JP2010061772A - Multilayer optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: when reading a signal recorded in a multilayer optical disks, focusing control is adversely affected by stray light which is a laser beam reflected by other signal recording layers than the layer in the multilayer optical disk. <P>SOLUTION: The multilayer optical disk has at least three or more signal recording layers. A polarization direction of polarization reflection coating applied to two signal recording layers continuously disposed from the surface receiving the laser beam for reading a signal and a polarization direction of a polarization reflection coating applied to an adjacent signal recording layer are opposite to each other. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multilayer type optical disc that is configured to perform a signal recording / reproducing operation by a laser beam irradiated from an optical pickup device and that is provided with a plurality of signal recording layers.

  2. Description of the Related Art Optical disk apparatuses that can perform a signal read operation by irradiating a signal recording layer provided on 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 However, since such a technique is well known, the description thereof is omitted.

  Recently, an optical disc in which two signal recording layers are provided instead of one has been commercialized, and a signal recorded on the signal recording layer provided in such an optical disc is read out. Optical pickup devices that can be used are also commercialized.

  When performing a read operation of a signal recorded on a two-layer optical disc, a focusing control operation and a tracking control operation are performed on the signal recording layer on which the read operation is performed, but the read operation is not performed. Laser light is also reflected from the signal recording layer that is not present. Laser light reflected from the signal recording layer on which the reading operation is not performed is generally called stray light, and such stray light is used as a focus error signal used for focusing control operation by the differential astigmatism method. There is a problem in that the focusing control operation cannot be performed accurately because an offset is generated in the focus error signal due to this stray light and the amplitude fluctuation occurs due to this stray light.

As a method for solving such a problem caused by stray light, a light detector having a shape that eliminates the influence of stray light has been proposed. (See Patent Document 1.)
JP 2007-42236 A

  The prior art disclosed in the above-mentioned patent document suppresses the influence of stray light in a multilayer optical disc provided with a plurality of signal recording layers, but receives the area of the light receiving portion that receives the main beam and the sub beam. Since the area of the light receiving portion is substantially the same, there is a problem that it is easily affected by stray light generated from the main beam.

  In order to solve such a problem, in recent optical pickup devices, the area of the light receiving unit that receives the sub beam is made smaller than the area of the light receiving unit that receives the main beam to suppress the influence of stray light. Technology has been developed.

  Further, the focusing control operation in the optical disc apparatus is such that the objective lens incorporated in the optical pickup device is first largely displaced to the operating position, that is, the position where the laser beam is condensed on the signal recording layer, and then the optical disc is subjected to plane vibration. In order to correct the shift in focusing due to the above, it is performed by a combination of operations for finely displacing the position of the objective lens.

  In such focusing control operation, when the objective lens is displaced to the operating position, the laser spot irradiated to the sub-beam light-receiving unit and the main beam light-receiving unit provided in the photodetector greatly expands, so unnecessary laser light In particular, a spot of the main beam having a high light intensity is irradiated to the light receiving unit for the sub beam, which causes a problem of adversely affecting the focusing control operation.

  The above-mentioned problem caused by stray light is that the laser beam reflected from the signal recording layer at the back of the signal recording layer performing the signal reading operation is a signal in front of the signal recording layer performing the signal reading operation. There is a characteristic that it is larger than the laser beam reflected from the recording layer.

  Therefore, there is a method for increasing the thickness of the transparent protective layer provided between the signal recording layer and the signal recording layer as a method for reducing the influence of such stray light. In such a method, the thickness is caused by the thickness of the protective layer. In addition to the problem that the amount of spherical aberration generated increases, there is a problem that the number of signal recording layers cannot be increased.

  In addition, an optical pickup device configured to improve the influence of stray light by changing the shape and area of the light receiving unit that constitutes the above-described photodetector is provided at the back of the signal recording layer that performs the signal reading operation. Is designed to maximize the effect of stray light reflected from the signal recording layer arranged at the back, so that it is possible to avoid the influence of stray light reflected from the signal recording layer arranged at the back. There is a problem that it cannot be done.

  That is, since the optical pickup device with such a countermeasure against stray light is designed on the assumption of an optical disc having two signal recording layers, stray light in a multilayer optical disc having three or more signal recording layers is designed. There is a problem that the influence of is inevitable. Furthermore, it is difficult to cope with stray light countermeasures in a multilayer optical disc having three or more signal recording layers by changing the shape of the light receiving portion constituting the photodetector.

  The present invention is intended to provide a multilayer optical disc that can solve the problem caused by stray light that occurs when a signal is read from a multilayer optical disc provided with three or more signal recording layers.

  The present invention relates to a multi-layered optical disc provided with at least three signal recording layers, and two signal recording layers arranged continuously from the side on which a laser beam for performing a signal reading operation is incident. And the polarization direction of the polarization reflection coat applied to the adjacent signal recording layer is opposite to each other.

  Further, according to the present invention, in a multilayer type optical disc provided with at least four even numbered signal recording layers, the laser beam for performing a signal reading operation is continuously arranged from the side on which the laser beam is incident 2. The polarization direction of the polarization reflection coat applied to the signal recording layer of the first layer and the polarization direction of the polarization reflection coat applied to the two adjacent signal recording layers are opposite to each other. Is.

