JP2005293809A - Optical disk recording and/or reproducing apparatus and signal detection method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a phenomenon that an arithmetic operation of a differential push-pull error signal is inaccurate at recording/reproduction of an optical disk having a plurality of information recording layers and detect a proper track control error signal. <P>SOLUTION: The size of a light receiving face of two-division light receiving elements 274, 275 for detecting a sub beam used for only detecting the track control error signal is made smaller than the size of a light receiving face of a 4-division light receiving element 273 for a major beam for reproducing an information signal. Concretely, the light receiving elements 274, 275 resulting from obliquely cutting off the four corners of the light receiving elements each having a square outer shape are employed. Further, in addition, the effect due to inter-layer stray light can be more reduced by selecting a coefficient (k) in an error computing equation (10) depending on the number of layers of the optical disk such as a single layer disk or a double layer disk. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical disc recording and / or reproducing apparatus for irradiating an optical disc with a main beam and a sub beam, and detecting a track control error signal or the like by a differential push-pull method using these return lights, and its signal detection Regarding the method.

Conventionally, in this type of optical disc recording / reproducing apparatus, an information signal is obtained by following a focused spot of a light beam from an optical pickup with respect to a signal track composed of a guide groove (groove) previously formed in a spiral shape on an optical disc. As a method for performing this follow-up control, a method for detecting a push-pull error signal (so-called push-pull detection method) is generally used.
In this push-pull detection method, reflected light diffracted by the groove shape is divided into four light receiving elements having four light receiving regions divided in the track tangential direction of the optical disk and the optical disk radial direction as shown in FIG. A track control error signal is generated by detecting the interference intensity distribution of the 0th-order diffracted light (main beam) and ± 1st-order diffracted light (sub beam).

On the other hand, a differential push-pull detection method has been proposed as a method for reducing the effects of fluctuations in the amount of light in the push-pull error signal, lens offset, and disk tilt (see, for example, Patent Document 1).
In this differential push-pull detection method, for example, three divided light receiving elements as shown in FIG. 9 are used. That is, the divided light receiving elements are divided into four divided light receiving elements 270 that detect the return light of the main beam by four light receiving areas divided in the track tangential direction of the optical disk and the optical disk radial direction, and on both sides of the four divided light receiving elements 270. It is composed of two two-divided light receiving elements 271 and 272 that are arranged and detect return light of the sub beam by two light receiving regions that are divided in the track tangential direction.
Specifically, the differential push-pull error is obtained by subtracting the sum of the push-pull signals detected by the two sub beams by the coefficient (k) from the push-pull signal detected by the main beam. A signal is detected (details will be described later).
JP-A-61-94246

By the way, in the optical disc recording / reproducing apparatus that irradiates the main beam and the sub beam as described above, in general, the intensity ratio of the main beam and the sub beam is often set to about 10: 1. However, with this setting, for example, as shown in FIG. 10, in order to perform signal reproduction from an optical disc (so-called two-layer disc) 103 having two information recording layers 100 and 101, the information is collected on one information recording layer 100. When the light spot is irradiated, it is difficult to separate excess reflected light (stray light) from the other information recording layer 101, and this stray light component is also detected by the light receiving element.
This phenomenon is also referred to as interlayer stray light, but in generating differential push-pull signals, an AGC (Automatic Gain Control) circuit that normalizes error signals by disk reflectivity and irradiation power during recording or reproduction. However, there is a problem that the interlayer stray light of the main beam is detected by the light receiving element of the sub beam, and the standardization of the signal becomes inaccurate.
Therefore, the present invention can reduce the phenomenon that the calculation of the differential push-pull error signal becomes inaccurate during recording and / or reproduction of an optical disc having a plurality of information recording layers, and can detect an appropriate track control error signal. It is an object of the present invention to provide an optical disc recording and / or reproducing apparatus and a signal detection method thereof.

