JP2004220654A - Optical recording medium, master disk for manufacturing optical recording medium, recording/reproducing device, and recording/reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to increase the track density of a magneto-optical disk and perform stable tracking servo and seeking. <P>SOLUTION: First grooves GV1, second grooves GV2 and third grooves GV3 are so formed as to be adjacently arranged. The first grooves GV1 and the second grooves GV2 are the deep grooves and the third grooves GV3 are the shallow grooves. The first grooves GV1 and the second grooves GV2 are formed by being wobbled. The grooves are so formed that data is recorded in three tracks by the three grooves or the three lands between the respective grooves. A CTS signal is searched by a sum signal (A+B+C+D) of a photodetector 6 and a push-pull signal is searched by a differential signal (A+D)-(B+C) of a photodetector 8. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００８３】
下記の表２は、二つの深いグルーブの係数ｘの値をｘ＝２．９、すなわちグルーブ深さを１４２ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００８４】
【表２】

【００８５】
下記の表３は、二つの深いグルーブの係数ｘの値をｘ＝２．７、すなわちグルーブ深さを１５２ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００８６】
【表３】

【００８７】
下記の表４は、二つの深いグルーブの係数ｘの値をｘ＝２．５、すなわちグルーブ深さを１６５ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００８８】
【表４】

【００８９】
下記の表５は、二つの深いグルーブの係数ｘの値をｘ＝２．３、すなわちグルーブ深さを１７９ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００９０】
【表５】

【００９１】
下記の表６は、二つの深いグルーブの係数ｘの値をｘ＝２．１、すなわちグルーブ深さを１９６ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００９２】
【表６】

【００９３】
下記の表７は、二つの深いグルーブの係数ｘの値をｘ＝１．９、すなわちグルーブ深さを２１７ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００９４】
【表７】

【００９５】
下記の表８は、二つの深いグルーブの係数ｘの値をｘ＝１．８、すなわちグルーブ深さを２２９ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００９６】
【表８】

【００９７】
下記の表９は、二つの深いグルーブの係数ｘの値をｘ＝１．７、すなわちグルーブ深さを２４２ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【００９８】
【表９】

【００９９】
下記の表１０は、二つの深いグルーブの係数ｘの値をｘ＝１．６３、すなわちグルーブ深さを２５２ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【０１００】
【表１０】

【０１０１】
下記の表１１は、二つの深いグルーブの係数ｘの値をｘ＝３．３８、すなわちグルーブ深さを１２２ｎｍ（小数点以下、四捨五入）としたときの、浅いグルーブの深さを変化させた場合のプッシュプル信号とＣＴＳ信号の振幅変化を示している。
【０１０２】
【表１１】

【０１０３】
これらの表１から表１１において、太線で囲んで示す範囲は、その範囲に対応する深いグルーブと浅いグルーブの深さにおいて、プッシュプル信号またはＣＴＳ信号の信号量（絶対値）が約１４％以上であり、安定したトラッキングサーボが可能であった。
【０１０４】
下記の表１２は、深いグルーブと浅いグルーブに対して、上述した太線で囲んだ範囲の内、プッシュプル信号の信号量（絶対値）が１４％程度以上の領域のグルーブ深さをまとめたものである。
【０１０５】
【表１２】

