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JP5188461B2 - Optical pickup, optical information recording apparatus, and optical information reproducing apparatus - Google Patents

Optical pickup, optical information recording apparatus, and optical information reproducing apparatus Download PDF

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JP5188461B2
JP5188461B2 JP2009147181A JP2009147181A JP5188461B2 JP 5188461 B2 JP5188461 B2 JP 5188461B2 JP 2009147181 A JP2009147181 A JP 2009147181A JP 2009147181 A JP2009147181 A JP 2009147181A JP 5188461 B2 JP5188461 B2 JP 5188461B2
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邦一 大西
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Hitachi Media Electronics Co Ltd
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本発明は、光ピックアップおよびそれを搭載した光学的情報記録再生装置に関する。   The present invention relates to an optical pickup and an optical information recording / reproducing apparatus equipped with the optical pickup.

本技術に関する背景技術としては、例えば特開平7−272303号公報がある。本公報には、課題として「簡単な構成で、全体形状を小型化し得、必要に応じて組立作業を簡略化することができる光ディスク装置、光学ピックアップ及び光学ピックアップの組立方法を提供する」と記載があり、解決手段として「増幅回路15E及び15Hの前で、予め受光面E、G及びF、H間の出力信号を加算した後、増幅して出力する」と記載がある。   For example, Japanese Patent Application Laid-Open No. 7-272303 is a background art related to this technique. This publication describes, as a problem, “to provide an optical disc apparatus, an optical pickup, and an optical pickup assembling method capable of reducing the overall shape with a simple configuration and simplifying assembling work as necessary”. As a solving means, there is a description that "the output signals between the light receiving surfaces E, G, F, and H are added in advance and then amplified and output before the amplifier circuits 15E and 15H".

特開平7−272303号公報JP 7-272303 A

近年、光ディスク記録容量の大容量化を実現する手段として多層の記録層を備えた光学的情報記録媒体(以下簡単のため、光ディスクと記す。)関する技術が開発されている。   In recent years, as a means for realizing an increase in the recording capacity of an optical disk, a technique relating to an optical information recording medium (hereinafter referred to as an optical disk for the sake of simplicity) having a multi-layered recording layer has been developed.

また、光ディスクの記録層に設けられた所定の記録トラック上にレーザ光束を安定的かつ高精度に集光するための、いわゆるトラッキング制御がある。そして、このトラッキング制御信号検出方式として一般的なものに差動プッシュプル方式(以下簡単のため、この方式をDPP方式と記す。)がある。   In addition, there is so-called tracking control for stably and highly accurately condensing a laser beam on a predetermined recording track provided on a recording layer of an optical disc. As a general tracking control signal detection method, there is a differential push-pull method (hereinafter, this method is referred to as a DPP method).

本発明では、多層の記録層を備えた記録媒体に対しても安定的で精度が高い光ピックアップおよび光学的情報記録再生装置を提供することを目的とする。   An object of the present invention is to provide an optical pickup and an optical information recording / reproducing apparatus that are stable and highly accurate even for a recording medium having multiple recording layers.

上記目的は、特許請求の範囲に記載の構成により達成できる。   The above object can be achieved by the configurations described in the claims.

本発明によれば、安定的で精度が高い光ピックアップおよび光学的情報記録再生装置を提供できる。   According to the present invention, it is possible to provide a stable and highly accurate optical pickup and optical information recording / reproducing apparatus.

第1の実施例の主要部である光検出器を示す概略平面図。The schematic plan view which shows the photodetector which is the principal part of a 1st Example. 従来および本発明における光ピックアップの光学系構成をしめす概略正面図。FIG. 2 is a schematic front view showing a conventional optical system configuration of an optical pickup according to the present invention. 光検出器の従来例を示す概略平面図。The schematic plan view which shows the prior art example of a photodetector. 多層化された光ディスクの概略断面図。1 is a schematic sectional view of a multilayered optical disc. 多層化された光ディスクに入射した光束の光路を示した概略断面図。FIG. 3 is a schematic cross-sectional view showing an optical path of a light beam incident on a multilayered optical disc. 第2の実施例の主要部である光検出器を示す概略平面図。The schematic plan view which shows the photodetector which is the principal part of a 2nd Example. 第3の実施例で用いられる回折格子の形状を示す概略正面図。The schematic front view which shows the shape of the diffraction grating used by the 3rd Example. 第3の実施例で光検出器に入射する副光束スポットの状態を示す概略平面図。The schematic plan view which shows the state of the sub-light-beam spot which injects into a photodetector in a 3rd Example. 第1から第3実施例に係る光ピックアップを搭載した光学的情報記録再生装置概略図。FIG. 5 is a schematic diagram of an optical information recording / reproducing apparatus equipped with optical pickups according to first to third embodiments. 第4の実施例の主要部である光検出器を示す概略平面図。The schematic plan view which shows the photodetector which is the principal part of a 4th Example. 第5の実施例の主要部である光検出器を示す概略平面図。The schematic plan view which shows the photodetector which is the principal part of a 5th Example.

以下実施例を説明する。   Examples will be described below.

DPP方式について、簡単に説明する。   The DPP method will be briefly described.

図2は、DPP方式によるトラッキング制御信号検出手段を用いた光ピックアップの主要光学系の概略図である。   FIG. 2 is a schematic diagram of a main optical system of an optical pickup using tracking control signal detection means based on the DPP method.

半導体レーザ1から発したレーザ光束は、回折格子2などの光束分割素子によって実際に情報信号の再生または記録を行う主光束50(0次光)とトラッキング制御信号を生成するために用いられる2本の副光束51および52(±1次回折光)に分割される。そしてこれら各光束は、ハーフミラー3、コリメートレンズ4を経て対物レンズ5によって光ディスク10内の所定の記録層に各々独立に集光される。このとき主光束50の集光スポット(図示せず。)と副光束51および52の集光スポット(図示せず。)は、光ディスク10の半径方向に関する照射位置間隔が該光ディスク10の記録トラック間隔の略半分に一致するような配置で照射される。そしてこれら各集光スポットの光ディスク10からの反射光束は、再び対物レンズ5、コリメートレンズ4、ハーフミラー3を通り、さらに検出レンズ7を経て光検出器8に入射する。   Two laser beams emitted from the semiconductor laser 1 are used to generate a main light beam 50 (0th-order light) for actually reproducing or recording an information signal by a light beam splitting element such as a diffraction grating 2 and a tracking control signal. Are divided into sub-beams 51 and 52 (± first-order diffracted light). Each of these light fluxes is independently condensed on a predetermined recording layer in the optical disc 10 by the objective lens 5 through the half mirror 3 and the collimating lens 4. At this time, the condensing spot (not shown) of the main light beam 50 and the condensing spots (not shown) of the sub-light beams 51 and 52 are arranged such that the irradiation position interval in the radial direction of the optical disc 10 is the recording track interval of the optical disc 10. Irradiation is performed so as to match approximately half of the distance. Then, the reflected light beam from the optical disk 10 at each of these condensed spots passes through the objective lens 5, the collimating lens 4, and the half mirror 3 again, and then enters the photodetector 8 through the detection lens 7.

