
【0016】
本発明の光記録媒体の再生方法では、上記の課題を解決するために、光学情報を記録する記録層と、光照射または加熱されて屈折率が変化し、この変化が可逆的に生じる機能層とを備えた光記録媒体を使用し、光記録媒体に光束を入射することにより機能層に局所的な屈折率変化領域を生じさせ、屈折率変化領域で発生した近接場光と記録層との相互作用によって散乱した散乱光から記録層の光学情報を読み出し、かつ、光学情報を読み出す際、散乱光から得られる再生信号の信号量が極大値となるように、光記録媒体に照射する光束の光量、あるいは光記録媒体と光束との相対線速度を制御することを特徴としている。
【0017】
光束の光量(強度)と再生信号の信号量との関係から、上述のように、散乱光から得られる再生信号の信号量が極大値となるように、光束の光量、あるいは光記録媒体と光束との相対線速度を制御することで、機能層における屈折率変化領域の大きさを、屈折率変化領域以外の領域を透過する散乱光の強度が、屈折率変化領域を透過する散乱光の強度より大きくなるように適切に制御することが可能となる。したがって、これにおいても、再生信号のSN比を高くして、記録情報の再生を容易にできる。
【0018】
本発明の光記録媒体の再生装置は、上記の課題を解決するために、光学情報を記録する記録層と、光照射または加熱されて屈折率が変化し、この変化が可逆的に生じる機能層とを備えた光記録媒体を使用し、光記録媒体に光束を照射する一方、その反射光を受光する光束照射手段と、光記録媒体の回転を制御する回転制御手段と、光束照射手段にて読み取られた反射光より得られる再生信号を基に記録層の光学情報を再生する再生手段と、再生信号の極大値を検出する極大値検出手段と、極大値検出手段による検出結果を基に、再生信号が極大値となるように光束照射手段あるいは回転制御手段の少なくとも何れか一方を制御する制御手段とを備えたことを特徴としている。
【0019】
これによれば、極大値検出手段が再生信号の極大値を検出し、制御手段が、この検出結果を基に、散乱光から得られる再生信号の信号量が極大値となるように、光束照射手段あるいは回転制御手段の少なくとも何れか一方を制御する。これにより、機能層における屈折率変化領域の大きさが、屈折率変化領域以外の領域を透過する散乱光の強度が屈折率変化領域を透過する散乱光の強度より大きくなるように適切に制御され、再生信号のSN比を高くして、記録情報の再生を容易にできる。
【0020】
【発明の実施の形態】
本発明の実施の一形態を図1ないし図4に基づいて以下に説明する。
ここで使用される光記録媒体としての光ディスクは、相変化型であり、図1に示す構造となっている。同図において、光ディスク2は、基板11上に、保護層12、マスク層(機能層)13、保護層14、記録層15および保護層16がこの順に積層されたものである。
【0021】
基板11は、ガラスやポリカーボネートから形成され、保護層12・14・16は、SiNやZnS−SiO2 などの誘電体から形成されている。また、記録膜15は、Ge2 Sb2 Te5 などの相変化材料から形成されている。この記録層15は予め結晶化されており、アモルファス化することで記録マークMが形成される。したがって、記録層15は、アモルファス状態の記録マークMと、それ以外の結晶領域Nとからなる。
【0022】
マスク層13は、アンチモン膜から形成されている。マスク層13には、光ディスク2に対してレーザビーム(光束)1が照射された際に、レーザスポット1aの中心部分に相当する部分が不透明から透明に変化する性質を有するものが適しており、実験の結果、上記のアンチモン膜が最適であることが判明している。
【0023】
アンチモン膜を使用することで、レーザスポット1aが照射されると、マスク層13には、スポット径よりも小さい径のアパーチャ(屈折率変化領域)4が形成される。アパーチャ4の大きさは、レーザパワーを適切に調整することで、レーザ波長よりも十分に短くなり、アパーチャ4(アパーチャ周囲も含む)には近接場光(図示せず)が発生する。
【0024】
また、光ディスク2における各層の厚みであるが、基板11は、数mm〜十数mm、マスク層13、保護層14、記録層15の厚みは数十nmである。マスク層13と記録層15との間に位置する保護層14の厚みは、マスク層13に形成されたアパーチャ4において発生した近接場光が記録層115に到達する距離(到達距離)よりも短く設定されており、数十nm以下である。
【0025】
次に、上記光ディスク2に対して情報の記録再生動作を行う、本発明の光記録媒体の再生方法を用いた本発明の再生装置としての記録再生装置について説明する。
【0026】
記録再生装置は、図2に示す構成を備えている。即ち、この記録再生装置は、光学ピックアップ(光束照射手段)21、レーザ駆動回路(光束照射手段・制御手段)22、記録回路23、再生回路(再生手段)24、微分回路(極大値検出手段)25、および回転制御回路(回転制御手段・制御手段)26を備えている。
【0027】
この記録再生装置において、情報の記録時、記録回路23から出力された記録信号は、レーザ駆動回路22を経て、光学ピックアップ21が備える半導体レーザに送られ、記録用の強い強度のレーザビーム1として出力される。光学ピックアップ21は図1に示した対物レンズ5を備えており、対物レンズ5によりレーザビーム1を回転している光ディスク2上にレーザスポット1aとして集光させる。これにより、光ディスク2の記録層15に情報が記録マークMとして記録される。
【0028】
なお、この記録再生装置において、光学ピックアップ21の備える半導体レーザの出射光の光量調整はレーザ駆動回路22にて行われ、光ディスク2の回転調整は回転制御回路26にて行われる。
