JP2006309858A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device which can simply and effectively eliminate an influence of stray light on a focus error signal while operating a focus servo to an optical disk having two or more recording layers in the direction of lamination using the focus error signal based on the differential astigmatism method. <P>SOLUTION: For focus servo pull-in, the optical disk device uses the focus error signal based on the astigmatism method, and after the focus servo has been pulled in, the optical disk device is changed over to a focus servo using the focus error signal based on the differential astigmatism method. As shown in Fig.4, the stray light does not affect the focus error signal based on the astigmatism method. Therefore, the focus servo pull-in can be carried out smoothly using such a focus error signal. After that, a stable servo operation can be realized by changing over the device to use the focus error signal based on the differential astigmatism method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus, and is particularly suitable for use in applying focus servo to an optical disc having a plurality of recording layers in the stacking direction using a focus error signal based on a differential astigmatism method.

  Astigmatism has long been used as a method for generating a focus error signal.

  However, when the astigmatism method is used for an optical disc having a groove such as a DVD (Digital Versatile Disc) or a next-generation DVD, a signal component from the groove leaks into the focus error signal, and the focus error signal There arises a problem that a deviation occurs between the zero cross position and the on-focus position.

  Such a problem is solved by using a differential astigmatism method using three beams.

  FIG. 5 is a diagram showing a sensor pattern and a signal generation method used in the differential astigmatism method. Laser light from the semiconductor laser is divided into three beams using a diffraction grating and irradiated onto the disk. Of the reflected light from the disk, the reflected light for the main beam (0th order light) is received by a four-divided sensor composed of sensors A, B, C and D, and reflected for two sub beams (± first order light). Light is received by a four-divided sensor composed of sensors E, F, G, and H and a four-divided sensor composed of sensors I, J, K, and L, respectively. Assuming that signals from the sensors are A to L, the focus error signal FE by the differential astigmatism method is FE = (A + C) − (B + D) + k {(E + G + I + K) − (F + H + J + L) as shown in the lower part of FIG. } Is generated.

  When the focus error signal is generated in this way, the influence of the signal component from the groove is canceled by the addition of the signal by the sub beam, that is, the addition of k {(E + G + I + K) − (F + H + J + L)}. As a result, the shift of the focus error signal between the zero-cross position and the on-focus position is eliminated.

  However, when this differential astigmatism method is used for an optical disc having a plurality of recording layers in the stacking direction, stray light from other recording layers that are not the target of laser beam leakage leaks into the sub-beam receiving sensor. As a result, the focus error signal is disturbed.

  In the stray light shown in FIG. 5, the main beam is reflected by another recording layer and guided onto the optical sensor. For this reason, the intensity of the stray light is sufficiently small with respect to the intensity of the main beam in the figure, but is close to the intensity of the sub beam so as to affect the sensor output. The intensity of the sub beam is usually set to about 10 to 20 times the intensity of the main beam. Accordingly, when stray light for the main beam is applied to the sub-beam receiving sensor as shown in FIG. 5, the output from the sub-beam receiving sensor is greatly affected by the incidence of stray light.

  In the differential astigmatism method, since a focus error signal is generated according to the above calculation formula, the influence of stray light should theoretically be canceled by the addition of k {(E + G + I + K) − (F + H + J + L)}. However, when the effect is actually verified, the focus error signal is disturbed, and the manner and size of the occurrence vary depending on the apparatus.

  FIG. 6 shows a verification result when the effect of stray light on a Blu-ray disc, which is one of the next generation DVDs, is verified. Here, verification is performed on a two-layer disc in which two recording layers are arranged in the stacking direction. The numerical aperture of the objective lens is 0.85.

  As shown in the figure, when the objective lens is moved in the focus direction between two recording layers, in addition to the S curve for each layer, a waveform similar to the S curve appears in the period between the layers. This waveform adversely affects the focus servo pull-in or interlayer jump. That is, since it becomes difficult for the apparatus side to discriminate between the S curve for the first layer and the S curve for the second layer, the focus servo cannot be pulled in smoothly. A similar problem occurs when jumping between layers.

On the other hand, the sub-beam light receiving sensor is disposed at a position where stray light is not applied (Patent Document 1), or conversely, the sensor pitch is narrowed to reduce the difference in stray light incident on the sub-beam light receiving sensor (Patent Document 1). Reference 2) can also be taken. However, in this case, the design of the sensor pattern is restricted, and there is a problem that the sensor shape is enlarged and the sensor pattern is complicated. In addition, as shown in Patent Documents 3 and 4, a method of removing stray light using a pinhole may be employed, but this causes a problem that the optical system of the pickup becomes complicated and large due to the arrangement of the pinhole. Occurs.
WO96 / 20473 (Japanese Patent Application No. 8-520374) JP 2003-67949 A JP-A-8-185640 JP-A-9-320084

  Therefore, an object of the present invention is to provide an optical disc apparatus that can easily eliminate the influence of stray light while applying focus servo using a focus error signal based on the differential astigmatism method.

