JP2008243273A - Optical head and method for reproducing optical information recording medium - Google Patents

Optical head and method for reproducing optical information recording medium Download PDF

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JP2008243273A
JP2008243273A JP2007080452A JP2007080452A JP2008243273A JP 2008243273 A JP2008243273 A JP 2008243273A JP 2007080452 A JP2007080452 A JP 2007080452A JP 2007080452 A JP2007080452 A JP 2007080452A JP 2008243273 A JP2008243273 A JP 2008243273A
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light
lens
optical
signal
reflection mirror
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Shigeo Hashizume
滋郎 橋爪
Hideji Mikami
秀治 三上
Takeshi Shimano
健 島野
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Hitachi Ltd
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Hitachi Ltd
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<P>PROBLEM TO BE SOLVED: To precisely adjust an optical path difference by making an angle formed by the optical axis of signal light and that of reference light precisely coincident in an optical head utilizing interference of the signal light emitted to an optical disk and the reference light emitted to a reference mirror. <P>SOLUTION: The optical head has a splitting member which is suitable for miniaturization of an optical system and which splits light from a light source into the signal light and the reference light, an objective lens which condenses and collects the signal light on an optical information medium, and a reference light mirror system which reflects the reference light. As the reference light mirror system, a condensing lens 123 condensing a wave surface as a spherical wave with the surface of a reflection mirror 124 as a focal point is used. Even when the reflection mirror 124 is tilted, the reference light is reflected as the spherical wave with a focal point as a wave source and converted to a plane wave by the condensing lens. Thus, the incident angle and reflection angle to the reference mirror system are made precisely coincident with each other and the optical path difference is adjusted precisely. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、光ディスク装置の再生信号の高S/N化に関する。   The present invention relates to a high S / N ratio of a reproduction signal of an optical disc apparatus.

光ディスクは、青色半導体レーザと、高開口数(NA)対物レンズを用いるブルーレイディスクの製品化に至って、光学系の分解能としてはほぼ限界に達し、さらなる大容量化に向けては、今後、多層化が有力となると考えられる。多層光ディスクにおいては各層からの検出光量がほぼ同等となる必要性から、特定の層からの反射率は小さくせざるを得ない。ところが光ディスクは大容量化とともにビデオなどのダビング速度の高速化の必要性から、転送速度の高速化も続いており、そのままでは再生信号のS/N比が十分確保できなくなりつつある。したがって今後の多層化と高速化を同時に進めていくためには、検出信号の高S/N化が必須となる。   Optical discs have reached the limit of optical system resolution due to the commercialization of Blu-ray Discs that use blue semiconductor lasers and high numerical aperture (NA) objective lenses. Is considered to be influential. In a multilayer optical disc, the reflectance from a specific layer must be reduced because the amount of light detected from each layer needs to be substantially equal. However, since the optical disc needs to have a large capacity and a high dubbing speed for video and the like, the transfer speed is also increasing, and the S / N ratio of the reproduction signal cannot be secured sufficiently as it is. Therefore, in order to proceed with future multi-layering and speeding up at the same time, it is essential to increase the S / N of the detection signal.

光ディスクの再生信号の高S/N化に関する技術は、たとえば特許文献1,特許文献2などに述べられている。いずれも光磁気ディスクの再生信号の高S/N化に関して、半導体レーザからの光を光ディスクに照射する前に分岐して、光ディスクに照射しない光を、光ディスクからの反射光と合波して干渉させることにより、微弱な信号の振幅を、光ディスクに照射しない光の光量を大きくすることによって増幅することを狙ったものである。光磁気ディスクの信号検出で従来用いられている偏光ビームスプリッタの透過光と反射光の差動検出では、本質的にはもとの入射偏光成分と光磁気ディスクによる偏光回転によって生じる入射偏光方向と直交する偏光成分を干渉させて、入射偏光で直交偏光成分を増幅して検出を行うことになっている。したがって、もとの入射偏光成分を増大させれば信号を増大させることができるが、光ディスクに入射させる光強度は、データを消去したり上書きしたりしないようにするために、ある程度以下に抑える必要がある。これに対して上記従来の技術では、予め信号光と干渉させる光を分離しておいて、これをディスクに集光せずに信号光と干渉させ、信号増幅のため干渉させる光の強度を、ディスク表面の光強度と関係なく強くできるようにしているのである。これにより原理的には光強度の許す範囲で、強度を強くすればするほど、光検出器からの光電流を電圧変換するアンプのノイズや、光検出器で生じるショットノイズなどに比べたS/N比を高めることができる。   Techniques for increasing the S / N ratio of the reproduction signal of the optical disk are described in, for example, Patent Document 1 and Patent Document 2. In either case, regarding the increase in the S / N ratio of the reproduction signal of the magneto-optical disk, the light from the semiconductor laser branches before irradiating the optical disk, and the light not irradiated to the optical disk is combined with the reflected light from the optical disk to interfere. By doing so, the aim is to amplify the amplitude of the weak signal by increasing the amount of light that does not irradiate the optical disc. In the differential detection of the transmitted light and reflected light of the polarization beam splitter conventionally used in the signal detection of the magneto-optical disk, essentially the original incident polarization component and the incident polarization direction caused by the polarization rotation by the magneto-optical disk Detection is performed by interfering orthogonal polarization components and amplifying the orthogonal polarization components with incident polarization. Therefore, if the original incident polarization component is increased, the signal can be increased, but the intensity of the light incident on the optical disk must be kept below a certain level in order not to erase or overwrite the data. There is. On the other hand, in the above conventional technique, the light to be interfered with the signal light is separated in advance, and this is interfered with the signal light without condensing it on the disk, and the intensity of the light to be interfered for signal amplification is This makes it possible to increase the intensity regardless of the light intensity on the disk surface. As a result, in principle, the higher the intensity is within the allowable range of the light intensity, the more the S / R compared to the noise of the amplifier that converts the photocurrent from the photodetector into a voltage or the shot noise that occurs in the photodetector. The N ratio can be increased.