  In order to achieve the above object, an optical disk recording and / or reproducing apparatus according to the present invention includes an optical pickup that performs signal information recording and / or reproducing operations on an optical disk, and a light beam that is irradiated onto the optical disk by the optical pickup. Is divided into a main beam and sub-beams on both sides and supplied to the optical disc, a photodetector for detecting the return light from the optical disc, and a phase difference method and a difference using the detection signal from the photodetector. An arithmetic circuit for detecting a track control error signal by a dynamic push-pull method, and the photodetector detects the return light of the main beam by a light receiving region divided at least in the track tangential direction and the optical disc radial direction of the optical disc. An M-divided light receiving element to be detected and a light receiving area arranged on both sides of the M-divided light receiving element and divided at least in the track tangential direction M-divided light receiving elements for detecting the return light of the main beam, wherein the light receiving area of the N-divided light receiving element for detecting the return light of the sub-beam detects the return light of the main beam. The track control error signal is detected by a differential push-pull method using a light receiving area smaller than the element and using the M divided light receiving element and the N divided light receiving element.

  The signal detection method of the present invention also includes an optical pickup for recording and / or reproducing signal information with respect to an optical disc, and a light beam applied to the optical disc by the optical pickup is split into a main beam and sub beams on both sides. An optical element to be supplied to the optical disc, a photodetector for detecting return light from the optical disc, and detection of a track control error signal by a phase difference method and a differential push-pull method using a detection signal from the photodetector An M-divided light-receiving element that detects the return light of the main beam by a light-receiving region divided in at least the track tangential direction and the optical disc radial direction of the optical disc; Two detectors are provided on both sides of the light receiving element, and detect the return light of the sub beam by at least light receiving areas divided in the track tangential direction. A signal detection method for an optical disc recording and / or reproducing apparatus having an N-divided light receiving element, wherein the light receiving area of the N-divided light receiving element for detecting the return light of the sub beam detects the return light of the main beam. The track control error signal is detected by a differential push-pull method using a light receiving area smaller than the light receiving element and using the M divided light receiving element and the N divided light receiving element.

  According to the optical disk recording and / or reproducing apparatus and the signal detection method of the present invention, the light receiving area of the N-divided light receiving element for detecting the return light of the sub beam is the light receiving area of the M-divided light receiving element for detecting the return light of the main beam. Is smaller and the track control error signal is detected by the differential push-pull method using three divided light receiving elements, so that signal recording or signal reproduction on an optical disc having a plurality of information recording layers is possible. Sometimes it is possible to reduce the error of the calculation coefficient (k) of the differential push-pull method track error signal caused by interlayer stray light, and the differential push-pull method can be applied to various optical discs ranging from multi-layer discs to single-layer discs. There is an effect that appropriate track control can be performed.

  An optical disc recording and / or reproducing apparatus and a signal detection method thereof according to an embodiment of the present invention irradiate an optical disc by diffracting a light beam into a main beam (0th order diffracted light) and a sub beam (± 1st order diffracted light) through a diffraction grating. Then, the return light is received by a four-divided light receiving element for the main beam and the two-divided light receiving element for the sub beam, and information signals are reproduced and focus and tracking are controlled using the output signals of these divided light receiving elements. The tracking control uses a differential push-pull method, and the light receiving area of the two-divided light receiving element for detecting the return light of the sub beam is made smaller than the light receiving area of the four-divided light receiving element for detecting the return light of the main beam. Thus, the error of the calculation coefficient (k) of the differential push-pull type tracking error signal caused by the interlayer stray light of the multilayer disk is reduced.

FIG. 1 is a block diagram showing an example of the overall configuration of an optical disc recording / reproducing apparatus according to an embodiment of the present invention. FIGS. 2 and 3 show examples of the configuration of an optical pickup and a signal arithmetic circuit of the optical disc recording / reproducing apparatus shown in FIG. It is a block diagram.
4 is a cross-sectional view showing the objective lens driving unit and the optical disk of the optical disk recording / reproducing apparatus shown in FIG. 1, and FIG. 5 is a cross-sectional view showing the structure of the optical pickup for reproducing the optical disk of the optical disk recording / reproducing apparatus shown in FIG. 6 is an enlarged plan view showing a configuration of a divided light receiving element provided in the optical disc recording / reproducing apparatus shown in FIG.
The optical disk recording / reproducing apparatus of this embodiment is an example of an optical system used in an optical disk (Blu-ray Disc) recording / reproducing apparatus using a two-group objective lens having a numerical aperture of 0.85 and a blue-violet semiconductor laser light source having a wavelength of 405 nm. Is shown. Hereinafter, the present embodiment will be described focusing on a method for detecting a track control error signal used in such an optical disc recording / reproducing apparatus.