なお対物レンズ5には、これを所定の方向に駆動するためのアクチュエータ6が取り付けられており、このアクチュエータ6に後述するトラッキング制御信号をフィードバックして対物レンズの位置制御を行うことでトラッキング制御が実行される。   The objective lens 5 is provided with an actuator 6 for driving the objective lens 5 in a predetermined direction, and tracking control is performed by feeding back a tracking control signal described later to the actuator 6 to control the position of the objective lens. Executed.

ところで前記光検出器8は、例えば図3に示されるように、主光束50の光ディスク反射光からなる集光スポット60が入射する受光領域80と、副光束51および52の光ディスク反射光からなる光スポット61、62が入射する受光領域81および82が図の上下方向に並列して配置されている。このうち主光束50用の受光領域80は、例えば図中に示すように十文字状の分割線で4分割された受光面で構成され、一方、副光束用の受光領域81および82は、分割線83および84によって各々が図の上下方向に2分割された受光面で構成されている。そして分割された各受光面からはその入射光強度に応じた電流が発生し、電流−電圧変換増幅器201乃至208で各々独立に電流−電圧変換されたのち減算器210および211によって減算処理され、主光束50のプッシュプル信号(以下簡単のため、この信号をメインPP信号と記す。)と副光束51、52のプッシュプル信号が加算された信号(以下簡単のため、この信号をサブPP信号と記す。)が出力される。   By the way, for example, as shown in FIG. 3, the photodetector 8 is a light receiving region 80 on which the converging spot 60 made of the optical disk reflected light of the main light beam 50 enters and light made of the optical disk reflected light of the sub-light beams 51 and 52. Light receiving areas 81 and 82 on which the spots 61 and 62 are incident are arranged in parallel in the vertical direction of the figure. Of these, the light receiving area 80 for the main light beam 50 is constituted by a light receiving surface divided into four by a cross-shaped dividing line, for example, as shown in the figure, while the light receiving areas 81 and 82 for the sub light flux are divided lines. Each of the light receiving surfaces 83 and 84 is divided into two in the vertical direction in the figure. Then, a current corresponding to the incident light intensity is generated from each of the divided light receiving surfaces, and each current-voltage conversion is performed independently by the current-voltage conversion amplifiers 201 to 208, and then subtracted by the subtractors 210 and 211. A signal obtained by adding a push-pull signal of the main light beam 50 (hereinafter referred to as a main PP signal for simplicity) and a push-pull signal of the sub-light beams 51 and 52 (hereinafter referred to as sub PP signal for simplicity). Is output).

このとき出力されるメインPP信号とサブPP信号は、光ディスク10上の各集光スポットが上記したような配置になっているため、その信号位相が互いに180度ずれて出力される。このためこの両PP信号を増幅器212および213によってそれぞれ適当な増幅率K1およびK2で増幅したのち減算器214で減算処理することにより、メインPP信号とサブPP信号の両方に含まれる不要な直流成分や同位相の外乱成分が除去された良好なトラッキング制御信号が出力される仕組みになっている。   The main PP signal and the sub PP signal output at this time are output with their signal phases shifted from each other by 180 degrees because the respective focused spots on the optical disc 10 are arranged as described above. For this reason, both PP signals are amplified by the amplifiers 212 and 213 with appropriate amplification factors K1 and K2, respectively, and then subtracted by the subtractor 214, so that unnecessary DC components included in both the main PP signal and the sub PP signal are obtained. In other words, a good tracking control signal from which disturbance components having the same phase are removed is output.

このようにDPP方式は、簡単な光学系構成によって、例えば対物レンズのトラッキング変位などに伴って生じるトラッキング制御信号のオフセット等を除去し、高品質のトラッキング制御信号を安定的に検出することができるという利点があり、有効なトラッキング制御信号検出手段として広く用いられている。なお以下では、上記したようにトラッキング制御信号を検出するために構成された減算器210および211と増幅器212および213と減算器214からなる演算回路をトラッキング制御信号検出回路500と記する。   As described above, the DPP method can remove a tracking control signal offset caused by tracking displacement of an objective lens, for example, with a simple optical system configuration, and can stably detect a high-quality tracking control signal. It is widely used as an effective tracking control signal detection means. Hereinafter, an arithmetic circuit including subtractors 210 and 211, amplifiers 212 and 213, and subtracter 214 configured to detect a tracking control signal as described above is referred to as tracking control signal detection circuit 500.

なお、光ピックアップにおける対物レンズ5の位置制御は、上記したトラッキング制御だけに限定されるものではなく、当然のことながら光軸方向に沿った位置制御、いわゆるフォーカス制御も同時に行われる。そしてこのフォーカス制御に用いられるフォーカス制御信号の検出方式としては、例えば非点収差方式などが一般的に用いられており、上記トラッキング制御信号と同様に、例えば図3に示した光検出器8内の各受光面で検出された信号から所定の演算回路を経て生成可能である。   Note that the position control of the objective lens 5 in the optical pickup is not limited to the tracking control described above, and naturally, position control along the optical axis direction, so-called focus control, is simultaneously performed. As a detection method of the focus control signal used for the focus control, for example, an astigmatism method is generally used, and, for example, in the photodetector 8 shown in FIG. These signals can be generated from signals detected on the respective light receiving surfaces through a predetermined arithmetic circuit.

このように、DPP方式は広く用いられている方式である。   As described above, the DPP method is a widely used method.

しかしながら、このようなDPP方式によるトラッキング制御信号検出手段を記録層が多層化された光ディスクの再生または記録を行なう光ピックアップまたは光学的情報記録再生装置に用いた場合、新たに以下の課題が生じる。   However, when such a tracking control signal detection means based on the DPP method is used for an optical pickup or an optical information recording / reproducing apparatus for reproducing or recording an optical disk having a multi-layered recording layer, the following new problems arise.