特許文献1では、2つの光を干渉させて干渉強度を検出している。この際、干渉させるディスク非反射光の光路長を可変とし、干渉信号振幅の確保を狙っている。特許文献2では干渉強度検出に加えて、差動検出も行っている。これにより信号に寄与しない各光の強度成分をキャンセルし、これらの光の持つノイズ成分をキャンセルして高S/N化を図っている。この場合の差動検出には、無偏光のビームスプリッタを用いている。   In Patent Document 1, interference intensity is detected by causing two lights to interfere with each other. At this time, the optical path length of the disk non-reflected light to be interfered is made variable so as to secure the interference signal amplitude. In Patent Document 2, differential detection is performed in addition to interference intensity detection. As a result, the intensity component of each light that does not contribute to the signal is canceled, and the noise component of these lights is canceled to increase the S / N ratio. In this case, a non-polarized beam splitter is used for differential detection.

特開平5−342678号公報Japanese Patent Laid-Open No. 5-342678 特開平6−223433号公報JP-A-6-223433

上記従来技術に用いられている干渉計の光学系は、いずれもマッハツェンダー型の光学系であり、光学部品の点数が多く、光学系の小型化に不向きである。マッハツェンダー型の干渉計の光学系とは、最初に光を信号光と参照光に分割する分割手段と、信号光に信号としての何らかの変調が加えられたのち、参照光と再び合波させて干渉させるための手段が異なる干渉計である。これに対して、最初に分割する手段に再び信号光と参照光を戻すことによって干渉させるのが、トワイマングリーンあるいはマイケルソン型の干渉計の光学系である。上記従来例においてマッハツェンダー型の光学系を用いる理由について、上記文献には詳しく述べられていないが、光磁気ディスクの信号光が偏光回転により生じるため、干渉させる光の偏光方向の調整のため、回転調整のできるλ/2板(λ:波長)を干渉させる光路中に、往復でなく、片道方向だけ透過させるように配置させる必要があったため、と推測される。さらに他の問題として、2つの光の光路差の調整方法が特に述べられておらず、実用には難があることが挙げられる。特許文献2には、この問題に対して、干渉させる光を得るための参照ミラーをディスク上に記録膜と離して設置することが述べられているが、これは新規格のディスクを提案するものであり、既存のディスクを高S/N化するものではない。   All of the optical systems of the interferometers used in the above prior art are Mach-Zehnder type optical systems, which have a large number of optical components and are not suitable for miniaturization of the optical system. The optical system of the Mach-Zehnder interferometer is a dividing means that first divides light into signal light and reference light, and after some modulation as a signal is applied to the signal light, it is combined again with the reference light. Interferometers with different means for causing interference. On the other hand, the optical system of the Twiman Green or Michelson type interferometer causes interference by returning the signal light and the reference light to the means for dividing first. The reason why the Mach-Zehnder type optical system is used in the above-mentioned conventional example is not described in detail in the above-mentioned document, but since the signal light of the magneto-optical disk is generated by the polarization rotation, in order to adjust the polarization direction of the interference light, This is presumably because it was necessary to arrange the optical path to interfere with a λ / 2 plate (λ: wavelength) capable of rotation adjustment so as to transmit only in one direction rather than reciprocating. Still another problem is that a method for adjusting the optical path difference between the two lights is not particularly described, and there are difficulties in practical use. Patent Document 2 describes that a reference mirror for obtaining light to be interfered with is disposed on the disk apart from the recording film, and this proposes a new standard disk. This does not increase the S / N ratio of an existing disk.

さらに上記従来技術ではいずれも信号増幅のため、干渉強度が最大となるように信号光と参照光の光路差を高精度に調整することが必要となる。また、参照光を反射する反射ミラーは全反射ミラー面で反射した光の光路長を均一にする為、ミラーの傾き角を高精度に調整することが必要となる。   Further, in any of the above prior arts, since the signal is amplified, it is necessary to adjust the optical path difference between the signal light and the reference light with high accuracy so that the interference intensity becomes maximum. In addition, the reflection mirror that reflects the reference light needs to adjust the tilt angle of the mirror with high accuracy in order to make the optical path length of the light reflected by the total reflection mirror surface uniform.

この問題に対して、ミラーの傾き角を高精度に調整し、かつ光路長を高精度に調整するのは実際上極めて困難となる。   For this problem, it is actually very difficult to adjust the tilt angle of the mirror with high accuracy and to adjust the optical path length with high accuracy.

上記課題に鑑み、本発明の目的は、2つの光の光路差の高精度調整が容易で、ミラーの傾き角が信号増幅に対して感度が低く、信号増幅効果が高く、光学系の小型化に適した、干渉型の光ヘッドおよび光ディスク装置を提供することである。   In view of the above problems, the object of the present invention is to easily adjust the optical path difference between two light beams, to make the mirror tilt angle low in sensitivity to signal amplification, to have high signal amplification effect, and to downsize the optical system. It is an object of the present invention to provide an interference type optical head and an optical disc apparatus suitable for the above.

本発明の目的を達成するために以下の手段を用いた。   In order to achieve the object of the present invention, the following means were used.

本発明の光ヘッドは基本的に、半導体レーザなどの光源と、この光源からの光を第1と第2の光束に分割する偏光プリズムなどの第1の分割手段と、第1の光束を光情報記録媒体上に集光して照射する対物レンズなどの集光手段と、前記第2の光束を参照光として反射させる反射ミラーと、光情報記録媒体から反射した信号光と前記参照光を再び第1の分割手段に導いて重ね合わせて干渉させた光を分割するとともに、分割されたそれぞれの光に含まれる信号光と参照光の位相関係を互いに異ならしめる第2の分割手段と、分割された光を検出する複数の検出器と、から構成される。   The optical head of the present invention basically includes a light source such as a semiconductor laser, a first splitting unit such as a polarizing prism that splits light from the light source into first and second light beams, and a first light beam as a light beam. Condensing means such as an objective lens that condenses and irradiates the information recording medium, a reflection mirror that reflects the second light beam as reference light, the signal light reflected from the optical information recording medium, and the reference light again. A second splitting unit for splitting the light guided to the first splitting unit and overlapping and interfering, and for making the phase relationship between the signal light and the reference light included in each of the split light different from each other; And a plurality of detectors for detecting the light.

さらに前記反射ミラーを集光レンズと反射ミラーで構成される系で置き換える。集光レンズに入射された平面な波面はレンズ透過後、焦点で点波源となる球面に変換される。球面波は対物レンズの焦点面に配置した反射ミラーで反射され、レンズに回帰した光はレンズ通過後に再び平面な波面に変換される特徴を持つ。   Further, the reflection mirror is replaced with a system composed of a condenser lens and a reflection mirror. The planar wavefront incident on the condenser lens is converted into a spherical surface that becomes a point wave source at the focal point after passing through the lens. The spherical wave is reflected by a reflecting mirror disposed on the focal plane of the objective lens, and the light returning to the lens has a characteristic that it is converted again into a flat wavefront after passing through the lens.

