JP2012203930A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem due to stray light, which occurs in an optical pickup device for performing reading operation of a signal recorded in an optical disk with a plurality of signal recording layers provided.SOLUTION: An optical pickup device includes an objective lens 9 for focusing laser beams on a signal recording layer, a diffraction grating 2 to be made incident on by laser beams and for generating a main beam being 0-order light and a sub-beam being +1-order light and -1-order light, and a photodetector 11 comprising first and second light receiving parts for sub-beams to be irradiated with a sub-beam reflected from the signal recording layer to generate a tracking error signal and composed of four divided sensors and a light receiving part for a main beam to be irradiated with a main beam reflected from the signal recording layer to generate a reproduction signal and a focus error signal and composed of four divided sensors. The first and second light receiving parts for sub-beams and the light receiving part for a main beam are octagonal in shape.

Description

  The present invention relates to an optical pickup device that performs a read operation of a signal recorded on an optical disc using a laser beam.

  2. Description of the Related Art Optical disk apparatuses that can perform a signal read operation by irradiating a signal recording layer of an optical disk with laser light emitted from an optical pickup apparatus have become widespread.

  Reading operation of the signal recorded on the signal recording layer by the optical pickup device is performed by irradiating the signal recording layer with the laser light emitted from the laser diode, and detecting the change of the laser light reflected from the signal recording layer with a photodetector. Is done by detecting by.

  In order to read out the signal recorded on the signal recording layer by the laser beam, focusing control operation for condensing the laser beam on the signal recording layer and the laser beam follows the signal track provided in a spiral shape in the signal recording layer. It is necessary to accurately perform the tracking control operation.

  There are various methods for performing such a focusing control operation, but an astigmatism method using generation of astigmatism is generally performed. Although there are various tracking control methods, a three-beam method using a main beam and two sub beams is generally performed.

  Furthermore, recently, a differential astigmatism method that uses not only the main beam but also the sub beam has been adopted in order to perform an accurate focusing control operation. The astigmatism method, the differential astigmatism method and the three-beam method used for the tracking control operation used for the focusing control operation are the two sub-beam light receiving units and the main beam irradiated with the two sub-beams, respectively. It is configured to perform each control operation by generating a focus error signal and a tracking error signal from a signal obtained from the photodetector provided with a light receiving unit for main beam irradiated with ing.

  Recently, a four-layer type optical disc in which a plurality of signal recording layers are provided instead of one, for example, four layers, has been commercialized, and an optical disc having such a plurality of signal recording layers has been commercialized. An optical pickup device that can read out signals recorded in each signal recording layer has also been commercialized.

  FIG. 1 is an optical configuration diagram of an optical pickup device configured to read out signals recorded on signal recording layers L0, L1, L2, and L3 of a four-layer type optical disc D defined by the Blu-ray standard. The optical pickup device will be described with reference to FIG.

  In FIG. 1, reference numeral 1 denotes a laser diode that emits laser light that is blue-violet light having a wavelength of, for example, 405 nm. Reference numeral 2 denotes a diffraction grating on which laser light emitted from the laser diode 1 is incident. A diffraction grating portion 2a that separates light into a main beam, + 1st order light, and two subbeams that are −1st order light, and a ½ wavelength plate 2b that converts incident laser light into linearly polarized light in the S direction. It is configured.

  Reference numeral 3 denotes a polarization beam splitter on which the laser light transmitted through the diffraction grating 2 is incident. The control film 3a reflects most of the laser light converted into S-polarized light and transmits the laser light polarized in the P direction. Is provided. Reference numeral 4 denotes a monitor photodetector provided at a position to which the laser beam transmitted through the control film 3a of the polarization beam splitter 3 in the laser beam emitted from the laser diode 1 is irradiated. Is used to control the output of the laser light emitted from the laser diode 1.