【０１０６】
また、図５は、プッシュプル信号の信号量が１４％程度以上（太線の範囲）となる浅いグルーブと深いグルーブの位相深さの関係を示した図である。図５における縦軸は、浅いグルーブの位相深さＹを示し、横軸は、深いグルーブの位相深さＸを示す。例えば、点ａの座標（Ｘａ，Ｙａ）におけるＸａは、表１に示す深いグルーブの係数ｘの逆数、すなわち、「１／３．１」により、０．３２３…と求められ、Ｙａは、表１に示す浅いグルーブ（上限値）の係数ｘの逆数、すなわち、「１／６．１」により、０．１６４…と求められる。また例えば、点ｋの座標（Ｘｋ，Ｙｋ）におけるＸｋは、表１に示す深いグルーブの係数ｘの逆数、すなわち、「１／３．１」により、０．３２３…と求められ、Ｙｋは、表１に示す浅いグルーブ（下限値）の係数ｘの逆数、すなわち、「１／１６」により、０．０６２５と求められる。
【０１０７】
したがって、図５中の点ａ〜点ｉは、プッシュプル信号量が１４％程度以上となるグルーブ深さの上限値であり、点ｊ〜点ｔは、プッシュプル信号量が１４％程度以上となるグルーブ深さの下限値である。すなわち、点ａ〜点ｔに囲まれた領域内であれば、プッシュプル信号の信号量が１４％程度以上であり、安定したトラッキングサーボが可能であることがわかった。
【０１０８】
ここで、点ａ〜点ｉを結ぶ近似曲線Ｌ１は、下記の式（３）で表され、点ｊ〜点ｔを結ぶ近似曲線Ｌ２は、下記の式（４）で表された。
【０１０９】
Ｙ＝ −２．３８２６Ｘ^４ ＋１３．４９４Ｘ^３ −２８．５８２Ｘ^２ ＋２６．８７６Ｘ −９．２２７２ ・・・（３）
Ｙ＝ １．２３１４Ｘ^４ −５．９４０１Ｘ^３ ＋１０．６Ｘ^２ −８．２９３６Ｘ ＋２．４６２９ ・・・（４）
【０１１０】
したがって、点ａ〜点ｔで囲まれた領域は、下記の式（５）および式（６）を満たす領域として、近似的に表すことができる。
【０１１１】
Ｙ ≦ −２．３８２６Ｘ^４ ＋１３．４９４Ｘ^３ −２８．５８２Ｘ^２ ＋２６．８７６Ｘ −９．２２７２ ・・・（５）
Ｙ ≧ １．２３１４Ｘ^４ −５．９４０１Ｘ^３ ＋１０．６Ｘ^２ −８．２９３６Ｘ ＋２．４６２９ ・・・（６）
【０１１２】
すなわち、浅いグルーブの位相深さと深いグルーブの位相深さとを、上式（５）および式（６）を満たすように形成すれば、プッシュプル信号の信号量が１４％程度以上となり、安定したトラッキングサーボが可能となる。
【０１１３】
さらに、記録再生特性が良好であるかを評価するため、プッシュプル信号の信号量が１４％程度以上となる適切な深さの二つの深いグルーブと浅いグルーブまたは第１のランドＬｄ１、第２のランドＬｄ２、第３のランドＬｄ３の各３本の記録トラックすべての記録領域において、光磁気の記録再生を行った。そのときのジッタ値は、１５％程度であり、良好な記録再生特性を得られることがわかった。
【０１１４】
さらに、ウォブル振幅±１５ｎｍの深い（ウォブル）グルーブ、ウォブルしていない浅い（ＤＣ）グルーブのすべての部分において、ウォブル信号の再生が可能であった。
【０１１５】
また、レーザ光の波長λが６５０ｎｍであり、対物レンズの開口数ＮＡが０．５２であることから、光ピックアップのカットオフ周波数２ＮＡ／λは、１６００（本数／ｍｍ）である。一方、評価用光ディスクは、第１のグルーブＧｖ１と第２のグルーブＧｖ２との間隔をトラックピッチとすると、トラックピッチは３５０ｎｍとなるため、その空間周波数は、およそ２８５７（本数／ｍｍ）となる。したがって、光ピックアップのカットオフ周波数よりも高い空間周波数となるトラックピッチの光ディスクにおいても、十分なレベルのプッシュプル信号、ＣＴＳ信号を得られ、安定したトラッキングサーボ、シークが可能であることがわかる。
【０１１６】
図６は、上述した光磁気ディスクを使用する記録再生装置の構成例を示す。図６において、参照符号５１が上述したように、二つの深いウォブルグルーブと浅いグルーブとが交互に形成された光磁気ディスクである。入力端子５２には、記録するデータが供給される。データ変調器５３は、入力データに対してディジタル変調を施す。例えばＲＬＬ（１，７）によって入力データが変調される。ＲＬＬ（１，７）では、最短マーク長が２Ｔで最長マーク長が８Ｔである。
【０１１７】
データ変調器５３の出力データが記録ヘッド駆動部５４に供給される。記録ヘッド駆動部５４は、記録／再生部５５に含まれる記録ヘッドに変調データを供給する。記録／再生部５４には、光ピックアップが含まれている。記録時では、記録用のレーザ光を光ピックアップが光磁気ディスク５１に対して照射し、データを記録する。
【０１１８】
また、光ピックアップは、光磁気ディスク５１からの反射光からトラッキングエラー信号、フォーカスエラー信号およびアドレス情報を含むウォブル信号を生成する。トラッキングエラー信号は、プッシュプル信号またはＣＴＳ信号から形成される。記録／再生部５５からのトラッキングエラー信号およびフォーカスエラー信号は、サーボ部５６に対して出力される。サーボ部５６は、記録／再生部５５内の光ピックアップのトラッキングおよびフォーカスを制御する制御信号、光磁気ディスク３１の回転を制御する制御信号、並びに光ピックアップのディスク径方向の移動を制御する制御信号を生成する。
【０１１９】
ウォブル信号は、ウォブル信号検出部５７に出力される。ウォブル信号検出部５７は、ウォブル信号からアドレス情報を復調し、アドレス情報をアドレスデコーダ５８に対して出力する。さらに、ウォブル信号検出部５７は、ウォブル信号から正弦波のキャリア信号を抽出し、サーボ部５６に対して抽出したキャリア信号を供給する。
【０１２０】
アドレスデコーダ５８は、ウォブル信号検出部５７から供給されるアドレス情報信号からアドレスを算出し、そのアドレスをシステムコントローラ５９に対して出力する。システムコントローラ５９は、アドレスデコーダ５８から供給されるアドレス情報にしたがって、所定の制御信号をサーボ部５６に出力すると共に、入力装置６０から所定の操作に対応する信号が供給されると、その操作に応じた制御信号をサーボ部５６に出力し、記録／再生部５５を制御するようになされている。
【０１２１】
光磁気ディスク５１の光ピックアップによって読み出され、記録／再生部５５における処理によって得られた再生データがデータ復調器６１に供給される。データ復調器６１では、記録時に施されたディジタル変調例えばＲＬＬ（１，７）の復調処理がなされる。データ復調器６１の出力端子６２に対して再生データが取り出される。
【０１２２】
以上説明した一実施形態による光磁気ディスク１では、トラック密度を従来の３倍程度と格段に高密度化することができ、安定したトラッキングサーボおよびシークが行え、二つの深いグルーブおよび浅いグルーブ、または三つのランドによる合計３本の記録トラックの記録再生特性が良好であり、ウォブル再生特性も良好である。また、レーザカッティング装置１０は、上述した光磁気ディスク１の作成に用いることができ、図６を参照して説明した記録再生装置では、上述した光磁気ディスク１の記録または再生が可能である。
【０１２３】
この発明は、上述したこの発明の一実施形態に限定されるものでは無く、この発明の要旨を逸脱しない範囲内で様々な変形や応用が可能である。この発明は、記録トラックに沿ってグルーブが形成されてなる光記録媒体、並びにその製造に使用される光記録媒体製造用原盤に対して広く適用可能であり、この発明の対象となる光記録媒体は、例えば、再生専用の光記録媒体、繰り返しデータの書き換えが可能な光記録媒体、或いはデータの追記は可能だか消去はできないような光記録媒体のいずれでもよい。
【０１２４】
また、データの記録方法も特に限定されるものではなく、この発明の対象となる光記録媒体は、例えば、予めデータが書き込まれている再生専用の光記録媒体、磁気光学効果を利用してデータの記録再生を行う光磁気記録媒体、或いは記録層の相変化を利用してデータの記録再生を行う相変化型光記録媒体などのいずれでもよい。
【０１２５】
また、この発明は、記録領域の少なくとも一部にグルーブが形成されている光記録媒体、並びにその製造に使用される光記録媒体製造用原盤に対して広く適用可能である。すなわち、例えば、記録領域全体にグルーブが形成されていてもよいし、或いは、グルーブが形成されることなくエンボスピットによってデータが記録されているような領域が記録領域内に存在していてもよい。
【０１２６】
【発明の効果】
以上詳細に説明したように、この発明によれば、記録領域を第１〜第３のグルーブ、または第１〜第３のランドの合計３トラックにすることにより、トラック密度の高密度化を実現することができる。また、第１および第２のグルーブを深いグルーブとし、第３のグルーブを浅いグルーブとすることで、これらグルーブの深さを適切に設定することにより、プッシュプル信号およびＣＴＳ信号の信号量が充分得られ、安定したトラッキングサーボおよびシークが可能であり、記録再生特性が良好な光記録媒体、およびそのような光記録媒体を製造することができる光記録媒体製造用原盤、ならびにそのような光記録媒体に対して記録再生を行う記録再生装置を提供することができる。
【図面の簡単な説明】
【図１】この発明を適用した光磁気ディスクの一例について、その要部を拡大して示す断面図である。
【図２】この発明を適用した光磁気ディスクの記録領域の一部とＣＴＳ信号の波形とプッシュプル信号の波形を示す略線図である。
【図３】この発明に係る記録媒体および記録媒体製造用原盤を作成する際に使用されるレーザカッティング装置の一例について、その光学系の概要を示す略線図である。
【図４】この発明に係る記録媒体製造用原盤の作成について説明するための原盤の一部断面図である。
【図５】プッシュプル信号量が１４％程度以上となるときの、深いグルーブの深さと浅いグルーブの深さとの関係を示す略線図である。
【図６】この発明を適用した光磁気ディスクに対して記録再生を行う記録再生装置の一例のブロック図である。
【図７】従来の光磁気ディスクの記録領域の一部とＣＴＳ信号の波形とプッシュプル信号の波形を示す略線図である。
【図８】ＤＷＤＤ超解像度光磁気ディスクの説明に用いる一部断面図である。
【符号の説明】
１・・・光磁気ディスク、２・・・ディスク基板、３・・・記録層、４・・・保護層、１０・・・レーザカッティング装置、１１・・・ガラス基板、１２・・・フォトレジスト、１３・・・光源、１４・・・電気光学変調器、１８，２１・・・変調光学系、２４・・・音響光学偏光器（ＡＯＤ）、２７・・・電圧制御発振器、２８・・・対物レンズ、Ｌ３・・・拡大レンズ、Ｇｖ１・・・第１のグルーブ、Ｇｖ２・・・第２のグルーブ、Ｇｖ３・・・第３のグルーブ、Ｌｄ１・・・第１のランド、Ｌｄ２・・・第２のランド、Ｌｄ３・・・第３のランド[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical recording medium having a groove formed along a recording track, and an optical recording medium manufacturing master used when manufacturing such an optical recording medium. The present invention also relates to a recording / reproducing apparatus and a recording / reproducing method for performing recording and / or reproducing processing on an optical recording medium having grooves formed along recording tracks.
[0002]
[Prior art]
Conventional recordable disc-shaped recording media include MD (Mini Disc), CD (Compact Disc) -R (Recordable), CD-RW (ReWritable), DVD (Digital Versatile Disc or Digital Video Disc) + RW (ReWritable DVD). -R (Recordable), DVD-RW (ReWritable) and the like have been proposed. In the format of these disc-shaped recording media, a groove recording format for recording in a groove is adopted.
[0003]
A land recording format for recording on lands (between grooves) has been proposed in each format of an ISO (International Organization for Standardization) magneto-optical (MO; Magneto Optical 1) disk. In a DVD-RAM (Digital Video Disc-Random Access Memory) or the like, as one method for realizing high density of an optical disk, the track density is doubled by recording on both the groove and between the grooves (land). (Land / groove recording) has been proposed. Here, the groove is a so-called guide groove formed along a recording track in order to mainly perform tracking servo. A portion closer to the optical pickup is called a groove, and a portion farther from the optical pickup is called a land. The portion between the grooves is called a land.
[0004]
Then, as shown in FIG. 7, in an optical recording medium having grooves formed therein, tracking servo is usually performed by using a push-pull signal. The push-pull signal is a difference signal, which irradiates the optical recording medium with a light beam, and the light beam reflected by the optical recording medium arranges two light detectors symmetrically with respect to the track center. A and B are obtained by taking the difference (AB) between the outputs from these two photodetectors A and B.
[0005]
The amount of light reflected by the optical recording medium is detected as the sum (A + B) of these two photodetectors. Here, a signal obtained by detecting the amount of reflected light of the light beam by the optical recording medium, that is, the sum signal of the outputs from the two photodetectors A and B indicates how many spots of the light beam move when the spot moves. This signal is used to detect whether a track has crossed a track, and is generally called a cross track signal (CTS: Cross Track Signal).
[0006]
The MD or CD-R is selected so that the groove width / track pitch is about 1/3 or about 2/3 so that a sufficient amount of push-pull signal and CTS signal can be obtained. That is, in the case of MD, the groove width / track pitch = 1.1 μm / 1.6 μm = 69%, and in the case of CD-R, the groove width / track pitch = 0.5 μm / 1.6 μm = 31%. Have been.
[0007]
Further, as a technique for improving the recording density in the linear direction, DWDD (Domain Wall Displacement Detection) has been proposed. This is one of the magnetic domain enlarging and reproducing techniques used in magneto-optical disks. For example, Patent Literature 1 below discloses a technology regarding the DWDD method.
[0008]
[Patent Document 1]
JP-A-6-290496
[0009]
FIG. 8 is an enlarged partial cross-sectional view of the magneto-optical disk disclosed in Patent Document 1. Reference numeral 71 indicates a substrate, reference numeral 72 indicates a dielectric layer, reference numeral 73 indicates a recording layer, and reference numeral 74 indicates a dielectric layer. Reference numeral 75 denotes a groove, and reference numeral 76 denotes a land.
[0010]
The recording layer 73 is formed by sequentially laminating a first magnetic layer, a second magnetic layer, and a third magnetic layer. The first magnetic layer is composed of a perpendicular magnetization film having a smaller domain wall coercive force and a larger domain wall mobility than the third magnetic layer at a temperature near the ambient temperature, and the second magnetic layer is formed of the first magnetic layer. The magnetic layer comprises a magnetic layer and a magnetic layer having a lower Curie temperature than the third magnetic layer, and the third magnetic layer is a perpendicular magnetization film. The data signal is recorded by modulating an external magnetic field while irradiating a power laser beam such that the third magnetic layer has a Curie temperature or higher while moving the medium.
[0011]