信号光と参照光を干渉させるときに参照光が傾くと干渉によって生じる干渉縞が多数発生して干渉強度が平均化されて低下する。ところが上記の光学系では反射ミラーが傾いても入射波面と反射波面は平行となり、光の干渉強度の低下が低減される特徴を持つ。   If the reference light is inclined when the signal light and the reference light are caused to interfere, many interference fringes are generated due to the interference, and the interference intensity is averaged and lowered. However, the above optical system has a feature that even if the reflecting mirror is tilted, the incident wavefront and the reflected wavefront are parallel to each other, and the reduction of the light interference intensity is reduced.

さらに反射ミラーと集光レンズを一体とし、光軸方向に可動する1次元アクチュエータに搭載することにより、ミラーを焦点位置に固定した状態で光路長を精密に制御が可能となる。   Furthermore, by integrating the reflecting mirror and the condensing lens into a one-dimensional actuator that moves in the optical axis direction, the optical path length can be precisely controlled with the mirror fixed at the focal position.

信号光と参照光の光路差の調整が容易で、信号増幅効果が高く、さらに反射ミラーの傾きに対して信号光強度劣化が小さい、小型化に適した光学系の干渉型の光ヘッドおよび光ディスク装置を提供することができる。   Interference type optical head and optical disk of an optical system suitable for miniaturization, with easy adjustment of the optical path difference between signal light and reference light, high signal amplification effect, and small signal light intensity deterioration with respect to the tilt of the reflection mirror An apparatus can be provided.

これにより、参照光ミラーによる高精度の光路長調整が簡易に可能となり、多層光ディスクなど、信号に対して相対的なノイズが増加する場合などに、信号増幅によって再生信号品質を向上させることが可能となる。   This makes it possible to easily adjust the optical path length with a reference light mirror easily and to improve the quality of the reproduced signal by signal amplification when the noise relative to the signal increases, such as in a multilayer optical disk. It becomes.

以下、図を用いて本発明の実施形態を説明する。   Hereinafter, embodiments of the present invention will be described with reference to the drawings.

図1は本発明の基本的な実施形態である。半導体レーザ101からの光をコリメートレンズ102によって平行光として、λ/2板103を透過させて偏光プリズム104に入射させる。偏光プリズム104は分離面に入射するP偏光をほぼ100%透過し、S偏光をほぼ100%反射させる機能を有している。このときλ/2板103の光軸周りの回転角度を調整することにより、一部の光をS偏光として偏光プリズム104を反射させ、一部の光をP偏光として透過させるようにすることができる。反射する光はλ/4板105を透過して円偏光に変換され、2次元アクチュエータ106に搭載された対物レンズ107により、光ディスク108上の記録膜に集光される。光ディスクからの反射光は同じ光路を戻り、対物レンズ107によって平行光とされ、λ/4板105により最初に入射したときとは90°偏光方向が回転した直線偏光となって偏光プリズム104に入射する。すると偏光が回転しているため、この光ディスク108からの反射光はP偏光となって偏光プリズム104を透過し、偏光プリズム113に入射する。一方、半導体レーザ101からの光のうち、偏光プリズム104を透過したP偏光はλ/4板110により円偏光に変換され、光軸方向に可動する1次元アクチュエータ122に搭載された集光レンズ123に入射する。集光レンズで集光された光は、焦点に配置した反射ミラー124によって反射され、逆周り円偏光に変換される。反射光は光軸を同じくして同じ光路を戻り、λ/4板110により入射時と偏光方向が90°回転した直線偏光となって偏光プリズム104に入射する。すると偏光が回転しているため、この集光レンズと反射ミラー124からの反射光はS偏光となって偏光プリズム104を反射し、光ディスク108からの反射光と重なり合って偏光プリズム113に入射する。ただし光ディスク108からの反射光と反射ミラー124からの反射光は互いに直交する直線偏光となっている。偏光プリズム113は偏光プリズム104と異なり、P偏光の一部を透過させ、S偏光をほぼ100%反射させる機能を有する。これにより反射ミラー124からの反射光はほぼ100%反射され、ディスクからの反射光は一部が偏光プリズム113を透過し、一部が反射される。反射された光は偏光位相変換分離素子114に入射し、光ディスク108からの反射光と反射ミラー124からの反射光を重ねたまま、2つの光の干渉の位相差が異なる4つの光に分割されて、集光レンズ115により4分割光検出器116上に設けられた4つの受光部でそれぞれ別々に検出される。図では簡略化して2本の集光光束に分離集光されているように示しているが、実際は4本の集光光束となる。検出された信号からRF信号演算回路120により、再生RF信号(RFS)を出力する。一方、偏光プリズム113を透過した光ディスク108からの反射光は、集光レンズ117,シリンドリカルレンズ118により非点収差を与えられて4分割光検出器119に集光され、その出力信号からサーボ信号演算回路121により焦点ずれ信号(FES)とトラッキング誤差信号(TES)を出力する。焦点ずれ信号は対物レンズ107を搭載した2次元アクチュエータ106のフォーカス駆動端子にフィードバックされ焦点位置が閉ループ制御される。さらに同じ信号が反射ミラー124を搭載した1次元アクチュエータ122にもフィードバックされ対物レンズ
107と連動して反射ミラー124も駆動される。これにより光ディスク108を反射した信号光と、反射ミラー124を反射した参照光との光路差をほぼ0に保つことができる。通常の半導体レーザのコヒーレンス長は数10μmであるため、光路差の調整精度はこの範囲以下になっていればよい。トラッキング誤差信号は対物レンズ107を搭載した2次元アクチュエータのトラッキング駆動端子にフィードバックされ閉ループ制御される。
FIG. 1 shows a basic embodiment of the present invention. Light from the semiconductor laser 101 is converted into parallel light by the collimator lens 102 and transmitted through the λ / 2 plate 103 to enter the polarizing prism 104. The polarizing prism 104 has a function of transmitting almost 100% of the P-polarized light incident on the separation surface and reflecting almost 100% of the S-polarized light. At this time, by adjusting the rotation angle around the optical axis of the λ / 2 plate 103, a part of the light is reflected as the S-polarized light and the polarizing prism 104 is reflected, and a part of the light is transmitted as the P-polarized light. it can. The reflected light passes through the λ / 4 plate 105 and is converted into circularly polarized light, and is condensed on the recording film on the optical disk 108 by the objective lens 107 mounted on the two-dimensional actuator 106. The reflected light from the optical disk returns to the same optical path, is converted into parallel light by the objective lens 107, and enters the polarizing prism 104 as linearly polarized light whose rotation direction is rotated by 90 ° from the time when it is first incident by the λ / 4 plate 105. To do. Then, since the polarized light is rotated, the reflected light from the optical disk 108 becomes P-polarized light, passes through the polarizing prism 104, and enters the polarizing prism 113. On the other hand, of the light from the semiconductor laser 101, the P-polarized light transmitted through the polarizing prism 104 is converted into circularly polarized light by the λ / 4 plate 110, and the condenser lens 123 mounted on the one-dimensional actuator 122 movable in the optical axis direction. Is incident on. The light condensed by the condenser lens is reflected by the reflection mirror 124 arranged at the focal point, and converted into reverse circularly polarized light. The reflected light returns along the same optical path with the same optical axis, and enters the polarizing prism 104 as linearly polarized light whose polarization direction is rotated by 90 ° by the λ / 4 plate 110. Then, since the polarized light is rotated, the reflected light from the condensing lens and the reflecting mirror 124 becomes S-polarized light, reflects off the polarizing prism 104, and enters the polarizing prism 113 so as to overlap with the reflected light from the optical disk 108. However, the reflected light from the optical disk 108 and the reflected light from the reflecting mirror 124 are linearly polarized light orthogonal to each other. Unlike the polarizing prism 104, the polarizing prism 113 has a function of transmitting part of the P-polarized light and reflecting almost 100% of the S-polarized light. As a result, almost 100% of the reflected light from the reflecting mirror 124 is reflected, and a part of the reflected light from the disk is transmitted through the polarizing prism 113 and a part of the reflected light is reflected. The reflected light enters the polarization phase conversion / separation element 114 and is divided into four lights having different phase differences of interference between the two lights while the reflected light from the optical disk 108 and the reflected light from the reflecting mirror 124 are overlapped. Thus, the light is separately detected by the four light receiving portions provided on the four-divided photodetector 116 by the condenser lens 115. In the drawing, it is simplified and shown as being separated and collected by two condensed light beams, but actually, it becomes four condensed light beams. From the detected signal, the RF signal arithmetic circuit 120 outputs a reproduction RF signal (RFS). On the other hand, the reflected light from the optical disk 108 that has passed through the polarizing prism 113 is given astigmatism by the condensing lens 117 and the cylindrical lens 118 and is condensed on the quadrant photodetector 119, and servo signal calculation is performed from the output signal. The circuit 121 outputs a defocus signal (FES) and a tracking error signal (TES). The defocus signal is fed back to the focus drive terminal of the two-dimensional actuator 106 on which the objective lens 107 is mounted, and the focus position is controlled in a closed loop. Further, the same signal is fed back to the one-dimensional actuator 122 on which the reflection mirror 124 is mounted, and the reflection mirror 124 is driven in conjunction with the objective lens 107. Thereby, the optical path difference between the signal light reflected from the optical disk 108 and the reference light reflected from the reflecting mirror 124 can be kept substantially zero. Since the coherence length of a normal semiconductor laser is several tens of μm, the adjustment accuracy of the optical path difference only needs to be within this range. The tracking error signal is fed back to the tracking drive terminal of the two-dimensional actuator equipped with the objective lens 107 and is subjected to closed loop control.