【0029】
一方、再生時においては、光学ピックアップ21が、半導体レーザより弱い強度の再生用のレーザビーム1を出射し、図1に示すように、対物レンズ5によりレーザビーム1を回転している光ディスク2上にレーザスポット1aとして集光させる。レーザスポット1aが集光されることで、マスク層13にはアパーチャ4が形成され、このアパーチャ4で発生した近接場光が、記録層15における記録マークMとの相互作用で散乱して、記録マークMの情報を含んだ散乱光となる。散乱光は、アパーチャ4を透過するeと、アパーチャ4以外の透過領域を透過するfとからなる。これら散乱光e・fを含む反射光を光学ピックアップ21が備えるフォトディテクタにより電気信号に変換して再生信号aを生成する。再生信号aは、再生回路24と微分回路25とにそれぞれ送られ、再生回路24では、再生信号aより記録された情報を再生する。
【0030】
一方、微分回路25においては、このとき得られた再生信号aの信号量の極大値を検出して検出信号bを生成し、この検出信号bを上記のレーザ駆動回路22と回転制御回路26とにフィードバックする。レーザ駆動回路22および回転制御回路26では、この検出信号bを基に、再生信号aの信号量が極大値となるように、半導体レーザの光量(強度)および光ディスク2の回転数を制御する。なお、検出信号bを基に、再生信号aの信号量が極大値となるように、半導体レーザの光量(強度)、或いは光ディスク2の回転数の何れか一方を制御する構成でもよい。
【0031】
このように、微分回路25からフィードバックされる検出信号bを基に、レーザ駆動回路22および回転制御回路26が、再生信号aの信号量が極大値となるように、半導体レーザの光量及び/又は光ディスク2の回転数を制御することで、再生信号aのSN比が高くなり、SN比の高い再生が可能となる。
【0032】
以下、上記の記録再生装置において用いられている再生方法と共に、再生信号aのSN比を高くできる理由を、図3および図4により説明する。
図3は、光ディスク2に対して、再生用のレーザビーム1を対物レンズ5を介して光ディスク2に照射したときの状態と、レーザスポット1aのマスク層13における照射領域の温度分布を示す図である。温度分布8aが、レーザビーム1のパワーが低い場合のマスク層13におけるレーザスポット1aの照射領域の温度分布であり、温度分布8bが、パワーが高い場合の温度分布である。このように、照射領域の温度は、レーザビーム1のパワーに依存する。そして、図中、7にて示すラインが、閾値温度であり、この閾値温度7を越えた高温部分の屈折率が変化して透過率が上がりアパーチャとなる。したがって、アパーチャの大きさは、レーザビーム1のパワーが低い場合は小さいアパーチャ4aとなり、高い場合は大きいアパーチャ4bとなる。
【0033】
再生時、マスク層13のアパーチャ4a(あるいは4b)で発生した近接場光と記録層15の記録マークMとの相互作用によって散乱が起こり散乱光が生じる。この生じた散乱光を、前述の図2に示した光学ピックアップ21が備えるフォトディテクタが電気信号に変換して、再生信号aを生成して記録マークMを再生するが、この散乱光は、アパーチャ4a(あるいは4b)を通って再生される散乱光eと、それ以外の領域を通って再生される散乱光fとから成る。
【0034】
通常、アパーチャ4a(あるいは4b)は透過率が高いため、散乱光eの方が再生されやすい。しかしながら、アパーチャ4a(あるいは4b)の面積は、レーザスポット1aにおけるアパーチャ4a(あるいは4b)以外の面積に比べて小さい。したがって、アパーチャ4a(あるいは4b)から再生される散乱光eのトータルの強度としては、アパーチャ4a(あるいは4b)の面積とアパーチャ4a(あるいは4b)の透過率との積を考慮する必要がある。また、同様に、アパーチャ4a(あるいは4b)以外の領域から再生される散乱光fのトータル強度も、アパーチャ4a(あるいは4b)を除くスポット面積とこの部分の透過率との積に比例する。
【0035】
つまり、このことから、再生時、レーザビーム1のパワーを下げて、アパーチャ4aのようにアパーチャの面積を小さく制御することで、アパーチャを透過して再生される散乱光eの強度よりもアパーチャ以外の領域を透過して再生される散乱光fの強度の方を大きくし(換言すれば、散乱光fの比率を散乱光eNO比率より上げる)、この強度の高い散乱光fを基にして記録マークMを再生することで、記録マークMの情報を含む散乱光として十分な光量を確保でき、SN比の高い再生が可能となる。
【0036】
図4は、CNR(Carrier Noise Ratio:記録マークMを再生したときの再生信号の信号量に比例)の測定結果を用いて、散乱光の強度の変化を説明する図である。(但し、実際は、ドライブ装置でCNRを測定することが困難であるので、CNRに比例するドライブ装置で実際に測定できる信号量(再生信号の振幅や実効値)を使用している。)
レーザビーム1の強度が強度Ptよりも高いと(領域d)、アパーチャが大きくなり、アパーチャ内からの散乱光eの強度の方がそれ以外の散乱光fの強度よりも大きくなる。一方、レーザビーム1の強度が強度Pよりも低いと(領域c)、アパーチャが小さくなり、逆にそれ以外の散乱光fの強度の方がアパーチャ内からの散乱光eの強度よりも大きくなる。
【0037】
一方、記録マークMを記録すると、記録マークMの大きさとアパーチャの大きさとの相対関係によって、レーザビーム1の強度が高いほどアパーチャ内に占める記録マークMがの面積が小さくなるため、分解能が低下する。
【0038】