  A quarter wave plate 5 is provided at a position where the laser beam reflected by the control film 3a of the polarization beam splitter 3 is incident. The incident laser beam is changed from linearly polarized light to circularly polarized light. On the other hand, it also functions to convert circularly polarized light into linearly polarized light. Reference numeral 6 denotes a collimating lens for converting the incident laser light into parallel light as the laser light transmitted through the quarter-wave plate 5 is incident thereon, so that it can be displaced in the optical axis direction by the aberration correction motor 7. It is configured. Spherical aberration caused by the difference in the thickness of the protective layer provided between the signal recording layers L0, L1, L2, L3 of the optical disc D and the disc surface by the displacement operation of the collimating lens 6 in the optical axis direction. It is comprised so that it can correct | amend.

  Reference numeral 8 denotes a rising mirror provided at a position where the laser beam transmitted through the collimating lens 6 is incident. The emitting mirror 8 changes the emission direction of the incident laser beam by 90 degrees, and the laser beam is recorded on the optical disc D. The light is reflected in the direction of the objective lens 9 provided to be condensed on the layers L0, L1, L2, and L3.

  In such a configuration, the laser light emitted from the laser diode 1 is incident on the objective lens 9 via the diffraction grating 2, the polarization beam splitter 3, the quarter wavelength plate 5, the collimator lens 6, and the rising mirror 8. After that, the signal recording layers L0, L1, L2, and L3 of the optical disk D are irradiated as laser spots by the focusing operation of the objective lens 9, and the laser irradiated to the signal recording layers L0, L1, L2, and L3 The light is reflected as return light to the objective lens 9 side.

  The return light reflected from the signal recording layers L0, L1, L2, and L3 of the optical disc D passes through the objective lens 9, the rising mirror 8, the collimator lens 6 and the quarter wavelength plate 5 to the control film 3a of the polarization beam splitter 3. Incident. The return light incident on the control film 3 a of the polarization beam splitter 3 in this way is changed to linearly polarized light in the P direction by the phase changing operation by the quarter wavelength plate 5. Therefore, such return light is not reflected by the control film 3a, but passes through the control film 3a as control laser light.

  Reference numeral 10 denotes a sensor lens into which the control laser light transmitted through the control film 3a of the polarizing beam splitter 3 is incident. Astigmatism is added to the control laser light in the light receiving portion provided in the photodetector 11 called PDIC. The effect of irradiating with the addition of. The photodetector 11 is provided with a quadrant sensor, which will be described later, and is accompanied by a read operation of signals recorded on the signal recording layers L0, L1, L2, and L3 of the optical disc D by the main beam irradiation operation. A focus error signal generation operation for performing a signal generation operation and a focus control operation by an astigmatism method, and a tracking error signal generation operation for performing a tracking control operation by an irradiation operation of two sub beams are configured. ing.

  As the light receiving section provided in the photodetector 11, as shown in FIG. 3, the main beam light receiving section used for the signal reading operation and the focusing control operation while being irradiated with the main beam M which is zero-order light. The preceding sub-beam S1 that is the MD and + 1st order light is irradiated, and the preceding subbeam light receiving part SD1 that is the first subbeam light receiving part used for the tracking control operation and the subsequent subbeam S2 that is the −1st order light are irradiated. And a subsequent sub-beam light receiving part SD2 which is a second sub-beam light receiving part used for the tracking control operation.

  As described above, the photodetector 11 is provided with the main beam light receiving part MD, the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 on the same straight line. When the direction, that is, the spot condensed and generated by the objective lens 9 is displaced in the radial direction of the optical disc D, the main beam light receiving part MD, the preceding sub beam light receiving part SD1, and the subsequent sub beam light receiving part SD2 are respectively irradiated. The beam M, the preceding sub beam S1, and the subsequent sub beam S2 are configured to coincide with the displacement directions.