  The multilayer optical disk of the present invention is a signal adjacent to the polarization direction of the polarization reflection coat applied to the two signal recording layers arranged continuously from the side on which the laser beam for performing the signal reading operation is incident. Since the polarization direction of the polarizing reflective coat applied to the recording layer is reversed, the signal recording layer that performs the read operation is selected by switching the polarization direction of the laser light emitted from the optical pickup device. If configured to do so, the influence of stray light can be eliminated.

  1, 2, 3 and 4 are sectional views showing different operating states of the multilayer optical disc and the objective lens according to the present invention, respectively, and FIG. 5 is a readout of signals recorded on the multilayer optical disc of the present invention. It is a block diagram which shows one Example of the optical pick-up apparatus which operate | moves.

  As shown in the cross-sectional view of FIG. 1, the multilayer optical disc D according to the present invention includes, for example, a first signal recording layer L1 and a second signal recording layer from the incident surface D1 side on which laser light emitted from an optical pickup device is incident. Four signal recording layers, L2, a third signal recording layer L3, and a fourth signal recording layer L4 are provided. Between the incident surface D1 and the first signal recording layer L1, the first signal recording layer L1 and the second signal recording layer L1 are provided. A transparent protective layer G1, between the signal recording layer L2, between the second signal recording layer L2 and the third signal recording layer L3, and between the third signal recording layer L3 and the fourth signal recording layer L4, respectively. G2, G3 and G4 are provided.

  In addition, the multilayer optical disc D according to the present invention emits laser light in each signal recording layer of the first signal recording layer L1, the second signal recording layer L2, the third signal recording layer L3, and the fourth signal recording layer L4. On the incident side surface, a first polarization reflection coat P1, a second polarization reflection coat P2, a third polarization reflection coat P3, and a fourth polarization reflection coat P4 are respectively attached.

  In such a configuration, the polarization directions of the first polarization reflection coat P1 and the second polarization reflection coat P2 applied to the first signal recording layer L1 and the second signal recording layer L2 provided on the incident surface D1 side. And the polarization directions of the third polarization reflection coat P3 and the fourth polarization reflection coat P4 attached to the third signal recording layer L3 and the fourth signal recording layer L4, which are signal recording layers provided on the back side, are reversed. To be.

  That is, for example, the polarization direction of the first polarization reflection coat P1 and the second polarization reflection coat P2 applied to the first signal recording layer L1 and the second signal recording layer L2 is set to be the P direction of linearly polarized light. The polarization directions of the third polarization reflection coat P3 and the fourth polarization reflection coat P4 attached to the third signal recording layer L3 and the fourth signal recording layer L4 are set to be the S direction of linearly polarized light. .

  In the multilayer optical disc D having such a configuration, the first polarization reflection coat P1 attached to the first signal recording layer L1 and the second polarization reflection coat P2 attached to the second signal recording layer L2 are P-polarized light. However, it acts to transmit S-polarized light. The third polarization reflection coat P3 attached to the third signal recording layer L3 and the fourth polarization reflection coat P4 attached to the fourth signal recording layer L4 reflect S-polarized light, but P-polarized light. Will act to penetrate.

  In the multilayer optical disc D having such a configuration, the signal layer composed of the first signal recording layer L1 and the first polarizing reflection coat P1 does not reflect all of the incident P-polarized light, and the second signal The laser beam of the level required for performing the reading operation of the signal recorded on the recording layer L2 can be transmitted. The signal layer composed of the third signal recording layer L3 and the third polarization reflection coat P3 does not reflect all of the incident S-polarized light, and does not reflect the signal recorded in the fourth signal recording layer L4. The laser beam of a level necessary for performing the reading operation can be transmitted.

  As described above, the multilayer optical disc D of the present invention is configured. Next, the light that can perform the read operation of the signals recorded on each signal recording layer of the multilayer optical disc D having the above configuration. The pickup device will be described with reference to the embodiment shown in FIG.

  In FIG. 5, reference numeral 1 denotes a laser diode that emits an output laser beam corresponding to a drive signal supplied from a laser drive circuit, and is configured to emit an S-polarized laser beam, for example. In such a configuration, the magnitude of the drive signal supplied to the laser diode 1 is changed and controlled in accordance with the signal recording layer that performs the signal reading operation.

  Reference numeral 2 denotes a diffraction grating on which the laser light emitted from the laser diode 1 is incident. The diffraction grating 2 generates and emits laser light composed of zero-order light as a main beam and + 1st-order light and −1st-order light as sub-beams. It is to be made.

  Reference numeral 3 denotes a polarization beam splitter on which the laser beam emitted from the diffraction grating 2 is incident, and is a front monitor provided to transmit the laser beam irradiated to the multilayer optical disc D and to control the output of the laser beam. A control film 3a for reflecting the monitoring laser light irradiated to the diode 4 is provided. The control film 3a is also configured to reflect the return light reflected from each signal recording layer provided on the multilayer optical disc D as control laser light, as will be described later.