First, a two-group objective lens for an optical disc optical system in the present embodiment will be described with reference to FIG.
As shown in the figure, the objective lens driving unit of the present embodiment is composed of the first lens 12 and the second lens 14 constituting the second group objective lens, the lens holder 13, the biaxial electromagnetic actuator 15, and the like. The optical disc 11 is disposed so as to face the signal recording surface in the vicinity.
The second lens 14 is mounted on a biaxial electromagnetic actuator 15 having a structure movable in the optical axis direction and in a direction orthogonal to the signal track (tangent). The first lens 12 is supported by the lens holder 13 so as to be positioned on the same optical axis as the second lens 14, and these two lenses 12 and 14 are integrated with a numerical aperture of 0.85. Functions as a two-group objective lens. A beam from a semiconductor laser light source (not shown in FIG. 4) is focused on the optical disk 11 by passing through these two lenses.
Note that the increase in the numerical aperture of the objective lens generally decreases the disc tilt tolerance in the optical disc recording / reproducing apparatus. Accordingly, even in an optical disk recording / reproducing apparatus having a lens numerical aperture increased to 0.85, the thickness of the light transmission protective layer (cover layer) 11a is set to 0 in order to obtain a tilt tolerance substantially equal to that of a DVD (Digital Versatile Disc). A method for reducing the thickness to about 1 mm has been proposed.

Next, the configuration of the optical pickup for reproducing an optical disk will be described with reference to FIG.
First, the emitted light from the semiconductor laser 16 is converted into parallel light by the collimator lens 17 and passes through a diffraction grating 19 for generating a sub beam (± first order diffracted light) used for generating a track control error signal. Condensed on the optical disk 11 by the second group objective lenses 12 and 14.
A part of the emitted light is reflected by the polarization beam splitter 20 and then guided to the light output detector 22 for detecting the light output by the condenser lens 21 and used for the purpose of controlling the laser output to a constant value. The amount of light incident on the photodetector 22 can be adjusted by rotating the half-wave plate 18, and the actual laser output can be arbitrarily set by an automatic power control (APC) circuit (not shown). The light emission output value is controlled.
The liquid crystal element 23 has a concentric electrode pattern and plays a role of correcting spherical aberration caused by the thickness error of the cover layer according to the voltage applied to each electrode. A quarter wavelength plate 24 for converting linearly polarized light of the semiconductor laser 16 into circularly polarized light is disposed in front of the second group lens.

On the other hand, the reflected light from the optical disk 11 is reflected by the beam splitter 20 and then guided to the detection optical path. In this example, the astigmatism method is used as the focus control error signal, the phase difference method (for example, see Japanese Patent Laid-Open No. 58-150145), and the differential push-pull method (for example, Japanese Patent Laid-Open No. 61-61) as the track control error signal. -94246), the convergent light passing through the condensing lens 25 and the multi-lens 26 enters the photodetector 27 for detecting the servo error signal and the RF signal, and is subjected to photoelectric conversion. .
As shown in FIG. 6, the photodetector 27 includes one quadrant light receiving element 273 and two two-divided light receiving elements 274 and 275. Note that circles S1, S2, and S3 in the figure indicate the spots of the main beam and the sub beam, respectively.
The four-divided light receiving element 273 has four divided light receiving areas A to D arranged in four in the track tangential direction indicated by the arrow α and in the orthogonal direction (optical disc radial direction). A beam spot S1 is incident. Each of the divided light receiving areas A to D has a broadband characteristic, and has a positional relationship in which the light receiving area A and the light receiving area D and the light receiving area B and the light receiving area C face each other in the track tangential direction.