すなわち、多層化された光ディスク内の各記録層の中で実際に信号の記録または再生の対象になっている記録層(以下簡単のため、この記録層を対象層と記す。)に各光束を集光した場合、その光量の一部がこの対象層を反射せず、対象層以外の記録層で反射してしまい実際の信号検出には寄与しない不要光束となって、本来の信号光束とほぼ同様の光路をたどって光検出器内の各受光面に入射してしまうという問題が生じる。この受光面に入射した不要光束は受光面上で本来の信号光束と干渉をおこし、その干渉縞による光量アンバランスによって、結果的に各受光面から出力される信号に不要な外乱成分が漏れ込んでしまう。   That is, each light beam is applied to a recording layer that is actually a signal recording or reproducing target (hereinafter, this recording layer is referred to as a target layer for the sake of simplicity) among the recording layers in the multilayered optical disc. When condensed, a part of the amount of light does not reflect this target layer, but is reflected by the recording layer other than the target layer and becomes an unnecessary light beam that does not contribute to actual signal detection, and is almost the same as the original signal light beam. There arises a problem that the light follows the same optical path and enters each light receiving surface in the photodetector. The unwanted light flux incident on the light receiving surface interferes with the original signal light flux on the light receiving surface, and unnecessary disturbance components leak into the signal output from each light receiving surface as a result of the light quantity imbalance due to the interference fringes. It will end up.

この現象を図4に示したような2層の記録層(層間隔δ)100および101を備えた光ディスク10を例にとって具体的に説明する。   This phenomenon will be specifically described by taking as an example an optical disc 10 having two recording layers (layer spacing δ) 100 and 101 as shown in FIG.

例えば図5は、図4と同じ2層の記録層100および101を持つ光ディスク10に主光束50および副光束51、52(図示せず)を図の下側から集光させた状態を概略的に示した図である。   For example, FIG. 5 schematically shows a state in which a main light beam 50 and sub-light beams 51 and 52 (not shown) are condensed from the lower side of the drawing onto the optical disk 10 having the same two recording layers 100 and 101 as FIG. It is the figure shown in.

まず図5(a)は、各光束が手前側(図の下側)の記録層100上に集光した場合、すなわち記録層100が対象層である場合を示している。このような場合、記録層100上に集光された光スポットの光量の一部が記録層100を透過し、その奥側(図の上側)にある記録層101で反射して不要光束53となる。   First, FIG. 5A shows a case where each light beam is condensed on the recording layer 100 on the near side (the lower side in the figure), that is, a case where the recording layer 100 is a target layer. In such a case, a part of the light amount of the light spot condensed on the recording layer 100 is transmitted through the recording layer 100 and reflected by the recording layer 101 on the back side (upper side in the figure) to be an unnecessary light beam 53. Become.

また図5(b)は、前記図5(a)の場合とは逆に、各光束が奥側(図の上側)の記録層101上に集光した場合、すなわち記録層101が対象層である場合を示している。このような場合、光束は手前(図の下側)にある記録層100を一旦透過したのち記録層101上に集光されるが、このとき一部の光量が記録層100を反射して不要光束54となる。   5B shows the case where each light beam is condensed on the recording layer 101 on the back side (upper side in the figure), that is, the recording layer 101 is the target layer, contrary to the case of FIG. It shows a case. In such a case, the light beam once passes through the recording layer 100 on the near side (the lower side of the figure) and then is condensed on the recording layer 101. At this time, a part of the light quantity reflects the recording layer 100 and is unnecessary. A light beam 54 is obtained.

このような不要光束53、54は、いずれも本来の信号光束とほぼ同様の光路をたどって光検出器に達するが、このとき光検出器内の各受光面上に大きく広がって照射される。そしてその一部の光が各受光領域上に照射される本来の信号光束に重なり干渉が生じる。その結果、各受光領域上で明暗の干渉縞が生じ、その干渉縞によって生じた局所的な光量アンバランスにより、各受光面から検出される信号に不要な外乱成分が漏れこんでしまう。   Such unnecessary light fluxes 53 and 54 follow the optical path almost the same as the original signal light flux and reach the photodetector, but at this time, they are irradiated with a large spread on each light receiving surface in the photodetector. Then, a part of the light overlaps with an original signal light beam irradiated on each light receiving region, thereby causing interference. As a result, bright and dark interference fringes are generated in each light receiving region, and unnecessary disturbance components leak into signals detected from the respective light receiving surfaces due to local light quantity imbalance caused by the interference fringes.

そして特に、DPP方式によるトラッキング制御信号検出に用いられるサブPP信号は、一般的にメインPP信号に比べて信号強度が小さく、このために上記した不要光束と信号光束との干渉による光量アンバランスが大きく影響し、実際の信号振幅に対して比較的大きな外乱成分が漏れこんでしまう。その結果、DPP方式によって検出されたトラッキング制御信号に大きな波形歪や揺らぎが発生し、信号品質が劣化してしまう。   In particular, the sub PP signal used for tracking control signal detection by the DPP method generally has a signal intensity smaller than that of the main PP signal. Therefore, the light amount imbalance due to the interference between the unnecessary light beam and the signal light beam is not generated. This greatly affects and a relatively large disturbance component leaks from the actual signal amplitude. As a result, large waveform distortion and fluctuation occur in the tracking control signal detected by the DPP method, and the signal quality is deteriorated.

なお、このような不要光束と信号光束の干渉がサブPP信号に及ぼす影響度合いについて発明者が検討したところ、前記干渉によって生じる各受光領域内の光量アンバランスのうち、サブPP信号検出用受光領域(図3における受光領域81および82)内に設けた分割線(図3における83および84)の上およびその近傍で発生する光量アンバランスが、サブPP信号の品質に最も悪影響を及ぼすことが判明した。   The inventor examined the degree of influence of the interference between the unnecessary light flux and the signal light flux on the sub PP signal. Of the light quantity imbalance in each light receiving area caused by the interference, the light receiving area for detecting the sub PP signal is used. It has been found that the light quantity imbalance generated on and near the dividing lines (83 and 84 in FIG. 3) provided in (light receiving areas 81 and 82 in FIG. 3) has the most adverse effect on the quality of the sub PP signal. did.