上記CNRは散乱光の強度と分解能との積に比例するため、CNRは、レーザビームの強度が、図4における領域cで極大となり、領域dに移るにつれて次第に減少する。したがって、CNRが最大(極大値)、つまり、再生信号の振幅や実効値(CNRに比例)が極大となるように、レーザビーム1のパワーを調節することで、アパーチャの大きさを、散乱光fの強度の方が散乱光eの強度よりも大きくなるように制御することができる。但し、アパーチャの大きさは前述したように温度分布によって決まるため、レーザビーム1のパワーに限らず、光ディスク2の回転数を調整して、レーザビーム1と光ディスク2との相対線速度を調整することによって制御することもできる。
【0039】
【発明の効果】
本発明の光記録媒体の再生方法は、以上のように、光学情報を記録する記録層と、光照射または加熱により屈折率が変化し、この変化が可逆的に生じる機能層とを備えた光記録媒体を使用し、光記録媒体に光束を入射することにより機能層に局所的な屈折率変化領域を生じさせ、屈折率変化領域で発生した近接場光と記録層との相互作用によって散乱した散乱光であり、屈折率変化領域以外の領域を透過する散乱光から記録層の光学情報を読み出すものである。
【0040】
これにより、屈折率変化領域を大きくすることなく、記録層の光学情報を含んだ散乱光の光量を上げることができるので、再生信号のSN比を高くでき、記録情報の再生が容易になるという効果を奏する。
【0041】
また、本発明の光記録媒体の再生方法は、以上のように、上記の本発明の光記録媒体の再生方法においてさらに、光記録媒体に照射する光束の光量、あるいは上記光記録媒体と照射する光束との相対線速度を制御して、屈折率変化領域以外の領域を透過する散乱光の強度を屈折率変化領域を透過する散乱光の強度より大きくするものである。
【0042】
これにより、屈折率変化領域の大きさが適切に制御されて、再生に寄与する屈折率変化領域以外の領域を透過する散乱光が増大するので、より効率よく、再生信号のSN比を高くして、記録情報の再生を容易にできるという効果を奏する。
【0043】
また、本発明の光記録媒体の再生方法は、以上のように、光学情報を記録する記録層と、光照射または加熱されて屈折率が変化し、この変化が可逆的に生じる機能層とを備えた光記録媒体を使用し、光記録媒体に光束を入射することにより機能層に局所的な屈折率変化領域を生じさせ、屈折率変化領域で発生した近接場光と記録層との相互作用によって散乱した散乱光から記録層の光学情報を読み出し、かつ、光学情報を読み出す際、散乱光から得られる再生信号の信号量が極大値となるように、光記録媒体に照射する光束の光量、あるいは光記録媒体と光束との相対線速度を制御するものである。
【0044】
これにより、機能層における屈折率変化領域の大きさを、屈折率変化領域以外の領域を透過する散乱光の強度が、屈折率変化領域を透過する散乱光の強度より大きくなるように適切に制御することが可能となるので、これにおいても、再生信号のSN比を高くして、記録情報の再生を容易にできるという効果を奏する。
【0045】
本発明の光記録媒体の再生装置は、以上のように、光学情報を記録する記録層と、光照射または加熱されて屈折率が変化し、この変化が可逆的に生じる機能層とを備えた光記録媒体を使用し、光記録媒体に光束を照射する一方、その反射光を受光する光束照射手段と、光記録媒体の回転を制御する回転制御手段と、光束照射手段にて読み取られた反射光より得られる再生信号を基に記録層の光学情報を再生する再生手段と、再生信号の極大値を検出する極大値検出手段と、極大値検出手段による検出結果を基に、再生信号が極大値となるように光束照射手段あるいは回転制御手段の少なくとも何れか一方を制御する制御手段とを備えた構成である。
【0046】
これにより、光束照射手段あるいは回転制御手段の少なくとも何れか一方が散乱光から得られる再生信号の信号量が極大値となるように制御される結果、機能層における屈折率変化領域の大きさが、屈折率変化領域以外の領域を透過する散乱光の強度が屈折率変化領域を透過する散乱光の強度より大きくなるように適切に制御されることとなり、再生信号のSN比を高くして、記録情報の再生を容易にできるという効果を奏する。
【図面の簡単な説明】
【図1】本発明の実施の一形態を示すもので、記録再生が行われる光ディスクの構成、および再生方法を示す説明図である。
【図2】図1における光ディスクが再生される記録再生装置の構成を示す説明図である。
【図3】図2における記録再生装置に用いられている再生方法を説明するための説明図である。
【図4】アパーチャの大きさを決定するレーザ光強度と信号品質との関係を示す説明図である。
【図5】従来の光ディスクの構成、および再生方法を示す説明図である。
【符号の説明】
1 レーザビーム(光束)
2 光ディスク(光記録媒体)
4 アパーチャ(屈折率変化領域)
5 対物レンズ
11 基板
12 保護層
13 マスク層(機能層)
14 保護層
15 記録層
16 保護層
21 光学ピックアップ(光束照射手段)
22 レーザ駆動回路(光束照射手段・制御手段)
24 再生回路(再生手段)
25 微分回路(極大値検出手段)
26 回転制御回路(回転制御手段・制御手段)
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reproducing method and reproducing apparatus for an optical recording medium that exceeds the diffraction limit of light by using near-field light.