  The control film 3a provided on the polarization beam splitter 3 is configured to transmit, for example, a laser beam having a half light amount of S-polarized light and reflect a laser light having a half light amount.

  Reference numeral 5 denotes a collimating lens on which the laser beam that has passed through the control film 3a of the polarizing beam splitter 3 is incident. The collimating lens 5 changes the incident laser beam to a laser beam that is a parallel beam. Reference numeral 6 denotes a reflection mirror on which the laser beam is incident, and has a function of reflecting all of the incident laser beam in the direction of the multilayer optical disc D. Such a reflection mirror 6 is generally called a raising mirror.

Reference numeral 7 denotes an objective lens to which the laser beam reflected from the reflection mirror 6 is incident. The objective lens 7 has a function of condensing as a laser beam focused on each signal recording layer provided in the multilayer optical disk D. The objective lens 7 performs a focusing control operation by a displacement operation in a direction perpendicular to the signal surface of the multilayer optical disc D, and performs a tracking control operation by a displacement operation in the radial direction of the multilayer optical disc D. It is configured. The objective lens that performs such an operation is fixed on a member called a lens holder that is supported by, for example, four support wires so as to be able to be displaced in the focusing control direction and the tracking control direction. Since the configuration is well known, the description thereof is omitted.

  Laser light applied to each signal recording layer of the multilayer optical disc D by the focusing operation of the objective lens 7 is incident on the objective lens 7 from the optical disc D side as return light reflected from the signal recording layer. The return light incident on the objective lens 7 is incident on the polarization beam splitter 3 through the reflection mirror 6 and the collimator lens 5.

  In this way, the return light incident on the polarizing beam splitter 3 is reflected as control laser light by the control film 3 a formed on the polarizing beam splitter 3.

  Reference numeral 8 denotes a sensor lens on which the control laser light reflected by the control film 3a of the polarization beam splitter 3 is incident. The control laser light is applied to a light receiving unit provided in a photodetector 9 called a PDIC. It has the effect of irradiating as condensed laser light. The sensor lens 8 incorporates a cylindrical lens and the like, and is configured to generate astigmatism in order to perform a focusing control operation by the astigmatism method, which is well known. Therefore, the description is omitted.

  A polarization direction control plate 10 is provided in the optical path between the collimating lens 5 and the reflection mirror 6 and selectively switches the polarization direction of linearly polarized light. The first operating position displaced in the direction of arrow A And a second operation position displaced in the B direction are provided so as to be displaceable. Reference numeral 11 denotes a half-wave plate provided on the polarization direction control plate 10, and is configured to be disposed in the optical path when the polarization direction control plate 10 is in the illustrated first operating position. A through-hole 12 is provided in the polarization direction control plate 10 so that the polarization direction control plate 10 is disposed in the optical path when the polarization direction control plate 10 is in the second operating position displaced in the direction of arrow B from the illustrated state. It is configured.

  In the optical pickup device having such a configuration, the shape of the light receiving unit that receives the main beam and the sub beam received in the photodetector 9 is the back of the signal recording layer that performs the signal reading operation, that is, adjacent to the signal recording layer. Thus, it is designed to eliminate as much as possible the adverse effects of the return light reflected from the signal recording layer, that is, stray light.

  As described above, an optical pickup device capable of reading signals recorded on a plurality of signal recording layers provided in the multilayer optical disc D of the present invention is configured. A read operation will be described.

  First, an operation for reading a signal recorded in the first signal recording layer L1 will be described. Since the first signal recording layer L1 is provided with the first polarization reflection coat P1 that reflects the polarized light in the P direction, the polarization direction control plate 10 is displaced and held at the first operation position shown in FIG. is there. That is, the half-wave plate 11 provided on the polarization direction control plate 10 is in a state of being disposed in the optical path of the laser light.

In such a state, when a command signal for performing a read operation of the signal recorded in the first signal recording layer L1 is output from the control circuit incorporated in the optical disc apparatus, the optical pickup apparatus is incorporated in the optical pickup apparatus. A drive signal for radiating a laser beam having a size necessary for reading the signal recorded in the first signal recording layer L1 is supplied from the laser diode drive circuit to the laser diode 1.

  When such a drive signal is supplied to the laser diode 1, the laser diode 1 emits a laser beam having a size necessary for reading out the S-polarized light and the signal recorded in the first signal recording layer L1. The The laser light emitted from the laser diode 1 is incident on the diffraction grating 2 and is emitted by the diffraction grating 2 as laser light composed of a main beam and a sub beam.

  The laser light emitted from the diffraction grating 2 is incident on the polarization beam splitter 3 and is separated into transmitted laser light and reflected laser light by the control film 3 a provided on the polarization beam splitter 3. Since the control film 3a is configured to transmit half the light amount of the S-polarized laser beam and reflect half the light amount, the laser beam for performing a signal read operation for half of the incident laser beam. And the other half is reflected in the direction of the front monitor diode 4 as a laser beam for monitoring.