図2は図1の4分割光検出器116の受光部配置とRF信号演算回路120の配置と機能を示す図である。4分割光検出器116は図2に示した4つの光を受光するための4つの受光部301,302,303,304を有し、それぞれ位相差0°,90°,270°,180°の干渉位相差差の干渉強度を受光する。それぞれの出力を差動増幅器305,306によって差動演算を行ったのち、2乗加算平方根演算回路307によりRF信号を検出する。   FIG. 2 is a diagram showing the arrangement and function of the light receiving section of the quadrant photodetector 116 of FIG. 1 and the RF signal arithmetic circuit 120. The quadrant photodetector 116 has four light receiving portions 301, 302, 303, and 304 for receiving the four lights shown in FIG. 2, and has phase differences of 0 °, 90 °, 270 °, and 180 °, respectively. The interference intensity of the interference phase difference is received. Each output is subjected to differential operation by the differential amplifiers 305 and 306, and then an RF signal is detected by the square addition square root operation circuit 307.

さらにこれらを数式で示し、図2に示した演算により再生RF信号が参照光によって増幅されることを説明する。PD1,PD2,PD3,PD4に入射する光の干渉強度はそれぞれ   Furthermore, these will be expressed by mathematical formulas, and explanation will be given of the fact that the reproduction RF signal is amplified by the reference light by the calculation shown in FIG. The interference intensity of light incident on PD1, PD2, PD3 and PD4 is respectively

Figure 2008243273
Figure 2008243273

Figure 2008243273
Figure 2008243273

Figure 2008243273
Figure 2008243273

Figure 2008243273
Figure 2008243273

のように表せる。これらから、図2における差動増幅器305,306の出力信号Sig1,Sig2は、 It can be expressed as From these, the output signals Sig1, Sig2 of the differential amplifiers 305, 306 in FIG.

Figure 2008243273
Figure 2008243273

Figure 2008243273
Figure 2008243273

のように表せる。したがってこれらの2乗和をとって平方根をとる演算を行うと、 It can be expressed as Therefore, when calculating the square root by taking these sums of squares,

Figure 2008243273
Figure 2008243273

のように、再生信号の電界振幅が参照光の電界振幅で増幅された信号が検出できることになる。ここでこの2乗加算の演算を行うことにより、参照光と信号光に位相差が最終的に得られる信号に影響しないことがわかる。したがって従来技術に述べられていたような、波長の数分の1という光路差調整が不要となるのである。 As described above, a signal in which the electric field amplitude of the reproduction signal is amplified by the electric field amplitude of the reference light can be detected. Here, it can be seen that the calculation of the square addition does not affect the signal in which the phase difference is finally obtained between the reference light and the signal light. Therefore, the optical path difference adjustment of a fraction of the wavelength as described in the prior art becomes unnecessary.

