JP2008171470A - Optical pickup device - Google Patents
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本発明は光ピックアップ装置に係り、特に対物レンズと光検出器の間に回折型光学素子を備え、単層光ディスクだけでなく多層光ディスクにも良好な記録又は再生を実現する光ピックアップ装置に関する。 The present invention relates to an optical pickup device, and more particularly to an optical pickup device that includes a diffractive optical element between an objective lens and a photodetector and realizes good recording or reproduction on a multilayer optical disc as well as a single-layer optical disc.
一般的に、円盤状の光学的記録媒体である光ディスクは、映像情報とか音声情報やコンピュータデータなどの情報信号を透明基板上で螺旋状又は同心円状に形成したトラックに高密度に記録し、かつ、記録済みのトラックを再生する際に所望のトラックを高速にアクセスできることから多用されている。 In general, an optical disk, which is a disk-shaped optical recording medium, records information signals such as video information, audio information, and computer data on a transparent substrate in a spiral or concentric pattern on a high density, and It is often used because a desired track can be accessed at a high speed when a recorded track is reproduced.
この種の光ディスクとして例えばＣＤ(Compact Disc)やＤＶＤ(Digital Versatile Disc)などは既に市販され、最近では、より一層高密度化を図った２種類の高密度光記録媒体が流通している。すなわち、ＢＤ（Blu-ray Disc）及びＨＤ−ＤＶＤ（High Definition DVD）である。 For example, CD (Compact Disc) and DVD (Digital Versatile Disc) are already on the market as this type of optical disc, and recently, two types of high-density optical recording media with higher density are in circulation. That is, BD (Blu-ray Disc) and HD-DVD (High Definition DVD).
また、各光ディスクを大容量化するために多層に信号記録面がある多層光ディスクの開発と規格化が進展している。ＤＶＤ−ＲＯＭ、ＤＶＤ−Ｒの片面２層光ディスクは既に市販され、ＤＶＤ−ＲＷ、ＢＤ、ＨＤ−ＤＶＤも片面２層光ディスクの規格化が進んでいる。更に、最近の学会ではＢＤの４層ディスク、８層光ディスクの開発の発表も出てきている。 In addition, in order to increase the capacity of each optical disc, development and standardization of a multilayer optical disc having a signal recording surface in multiple layers is progressing. DVD-ROM and DVD-R single-sided dual-layer optical discs are already commercially available, and DVD-RW, BD, and HD-DVD are also being standardized for single-sided dual-layer optical discs. In addition, recent conferences have announced the development of BD 4-layer discs and 8-layer optical discs.
ところで、前記した片面２層光ディスクを記録又は再生するためにＤＶＤの再生型ピックアップ装置では、１ビームによるＤＰＤ法（位相差トラッキング法）を用いてトラッキングエラー信号（ＤＰＤ信号）の検出を行っている。記録型光ディスクであるＤＶＤ−ＲやＤＶＤ−ＲＷについては、信号を記録した後はＤＰＤ信号を検出できるが、信号を記録する前では検出できない。そこで、ＤＶＤの記録型光ディスクに対しては３ビームによるＤＰＰ法（差動プッシュプル法）を用いてトラッキングエラー信号（ＤＰＰ信号）の検出を行っている。 By the way, in order to record or reproduce the single-sided double-layer optical disc described above, a DVD reproduction type pickup apparatus detects a tracking error signal (DPD signal) by using a one-beam DPD method (phase difference tracking method). . With respect to DVD-R and DVD-RW, which are recordable optical disks, the DPD signal can be detected after recording the signal, but cannot be detected before the signal is recorded. Therefore, the tracking error signal (DPP signal) is detected by using the three-beam DPP method (differential push-pull method) for the DVD recording type optical disc.
波長４０５ｎｍ程度の青色レーザ光源を用いて記録又は再生するＨＤ−ＤＶＤでは、再生型、記録型それぞれＤＶＤと同様のトラッキングエラー信号検出を使っている。一方、波長４０５ｎｍ程度の青色レーザ光源を用いて記録又は再生する別の規格であるＢＤでは、ＢＤ−ＲＯＭのトラッキングエラー信号の検出ではＤＰＤ信号を検出できるが、記録型光ディスクの信号を記録した後の状態でＤＰＤ信号の検出が規格として保証されていない。そのため、記録型でも再生型でもＤＰＰ信号を検出するのが一般的である。 In an HD-DVD that is recorded or reproduced using a blue laser light source having a wavelength of about 405 nm, the same tracking error signal detection as that of the DVD is used for each of the reproduction type and the recording type. On the other hand, in the BD, which is another standard for recording or reproducing using a blue laser light source having a wavelength of about 405 nm, the DPD signal can be detected by detecting the tracking error signal of the BD-ROM. In this state, detection of the DPD signal is not guaranteed as a standard. Therefore, it is common to detect the DPP signal in both the recording type and the reproducing type.
ここで、片面２層光ディスクにおいてＤＰＰ法を用いた場合は、再生していない他の層（デフォーカスしている層）からの反射光がクロストーク光として、光検出器に入射し、再生している層の信号検出光と重なることで干渉性のノイズを発生する問題がある。この干渉性のノイズの振る舞いは、干渉する二つの光の間の光路差、すなわち、光ディスクの層間距離等による光路差で決まる。更に、光ディスクの位置による層間距離の変動や、光ディスクのチルトの状態、再生している記録用のガイドトラック（グルーブ）の影響なども受けて、極めて複雑な振る舞いをする。 Here, when the DPP method is used for a single-sided dual-layer optical disc, reflected light from another layer that has not been reproduced (defocused layer) enters the photodetector as crosstalk light and is reproduced. There is a problem in that coherent noise is generated by overlapping with the signal detection light of the layer. The behavior of this coherent noise is determined by the optical path difference between two interfering lights, that is, the optical path difference due to the interlayer distance of the optical disk. Furthermore, it behaves extremely complicated under the influence of fluctuations in the interlayer distance depending on the position of the optical disc, the tilt state of the optical disc, and the guide track (groove) for recording being reproduced.
また、ＤＰＰ信号を用いた場合は、記録時のサブビームによる誤記録を防ぐため、及び光の効率的な利用のため、サブビームの光量はメインビームよりも小さく設定されている。このため、サブビームは、デフォーカスしている層からのクロストーク光の影響をメイン光よりも大きく受けるために、前記の問題が生じる。 When the DPP signal is used, the light amount of the sub beam is set smaller than that of the main beam in order to prevent erroneous recording due to the sub beam at the time of recording and to use light efficiently. For this reason, the above problem arises because the sub beam is more greatly affected by the crosstalk light from the defocused layer than the main light.
このクロストーク光の影響は、ＤＶＤの２層光ディスクの場合もあったが、ＢＤシステムでは、より顕著に安定な記録、再生ができないという重大な問題が発生することが報告されている（例えば、非特許文献１参照）。その理由は、次の通りである。第１に、層間距離がＤＶＤよりも狭くなって光路差が小さくなり、クロストーク光の大きさが大きくなったことである。第２に、波長４０５ｎｍの青色レーザ光源では、レーザの干渉性が上がっていることである。第３に、ＢＤにおいては、対物レンズの開口数（ＮＡ）が上がっているため、クロストーク光もより大きく光検出器に戻るようになっていることである。 The influence of the crosstalk light has been sometimes caused by a double-layer optical disc of DVD, but it has been reported that a serious problem that the recording and reproduction cannot be performed more remarkably occurs in the BD system (for example, Non-patent document 1). The reason is as follows. First, the interlayer distance is narrower than that of DVD, the optical path difference is reduced, and the size of crosstalk light is increased. Secondly, in the blue laser light source having a wavelength of 405 nm, the laser coherence is improved. Third, in the BD, the numerical aperture (NA) of the objective lens is increased, so that crosstalk light also returns to the photodetector more greatly.
そこで、これらの問題を解決する方法として、１ビーム方式によるＰＰ法（プッシュプル法）を用いるトラッキングエラー信号検出方法が提案されている（例えば、非特許文献２参照）。 Therefore, as a method for solving these problems, a tracking error signal detection method using a PP method (push-pull method) using a one-beam method has been proposed (for example, see Non-Patent Document 2).
図１１は非特許文献２記載の従来の光ピックアップ装置の検出系の一例の構成図、図１２は非特許文献２記載の従来の光ピックアップ装置の検出系に用いるＨＯＥパターン（ファーフィールドパターン）の一例を示した図、図１３は非特許文献２記載の従来の光ピックアップ装置のクロストーク光の広がりの一例を示した図である。 11 is a configuration diagram of an example of a detection system of a conventional optical pickup device described in Non-Patent Document 2, and FIG. 12 is a diagram of a HOE pattern (far field pattern) used in the detection system of the conventional optical pickup device described in Non-Patent Document 2. FIG. 13 is a diagram showing an example, and FIG. 13 is a diagram showing an example of the spread of crosstalk light in the conventional optical pickup device described in Non-Patent Document 2.
図１１、図１２、図１３を用いて、光ディスクから反射した反射光がＰＤ（光検出器）へ戻り受光するまでの従来の光ピックアップ装置の動作を簡単に説明する。図１１において、フォーカスエラー信号の検出には、光ディスクからの反射光がホログラム光学素子（ＨＯＥ）１０１によって回折作用がなく透過し、レンズ１０２を通って収束光となり、シリンドリカルレンズ１０３を通って非点収差が与えられフォーカス用ＰＤ（光検出器）１０４で受光した信号を用いる。 The operation of the conventional optical pickup apparatus until the reflected light reflected from the optical disk returns to the PD (light detector) and is received will be briefly described with reference to FIGS. In FIG. 11, in detecting the focus error signal, the reflected light from the optical disk is transmitted by the hologram optical element (HOE) 101 without diffracting action, becomes convergent light through the lens 102, and passes through the cylindrical lens 103 to be astigmatic. A signal given aberration and received by a focusing PD (light detector) 104 is used.
一方、トラッキングエラー信号の検出には、光ディスクからの反射光がＨＯＥ１０１によって回折され、レンズ１０２を通って収束光となり、シリンドリカルレンズ１０３でＨＯＥ１０１によって生じる非点収差をキャンセルし、トラッキング用ＰＤ（光検出器）１０５で受光した信号を用いる。 On the other hand, for the detection of the tracking error signal, the reflected light from the optical disk is diffracted by the HOE 101, passes through the lens 102 and becomes convergent light, and the astigmatism caused by the HOE 101 is canceled by the cylindrical lens 103, and tracking PD (light detection) The signal received by the device 105 is used.