一方、メインPP信号やサブPP信号それ自体は、主に各受光領域に集光される光スポット(すなわち図3の60乃至62)各々のスポット周辺部での光量変化によって生成されており、光ディスクの情報信号記録密度が高く、それに伴い記録トラック間隔が狭く設定されているディスクほどその傾向が大きいこともわかっている。   On the other hand, the main PP signal and the sub PP signal itself are generated mainly by the change in the amount of light at the periphery of each spot of the light spots (ie, 60 to 62 in FIG. 3) focused on each light receiving area. It is also known that the higher the information signal recording density is, the higher the tendency is as the recording track interval is narrower.

以上の状況を踏まえ、DPP方式によるトラッキング制御信号検出手段を用い、かつ記録層が2層以上に多層化された光ディスクに情報信号を記録または記録された情報信号を再生する機能を備えた光ピックアップおよびそれを搭載した光学的情報再生装置において、対象層以外の記録層から生じた不要光束と本来の信号光束が光検出器の各受光領域上で干渉することによって生じるトラッキング制御信号の品質劣化を良好に改善し、安定的かつ高精度のトラッキング制御信号を検出できる光ピックアップおよびそれを搭載した光学的情報再生装置を提供することにある。   Based on the above situation, an optical pickup using a tracking control signal detection means based on the DPP method and having a function of recording an information signal on an optical disc having two or more recording layers or reproducing the recorded information signal And in an optical information reproducing apparatus equipped with the same, the quality deterioration of the tracking control signal caused by the interference between the unnecessary light beam generated from the recording layer other than the target layer and the original signal light beam on each light receiving area of the photodetector. An object of the present invention is to provide an optical pickup that can be satisfactorily improved and can detect a stable and highly accurate tracking control signal, and an optical information reproducing apparatus equipped with the optical pickup.

図1は第1の実施例の主要部である光検出器の構成を示した図である。なお図1においては、既に図3で説明した光検出器と同じ構成要素には同じ番号を付している。   FIG. 1 is a diagram showing a configuration of a photodetector which is a main part of the first embodiment. In FIG. 1, the same components as those of the photodetector already described with reference to FIG.

また本実施例における光ピックアップの光学系構成は、例えば図2に示した光ピックアップと同様の構成で構わない。図2と異なる点は、光検出器8内の受光面パターンである。図1に示した本実施例の光検出器8の受光面パターンと、図3に示した光検出器8の受光面パターンを比較すると明らかなように、本実施例では副光束の集光スポット61および62がそれぞれ入射する受光領域81および82の中央部分割線(図3の従来例における分割線83および84にあたる。)上に、短辺側の幅Wが後述するような所定の寸法に設定された遮光帯または不感帯73および74を設けてある。このうち遮光帯については、例えばアルミニウム等の光を通さない媒体を受光面上に蒸着することで、この遮光帯でカバーされた受光面に直接光束が入射しないようにすることで実現できる。これにより本実施例に対応していない光ピックにも簡易的に本実施例を適用できる。また不感帯については、例えば該当部分の受光面を削除するなどして、その部分に実際に光束が入射してもそれに応じた信号電流が発生しないようにすることで実現できる。   The optical system configuration of the optical pickup in this embodiment may be the same as that of the optical pickup shown in FIG. A difference from FIG. 2 is a light receiving surface pattern in the photodetector 8. As is clear from the comparison of the light receiving surface pattern of the photodetector 8 of this embodiment shown in FIG. 1 and the light receiving surface pattern of the photodetector 8 shown in FIG. The width W on the short side is set to a predetermined dimension as will be described later on the center parting line (corresponding to parting lines 83 and 84 in the conventional example of FIG. 3) of the light receiving regions 81 and 82 into which 61 and 62 respectively enter. A set shading zone or dead zone 73 and 74 is provided. Of these, the light shielding band can be realized by depositing a light-impermeable medium such as aluminum on the light receiving surface so that the light beam does not directly enter the light receiving surface covered with the light shielding band. Thus, the present embodiment can be easily applied to an optical pick that is not compatible with the present embodiment. In addition, the dead zone can be realized by, for example, deleting the light receiving surface of the corresponding part so that a signal current corresponding to the light beam is not generated even if the light beam is actually incident on the part.

なお上記遮光帯としては、上記したようなアルミニウム等の全波長帯域の光に対して透過率がほぼゼロとなる媒体に限定されるものではなく、例えば特定の波長帯に光に対してのみ透過率がほぼゼロとなるような波長選択性ある媒体を遮光帯としても構わない。   The light-shielding band is not limited to a medium whose transmittance is almost zero with respect to light in the entire wavelength band such as aluminum as described above. For example, it transmits only light in a specific wavelength band. A medium having wavelength selectivity such that the rate is substantially zero may be used as the light shielding band.

これにより安価に本実施例に対応する光ピックアップを生成できる。このような遮光帯または不感帯を副光束用の受光領域81、82上に設けることにより、前記したような多層ディスクにおける再生または記録対象層以外の記録層から生じる不要光束と記録・再生対象層から得られる本来の信号光束との干渉が生じても、それによってサブPP信号に漏れ込む外乱成分を効果的に低減できる。   Thereby, an optical pickup corresponding to the present embodiment can be generated at low cost. By providing such a light-shielding zone or dead zone on the light-receiving areas 81 and 82 for the sub-beams, the unwanted light flux generated from the recording layer other than the reproduction or recording target layer and the recording / reproduction target layer in the multi-layer disc as described above. Even if interference with the original signal light beam obtained occurs, it is possible to effectively reduce the disturbance component that leaks into the sub PP signal.

一方、サブPP信号それ自体は、上記したように主に各受光領域に集光される各光スポットの周辺部での光量変化によって生成されるので、上記遮光帯または不感帯による影響はほとんど無い。したがってその結果、記録層が多層化された光ディスクにおいても、DPP方式によるトラッキング制御信号を高精度かつ安定的に検出することができる。   On the other hand, since the sub PP signal itself is generated mainly by the change in the amount of light at the periphery of each light spot condensed in each light receiving region as described above, there is almost no influence by the light shielding zone or the dead zone. Therefore, as a result, even in an optical disc having a multi-layered recording layer, a tracking control signal based on the DPP method can be detected with high accuracy and stability.