  The main beam light receiving part MD, the preceding sub beam light receiving part SD1, and the subsequent sub beam light receiving part SD2 are each composed of, for example, sensors divided into four as shown in the figure. Then, a signal recorded on the optical disk D is added as a read signal by adding signals corresponding to the light amounts of the main beams irradiated to all the sensors A, B, C, and D constituting the main beam light receiving unit MD. It is configured to read.

  Then, a signal obtained from a diagonal sensor among the four-divided sensors constituting the main beam light receiving part MD is added, and a signal obtained from the other diagonal sensor is added from the added signal. The focus error signal is generated by subtracting the signal, and the focusing control operation is performed by using the focus error signal. Such focusing control operation is called the astigmatism method. Since this is a method, its description is omitted.

  To such an astigmatism method, signals obtained from diagonal sensors among the four-divided sensors constituting the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 are added and this addition is performed. A subfocus error signal is generated by subtracting a signal obtained by adding a signal obtained from the other diagonal sensor from the signal, and these subfocus error signals and the four divisions constituting the main beam light-receiving unit MD are generated. A focus error signal is calculated and generated from a main focus error signal obtained from the sensor, and a focusing control operation is performed. Such a focusing control operation is a control method called a differential astigmatism method.

  Next, the focusing control operation by the above-described differential astigmatism method will be described. As described above, the focusing control operation is performed using the main focus error signal and the sub focus error signal generated from the main beam light receiving part MD, the preceding sub beam light receiving part SD1, and the subsequent sub beam light receiving part SD2. Is called.

  The signals obtained from the two sensors A and C in the four-divided sensors constituting the main beam light receiving unit MD are added, and the signal obtained by adding the signals obtained from the two sensors B and D is subtracted from the added signal. To obtain the main focus error signal.

  A signal obtained by adding the signals obtained from the two sensors I and K in the four-divided sensors constituting the preceding sub-beam light receiving unit SD1 and adding the signals obtained from the two sensors J and L from the added signal is obtained. The first control signal is obtained by subtraction, and the signals obtained from the two sensors E and G in the four-divided sensors constituting the subsequent sub-beam light receiving unit SD2 are added and the two sensors F are added from the added signal. , The signal obtained by adding the signals obtained from H is subtracted to obtain the second control signal, and the first control signal and the second control signal obtained in this way are processed to obtain the sub focus error signal. obtain.

  The focus error signal in the differential astigmatism method subtracts the sub focus error signal obtained from the preceding sub beam light receiving part SD1 and the subsequent sub beam light receiving part SD2 from the main focus error signal obtained from the main beam light receiving part MD. It is configured to obtain by

  Next, the focus error signal generating operation will be described with reference to the reference numerals of the sensor units shown in FIG. If the main focus error signal is MFE, MFE = (A + C) − (B + D), and if the sub focus error signal is SFE, SFE = {(E + G) − (F + H)} + {(I + K) − (J + L). )}.

  The focusing control operation in the differential astigmatism method is performed based on the differential push-pull signal DPP. This DPP signal is obtained as DPP = MFE-k × SFE. Here, k is a constant determined based on the light intensity of the main beam and the light intensity of the sub beam.

  An optical pickup device configured to perform a focusing control operation in which the main beam and the sub beam are combined as described above has been developed. Next, a tracking control operation in the optical pickup device having such a configuration will be described.

  Such a tracking control operation is performed by the irradiation operation of the preceding sub beam S1 to the light receiving unit SD1 for the preceding sub beam and the irradiation operation of the subsequent sub beam S2 to the light receiving unit SD2 for the subsequent sub beam.

  For example, the signals obtained from the two sensors I and J on the upper side of the four-divided sensors constituting the preceding sub-beam light receiving part SD1 are added and obtained from the two sensors L and K on the lower side from this added signal. The first control signal is obtained by subtracting the signal obtained by adding the obtained signals, and the signals obtained from the two sensors E and F on the upper side of the four-divided sensors constituting the subsequent sub-beam light receiving unit SD2 are added. At the same time, a signal obtained by adding the signals obtained from the two lower sensors H and G is subtracted from the added signal to obtain a second control signal, and the first control signal and the second control thus obtained are obtained. The tracking error signal is generated by performing arithmetic processing on the signal, but such an operation is well known and will not be described.