図１２はＨＯＥ１０１のパターンを示しており、ＨＯＥ１０１は５つの領域Ａ，Ｂ，Ｃ，Ｄ，Ｘに分割されている。図１３はフォーカシング用ＰＤ１０４、トラッキング用ＰＤ１０５でのクロストーク光の状態を示している。再生している層からの反射光でＨＯＥ１０１の領域Ａを通った光はＰＤ１０５の受光部１０５Ａ、ＨＯＥ１０１の領域Ｂを通った光はＰＤ１０５の受光部１０５Ｂ、ＨＯＥ１０１の領域Ｃを通った光はＰＤ１０５の受光部１０５Ｃ、ＨＯＥ１０１の領域Ｄを通った光はＰＤ１０５の受光部１０５Ｄでスポットを形成する。なお、再生していない層（他層）からのクロストーク光は灰色部分である。 FIG. 12 shows a pattern of the HOE 101, and the HOE 101 is divided into five areas A, B, C, D, and X. FIG. 13 shows the state of crosstalk light in the focusing PD 104 and tracking PD 105. The light passing through the region A of the HOE 101 by the reflected light from the reproducing layer is light receiving part 105A of the PD 105, the light passing through the region B of the HOE 101 is light passing through the light receiving part 105B of the PD 105, and the region C of the HOE 101 is PD 105. The light that passes through the region D of the light receiving unit 105C and the HOE 101 forms a spot at the light receiving unit 105D of the PD 105. Note that crosstalk light from a layer that is not reproduced (other layer) is a gray portion.
他層からのクロストーク光のうち、ＨＯＥ１０１で回折しない光（０次回折光）については、フォーカシング用ＰＤ１０４にはかかるもののトラッキング用ＰＤ１０５にはかからない。なお、回折しない光であるから、ＨＯＥ１０１のいずれの領域を通っても同じ位置にスポットができる。 Of crosstalk light from other layers, light that is not diffracted by the HOE 101 (0th order diffracted light) is applied to the focusing PD 104 but is not applied to the tracking PD 105. Since the light is not diffracted, a spot can be formed at the same position regardless of the region of the HOE 101.
一方、他層から反射したクロストーク光のうち、ＨＯＥ１０１で回折した光（回折光）については、ＨＯＥ１０１の通る領域によってスポット位置が異なる。領域Ｘを通ったクロストーク光の回折光はフォーカシング用ＰＤ１０４の左右に位置し、トラッキング用ＰＤ１０５にはかからない。また、領域Ａ，Ｂ，Ｃ，Ｄを通ったクロストーク光の回折光はトラッキング用ＰＤ１０５の周辺に位置し、トラッキング用ＰＤ１０５にはかからない。そして、トラッキングエラー信号ＡＰＰは、受光部１０５Ａで得られる信号をＴＡ、受光部１０５Ｂで得られる信号をＴＢ、受光部１０５Ｃで得られる信号をＴＣ、受光部１０５Ｄで得られる信号をＴＤとするとき、次の式で計算される。 On the other hand, among crosstalk light reflected from other layers, the spot position of light diffracted by the HOE 101 (diffracted light) differs depending on the region through which the HOE 101 passes. The diffracted light of the crosstalk light that has passed through the region X is positioned on the left and right of the focusing PD 104 and does not reach the tracking PD 105. Further, the diffracted light of the crosstalk light that has passed through the regions A, B, C, and D is positioned around the tracking PD 105 and does not reach the tracking PD 105. The tracking error signal APP is obtained when TA is a signal obtained by the light receiving unit 105A, TB is a signal obtained by the light receiving unit 105B, TC is a signal obtained by the light receiving unit 105C, and TD is a signal obtained by the light receiving unit 105D. Is calculated by the following formula.
ＡＰＰ＝（ＴＣ−ＴＤ）−ｋ（ＴＡ−ＴＢ） （１）
ただし、上式中、ｋは定数である。
APP = (TC-TD) -k (TA-TB) (1)
In the above formula, k is a constant.
また、クロストーク光の問題を解決する他の方法として、非特許文献２と同様に１ビーム方式によるＰＰ法を用いるトラッキングエラー信号検出方法が提案されている（例えば、非特許文献３参照）。図１４は上記の非特許文献３記載の従来の光ピックアップ装置の検出系に用いる液晶素子の一例の構造図、図１５は非特許文献３記載の従来の光ピックアップ装置の受光セルへビームが集光する状態を示した図である。 As another method for solving the problem of crosstalk light, a tracking error signal detection method using a PP method using a one-beam method has been proposed as in Non-Patent Document 2 (for example, see Non-Patent Document 3). FIG. 14 is a structural diagram of an example of a liquid crystal element used in the detection system of the conventional optical pickup device described in Non-Patent Document 3, and FIG. 15 is a diagram showing a beam collected in the light receiving cell of the conventional optical pickup device described in Non-Patent Document 3. It is the figure which showed the state which shines.
図１４及び図１５を用いて光ディスクで反射した反射光を検出するまでの非特許文献３記載の従来の光ピックアップ装置の動作を簡単に説明すると、液晶素子１１０は３層からなり、光ディスク（不図示）側から非偏光ＨＯＥ１１１、液晶アクティブローテータ１１２、偏光ＨＯＥ１１３の順に形成される。 The operation of the conventional optical pickup device described in Non-Patent Document 3 until the reflected light reflected by the optical disk is detected using FIGS. 14 and 15 will be briefly described. The non-polarized HOE 111, the liquid crystal active rotator 112, and the polarized HOE 113 are formed in this order from the side shown.
非偏光ＨＯＥ１１１はレンズ効果を持たせ、±１次回折光を発生させフォーカスエラー信号を検出するためのものである。液晶アクティブローテータ１１２は電圧のオン（ＯＮ）、オフ（ＯＦＦ）で偏光方向を変えるものである。偏光ＨＯＥ１１３は記録型用のパターン１１３Ａ、再生型用のパターン１１３Ｂからなる。 The non-polarized HOE 111 has a lens effect, generates ± first-order diffracted light, and detects a focus error signal. The liquid crystal active rotator 112 changes the polarization direction according to voltage on (ON) and off (OFF). The polarization HOE 113 includes a recording pattern 113A and a reproduction pattern 113B.
記録型のトラッキングエラー信号を検出する場合には、図１５（ａ）に示すように、液晶アクティブローテータ１１２で電圧をオフにして、入射偏光方向と垂直な方向に偏光方向を変える。そして、偏光ＨＯＥ１１３のうち記録型用のパターン１１３Ａを作用させ、非特許文献２と同様のＰＰ法を用いてトラッキングエラー信号を検出する。記録型用のパターン１１３Ａの中央の領域Ｅはトラッキングエラー信号の演算から除かれ、他層からのクロストーク光の影響を減らしている。 When a recording type tracking error signal is detected, as shown in FIG. 15A, the voltage is turned off by the liquid crystal active rotator 112 and the polarization direction is changed to a direction perpendicular to the incident polarization direction. Then, the pattern 113A for recording type is made to act on the polarization HOE 113, and the tracking error signal is detected using the PP method similar to Non-Patent Document 2. The central region E of the recording pattern 113A is excluded from the calculation of the tracking error signal to reduce the influence of crosstalk light from other layers.
一方、再生型のトラッキングエラー信号を検出する場合には、図１５（ｂ）に示すように、液晶アクティブローテータ１１２で電圧をオンにして、入射偏光方向と出射偏光方向を同じにする。そして、偏光ＨＯＥ１１３のうち再生型用のパターン１１３Ｂを作用させ、ＤＰＤ法を用いてトラッキングエラー信号を検出する。 On the other hand, when detecting a regenerative tracking error signal, as shown in FIG. 15B, the voltage is turned on by the liquid crystal active rotator 112 to make the incident polarization direction and the outgoing polarization direction the same. Then, the reproduction-type pattern 113B of the polarization HOE 113 is applied, and the tracking error signal is detected using the DPD method.
図１１〜図１３と共に説明した非特許文献２記載の従来の光ピックアップ装置によれば、トラッキング用ＰＤ１０５にクロストーク光の影響が生じないようにしてトラッキングエラー信号を安定にしている。しかし、フォーカス用ＰＤ１０４とトラッキング用ＰＤ１０５と検出ビームを２つに分け、フォーカス用ＰＤ１０４から得られる信号はメイン信号の検出には用いることができないので、信号出力が低下し、信号検出のＳ／Ｎが低下する。特に、高速な再生を行う場合には顕著に問題となる。 According to the conventional optical pickup device described in Non-Patent Document 2 described with reference to FIGS. 11 to 13, the tracking error signal is stabilized so that the tracking PD 105 is not affected by the crosstalk light. However, since the focus PD 104, the tracking PD 105, and the detection beam are divided into two and the signal obtained from the focus PD 104 cannot be used for the detection of the main signal, the signal output is reduced, and the S / N of the signal detection is reduced. Decreases. In particular, this is a significant problem when performing high-speed playback.
また、図１４及び図１５と共に説明した非特許文献３記載の従来の光ピックアップ装置によれば、クロストーク光の影響を少なくして、記録型、再生型のトラッキングエラー信号検出を行うことができるものの、２パターン１１３Ａ、１１３Ｂの偏光ＨＯＥ１１３や液晶アクティブローテータ１１２など高価な部品が多い構成であるため、装置全体が高価であるという問題がある。 In addition, according to the conventional optical pickup device described in Non-Patent Document 3 described with reference to FIGS. 14 and 15, it is possible to detect the recording type and the reproduction type tracking error signal while reducing the influence of the crosstalk light. However, since there are many expensive parts such as the polarization HOE 113 of the two patterns 113A and 113B and the liquid crystal active rotator 112, there is a problem that the entire apparatus is expensive.
本発明は以上の点に鑑みなされたもので、多層光ディスクを記録又は再生する場合に、信号のＳ／Ｎが良く、かつ、低コストで実現できる光ピックアップ装置を提供することを目的とする。 The present invention has been made in view of the above points, and an object of the present invention is to provide an optical pickup device that has a good signal S / N and can be realized at low cost when recording or reproducing a multilayer optical disk.
上記の目的を達成するため、第１の発明は、光を出射する光源と、光源から出射された光を光ディスクに集光してスポットを形成する対物レンズと、対物レンズを透過した光ディスクからの反射光を回折して所定の方向に出射する回折型光学素子と、回折型光学素子から出射された光を受光して光電変換する光検出器と、光源から出射して対物レンズヘ向かう光と光ディスクから反射し対物レンズを透過して光検出器へ向かう反射光とを分離する光路分離素子とを備える光ピックアップ装置であって、
回折型光学素子は、光ディスクのトラックを投影した時のそのトラックの方向と垂直な方向に反射光の光束を分割する第１の分割線と、トラックの方向と平行な方向に対して各々反対方向に略４５°方向に反射光の光束を分割する第２及び第３の分割線とにより、少なくとも６つの分割領域に分割され、６つの分割領域は各々入射する反射光を回折して方向を変化させ、前記反射光は、回折型光学素子の分割領域のうち２つ以上、もしくはシリンドリカルレンズにより非点収差を付与され、
光検出器は、回折型光学素子の６つの分割領域を通してそれぞれ出射する光を個別に受光する少なくとも６つの受光セルから構成されると共に、６つの受光セルで受光される各スポットが、非点収差を付与された回折光により生じる２つの焦線のほぼ中間の最小錯乱円になる位置に配置され、かつ、少なくとも６つの分割領域の中でトラックの方向と同一方向を含む２つの分割領域を通して出射する光を受光する２つの受光セルが、トラックの方向と垂直な方向の分割線でそれぞれ２分割されている構成であることを特徴とする。
In order to achieve the above object, a first invention includes a light source that emits light, an objective lens that collects light emitted from the light source on an optical disc to form a spot, and an optical disc that passes through the objective lens. A diffractive optical element that diffracts reflected light and emits it in a predetermined direction, a photodetector that receives and photoelectrically converts the light emitted from the diffractive optical element, and an optical disk that emits light from the light source and travels toward the objective lens An optical pickup device comprising an optical path separation element that separates reflected light from the reflected light that passes through the objective lens and travels toward the photodetector,
The diffractive optical element has a first dividing line that divides the reflected light beam in a direction perpendicular to the direction of the track when the track of the optical disk is projected, and a direction opposite to the direction parallel to the direction of the track. Are divided into at least six divided areas by the second and third dividing lines that divide the luminous flux of the reflected light in the direction of approximately 45 °, and the six divided areas each change the direction by diffracting the incident reflected light. The reflected light is given astigmatism by two or more of the divided regions of the diffractive optical element, or by a cylindrical lens,
The photodetector is composed of at least six light receiving cells that individually receive light emitted through the six divided regions of the diffractive optical element, and each spot received by the six light receiving cells has astigmatism. Is emitted through two divided regions including the same direction as the direction of the track among at least six divided regions. The two light receiving cells that receive the light to be transmitted are each divided into two by a dividing line in a direction perpendicular to the track direction.