図3は別の実施形態として、トラッキング信号検出方式として差動プッシュプル法を用いる場合である。差動プッシュプル法ではディスクに入射する光を、回折格子801を用いて3ビームとする。そしてディスク上のメインスポットを情報トラックに配置する場合、2つのサブスポットが隣接するトラック間に配置されるように回折格子801の回転調整を行う。ここでは参照光も3ビームとなるが、これも信号光のそれぞれ対応するビーム同士で干渉させて、トラッキング誤差信号も差動演算により増幅する。また焦点ずれ信号も回折格子801による0次光を4つの各干渉位相差でそれぞれ4分割検出することにより、非点収差法の焦点ずれ信号をやはり干渉差動検出により増幅する。これを1つにパッケージ化された光検出器802により受光し、信号演算回路803により信号演算を行う。   FIG. 3 shows a case where a differential push-pull method is used as a tracking signal detection method as another embodiment. In the differential push-pull method, light incident on the disk is made into three beams using a diffraction grating 801. When the main spot on the disc is arranged on the information track, the rotation of the diffraction grating 801 is adjusted so that the two sub-spots are arranged between adjacent tracks. Here, the reference light also has three beams, which are also caused to interfere with each other by corresponding beams of signal light, and the tracking error signal is also amplified by differential calculation. The defocus signal is also detected by dividing the zero-order light from the diffraction grating 801 into four by the four interference phase differences, thereby amplifying the defocus signal by the astigmatism method. This is received by a photodetector 802 packaged in one, and a signal calculation circuit 803 performs signal calculation.

図4は図3に対応して、信号光と参照光の干渉位相差0°,180°,90°,270°の4つの干渉光に対してそれぞれメインビーム用の4分割光検出器902,サブビーム用の2分割光検出器901,903、加算アンプ904,差動増幅器905,906を用い、各4つのRF信号(RFS1,RFS2,RFS3,RFS4),焦点ずれ信号(FES1,FES2,FES3,FES4),トラッキング誤差信号(TES1,TES2,TES3,TES4)を検出する回路構成を示している。これらの差動増幅回路などは図3の信号演算回路803の中に内蔵されている。   FIG. 4 corresponds to FIG. 3 with respect to the four interference lights having the interference phase differences of 0 °, 180 °, 90 °, and 270 ° between the signal light and the reference light, respectively. Using sub-beam two-divided photodetectors 901 and 903, summing amplifier 904, differential amplifiers 905 and 906, each of four RF signals (RFS1, RFS2, RFS3, RFS4), defocus signals (FES1, FES2, FES3, FES4), a circuit configuration for detecting tracking error signals (TES1, TES2, TES3, TES4) is shown. These differential amplifier circuits and the like are built in the signal arithmetic circuit 803 in FIG.

図5はこれらの各干渉位相差の信号から、それぞれ差動検出と2乗加算平方根演算により増幅信号を検出する回路構成を示す図である。これも差動アンプ1001により0°と180°、90°と270°の差動信号を求めた後、二乗加算平方根演算回路1002により、それぞれRF信号,焦点ずれ信号,トラッキング誤差信号を求めることができる。このような構成とすると、多層ディスクなどの場合に、焦点が大きくずれた多層からの信号もれ込みに対して、検出すべき層からの光による信号を選択的に増幅でき、クロストーク低減に有利となる。   FIG. 5 is a diagram showing a circuit configuration for detecting an amplified signal from these interference phase difference signals by differential detection and square addition square root calculation. Also, after obtaining differential signals of 0 ° and 180 °, 90 ° and 270 ° by the differential amplifier 1001, an RF signal, a defocus signal, and a tracking error signal can be obtained by a square addition square root calculation circuit 1002, respectively. it can. With such a configuration, in the case of a multi-layer disc or the like, it is possible to selectively amplify a signal due to light from a layer to be detected against leakage of a signal from a multi-layer whose focus is greatly shifted, thereby reducing crosstalk. It will be advantageous.

図6(a)は前記反射ミラー124を集光レンズ123と反射ミラー124で構成される系で置き換えた時の入射光と反射光の光路と、その同位相となる波面を示している。平面波で集光レンズ123に入射された光束は、レンズ透過によりレンズの焦点を波源とする球面波に波面が変換される。この焦点に配置された反射ミラー124で反射された光は、焦点を波源としている球面波となるので、集光レンズ123で、再び平面波として変換される。   FIG. 6A shows an optical path of incident light and reflected light and a wavefront having the same phase when the reflecting mirror 124 is replaced with a system composed of a condenser lens 123 and a reflecting mirror 124. The light beam incident on the condensing lens 123 as a plane wave is converted into a spherical wave having the focal point of the lens as a wave source through lens transmission. Since the light reflected by the reflecting mirror 124 arranged at the focal point becomes a spherical wave having the focal point as a wave source, it is converted again as a plane wave by the condenser lens 123.

一方、図6(b)に示すように、反射ミラー124が傾いた時でも、反射光は集光レンズの焦点からの光であるので、反射光の光軸はずれるが同一波面で反射される。ここで、信号光と参照光の干渉はそれぞれの光線の位相が同位相となる時、偏光プリズム104において信号光干渉強度は最大となる。その為、信号光と参照光の光軸の傾きが同一でありかつ平面波である時、同位相となる面積最大となり干渉強度最大となる。なおこの時、反射ミラー傾きにより光軸が平行に多少ずれても干渉面積減少は小さく、干渉強度劣化は小さくなる。一方、信号光か参照光のどちらか一方でも平面波で無い場合は、同一位相となる面積が極端に減少するため、干渉強度が大きく劣化する。従って、本実施例においては、反射ミラーが傾いた場合でも、光軸は多少ずれるが参照光の入射角と反射角がともに平面波として高精度に一致し、干渉強度劣化が小さく信号劣化低減に有効となる。   On the other hand, as shown in FIG. 6B, even when the reflecting mirror 124 is tilted, the reflected light is light from the focal point of the condenser lens, so that the reflected light is reflected on the same wavefront although it deviates from the optical axis. Here, the interference between the signal light and the reference light has the maximum signal light interference intensity in the polarizing prism 104 when the phase of each light beam is the same. Therefore, when the inclinations of the optical axes of the signal light and the reference light are the same and are plane waves, the area having the same phase is maximized and the interference intensity is maximized. At this time, even if the optical axis is slightly deviated in parallel due to the tilt of the reflecting mirror, the decrease in interference area is small and the degradation of interference intensity is small. On the other hand, when either the signal light or the reference light is not a plane wave, the area having the same phase is extremely reduced, so that the interference intensity is greatly deteriorated. Therefore, in this embodiment, even when the reflection mirror is tilted, the optical axis is slightly shifted, but both the incident angle and the reflection angle of the reference light coincide with each other with high accuracy as a plane wave, and the interference intensity deterioration is small and effective in reducing signal deterioration. It becomes.