  In addition to the tracking control operation described above, recently, a tracking control operation is performed using a tracking error signal obtained from the main beam light receiving part MD irradiated with the main beam M as well as the sub beams S1 and S2. A so-called differential push-pull method is employed to improve accuracy.

  The tracking error signal in such a system is obtained by subtracting the sub-tracking error signal obtained from the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 from the main tracking error signal obtained from the main beam light-receiving part MD. It is configured as follows.

  The description will be made with reference to the reference numerals of the illustrated sensor unit. If the main tracking error signal is MTE, MTE = (A + B) − (C + D), and if the sub tracking error signal is STE, STE = {(E + F) − (G + H)} + {(I + J) − (L + K )}.

  The tracking control operation in the differential push-pull method is performed based on the differential push-pull signal DPP, and this DPP signal is obtained as DPP = MTE-k × STE. Here, k is a constant determined based on the light intensity of the main beam and the light intensity of the sub beam.

  In this way, an optical pickup device that performs a tracking control operation combining a sub beam and a main beam has been developed.

  The laser light emitted from the laser diode 1 is incident on the polarization beam splitter 3 as the laser light diffracted by the diffraction grating 2, and a part of the laser light is transmitted through the control film 3a as the monitoring laser light. Irradiated to the monitor photodetector 4.

  The monitoring laser light applied to the monitoring photodetector 4 changes according to the output level of the laser light emitted from the laser diode 1. Therefore, the output of the laser light emitted from the laser diode 1 is predetermined by feeding back the monitor signal generated by the monitoring photodetector 4 to a drive circuit provided to supply a drive signal to the laser diode 1. Laser servo operation can be performed to control the value. Such laser servo operation is well known and will not be described.

  As described above, the focus error signal and the tracking error signal are generated from the signals obtained from the main beam light receiving part MD, the preceding sub beam light receiving part SD1 and the subsequent sub beam light receiving part SD2, and the focus error signal and the tracking error signal are generated. Based on this, focusing control operation and tracking control operation are performed. Such focusing control operation is performed by displacing the objective lens 9 in a direction perpendicular to the signal surface of the optical disc D, and the tracking control operation is performed by moving the objective lens 9. This is performed by displacing the optical disk D in the radial direction.

  As described above, the conventional optical pickup device is configured, but the return reflected from the other signal recording layers in the state in which the signal recorded in the desired signal recording layer is being read out next. A problem caused by light, that is, stray light will be described.

  FIG. 3 shows the relationship between the main beam light receiving part MD, the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 and the stray light, and the part inside the ring P indicated by the broken line is the stray light. This is the laser beam irradiation part.

  As is apparent from this figure, stray light is irradiated onto the main beam light receiving part MD, the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 provided in the photodetector 11.

  The 0th-order light that is the main beam and the + 1st-order light and the −1st-order light that are the sub-beams are generated by the diffraction grating 2, and the light quantity ratio, that is, the light quantity ratio of one sub-beam to the main beam is generally 1 to 15. Is set to about. Accordingly, for example, when a signal recorded in the signal recording layer L0 is read, the amount of sub-beams reflected as stray light from the other signal recording layers L1, L2, and L3 is the main beam reflected as stray light. Therefore, the influence on the focusing control operation and the like can be ignored.

  Further, when performing a read operation of the main beam M irradiated to the main beam light receiving part MD, for example, a signal recorded in the signal recording layer L0, the light amount of the main beam M reflected from the signal recording layer L0 is: Since the amount of the stray light beam reflected from the other signal recording layers L1, L2, and L3 is sufficiently larger, the signal generating operation by the main beam light receiving unit MD, that is, the operation of reading the signal recorded in the signal recording layer L0, and There is no adverse effect on the operation of generating the focus error signal.