In the following Patent Documents 2 and 3, the recording density is equivalent to that of land / groove recording, the depth of two grooves is appropriately changed, and two grooves having different depths are arranged adjacent to each other. However, there has been proposed a preformat capable of obtaining a sufficient CTS signal amplitude and push-pull signal amplitude even if the cut-off frequency is exceeded. This preformat realizes stable tracking servo at a track pitch exceeding the cutoff frequency. In this preformat, a deep groove and a shallow groove are arranged adjacent to each other, an interval between deep grooves (or an interval between shallow grooves) is defined as a track period (1.0 μm), and an interval between a deep groove and a shallow groove is defined as a track pitch (0. 5 μm). Two lands (track A and track B) on both sides of the shallow groove sandwiched between the deep grooves are recording areas. Therefore, the track density in this preformat is twice as high as the conventional one, that is, the same as the land / groove recording density.
[0012]
[Patent Document 2]
JP-A-11-296910
[0013]
[Patent Document 3]
JP-A-2000-40259
[0014]
[Problems to be solved by the invention]
That is, the track density of land / groove recording is about twice as high as that of the related art, and even in the preformat described above, the recording area is two lands (track A and track B) on both sides of the shallow groove. It is equivalent to the recording density of recording. Therefore, it has been difficult to increase the track density to at least twice the conventional density.
[0015]
In the land / groove recording, the groove width and the land width are almost the same. If the groove width and the land width are approximately the same, the push-pull signal has a maximum and sufficient signal amount as shown in FIG. 7, but the signal amount of the CTS signal is insufficient. In a normal disk reproducing apparatus, a signal amount of a signal for counting the number of tracks is required to be about 6% to 7% for a seek operation, and a signal amount of about 14% is required for a detection signal for tracking servo. It is said. Here, the signal amount is defined as 100% of a signal obtained on a surface on which no groove or pit is formed (a so-called dummy surface).
[0016]
As described above, if the signal amount of the CTS signal is insufficient, the number of traversed tracks cannot be accurately detected from the CTS signal during a seek operation for moving to a target address at a high speed, and the seek operation using the CTS signal is not possible. There was a difficult problem to do. Of course, it was impossible to apply the tracking servo with a CTS signal having a small signal amount.
[0017]
Further, in order to obtain the push-pull signal and the CTS signal of these required signal amounts, the spatial frequency of the track pitch needs to be about 1/2 to 2/3 of the cutoff frequency of the optical pickup of the reproducing apparatus. . Here, the cut-off frequency is a frequency at which the amplitude of the reproduced signal becomes substantially zero, and when the wavelength of the laser beam used for reproducing the data is λ and the numerical aperture of the objective lens is NA, 2NA / Λ.
[0018]
Accordingly, it is an object of the present invention to realize a high-density track and to achieve a sufficient signal amount of a push-pull signal and a CTS signal even when a groove width and a land width are substantially the same. An object of the present invention is to provide a recording medium, a master for producing an optical recording medium, a recording / reproducing apparatus, and a recording / reproducing method.
[0019]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention of claim 1 is
An optical recording medium in which a groove is formed along a recording track and irradiated with light having a predetermined wavelength λ to perform recording and / or reproduction,
The first and second grooves and a third groove shallower than the first and second grooves are formed so as to be adjacent to each other, and
An optical recording medium characterized in that signals are recorded on first to third grooves or three lands between the first to third grooves.
[0020]
The invention of claim 6 is
A groove is formed along the recording track, an optical recording medium manufacturing master used when manufacturing an optical recording medium on which recording and / or reproduction is performed by irradiating light of a predetermined wavelength λ,
The first and second grooves and a third groove shallower than the first and second grooves are formed so as to be adjacent to each other, and
An optical recording medium manufacturing master, wherein signals are recorded on three lands between the first to third grooves or the first to third grooves, respectively.
[0021]
The invention of claim 7 is
A groove is formed along a recording track, a recording and reproducing apparatus of an optical recording medium in which recording and / or reproducing is performed by irradiating light of a predetermined wavelength λ,
The first and second grooves and a third groove shallower than the first and second grooves are formed so as to be adjacent to each other, and
A recording / reproducing apparatus characterized in that a signal is recorded or reproduced on three lands between the first to third grooves or between the first to third grooves.
[0022]
The invention of claim 10 is
A recording / reproducing method for an optical recording medium in which a groove is formed along a recording track, and light having a predetermined wavelength λ is irradiated to perform recording and / or reproduction,
The first and second grooves and a third groove shallower than the first and second grooves are formed so as to be adjacent to each other, and
A recording / reproducing method characterized in that a signal is recorded or reproduced on three lands between the first to third grooves or each of the first to third grooves.
[0023]
According to the present invention, by making the recording area a total of three tracks of the first to third grooves or the first to third lands, the track density can be remarkably increased to about three times the conventional one. is there. Further, by setting the first and second grooves to be deep grooves and setting the third groove to be shallow grooves, by appropriately setting the depths of these grooves, the push-pull signal amount and the CTS signal amount can be sufficiently obtained. As a result, stable tracking servo and seek can be performed, and a preformat optimal for an optical recording medium having good recording and reproducing characteristics can be provided.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged sectional view of a main part of a magneto-optical disk to which the present invention is applied. FIG. 1A shows a configuration of a magneto-optical disk, and FIG. 1B shows an example of a specific configuration of a recording track. FIG. 2 is a diagram relating to a recording area of a magneto-optical disk. 2A is an enlarged view of a part of the recording area, FIG. 2B shows an output waveform of a CTS signal by a photodetector, and FIG. 2C shows an output waveform of a push-pull signal by a photodetector.
[0025]
Reference numeral 1 in FIG. 1A indicates a magneto-optical disk. The magneto-optical disk 1 is formed in a disk shape, and records and reproduces data using a magneto-optical effect. The magneto-optical disk 1 has a recording layer 3 on which magneto-optical recording is performed and a protective layer for protecting the recording layer 3 on a disk substrate 2 made of polymethyl methacrylate (PMMA), polycarbonate (PC), or the like. 4 are formed. Here, the recording layer 3 is made of, for example, silicon nitride (Si ₃ N ₄ ) Or the like, a magnetic film 3b, a silicon nitride (Si) ₃ N ₄ ), And a reflective film 3d made of an Al—Ti alloy or the like. The protective layer 4 is formed, for example, by spin-coating an ultraviolet curable resin on the recording layer 3 and irradiating the ultraviolet ray. The magnetic film 3b is formed by sequentially laminating a first magnetic layer, a second magnetic layer, and a third magnetic layer to perform data recording. In the present invention, the configurations of the recording layer 3 and the protective layer 4 are arbitrary, and are not limited to this example.
[0026]
As shown in FIG. 2A in which a part of a recording area is enlarged, a groove is formed in a spiral shape along a recording track of the magneto-optical disk 1, and light of a predetermined wavelength λ is irradiated by an optical pickup 5 for recording. And / or regeneration. As the groove, the first groove Gv1, the second groove Gv2, and the third groove Gv3 are formed so as to be adjacent to each other.
[0027]
The first groove Gv1 and the second groove Gv2 are deep grooves, and the third groove Gv3 is a shallow groove. Then, three grooves of the first groove Gv1 and the second groove Gv2 (hereinafter, appropriately referred to as a deep groove), the third groove Gv3 (hereinafter, appropriately referred to as a shallow groove), or the first groove Gv1 and the third groove Gv1 The first land Ld1 between the second groove Gv2, the second land Ld2 between the second groove Gv2 and the third groove Gv3, and the first land Ld2 between the third groove Gv3 and the first groove Gv1. Signals are recorded on three lands of the third land Ld3. That is, in the magneto-optical disk 1, the first groove Gv1, the second groove Gv2, the third groove Gv3, and the first land Ld1, the second land Ld2, and the third land Ld are formed in a spiral shape. And has three recording tracks by each groove or each land.
[0028]