図7は別の実施形態として、参照光を反射ミラー124に集光する集光レンズ123直前に、ビームエキスパンダ125,126を配置する場合である。ビームエキスパンダを構成するレンズ群、例えば平凸レンズ125と平凹レンズ126は、λ/4板110から反射ミラー124の方向に進行する参照光を波面を保存し、光束径のみを任意の倍率で縮小、一方反射ミラー124からλ/4板110へ反射された参照光の光束径を前記同一の倍率で拡大されることを特徴とする。   FIG. 7 shows a case where the beam expanders 125 and 126 are arranged immediately before the condenser lens 123 that condenses the reference light on the reflection mirror 124 as another embodiment. The lens group constituting the beam expander, for example, the plano-convex lens 125 and the plano-concave lens 126 preserves the wavefront of the reference light traveling in the direction from the λ / 4 plate 110 to the reflection mirror 124, and reduces only the beam diameter at an arbitrary magnification. On the other hand, the light beam diameter of the reference light reflected from the reflection mirror 124 to the λ / 4 plate 110 is enlarged at the same magnification.

以下の式に示すように、ビームエキスパンダ125,126により反射ミラー124に集光する集光レンズ123での光束径(D)を縮小することにより、レンズの開口数
(NA)は光束径に比例して小さくなる。
As shown in the following formula, the numerical aperture (NA) of the lens is reduced to the beam diameter by reducing the beam diameter (D) at the condenser lens 123 that is condensed on the reflection mirror 124 by the beam expanders 125 and 126. Proportionally decreases.

Figure 2008243273
Figure 2008243273

なお、fはレンズの焦点距離である。反射ミラー124の位置が集光レンズ123の焦点からずれる時、反射ミラー124からの反射光が集光レンズ123を通過したとき、波面は完全な平面波に復元されず、前記焦点と反射ミラーの位置ずれ距離に依存した信号強度劣化を引き起こす。   Here, f is the focal length of the lens. When the position of the reflection mirror 124 deviates from the focus of the condenser lens 123, when the reflected light from the reflection mirror 124 passes through the condenser lens 123, the wavefront is not restored to a perfect plane wave, and the position of the focus and the reflection mirror It causes signal strength degradation depending on the shift distance.

一方、通常集光レンズの開口数を小さくすると、上記位置ずれによる波面の歪みも小さくなる傾向がある。これは、開口数が小さくなるに従い、レンズの焦点深度が深くなり、反射ミラーの位置と集光レンズの焦点の位置とのずれに対してピントが合い易くなる為である。   On the other hand, when the numerical aperture of the normal condensing lens is reduced, the wavefront distortion due to the above-mentioned positional deviation tends to be reduced. This is because as the numerical aperture decreases, the depth of focus of the lens increases, and it becomes easier to focus on the deviation between the position of the reflecting mirror and the position of the focus of the condenser lens.

図8は反射ミラー124の焦点と反射ミラーの位置ずれにより信号強度が2分の1に劣化する距離とレンズの開口径との関係を解析した一例である。これより、信号強度が2分の1に劣化する距離は、開口数が小さいほど大きくなることがわかる。従って、ビームエキスパンダ125,126を用いることにより、参照光の光束径の縮小化による開口数低減が、反射ミラー124の焦点位置からのずれに対する信号劣化低減に有効である。また、上記信号強度劣化低減は、ほぼ開口数の2乗に反比例する。   FIG. 8 shows an example in which the relationship between the distance at which the signal intensity deteriorates by one half due to the misalignment between the focal point of the reflecting mirror 124 and the reflecting mirror and the aperture diameter of the lens is analyzed. From this, it can be seen that the distance at which the signal intensity deteriorates by half increases as the numerical aperture decreases. Therefore, by using the beam expanders 125 and 126, the numerical aperture reduction by reducing the beam diameter of the reference light is effective in reducing the signal deterioration due to the deviation of the reflection mirror 124 from the focal position. The reduction in signal strength deterioration is almost inversely proportional to the square of the numerical aperture.

集光レンズ123を用い反射ミラー127に集光する手法では、反射ミラー127を集光レンズ123の焦点面近傍に保持しておく必要がある。しかし、光ディスク装置の温度変化による熱膨張により、集光レンズ123と反射ミラー127の光路長は変動し、位置ずれ距離に依存した信号強度劣化を引き起こす。   In the method of condensing on the reflecting mirror 127 using the condensing lens 123, it is necessary to hold the reflecting mirror 127 in the vicinity of the focal plane of the condensing lens 123. However, due to thermal expansion due to the temperature change of the optical disk device, the optical path lengths of the condenser lens 123 and the reflection mirror 127 vary and cause signal strength deterioration depending on the displacement distance.