  On the other hand, as described above, the light amounts of the preceding sub-beam S1 and the succeeding sub-beam S2 irradiated to generate the focus error signal to the preceding sub-beam light receiving portion SD1 and the succeeding sub-beam light receiving portion SD2 are larger than the light amount of the main beam M. It is set to be smaller. Therefore, the gain of the amplifier provided to amplify the signal obtained from the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 is provided to amplify the signal obtained from the main beam light-receiving part MD. Generally, it is set to be higher than the gain of the amplifier.

  As a result, stray light generated from the main beam M reflected from the signal recording layers L1, L2, and L3 that are not the signal recording layer L0 that performs the signal reading operation causes the preceding sub-beam light-receiving unit SD1 and the subsequent sub-beam light-receiving unit SD2. The degree of the influence received by irradiating on becomes large. That is, since a signal corresponding to the light intensity of stray light acts on the focus error signals obtained from the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2, an accurate focus error signal cannot be obtained, and as a result There is a problem that the focusing control operation becomes unstable.

  Similarly, when a tracking error signal is generated from signals obtained from the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 and the tracking control operation is performed using this tracking error signal, it is also affected by stray light. There is a problem that the tracking control operation cannot be performed accurately.

  As a method for solving such a problem caused by stray light, a technique has been developed in which the shape of the photodetector is shaped to eliminate the influence of stray light. (See Patent Document 1.)

JP 2009-176367 A

  The technique described in Patent Document 1 reduces the area of the sub-beam light-receiving part relative to the area of the main-beam light-receiving part incorporated in the photodetector, and further reduces the shape of the sub-beam light-receiving part. Although the problem due to stray light is solved by making it square, no countermeasures against stray light are made for the light receiving part for the main beam.

  The reason for not taking the stray light countermeasures for the main beam light-receiving unit is that the main beam level reflected from the other signal recording layers with respect to the main beam level reflected from the signal recording layer performing the signal reading operation In addition, since the level of the sub beam is small, it is not affected by stray light.

  However, in the four-layer type optical disc D defined by the Blu-ray standard, the distance between the signal recording layer and the signal recording layer is very narrow, so that the signal recording adjacent to the signal recording layer from which signals are read is recorded. The level of stray light generated from the main beam and the sub beam reflected from the layer is so large that it cannot be ignored. In particular, in an optical pickup device configured to perform a reproduction operation instead of a signal recording operation, the light amount ratio between the sub beam and the main beam is set to be as small as, for example, 1 to 6, so that the stray light generated from the sub beam is used. The influence can no longer be ignored.

  Therefore, in recent optical pickup devices, malfunction due to stray light has become a problem when performing a focusing control operation or a tracking control operation using a signal obtained from a main beam light receiving unit.

  The present invention is intended to provide an optical pickup device that can solve such a problem.

  The present invention provides an objective lens for condensing a laser beam on a signal recording layer in order to read a signal recorded on an optical disc, a main beam that is zero-order light, + 1st-order light, and −1. A diffraction grating for generating a sub beam as the next light, a sub beam reflected from the signal recording layer, and a tracking error signal are generated, and light reception for the first and second sub beams configured by a quadrant sensor And a main beam reflected from the signal recording layer and generating a reproduction signal and a focus error signal, and comprising a photodetector comprising a main beam light-receiving unit configured by a four-divided sensor, The first and second sub-beam light-receiving portions and the main beam light-receiving portion are octagonal in shape.

  In addition, the present invention is characterized in that the area of the first and second sub-beam light receiving parts is smaller than the area of the main beam light receiving part.

  The present invention is characterized in that the tracking control operation by the differential push-pull method is performed by using signals obtained from the first and second sub-beam light-receiving units and the main beam light-receiving unit. It is.