[0002]
[Prior art]
Conventionally, various methods have been developed to increase the density of optical recording. For example, the magazine “Electronics” (published by Ohmsha), October 100 issue, pages 100 to 102, or the journal Applied Physics Letters, Vol. 73, No. 15, 12 October 1998, pp2078-2080 A recording / reproducing system using light is disclosed. Near-field light is one in which an electromagnetic field generated by light in a medium oozes slightly on the surface of the medium, and is localized so as to cling to the very vicinity of the surface of the medium.
[0003]
A conventional reproducing method using the near-field light will be described with reference to FIG.
As shown in the figure, the optical disk 102 used in this method has a structure in which a protective layer 112, a mask layer 113, a protective layer 114, a recording layer 115, and a protective layer 116 are sequentially formed on a substrate 111. Here, Ge 2 Sb 2 Te 5 which is a phase change material is used for the recording film 115, and information is recorded with a recording mark m. The mask layer 113 is made of an antimony film, which is a substance having a property that only the high temperature portion at the center of the irradiated laser spot 101a reversibly changes from opaque to transparent.
[0004]
When such an optical disk 102 is irradiated with the laser beam 101 through the objective lens 105, the refractive index changes at the high temperature portion at the center of the laser spot 101a of the antimony film forming the mask layer 113, and changes from opaque to transparent, An aperture 103 smaller than the spot diameter is formed on the mask layer 113. The aperture 103 is a fine opening of several nm to several hundred nm.
[0005]
In this aperture 103 (including the periphery of the aperture), near-field light 104 is generated, and the generated near-field light 104 reaches the recording layer 115 from the aperture 103 and is scattered by the interaction with the recording layer 115 to the recording layer 115. It becomes the scattered light containing the information of the recorded recording mark m. Then, the scattered light is received through the aperture 103 to reproduce the information of the recording mark m of the recording layer 115. Thereby, it is possible to reproduce the recording mark m of 100 nm or less which is smaller than the laser wavelength.
[0006]
In order to enable such reproduction, the thickness of the protective layer 114 between the recording layer 115 and the mask layer 113 in the optical disc 102 is such that the near-field light 104 generated by the aperture 103 reaches the recording layer 115. It is set to the distance to be.
[0007]
[Problems to be solved by the invention]
However, in the above-described reproduction method, light is blocked in the area other than the aperture 103 in the mask layer 113 and the scattered light is received through the aperture 103 which is a fine opening, and thus information on the recording mark m is included. The amount of scattered light is small. Therefore, there is a problem that the S / N ratio of the reproduction signal is lowered and it becomes difficult to reproduce information.
[0008]
The amount of scattered light transmitted through the aperture 103 can be increased by increasing the size of the aperture 103. However, since the resolution decreases when the aperture 103 is increased, the aperture 103 is reversed. It is not preferable to increase the SN ratio of the reproduction signal by increasing it.
[0009]
The present invention has been made in view of the above-described problems, and is an optical recording medium that can be used for information reproduction and can reproduce with a high S / N ratio by increasing the amount of scattered light including information on recording marks. An object of the present invention is to provide a reproducing method and a reproducing apparatus.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the optical recording medium reproducing method of the present invention includes a recording layer for recording optical information, a functional layer in which the refractive index changes due to light irradiation or heating, and the change occurs reversibly. When the optical recording medium is provided with a light beam incident on the optical recording medium, a local refractive index change region is generated in the functional layer, and the near-field light generated in the refractive index change region is correlated with the recording layer. The optical information of the recording layer is read out from the scattered light scattered by the action and transmitted through the region other than the refractive index changing region.
[0011]
Scattered light that is scattered by the interaction between the near-field light generated in the refractive index change region of the functional layer and the recording layer, and the scattered light including optical information recorded in the recording layer is reflected in the refractive index changing region in the functional layer. And those that transmit a wide area other than the refractive index change region.
[0012]
Of these, the scattered light transmitted through the refractive index changing region has a high intensity because of its high transmittance, but if the area of the refractive index changing region cannot be increased because the area of the refractive index changing region is small, the amount of scattered light is When viewed in total, it becomes smaller than the scattered light transmitted through the region other than the refractive index changing region. On the other hand, scattered light that passes through areas other than the refractive index changing region has low intensity because of its low transmittance, but the smaller the area of the refractive index changing region, the larger the area, so the total amount of light is growing.
[0013]
Therefore, in the present invention, as described above, the optical information of the recording layer is read from the scattered light that has been shielded in the past and transmits through the region other than the refractive index changing region. Accordingly, the amount of scattered light including the optical information of the recording layer can be increased without increasing the refractive index change region, so that the SN ratio of the reproduction signal can be increased and the reproduction of the recorded information is facilitated.
[0014]
Further, in the above-described method for reproducing an optical recording medium of the present invention, the light quantity of the light beam applied to the optical recording medium or the relative linear velocity between the optical recording medium and the applied light beam is controlled, so that the region other than the refractive index change region is controlled. It is desirable to make the intensity of the scattered light transmitted through the region larger than the intensity of the scattered light transmitted through the refractive index changing region.