As shown in FIG. 1B, each groove and each land are formed with a width substantially equal to 130 nm, for example. That is, the width of the three lands (the first land Ld1, the second land Ld2, and the third land Ld3) and the top width (upper width) of the deep groove (the first groove Gv1 and the second groove Gv2). , The top width (upper width) of the shallow groove (third groove Gv3) is substantially the same. By making the widths of the recording tracks substantially the same, the recording / reproducing characteristics can be improved.
[0029]
Further, the period of each of the three recording tracks is, for example, 1240 nm, and the bottom width of the first groove Gv1, that is, between the third land Ld3 and the first land Ld1 and the second groove Gv2. The bottom width, that is, the distance between the first land Ld1 and the second land Ld2 is, for example, the same as 285 nm, and the bottom width of the third groove Gv3, that is, the distance between the second land Ld2 and the third land Ld3. The interval is, for example, 280 nm.
[0030]
The wobble groove is formed such that a deep groove and / or a shallow groove meander. In the example of FIG. 1, as shown in FIG. 2A, the first groove Gv1 and the second groove Gv2 which are deep grooves are wobbled grooves. The amplitude of the wobble is, for example, ± 15 nm.
[0031]
By forming three recording tracks in this manner, the magneto-optical disk 1 can have a track density nearly three times that of the conventional one.
[0032]
As shown in FIG. 2A, the magneto-optical disk 1 to which the present invention is applied is reproduced by three beams. The center beam is located at the center of one of the two adjacent deep grooves, and the two side beams are aligned with the centers of the shallow grooves located on both sides of the two adjacent deep grooves. The reflected light of the center beam is detected by the 4-split photodetector 6, and the reflected light of the side beam is detected by the 2-split photodetectors 7a and 7b.
[0033]
The CTS signal shown in FIG. 2B is obtained from the sum signal (A + B + C + D) of the quadrant photodetector 6. The CTS signal thus obtained has a period equal to the track period, has a sufficient amplitude, becomes maximum at the center position between two adjacent deep grooves, and becomes minimum at the center position of the shallow groove.
[0034]
When the tracking servo is applied by the sum signal, a tracking error is obtained from the difference (E + F)-(G + H) between the sum signals of the side beams 7a and 7b. The push-pull signal shown in FIG. 2C obtains the sum (A + D) and (B + C) of the detection signals of two areas located on both sides of the four-division photodetector 6 in the track extension direction, and calculates the difference ( A + D)-(B + C). The push-pull signal thus obtained has a period equal to the track period, and becomes zero at the center position between two adjacent deep grooves and the center position of a shallow track.
[0035]
As described above, data is recorded in the first groove Gv1, the second groove Gv2, the third groove Gv3, or the first land Ld1, the second land Ld2, and the third land Ld3. It is. When seeking to the first groove Gv1, for example, a position where the push-pull signal is −85%, the CTS signal rises to the right, and is larger than the central value (average value) is searched. When seeking to the second groove Gv2, for example, a position where the push-pull signal is + 85%, the CTS signal is lower right and larger than the median value (average value) is searched. When seeking to the third groove Gv3, for example, a position where the push-pull signal is 0 and the CTS signal is the minimum value is searched.
[0036]
When seeking to the first land Ld1, for example, a position where the push-pull signal is 0 and the CTS signal has the maximum value is searched. When seeking to the second land Ld2, for example, a position where the push-pull signal is + 85% and the CTS signal is lower right and smaller than the median value (average value) is searched. When seeking to the third land Ld3, for example, a position where the push-pull signal is -85%, the CTS signal rises to the right, and is smaller than the median value (average value) is searched.
[0037]
When manufacturing the above-described magneto-optical disk 1, it is necessary to manufacture an optical recording medium manufacturing master, which is the master of the magneto-optical disk 1, and a laser cutting device is used for that purpose. Hereinafter, an example of a laser cutting device used for manufacturing an optical recording medium manufacturing master will be described in detail with reference to FIG.
[0038]
An example of a laser cutting device described here is a laser beam emitted from a light source, which is split by a beam splitter and a mirror into a first exposure beam (for forming a wobbled deep groove) and a second exposure beam (for forming a shallow wobbled groove). The first exposure beam is deflected to form a wobble groove, and the polarized first exposure beam is split into two exposure beams (1-1-1) by a beam splitter and a mirror. Beam and the first- (2) exposure beam), the three divided exposure beams are radially arranged at appropriate intervals, and the respective exposure powers are appropriately selected, whereby two deep grooves are formed. And one shallow groove form a concavo-convex pattern alternately arranged at equal intervals in the radial direction.
[0039]
The laser cutting apparatus 10 shown in FIG. 3 is for exposing a photoresist 12 applied on a glass substrate 11 to form a latent image on the photoresist 12. When a latent image is formed on the photoresist 12 by the laser cutting device 10, the glass substrate 11 coated with the photoresist 12 is attached to a rotary driving device provided on a movable optical table. When exposing the photoresist 12, the glass substrate 11 is driven to rotate by a rotation driving device and is translated by a moving optical table so that exposure with a desired pattern is performed over the entire surface of the photoresist 12. You.
[0040]
The laser cutting device 10 includes a light source 13 that emits a laser beam, an electro-optic modulator (EOM: E1 Electro Optical Modulator) 14 for adjusting the light intensity of the laser beam emitted from the light source 13, and an electro-optic modulator. An analyzer 15 arranged on the optical axis of the laser light emitted from the light source 14, a first beam splitter BS1 and a second beam splitting the laser light transmitted through the analyzer 15 into reflected light and transmitted light A signal electric field is applied to the splitter BS2, a photodetector (PD) 16 that detects the laser beam transmitted through the second beam splitter BS2, and the electro-optic modulator 14, and the light is emitted from the electro-optic modulator 14. Output controller (APC: Auto Power Cont) for adjusting the intensity of the laser beam oller) and a 17.
[0041]
The laser light emitted from the light source 13 is first given a predetermined light intensity by an electro-optic modulator 14 driven by a signal electric field applied from the APC 17 and then enters the analyzer 15. Here, the analyzer 15 is an analyzer that transmits only S-polarized light, and the laser light transmitted through the analyzer 15 becomes S-polarized light.
[0042]
Although any light source can be used as the light source 13, a light source that emits laser light of a short wavelength is preferable. Specifically, for example, a Kr laser that emits a laser beam having a wavelength of 351 nm, a He-Cd laser that emits a laser beam having a wavelength of 442 nm, or the like is suitable as the light source 13.
[0043]
The light intensity of the laser light transmitted through the beam splitters BS1 and BS2 is detected by the photodetector 16, and a signal corresponding to the light intensity is transmitted from the photodetector 16 to the APC 17. Then, the APC 17 adjusts the signal electric field applied to the electro-optic modulator 14 so that the light intensity detected by the photodetector 16 becomes constant at a predetermined level. As a result, feedback control is performed so that the light intensity of the laser light emitted from the electro-optic modulator 14 becomes constant, and a stable laser light with less noise is obtained.
[0044]
The laser light emitted from the light source 13 is reflected by the beam splitter BS1, and the reflected light from the beam splitter BS1 is incident on a modulation optical system (shown as OM1 in FIG. 3) 18. The beam relay optical system and the AOM 19 between them are arranged so as to satisfy the Bragg condition. The relay optical system is arranged so that the laser light emitted from the light source 13 is focused on the AOM 19 using the focusing lens L11. The intensity of the laser light is modulated based on the ultrasonic waves supplied to the AOM 19. A drive signal is supplied from the driver 20 to the AOM 19.
[0045]
This drive signal is a DC signal when a groove is formed. If a pit is to be formed, the modulated signal is a DC signal. The laser beam is continuously modulated according to the DC signal, and an exposure beam B1 for forming a deep groove is formed.
[0046]
The laser beam diverged by intensity modulation by the AOM 19 is converted into a parallel beam by the lens L12. Then, the exposure beam B1 emitted from the modulation optical system 18 (OM1) is reflected by the mirror M1, and is guided horizontally and parallel to the moving optical table 18.
[0047]