  Since the laser beam reflected as the laser beam for monitoring by the control film 3a provided on the polarizing beam splitter 3 is irradiated to the front monitor diode 4, it corresponds to the level of the laser beam from the front monitor diode 4. Thus, a signal having a magnitude, that is, a monitor signal is obtained. Therefore, the intensity of the laser beam can be controlled to a desired value by feeding back such a monitor signal to a laser diode drive circuit provided to supply a drive signal to the laser diode 1. Since the circuit for performing such an operation is well known, its description is omitted.

  The laser beam that has passed through the control film 3 a provided in the polarizing beam splitter 3 as a laser beam for performing a signal reading operation is incident on the collimator lens 5 and is converted into parallel light by the collimator lens 5. The laser light converted into parallel light by the collimator lens 5 is transmitted through a half-wave plate 11 provided on the polarization direction control plate 10 and is incident on the reflection mirror 6, and the objective lens is reflected by the reflection mirror 6. Reflected in seven directions.

  The polarization direction of the laser light reflected by the reflection mirror 6 and incident on the objective lens 7 is converted from S-polarized light to P-polarized light by the conversion action of the polarization direction by the half-wave plate 11. FIG. 1 shows a state in which the laser beam of P-polarized light is condensed on the first signal recording layer L1 by the objective lens 7. As apparent from FIG. 1, the laser is applied to the first signal recording layer L1. As the light is condensed, a part of the laser light passes through the first signal recording layer L1 as indicated by a broken line.

  Since the laser beam focused on the first signal recording layer L1 is P-polarized light, it is reflected by the first polarization reflection coat P1 attached to the first signal recording layer L1. Since the laser light reflected by the first polarization reflection coat P1 is incident on the objective lens 7 from the optical disc D side, the half-wave plate 11 provided on the reflection mirror 6 and the polarization direction control plate 10 and The light enters the polarizing beam splitter 3 through the collimating lens 5.

  The polarization direction of the laser light, which is the reflected light from the first signal recording layer L1 incident on the polarizing beam splitter 3, is converted from P-polarized light to S-polarized light by the polarization action of the half-wave plate 11. Therefore, half of the light amount is reflected to the sensor lens 8 side by the control film 3 a provided on the polarization beam splitter 3.

The laser light reflected by the control film 3 a and incident on the sensor lens 8 is added with astigmatism by the sensor lens 8 and is irradiated to the photodetector 9. When the laser beam is irradiated on the photodetector 9 in this way, a focusing error signal, a tracking error signal, and a data signal are generated by a quadrant sensor (not shown) incorporated in the photodetector 9. A focusing control operation, a tracking control operation, and a data signal demodulation operation based on such a signal are performed. Since such an operation is well known, its description is omitted.

  By such an operation, the signal picked up by the optical pickup device is read out from the signal recorded in the first signal recording layer L1 provided in the multilayer optical disc D. When such an operation is performed, the first operation is performed as described above. A part of the laser beam condensed on the one signal recording layer L1 passes through the first signal recording layer L1.

  Laser light that is P-polarized light that has passed through the first signal recording layer L1 is applied to the second signal recording layer L2 that is disposed adjacent to the back of the first signal recording layer L1. Since the second signal recording layer L2 is provided with a second polarization reflection coat P2 which is a P polarization reflection coat, the laser light is first reflected by the second polarization reflection coat P2 as shown by a broken line in FIG. The light is reflected to the signal recording layer L1 side.

  The return light reflected from the second polarizing reflection coat P2 attached to the second signal recording layer L2 to the first signal recording layer L1 side passes through the first signal recording layer L1, and then is applied to the objective lens 7 as an optical disk. Incident from the D side. Such return light is transmitted through the reflection mirror 6, the half-wave plate 11 and the collimating lens 5 provided on the polarization direction control plate 10 in the same manner as the laser light reflected from the first signal recording layer L 1 described above. The light enters the polarizing beam splitter 3.

  Thus, the polarization direction of the laser light, which is the reflected light from the second signal recording layer L2 incident on the polarization beam splitter 3, is converted from P-polarized light to S-polarized light by the polarization action of the half-wave plate 11. Therefore, half of the light amount is reflected to the sensor lens 8 side by the control film 3 a provided on the polarization beam splitter 3.

  The laser light reflected by the control film 3a and incident on the sensor lens 8 is laser light called stray light. The laser light is added with astigmatism by the sensor lens 8 and is detected by a photodetector. 9 will be irradiated. In this way, the laser light which is stray light is irradiated to the light receiving unit incorporated in the photodetector 9, and the light receiving unit is reflected by the stray light reflected from the adjacent signal recording layer and irradiated to the light receiving unit. Since it is designed to eliminate adverse effects as much as possible, the focusing control operation, tracking control operation and data signal demodulation operation can be performed without any trouble.

  In this way, countermeasures against stray light that is laser light reflected from the second signal recording layer L2 are taken. Next, laser light that passes through the second signal recording layer L2 will be described. The laser light applied to the second signal recording layer L2 is reflected and partially transmitted by the second signal recording layer L2, as indicated by a broken line in FIG.