[0015]
The size of the refractive index change region formed in the functional layer is determined by the temperature distribution in the functional layer. Therefore, as described above, the intensity of the scattered light transmitted through the region other than the refractive index changing region by controlling the light amount of the light beam irradiated on the optical recording medium or the relative linear velocity between the optical recording medium and the irradiated light beam. Is made larger than the intensity of the scattered light transmitted through the refractive index changing region, the size of the refractive index changing region is appropriately controlled, and the scattering transmitted through the region other than the refractive index changing region contributing to the reproduction. By increasing the light, it is possible to increase the S / N ratio of the reproduction signal more efficiently and to easily reproduce the recorded information.
[0016]
In the reproducing method of the optical recording medium of the present invention, in order to solve the above-mentioned problem, a recording layer for recording optical information, and a functional layer in which the refractive index changes upon irradiation or heating with light and this change occurs reversibly And a local refractive index changing region is generated in the functional layer by making a light beam incident on the optical recording medium, and the near-field light generated in the refractive index changing region and the recording layer When the optical information of the recording layer is read out from the scattered light scattered by the interaction, and the optical information is read out, the light flux irradiated to the optical recording medium is set so that the signal amount of the reproduction signal obtained from the scattered light becomes a maximum value. It is characterized by controlling the amount of light or the relative linear velocity between the optical recording medium and the light beam.
[0017]
From the relationship between the light amount (intensity) of the light beam and the signal amount of the reproduction signal, as described above, the light amount of the light beam or the optical recording medium and the light beam so that the signal amount of the reproduction signal obtained from the scattered light becomes a maximum value. By controlling the relative linear velocity to the size of the refractive index change region in the functional layer, the intensity of the scattered light that passes through the region other than the refractive index change region is the intensity of the scattered light that passes through the refractive index change region. It becomes possible to control appropriately so that it may become larger. Therefore, the recorded information can be easily reproduced by increasing the SN ratio of the reproduced signal.
[0018]
In order to solve the above problems, an optical recording medium reproducing apparatus of the present invention includes a recording layer for recording optical information, and a functional layer in which the refractive index changes upon irradiation or heating with light and this change occurs reversibly. The optical recording medium is used to irradiate the optical recording medium with a light beam, while receiving the reflected light, a light beam irradiating means, a rotation control means for controlling the rotation of the optical recording medium, and a light beam irradiating means. Based on the detection result by the reproduction means for reproducing the optical information of the recording layer based on the reproduction signal obtained from the read reflected light, the maximum value detection means for detecting the maximum value of the reproduction signal, and the detection result by the maximum value detection means, And a control unit that controls at least one of the light beam irradiation unit and the rotation control unit so that the reproduction signal becomes a maximum value.
[0019]
According to this, the maximum value detection means detects the maximum value of the reproduction signal, and the control means, based on the detection result, emits the light flux so that the signal amount of the reproduction signal obtained from the scattered light becomes the maximum value. Or at least one of the rotation control means. As a result, the size of the refractive index change region in the functional layer is appropriately controlled so that the intensity of the scattered light transmitted through the region other than the refractive index change region is greater than the intensity of the scattered light transmitted through the refractive index change region. The recorded signal can be easily reproduced by increasing the SN ratio of the reproduction signal.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
An optical disk as an optical recording medium used here is a phase change type and has a structure shown in FIG. In the figure, an optical disc 2 is obtained by laminating a protective layer 12, a mask layer (functional layer) 13, a protective layer 14, a recording layer 15 and a protective layer 16 in this order on a substrate 11.
[0021]
The substrate 11 is made of glass or polycarbonate, and the protective layers 12, 14, and 16 are made of a dielectric material such as SiN or ZnS—SiO 2 . The recording film 15 is formed of a phase change material such as Ge 2 Sb 2 Te 5 . The recording layer 15 is crystallized in advance, and the recording mark M is formed by making it amorphous. Therefore, the recording layer 15 includes the recording mark M in an amorphous state and the other crystal region N.
[0022]
The mask layer 13 is formed from an antimony film. The mask layer 13 is suitable to have a property that the portion corresponding to the central portion of the laser spot 1a changes from opaque to transparent when the optical disc 2 is irradiated with a laser beam (light beam) 1. As a result of experiments, it has been found that the above antimony film is optimal.
[0023]
By using the antimony film, when the laser spot 1 a is irradiated, an aperture (refractive index changing region) 4 having a diameter smaller than the spot diameter is formed in the mask layer 13. The size of the aperture 4 is sufficiently shorter than the laser wavelength by appropriately adjusting the laser power, and near-field light (not shown) is generated in the aperture 4 (including the periphery of the aperture).
[0024]
The thickness of each layer in the optical disc 2 is several mm to several tens mm, and the thickness of the mask layer 13, the protective layer 14, and the recording layer 15 is several tens of nm. The thickness of the protective layer 14 positioned between the mask layer 13 and the recording layer 15 is shorter than the distance (reach distance) that the near-field light generated in the aperture 4 formed in the mask layer 13 reaches the recording layer 115. It is set and is several tens of nm or less.
[0025]
Next, the recording / reproducing apparatus as the reproducing apparatus of the present invention using the optical recording medium reproducing method of the present invention for performing the information recording / reproducing operation on the optical disc 2 will be described.
[0026]
The recording / reproducing apparatus has the configuration shown in FIG. That is, this recording / reproducing apparatus includes an optical pickup (light beam irradiation means) 21, a laser drive circuit (light beam irradiation means / control means) 22, a recording circuit 23, a reproduction circuit (reproduction means) 24, and a differentiation circuit (maximum value detection means). 25, and a rotation control circuit (rotation control means / control means) 26.