  In the optical pickup device of the present invention, not only the first and second sub-beam light receiving portions but also the main beam light receiving portion has an octagonal shape, so that the light receiving area irradiated with stray light can be reduced, and as a result. The adverse effects of stray light can be eliminated.

  Therefore, the present invention is very effective when applied to an optical pickup apparatus configured to read out signals recorded on an optical disk having a narrow interval between signal recording layers.

1 is a schematic view of an optical pickup device according to the present invention. It is a figure for demonstrating the relationship between the photodetector and laser beam in the optical pick-up apparatus which concerns on this invention. It is a figure for demonstrating the relationship between the photodetector and laser beam in the conventional optical pick-up apparatus.

  In an optical pickup device configured to generate a laser spot by condensing laser light on a plurality of signal recording layers provided on an optical disc, the signal pickup layer is not a signal recording layer that performs a signal read operation. Provided is an optical pickup device capable of suppressing the influence of laser light reflected from a signal recording layer, that is, stray light.

  FIG. 2 shows an embodiment of the present invention, which is characterized in that not only the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 but also the shape of the main beam light receiving part MD is an octagon. is there. In the figure, the portion inside the ring P indicated by a broken line is a portion irradiated with laser light called stray light.

  In the illustrated embodiment, the areas of the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 are configured to be smaller than the area of the main beam light-receiving part MD.

  The reason why the areas of the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 are smaller than the area of the main beam light-receiving part MD is that the spot diameters of the preceding sub-beam S1 and the subsequent sub-beam S2 are larger than the spot diameter of the main beam M. There is a small point. That is, if the areas of the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 are reduced in accordance with the spot diameters of the preceding sub-beam S1 and the subsequent sub-beam S2, the area of the stray light receiving part relative to the area of the signal light receiving part is reduced. As a result, the influence of stray light can be reduced.

  According to such a configuration, since the area where the stray light is irradiated to the preceding sub-beam light receiving part SD1, the subsequent sub-beam light receiving part SD2, and the main beam light-receiving part MD is reduced, the generation operation of each signal by stray light is adversely affected. The degree is reduced. As described above, according to the present invention, since it is difficult to be affected by stray light, the differential bush-pull tracking control operation using the signals obtained from the two sub-beam light-receiving units and the main beam light-receiving unit is performed without any trouble. I can do it.

  Although the present invention has been described with respect to an optical pickup device that performs an operation of reading a signal recorded on an optical disc of the Blu-ray standard, it can also be applied to optical pickup devices of different standards. Further, although the optical disc having four signal recording layers has been described, the light for performing the reading operation of the signal recorded on the optical disc provided with two or three signal recording layers or more signal recording layers. It can also be applied to a pickup device.

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Diffraction grating 3 Polarizing beam splitter 6 Collimating lens 9 Objective lens 11 Optical detector D Optical disk

Claims (3)

An objective lens for condensing the laser beam on the signal recording layer to read out the signal recorded on the optical disc, and the main beam, the + 1st order light, and the −1st order light as the 0th order light enters the laser light. A diffraction grating for generating a sub-beam, a sub-beam reflected from the signal recording layer, and a tracking error signal are generated, and the first and second sub-beam light receiving units and signal recordings configured by four-divided sensors An optical pickup device including a photodetector that is irradiated with a main beam reflected from a layer and generates a reproduction signal and a focus error signal and includes a light receiving unit for a main beam configured by a quadrant sensor An optical pickup characterized in that the first and second sub-beam light receiving portions and the main beam light receiving portion are octagonal in shape. Location. 2. The optical pickup device according to claim 1, wherein the area of the first and second sub-beam light receiving parts is smaller than the area of the main beam light receiving part. 3. The tracking control operation by the differential push-pull method is performed by using signals obtained from the first and second sub beam light receiving units and the main beam light receiving unit. The optical pickup device described in 1.

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