Further, the laser light emitted from the light source 13 is reflected by the beam splitter BS2, and the reflected light of the beam splitter BS2 enters a modulation optical system (shown as OM2 in FIG. 3) 21. The beam relay optical system (lenses L21 and L22) and the AOM 22 therebetween are arranged so as to satisfy the Bragg condition. The intensity of the laser light is modulated based on the ultrasonic waves supplied to the AOM 22. A DC signal is supplied from the driver 23 to the AOM 22. The laser beam is continuously modulated in accordance with the level of the DC signal, and an exposure beam B2 for forming a shallow groove is formed. The divergent laser light that has been intensity-modulated by the AOM 22 is converted into a parallel beam by the lens L22, reflected by the mirror M2, and incident on the polarization beam splitter PBS via an HWP (half-wave plate).
[0048]
The laser beam (exposure beam B1) reflected by the mirror M1 and guided horizontally on the movable optical table 18 is optically deflected by the deflection optical system OD, and then enters the beam splitter BS3, where it is first deepened. It is split into an exposure beam B1- (1) for forming a groove and a second exposure beam B1- (2) for forming a deep groove. The exposure beam B1- (1) is reflected by the mirror M3, and the exposure beam B1- (2) is reflected by the mirror M4 and the traveling direction is bent by 90 °. Then, these two divided exposure beams (exposure beam B1- (1) and exposure beam B1-2) are recombined by the beam splitter BS4 before being incident on the polarization beam splitter PBS.
[0049]
The deflection optical system OD is for optically deflecting the laser light so as to correspond to a deep groove wobble. That is, the laser light incident on the deflecting optical system OD is incident on an acousto-optic deflector (AOD) 24 via a wedge prism 23, and the acousto-optic deflector 24 corresponds to a desired exposure pattern. Optical deflection is performed as described above. Here, as an acousto-optic element used for the acousto-optic deflector 24, for example, tellurium oxide (TeO ₂ An acousto-optic element comprising: The laser light that has been optically deflected by the acousto-optic deflector 24 is emitted from the deflection optical system OD via the wedge prism 25.
[0050]
The wedge prisms 23 and 25 allow the laser light to be incident on the lattice plane of the acousto-optic device of the acousto-optic deflector 24 so as to satisfy the Bragg condition. Optical deflection to change the horizontal height of the beam.
[0051]
Here, a driving driver 26 for driving the acousto-optic deflector 24 is connected to the acousto-optic deflector 24. The driving driver 26 is supplied with a DC voltage and a signal in which a high frequency signal from a voltage controlled oscillator (VCO) 27 is FM-modulated by a control signal including address information. Then, the acousto-optic deflector 24 is driven by the drive driver 26 in accordance with the signal, whereby the laser light is optically deflected.
[0052]
Specifically, for example, address information is added to the groove by wobbling the groove with an FM modulation signal having a frequency of 84.672 kHz as a carrier. In this case, in order to create a phase grating of the acousto-optic deflector 24, a signal obtained by superimposing a high-frequency signal having a center frequency of 224 MHz on a signal obtained by FM-modulating a frequency of 84.672 kHz is transmitted from the voltage-controlled oscillator 27 to the driving driver 26. To supply.
[0053]
Then, the acousto-optic deflector 24 is driven by the driving driver 26 in accordance with this signal, and the Bragg angle of the acousto-optic element of the acousto-optic deflector 24 is changed. As a result, the light is focused on the photoresist 12. The position of the light spot of the laser light is oscillated in the radial direction of the glass substrate 11 at a frequency of 84.672 kHz and an amplitude of ± 15 nm.
[0054]
Then, the laser beam optically deflected so as to correspond to the wobble of the wobble groove by such a deflection optical system OD is subjected to two exposure beams B1- (1) and B1- (2) by the beam splitter BS3. After being split into two and recombined by the mirror M3, the mirror M4, and the beam splitter BS4, the light is incident on the polarization beam splitter PBS.
[0055]
Here, the polarization beam splitter PBS reflects S-polarized light and transmits P-polarized light. The exposure beam B1- (1) and the exposure beam B1- (2) optically polarized so as to wobble by the modulation optical system OD are S-polarized light and are incident on the polarization beam splitter PBS via the HWP. Exposure beam B2 is P-polarized light. Therefore, the exposure beam B1- (1) and the exposure beam B1-2 are reflected by the polarization beam splitter PBS, and the exposure beam B2 passes through the polarization beam splitter PBS. Thus, the exposure beam B1- (1), the exposure beam B1-2 and the exposure beam B2 are recombined so that the traveling directions are the same.
[0056]
The exposure beam B1- (1), the exposure beam B1-2, and the exposure beam B2 recombined so that the traveling directions are the same and emitted from the polarization beam splitter PBS are given a predetermined beam diameter by the magnifying lens L3. Then, the light is reflected by the mirror M5, guided to the objective lens 28, and condensed on the photoresist 12 by the objective lens 28. Note that the exposure beam B1- (1), the exposure beam B1-2, and the exposure beam B2, which are recombined so that the traveling directions are the same direction and are emitted from the polarization beam splitter PBS, are the polarization beam splitter PBS and the beam. By changing the angle of the splitter BS4, it is possible to irradiate the photoresist 12 at appropriate intervals in the radial direction on the photoresist 12. Then, by making it possible to adjust the intensity of the laser light so as to be different, it is possible to form recording areas arranged at appropriate intervals by three laser lights.
[0057]
The photoresist 12 is exposed by these three laser beams, and a latent image is formed on the photoresist 12. At this time, the glass substrate 11 on which the photoresist 12 is applied is driven to rotate by a rotation driving device so that exposure with a desired pattern is performed over the entire surface of the photoresist 12, and the laser light is moved by a moving optical table. Is moved in the radial direction. As a result, a latent image corresponding to the irradiation locus of the laser beam is formed over the entire surface of the photoresist 12.
[0058]
The objective lens 28 for condensing the laser light on the photoresist 12 preferably has a larger numerical aperture NA so that a finer groove pattern can be formed. An objective lens having a numerical aperture of about 0.9 is preferable.
[0059]
As an example, the focal lengths of the condenser lenses L11 and L21 of the modulation optical systems 18 and 21 are set to 80 mm, the focal lengths of the collimating lenses L12 and L22 are set to 120 mm, and the focal length of the magnifying lens L3 is set to 50 mm. In this case, the laser power is selected to be 0.35 mj / m for the two deep grooves, and the laser power is selected to be 0.15 mj / m for the shallow grooves. In the case of a deep groove, since exposure is performed so as to penetrate the photoresist 12, a change in the depth of the deep groove can be obtained by a change in the thickness of the photoresist 12. On the other hand, in the case of a shallow groove, since it does not penetrate the photoresist 12, a change in the depth of the shallow groove can be obtained by a change in the laser power. In consideration of this point, the depths of the two grooves are set to be appropriate.
[0060]
Next, a method for manufacturing the magneto-optical disk 1 shown in FIG. 1 will be described in detail using a specific example. In the manufacture of the magneto-optical disk 1, in a mastering process, first, a glass master serving as a base of an optical recording medium manufacturing master is manufactured. In manufacturing a glass master, first, a disk-shaped glass substrate 11 whose surface is polished is washed and dried, and then a photoresist 12 as a photosensitive material is applied on the glass substrate 11. Next, the photoresist 12 is exposed by the laser cutting device 10 described above, and latent images corresponding to three types of grooves are formed on the photoresist 12.
[0061]
After the latent image is formed on the photoresist 12, the glass substrate 11 is placed on a turntable of a developing machine such that the surface on which the photoresist 12 is applied is the upper surface. Then, while rotating the glass substrate 11 by rotating the turntable, a developing solution is dropped on the photoresist 12 to perform a developing process, and two deep grooves and a shallow groove are formed on the glass substrate 11 respectively. The formed concavo-convex pattern is formed.
[0062]
Here, a specific example of a method of forming a glass master using the laser cutting apparatus 10 will be described in detail with reference to the drawings. FIG. 4 is a cross-sectional view of the master during the glass master forming process. The dashed lines shown in FIG. 4A indicate the respective laser powers when forming the deep grooves 31, 32 and the shallow groove 33. The higher the wavy line, the higher the laser power. The deep groove 31 is for forming the first groove Gv1, the deep groove 32 is for forming the second groove Gv2, and the shallow groove 33 is for forming the third groove Gv3. belongs to. Accordingly, a latent image for the deep groove 31 is formed on the photoresist 12 by the irradiation of the exposure beam B1- (1), and a latent image for the deep groove 32 is formed on the photoresist 12 by the irradiation of the exposure beam B1- (2). And a latent image for the shallow groove 33 is formed on the photoresist 12 by the irradiation of the exposure beam B2.