[0027]
In this recording / reproducing apparatus, at the time of recording information, a recording signal output from the recording circuit 23 is sent to a semiconductor laser provided in the optical pickup 21 through a laser driving circuit 22 and is used as a laser beam 1 having a high intensity for recording. Is output. The optical pickup 21 includes the objective lens 5 shown in FIG. 1, and the objective lens 5 focuses the laser beam 1 on the rotating optical disk 2 as a laser spot 1a. As a result, information is recorded as recording marks M on the recording layer 15 of the optical disc 2.
[0028]
In this recording / reproducing apparatus, the light amount adjustment of the emitted light of the semiconductor laser included in the optical pickup 21 is performed by the laser drive circuit 22, and the rotation adjustment of the optical disc 2 is performed by the rotation control circuit 26.
[0029]
On the other hand, at the time of reproduction, the optical pickup 21 emits a reproduction laser beam 1 having a weaker intensity than that of the semiconductor laser, and on the optical disk 2 rotating the laser beam 1 by the objective lens 5 as shown in FIG. Is condensed as a laser spot 1a. The aperture 4 is formed in the mask layer 13 by condensing the laser spot 1a, and the near-field light generated by the aperture 4 is scattered by the interaction with the recording mark M in the recording layer 15, and recorded. The scattered light includes the information of the mark M. The scattered light is composed of e that transmits through the aperture 4 and f that transmits through a transmission region other than the aperture 4. The reflected light including the scattered light e · f is converted into an electric signal by a photodetector provided in the optical pickup 21 to generate a reproduction signal a. The reproduction signal a is sent to the reproduction circuit 24 and the differentiation circuit 25, and the reproduction circuit 24 reproduces information recorded from the reproduction signal a.
[0030]
On the other hand, in the differentiation circuit 25, the maximum value of the signal amount of the reproduction signal a obtained at this time is detected to generate a detection signal b, and this detection signal b is sent to the laser drive circuit 22 and the rotation control circuit 26. To give feedback. Based on this detection signal b, the laser drive circuit 22 and the rotation control circuit 26 control the light quantity (intensity) of the semiconductor laser and the rotation speed of the optical disc 2 so that the signal amount of the reproduction signal a becomes a maximum value. Note that, based on the detection signal b, the configuration may be such that either the light amount (intensity) of the semiconductor laser or the rotational speed of the optical disc 2 is controlled so that the signal amount of the reproduction signal a becomes a maximum value.
[0031]
As described above, based on the detection signal b fed back from the differentiation circuit 25, the laser drive circuit 22 and the rotation control circuit 26 allow the light quantity and / or the semiconductor laser so that the signal amount of the reproduction signal a becomes a maximum value. By controlling the rotation speed of the optical disc 2, the S / N ratio of the reproduction signal a increases, and reproduction with a high S / N ratio becomes possible.
[0032]
The reason why the S / N ratio of the reproduction signal a can be increased together with the reproduction method used in the recording / reproduction apparatus will be described below with reference to FIGS.
FIG. 3 is a diagram showing a state when the optical disc 2 is irradiated with the reproducing laser beam 1 through the objective lens 5 and the temperature distribution of the irradiation region in the mask layer 13 of the laser spot 1a. is there. The temperature distribution 8a is the temperature distribution of the irradiation region of the laser spot 1a in the mask layer 13 when the power of the laser beam 1 is low, and the temperature distribution 8b is the temperature distribution when the power is high. As described above, the temperature of the irradiation region depends on the power of the laser beam 1. In the figure, the line indicated by 7 is the threshold temperature, and the refractive index of the high temperature portion exceeding the threshold temperature 7 changes to increase the transmittance and become an aperture. Therefore, the size of the aperture is a small aperture 4a when the power of the laser beam 1 is low, and a large aperture 4b when the power is high.
[0033]
During reproduction, scattering occurs due to the interaction between the near-field light generated in the aperture 4a (or 4b) of the mask layer 13 and the recording mark M of the recording layer 15, and scattered light is generated. The generated scattered light is converted into an electrical signal by the photodetector included in the optical pickup 21 shown in FIG. 2 to generate a reproduction signal a to reproduce the recording mark M. This scattered light is transmitted through the aperture 4a. It consists of scattered light e reproduced through (or 4b) and scattered light f reproduced through other regions.
[0034]
Usually, since the aperture 4a (or 4b) has a high transmittance, the scattered light e is more easily reproduced. However, the area of the aperture 4a (or 4b) is smaller than the area other than the aperture 4a (or 4b) in the laser spot 1a. Therefore, as the total intensity of the scattered light e reproduced from the aperture 4a (or 4b), it is necessary to consider the product of the area of the aperture 4a (or 4b) and the transmittance of the aperture 4a (or 4b). Similarly, the total intensity of the scattered light f reproduced from a region other than the aperture 4a (or 4b) is also proportional to the product of the spot area excluding the aperture 4a (or 4b) and the transmittance of this portion.
[0035]
In other words, at the time of reproduction, the power of the laser beam 1 is lowered and the area of the aperture is controlled to be small like the aperture 4a, so that the other than the intensity of the scattered light e that is transmitted through the aperture and reproduced. The intensity of the scattered light f transmitted through the region is increased (in other words, the ratio of the scattered light f is increased from the ratio of the scattered light eNO), and recording is performed based on the highly scattered light f. By reproducing the mark M, it is possible to secure a sufficient amount of light as scattered light including information on the recording mark M, and reproduction with a high S / N ratio is possible.