  The laser light transmitted through the second signal recording layer L2 is irradiated to the third signal recording layer L3. The third signal recording layer L3 is provided with a third polarizing reflection coat P3 which is an S polarization reflection coat. Therefore, the laser beam is transmitted through the third signal recording layer L3 as indicated by a broken line in FIG. Accordingly, since no laser light is reflected from the third signal recording layer L3, unnecessary return light called stray light is not incident on the objective lens 7.

The laser light transmitted through the third signal recording layer L3 is applied to the fourth signal recording layer L4. The fourth signal recording layer L4 is also provided with a fourth polarizing reflection coat P4 which is an S polarization reflection coat. Therefore, the laser beam is transmitted through the fourth signal recording layer L4 in the same manner as the third signal recording layer L3. Accordingly, since no laser light is reflected from the fourth signal recording layer L4, unnecessary return light called stray light is not incident on the objective lens 7.

  As described above, the laser beam applied to the third signal recording layer L3 and the fourth signal recording layer L4 when performing the read operation of the signal recorded in the first signal recording layer L1 is the third signal recording layer. Since it transmits through L3 and the fourth signal recording layer L4, adverse effects due to stray light can be surely eliminated, so that the signal recorded in the first signal recording layer L1 can be read accurately.

  As described above, the read operation of the signal recorded in the first signal recording layer L1 is performed. Next, the operation in the case of reading the signal recorded in the second signal recording layer L2 will be described.

  Since the second signal recording layer L2 is provided with the second polarization reflection coating P2 that reflects the polarized light in the P direction, the polarization direction control plate 10 incorporated in the optical pickup device has the first signal recording layer L1. In the same manner as in the reading operation of the signal recorded in FIG. 5, the displacement is held at the first operation position shown in FIG. 5.

  In such a state, when a command signal for performing a read operation of the signal recorded in the second signal recording layer L2 is output from the control circuit incorporated in the optical disc apparatus, the signal is incorporated in the optical pickup apparatus. A drive signal for radiating a laser beam having a size necessary for reading out a signal recorded on the second signal recording layer L2 is supplied from the laser diode drive circuit to the laser diode 1.

  When such a drive signal is supplied to the laser diode 1, the laser diode 1 emits a laser beam having a size necessary for reading out the signal recorded in the second signal recording layer L2 as S-polarized light. The The laser light emitted from the laser diode 1 is incident on the diffraction grating 2 in the same manner as in the read operation of the signal recorded in the first signal recording layer L1 described above. Is emitted as a laser beam.

  The laser beam emitted from the diffraction grating 2 is incident on the polarizing beam splitter 3 and is separated into transmitted laser light and reflected laser light by the control film 3a provided on the polarizing beam splitter 3 as described above. Is done. Since the laser beam reflected by the control film 3a is irradiated to the front monitor diode 4 as a monitor laser beam, the intensity of the laser beam can be controlled to a desired value by the monitoring operation described above. I can do it.

  Further, the laser beam that has passed through the control film 3 a provided in the polarizing beam splitter 3 as a laser beam for performing a signal read operation is incident on the collimator lens 5, and is converted into parallel light by the collimator lens 5. . The laser light changed to parallel light by the collimator lens 5 is transmitted through the half-wave plate 11 provided on the polarization direction control plate 10 at the first operating position, and is incident on the reflection mirror 6, and is reflected therefrom. Reflected by the mirror 6 toward the objective lens 7.

The polarization direction of the laser light reflected by the reflecting mirror 6 and incident on the objective lens 7 is transmitted through the half-wave plate 11 that is a polarizing element, and thus is converted into P-polarized light. FIG. 2 shows a state in which such P-polarized laser light is condensed on the second signal recording layer L2 by the objective lens 7, and as is apparent from FIG. 2, the laser light passes through the first signal recording layer L1. Then, the laser beam is focused on the second signal recording layer L2, and a part of the laser beam is transmitted through the second signal recording layer L2 as indicated by a broken line.

  Since the laser beam focused on the second signal recording layer L2 is P-polarized light, a part of the first polarization-reflecting coat P1, which is a P-polarized reflection coat attached to the first signal recording layer L1, is used. The reflected laser beam is reflected and condensed on the second signal recording layer L2. The laser light reflected by the first polarization reflection coat P1 is incident on the objective lens 7, but the level of the return light that is incident on the objective lens 7 and returns to the photodetector 9 is very small. There is no adverse effect on the control operation of the optical pickup device.

  The laser beam condensed on the second signal recording layer L2 is reflected by the second polarization reflection coat P2 attached to the second signal recording layer L2. Since the laser beam reflected by the second polarization reflection coat P2 passes through the first signal recording layer L1 and enters the objective lens 7 from the optical disc D side, it is provided on the reflection mirror 6 and the polarization direction control plate 10. The light is incident on the polarization beam splitter 3 through the half-wave plate 11 and the collimator lens 5.

  Since the polarization direction of the laser light, which is the reflected light from the second signal recording layer L2 incident on the polarization beam splitter 3, is converted to S-polarized light, the control film 3a provided on the polarization beam splitter 3 is provided. Accordingly, half of the light amount is reflected to the sensor lens 8 side.