図9は別の実施形態として、図1または図3の反射ミラー124に、例えば珪素とアルミニウムなどの熱膨張係数の異なる2種の材料を張り合わせた反射ミラー127を置き換えた場合である。反射ミラー127は一部を固定された、例えば片持ち梁構造となっており、反射ミラーの一部が、温度変化により2種材料の積層方向に反ることを特徴とする。例えば、外気の温度変化により、集光レンズ123と反射ミラー127を固定している1次元アクチュエータが熱膨張を起こしたとき、反射ミラー127が入射方向に反るようにして、反射ミラー127と集光レンズ123の焦点の位置ずれを抑えることができる。反射ミラー127が反る量については、参照光が照射される反射ミラー127面が、前記の伸びた距離と同一の距離となるように、反射ミラー127の膜厚や材質などを最適化することが望ましい。また、逆に1次元アクチュエータが温度変化により縮むときには、反射ミラー127は集光レンズ123とは逆側に反るようにするように反射ミラー127の材質を選択するとよい。このようにすると、温度変化による集光レンズ123の焦点と反射ミラー127の距離を一定に保つことができ、温度変化による信号強度劣化の低減に有効である。なお、反射ミラー127を片持ちとして反らせたため、温度変化したときに反射ミラー127が傾くが、前述したように本発明では反射ミラー127が集光レンズ123の焦点上にあれば、反射した球面波が集光レンズ123を通過して平面波となるので、偏光プリズム104では問題なく光を干渉することができる。   FIG. 9 shows another embodiment in which the reflection mirror 127 in which two materials having different thermal expansion coefficients such as silicon and aluminum are bonded to the reflection mirror 124 of FIG. 1 or 3 is replaced. The reflection mirror 127 has a fixed part, for example, a cantilever structure, and a part of the reflection mirror is warped in the stacking direction of the two kinds of materials due to temperature change. For example, when a one-dimensional actuator that fixes the condenser lens 123 and the reflection mirror 127 is thermally expanded due to a change in temperature of the outside air, the reflection mirror 127 and the reflection mirror 127 are collected so that the reflection mirror 127 is warped in the incident direction. The positional deviation of the focus of the optical lens 123 can be suppressed. Regarding the amount of reflection mirror 127 warping, the film thickness, material, etc. of reflection mirror 127 are optimized so that the surface of reflection mirror 127 irradiated with reference light is the same distance as the extended distance. Is desirable. Conversely, when the one-dimensional actuator contracts due to temperature change, the material of the reflecting mirror 127 may be selected so that the reflecting mirror 127 is warped on the opposite side of the condenser lens 123. In this way, the distance between the focal point of the condensing lens 123 and the reflecting mirror 127 due to temperature change can be kept constant, which is effective in reducing signal strength degradation due to temperature change. Since the reflecting mirror 127 is bent as a cantilever, the reflecting mirror 127 tilts when the temperature changes. As described above, in the present invention, if the reflecting mirror 127 is on the focal point of the condenser lens 123, the reflected spherical wave is reflected. Passes through the condenser lens 123 and becomes a plane wave, so that the polarizing prism 104 can interfere with light without any problem.

本発明により、大容量多層高速光ディスクの再生信号が安定に、高品質で検出することが可能となり、大容量ビデオレコーダや、ハードディスクデータバックアップ装置,保存情報アーカイブ装置など、幅広い産業応用が期待できる。   According to the present invention, it becomes possible to detect a reproduction signal of a large-capacity multilayer high-speed optical disk stably and with high quality, and a wide range of industrial applications such as a large-capacity video recorder, a hard disk data backup device, and a stored information archive device can be expected.

本発明の実施例に係る断面図である。It is sectional drawing which concerns on the Example of this invention. RF信号受光部と演算回路説明図である。It is RF signal light-receiving part and arithmetic circuit explanatory drawing. 差動プッシュプル法によるトラッキング検出を行う実施例に係る断面図である。It is sectional drawing which concerns on the Example which performs the tracking detection by a differential push pull method. 各干渉位相差でのRF信号,焦点ずれ信号,トラッキング誤差信号を検出する構成を示す図である。It is a figure which shows the structure which detects RF signal in each interference phase difference, a focus shift signal, and a tracking error signal. 差動検出による信号増幅を行う回路構成を示す図である。It is a figure which shows the circuit structure which performs signal amplification by differential detection. 反射ミラーの傾きの有無による入射光と反射光の光路と、その波面を示す図である。It is a figure which shows the optical path of the incident light and reflected light by the presence or absence of the inclination of a reflective mirror, and its wavefront. ビームエキスパンダにより参照光の光束径の小径化を行う実施形態に係る断面図である。It is sectional drawing which concerns on embodiment which reduces the light beam diameter of reference light with a beam expander. 開口数と信号強度が2分の1に劣化する集光レンズの焦点と反射ミラーの距離の関係である。This is the relationship between the focal point of the condensing lens and the distance between the reflecting mirrors where the numerical aperture and signal intensity deteriorate by a factor of two. 熱変形する反射ミラーを備える実施形態に係る断面図である。It is sectional drawing which concerns on embodiment provided with the reflective mirror which deforms thermally.

符号の説明Explanation of symbols

101 半導体レーザ
102 コリメートレンズ
103 λ/2板
104 偏光プリズム
105,110 λ/4板
106 2次元アクチュエータ
107 対物レンズ
108 光ディスク
109 スピンドルモータ
111,122 1次元アクチュエータ
112 コーナープリズム
113 偏光プリズム(S偏光反射率100%)
114 偏光位相変換分離素子
115,117 集光レンズ
116,119,902 4分割光検出器
118 シリンドリカルレンズ
120 RF信号演算回路
121 サーボ信号演算回路
123 集光レンズ
124 反射ミラー
125,126 ビームエキスパンダ
127 2材料で構成された反射ミラー
201 信号光偏光方向
202 参照光偏光方向
203 無偏光回折格子
204 角度選択性偏光変換素子
205 偏光分離回折格子
206,207 光学軸
301,302,303,304 受光部
305,306,905,906,1001 差動増幅器
307 2乗加算平方根演算回路
801 回折格子
802 光検出器
803 信号演算回路
901,903 2分割光検出器
904 加算アンプ
1002 二乗加算平方根演算回路
DESCRIPTION OF SYMBOLS 101 Semiconductor laser 102 Collimating lens 103 (lambda) / 2 board 104 Polarizing prism 105,110 (lambda) / 4 board 106 Two-dimensional actuator 107 Objective lens 108 Optical disk 109 Spindle motor 111,122 One-dimensional actuator 112 Corner prism 113 Polarizing prism (S polarization reflectance) 100%)
114 Polarization phase conversion separation elements 115 and 117 Condensing lenses 116, 119 and 902 Quadrant light detector 118 Cylindrical lens 120 RF signal arithmetic circuit 121 Servo signal arithmetic circuit 123 Condensing lens 124 Reflecting mirrors 125 and 126 Beam expander 127 2 Reflective mirror 201 composed of material Signal light polarization direction 202 Reference light polarization direction 203 Non-polarization diffraction grating 204 Angle selective polarization conversion element 205 Polarization separation diffraction grating 206, 207 Optical axes 301, 302, 303, 304 Light receiving unit 305, 306, 905, 906, 1001 Differential amplifier 307 Square addition square root arithmetic circuit 801 Diffraction grating 802 Photo detector 803 Signal arithmetic circuit 901, 903 Two-divided photodetector 904 Addition amplifier 1002 Square addition square root arithmetic circuit