なお、上記遮光帯または不感帯の短辺側の幅Wに関しては、発明者の検討の結果、受光領域81および82に入射する副光束の集光スポット61および62の直径に対して約20%〜40%の範囲内に設定することが上記外乱成分の点で最も効果的であることがわかっている。さらに具体的に言えば、通常の光ピックアップでは受光領域81および82に入射する副光束の集光スポット61および62の直径は約100μm程度になるように設計するのが最も一般的なので、上記の遮光帯または不感帯短辺側の幅Wは約20μm〜40μm程度の範囲内に設定するのが望ましい。   The width W on the short side of the light-shielding zone or dead zone is about 20% to the diameter of the condensing spots 61 and 62 of the sub-beams incident on the light-receiving regions 81 and 82 as a result of the inventors' investigation. It has been found that setting within the range of 40% is most effective in terms of the disturbance component. More specifically, in a normal optical pickup, the diameter of the condensing spots 61 and 62 of the sub-beams incident on the light receiving regions 81 and 82 is most commonly designed to be about 100 μm. The width W on the short side of the light shielding zone or dead zone is preferably set within a range of about 20 μm to 40 μm.

次に第2の実施例について図6を用いて説明する。   Next, a second embodiment will be described with reference to FIG.

図6は第2の実施例の主要部を示したものである。また本図においても、図1および図3に示した構成要素と同じ構成要素には同じ番号を付している。   FIG. 6 shows the main part of the second embodiment. Also in this figure, the same components as those shown in FIGS. 1 and 3 are denoted by the same reference numerals.

本実施例は、図1に示した第1実施例のような遮光帯または不感帯を設ける代わりに、副光束用受光領域81、82内に設けた本来の分割線83、84の上下に新たに83、84に略平行な分割線85および86と87および88を設け、この各3本ずつの分割線で受光領域81を81a乃至81dの4つの受光面に、受光領域82を82a乃至82dの4つの受光面にそれぞれ分割している。なおこの時、分割線85と86の間隔および分割線87と88の間隔Wは、図1に示した第1実施例における遮光帯または不感帯の短辺側の幅Wと同程度の寸法になっている。このように4分割された受光面のうち、例えば受光面81aから電流−電圧変換増幅器201を経て信号線301から出力した信号と、受光面81dから電流−電圧変換増幅器202を経て信号線301から出力した信号とからサブPP信号を生成すると、この信号は図1で示した第1の実施例の光検出器から得られるサブPP信号と全く同等の信号になる。全く同様に受光面82aから電流−電圧変換増幅器207を経て信号線305から出力した信号と、受光面82dから電流−電圧変換増幅器208を経て信号線308から出力した信号とから生成されたサブPP信号も第1の実施例の光検出器から得られるサブPP信号と全く同等の信号になる。一方、受光面81aあるいは受光面82aから電流−電圧変換増幅器201あるいは207を経て検出された信号と受光面81bあるいは受光面82bから電流−電圧変換増幅器209あるいは211を経て検出された信号を加算器215あるいは217で加算処理し信号線302あるいは306から出力した信号と、受光面81dあるいは受光面82dから電流−電圧変換増幅器202あるいは208を経て検出された信号と受光面81cあるいは受光面82cから電流−電圧変換増幅器210あるいは212を経て検出された信号を加算器216あるいは218で加算処理し信号線303あるいは307から出力した信号とからサブPP信号を生成すると、この信号は図3で示した従来の光検出器から得られるサブPP信号と全く同等の信号になる。そこで本実施例では、切り替えスイッチ401および402を用いてサブPP信号生成する信号線を前記のように選択的に切り替えることで、1個の光検出器で本発明の光検出器と従来の光検出器の両方の機能を兼用させることができる。したがって光ディスクの種類、例えば多層化されたディスクか従来の単層記録のディスクかによって上記の機能を使い分けることで、光ピックアップの汎用性を向上させることができる。   In this embodiment, instead of providing a light shielding zone or a dead zone as in the first embodiment shown in FIG. 1, newly above and below the original dividing lines 83 and 84 provided in the sub-beam light receiving areas 81 and 82 are newly provided. 83, 84 are provided with dividing lines 85, 86, 87, and 88, and each of these three dividing lines provides light receiving area 81 on four light receiving surfaces 81a to 81d and light receiving area 82 on 82a to 82d. Each is divided into four light receiving surfaces. At this time, the interval between the dividing lines 85 and 86 and the interval W between the dividing lines 87 and 88 are approximately the same as the width W on the short side of the light shielding zone or dead zone in the first embodiment shown in FIG. ing. Among the light receiving surfaces divided into four in this way, for example, a signal output from the light receiving surface 81a via the current-voltage conversion amplifier 201 and the signal line 301, and a light receiving surface 81d from the signal line 301 via the current-voltage conversion amplifier 202. When a sub PP signal is generated from the output signal, this signal becomes exactly the same signal as the sub PP signal obtained from the photodetector of the first embodiment shown in FIG. In exactly the same manner, the sub PP generated from the signal output from the signal line 305 via the current-voltage conversion amplifier 207 from the light receiving surface 82a and the signal output from the signal line 308 via the current-voltage conversion amplifier 208 from the light receiving surface 82d. The signal is also exactly the same as the sub PP signal obtained from the photodetector of the first embodiment. On the other hand, the signal detected from the light receiving surface 81a or the light receiving surface 82a via the current-voltage conversion amplifier 201 or 207 and the signal detected from the light receiving surface 81b or the light receiving surface 82b via the current-voltage conversion amplifier 209 or 211 are added. A signal output from the signal line 302 or 306 after addition processing at 215 or 217, a signal detected from the light receiving surface 81d or the light receiving surface 82d via the current-voltage conversion amplifier 202 or 208, and a current from the light receiving surface 81c or the light receiving surface 82c. When the signal detected via the voltage conversion amplifier 210 or 212 is added by the adder 216 or 218 and the sub PP signal is generated from the signal output from the signal line 303 or 307, this signal is converted into the conventional signal shown in FIG. Is exactly the same as the sub PP signal obtained from the photo detector It becomes No.. Therefore, in this embodiment, the signal line for generating the sub PP signal is selectively switched as described above by using the changeover switches 401 and 402, so that the photodetector of the present invention and the conventional light can be obtained with one photodetector. Both functions of the detector can be combined. Therefore, the versatility of the optical pickup can be improved by properly using the above functions depending on the type of optical disk, for example, a multilayered disk or a conventional single-layer recording disk.