  The laser light reflected by the control film 3 a and incident on the sensor lens 8 is irradiated with astigmatism by the sensor lens 8 and irradiated on the photodetector 9. When the laser light is irradiated on the photodetector 9 in this way, a focusing error signal, a tracking error signal, and a data signal are generated by a quadrant sensor or the like incorporated in the photodetector 9. The focusing control operation, the tracking control operation, and the data signal demodulation operation based on the signal are performed in the same manner as the signal reading operation recorded on the first signal recording layer L1.

  As a result of the above operation, the signal picked up by the optical pickup device is read out from the signal recorded on the second signal recording layer L2 provided in the multilayer optical disc D. Part of the laser light focused on the two-signal recording layer L2 passes through the second signal recording layer L2.

  The laser beam that is P-polarized light that has passed through the second signal recording layer L2 is applied to the third signal recording layer L3 that is disposed adjacent to the back of the second signal recording layer L2. Since the signal recording layer L3 is provided with a third polarization reflection coat P3 which is an S polarization reflection coat, the laser light is transmitted through the third signal recording layer L3 as indicated by a broken line in FIG. Accordingly, since no laser light is reflected from the third signal recording layer L3, unnecessary return light called stray light is not incident on the objective lens 7. Therefore, the third signal recording layer L3 does not adversely affect the read operation of the signal recorded on the second signal recording layer L2 of the optical pickup device.

  In addition, the laser light transmitted through the third signal recording layer L3 is irradiated to the fourth signal recording layer L4 disposed adjacent to the third signal recording layer L3. Since the fourth polarization reflection coat P4, which is an S polarization reflection coat, is applied, the laser light passes through the fourth signal recording layer L4 as shown by the broken line in FIG. Therefore, since no laser light is reflected from the fourth signal recording layer L4, unnecessary return light called stray light is not incident on the objective lens 7. Therefore, the fourth signal recording layer L4 does not adversely affect the read operation of the signal recorded on the second signal recording layer L2 of the optical pickup device.

  As described above, the read operation of the signals recorded in the first signal recording layer L1 and the second signal recording layer L2 is performed, and then the read operation of the signals recorded in the third signal recording layer L3 is performed. Will be described.

  Since the third signal recording layer L3 is provided with the third polarization reflection coating P3 for reflecting the polarized light in the S direction, the polarization direction control plate 10 incorporated in the optical pickup device performs the first operation shown in FIG. It is displaced to the second operating position displaced in the opposite direction of the position, that is, in the direction of arrow B. When the polarization direction control plate 10 is in the second operating position, the through hole 12 provided in the polarization direction control plate 10 is in a state of being disposed in the optical path of the laser light.

  In such a state, when a command signal for performing a read operation of the signal recorded in the third signal recording layer L3 is output from the control circuit incorporated in the optical disc apparatus, it is incorporated in the optical pickup apparatus. A drive signal for radiating a laser beam having a size necessary for reading the signal recorded in the third signal recording layer L3 is supplied from the laser diode drive circuit to the laser diode 1.

  When such a drive signal is supplied to the laser diode 1, the laser diode 1 emits a laser beam having a size necessary for reading out the S-polarized light and the signal recorded in the third signal recording layer L 3. The The laser light emitted from the laser diode 1 is incident on the diffraction grating 2 in the same manner as in the read operation of the signals recorded in the first signal recording layer L1 and the second signal recording layer L2, and the diffraction grating 2 is emitted as a laser beam composed of a main beam and a sub beam.

  The laser beam emitted from the diffraction grating 2 is incident on the polarizing beam splitter 3 and is separated into transmitted laser light and reflected laser light by the control film 3a provided on the polarizing beam splitter 3 as described above. Is done. Since the laser beam reflected by the control film 3a is irradiated to the front monitor diode 4 as a monitor laser beam, the intensity of the laser beam can be controlled to a desired value by the monitoring operation described above. I can do it.

  Further, the laser beam that has passed through the control film 3 a provided in the polarizing beam splitter 3 as a laser beam for performing a signal read operation is incident on the collimator lens 5, and is converted into parallel light by the collimator lens 5. . The laser light changed into parallel light by the collimating lens 5 is transmitted through the through-hole 12 provided in the polarization direction control plate 10 at the second operation position and is incident on the reflection mirror 6. Thus, the light is reflected in the direction of the objective lens 7.

  The polarization direction of the laser light reflected by the reflection mirror 6 and incident on the objective lens 7 does not pass through the half-wave plate 11 that is a polarizing element, and thus remains as S-polarized light. FIG. 3 shows a state in which the S-polarized laser beam is focused on the third signal recording layer L3 by the focusing operation of the objective lens 7. As is apparent from FIG. 3, the first signal recording is performed. The laser beam passes through the layer L1 and the second signal recording layer L2 and is condensed on the third signal recording layer L3, and a part of the laser light passes through the third signal recording layer L3 as indicated by a broken line.

  Since the first signal recording layer L1 and the second signal recording layer L2 are provided with the first polarization reflection coat P1 and the second polarization reflection coat P2 for reflecting the polarized light in the P direction, they are S polarized light. The laser light is irradiated to the third signal recording layer L3 without being attenuated by the first signal recording layer L1 and the second signal recording layer L2.