この発明では、１ビームにより得られた光ディスクからの反射光を、少なくとも６つの分割領域を有する回折型光学素子に入射して、各分割領域で回折されて方向を変化させ、また、非点収差を付与させ、それらを光検出器の少なくとも６つの受光セルでそれぞれ受光させることにより、それら少なくとも６つの受光セルの出力信号からトラッキングエラー信号、非点収差法によるフォーカスエラー信号を生成することができる。 In this invention, the reflected light from the optical disk obtained by one beam is incident on a diffractive optical element having at least six divided regions, is diffracted in each divided region, changes its direction, and has astigmatism. And at least six light receiving cells of the photodetector respectively receive the light, thereby generating a tracking error signal and a focus error signal by the astigmatism method from the output signals of the at least six light receiving cells. .
ここで、第２の発明は、第１の発明における回折型光学素子の各分割領域を、各々レンズ作用を有し、回折型光学素子の各分割領域とそれに対応した光検出器の各受光セルの距離の差を補正することを特徴とする。 Here, in the second invention, each divided region of the diffractive optical element in the first invention has a lens function, and each divided region of the diffractive optical element and each light receiving cell of the photodetector corresponding thereto. It is characterized in that the difference in distance between the two is corrected.
また、第３の発明は、第１の発明における回折型光学素子の各分割領域を、各々レンズ作用を有し、回折型光学素子の各分割領域とそれに対応した光検出器の各受光セルとの距離の差を補正し、かつ、光源から光ディスクまでの結像倍率と、光ディスクから光検出器までの結像倍率の違いを補正することを特徴とする。 According to a third aspect of the present invention, each of the divided regions of the diffractive optical element according to the first invention has a lens function, and each divided region of the diffractive optical element and each light receiving cell of the photodetector corresponding thereto And a difference between the imaging magnification from the light source to the optical disc and the imaging magnification from the optical disc to the photodetector are corrected.
また、第４の発明は、上記の目的を達成するため、回折型光学素子の６つの分割領域の中でトラックの方向と同一方向を含む２つの分割領域を第１の分割領域及び第２の分割領域とし、残りの４つの分割領域を、トラックの方向と同一方向で、かつ、反射光の光束中心を通る仮想線で分けたとき、一方の同じ側に属する２つの分割領域を第３の分割領域及び第４の分割領域とし、かつ、他方の同じ側に属する２つの分割領域を第５の分割領域及び第６の分割領域としたとき、第３の分割領域及び第４の分割領域により回折された回折光をそれぞれ受光する光検出器の２つの受光セルの出力信号Ａ及びＢと、第５の分割領域及び第６の分割領域により回折された回折光をそれぞれ受光する光検出器の他の２つの受光セルの出力信号Ｃ及びＤとを用いて、次式
ＰＰ＝（Ａ＋Ｂ）−（Ｃ＋Ｄ）
によりトラッキングエラー信号ＰＰを生成するトラッキングエラー信号生成手段を有することを特徴とする。この発明では、プッシュプル法によりトラッキングエラー信号を生成することができる。
According to a fourth aspect of the present invention, in order to achieve the above object, two divided areas including the same direction as the track direction are divided into the first divided area and the second divided area among the six divided areas of the diffractive optical element. When the remaining four divided areas are divided into imaginary lines that pass in the same direction as the track direction and pass through the center of the reflected light, the two divided areas belonging to one same side are defined as the divided areas. When the divided area and the fourth divided area are used, and the other two divided areas belonging to the same side are the fifth divided area and the sixth divided area, the third divided area and the fourth divided area The output signals A and B of the two light receiving cells of the photodetector that respectively receive the diffracted diffracted light, and the photodetector that receives the diffracted light diffracted by the fifth divided region and the sixth divided region, respectively. Output signals C and D of the other two light receiving cells Stomach, following equation
PP = (A + B)-(C + D)
And tracking error signal generation means for generating a tracking error signal PP. In the present invention, the tracking error signal can be generated by the push-pull method.
また、上記の目的を達成するため、第５の発明は、回折型光学素子の６つの分割領域の中でトラックの方向と同一方向を含む２つの分割領域を第１の分割領域及び第２の分割領域とし、残りの４つの分割領域を、トラックの方向と同一方向で、かつ、反射光の光束中心を通る仮想線で分けたとき、一方の同じ側に属する２つの分割領域を第３の分割領域及び第４の分割領域とし、かつ、他方の同じ側に属する２つの分割領域を第５の分割領域及び第６の分割領域としたとき、光検出器は、第１、第２、第３、第４、第５及び第６の分割領域によりそれぞれ回折された回折光を個別に受光する第１、第２、第３、第４、第５及び第６の受光セルからなり、かつ、第１の受光セルと第２の受光セルとは、トラックの方向と直交する方向の分割線でそれぞれ２分割されており、
第３の分割領域及び第４の分割領域により回折された回折光をそれぞれ受光する第３及び第４の受光セルの出力信号Ａ及びＢと、第５の分割領域及び第６の分割領域により回折された回折光をそれぞれ受光する第５及び第６の受光セルの出力信号Ｃ及びＤと、各々２分割されている第１及び第２の受光セルをトラックの方向と同一方向の仮想線で分けたとき、一方の同じ側に属する第１及び第２の受光セルの２つの分割受光セル部の出力信号Ｅ１及びＦ１と、他方の同じ側に属する第１及び第２の受光セルの残りの２つの分割受光セル部の出力信号Ｅ２及びＦ２とを用いて、次式
ＡＰＰ＝（Ａ＋Ｂ）−（Ｃ＋Ｄ）−ｋ｛（Ｅ１＋Ｆ１）−（Ｅ２＋Ｆ２）｝
（ただし、ｋは定数）
によりトラッキングエラー信号ＡＰＰを生成するトラッキングエラー信号生成手段を有することを特徴とする。この発明では、新プッシュプル法によりトラッキングエラー信号を生成することができる。
In order to achieve the above object, according to a fifth aspect of the present invention, two divided areas including the same direction as the track direction among the six divided areas of the diffractive optical element are divided into the first divided area and the second divided area. When the remaining four divided areas are divided into imaginary lines that pass in the same direction as the track direction and pass through the center of the reflected light, the two divided areas belonging to one same side are defined as the divided areas. When the divided area and the fourth divided area are used, and the other two divided areas belonging to the same side are the fifth divided area and the sixth divided area, the photodetector has the first, second, and second divided areas. Comprising first, second, third, fourth, fifth and sixth light receiving cells that individually receive diffracted light diffracted by the third, fourth, fifth and sixth divided regions, and The first light receiving cell and the second light receiving cell are dividing lines in a direction perpendicular to the track direction. Respectively 2 is divided,
Output signals A and B of the third and fourth light receiving cells that receive the diffracted light diffracted by the third divided region and the fourth divided region, respectively, and diffracted by the fifth divided region and the sixth divided region The output signals C and D of the fifth and sixth light receiving cells that respectively receive the diffracted light and the first and second light receiving cells that are divided into two are divided by virtual lines in the same direction as the track direction. Output signals E1 and F1 of the two divided light receiving cell portions of the first and second light receiving cells belonging to one same side, and the remaining two of the first and second light receiving cells belonging to the other same side. Using the output signals E2 and F2 of the two divided light receiving cell sections, the following expression APP = (A + B) − (C + D) −k {(E1 + F1) − (E2 + F2)}
(Where k is a constant)
And a tracking error signal generating means for generating a tracking error signal APP. In the present invention, the tracking error signal can be generated by the new push-pull method.
更に、上記の目的を達成するため、第６の発明は、回折型光学素子の６つの分割領域の中でトラックの方向と同一方向を含む２つの分割領域を第１の分割領域及び第２の分割領域としたとき、光検出器は、第１の分割領域及び第２の分割領域によりそれぞれ非点収差を付与され回折された回折光、もしくは第１の分割領域及び第２の分割領域によりそれぞれ回折され、前記シリンドリカルレンズにより非点収差を付与された回折光を個別に受光する第１の受光セルと第２の受光セルを少なくとも有しており、第１の受光セルと第２の受光セルとは、トラックの方向と直交する方向の分割線でそれぞれ２分割されており、
第１及び第２の受光セルをトラックの方向と同一方向の仮想線で分けたとき、一方の同じ側に属する第１及び第２の受光セルの２つの分割受光セル部の出力信号Ｅ１及びＦ１と、他方の同じ側に属する第１及び第２の受光セルの残りの２つの分割受光セル部の出力信号Ｅ２及びＦ２とを用いて、次式
ＦＥ＝（Ｅ１＋Ｆ２）−（Ｅ２＋Ｆ１）
によりフォーカスエラー信号ＦＥを生成するフォーカスエラー信号生成手段を有することを特徴とする。
In order to achieve the above object, according to a sixth aspect of the present invention, two divided regions including the same direction as the track direction among the six divided regions of the diffractive optical element are divided into the first divided region and the second divided region. When the divided regions are used, the photodetector is respectively diffracted light diffracted with astigmatism given by the first divided region and the second divided region, or the first divided region and the second divided region, respectively. It has at least a first light receiving cell and a second light receiving cell for individually receiving the diffracted light diffracted and given astigmatism by the cylindrical lens, and the first light receiving cell and the second light receiving cell. Are divided in two by dividing lines in a direction perpendicular to the direction of the track,
When the first and second light receiving cells are divided by virtual lines in the same direction as the track direction, the output signals E1 and F1 of the two divided light receiving cell portions of the first and second light receiving cells belonging to one same side And the output signals E2 and F2 of the remaining two divided light receiving cells of the first and second light receiving cells belonging to the other side, the following equation FE = (E1 + F2) − (E2 + F1)
And a focus error signal generating means for generating a focus error signal FE.