  In view of the above problems, the present invention has the following features.

  According to the first aspect of the present invention, in the optical disc apparatus, the first signal generating means for generating the focus error signal based on the astigmatism method and the second signal generating the focus error signal based on the differential astigmatism method. After the focus servo is pulled in based on the signal generation means and the focus error signal from the first signal generation means, the focus error signal referenced during the focus servo is used as the focus error signal from the second signal generation means. And a focus servo means for switching to.

  According to a second aspect of the present invention, in the optical disc apparatus according to the first aspect, when the focus servo is applied to one of the plurality of recording layers arranged in the incident direction of the laser beam, the focus servo means After the focus servo is pulled into the recording layer based on the focus error signal from the first signal generation means, the focus error signal referred to during the focus servo is switched to the focus error signal from the second signal generation means Thus, the focus servo for the recording layer is performed.

  According to a third aspect of the present invention, in the optical disk device according to the first or second aspect, the convergence position of the laser light emitted from the optical pickup is determined from the first recording layer in the disk to the recording layer. When moving to the second recording layer shifted in the optical axis direction, the focus servo means pulls the focus servo into the second recording layer based on the focus error signal from the first signal generating means. Then, the focus error signal referred to during focus servo is switched to the focus error signal from the second signal generating means, and focus servo is performed on the second recording layer.

  According to the present invention, the focus error signal based on the astigmatism method is used at the time of focus servo pull-in, and after the servo pull-in, the focus servo using the focus error signal based on the differential astigmatism method is switched. By using a focus error signal based on the astigmatism method at the time of focus servo pull-in, the focus servo pull-in operation can be performed smoothly. After that, since focus servo is applied using a focus error signal based on the differential astigmatism method, a stable focus servo operation can be realized.

  FIG. 4 shows the state of the focus error signal verified under the same conditions as in FIG. As shown in the figure, when the astigmatism method is used, a waveform similar to the S curve is not generated in the period between the first layer and the second layer. Therefore, when the focus servo is pulled in using the focus error signal based on the astigmatism method as in the present invention, the focus servo pull-in operation can be performed smoothly.

The features of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely an example of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment. .

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, an optical disc apparatus compatible with next-generation DVD / DVD / CD using laser light of blue / red / infrared wavelengths is shown. In the present embodiment, the configuration of the recording system is omitted, and only the configuration of the reproduction system is shown. In the present embodiment, next-generation DVDs and DVDs having a plurality of recording layers in the stacking direction can be mounted.

  FIG. 1 shows a configuration of an optical disc apparatus according to the embodiment.

  As shown in the figure, the optical disc apparatus includes an optical pickup 10, a signal generation circuit 20, an ACT (actuator) drive circuit 30, an LD (laser diode) drive circuit 40, a motor drive circuit 50, a spindle motor 60, and a control. A circuit 70 is provided.

  An optical pickup 10 includes a semiconductor laser that emits blue / red / infrared laser light, an optical system that guides the laser light of each wavelength to an objective lens, and an objective lens actuator that drives the objective lens in a focus direction and a tracking direction. And a photodetector that receives reflected light from the disk and outputs an electrical signal. The photodetector has a sensor pattern for generating various signals such as an RF signal, a focus error signal, and a tracking error signal. The configuration of the optical system will be described in detail later with reference to FIG.

  The signal generation circuit 20 performs arithmetic processing on the electrical signal input from the photodetector in the optical pickup 10, generates various signals such as an RF signal, a focus error signal, and a tracking error signal, and outputs them to the control circuit 70. .

  The ACT drive circuit 30 generates a drive signal based on the focus servo signal and tracking servo signal generated by the control circuit 70 and outputs them to the objective lens actuator in the optical pickup 10.

  The LD drive circuit 40 drives the semiconductor laser in the optical pickup 10 according to the control signal input from the control circuit 70, and emits one of the blue / red / infrared laser beams from the optical pickup 10. .

  The motor drive circuit 50 drives the disk drive spindle motor 60 in accordance with a control signal input from the control circuit 70, and rotates the disk at a predetermined speed.