The two-divided light receiving elements 274 and 275 are arranged on both sides in the orthogonal direction to the track tangential direction with the four-divided light receiving element 273 interposed therebetween, and the two-divided light receiving elements 274 are arranged in two in the orthogonal direction to the track tangential direction. There are two divided light receiving areas E and F, and a sub beam spot S2 is incident as shown in the figure. The two-divided light receiving element 275 also has two divided light receiving regions G and H that are divided into two in the direction orthogonal to the track tangential direction, and a main beam spot S3 is incident as shown in the figure.
In the photodetector 27 of this embodiment, as can be seen from the comparison with the conventional example shown in FIG. 9, the light receiving surfaces of the two-divided light receiving elements 274 and 275 that receive the sub-beam receive the main beam. The area is smaller than the light receiving surface of the element 273. That is, in the illustrated example, the light receiving surface of the four-divided light receiving element 273 is formed over the entire outer shape and is common to the conventional element shown in FIG. 9, but the light receiving surfaces of the two-divided light receiving elements 274 and 275 are The four outer corners are cut obliquely, and the area is smaller than that of the light receiving surface of the quadrant light receiving element 273. In addition, the effect which formed each division | segmentation light receiving element 273,274,275 in such a shape is explained in full detail behind.
Of the illumination light divided into three beams of zero-order light (main beam) and ± first-order light (sub-beam) by the diffraction grating 19 with respect to such a photodetector 27, the reflected light of the zero-order light is For example, the light is received by the light receiving areas A to D of the four-divided light receiving element 273 as indicated by the spot S1, and the reflected light of ± 1st order light is divided into the two-divided light receiving elements 274, as indicated by the spots S2 and S3, The light is received by the light receiving region 275 from E to H.
Based on the outputs of these light receiving areas A to H, a focus control error signal FE and a differential push-pull error signal DPP (Differential Push-Pull Detection Method) as a track control error signal are calculated.

Next, a configuration for executing the differential push-pull detection method in this embodiment will be described with reference to FIGS.
As shown in the figure, the optical pickup of the present embodiment performs a difference calculation of the outputs of the head amplifiers 31a to 31h for amplifying the detection signals from the respective divided light receiving regions of the photodetector 27 and the head amplifiers 31a to 31h. Operational amplifiers 32a to 32h, automatic gain controller (AGC) circuits 33a to 33c for automatically adjusting the gains of the operation result signals of the operational amplifiers 32a to 32h, SPP1 signals and SPP2 signals from the AGC circuits 33a to 33c And operational amplifiers 32i and 32j for calculating a differential push-pull error control signal using the MPP signal.

Next, arithmetic processing by such an arithmetic circuit will be described.
The reproduction signal read from the optical disk 11 by the light receiving element shown in FIG. 6 is input to the head amplifiers 31a to 31h. Each of the head amplifiers 31a to 31h photoelectrically converts a reproduction signal from the optical system (here, the amount of light received in each divided light receiving region shown in FIG. 6) and amplifies it to a predetermined level necessary for processing in the subsequent stage. .
A push-pull signal (MPP) is obtained by performing the calculation shown in Expression (1) on the outputs of the head amplifiers 31a to 31d of the light receiving elements A to D with respect to the main beam.
MPP = (A + B) − (C + D) (1)
M_SUM = A + B + C + D (2)
Further, AGC is applied to the push-pull signal of the main beam by normalizing the signal using the sum of the head amplifier outputs of the light receiving elements A to D (formula (2), M_SUM signal).
MPP_AGC = MPP / M_SUM (3)

Similarly, the push-pull signals (SPP1, SPP2) of the sub beam and the sum signal are obtained by performing the calculations shown in the equations (4) to (7) for the reflected light of the + 1st order light and the −1st order diffracted light. As a result, the AGC operation is realized by normalizing these signals according to the equations (8) and (9).
SPP1 = EF (4)
SPP2 = GH (5)
S1_SUM = E + F (6)
S2_SUM = G + H (7)
SPP1_AGC = SPP1 / S1_SUM (8)
SPP2_AGC = SPP2 / S2_SUM (9)
Finally, the following calculation is performed on the output signals of Expression (3), Expression (8), and Expression (9) to calculate the differential push-pull error signal (DPP).
DPP = MPP_AGC-k (SPP1_AGC + SPP2_AGC) (10)
Note that the value of k in equation (10) can be set to an arbitrary value by changing the resistance value of the variable resistor R4 shown in FIG. 3, for example.
The differential push-pull error signal obtained by the circuit configuration shown in FIGS. 2 and 3 is generated when the irradiation spot is diffracted and reflected by the groove structure formed on the optical disc or the information pit row. .