この発明では、記録型光ディスクのトラッキング用のグルーブや再生型光ディスクのトラック方向のピットで回折して生じる０次光と１次光の干渉する光束が通過する回折型光学素子の第４乃至第６の分割領域以外の第１の分割領域及び第２の分割領域によりそれぞれ非点収差を付与された回折光を個別に受光する第１の受光セルと第２の受光セルの出力信号を用いてフォーカスエラー信号ＦＥを生成することができる。 According to the present invention, the fourth to sixth diffractive optical elements through which a light beam that interferes with the zero-order light and the first-order light generated by diffracting at the tracking groove of the recording optical disk or the pit in the track direction of the reproducing optical disk pass. Focus using the output signals of the first light receiving cell and the second light receiving cell that individually receive the diffracted light that has been provided with astigmatism by the first divided region and the second divided region other than the first divided region. An error signal FE can be generated.
第１の発明によれば、１ビームにより得られた光ディスクからの反射光を、少なくとも６つの分割領域を有する回折型光学素子に入射して、各分割領域に応じて非点収差を付与した回折光を出射させ、もしくは各分割領域で回折された回折光に非点収差を付与させて、それらを光検出器の少なくとも６つの受光セルでそれぞれ受光させることにより、それら少なくとも６つの受光セルの出力信号からトラッキングエラー信号を生成でき、特に光ディスクが多層光ディスクである場合は、上記の少なくとも６つの受光セルを、再生する記録層以外の他の記録層からのクロストーク光を受光しないような配置とすることができるので、信号のＳ／Ｎが良く、かつ、安定したトラッキングエラー信号を生成することができる。 According to the first invention, the reflected light from the optical disk obtained by one beam is incident on a diffractive optical element having at least six divided regions, and diffraction is provided with astigmatism according to each divided region. Output light of at least six light receiving cells by emitting light or adding astigmatism to the diffracted light diffracted in each divided region and receiving them by at least six light receiving cells of the photodetector. A tracking error signal can be generated from the signal, and particularly when the optical disc is a multilayer optical disc, the at least six light receiving cells are arranged so as not to receive crosstalk light from other recording layers other than the recording layer to be reproduced. Therefore, it is possible to generate a stable tracking error signal with a good signal S / N ratio.
また、第１の発明によれば、回折型光学素子の各分割領域のそれぞれで非点収差を付与した回折光を出射することで、シリンドリカルレンズの機能を回折型光学素子に組み入れることが可能で、これにより部品点数を少なくでき、また、光検出器上の受光セルが従来の非特許文献２と比較しても少ない構成が可能なので、回路規模が小さく、ノイズも小さく、かつ、低コストで実現でき、また、１ビーム方式なので、３ビーム方式と比較してグレーティングによる光量ロスもなく、グレーティング調整も不要で、トラックピッチが異なる光ディスクや、方式が異なる光ディスクに対しても容易に対応できる。 According to the first invention, the function of the cylindrical lens can be incorporated into the diffractive optical element by emitting the diffracted light with astigmatism in each divided region of the diffractive optical element. As a result, the number of parts can be reduced, and the number of light receiving cells on the photodetector can be reduced compared to the conventional non-patent document 2, so that the circuit scale is small, the noise is small, and the cost is low. Since it is a 1-beam system, there is no light loss due to the grating as compared with the 3-beam system, no grating adjustment is required, and it is possible to easily cope with optical disks with different track pitches and optical systems with different systems.
また、第２の発明によれば、回折型光学素子の分割領域ごとにレンズパワーをもたせることにより、受光セルの配置に自由度をもたせることができ、第３の発明によれば、結像倍率の違いを補正することができるので、光源と光検出器の配置が共役にある必要がないので、これらの配置に自由度をもたせることができる。 Further, according to the second invention, the lens power is given to each divided region of the diffractive optical element, whereby the degree of freedom can be given to the arrangement of the light receiving cells. According to the third invention, the imaging magnification is increased. Therefore, the arrangement of the light source and the light detector does not need to be conjugate, so that the arrangement can be given a degree of freedom.
また、第４の発明によれば、一般的なプッシュプル法によってトラッキングエラー信号ＰＰを生成でき、第５の発明によれば、新プッシュプル法によってトラッキングエラー信号ＡＰＰを生成できるので、記録、未記録境界でトラッキングエラー信号ＡＰＰにオフセットが生じないため、安定したトラッキングをかけることができる。そして、回折型光学素子の分割領域と計算方法により、瞳中心部分の回折光の重なりによる影響を低減できる。さらに、トラッキングエラー信号はＡＰＰ信号だけでなく、一般的なＤＰＤ信号も得ることができる。 According to the fourth invention, the tracking error signal PP can be generated by a general push-pull method, and according to the fifth invention, the tracking error signal APP can be generated by a new push-pull method. Since no tracking error signal APP is offset at the recording boundary, stable tracking can be applied. The influence of overlapping of diffracted light at the center of the pupil can be reduced by the divided area of the diffractive optical element and the calculation method. Furthermore, a general DPD signal can be obtained as a tracking error signal as well as an APP signal.
更に、第６の発明によれば、記録型光ディスクのトラッキング用のグルーブや再生型光ディスクのトラック方向のピットで回折して生じる０次光と１次光の干渉する光が通過する回折型光学素子の第３乃至第６の分割領域以外の第１の分割領域及び第２の分割領域を通過する光に非点収差を付与させ、各回折光を個別に受光する第１の受光セルと第２の受光セルの出力信号を用いてフォーカスエラー信号ＦＥを生成するようにしたため、トラッキング用のグルーブなどを横断する際の光量変化が少なく、フォーカスエラー信号の変動を少なくでき、また、従来のフロントエンドプロセッサ（ＦＥＰ）との親和性が高い非点収差法によるフォーカスエラー信号を生成することができる。 Furthermore, according to the sixth invention, a diffractive optical element through which light of interference between the zeroth order light and the first order light diffracted by a tracking groove of a recordable optical disc or a pit in the track direction of a reproduction type optical disc passes. Astigmatism is imparted to the light passing through the first divided region and the second divided region other than the third to sixth divided regions, and the first light receiving cell and the second light receiving cell individually receive each diffracted light. Since the focus error signal FE is generated using the output signal of the light receiving cell, there is little change in the amount of light when traversing the tracking groove, etc., and fluctuation of the focus error signal can be reduced. A focus error signal can be generated by the astigmatism method having high affinity with the processor (FEP).
次に、本発明の実施の形態について図１〜図１０を参照して詳細に説明する。図１は本発明になる光ピックアップ装置の一実施の形態の全体構成図を示す。図１において、光ピックアップ装置１は、波長λが４０５ｎｍのレーザ光ＬＳを出射するレーザ光源２からのレーザ光ＬＳを用いて、基板厚さｔが０.０７５ｍｍと０.１ｍｍの２つの記録層に信号面１１Ｂを有する、Ｂｌｕ−Ｒａｙ規格の片面２層の光ディスク（ＢＤ）１１を記録又は再生する装置である。 Next, an embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is an overall configuration diagram of an embodiment of an optical pickup device according to the present invention. In FIG. 1, an optical pickup device 1 uses two laser recording layers having a substrate thickness t of 0.075 mm and 0.1 mm using laser light LS from a laser light source 2 that emits laser light LS having a wavelength λ of 405 nm. This is a device for recording or reproducing a Blu-Ray standard single-sided dual-layer optical disc (BD) 11 having a signal surface 11B.
本実施の形態では対物レンズ７は２つの記録層の信号面の中間、すなわち０.０８７５ｍｍでレーザ光を集束するように最適に設計されていて、コリメータレンズ４を光路方向に移動することによって、ｔ＝０.０７５ｍｍの第１の記録層を記録又は再生する場合は僅かに収束光、ｔ＝０.１ｍｍの第２の記録層を記録又は再生する場合は僅かに発散光として良好に記録又は再生ができる。ここでは、基板厚さｔ＝０.０７５ｍｍの第１の記録層の記録信号を再生する場合について説明する。 In the present embodiment, the objective lens 7 is optimally designed to focus the laser light at the middle of the signal surfaces of the two recording layers, that is, 0.0875 mm. By moving the collimator lens 4 in the optical path direction, When recording or reproducing the first recording layer of t = 0.075 mm, slightly converged light, and when recording or reproducing the second recording layer of t = 0.1 mm, recording or reproducing as slightly divergent light Can play. Here, a case where the recording signal of the first recording layer having the substrate thickness t = 0.075 mm is reproduced will be described.
レーザ光源２を出射したレーザ光ＬＳはｐ偏光の直線偏光であり、偏光ビームスプリッタ（光路分離素子）３の偏光選択性誘電体多層膜３Ａ（ｐ偏光：透過、ｓ偏光：反射）を透過した後、コリメータレンズ４により僅かに収束光とされ、立上ミラー５の反射膜５Ａにより９０°方向を転じて、１／４波長板６によりλ／４の位相差が与えられ、円偏光となり対物レンズ７に入射する。対物レンズ７で絞って得られたビームは光ディスク１１のビーム入射面１１Ａから入射させて、基板厚さｔ＝０.０７５ｍｍの第１の記録層の信号面１１Ｂ上で収差が良好な状態で集光して、記録又は再生が行われる。 The laser light LS emitted from the laser light source 2 is p-polarized linearly polarized light, and is transmitted through the polarization-selective dielectric multilayer film 3A (p-polarized light: transmissive, s-polarized light: reflected) of the polarizing beam splitter (optical path separating element) 3. Thereafter, the light is slightly converged by the collimator lens 4, turned 90 ° by the reflective film 5 A of the rising mirror 5, and given a phase difference of λ / 4 by the quarter-wave plate 6, becomes circularly polarized light and becomes objective The light enters the lens 7. The beam obtained by focusing with the objective lens 7 is made incident from the beam incident surface 11A of the optical disk 11, and collected with good aberration on the signal surface 11B of the first recording layer having the substrate thickness t = 0.075 mm. Light is recorded or reproduced.
そして、光ディスク１１の信号面１１Ｂで反射されたレーザ光（反射光）ＬＴは、対物レンズ７に再入射し、この対物レンズ１１により僅かに発散光となり、１／４波長板６に入射してλ／４の位相差が与えられ、ｓ偏光の直線偏光となり立上ミラー５の反射膜５Ａで９０°光線方向を転じ、コリメータレンズ４により収束光となり、偏光ビームスプリッタ３に入射する。 Then, the laser light (reflected light) LT reflected by the signal surface 11B of the optical disk 11 is incident on the objective lens 7 again, becomes slightly divergent light by the objective lens 11, and enters the quarter wavelength plate 6. A phase difference of λ / 4 is given, and the light is converted into s-polarized linearly polarized light, turned 90 ° by the reflecting film 5 A of the rising mirror 5, converged by the collimator lens 4, and incident on the polarizing beam splitter 3.
偏光ビームスプリッタ３に入射したｓ偏光の反射光は、偏光性誘電体多層膜３Ａで反射され、回折型光学素子８に入射しＨＯＥ面８Ｚで回折されて、シリンドリカルレンズ９により非点収差が与えられた後、光検出器１０の後述する６分割された受光セル１０Ａ〜１０Ｆで受光される。光検出器１０はその受光セル１０Ａ〜１０Ｆで受光した光をそれぞれ光電変換した後、各電気信号に対してそれぞれ後述する所定の演算式に従って、トラッキングエラー信号，フォーカスエラー信号，メインデータ信号を演算算出する。 The s-polarized reflected light incident on the polarizing beam splitter 3 is reflected by the polarizing dielectric multilayer film 3A, incident on the diffractive optical element 8, diffracted by the HOE surface 8Z, and given astigmatism by the cylindrical lens 9. After being received, the light is received by the six divided light receiving cells 10A to 10F described later of the photodetector 10. The photodetector 10 photoelectrically converts the light received by the light receiving cells 10A to 10F, and then calculates a tracking error signal, a focus error signal, and a main data signal according to predetermined arithmetic expressions described later for each electric signal. calculate.