次に第3の実施例を図7および図8を用いて説明する。本実施例では光ピックアップの光学系構成および光検出器8の構成は、それぞれ図2および図3に示した構成と同様かまわない。その代わり光束分割素子として用いられる回折格子2が従来の格子と異なる構造を備えている。図7は本実施例で用いられる回折格子2の構造を示した概略平面図である。本実施例では回折格子2を格子溝方向(すなわち回折格子2上でディスク半径方向に相当する方向)に対して略垂直な方向(すなわち回折格子2上でディスクの接線方向に相当する方向)に延びた2本の分割線によって領域21、22および23の3領域に分割されており、このうち中央部領域22を挟む2領域21および23には格子溝が刻まれているが、中央部領域22には格子は透明平板となっている。   Next, a third embodiment will be described with reference to FIGS. In the present embodiment, the optical system configuration of the optical pickup and the configuration of the photodetector 8 may be the same as those shown in FIGS. 2 and 3, respectively. Instead, the diffraction grating 2 used as a light beam splitting element has a different structure from the conventional grating. FIG. 7 is a schematic plan view showing the structure of the diffraction grating 2 used in this embodiment. In this embodiment, the diffraction grating 2 is placed in a direction substantially perpendicular to the grating groove direction (that is, the direction corresponding to the disk radial direction on the diffraction grating 2) (that is, the direction corresponding to the tangential direction of the disk on the diffraction grating 2). It is divided into three regions 21, 22, and 23 by two extending dividing lines. Of these, the lattice regions are engraved in the two regions 21 and 23 that sandwich the central region 22. In 22, the lattice is a transparent flat plate.

このような構造の回折格子2にレーザ光源から出射された光束が入射すると、中央部領域22を通過する光束部分だけが回折せず、回折して主光束から分離した副光束は中央部分だけが略帯状に抜けた状態の光束となる。このため光ディスクを経て最終的に光検出器8内の受光領域81および82に入射した副光束の集光スポットも図8に示すように、ちょうど分割線83、84上およびその近傍に入射するはずの光束部分が帯状に抜けて、61aと61bおよび62aと62bのように2分割された集光スポットとなって各受光面に入射する。   When the light beam emitted from the laser light source enters the diffraction grating 2 having such a structure, only the light beam portion passing through the central region 22 is not diffracted, and only the central light beam is diffracted and separated from the main light beam. The light flux is in a state of being removed in a substantially band shape. For this reason, the condensing spot of the sub-light beam finally incident on the light receiving areas 81 and 82 in the photodetector 8 through the optical disk should also be incident on the dividing lines 83 and 84 and in the vicinity thereof, as shown in FIG. The light flux part of the light beam passes through in a band shape, and becomes a condensing spot divided into two like 61a and 61b and 62a and 62b, and is incident on each light receiving surface.

このため光検出器8の受光領域が、遮光帯や不感帯を設けていない構成であっても、図1に示した第1の実施例と同様の効果を得ることができる。   For this reason, even if the light receiving region of the photodetector 8 has a configuration in which no light shielding zone or dead zone is provided, the same effect as that of the first embodiment shown in FIG. 1 can be obtained.

一般に、本実施例のように回折格子の構造を図7のような3分割構造にする方が、光検出器のような精密で高価な部品に遮光帯や不感帯を設けるよりも、コスト面や作業性の面で有利であるという利点がある。   In general, the structure of the diffraction grating as shown in FIG. 7 as in this embodiment is more cost-effective than providing a light-shielding zone or dead zone in a precise and expensive component such as a photodetector. There is an advantage that it is advantageous in terms of workability.

なお、図7に示した3分割格子の中央部領域22の幅W‘については、光検出器8の受光領域81および82上の集光スポット61aと61bあるいは62aと62b間の間隔Wが、図1の実施例における遮光帯や不感帯のWと同等になるように設計されることが望ましい。   For the width W ′ of the central region 22 of the three-part grid shown in FIG. 7, the interval W between the focused spots 61a and 61b or 62a and 62b on the light receiving regions 81 and 82 of the photodetector 8 is It is desirable to design so as to be equivalent to W of the shading zone or the dead zone in the embodiment of FIG.