In addition, the interlayer stray light intensity ratio (η) in a two-layer disc is approximately given by equation (11) when the reflectances of the two information recording layers (L0 layer and L1 layer) shown in FIG. 10 are equal.
η = S / η / M2 · (2d / tan θ) ² (11)
In equation (11), S represents the area of the light receiving element, M represents the magnification of the detection optical system, d represents the interlayer distance, and θ represents the angle formed by the optical axis and the outermost edge beam of the condensed beam in the disk medium. In the case of a combination of an objective lens with a numerical aperture of 0.85 and an optical disk having a cover layer with a refractive index of 1.6, θ is about 32 degrees, the light receiving element is 150 μm square, the optical system magnification is 20 times, and the interlayer spacing is Assuming 25 μm, η = 1.8% is obtained.
Therefore, although the influence on the interlayer stray light between the main beams is small, the influence of the main beam having the intensity ratio of 10: 1 on the sub beam is ten times this and cannot be ignored. In addition, when signals are recorded only on one layer, even larger interlayer stray light is generated, which greatly affects the calculation of the differential push-pull signal, which affects the field of view of the objective lens caused by tracking the track. On the other hand, a residual error (Detrack) may occur.

Therefore, in order to reduce this influence, in this embodiment, the size of the light receiving surface of the two-part light receiving elements 274 and 275 for sub-beam detection used only for detecting the track control error signal is used to reproduce the information signal. A method of making the beam smaller than the light receiving surface of the quadrant light receiving element 273 can be considered.
Specifically, as shown in FIG. 6, for each light-receiving element having a square outer shape, the shape of the light-receiving beam is close to a circular spot. Therefore, for example, the light-receiving element 274 having a shape in which four corners are cut off obliquely, By using 275, it is possible to efficiently reduce only the interlayer stray light.
As an example, according to this example, when the light receiving area of the sub beam light receiving elements 274 and 275 is reduced by 30% with respect to the light receiving area in the main beam light receiving element 273, the balance error of the differential push-pull signal due to interlayer stray light is reduced by about 3 dB. It becomes possible to do.

In addition, the influence of interlayer stray light can be further reduced by switching the coefficient (k) in the equation (10) according to the number of layers of an optical disk such as a single-layer disk or a double-layer disk.
For example, in the control unit that controls the optical disk recording / reproducing apparatus, the number of layers of the optical disk to be used is recognized by identifying the specification of the optical disk set in the apparatus or by the user setting, and the above-described arithmetic expression The coefficient (k) in (10) is switched.

Next, the overall configuration of an optical disc recording / reproducing apparatus to which this embodiment is applied will be described with reference to FIG. In FIG. 1, the arithmetic circuits for detecting each error signal and sum signal described above are represented by blocks 81, 82, and 83, respectively.
Then, the reproduced RF signal obtained by the calculation of Expression (2) is waveform-equalized by an equalizer / amplifier unit (RF EQ) 60 and then supplied to a signal processing system indicated by blocks 81, 82, 83, etc. .
A DSP (Digital Signal Processor) 64 controls the operation of the entire optical disc recording / reproducing apparatus, controls the drive circuit 70 of the spindle motor 71, and also has main functions for focus control of the optical system and track control. .
Each arithmetic output is converted into a digital signal by the A / D converters 61, 62, and 63, and the DSP 64 performs gain adjustment and phase compensation related to focus control and track control. The output of the DSP is converted into an analog signal by the D / A converters 65 and 66 and then amplified to a necessary signal amplitude by the amplification units 67 and 68 to drive the two-axis electromagnetic actuator 15 mounted on the optical pickup 10. Thus, it is used for controlling the lens position. The liquid crystal device 23 which is a spherical aberration correction element is controlled by an LC control unit (LC Control) 71, and the drive signal is transmitted to the optical pickup 10 via the amplification amplifier 72.