[0063]
First, a photoresist 12 is applied to a thickness of 150 nm on a glass substrate 11. Next, in a region where a deep groove shape is to be formed, that is, in a region where the deep grooves 31 and 32 are formed on the surface of the photoresist 12, a laser power for exposing the surface of the glass substrate 11 to the surface, for example, a laser beam of about 0.35 mj / m. To form a latent image for the U-shaped deep grooves 31 and 32 in the photoresist 12.
[0064]
In addition, a region where a shallow groove shape is to be formed by applying a laser power smaller than that when the deep grooves 31 and 32 are formed, for example, about 0.15 mj / m, that is, a region where the shallow groove 33 on the surface of the photoresist 12 is formed. To form a latent image in the photoresist 12 for the shallow groove 33 that does not reach the surface of the glass substrate 11. Specifically, a latent image is formed with a laser power such that the depth of the shallow groove 33 is 50 nm to 100 nm.
[0065]
By melting the formed latent image portion with a developing solution, a glass substrate 11 having a photoresist 12 having three spiral grooves formed on one surface as shown in FIG. 4A is formed.
[0066]
Next, CHF ₃ First plasma etching is performed on the surface to which the photoresist 12 is applied in a gas atmosphere such as a gas. As a result, the etching proceeds in the deep grooves 31 and 32 where the surface of the glass substrate 11 is exposed, and a groove is formed in the glass substrate 11. Etching is not performed because it serves as a mask. At this time, the etching amount in the deep grooves 31 and 32 is about 90 nm. As a result, the deep grooves 31, 32 shown in FIG. 4A become the deep grooves 31, 32 shown in FIG. 4B.
[0067]
Next, as shown in FIG. 4C, the photoresist 12 is removed until the bottom of the shallow groove 33 reaches the surface of the glass substrate 11. ₂ Ashing. Here, the ashing amount of the photoresist 12 is about 80 nm. Thus, the residual film thickness of the photoresist 12 becomes about 70 nm.
[0068]
Next, CHF ₃ A second plasma etching is performed on the surface to which the photoresist 12 is applied in a gas atmosphere such as a gas. Specifically, the etching is performed so that the etching depth of the shallow groove 33 portion of the glass substrate 11 becomes about 26 nm to 110 nm. At this time, the deep grooves 31 and 32 of the glass substrate 11 are also etched. The etching depth of the deep grooves 31 and 32 is about 120 nm to 250 nm together with the first etching depth. Thereby, the deep grooves 31, 32 and the shallow groove 33 shown in FIG. 4C become the deep groove 31, the deep groove 32 and the shallow groove 33 as shown in FIG. 4D.
[0069]
Finally, as shown in FIG. ₂ By completely removing the photoresist 12 from the glass substrate 11 by ashing, the deep grooves 31, 32 (two deep grooves) having a depth of about 120 nm to 250 nm and the shallow grooves 33 (shallow grooves) having a depth of about 26 nm to 110 nm are formed. An optical disk glass master having the following is obtained. Since the groove shape obtained in this way is obtained by plasma etching, the groove shape is not a V shape but a U shape. As described above, the glass master having the concave and convex patterns respectively corresponding to the two deep grooves and the shallow grooves is completed.
[0070]
In the mastering step, a conductive film made of nickel or the like is formed on the concavo-convex pattern of the completed glass master by an electroless plating method, and then the glass substrate 11 on which the conductive film is formed is attached to an electroforming apparatus. Then, a nickel plating layer is formed on the conductive film by electroplating so as to have a thickness of about 300 ± 5 [μm]. Thereafter, the plating layer is peeled off, and the peeled-off plating is washed with acetone or the like to remove the photoresist 12 remaining on the surface to which the concavo-convex pattern has been transferred.
[0071]
Through the above steps, an optical recording medium manufacturing master made of plating to which an uneven pattern formed on the glass substrate 11 has been transferred, that is, an optical recording medium having an uneven pattern corresponding to a deep groove and a shallow groove, respectively. A master for production (a so-called stamper) is completed.
[0072]
Next, as a transfer step, a disk substrate on which the surface shape of an optical recording medium manufacturing master has been transferred is manufactured using a photopolymer method (a so-called 2P method). Specifically, first, a photopolymer is applied smoothly on the surface of the master for producing an optical recording medium on which the concavo-convex pattern has been formed to form a photopolymer layer, and then bubbles and dust are formed on the photopolymer layer. The base plate is brought into close contact with the photopolymer layer while preventing it from entering. Here, as the base plate, for example, a base plate made of polymethyl methacrylate (refractive index: 1.49) having a thickness of 1.2 mm is used.
[0073]
Thereafter, the photopolymer is cured by irradiating ultraviolet rays, and thereafter, the optical recording medium manufacturing master is peeled off, thereby producing the disk substrate 2 on which the surface shape of the optical recording medium manufacturing master has been transferred.
[0074]
Here, an example is described in which the disk substrate 2 is manufactured using the 2P method so that the concavo-convex pattern formed on the optical recording medium manufacturing master is more accurately transferred to the disk substrate 2. Needless to say, when mass-producing the disk substrate 2, the disk substrate 2 may be manufactured by injection molding using a transparent resin such as polymethyl methacrylate or polycarbonate.
[0075]
Next, as a film forming step, the recording layer 3 and the protective layer 4 are formed on the disk substrate 2 on which the surface shape of the optical recording medium manufacturing master has been transferred. Specifically, for example, first, silicon nitride (Si) is formed on the surface of the disk substrate 2 on which the concavo-convex pattern is formed by using a sputtering device or the like. ₃ N ₄ ), A magnetic layer 3b as a magneto-optical recording layer made of terbium iron cobalt (TbFeCo), etc., and silicon nitride (Si). ₃ N ₄ ) And a light reflection film 3d made of an aluminum alloy (for example, Al—Ti).
[0076]
As a result, the recording layer 3 including the first dielectric film 3a, the magnetic layer 3b, the second dielectric film 3c, and the light reflection film 3d is formed. Thereafter, an ultraviolet curable resin is smoothly applied by a spin coating method or the like on the recording layer 3 so as to substantially cover the entire substrate, and the protective layer 4 is formed by irradiating the ultraviolet curable resin with ultraviolet light and curing. Is done. Through the above steps, the magneto-optical disk 1 is completed.
[0077]
Next, a description will be given of the results of producing a plurality of evaluation magneto-optical disks by the above-described manufacturing method (2P method) or injection molding, and evaluating them. The evaluation work is performed using an MD evaluator equipped with an optical pickup (wavelength λ = 650 nm, NA = 0.52).
[0078]
In the evaluation operation, even if the three land widths of the land Ld1, the land Ld2, and the land Ld3, the two deep groove widths of the grooves Gv1 and Gv2, and the shallow groove width of the groove Gv3 are almost the same, It is evaluated whether tracking servo can be applied by a push-pull signal or a CTS signal by providing a deep groove and a shallow groove, and appropriately selecting the depth of the deep groove and the shallow groove. In the magneto-optical disk as in this embodiment, the recording / reproducing characteristics of three recording tracks and the wobble reproducing characteristics of a wobble groove are evaluated.
[0079]
In the case where the upper groove width and the land width are the same, a push-pull signal or CTS of a signal amount (for example, about 14% or more) for which tracking servo can be applied to the deep groove depth and the shallow groove depth. It was evaluated whether a signal could be obtained. The evaluation values in Tables 1 to 11 relate to evaluation disks having the structure shown in FIG.
[0080]
In the table, λ / xn represents the depth of the groove, λ is the wavelength of the laser beam, for example, 650 nm, and n is the refractive index of the disk substrate from the light incident surface to the groove, for example, 1.58. , X indicate a coefficient. The value of x is changed. The value of x defines the groove depth (nm). For example, when x = 8, 650 nm / (8 × 1.58) = 650 nm / 12.64 ≒ 51 nm. Here, the coefficient x of the deep groove and the coefficient y of the shallow groove are both defined as the groove depth coefficient x.
[0081]
Table 1 below shows that when the value of the coefficient x of two deep grooves is x = 3.1, that is, when the groove depth is 133 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown. As evaluation disks, one evaluation disk is manufactured corresponding to each depth of the shallow groove. Alternatively, an evaluation disk in which the depth of a shallow groove changes sequentially on one disk is manufactured.
[0082]
[Table 1]