次に、本実施の形態の要部である検出系について、図２〜図４と共に説明する。ここで、図２は光ピックアップ装置１の検出系を詳細に示した図、図３はＨＯＥ面８Ｚの分割領域８Ａ〜８Ｆを示した図、図４は光検出器１０の受光セル１０Ａ〜１０Ｆの配置を示した図である。図２において、偏光ビームスプリッタ３で反射され、回折型光学素子８に入射した光束は、回折型光学素子８のＨＯＥ面８Ｚの６つの分割領域８Ａ〜８Ｆからなるホログラムパターンでそれぞれ回折される。 Next, a detection system that is a main part of the present embodiment will be described with reference to FIGS. 2 is a diagram showing in detail the detection system of the optical pickup device 1, FIG. 3 is a diagram showing the divided regions 8A to 8F of the HOE surface 8Z, and FIG. 4 is a light receiving cell 10A to 10F of the photodetector 10. It is the figure which showed arrangement | positioning. In FIG. 2, the light beam reflected by the polarization beam splitter 3 and incident on the diffractive optical element 8 is diffracted by a hologram pattern composed of six divided regions 8 </ b> A to 8 </ b> F on the HOE surface 8 </ b> Z of the diffractive optical element 8.
上記の６つの分割領域は図３に示すように、全体として円形の光入射領域を光ディスク１１のトラックを投影した時のそのトラックの方向と垂直な方向（ラジアル方向）に２分割する分割線８ｋが入っている。そして、円形の光入射領域の中心を通り、かつ、上記の分割線８ｋに対し、±４５°方向に分割線８ｉ，８ｊが入っている。この３つの分割線８ｋ，８ｉ，８ｊにより、円形の光入射領域は６つの分割領域８Ａ〜８Ｆに分割され、それらの分割領域毎に異なる回折構造をもつホログラムパターンとなっている。また、回折構造はブレーズ状もしくは階段状で形成され、１次回折光の強度が７０％以上になるよう設計されており、６つの分割領域８Ａ〜８Ｆに対応した６つの１次回折光が生じる。なお、対物レンズ７でのレンズシフトやレンズチルトがない状態では、光ディスク１１からの反射光の光束中心は円形の光入射領域のほぼ中心を通るものである。 As shown in FIG. 3, the above six divided areas are divided into lines 8k that divide a circular light incident area into two in the direction (radial direction) perpendicular to the direction of the track when the track of the optical disk 11 is projected. Is included. The dividing lines 8i and 8j are inserted in the direction of ± 45 ° with respect to the dividing line 8k through the center of the circular light incident area. By these three dividing lines 8k, 8i, and 8j, the circular light incident area is divided into six divided areas 8A to 8F, and each of the divided areas has a hologram pattern having a different diffraction structure. The diffractive structure is formed in a blazed shape or stepped shape, and is designed so that the intensity of the first-order diffracted light is 70% or more, and six first-order diffracted lights corresponding to the six divided regions 8A to 8F are generated. In the state where there is no lens shift or lens tilt at the objective lens 7, the light flux center of the reflected light from the optical disk 11 passes through almost the center of the circular light incident area.
その後、回折型光学素子８からの光は、図２のシリンドリカルレンズ９で非点収差が与えられた後、光検出器１０の対応した受光セル１０Ａ〜１０Ｆにスポットとして集光する。ここで、受光セル１０Ａ〜１０Ｆは回折型光学素子８の分割領域８Ａ〜８Ｆのそれぞれの回折方向に応じて図４に示すように配置されており、上記分割領域８Ａからの１次回折光は受光セル１０Ａで受光され、同様に上記分割領域８Ｂからの１次回折光は受光セル１０Ｂで、上記分割領域８Ｃからの１次回折光は受光セル１０Ｃで、上記分割領域８Ｄからの１次回折光は受光セル１０Ｄで、上記分割領域８Ｅからの１次回折光は受光セル１０Ｅ（１０Ｅ１と１０Ｅ２にまたがる）で、上記分割領域８Ｆからの１次回折光は受光セル１０Ｆ（１０Ｆ１と１０Ｆ２にまたがる）でそれぞれ受光される。ＨＯＥ面８Ｚの光入射領域の中心と光検出器１０の中心は光軸方向に略一致している。 Thereafter, the light from the diffractive optical element 8 is given astigmatism by the cylindrical lens 9 in FIG. 2 and then condensed as a spot on the corresponding light receiving cells 10A to 10F of the photodetector 10. Here, the light receiving cells 10A to 10F are arranged as shown in FIG. 4 according to the diffraction directions of the divided regions 8A to 8F of the diffractive optical element 8, and the first-order diffracted light from the divided region 8A is received. Similarly, the first order diffracted light from the divided region 8B is received by the light receiving cell 10B, the first order diffracted light from the divided region 8C is received by the light receiving cell 10C, and the first order diffracted light from the divided region 8D is received by the light receiving cell. 10D, the first-order diffracted light from the divided region 8E is received by the light receiving cell 10E (10E1 and 10E2), and the first-order diffracted light from the divided region 8F is received by the light receiving cell 10F (10F1 and 10F2). . The center of the light incident area of the HOE surface 8Z and the center of the photodetector 10 are substantially aligned with the optical axis direction.
各受光セル１０Ａ〜１０Ｆ上での各スポットは分割領域に応じた扇形の形状となるが、分割領域がなく円形状のホログラムパターンで最小錯乱円の円形状スポットとなると考えた場合に適切な３次非点収差を有し、他の収差がとれているものである。そして、３次非点収差により生じる２つの焦線のほぼ中間で最小錯乱円となる。受光セルの形状から３次非点収差は４５°方向にもつことが望ましい。 Each spot on each of the light receiving cells 10A to 10F has a fan-shaped shape corresponding to the divided area, but is suitable when it is considered that there is no divided area and a circular hologram pattern is a circular spot of the least circle of confusion. It has second-order astigmatism and other aberrations. And it becomes a circle of minimum confusion almost halfway between two focal lines generated by third-order astigmatism. It is desirable that the third-order astigmatism is in the 45 ° direction due to the shape of the light receiving cell.
すなわち、本実施の形態の光ピックアップ装置では、ホログラムパターン自体に各収差やパワーなどの成分をもたせることができるので、回折型光学素子８のＨＯＥ面８Ｚの各分割領域８Ａ〜８Ｆでは入射した光を回折し、かつ略４５°方向の非点収差を付与するようにシリンドリカルレンズの機能をホログラムパターンと一体にすることが可能である。また、後述するフォーカスエラー信号を得るための分割領域は８Ｅ，８Ｆの２つが対応しており、シリンドリカルレンズの機能をホログラムパターンと一体にした場合には、この２つの分割領域には少なくとも非点収差を付与する機能をもたせる。また、フォーカスエラー信号やトラッキングエラー信号などのサーボ信号によって光ピックアップ装置の調整をする場合を考慮すれば、すべての分割領域に同方向の非点収差をもたせることが望ましい。そして、光検出器１０の受光セル上で集光される各スポットが、非点収差が付与された回折光により生じる２つの焦点のほぼ中間の最小錯乱円になる位置に光検出器１０が配置される。 That is, in the optical pickup device of the present embodiment, since the hologram pattern itself can have components such as aberrations and power, the incident light is incident on the divided regions 8A to 8F of the HOE surface 8Z of the diffractive optical element 8. It is possible to integrate the function of the cylindrical lens with the hologram pattern so as to give astigmatism in the direction of approximately 45 °. Further, two divided areas 8E and 8F correspond to a focus error signal described later. When the function of the cylindrical lens is integrated with the hologram pattern, the two divided areas are at least astigmatized. Provide a function to add aberration. In consideration of the case where the optical pickup device is adjusted by a servo signal such as a focus error signal or a tracking error signal, it is desirable that all divided regions have astigmatism in the same direction. Then, the photodetector 10 is arranged at a position where each spot condensed on the light receiving cell of the photodetector 10 becomes a minimum circle of confusion between the two focal points generated by the diffracted light to which astigmatism is given. Is done.
図５は１つの円形状のホログラムパターンで回折した光束における受光セルでのスポットの一例を示す。図５（ａ）は、分割領域がなく、１つの円形状のホログラムパターンとしたとき、受光セル上でのスポットが最小錯乱円になる場合を示している。このスポットは、コマ収差や球面収差がなく、４５°方向の３次非点収差のみが大きいものである。これは、ホログラムパターンとシリンドリカルレンズを組合せた設計で決められる。ホログラムパターン自体は各収差やパワーなどの成分をもたせることができるので、本実施の形態（図５）では、４５°方向の３次非点収差をもたせてシリンドリカルレンズの機能をホログラムパターンと一体にしている。 FIG. 5 shows an example of a spot at the light receiving cell in the light beam diffracted by one circular hologram pattern. FIG. 5A shows a case where the spot on the light receiving cell becomes a minimum circle of confusion when there is no divided region and a single hologram pattern is formed. This spot is free from coma and spherical aberration and has only a large third-order astigmatism in the 45 ° direction. This is determined by a combination of a hologram pattern and a cylindrical lens. Since the hologram pattern itself can have components such as various aberrations and powers, in this embodiment (FIG. 5), the third-order astigmatism in the 45 ° direction is provided so that the function of the cylindrical lens is integrated with the hologram pattern. ing.
また、図３のＨＯＥ面８Ｚの各分割領域８Ａ〜８Ｆは各々レンズ作用（レンズパワー）を有する。ここで、図３のＨＯＥ面８Ｚの各分割領域８Ａ〜８Ｆとそれに対応する図４の受光セル１０Ａ〜１０Ｆまでの距離は図から明確なように微妙に異なることになる。よって、各分割領域８Ａ〜８Ｆのホログラムパターンはレンズ作用（レンズパワー）に若干の差をつけて受光セル上で同じスポット径で最小錯乱円とすることが望ましい。 Further, each of the divided regions 8A to 8F of the HOE surface 8Z in FIG. 3 has a lens action (lens power). Here, the distances between the divided regions 8A to 8F of the HOE surface 8Z in FIG. 3 and the corresponding light receiving cells 10A to 10F in FIG. 4 are slightly different as is clear from the drawing. Therefore, it is desirable that the hologram patterns in the divided regions 8A to 8F have a minimum confusion circle with the same spot diameter on the light receiving cell with a slight difference in lens action (lens power).