By adopting the method of the present embodiment as described above, the error of the arithmetic coefficient (k) of the track error signal of the differential push-pull method caused by the interlayer stray light at the time of signal recording or signal reproduction with respect to the multilayer disk is reduced. Therefore, track control using a differential push-pull method can be performed on various optical disks ranging from single-layer disks to multi-layer disks, and robust track control can be realized with respect to the field of view of the objective lens.
In the first embodiment described above, the light receiving element that detects the main beam is a four-divided light receiving element, and the light receiving element that receives the sub-beam is a two-divided light receiving element. However, light receiving elements having other division numbers are used. It is also possible.
Further, as a method for reducing the light receiving area of the sub beam light receiving element to be smaller than the light receiving area of the main beam light receiving element, the outer edge portion of the sub beam light receiving element is cut off. While maintaining this shape, the size of one side may be reduced. Specifically, various forms are possible, and there is no particular limitation.
In the above embodiments, the present invention is configured as a Blu-ray Disc recording / reproducing apparatus. However, the present invention can also be applied to other optical disk recording / reproducing apparatuses.
In the embodiment, the case where a two-unit lens unit is used as an example of a high numerical aperture objective lens has been described. However, an optical head having an equivalent numerical aperture can be realized even with a single lens.

In Embodiment 2 of the present invention, when the push-pull differential calculation of the main beam and the sub beam described above is performed, the coefficient (k) to be multiplied by the sub beam in the calculation formula (10) is set to the main beam and sub beam in each light receiving element. It is made to change according to the light reception intensity ratio of the beam.
That is, in the first embodiment, the configuration in which the coefficient (k) of the arithmetic expression (10) is switched according to the number of layers of the optical disk is described. In the second embodiment, the light reception of the main beam and the sub beam in each light receiving element. By detecting the intensity and changing the intensity according to the intensity ratio, the influence of interlayer stray light is reduced.
As a method for adjusting the balance at the time of differential push-pull signal calculation, those disclosed in Japanese Patent Laid-Open Nos. 2000-331355 and 2000-331356 have been proposed. The focus is on removing spectral ratios and optical system adjustment errors using circuit-based techniques.
Japanese Patent Laid-Open No. 2002-230805 proposes a method for adjusting the coefficient (k) between the signal recorded area and the unrecorded area. However, neither of these methods provides a solution for interlayer stray light during signal recording or signal reproduction on a multilayer disk.
Therefore, the second embodiment provides a very effective method for reducing the inaccuracy of the differential push-pull error signal due to the effect of interlayer stray light during signal recording on the multilayer disk or during signal reproduction.

FIG. 7 is a block diagram illustrating a configuration example of an optical pickup and a signal arithmetic circuit of the optical disc recording / reproducing apparatus according to the second embodiment. In addition, about the structure which is common in FIG. 2, the same code | symbol is attached | subjected.
In Realization Example 2, the sum signal of the respective light receiving beam outputs is input to the DSP 64 from the operational amplifiers 32d, 32f, and 32h. The DSP 64 holds, for example, the coefficient (k _SL ) of the single-layer disc set at the time of adjusting the optical system and the subsequent reproduction of the single-layer disc, and calculates the received signal intensity ratio between the main beam and the sub beam.
In the dual-layer disc, the light-receiving signal intensity ratio of the main beam and the sub-beam changes from the value in the single-layer disc, so that the sub-beam push-pull signal among the inputs of the operational amplifier 36 that performs the differential push-pull signal calculation. The output of a certain operational amplifier 34 is changed by passing it through a variable amplifier (GCA: Gain Control Amplifier) 35 and amplified by a ratio corresponding to the intensity ratio. That is, in the dual-layer disc, the differential push-pull signal can be accurately calculated by adjusting the coefficient (k) in Equation (10) to k _DL different from k _SL .
In this embodiment, the signal level is adjusted after adding the sub-beam push-pull signal. However, the same adjustment can be applied to each sub-beam (SPP1, SPP2) individually. is there. The same effect can be obtained by adjusting the signal level on the main beam side. In addition, the differential push-pull error signal detection method can be applied to an optical disc having an information recording layer exceeding two layers (for example, a four-layer disc) by using the same method.
Further, it is desirable that the coefficient (k) is optimized only at the time of signal reproduction, and at the time of signal recording, the coefficient in the immediately previous reproduction state is retained. This is because, in the medium area irradiated with the main beam at the time of signal recording, the reflectance change accompanying the signal recording process (record mark formation) is usually accompanied. Therefore, the main beam and the sub beam detected by the light receiving element are This is because a difference occurs in the intensity ratio.