[0036]
FIG. 4 is a diagram for explaining the change in the intensity of the scattered light using the measurement result of CNR (Carrier Noise Ratio: proportional to the signal amount of the reproduction signal when the recording mark M is reproduced). (However, since it is actually difficult to measure the CNR with the drive device, a signal amount (amplitude and effective value of the reproduction signal) that can be actually measured with the drive device proportional to the CNR is used.)
When the intensity of the laser beam 1 is higher than the intensity Pt (region d), the aperture becomes large, and the intensity of the scattered light e from within the aperture becomes larger than the intensity of the other scattered light f. On the other hand, when the intensity of the laser beam 1 is lower than the intensity P (region c), the aperture becomes small, and conversely, the intensity of the other scattered light f becomes larger than the intensity of the scattered light e from the aperture. .
[0037]
On the other hand, when the recording mark M is recorded, the area of the recording mark M in the aperture becomes smaller as the intensity of the laser beam 1 is higher due to the relative relationship between the size of the recording mark M and the size of the aperture. To do.
[0038]
Since the CNR is proportional to the product of the intensity of scattered light and the resolution, the CNR becomes maximum in the region c in FIG. 4 and gradually decreases as the region moves to the region d. Therefore, by adjusting the power of the laser beam 1 so that the CNR is maximized (maximum value), that is, the amplitude or effective value (proportional to CNR) of the reproduction signal is maximized, the size of the aperture is reduced. The intensity of f can be controlled to be greater than the intensity of scattered light e. However, since the size of the aperture is determined by the temperature distribution as described above, not only the power of the laser beam 1 but also the rotational speed of the optical disc 2 is adjusted to adjust the relative linear velocity between the laser beam 1 and the optical disc 2. Can also be controlled.
[0039]
【The invention's effect】
As described above, the reproducing method of the optical recording medium of the present invention is a light having a recording layer for recording optical information, and a functional layer in which the refractive index changes due to light irradiation or heating, and this change occurs reversibly. Using a recording medium, a light beam is incident on the optical recording medium, thereby causing a local refractive index change region in the functional layer, and scattered by the interaction between the near-field light generated in the refractive index change region and the recording layer. The optical information of the recording layer is read out from the scattered light that is scattered light and transmits through the region other than the refractive index changing region.
[0040]
As a result, the amount of scattered light including the optical information of the recording layer can be increased without increasing the refractive index change region, so that the S / N ratio of the reproduction signal can be increased and the reproduction of the recorded information is facilitated. There is an effect.
[0041]
In addition, as described above, the optical recording medium reproducing method of the present invention further irradiates the optical recording medium with the light amount of the light beam applied to the optical recording medium or the optical recording medium. The relative linear velocity with respect to the light beam is controlled so that the intensity of the scattered light that passes through the region other than the refractive index changing region is larger than the intensity of the scattered light that passes through the refractive index changing region.
[0042]
As a result, the size of the refractive index changing region is appropriately controlled, and the scattered light transmitted through the region other than the refractive index changing region contributing to reproduction increases, so that the S / N ratio of the reproduction signal is increased more efficiently. Thus, the recorded information can be easily reproduced.
[0043]
In addition, as described above, the method for reproducing an optical recording medium of the present invention includes a recording layer for recording optical information, and a functional layer in which the refractive index changes upon irradiation or heating with light and the change occurs reversibly. By using the optical recording medium provided and making the light beam incident on the optical recording medium, a local refractive index change region is generated in the functional layer, and the near-field light generated in the refractive index change region interacts with the recording layer. When the optical information of the recording layer is read out from the scattered light scattered by the optical information, and the optical information is read out, the light amount of the light beam applied to the optical recording medium so that the signal amount of the reproduction signal obtained from the scattered light becomes a maximum value, Alternatively, the relative linear velocity between the optical recording medium and the light beam is controlled.
[0044]
As a result, the size of the refractive index changing region in the functional layer is appropriately controlled so that the intensity of the scattered light that passes through the region other than the refractive index changing region is larger than the intensity of the scattered light that passes through the refractive index changing region. In this case, the S / N ratio of the reproduction signal is increased, and the recorded information can be easily reproduced.
[0045]
As described above, the optical recording medium reproducing apparatus of the present invention includes the recording layer for recording optical information, and the functional layer in which the refractive index is changed by light irradiation or heating and the change is reversibly generated. The optical recording medium is used to irradiate the optical recording medium with a light beam, while receiving the reflected light, a light beam irradiating means, a rotation control means for controlling the rotation of the optical recording medium, and a reflection read by the light beam irradiating means. Based on the detection results of the reproducing means for reproducing the optical information of the recording layer based on the reproduction signal obtained from light, the maximum value detecting means for detecting the maximum value of the reproduction signal, and the maximum value detecting means, the reproduction signal is maximized. And a control means for controlling at least one of the light beam irradiation means and the rotation control means so as to obtain a value.
[0046]
As a result, at least one of the light beam irradiation means and the rotation control means is controlled so that the signal amount of the reproduction signal obtained from the scattered light becomes a maximum value, so that the size of the refractive index change region in the functional layer is The intensity of the scattered light that passes through the area other than the refractive index changing area is appropriately controlled so as to be greater than the intensity of the scattered light that passes through the refractive index changing area. There is an effect that information can be easily reproduced.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a configuration of an optical disc on which recording and reproduction are performed and a reproduction method according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a configuration of a recording / reproducing apparatus that reproduces the optical disc in FIG. 1;
FIG. 3 is an explanatory diagram for explaining a reproducing method used in the recording / reproducing apparatus in FIG. 2;
FIG. 4 is an explanatory diagram showing the relationship between laser light intensity and signal quality for determining the size of an aperture.