すなわち、図１０に示すように、光検出器１０の受光セル１０Ａ〜１０Ｆの中心位置Ｏからの距離５０ａ〜５０ｆが集光位置によって少し変わる（特に距離５０ｅと５０ｆとは同じにすることが困難）。そのため、図３のＨＯＥ面８Ｚの各分割領域８Ａ〜８Ｆが各々有するレンズ作用（レンズパワー）を、平面状に受光セル１０Ａ〜１０Ｆを配置できるように上記の距離５０ａ〜５０ｆの差を補正する。 That is, as shown in FIG. 10, the distances 50a to 50f from the center position O of the light receiving cells 10A to 10F of the photodetector 10 vary slightly depending on the condensing position (particularly, it is difficult to make the distances 50e and 50f the same). ). Therefore, the difference in the distances 50a to 50f is corrected so that the light receiving cells 10A to 10F can be arranged in a planar shape with respect to the lens action (lens power) of each of the divided regions 8A to 8F of the HOE surface 8Z in FIG. .
また、ＨＯＥ面８Ｚの各分割領域８Ａ〜８Ｆにもたせるレンズ作用（レンズパワー）は任意であり、正のパワー、負のパワーをもたせることにより任意に光検出器１０の位置、すなわち検出系の焦点距離を変えることができる。よって、出射側で制約のあるコリメータレンズ４の焦点距離によらず、検出系の倍率を異ならしめることが可能である。そこで、本実施の形態では、ＨＯＥ面８Ｚの各分割領域８Ａ〜８Ｆにもたせるレンズ作用（レンズパワー）で、レーザ光源２から光ディスク１１までの結像倍率と、光ディスク１１から光検出器１０までの結像倍率の違いを補正するようにしている。 Further, the lens action (lens power) applied to each of the divided regions 8A to 8F of the HOE surface 8Z is arbitrary, and the position of the photodetector 10, that is, the focus of the detection system can be arbitrarily set by giving positive power and negative power. You can change the distance. Therefore, the magnification of the detection system can be made different regardless of the focal length of the collimator lens 4 that is restricted on the emission side. Therefore, in the present embodiment, with the lens action (lens power) applied to each of the divided regions 8A to 8F on the HOE surface 8Z, the imaging magnification from the laser light source 2 to the optical disc 11 and the optical disc 11 to the photodetector 10 are increased. The difference in imaging magnification is corrected.
そして、図５（ｂ）、（ｃ）は図５（ａ）から光ディスクをデフォーカスさせた場合のスポット形状を示している。デフォーカスさせることにより、±４５°方向にスポットが伸び非点収差法によりフォーカスエラー信号を得ることができる。そのような状態でＨＯＥ面８Ｚに分割線を割り当てることにより、図５（ｄ）のように扇形のスポットとなり、各受光セル上に集光するようにできる。 5B and 5C show spot shapes when the optical disk is defocused from FIG. 5A. By defocusing, the spot extends in the direction of ± 45 °, and a focus error signal can be obtained by the astigmatism method. By assigning a dividing line to the HOE surface 8Z in such a state, it becomes a fan-shaped spot as shown in FIG. 5D and can be condensed on each light receiving cell.
図６はフォーカスエラー信号を得るためのＳカーブとスポット形状を示している。図６（ａ）は光ディスク１１が対物レンズ７に近く、Ｓカーブが最大となるときの、受光セル１０Ｅ１、１０Ｆ２のスポット形状を示している。このとき、受光セル１０Ｅ２、１０Ｆ１にはスポットが存在しない。図６（ｂ）は光ディスク１１が対物レンズ７から遠く、Ｓカーブが最小となるときの、受光セル１０Ｅ２、１０Ｆ１のスポット形状を示す。このとき、受光セル１０Ｅ１、１０Ｆ２にはスポットが存在しない。 FIG. 6 shows an S curve and a spot shape for obtaining a focus error signal. FIG. 6A shows the spot shape of the light receiving cells 10E1 and 10F2 when the optical disk 11 is close to the objective lens 7 and the S curve is maximized. At this time, no spots exist in the light receiving cells 10E2 and 10F1. FIG. 6B shows the spot shape of the light receiving cells 10E2 and 10F1 when the optical disk 11 is far from the objective lens 7 and the S curve is minimized. At this time, no spots exist in the light receiving cells 10E1 and 10F2.
そして、デフォーカスを変化させてフォーカスエラー信号ＦＥを計算することで、図６（ｃ）に示すように良好なＳカーブ特性を得ることができる。図６（ｃ）の横軸はデフォーカス量（１目盛り４μｍ）、縦軸はフォーカスエラー信号のレベルを示す。なお、デフォーカスが全く無いときは、受光セル１０Ｅ１、１０Ｅ２、１０Ｆ１、１０Ｆ２に均等に扇形状スポットが形成される。 Then, by calculating the focus error signal FE while changing the defocus, a good S curve characteristic can be obtained as shown in FIG. In FIG. 6C, the horizontal axis indicates the defocus amount (one scale of 4 μm), and the vertical axis indicates the level of the focus error signal. When there is no defocus at all, fan-shaped spots are uniformly formed in the light receiving cells 10E1, 10E2, 10F1, and 10F2.
図７はフォーカスエラー信号ＦＥとトラッキングエラー信号を算出する演算回路の一例の回路系統図を示す。同図において、受光セル１０Ｅ１の信号Ｅ１、受光セル１０Ｅ２の信号Ｅ２、受光セル１０Ｆ１の信号Ｆ１，受光セル１０Ｆ２の信号Ｆ２を用いて、加算器２６、２７及び減算器３４により
ＦＥ＝（Ｅ１＋Ｆ２）−（Ｅ２＋Ｆ１）
なる式によりフォーカスエラー信号ＦＥが算出される。そのフォーカスエラー信号ＦＥの特性は前記図６（ｃ）のＳカーブを示す。このように非点収差法をフォーカスエラー検出に使えるので、従来のＦＥＰに対して親和性が高い。
FIG. 7 is a circuit diagram showing an example of an arithmetic circuit for calculating the focus error signal FE and the tracking error signal. In the figure, by using the signal E1 of the light receiving cell 10E1, the signal E2 of the light receiving cell 10E2, the signal F1 of the light receiving cell 10F1, and the signal F2 of the light receiving cell 10F2, the adders 26 and 27 and the subtractor 34 make FE = (E1 + F2) -(E2 + F1)
The focus error signal FE is calculated by the following formula. The characteristic of the focus error signal FE shows the S curve in FIG. Since the astigmatism method can be used for focus error detection in this way, the affinity for the conventional FEP is high.
次に、トラッキングエラー信号を計算する方法について説明する。光ディスクのグルーブやピットを再生した場合に回折して生じる０次光と１次光の干渉した光束が通過する回折型光学素子８の４つの分割領域（図３の領城８Ａ，８Ｂ，８Ｃ，８Ｄ）からの光を受光する、図４の受光セル１０Ａ、１０Ｂ、１０Ｃ、１０Ｄの各出力信号をそれぞれＡ、Ｂ，Ｃ，Ｄとすると、これらの信号Ａ〜Ｄを用いることにより、通常のプッシュプル法によるトラッキングエラー信号ＰＰを、図７の加算器２１、２２及び減算器２５により式により計算できる。 Next, a method for calculating the tracking error signal will be described. Four divided regions (the castles 8A, 8B, 8C, FIG. 3) of the diffractive optical element 8 through which the light beams of the 0th order light and the 1st order light that are diffracted when the grooves and pits of the optical disk are reproduced are passed. 8D), each of the output signals of the light receiving cells 10A, 10B, 10C, and 10D in FIG. 4 is denoted as A, B, C, and D, respectively. The tracking error signal PP by the push-pull method can be calculated by the adders 21 and 22 and the subtracter 25 in FIG.
ＰＰ＝（Ａ＋Ｂ）−（Ｃ＋Ｄ）
図８（ａ）はＢｌｕ−ｒａｙ規格の光ディスク（ＢＤ）を再生した場合、図８（ｂ）はＨＤ−ＤＶＤ規格の光ディスクを再生した場合の、ＨＯＥ面８Ｚ上での光ディスクの信号面から反射してきた回折光を含むスポット形状を示している。光ディスクからの反射光にはトラック溝やピット（以下トラックと記す）によって回折した１次光と回折しない０次光とが重なる部分（図８（ａ）、（ｂ）斜線部分）が生じ、その部分が干渉する。この重なる部分（干渉する部分）の左右の光強度の違いによってプッシュプル信号が得られることが知られている。
PP = (A + B)-(C + D)
8A shows a case where a Blu-ray standard optical disc (BD) is reproduced, and FIG. 8B shows a case where a HD-DVD standard optical disc is reproduced, which is reflected from the signal surface of the optical disc on the HOE surface 8Z. The spot shape including the diffracted light thus produced is shown. The reflected light from the optical disc has a portion where the primary light diffracted by the track grooves and pits (hereinafter referred to as tracks) overlaps the non-diffracted zero-order light (FIGS. 8A and 8B). Part interferes. It is known that a push-pull signal can be obtained by the difference in the left and right light intensity of this overlapping portion (interfering portion).
回折光の重なる部分の大きさは光ディスクの規格で決まり、図８（ａ）、（ｂ）は１次光と０次光の重なる割合が異なる。対物レンズ７の開口数（ＮＡ）、記録再生用レーザ光の波長、光ディスク上のトラックピッチで１次光と０次光の重なる割合が一義的に定まり、図８において、分割線８ｋから±４５°方向の分割線８ｉ，８ｊ（図３、図８）でＨＯＥ面８Ｚを分割すると、ＢＤの場合の、図８（ａ）の分割線８ｋ，８ｊはスポット半径に対し約７％の余裕、ＨＤ−ＤＶＤの場合の、図８（ｂ）の分割線８ｋ，８ｊはスポット半径に対し約１４％の余裕をもつのみである。 The size of the overlapping portion of the diffracted light is determined by the standard of the optical disc, and FIGS. 8A and 8B are different in the overlapping ratio of the first-order light and the zero-order light. The overlapping ratio of the first-order light and the zero-order light is uniquely determined by the numerical aperture (NA) of the objective lens 7, the wavelength of the recording / reproducing laser beam, and the track pitch on the optical disk. In FIG. When the HOE plane 8Z is divided by dividing lines 8i and 8j in the direction of ° (FIGS. 3 and 8), the dividing lines 8k and 8j in FIG. 8A in the case of BD have a margin of about 7% with respect to the spot radius, In the case of HD-DVD, the dividing lines 8k and 8j in FIG. 8B only have a margin of about 14% with respect to the spot radius.
よって、回折光の重なる部分がフォーカスエラー信号ＦＥの計算で用いる分割領域８Ｅ，８Ｆにかかることがなく、トラックを横断する際の光量変化が生じにくいため、トラック横断によるフォーカスエラー信号ＦＥの変動が生じない。逆に、プッシュプル信号ＰＰにも回折光が重ならない部分（特に光束中心付近）が必要以上に含まれないため、トラックピッチの２倍の周期の回折光の影響を排除できる。分割線８ｋ、８ｊは±４５°が最も望ましいが、回折光の重なる部分が若干分割領域８Ｅ，８Ｆにかかることは影響が少ないので、±４５±５°でも十分対応できる。 Therefore, the overlapping portion of the diffracted light does not cover the divided regions 8E and 8F used in the calculation of the focus error signal FE, and the change in the light amount when traversing the track hardly occurs. Does not occur. On the contrary, since the push-pull signal PP does not include a portion where the diffracted light does not overlap (particularly near the center of the light beam) more than necessary, the influence of the diffracted light having a cycle twice the track pitch can be eliminated. The division lines 8k and 8j are most preferably ± 45 °, but it is less affected when the overlapping portions of the diffracted light are slightly applied to the divided regions 8E and 8F, so that ± 45 ± 5 ° can be sufficiently handled.