According to the second embodiment as described above, when the track control to the multilayer disk is performed using the differential push-pull error signal, the calculation coefficient (k) is corrected, and the main beam and the sub beam generated by the interlayer stray light are corrected. It is possible to reduce the amplitude deviation of the beam after AGC. Therefore, track control using a differential push-pull method is possible for various optical disks ranging from a single-layer disk to a multi-layer disk having two or more information recording layers, which is robust against the field of view of the objective lens. Track control can be realized.
Other configurations are the same as those in the first embodiment, and thus description thereof is omitted. In the second embodiment, the light receiving element for detecting the main beam is a four-divided light receiving element, and the light receiving element for receiving the sub-beam is a two-divided light receiving element. However, a light receiving element having other division numbers is used. Is also possible.
Also, the second embodiment is not limited to the Blu-ray Disc recording / reproducing apparatus, but can be applied to other optical disk recording / reproducing apparatuses.
Further, the case where a lens unit having a two-group configuration is used as an example of a high numerical aperture objective lens has been described, but an optical head having an equivalent numerical aperture can be realized even with a single lens.
In the first and second embodiments, an apparatus having both a recording function and a reproducing function has been described. However, the present invention can also be applied to an apparatus having either a recording or reproducing function. Recording and / or playback devices are meant to include them.

1 is a block diagram showing a configuration of an optical disc recording / reproducing apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram illustrating a configuration example of an optical pickup and a signal arithmetic circuit of the optical disc recording / reproducing apparatus illustrated in FIG. 1. FIG. 2 is a block diagram illustrating a configuration example of an optical pickup and a signal arithmetic circuit of the optical disc recording / reproducing apparatus illustrated in FIG. 1. It is sectional drawing which shows the objective lens drive part and optical disk of the optical disk recording / reproducing apparatus shown in FIG. It is sectional drawing which shows the structure of the optical pick-up for optical disk reproduction | regeneration of the optical disk recording / reproducing apparatus shown in FIG. FIG. 2 is an enlarged plan view showing a configuration of a divided light receiving element provided in the optical disc recording / reproducing apparatus shown in FIG. 1. It is a block diagram which shows the structural example of the optical pick-up and signal arithmetic circuit of the optical disk recording / reproducing apparatus by Example 2 of this invention. It is an enlarged plan view which shows the example of the division | segmentation light receiving element used for the push pull detection method with the conventional optical disk recording / reproducing apparatus. It is an enlarged plan view which shows the example of the division | segmentation light receiving element used for the differential push pull detection method with the conventional optical disk recording / reproducing apparatus. It is sectional drawing explaining the principle of the interlayer stray light produced at the time of recording and reproduction | regeneration of a multilayer disk with the conventional optical disk recording / reproducing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical pick-up, 11 ... Optical disk, 27 ... Photodetector, 31a-31h ... Head amplifier, 32a-32j ... Operational amplifier, 33a-33c ... AGC circuit, 64 ... DSP.