Since the third signal recording layer L3 is provided with a third polarization reflection coat P3 that reflects polarized light in the S direction, a part of the laser light is reflected and the other laser light is reflected in the third signal recording. It passes through the layer L3.

  Since the laser beam reflected by the third polarizing reflection coat P3 is incident on the objective lens 7 from the optical disk D side, the reflection mirror 6, the through-hole 12 provided in the polarization direction control plate 10, and the collimating lens 5 are used. Through the polarization beam splitter 3.

  Since the polarization direction of the laser light, which is the reflected light from the third signal recording layer L3 incident on the polarizing beam splitter 3, is S-polarized light, the amount of light is controlled by the control film 3a provided on the polarizing beam splitter 3. Half of the light is reflected to the sensor lens 8 side.

  The laser light reflected by the control film 3 a and incident on the sensor lens 8 is irradiated with astigmatism by the sensor lens 8 and irradiated on the photodetector 9. When the laser light is irradiated on the photodetector 9 in this way, a focusing error signal, a tracking error signal, and a data signal are generated by a quadrant sensor or the like incorporated in the photodetector 9. A focusing control operation, a tracking control operation, and a data signal demodulation operation based on such a signal are performed in the same manner as in the signal reading operation recorded on the first signal recording layer L1 and the second signal recording layer L2.

  As a result of the above operation, the signal picked up by the optical pickup device is read out from the signal recorded on the third signal recording layer L3 provided in the multilayer optical disc D. A part of the laser beam condensed on the three-signal recording layer L3 passes through the third signal recording layer L3.

  Laser light that is S-polarized light that has passed through the third signal recording layer L3 is applied to a fourth signal recording layer L4 that is disposed adjacent to the back of the third signal recording layer L3. Since the fourth signal recording layer L4 is provided with a fourth polarization reflection coat P4 which is an S polarization reflection coat, the laser light is transmitted by the fourth polarization reflection coat P4 as shown by a broken line in FIG. The light is reflected to the signal recording layer L3 side.

  The return light reflected from the fourth polarization reflection coat P4 applied to the fourth signal recording layer L4 to the third signal recording layer L3 side is reflected by the third signal recording layer L3, the second signal recording layer L2, and the second signal recording layer L2. After passing through one signal recording layer L1, it enters the objective lens 7 from the optical disc D side. Similar to the laser light reflected from the third signal recording layer L3, the return light passes through the reflection mirror 6, the through-hole 12 provided in the polarization direction control plate 10, and the collimating lens 5, and the polarization beam splitter. 3 is incident.

  Since the laser light that is the reflected light from the fourth signal recording layer L4 incident on the polarization beam splitter 3 in this way is S-polarized light, the amount of light is reduced by the control film 3a provided on the polarization beam splitter 3. Half of the light is reflected to the sensor lens 8 side.

  The laser light reflected by the control film 3a and incident on the sensor lens 8 is laser light called stray light. The laser light is added with astigmatism by the sensor lens 8 and is detected by a photodetector. 9 will be irradiated. In this way, the laser light which is stray light is irradiated to the light receiving unit incorporated in the photodetector 9, and the light receiving unit is reflected by the stray light reflected from the adjacent signal recording layer and irradiated to the light receiving unit. Since it is designed to eliminate adverse effects as much as possible, the focusing control operation, tracking control operation and data signal demodulation operation can be performed without any trouble.

As described above, the first signal recording layer L1, the second signal recording layer L2, and the third signal recording layer L.
3 is performed. Next, the operation of reading the signal recorded in the fourth signal recording layer L4 will be described.

  Since the fourth signal recording layer L4 is provided with the fourth polarization reflection coat P4 that reflects the polarized light in the S direction, the polarization direction control plate 10 incorporated in the optical pickup device is attached to the third signal recording layer L3. Similarly to the read operation of the recorded signal, the signal is displaced to the second operation position opposite to the first operation position. When the polarization direction control plate 10 is in the second operating position, the through hole 12 provided in the polarization direction control plate 10 is in a state of being disposed in the optical path of the laser light.

  In such a state, when a command signal for performing a read operation of the signal recorded in the fourth signal recording layer L4 is output from the control circuit incorporated in the optical disc apparatus, the signal is incorporated in the optical pickup apparatus. A drive signal for radiating a laser beam having a size necessary for reading the signal recorded in the fourth signal recording layer L4 is supplied from the laser diode drive circuit to the laser diode 1.

  When such a drive signal is supplied to the laser diode 1, the laser diode 1 emits a laser beam having a size necessary for reading the S-polarized light and the signal recorded in the fourth signal recording layer L4. The The laser light emitted from the laser diode 1 is incident on the diffraction grating 2 in the same manner as the signal reading operation recorded on each signal recording layer, and a laser beam composed of a main beam and a sub beam by the diffraction grating 2. It is emitted as light.

  The laser beam emitted from the diffraction grating 2 is incident on the polarizing beam splitter 3 and is separated into transmitted laser light and reflected laser light by the control film 3a provided on the polarizing beam splitter 3 as described above. Is done. Since the laser beam reflected by the control film 3a is irradiated to the front monitor diode 4 as a monitor laser beam, the intensity of the laser beam can be controlled to a desired value by the monitoring operation described above. I can do it.