[0083]
Table 2 below shows that, when the value of the coefficient x of the two deep grooves is x = 2.9, that is, when the groove depth is 142 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0084]
[Table 2]

[0085]
Table 3 below shows that, when the value of the coefficient x of the two deep grooves is x = 2.7, that is, when the groove depth is 152 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0086]
[Table 3]

[0087]
Table 4 below shows that when the value of the coefficient x of two deep grooves is x = 2.5, that is, when the groove depth is 165 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0088]
[Table 4]

[0089]
Table 5 below shows that when the value of the coefficient x of two deep grooves is x = 2.3, that is, when the groove depth is 179 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0090]
[Table 5]

[0091]
Table 6 below shows that when the value of the coefficient x of two deep grooves is x = 2.1, that is, when the groove depth is 196 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0092]
[Table 6]

[0093]
Table 7 below shows that when the value of the coefficient x of two deep grooves is x = 1.9, that is, when the groove depth is 217 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0094]
[Table 7]

[0095]
Table 8 below shows that, when the value of the coefficient x of the two deep grooves is x = 1.8, that is, when the groove depth is 229 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0096]
[Table 8]

[0097]
Table 9 below shows that, when the value of the coefficient x of the two deep grooves is x = 1.7, that is, when the groove depth is 242 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0098]
[Table 9]

[0099]
Table 10 below shows that, when the value of the coefficient x of two deep grooves is x = 1.63, that is, when the groove depth is 252 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0100]
[Table 10]

[0101]
Table 11 below shows that when the value of the coefficient x of two deep grooves is x = 3.38, that is, when the groove depth is 122 nm (decimal point, rounded off), the depth of the shallow groove is changed. The amplitude change of the push-pull signal and the CTS signal is shown.
[0102]
[Table 11]

[0103]
In Tables 1 to 11, the range surrounded by the thick line indicates that the signal amount (absolute value) of the push-pull signal or the CTS signal is about 14% or more at the depth of the deep groove and the shallow groove corresponding to the range. And stable tracking servo was possible.
[0104]
Table 12 below summarizes the groove depth of the region where the signal amount (absolute value) of the push-pull signal is about 14% or more in the range surrounded by the thick line for the deep groove and the shallow groove. It is.
[0105]
[Table 12]