Claims (12)

An optical pickup for recording and / or reproducing signal information with respect to an optical disc;
An optical element that divides a light beam applied to the optical disc by the optical pickup into a main beam and sub beams on both sides and supplies the optical beam to the optical disc;
A photodetector for detecting return light from the optical disc;
An arithmetic circuit that detects a track control error signal by a phase difference method and a differential push-pull method using a detection signal from the photodetector;
The photodetector is disposed on both sides of the M-divided light receiving element, the M-divided light receiving element for detecting the return light of the main beam by the light receiving region divided at least in the track tangential direction and the optical disc radial direction of the optical disc, Two N-divided light receiving elements for detecting the return light of the sub-beam by a light receiving region divided in the track tangential direction,
The light receiving area of the N-divided light receiving element for detecting the return light of the sub-beam is smaller than the light receiving area of the M-divided light receiving element for detecting the return light of the main beam, and the M-divided light receiving element and the N-divided light receiving element are Used to detect track control error signal by differential push-pull method,
An optical disc recording and / or reproducing apparatus characterized by the above.   The N-divided light receiving element for detecting the return light of the sub beam has a light receiving surface having a shape obtained by cutting an outer edge portion of the light receiving surface of the M-divided light receiving element for detecting the return light of the main beam. The optical disk recording and / or reproducing apparatus according to 1.   The N-divided light receiving element for detecting the return light of the sub-beam has a light receiving surface having a shape obtained by reducing the light receiving surface of the M-divided light receiving element for detecting the return light of the main beam. Optical disc recording and / or playback device.   2. The optical disc recording and / or reproducing apparatus according to claim 1, wherein the optical disc has a plurality of information recording layers, and information signals are recorded or reproduced on each information recording layer.   Differential calculation means for subtracting the push-pull signal obtained by the sub-beam from the push-pull signal obtained by the main beam, and the differential calculation means uses the coefficient (k) multiplied by the sub-beam as information on the optical disc. 5. The optical disc recording and / or reproducing apparatus according to claim 4, wherein the differential operation is performed by changing the number of recording layers according to the number of recording layers.   2. The optical disk recording and / or reproducing apparatus according to claim 1, wherein the M-divided light receiving element is a four-divided light receiving element, and the N-divided light receiving element is a two-divided light receiving element. An optical pickup for recording and / or reproducing signal information with respect to an optical disc;
An optical element that divides a light beam applied to the optical disc by the optical pickup into a main beam and sub beams on both sides and supplies the optical beam to the optical disc;
A photodetector for detecting return light from the optical disc;
An arithmetic circuit that detects a track control error signal by a phase difference method and a differential push-pull method using a detection signal from the photodetector;
The photodetector is disposed on both sides of the M-divided light receiving element, the M-divided light receiving element for detecting the return light of the main beam by the light receiving region divided at least in the track tangential direction and the optical disc radial direction of the optical disc, A signal detection method for an optical disc recording and / or reproducing apparatus, comprising two N-divided light receiving elements for detecting return light of the sub beam by a light receiving region divided in a track tangential direction,
The light receiving area of the N-divided light receiving element for detecting the return light of the sub-beam is smaller than the light receiving area of the M-divided light receiving element for detecting the return light of the main beam, and the M-divided light receiving element and the N-divided light receiving element are Used to detect track control error signal by differential push-pull method,
A signal detection method for an optical disc recording and / or reproducing apparatus.   The N-divided light receiving element for detecting the return light of the sub beam has a light receiving surface having a shape obtained by cutting an outer edge portion of the light receiving surface of the M-divided light receiving element for detecting the return light of the main beam. 8. A signal detection method for an optical disk recording and / or reproducing apparatus according to claim 7.   8. The N-divided light receiving element for detecting the return light of the sub beam has a light receiving surface having a shape obtained by reducing the light receiving surface of the M-divided light receiving element for detecting the return light of the main beam. Signal detection method for optical disc recording and / or reproducing apparatus.   8. The signal detection method of an optical disc recording and / or reproducing apparatus according to claim 7, wherein the optical disc has a plurality of information recording layers, and information signals are recorded or reproduced on each information recording layer.   A differential operation for subtracting the push-pull signal obtained by the sub-beam from the push-pull signal obtained by the main beam is performed, and a coefficient (k) to be multiplied by the sub-beam in this differential operation is calculated in the information recording layer of the optical disc. 11. The signal detection method for an optical disc recording and / or reproducing apparatus according to claim 10, wherein the differential operation is performed in accordance with the number of layers. 8. The signal detection method for an optical disc recording and / or reproducing apparatus according to claim 7, wherein the M-divided light receiving element is a four-divided light receiving element, and the N-divided light receiving element is a two-divided light receiving element.

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