ところで、トラッキングエラー信号ＰＰはレンズシフトやラジアル方向のディスクチルト時にオフセットが出ることが知られている。そこで、図７に示す加算器２１〜２４、減算器２５、３１、３３、乗算器３２を用いて次式
ＡＰＰ＝（Ａ＋Ｂ）−（Ｃ＋Ｄ）−ｋ｛（Ｅ１＋Ｆ１）−（Ｅ２＋Ｆ２）｝ (4)
によりトラッキング信号エラーＡＰＰを計算することによって、上記にあげたオフセットのみならず、記録マークの境界で生じるオフセットも低減することが可能である。
By the way, it is known that the tracking error signal PP is offset when the lens is shifted or the disc is tilted in the radial direction. Therefore, using the adders 21 to 24, the subtracters 25, 31, 33, and the multiplier 32 shown in FIG. 7, the following expression APP = (A + B) − (C + D) −k {(E1 + F1) − (E2 + F2)} (4 )
By calculating the tracking signal error APP according to the above, it is possible to reduce not only the above-described offset but also the offset generated at the boundary of the recording mark.
すなわち、信号Ｅ１と信号Ｆ１の和から信号Ｅ２と信号Ｆ２の差をとったＤＣ成分で補正することによりオフセットが低減できる。なお、（４）式中の乗算係数ｋ（図７で示した乗算器３２による乗算係数）はレンズシフトと記録境界でのオフセットを補正し、外乱などがあってもオフセットの発生が小さくなるように最適化したものである。 That is, the offset can be reduced by correcting with the DC component obtained by taking the difference between the signal E2 and the signal F2 from the sum of the signal E1 and the signal F1. Note that the multiplication coefficient k (multiplication coefficient by the multiplier 32 shown in FIG. 7) in the equation (4) corrects the lens shift and the offset at the recording boundary so that the occurrence of the offset is reduced even if there is a disturbance or the like. Is optimized.
図９は基板厚さｔ＝０.０７５ｍｍの第１の記録層の信号面を再生する場合の光検出器１０上でのクロストーク光の状態を示した図である。光ディスク１１のｔ＝０.０７５ｍｍの再生すべき第１の記録層の信号面１１Ｂから反射し、回折型光学素子８のＨＯＥ面８Ｚで回折した１次回折光は、図９において光検出器１０の受光セル１０Ａ〜１０Ｆに４０ａ〜４０ｆで示すように集光するが、ＨＯＥ面８Ｚで他の次数で回折した光（０次回折光も含む）はクロストーク光となる。受光セル１０Ａ〜１０Ｆの近くにスポットを形成するのは０次回折光と−１次回折光である。高次光は受光セルより離れる方向に行くので問題とならない。 FIG. 9 is a diagram showing the state of crosstalk light on the photodetector 10 when reproducing the signal surface of the first recording layer having the substrate thickness t = 0.075 mm. The first-order diffracted light reflected from the signal surface 11B of the first recording layer to be reproduced at t = 0.075 mm of the optical disk 11 and diffracted by the HOE surface 8Z of the diffractive optical element 8 is shown in FIG. Light is condensed on the light receiving cells 10A to 10F as indicated by 40a to 40f, but light diffracted by other orders on the HOE surface 8Z (including 0th order diffracted light) becomes crosstalk light. It is the 0th-order diffracted light and the -1st-order diffracted light that form spots near the light receiving cells 10A to 10F. Since higher order light goes away from the light receiving cell, there is no problem.
まず、再生すべき第１の記録層の信号面１１Ｂからの０次回折光は図９に４１で示すように受光セル１０Ａ〜１０Ｆの中心位置に小径の円形スポットを形成して略集光する。よって、受光セル１０Ａ〜１０Ｆが光検出器１０の受光面の中心位置からそれぞれ若干離れていれば０次回折光の影響はない。次に、再生すべき第１の記録層の信号面１１Ｂからの−１次回折光は図９に４２ａ、４２ｂ、４２ｃで示すように、受光セル１０Ａ〜１０Ｆの中心位置とトラック方向を軸に対称に生じるので、主にトラック方向の配置次第で上記の−１次回折光が受光セル１０Ａ〜１０Ｆにかからないようにすることが可能である。 First, the 0th-order diffracted light from the signal surface 11B of the first recording layer to be reproduced forms a small-diameter circular spot at the center position of the light receiving cells 10A to 10F as shown by 41 in FIG. Therefore, if the light receiving cells 10A to 10F are slightly separated from the center position of the light receiving surface of the photodetector 10, there is no influence of the 0th order diffracted light. Next, the −1st order diffracted light from the signal surface 11B of the first recording layer to be reproduced is symmetric with respect to the center position and the track direction of the light receiving cells 10A to 10F as indicated by 42a, 42b and 42c in FIG. Therefore, depending on the arrangement in the track direction, it is possible to prevent the -1st order diffracted light from being applied to the light receiving cells 10A to 10F.
また、光ディスク１１の基板厚さｔ＝０.１ｍｍの再生しない第２の記録層の信号面１１Ｂから反射し、ＨＯＥ面８Ｚで回折した光もクロストーク光となる。これらのクロストーク光は倍率に合わせて大きく広がるため、１次回折光の影響が主で、０次回折光まで考えればよい。まず、再生しない第２の記録層（他層）で反射し、ＨＯＥ面８Ｚで回折した光の１次回折光（クロストーク光の１次回折光）は回折型光学素子８の６つの分割領域８Ａ〜８Ｆのもつそれぞれの扇形の中心角で広がり、図９に４４ａ、４４ｂ、４４ｃ、４４ｄ、４４ｅ、４４ｆで示すような扇形の形状で光検出器１０の受光面に集光する。このクロストーク光の１次回折光は主にラジアル方向の配置で、受光セル１０Ａ〜１０Ｆにかからないようにすることが可能である。 Further, the light reflected from the signal surface 11B of the second recording layer that is not reproduced and having a substrate thickness t = 0.1 mm of the optical disk 11 and diffracted by the HOE surface 8Z also becomes crosstalk light. Since these crosstalk lights greatly spread according to the magnification, the influence of the first-order diffracted light is the main, and it is sufficient to consider even the zero-order diffracted light. First, first-order diffracted light (first-order diffracted light of crosstalk light) reflected by the second recording layer (other layer) that is not reproduced and diffracted by the HOE surface 8Z is divided into six divided regions 8A to 8D of the diffractive optical element 8. It spreads at the central angle of each fan shape of 8F, and is condensed on the light receiving surface of the photodetector 10 in the fan shape shown by 44a, 44b, 44c, 44d, 44e, 44f in FIG. The first-order diffracted light of the crosstalk light is mainly arranged in the radial direction and can be prevented from being applied to the light receiving cells 10A to 10F.
また、他層で反射し、ＨＯＥ面８Ｚで回折した光の０次回折光（クロストーク光の０次回折光）は図９に４３で示すように、その中心位置が受光セル１０Ａ〜１０Ｆの中心位置に略一致し、かつ、上記のスポット４１よりもかなり大径の円形スポットを形成して集光するものの、ラジアル方向、トラック方向の配置を適切にすれば受光セル１０Ａ〜１０Ｆにかからないようにすることが可能である。 Further, the zero-order diffracted light (the zero-order diffracted light of the crosstalk light) reflected by the other layer and diffracted by the HOE surface 8Z is centered at the center position of the light receiving cells 10A to 10F, as indicated by 43 in FIG. The circular spot having a diameter substantially larger than that of the spot 41 is formed and condensed. However, if the arrangement in the radial direction and the track direction is made appropriate, the light receiving cells 10A to 10F are not covered. It is possible.
よって、以上より、上記の分割領域８Ａ〜８Ｆと受光セル１０Ａ〜１０Ｆの配置を図３，図４のようにすることで、クロストーク光が受光セル１０Ａ〜１０Ｆに重ならないため、多層ディスクの安定した記録又は再生が可能となる。また、クロストーク光の０次回折光を受光セル１０Ａ〜１０Ｆすべてにかかるようにして、すべての受光セルに均等にオフセットを与えて安定した記録又は再生をすることも可能である。 Therefore, by arranging the divided regions 8A to 8F and the light receiving cells 10A to 10F as shown in FIGS. 3 and 4 as described above, the crosstalk light does not overlap the light receiving cells 10A to 10F. Stable recording or reproduction is possible. In addition, it is possible to perform stable recording or reproduction by equally offsetting all the light receiving cells by applying the zero-order diffracted light of the crosstalk light to all the light receiving cells 10A to 10F.
なお、メイン信号ＲＦは図７に示すように、加算器２１〜２４、２８、２９及び３０により次式に示す各受光セル１０Ａ〜１０Ｆからの信号Ａ〜Ｄ、Ｅ１、Ｅ２、Ｆ１、Ｆ２の総和で求められる。 As shown in FIG. 7, the main signal RF is sent from the light receiving cells 10A to 10F represented by the following equations by the adders 21 to 24, 28, 29, and 30 to the signals A to D, E1, E2, F1, and F2. Calculated as the sum.
ＲＦ＝Ａ＋Ｂ＋Ｃ＋Ｄ＋Ｅ１＋Ｅ２＋Ｆ１＋Ｆ２ （５）
また、ＢＤ−ＲＯＭなどの再生型光ディスクに対応して、ＤＰＤ法によるトラッキングエラー信号検出も可能である。すなわち、信号Ａと信号Ｃの和（Ａ＋Ｃ）と信号Ｂと信号Ｄの和（Ｂ＋Ｄ）を比較演算すればよく、トラッキングエラー信号は新プッシュプル法に基づくＡＰＰ信号とＤＰＤ法に基づくＤＰＤ信号が両立できる構成である。
RF = A + B + C + D + E1 + E2 + F1 + F2 (5)
In addition, tracking error signals can be detected by the DPD method in correspondence with a reproduction type optical disc such as a BD-ROM. That is, the sum of the signals A and C (A + C) and the sum of the signals B and D (B + D) may be compared, and the tracking error signal is determined by the APP signal based on the new push-pull method and the DPD signal based on the DPD method. This is a compatible configuration.
さらに、図４に示したように本実施の形態では受光セルの数も少なく、よって回路規模が小さくコスト安であり、ノイズを抑えることも可能であり、図１に示したようにグレーティングが不要なのでトラックピッチが異なる光ディスクにも対応が容易である利点がある。 Furthermore, as shown in FIG. 4, in the present embodiment, the number of light receiving cells is small, so that the circuit scale is small, the cost is low, and noise can be suppressed, and no grating is required as shown in FIG. Therefore, there is an advantage that it can be easily applied to optical disks having different track pitches.