  The control circuit 70 processes the RF signal input from the signal generation circuit 20 to generate reproduction data and outputs it to the subsequent circuit. Further, the focus error signal and the tracking error signal input from the signal generation circuit 20 are processed to generate a focus servo signal and a tracking servo signal and output them to the ACT drive circuit 30. Further, the wobble signal and the synchronization signal input from the signal generation circuit 20 are processed to generate a motor servo signal and output it to the motor drive circuit 50. Further, a control signal for emitting a laser beam having a wavelength corresponding to the loaded disc is output to the LD drive circuit 40.

  In addition, the control circuit 70 outputs a control signal corresponding to a processing flow described later to the ACT drive circuit 30, the LD drive circuit 40, and the motor drive circuit 50 during the focus servo pull-in operation and the interlayer jump.

  FIG. 2 is a diagram illustrating an optical system of the optical pickup 10.

  A laser beam having an infrared wavelength emitted from an infrared LD (Laser Diode) 101 is made into three beams by a diffraction grating 102, and then a divergent lens 103 that adjusts optical magnifications of a red laser system and an infrared laser system. , And a part thereof is reflected by a BS (beam splitter) 106. The red wavelength laser light emitted from a red LD (Laser Diode) 104 is made into three beams by the diffraction grating 105 and then part of the laser light passes through a BS (beam splitter) 106. These laser beams are collimated by the collimating lens 107 and then reflected by the BS (polarization beam splitter) 108, and the BS (wavelength selective polarization beam splitter) 112 acting only on the blue wavelength laser beam. Transparent. Then, the light enters the expander 113.

  The blue wavelength laser light emitted from a blue LD (Laser Diode) 109 is made into three beams by the diffraction grating 110, then becomes parallel light by the collimator lens 111, and enters the BS 112. Then, it is totally reflected by the BS 112 and enters the expander 113.

  The infrared, red, and blue wavelength laser beams incident on the expander 113 in this manner are reflected by the mirror 114 after the beam diffusion state or wavefront state is adjusted here. Then, after being converted into circularly polarized light by the λ / 4 plate 115, it is converged on the disk by the objective lens 116.

  The laser light of each wavelength reflected from the disk is converted by the λ / 4 plate 115 into linearly polarized light that is orthogonal to the plane of polarization at the time of incidence of the disk, and then reverses the optical path at the time of incidence of the disk. The light passes through and enters the dichroic mirror 117. The infrared and red wavelength laser beams are reflected by the dichroic mirror 117 and converged on the photodetector 119 via the converging lens 118. The blue wavelength laser light passes through the dichroic mirror 117 and is then converged on the photodetector 121 via the converging lens 120.

  The converging lenses 118 and 120 introduce astigmatism into the laser light of each wavelength. Further, the photodetectors 119 and 121 have a sensor pattern as shown in FIG. 5, and a main beam (0th order light) and sub beams (± 1) of each wavelength divided into three beams by the diffraction gratings 102 and 110. Next light) is received by the corresponding quadrant sensor.

  The signal generation circuit 20 shown in FIG. 1 executes the arithmetic processing shown in the lower part of FIG. 5 based on the signals from the photodetectors 119 and 121, and generates two types of focus error signals. Further, the signals A, B, C, and D from the quadrant sensor that receives the main beam are added to generate a SUM signal, which is output to the controller 70 as a reproduction RF signal. Further, a tracking error signal is generated according to a predetermined method, and this is output to the controller 70. If the signals A to L based on the sensor pattern shown in FIG. 5 are not sufficient in the generation of the tracking error signal, a sensor pattern corresponding to the signal is added to the photodetectors 119 and 121. Note that the method for generating the tracking error signal is not the gist of the present invention, and therefore the description thereof is omitted here.

  FIG. 3 shows a processing flowchart at the time of focus servo pull-in and a processing flowchart at the time of interlayer jump.

  First, with reference to FIG. 3A, processing at the time of pulling in the focus servo will be described. Note that the processing flow in the figure is for when a disc having a plurality of recording layers in the stacking direction is loaded. Processing when a disc having only one recording layer is mounted is performed according to a conventionally known processing flow.

  When the focus servo pull-in process is started, the disk is rotated at a predetermined speed (S101), and an LD (Laser Diode) having a wavelength corresponding to the disk is turned on (S102). Then, after the expander 113 is adjusted to a state corresponding to the wavelength, the objective lens is driven toward the disc surface direction, and a focus search is started. In the focus search, a focus error signal according to the astigmatism method is used among the focus error signals generated by the signal generation circuit 20 (S103). Then, it is determined whether or not the S curve corresponding to the recording layer to be pulled in has been detected (S104). If detected, the focus servo is turned on, for example, at the zero cross position of the S curve (S105). Here again, a focus error signal according to the astigmatism method is used.