[0106]
FIG. 5 is a diagram showing the relationship between the phase depth of the shallow groove and the phase depth of the deep groove where the signal amount of the push-pull signal is about 14% or more (range of the thick line). The vertical axis in FIG. 5 indicates the phase depth Y of the shallow groove, and the horizontal axis indicates the phase depth X of the deep groove. For example, Xa at the coordinates (Xa, Ya) of the point a is obtained as 0.323... From the reciprocal of the coefficient x of the deep groove shown in Table 1, that is, "1 / 3.1". The reciprocal of the coefficient x of the shallow groove (upper limit value) shown in FIG. 1, that is, “1 / 6.1”, is obtained as 0.164. Further, for example, Xk at the coordinates (Xk, Yk) of the point k is obtained as 0.323... By the reciprocal of the coefficient x of the deep groove shown in Table 1, that is, "1 / 3.1". 0.0625 is obtained from the reciprocal of the coefficient x of the shallow groove (lower limit) shown in Table 1, that is, “1/16”.
[0107]
Therefore, points a to i in FIG. 5 are the upper limit values of the groove depth at which the push-pull signal amount is about 14% or more, and points j to t are that the push-pull signal amount is about 14% or more. This is the lower limit value of the groove depth. That is, within the area surrounded by points a to t, the signal amount of the push-pull signal was about 14% or more, and it was found that stable tracking servo was possible.
[0108]
Here, the approximate curve L1 connecting the points a to i is expressed by the following equation (3), and the approximate curve L2 connecting the points j to t is expressed by the following equation (4).
[0109]
Y = −2.3826X ⁴ + 13.494X ³ -28.582X ² + 26.876X-9.2272 (3)
Y = 1.2314X ⁴ -5.9401X ³ + 10.6X ² −8.2936X + 2.4629 (4)
[0110]
Therefore, a region surrounded by points a to t can be approximately represented as a region satisfying the following equations (5) and (6).
[0111]
Y ≦ −2.3826X ⁴ + 13.494X ³ -28.582X ² + 26.876X-9.2272 (5)
Y ≧ 1.2314X ⁴ -5.9401X ³ + 10.6X ² −8.2936X + 2.4629 (6)
[0112]
That is, if the phase depth of the shallow groove and the phase depth of the deep groove are formed so as to satisfy the above equations (5) and (6), the signal amount of the push-pull signal becomes about 14% or more, and stable tracking is achieved. Servo becomes possible.
[0113]
Further, in order to evaluate whether the recording / reproducing characteristics are good, two deep grooves and a shallow groove or a first land Ld1 and a second land Ld each having an appropriate depth so that the signal amount of the push-pull signal becomes about 14% or more. Magneto-optical recording / reproduction was performed in all the recording areas of each of the three recording tracks of the land Ld2 and the third land Ld3. The jitter value at that time was about 15%, and it was found that good recording / reproducing characteristics could be obtained.
[0114]
Further, the wobble signal could be reproduced in all the deep (wobble) grooves having a wobble amplitude of ± 15 nm and the shallow (DC) grooves that were not wobbled.
[0115]
Since the wavelength λ of the laser light is 650 nm and the numerical aperture NA of the objective lens is 0.52, the cutoff frequency 2NA / λ of the optical pickup is 1600 (number / mm). On the other hand, in the optical disc for evaluation, if the interval between the first groove Gv1 and the second groove Gv2 is a track pitch, the track pitch is 350 nm, and the spatial frequency is about 2857 (number / mm). Therefore, even with an optical disc having a track pitch having a spatial frequency higher than the cut-off frequency of the optical pickup, a sufficient level of push-pull signal and CTS signal can be obtained, and it can be seen that stable tracking servo and seek are possible.
[0116]
FIG. 6 shows a configuration example of a recording / reproducing apparatus using the above-described magneto-optical disk. In FIG. 6, reference numeral 51 denotes a magneto-optical disk in which two deep wobble grooves and shallow grooves are alternately formed as described above. Data to be recorded is supplied to the input terminal 52. The data modulator 53 performs digital modulation on input data. For example, input data is modulated by RLL (1, 7). In RLL (1, 7), the shortest mark length is 2T and the longest mark length is 8T.
[0117]
The output data of the data modulator 53 is supplied to the recording head driving unit 54. The recording head drive unit 54 supplies modulated data to the recording head included in the recording / reproducing unit 55. The recording / reproducing unit 54 includes an optical pickup. At the time of recording, the optical pickup irradiates a recording laser beam to the magneto-optical disk 51 to record data.
[0118]
In addition, the optical pickup generates a tracking error signal, a focus error signal, and a wobble signal including address information from the reflected light from the magneto-optical disk 51. The tracking error signal is formed from a push-pull signal or a CTS signal. The tracking error signal and the focus error signal from the recording / reproducing unit 55 are output to the servo unit 56. The servo unit 56 includes a control signal for controlling tracking and focus of the optical pickup in the recording / reproducing unit 55, a control signal for controlling rotation of the magneto-optical disk 31, and a control signal for controlling movement of the optical pickup in the disk radial direction. Generate
[0119]
The wobble signal is output to wobble signal detection section 57. The wobble signal detection unit 57 demodulates address information from the wobble signal and outputs the address information to the address decoder 58. Further, the wobble signal detection section 57 extracts a sine wave carrier signal from the wobble signal and supplies the extracted carrier signal to the servo section 56.
[0120]
The address decoder 58 calculates an address from the address information signal supplied from the wobble signal detection unit 57, and outputs the address to the system controller 59. The system controller 59 outputs a predetermined control signal to the servo unit 56 according to the address information supplied from the address decoder 58, and when a signal corresponding to a predetermined operation is supplied from the input device 60, the system controller 59 performs the operation. A corresponding control signal is output to the servo unit 56 to control the recording / reproducing unit 55.
[0121]
Reproduced data read by the optical pickup of the magneto-optical disk 51 and obtained by the processing in the recording / reproducing unit 55 is supplied to the data demodulator 61. In the data demodulator 61, demodulation processing of digital modulation, for example, RLL (1, 7) performed at the time of recording is performed. Reproduction data is taken out from an output terminal 62 of the data demodulator 61.
[0122]
In the magneto-optical disk 1 according to the embodiment described above, the track density can be significantly increased to about three times that of the related art, stable tracking servo and seek can be performed, and two deep and shallow grooves, or The recording and reproducing characteristics of a total of three recording tracks by the three lands are good, and the wobble reproducing characteristics are also good. Further, the laser cutting device 10 can be used for producing the above-described magneto-optical disk 1, and the recording / reproducing device described with reference to FIG.
[0123]
The present invention is not limited to the embodiment of the present invention described above, and various modifications and applications are possible without departing from the gist of the present invention. INDUSTRIAL APPLICABILITY The present invention is widely applicable to an optical recording medium in which a groove is formed along a recording track and an optical recording medium manufacturing master used in the manufacturing thereof, and is an object of the present invention. For example, any of a read-only optical recording medium, an optical recording medium capable of repeatedly rewriting data, and an optical recording medium capable of additionally writing data but not erasing data may be used.
[0124]
Also, the data recording method is not particularly limited, and examples of the optical recording medium to which the present invention is applied include a read-only optical recording medium in which data is written in advance, and a data recording medium utilizing a magneto-optical effect. Or a phase-change type optical recording medium for recording and reproducing data utilizing a phase change of a recording layer.
[0125]
Further, the present invention can be widely applied to an optical recording medium in which a groove is formed in at least a part of a recording area, and an optical recording medium manufacturing master used for manufacturing the optical recording medium. That is, for example, a groove may be formed in the entire recording area, or an area in which data is recorded by embossed pits without forming a groove may exist in the recording area. .
[0126]
【The invention's effect】
As described in detail above, according to the present invention, the recording area is made to be the first to third grooves or the first to third lands, that is, a total of three tracks, thereby realizing a higher track density. can do. Further, by setting the first and second grooves to be deep grooves and setting the third groove to be shallow, the depths of these grooves are appropriately set, so that the signal amounts of the push-pull signal and the CTS signal are sufficient. An optical recording medium obtained, capable of stable tracking servo and seek, and having good recording / reproducing characteristics, an optical recording medium production master capable of producing such an optical recording medium, and such optical recording A recording / reproducing apparatus for recording / reproducing on / from a medium can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an enlarged main part of an example of a magneto-optical disk to which the present invention is applied.
FIG. 2 is a schematic diagram showing a part of a recording area of a magneto-optical disk to which the present invention is applied, a waveform of a CTS signal, and a waveform of a push-pull signal.
FIG. 3 is a schematic diagram showing an outline of an optical system of an example of a laser cutting apparatus used when producing a recording medium and a master for producing a recording medium according to the present invention.
FIG. 4 is a partial cross-sectional view of a master for explaining the creation of a master for manufacturing a recording medium according to the present invention.
FIG. 5 is a schematic diagram showing the relationship between the depth of a deep groove and the depth of a shallow groove when the push-pull signal amount is about 14% or more.
FIG. 6 is a block diagram of an example of a recording / reproducing apparatus for recording / reproducing a magneto-optical disk to which the present invention is applied.
FIG. 7 is a schematic diagram showing a part of a recording area of a conventional magneto-optical disk, a waveform of a CTS signal, and a waveform of a push-pull signal.
FIG. 8 is a partial cross-sectional view used for describing a DWDD super-resolution magneto-optical disk.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Magneto-optical disk, 2 ... Disk substrate, 3 ... Recording layer, 4 ... Protective layer, 10 ... Laser cutting device, 11 ... Glass substrate, 12 ... Photoresist , 13 ... light source, 14 ... electro-optic modulator, 18, 21 ... modulation optical system, 24 ... acousto-optic polarizer (AOD), 27 ... voltage-controlled oscillator, 28 ... Objective lens, L3 ... magnifying lens, Gv1 ... first groove, Gv2 ... second groove, Gv3 ... third groove, Ld1 ... first land, Ld2 ... Second land, Ld3 ... third land

Claims (12)

An optical recording medium in which a groove is formed along a recording track and irradiated with light having a predetermined wavelength λ to perform recording and / or reproduction,
The groove is formed such that first and second grooves and a third groove shallower than the first and second grooves are arranged adjacent to each other,
An optical recording medium, wherein signals are recorded on the first to third grooves or on three lands between the first to third grooves. In claim 1,
An optical recording medium, wherein at least one of the first and second grooves and the third groove is a wobble groove formed so as to meander. In claim 1,
When the numerical aperture of the objective lens used for recording and / or reproduction is NA and the wavelength of light is λ, the spatial frequency of the track pitch is higher than the cutoff frequency represented by 2 × NA / λ. Optical recording medium. In claim 1,
An optical recording medium, wherein the width of each of the three lands and the width of the top of the first to third grooves are substantially the same. In claim 1,
Let n be the refractive index of the medium from the light incident surface to the groove, x be the depth coefficient of the first and second grooves, and x × n / λ be the phase depth X of the first and second grooves, When the depth coefficient of the third groove is y and y × n / λ is the phase depth Y of the third groove, the depth coefficient x of the first and second grooves is equal to the third coefficient. An optical recording medium characterized in that a groove depth coefficient y satisfies the following equations (1) and (2).
Y ≦ −2.3826X ⁴ + 13.494X ³ −28.582X ² + 26.876X−9.2272 (1)
Y ≧ 1.2314X ⁴ −5.9401X ³ + 10.6X ² −8.2936X + 2.4629 (2) A groove is formed along the recording track, an optical recording medium manufacturing master used when manufacturing an optical recording medium on which recording and / or reproduction is performed by irradiating light of a predetermined wavelength λ,
The groove is formed such that first and second grooves and a third groove shallower than the first and second grooves are arranged adjacent to each other,
A master for producing an optical recording medium, wherein signals are recorded on the first to third grooves or on three lands between the first to third grooves, respectively. A groove is formed along a recording track, a recording and reproducing apparatus of an optical recording medium in which recording and / or reproducing is performed by irradiating light of a predetermined wavelength λ,
The groove is formed such that first and second grooves and a third groove shallower than the first and second grooves are arranged adjacent to each other,
A recording / reproducing apparatus for recording or reproducing a signal on or from three lands between the first to third grooves or each of the first to third grooves. In claim 7,
A wobble groove formed so that at least one of the first and second grooves and the third groove meanders;
A recording / reproducing apparatus for reproducing a wobble signal from the wobble groove. In claim 7,
A recording / reproducing apparatus wherein tracking servo is performed by a push-pull signal. A recording / reproducing method for an optical recording medium in which a groove is formed along a recording track, and light having a predetermined wavelength λ is irradiated to perform recording and / or reproduction,
The groove is formed such that first and second grooves and a third groove shallower than the first and second grooves are arranged adjacent to each other,
A recording / reproducing method, wherein a signal is recorded or reproduced to or from three lands between the first to third grooves or each of the first to third grooves. In claim 10,
A wobble groove formed so that at least one of the first groove and the second groove meanders;
A wobble signal is reproduced from the wobble groove. In claim 10,
A recording / reproducing method, wherein tracking servo is performed by a push-pull signal.

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