FIG. 5 is an explanatory diagram showing a configuration of a conventional optical disc and a reproducing method.
[Explanation of symbols]
1 Laser beam (light beam)
2 Optical disc (optical recording medium)
4 Aperture (refractive index change region)
5 Objective lens 11 Substrate 12 Protective layer 13 Mask layer (functional layer)
14 Protective layer 15 Recording layer 16 Protective layer 21 Optical pickup (light beam irradiation means)
22 Laser drive circuit (light beam irradiation means / control means)
24 Reproduction circuit (reproduction means)
25 Differentiation circuit (maximum value detection means)
26 Rotation control circuit (rotation control means / control means)

Claims (4)

光学情報を記録する記録層と、光照射または加熱により屈折率が変化し、この変化が可逆的に生じる機能層とを備え、上記機能層を介して発生する近接場光が上記記録層へ到達可能となっている光記録媒体を使用し、該光記録媒体に光束を入射することにより上記機能層に局所的な屈折率変化領域を生じさせ、該屈折率変化領域で発生した近接場光と上記記録層との相互作用によって散乱した散乱光を検出して上記記録層の光学情報を読み出す光記録媒体の再生方法において、
上記散乱光を検出するにあたり、上記屈折率変化領域以外の領域を透過する散乱光を検出することを特徴とする光記録媒体の再生方法。
A recording layer for recording optical information, and a functional layer in which the refractive index changes by light irradiation or heating and this change occurs reversibly, near-field light generated via the functional layer reaches the recording layer Using a possible optical recording medium, a light beam is incident on the optical recording medium to cause a local refractive index change region in the functional layer, and near-field light generated in the refractive index change region In the reproducing method of the optical recording medium for detecting the scattered light scattered by the interaction with the recording layer and reading the optical information of the recording layer ,
A method for reproducing an optical recording medium, comprising: detecting scattered light transmitted through a region other than the refractive index changing region when detecting the scattered light.
上記光記録媒体に照射する光束の光量、または上記光記録媒体と照射する光束との相対線速度を、上記屈折率変化領域以外の領域を透過する散乱光の強度が上記屈折率変化領域を透過する散乱光の強度よりも大きくなるように制御することを特徴とする請求項1に記載の光記録媒体の再生方法。 The intensity of the scattered light that passes through the region other than the refractive index changing region is transmitted through the refractive index changing region , or the relative linear velocity between the optical recording medium and the luminous flux irradiated to the optical recording medium. 2. The method of reproducing an optical recording medium according to claim 1, wherein the intensity of the scattered light is controlled to be larger than the intensity of the scattered light. 上記光記録媒体に照射する光束の光量、または上記光記録媒体と照射する光束との相対線速度を、散乱光より得られる読み出し信号の信号量が極大値となるように制御することを特徴とする請求項2に記載の光記録媒体の再生方法。 Controlling the light quantity of the light beam applied to the optical recording medium or the relative linear velocity between the optical recording medium and the applied light beam so that the signal amount of the readout signal obtained from the scattered light becomes a maximum value. A method for reproducing an optical recording medium according to claim 2 . 光学情報を記録する記録層と、光照射または加熱されて屈折率が変化し、この変化が可逆的に生じる機能層とを備え、上記機能層を介して発生する近接場光が上記記録層へ到達可能となっている光記録媒体を使用し、
上記光記録媒体に光束を照射して上記機能層に局所的な屈折率変化領域を生じさせる一方、上記屈折率変化領域で発生した近接場光と上記記録層との相互作用によって散乱した散乱光であって、上記屈折率変化領域以外の領域を透過した散乱光を含む、上記光記録媒体からの反射光を受光し、上記散乱光より再生信号を生成する光束照射手段と、
上記光記録媒体の回転を制御する回転制御手段と、
上記光束照射手段にて生成された上記再生信号を基に上記記録層の光学情報を再生する再生手段と、
上記再生信号の極大値を検出する極大値検出手段と、
該極大値検出手段による検出結果を基に、上記再生信号が極大値となるように、上記の光束照射手段または回転制御手段の少なくとも何れか一方を制御する制御手段とを備えたことを特徴とする光記録媒体の再生装置。
A recording layer that records optical information; and a functional layer that changes its refractive index when irradiated or heated with light, and the change occurs reversibly, and near-field light generated through the functional layer is transferred to the recording layer. Use optical recording media that are reachable ,
The optical recording medium is irradiated with a light beam to generate a local refractive index change region in the functional layer, while the scattered light scattered by the interaction between the near-field light generated in the refractive index change region and the recording layer A light beam irradiating means for receiving reflected light from the optical recording medium including scattered light transmitted through a region other than the refractive index changing region and generating a reproduction signal from the scattered light ;
Rotation control means for controlling the rotation of the optical recording medium;
Reproduction means for reproducing optical information of the recording layer based on the reproduction signal generated by the light beam irradiation means;
A maximum value detecting means for detecting a maximum value of the reproduction signal;
Based on the detection result of said polar large value detecting means, so that said reproduced signal becomes maximum value, and further comprising a control means for controlling at least one of said light beam irradiation means or rotation control means Reproducing apparatus for optical recording medium.
JP2000032412A 2000-02-09 2000-02-09 Optical recording medium reproducing method and reproducing apparatus Expired - Lifetime JP4290304B2 (en)

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