次に本発明の第4の実施例を図10を用いて説明する。本実施例では、図1に示した本発明の第1の実施例と同様、副光束用受光領域81および82の中央部分割線上に所定の遮光帯または不感帯73および74を設けてあるが、さらに各受光領域81,82に前記中央部分割線に対して略垂直な分割線を設けることにより、それぞれの受光領域を主光束用受光領域80と同様に4分割している。このように主光束用受光領域80以外に副光束用受光領域81および82も4分割する目的は、この副光束用受光領域81および82でも主光束用受光領域80と同様に非点収差方式によるフォーカス制御信号を検出するためである。なお、主光束用受光領域80および副光束用受光領域81および82のそれぞれから非点収差方式によるフォーカス制御信号を検出するためには、図10中に示すように、フォーカス制御信号検出回路501内に設けた加算器228乃至235と減算器236および237からなる演算回路が用いられるが、非点収差方式によるフォーカス誤差信号の検出については、既に公知の技術であるのでこれ以上の詳しい説明は省略する。なおフォーカス制御信号検出回路501内には上記した加算器および減算器以外に、副光束用受光領域81および82で検出されたフォーカス制御信号を所定の増幅率K3で増幅する増幅器238とこの増幅された副光束のフォーカス制御信号と主光束用受光領域80で検出された主光束のフォーカス制御信号とを加算処理する加算器239が配置されている。このように主光束のフォーカス制御信号と副光束のフォーカス制御信号とを加算処理した信号を新たなフォーカス制御信号とする手法は、差動非点収差方式(DAD方式)と呼ばれ、非点収差方式によるフォーカス制御信号内に漏れこむ外乱成分を除去し良好なフォーカス制御信号を検出するための有効な手法であるが、この方式自体は既に公知の技術であるので詳細な説明は省略する。なおフォーカス制御信号検出回路501内には、上記したような主光束のフォーカス制御信号と副光束のフォーカス制御信号が加算処理された信号と従来どおり主光束からのみ生成されたフォーカス制御信号をいずれかを切り替えて出力するための切り替えスイッチ403が設けられており、再生あるいは記録対象の光ディスクの種類などに応じてどちらのフォーカス制御信号を出力するか選択的に切り替えることができる。なお本実施例では、上記したフォーカス制御信号検出回路501以外に図1、図6などの実施例と同様のトラッキング制御信号検出回路500も配置されているが、このトラッキング制御信号検出回路の詳細については、既に図1、図3、図6等で説明しているので、ここでは詳しい説明は省略する。   Next, a fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, as in the first embodiment of the present invention shown in FIG. 1, predetermined light-shielding bands or dead bands 73 and 74 are provided on the center parting lines of the sub-beam light receiving areas 81 and 82. Further, by providing each light receiving region 81, 82 with a dividing line that is substantially perpendicular to the central part dividing line, each light receiving region is divided into four as with the main light receiving region 80. The purpose of dividing the sub-beam light-receiving areas 81 and 82 in addition to the main light-beam light-receiving area 80 in this way is to use the astigmatism method in the sub-beam light-receiving areas 81 and 82 as well as the main light-beam light-receiving area 80. This is for detecting the focus control signal. In order to detect the focus control signal by the astigmatism method from each of the main light beam receiving area 80 and the sub light beam light receiving areas 81 and 82, as shown in FIG. Although an arithmetic circuit comprising adders 228 to 235 and subtracters 236 and 237 provided in FIG. 1 is used, the detection of the focus error signal by the astigmatism method is already a well-known technique, and thus further detailed description is omitted. To do. In addition to the adder and subtractor described above, the focus control signal detection circuit 501 includes an amplifier 238 for amplifying the focus control signal detected in the sub-beam light receiving areas 81 and 82 at a predetermined amplification factor K3 and the amplified signal. An adder 239 for adding the sub-beam focus control signal and the main beam focus control signal detected in the main light-receiving area 80 is disposed. A method of adding a signal obtained by adding the focus control signal of the main light beam and the focus control signal of the sub light beam to a new focus control signal is called a differential astigmatism method (DAD method), and astigmatism. This method is an effective method for detecting a good focus control signal by removing a disturbance component leaking into the focus control signal by this method. However, since this method itself is a known technique, detailed description thereof is omitted. In the focus control signal detection circuit 501, either a signal obtained by adding the focus control signal of the main light beam and the focus control signal of the sub light beam as described above or a focus control signal generated only from the main light beam as in the conventional case. A change-over switch 403 is provided for switching and outputting, and it is possible to selectively switch which focus control signal is output according to the type of the optical disk to be reproduced or recorded. In this embodiment, in addition to the focus control signal detection circuit 501 described above, a tracking control signal detection circuit 500 similar to that in the embodiments of FIGS. 1 and 6 is also provided. Details of this tracking control signal detection circuit are provided. Has already been described with reference to FIGS. 1, 3, 6, etc., and detailed description thereof will be omitted here.

次に本発明の第5の実施例を図11を用いて説明する。本実施例では、図6に示した本発明の第2の実施例とほぼ同様の受光面構成になっているが、さらに副光束用受光領域81および82について、その分割線83、85、86および84、87、88に対して略垂直な分割線を設けることにより、それぞれの受光領域を全部で8領域ずつ分割している。これは図6に示した本発明の第2の実施例と同様、トラッキング制御信号検出回路500によってトラッキング制御信号検出を行なうとともに、図10に示した本発明の第4の実施例と同様、フォーカス制御信号501によってフォーカス制御信号検出も行なうことができるような構成になっている。トラッキング制御信号検出方式およびフォーカス制御信号検出方式それぞれの詳細な内容は、既に他の実施例で説明した内容と重複するので、ここでは詳細な説明は省略するが、本実施例のような構成にすることで、フォーカス制御信号とトラッキング制御信号のいずれもが、本発明の受光面構成による信号か、あるいは従来の受光面構成による信号かのどちらかを選択的に切り替えて検出することができる。   Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, the light receiving surface configuration is almost the same as that of the second embodiment of the present invention shown in FIG. 6, but the dividing lines 83, 85, 86 of the light receiving areas 81 and 82 for the sub-beams are further provided. , 84, 87, and 88, the light receiving areas are divided into eight areas in total by providing substantially perpendicular dividing lines. As in the second embodiment of the present invention shown in FIG. 6, the tracking control signal detection circuit 500 detects the tracking control signal, and in the same way as in the fourth embodiment of the present invention shown in FIG. The focus control signal can be detected by the control signal 501. The detailed contents of each of the tracking control signal detection method and the focus control signal detection method are the same as those already described in the other embodiments, so that detailed description is omitted here, but the configuration as in this embodiment is used. As a result, either the focus control signal or the tracking control signal can be selectively switched between the signal based on the light receiving surface configuration of the present invention or the signal based on the conventional light receiving surface configuration.

ところで、本発明を用いた光ピックアップとしては、以上の実施例で説明した光学系構成あるいは受光面構成に限定されるものではなく、トラッキング制御信号検出方式としてDPP方式もしくはDPP方式相当の検出方式を採用した光ピックアップまたはそれを搭載した光学的情報再生装置であるならば、どのような光学系構成あるいは受光面構成であっても一向に構わない。   By the way, the optical pickup using the present invention is not limited to the optical system configuration or the light receiving surface configuration described in the above embodiments, and a DPP method or a detection method equivalent to the DPP method is used as a tracking control signal detection method. Any optical system configuration or light receiving surface configuration can be used as long as the optical pickup is employed or an optical information reproducing apparatus equipped with the optical pickup.

図9は、第1から第4実施例に係る光ピックアップを搭載した光学的情報記録再生装置概略図である。900は光ディスク、910はレーザ点灯回路、920は光ピックアップ、930はスピンドルモータ、940はスピンドルモータ駆動回路、950はアクセス制御回路、960はアクチュエータ駆動回路、970はサーボ信号生成回路、980は情報信号再生回路、990は情報信号記録回路、9000はコントロール回路である。コントロール回路9000、サーボ信号生成回路970、アクチュエータ駆動回路960は、光ピックピックアップ920からの出力に応じて、アクチュエータを制御する。本実施例における光ピックアップからの出力をアクチュエータ制御に用いることにより、安定的かつ高精度の情報記録や情報再生ができる。   FIG. 9 is a schematic diagram of an optical information recording / reproducing apparatus equipped with the optical pickups according to the first to fourth embodiments. 900 is an optical disk, 910 is a laser lighting circuit, 920 is an optical pickup, 930 is a spindle motor, 940 is a spindle motor drive circuit, 950 is an access control circuit, 960 is an actuator drive circuit, 970 is a servo signal generation circuit, and 980 is an information signal A reproduction circuit, 990 is an information signal recording circuit, and 9000 is a control circuit. The control circuit 9000, the servo signal generation circuit 970, and the actuator drive circuit 960 control the actuator according to the output from the optical pick pickup 920. By using the output from the optical pickup in this embodiment for actuator control, stable and highly accurate information recording and information reproduction can be performed.