以上説明したように、本実施の形態の光ピックアップ装置によれば、単層光ディスクのみならず多層光ディスクを記録又は再生する場合も、ＨＯＥ面をトラック方向と垂直な方向（ラジアル方向）の分割線８ｋで分け、更にその分割線８ｋと略±４５°方向をなす２つの分割線８ｉ、８ｊで分けることで、少なくとも６個の分割領域に分けると共に、光検出器１０を少なくとも８つの対応した受光セル１０Ａ〜１０Ｆを設けることで、良好に記録又は再生することができる。 As described above, according to the optical pickup device of the present embodiment, the dividing line in the direction perpendicular to the track direction (radial direction) is used when recording or reproducing not only a single layer optical disc but also a multilayer optical disc. Divided into 8 divisions and further divided into two division lines 8i and 8j that form a direction of approximately ± 45 ° with the division line 8k, thereby dividing into at least 6 divisional areas and at least 8 corresponding light receiving elements. By providing the cells 10A to 10F, recording or reproduction can be favorably performed.
なお、上記の実施の形態では波長４０５ｎｍの青色レーザ光源１０を１つ用いてＢＤのみ１種類の光ディスクに対応する光ピックアップ装置の構成を示したが、本発明はこの実施の形態に限定されるものではなく、同じ青色レーザ光源を用いてＢＤ，ＨＤ−ＤＶＤの双方に対応する光ピックアップ装置、波長６５０ｎｍの赤色レーザ光源を用いてＤＶＤに対応する光ピックアップ装置、あるいはＣＤまで含めた複数の光ディスクに対応する光ピックアップ装置にも適用可能である。 In the above embodiment, the configuration of the optical pickup device corresponding to one type of optical disk using only one blue laser light source 10 having a wavelength of 405 nm is shown. However, the present invention is limited to this embodiment. Rather than an optical pickup device that supports both BD and HD-DVD using the same blue laser light source, an optical pickup device that supports DVD using a red laser light source with a wavelength of 650 nm, or a plurality of optical disks including a CD It can also be applied to an optical pickup device corresponding to the above.
１ 光ピックアップ装置
２ レーザ光源
３ 偏光ビームスプリッタ
３Ａ 偏光選択性誘電体多層膜
４ コリメータレンズ
５ 立上ミラー
５Ａ 反射膜
６ １／４波長板
７ 対物レンズ
８ 回折型光学素子
８Ａ〜８Ｆ 分割領域
８Ｚ ＨＯＥ面
８ｋ、８ｉ、８ｊ 分割線
９ シリンドリカルレンズ
１０ 光検出器
１０Ａ〜１０Ｆ、１０Ｅ１、１０Ｅ２、１０Ｆ１、１０Ｆ２ 受光セル
１１ 片面２層光ディスク
１１Ａ ビーム入射面
１１Ｂ 信号面
ＬＳ 出射光
ＬＴ 反射光
DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Laser light source 3 Polarizing beam splitter 3A Polarization selective dielectric multilayer film 4 Collimator lens 5 Standing mirror 5A Reflective film 6 1/4 wavelength plate 7 Objective lens 8 Diffractive optical element 8A-8F Division | segmentation area | region 8Z HOE Surface 8k, 8i, 8j Dividing line 9 Cylindrical lens 10 Photodetector 10A to 10F, 10E1, 10E2, 10F1, 10F2 Light receiving cell 11 Single-sided dual-layer optical disk 11A Beam incident surface 11B Signal surface LS Emission light LT Reflected light
Claims (6)
前記回折型光学素子は、
前記光ディスクのトラックを投影した時のそのトラックの方向と垂直な方向に前記反射光の光束を分割する第１の分割線と、前記トラックの方向と平行な方向に対して各々反対方向に略４５°方向に前記反射光の光束を分割する第２及び第３の分割線とにより、少なくとも６つの分割領域に分割され、該６つの分割領域は各々入射する反射光を回折して方向を変化させ、
前記反射光は、前記回折型光学素子の該分割領域のうち少なくとも２つ以上、もしくはシリンドリカルレンズにより非点収差を付与され、
前記光検出器は、
前記回折型光学素子の６つの分割領域を通してそれぞれ出射する光を個別に受光する少なくとも６つの受光セルから構成されると共に、前記６つの受光セルで受光される各スポットが、前記非点収差を付与された回折光により生じる２つの焦線のほぼ中間の最小錯乱円になる位置に配置され、かつ、少なくとも６つの前記分割領域の中で前記トラックの方向と同一方向を含む２つの分割領域を通して出射する光を受光する２つの受光セルが、前記トラックの方向と垂直な方向の分割線でそれぞれ２分割されている構成であることを特徴とする光ピックアップ装置。 A light source that emits light, an objective lens that collects the light emitted from the light source on an optical disc to form a spot, and diffracts reflected light from the optical disc that has passed through the objective lens and emits it in a predetermined direction A diffractive optical element that receives the light emitted from the diffractive optical element and photoelectrically converts the light, and the light emitted from the light source and directed to the objective lens and reflected from the optical disk, An optical pickup device comprising an optical path separation element that separates the reflected light that passes through and travels toward the photodetector,
The diffractive optical element is
A first dividing line that divides the luminous flux of the reflected light in a direction perpendicular to the direction of the track when the track of the optical disk is projected, and approximately 45 in a direction opposite to the direction parallel to the direction of the track. Divided into at least six divided areas by the second and third dividing lines that divide the luminous flux of the reflected light in the ° direction, and the six divided areas each change the direction by diffracting incident reflected light. ,
The reflected light is given astigmatism by at least two or more of the divided regions of the diffractive optical element, or a cylindrical lens,
The photodetector is
It is composed of at least six light receiving cells that individually receive light emitted through the six divided regions of the diffractive optical element, and each spot received by the six light receiving cells gives the astigmatism. Exits through two divided areas including the same direction as the direction of the track among at least six of the divided areas. An optical pickup device characterized in that two light receiving cells for receiving light are divided into two by dividing lines in a direction perpendicular to the track direction.
ＰＰ＝（Ａ＋Ｂ）−（Ｃ＋Ｄ）
によりトラッキングエラー信号ＰＰを生成するトラッキングエラー信号生成手段を有することを特徴とする請求項１乃至３のうちいずれか一項記載の光ピックアップ装置。 Among the six divided regions of the diffractive optical element, two divided regions including the same direction as the track direction are defined as a first divided region and a second divided region, and the remaining four divided regions are When divided by an imaginary line passing through the center of the reflected light in the same direction as the direction of the track, the two divided areas belonging to one same side are defined as a third divided area and a fourth divided area, When the other two divided regions belonging to the same side are the fifth divided region and the sixth divided region, the diffracted lights diffracted by the third divided region and the fourth divided region are received respectively. The other two light receiving cells of the photodetector for receiving the output signals A and B of the two light receiving cells of the photodetector and the diffracted light diffracted by the fifth divided region and the sixth divided region, respectively. Output signals C and D of Following equation
PP = (A + B)-(C + D)
4. The optical pickup device according to claim 1, further comprising tracking error signal generation means for generating a tracking error signal PP.
前記第３の分割領域及び第４の分割領域により回折された回折光をそれぞれ受光する前記第３及び第４の受光セルの出力信号Ａ及びＢと、前記第５の分割領域及び第６の分割領域により回折された回折光をそれぞれ受光する前記第５及び第６の受光セルの出力信号Ｃ及びＤと、各々２分割されている前記第１及び第２の受光セルを前記トラックの方向と同一方向の仮想線で分けたとき、一方の同じ側に属する前記第１及び第２の受光セルの２つの分割受光セル部の出力信号Ｅ１及びＦ１と、他方の同じ側に属する前記第１及び第２の受光セルの残りの２つの分割受光セル部の出力信号Ｅ２及びＦ２とを用いて、次式
ＡＰＰ＝（Ａ＋Ｂ）−（Ｃ＋Ｄ）−ｋ｛（Ｅ１＋Ｆ１）−（Ｅ２＋Ｆ２）｝
（ただし、ｋは定数）
によりトラッキングエラー信号ＡＰＰを生成するトラッキングエラー信号生成手段を有することを特徴とする請求項１乃至３のうちいずれか一項記載の光ピックアップ装置。 Among the six divided regions of the diffractive optical element, two divided regions including the same direction as the track direction are defined as a first divided region and a second divided region, and the remaining four divided regions are When divided by an imaginary line passing through the center of the reflected light in the same direction as the direction of the track, the two divided areas belonging to one same side are defined as a third divided area and a fourth divided area, In addition, when the two divided regions belonging to the other same side are defined as a fifth divided region and a sixth divided region, the photodetector includes the first, second, third, fourth, fifth and It comprises first, second, third, fourth, fifth and sixth light receiving cells that individually receive the diffracted light diffracted by the sixth divided region, respectively, and the first light receiving cell and the The second light receiving cell is a dividing line in a direction perpendicular to the track direction. Respectively divided into two parts,
Output signals A and B of the third and fourth light-receiving cells that receive the diffracted light diffracted by the third and fourth divided regions, respectively, and the fifth and sixth divided regions. The output signals C and D of the fifth and sixth light receiving cells that respectively receive the diffracted light diffracted by the region, and the first and second light receiving cells divided in two are the same as the direction of the track. When divided by imaginary lines in the direction, the output signals E1 and F1 of the two divided light receiving cell portions of the first and second light receiving cells belonging to one and the same side, and the first and second belonging to the other same side Using the output signals E2 and F2 of the remaining two divided light receiving cell portions of the two light receiving cells, the following expression APP = (A + B) − (C + D) −k {(E1 + F1) − (E2 + F2)}
(Where k is a constant)
4. The optical pickup device according to claim 1, further comprising tracking error signal generation means for generating a tracking error signal APP according to claim 1.
前記第１及び第２の受光セルを前記トラックの方向と同一方向の仮想線で分けたとき、一方の同じ側に属する前記第１及び第２の受光セルの２つの分割受光セル部の出力信号Ｅ１及びＦ１と、他方の同じ側に属する前記第１及び第２の受光セルの残りの２つの分割受光セル部の出力信号Ｅ２及びＦ２とを用いて、次式
ＦＥ＝（Ｅ１＋Ｆ２）−（Ｅ２＋Ｆ１）
によりフォーカスエラー信号ＦＥを生成するフォーカスエラー信号生成手段を有することを特徴とする請求項１乃至５のうちいずれか一項記載の光ピックアップ装置。 When two divided regions including the same direction as the track direction among the six divided regions of the diffractive optical element are defined as a first divided region and a second divided region, the photodetector is The diffracted light that is diffracted with astigmatism given by the first divided region and the second divided region, respectively, or is diffracted by the first divided region and the second divided region, and is astigmatized by the cylindrical lens. It has at least a first light receiving cell and a second light receiving cell that individually receive the diffracted light to which aberration is applied, and the first light receiving cell and the second light receiving cell are in the direction of the track. Are each divided into two by dividing lines in a direction perpendicular to
When the first and second light receiving cells are separated by a virtual line in the same direction as the track direction, the output signals of the two divided light receiving cell portions of the first and second light receiving cells belonging to the same one side Using E1 and F1 and the output signals E2 and F2 of the remaining two divided light receiving cell portions of the first and second light receiving cells belonging to the other side, the following expression FE = (E1 + F2) − (E2 + F1) )
6. The optical pickup device according to claim 1, further comprising a focus error signal generation unit configured to generate a focus error signal FE.
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