  Note that the process of S104 is performed, for example, by counting the number of S curves that appear after the start of the focus search. That is, when the laser beam is focused on the recording layer that appears first when viewed from the substrate surface, it is determined whether the first S curve is detected.

  Thus, when the focus servo is turned on, the position of the objective lens is converged to the zero cross position of the focus error signal according to the astigmatism method. Thereafter, the focus error signal used for the focus servo is switched from the focus error signal based on the astigmatism method to the focus error signal based on the differential astigmatism method (S106). Thereafter, the objective lens follows the zero cross position of the focus error signal based on the differential astigmatism method. Thus, when the objective lens is pulled into a position corresponding to the recording layer to be pulled in, processing such as tracking servo is subsequently started.

  Next, with reference to FIG. 3B, a process at the time of interlayer jump will be described.

  When the interlayer jump process is started, the focus servo is turned off (S201), and a control signal for moving the convergence position of the laser beam in the direction of the jump recording layer is input from the control circuit 70 to the ACT drive circuit 30 ( S202). As a result, the objective lens is moved in the direction of the recording layer at the jump destination, and at the same time, a focus search is started. In such a focus search, a focus error signal according to the astigmatism method is used among the focus error signals generated by the signal generation circuit 20 (S203). Then, it is determined whether or not the S curve corresponding to the recording layer of the jump destination has been detected (S204). If detected, the focus servo is turned on, for example, at the zero cross position of this S curve (S205). Here again, a focus error signal according to the astigmatism method is used. Note that the processing in S204 is performed by counting the number of S curves that appear after the jump, as in S104.

  Thus, when the focus servo is turned on, the position of the objective lens is converged to the zero cross position of the focus error signal according to the astigmatism method. Thereafter, the focus error signal used for the focus servo is switched from the focus error signal based on the astigmatism method to the focus error signal based on the differential astigmatism method (S206). Thereafter, the objective lens follows the zero cross position of the focus error signal based on the differential astigmatism method. Thus, when the objective lens is pulled into a position corresponding to the recording layer to which the jump is made, processing such as tracking servo is subsequently started.

  According to the present embodiment, since the focus error signal based on the astigmatism method is used at the time of focus servo pull-in, the focus servo pull-in operation can be performed smoothly. Further, after the servo pull-in, the focus servo is applied using the focus error signal based on the differential astigmatism method, so that a stable focus servo operation can be realized.

  Furthermore, according to the present embodiment, since the focus error signal based on the astigmatism method and the focus error signal based on the differential astigmatism method are only switched as appropriate, a sensor pattern corresponding to the differential astigmatism method is used. May be used as they are, and no additional configuration is required other than the switching of the focus error signal in the controller 70. Therefore, it is possible to effectively eliminate the influence of stray light while simplifying the configuration.

As mentioned above, although embodiment which concerns on this invention was described, this invention is not limited to the said embodiment. The embodiment of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims.

The figure which shows the structure of the optical disk apparatus which concerns on embodiment The figure which shows the optical system of the optical pick-up which concerns on embodiment Flowchart showing processing at the time of focus servo pull-in and interlayer jump according to the embodiment Diagram showing focus error signal based on astigmatism method The figure explaining the sensor pattern used for the differential astigmatism method and the generation method of a focus error signal Diagram showing focus error signal based on differential astigmatism method

Explanation of symbols

20 signal generation circuit 70 controller

Claims (3)

First signal generating means for generating a focus error signal based on the astigmatism method;
Second signal generating means for generating a focus error signal based on the differential astigmatism method;
Focus servo means for switching the focus error signal referred to during focus servo to the focus error signal from the second signal generation means after performing the focus servo pull-in based on the focus error signal from the first signal generation means When,
An optical disc apparatus comprising: In claim 1,
When focus servo is applied to one of the plurality of recording layers arranged in the incident direction of the laser beam, the focus servo means is configured to record the recording layer based on a focus error signal from the first signal generating means. After the focus servo is pulled in, the focus error signal to be referred to during the focus servo is switched to the focus error signal from the second signal generating means, and the focus servo for the recording layer is performed.
An optical disc device characterized by the above. In claim 1 or 2,
When the convergence position of the laser beam emitted from the optical pickup is moved from the first recording layer in the disc to the second recording layer shifted in the optical axis direction of the laser beam with respect to the recording layer, the focus The servo means pulls the focus servo into the second recording layer based on the focus error signal from the first signal generation means, and then generates a focus error signal to be referred to during focus servo as the second signal generation. Switching to a focus error signal from the means to perform focus servo on the second recording layer;
An optical disc device characterized by the above.

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