Claims (10)

光源と、
前記光源から出射した光を第1と第2の光束に分割する第1の分割手段と、
第1の光束を光情報記録媒体上に集光する集光手段と、
前記第2の光束を参照光として反射させる反射ミラーと、
光を検出する複数の検出器とを備え、
前記第1の光束が前記光情報記録媒体で反射した信号光と前記第2の光束が前記反射ミラーで反射した前記参照光とを第1の分割手段に導いて重ね合わせて干渉させ、前記干渉させた光を前記検出器で検出する光ヘッドであって、
前記第2の光束を前記反射ミラー上にレンズで集光することを特徴とする光ヘッド。
A light source;
First splitting means for splitting the light emitted from the light source into first and second light fluxes;
Condensing means for condensing the first light flux on the optical information recording medium;
A reflection mirror that reflects the second light flux as reference light;
A plurality of detectors for detecting light,
The signal light reflected by the optical information recording medium by the first light flux and the reference light reflected by the reflection mirror by the second light flux are guided to a first splitting unit and overlapped to interfere with each other. An optical head for detecting the detected light by the detector,
An optical head characterized in that the second light flux is collected on the reflection mirror by a lens.
請求項1において、
前記レンズは、前記反射ミラー上に焦点を有することを特徴とする光ヘッド。
In claim 1,
The optical head is characterized in that the lens has a focal point on the reflection mirror.
請求項1において、
前記反射した参照光は、前記レンズを通過して前記第1の分割手段に達することを特徴とする光ヘッド。
In claim 1,
The optical head according to claim 1, wherein the reflected reference light passes through the lens and reaches the first dividing means.
請求項3において、
前記レンズを透過する前の前記第2の光束は平面波であり、
前記レンズを透過した後の前記第2の光束は球面波であり、
前記反射ミラーで反射し、前記レンズを透過する前の前記参照光は球面波であり、
前記レンズを透過した後の前記参照光は平面波であることを特徴とする光ヘッド。
In claim 3,
The second light flux before passing through the lens is a plane wave,
The second light flux after passing through the lens is a spherical wave;
The reference light reflected by the reflecting mirror and transmitted through the lens is a spherical wave,
The optical head, wherein the reference light after passing through the lens is a plane wave.
請求項1において前記第一の分割手段と前記レンズの間の光路上に光束径を変化させるビームエキスパンダを備えたことを特徴とする光ヘッド。   2. The optical head according to claim 1, further comprising a beam expander that changes a light beam diameter on an optical path between the first dividing unit and the lens. 請求項5において、
前記ビームエキスパンダよりも前記レンズ側の前記光束径は、前記ビームエキスパンダよりも前記第1の分割手段側の前記光束径よりも小さいことを特徴とする光ヘッド。
In claim 5,
The optical head according to claim 1, wherein the light beam diameter on the lens side of the beam expander is smaller than the light beam diameter on the first splitting unit side of the beam expander.
前記反射ミラーに、複数の材料を積層した構造を用いる事を特徴とする請求項1に記載の光ヘッド。   2. The optical head according to claim 1, wherein a structure in which a plurality of materials are laminated is used for the reflection mirror. 請求項7において、
温度が変化したときに、前記反射ミラーは、レンズ焦点の位置が変化する方向と同じ側に変形することを特徴とする光ヘッド。
In claim 7,
The optical head is characterized in that when the temperature changes, the reflection mirror is deformed to the same side as the direction in which the lens focal point changes.
請求項1に記載の光ヘッドであって、前記反射ミラーと集光レンズは光軸方向に可動でき、前記信号光と前記参照光の光路差が調整されることを特徴とする光ヘッド。   2. The optical head according to claim 1, wherein the reflection mirror and the condenser lens are movable in an optical axis direction, and an optical path difference between the signal light and the reference light is adjusted. 光束を第1と第2の光束に分割し、
前記第1の光束を光情報記録媒体上に集光して信号光として反射させ、
前記第2の光束を反射ミラー上にレンズで集光して参照光として反射させ、
前記信号光と前記参照光とを干渉させ、
前記干渉した光束を検出する光情報記録媒体の再生方法。
Split the luminous flux into first and second luminous flux,
Condensing the first light flux on an optical information recording medium and reflecting it as signal light;
The second light flux is collected by a lens on a reflection mirror and reflected as reference light,
Causing the signal light and the reference light to interfere with each other;
A method of reproducing an optical information recording medium for detecting the interference light beam.
JP2007080452A 2007-03-27 2007-03-27 Optical head and method for reproducing optical information recording medium Pending JP2008243273A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010044832A (en) * 2008-08-13 2010-02-25 Hitachi Media Electoronics Co Ltd Method for detecting optical information, optical pickup, and optical information recording and reproducing device
WO2010103962A1 (en) * 2009-03-13 2010-09-16 日立コンシューマエレクトロニクス株式会社 Optical information reproduction method, optical head, and optical disc apparatus
CN102314895A (en) * 2010-07-06 2012-01-11 日立民用电子株式会社 Shaven head and optical disc apparatus
US8553516B2 (en) 2010-09-22 2013-10-08 Sony Corporation Reproducing device and optical path length servo control method
KR101867316B1 (en) * 2016-07-28 2018-07-19 한국기계연구원 Focusing error detecting apparatus and method thereof

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010044832A (en) * 2008-08-13 2010-02-25 Hitachi Media Electoronics Co Ltd Method for detecting optical information, optical pickup, and optical information recording and reproducing device
WO2010103962A1 (en) * 2009-03-13 2010-09-16 日立コンシューマエレクトロニクス株式会社 Optical information reproduction method, optical head, and optical disc apparatus
JP2010218591A (en) * 2009-03-13 2010-09-30 Hitachi Ltd Optical information reproduction method, optical head, and optical disc apparatus
CN102314895A (en) * 2010-07-06 2012-01-11 日立民用电子株式会社 Shaven head and optical disc apparatus
US8553516B2 (en) 2010-09-22 2013-10-08 Sony Corporation Reproducing device and optical path length servo control method
KR101867316B1 (en) * 2016-07-28 2018-07-19 한국기계연구원 Focusing error detecting apparatus and method thereof

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