上記した各手段を用いることにより、記録層が多層化された光ディスクから情報信号を再生もしくは記録層への情報信号の記録を行う際に、再生または記録の対象層以外の記録層から生じる不要光束と本来の信号光束との干渉によって生じるトラッキング制御信号の品質低下を良好に改善し、安定的かつ高精度のトラッキング制御信号を検出することができる。   By using each of the above-mentioned means, an unnecessary light beam generated from a recording layer other than the target layer to be reproduced or recorded when an information signal is reproduced or recorded on the recording layer from an optical disc having a multilayered recording layer It is possible to satisfactorily improve the deterioration of the quality of the tracking control signal caused by the interference with the original signal beam and to detect a stable and highly accurate tracking control signal.

1…半導体レーザ光源、2…回折格子、5…対物レンズ、8…光検出器、10…光ディスク、50…主光束、51、52…副光束、73、74…遮光帯または不感帯、80、81、82…受光領域、100、101…記録層、900…光ディスク、910…レーザ点灯回路、920…光ピックアップ、930…スピンドルモータ、940…スピンドルモータ駆動回路、950…アクセス制御回路、960…アクチュエータ駆動回路、970…サーボ信号生成回路、980…情報信号再生回路、990…情報信号記録回路、9000…コントロール回路 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser light source, 2 ... Diffraction grating, 5 ... Objective lens, 8 ... Optical detector, 10 ... Optical disk, 50 ... Main light beam, 51, 52 ... Sublight beam, 73, 74 ... Shading zone or dead zone, 80, 81 , 82: Light receiving area, 100, 101 ... Recording layer, 900 ... Optical disc, 910 ... Laser lighting circuit, 920 ... Optical pickup, 930 ... Spindle motor, 940 ... Spindle motor drive circuit, 950 ... Access control circuit, 960 ... Actuator drive Circuit, 970 ... Servo signal generation circuit, 980 ... Information signal reproduction circuit, 990 ... Information signal recording circuit, 9000 ... Control circuit

Claims (2)

半導体レーザ光源と、
該半導体レーザ光源から発したレーザ光束を主光束と副光束とに分割する機能を備えた光束分割素子と、
前記主光束および副光束の各々を光学的情報記録媒体内に備えられた所定の記録層に集光させる対物レンズと、
前記記録層を反射した前記主光束および副光束を各々独立に受光し所定の信号を検出する光検出器と、を備え、
前記光検出器は、前記主光束が入射しかつ互いに略垂直な2本の分割線によって4分割された主光束用受光面と、前記副光束が入射し、かつ、互いに略平行な3本の分割線と、
当該3本の分割線に略直交する1本の分割線とによって8分割された副光束用受光面と、前記光検出器からの所定の出力を遮断する遮断手段を有し
前記遮断手段は、前記光学的情報記録媒体が複数の層を有する場合は、前記遮断手段により前記副光束用受光面の略中央に位置する4つの受光領域からの出力を遮断し、前記光学的情報記録媒体が単一の層のみを有する場合は、前記遮断手段により遮断しないことを特徴とする光ピックアップ。
A semiconductor laser light source;
A beam splitter having a function of splitting a laser beam emitted from the semiconductor laser light source into a main beam and a sub beam;
An objective lens for condensing each of the main light beam and the sub light beam on a predetermined recording layer provided in an optical information recording medium;
A light detector that independently receives the main light beam and the sub light beam reflected from the recording layer and detects a predetermined signal; and
The photodetector includes a light receiving surface for main light flux that is divided into four by two split lines substantially perpendicular to each other on which the main light flux is incident, and three light beams that are incident on the sub-light flux and are substantially parallel to each other. A dividing line,
Has a secondary light beam-receiving surface which is divided into eight by the one dividing line which is substantially orthogonal to the three division lines, the shut-off means for cutting off a predetermined output from said photodetector,
When the optical information recording medium has a plurality of layers, the blocking means blocks the output from the four light receiving areas located substantially in the center of the light receiving surface for the sub-beam by the blocking means, and An optical pickup characterized in that when the information recording medium has only a single layer, it is not blocked by the blocking means .
半導体レーザ光源と、
該半導体レーザ光源から発したレーザ光束を主光束と副光束とに分割する機能を備えた光束分割素子と、
前記主光束および副光束の各々を光学的情報記録媒体内に備えられた所定の記録層に集光させる対物レンズと前記記録層を反射した前記主光束および副光束を各々独立に受光し所定の信号を検出する光検出器と、を備え、
前記光検出器は、前記主光束が入射しかつ互いに略垂直な2本の分割線によって4分割された主光束用受光面と、前記副光束が入射しかつ少なくとも1本の分割線で2分割された副光束用受光面と、該副光束用受光面内に備えられた前記分割線上およびその近傍に所定の幅を有する遮断手段を有し、
前記遮断手段は、前記光学的情報記録媒体が複数の層を有する場合は、前記副光束用受光面の略中央に位置する受光領域からの出力を遮断し、前記光学的情報記録媒体が単一の層のみを有する場合は、前記副光束用受光面の略中央に位置する受光領域からの出力を遮断しないことを特徴とする光ピックアップ。
A semiconductor laser light source;
A beam splitter having a function of splitting a laser beam emitted from the semiconductor laser light source into a main beam and a sub beam;
An objective lens for condensing each of the main light beam and the sub light beam on a predetermined recording layer provided in an optical information recording medium, and the main light beam and the sub light beam reflected by the recording layer are independently received and predetermined light is received. A photodetector for detecting the signal,
The photodetector includes a light receiving surface for main light flux that is divided into four by two split lines that are substantially perpendicular to each other where the main light flux is incident, and is divided into two by at least one split line that is incident on the sub light flux. a secondary light beam-receiving surface that is, has a blocking means for chromatic said line dividing and a predetermined width in the vicinity provided in sub beam light receiving plane,
When the optical information recording medium has a plurality of layers , the blocking means blocks an output from a light receiving area located substantially at the center of the light receiving surface for the sub-beam, and the optical information recording medium is a single optical information recording medium. In the case of having only this layer, the output from the light receiving region located substantially in the center of the light receiving surface for the sub-beam is not cut off .
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