  Further, the laser beam that has passed through the control film 3 a provided in the polarizing beam splitter 3 as a laser beam for performing a signal read operation is incident on the collimator lens 5, and is converted into parallel light by the collimator lens 5. . The laser light changed into parallel light by the collimating lens 5 is transmitted through the through-hole 12 provided in the polarization direction control plate 10 at the second operation position and is incident on the reflection mirror 6. Thus, the light is reflected in the direction of the objective lens 7.

  The polarization direction of the laser light reflected by the reflection mirror 6 and incident on the objective lens 7 does not pass through the half-wave plate 11 that is a polarizing element, and thus remains as S-polarized light. FIG. 4 shows a state in which the laser beam of S-polarized light is condensed on the fourth signal recording layer L4 by the condensing operation of the objective lens 7. As apparent from FIG. 4, the first signal recording is performed. The laser beam is transmitted through the layer L1, the second signal recording layer L2, and the third signal recording layer L3, and is condensed on the fourth signal recording layer L4. Will be transmitted.

  Since the first signal recording layer L1 and the second signal recording layer L2 are provided with the first polarization reflection coat P1 and the second polarization reflection coat P2 for reflecting the polarized light in the P direction, they are S polarized light. The laser light is irradiated to the third signal recording layer L3 without being attenuated by the first signal recording layer L1 and the second signal recording layer L2.

Since the third signal recording layer L3 is provided with the third polarization reflection coat P3 for reflecting the polarized light in the S direction, a part of the laser light is reflected by the third polarization reflection coat P3 and the outside thereof. The laser light passes through the third signal recording layer L3 and is focused on the fourth signal recording layer L4.

  Since the laser beam focused on the fourth signal recording layer L4 is S-polarized light, a part of the third polarized-light reflecting coat P3 which is an S-polarized reflecting coat applied to the third signal recording layer L3 is used. The reflected laser beam is reflected and condensed on the fourth signal recording layer L4. The laser light reflected by the third polarizing reflection coat P3 is incident on the objective lens 7, but the level of the return light that is incident on the objective lens 7 and returns to the photodetector 9 is very small. There is no adverse effect on the control operation of the optical pickup device.

  Further, since no reflection layer such as a signal recording layer is provided in the back of the fourth signal recording layer L4, the laser light transmitted through the fourth signal recording layer L4 is not reflected to the objective lens side. There is no influence on the control operation of the optical pickup device.

  The laser beam condensed on the fourth signal recording layer L4 is reflected by a fourth polarization reflection coat P4 attached to the fourth signal recording layer L4. The laser beam reflected by the fourth polarizing reflection coat P4 passes through the third signal recording layer L3, the second signal recording layer L2, and the first signal recording layer L1, and enters the objective lens 7 from the optical disc D side. Therefore, the light is incident on the polarization beam splitter 3 through the reflection mirror 6, the through hole 12 provided in the polarization direction control plate 10 and the collimator lens 5.

  Since the laser light, which is the reflected light from the fourth signal recording layer L4 incident on the polarizing beam splitter 3, is S-polarized light, half of the amount of light is sensored by the control film 3a provided on the polarizing beam splitter 3. It is reflected to the lens 8 side.

  The laser light reflected by the control film 3 a and incident on the sensor lens 8 is irradiated with astigmatism by the sensor lens 8 and irradiated on the photodetector 9. When the laser light is irradiated on the photodetector 9 in this way, a focusing error signal, a tracking error signal, and a data signal are generated by a quadrant sensor or the like incorporated in the photodetector 9. A focusing control operation, a tracking control operation, and a data signal demodulation operation based on such signals are performed in the same manner as the signal reading operation recorded on each signal recording layer described above.

  As described above, the signals recorded in the first signal recording layer L1, the second signal recording layer L2, the third signal recording layer L3, and the fourth signal recording layer L4 are read out. The difference in the read operation of the recorded signal is that the magnitude of the drive signal supplied to the laser diode 1 is changed and the operation for detecting the signal recording layer that performs the condensing operation is performed. It is in.

  That is, the read operation of the signals recorded in the first signal recording layer L1 and the second signal recording layer L2 is performed by polarized light in the P direction, but the second signal recording layer L2 is more than the first signal recording layer L1. This is also because the light intensity is attenuated by the first signal recording layer L1 and the intensity of the laser light emitted from the laser diode 1 needs to be increased.

  As described above, the read operation of the signal recorded in the second signal recording layer L2 is performed by changing the magnitude of the drive signal supplied to the laser diode 1 to the read operation of the signal recorded in the first signal recording layer L1. This is performed by performing an operation of discriminating between the first signal recording layer L1 and the second signal recording layer L2 after performing a switching operation that is larger than the switching operation.

  Such a signal recording layer identification operation can be performed by detecting a focus error signal obtained when the objective lens 7 is moved in a direction approaching from a position away from the incident surface D1 of the multilayer optical disc D. . That is, as is well known, when the objective lens 7 is displaced in the direction perpendicular to the signal surface of the optical disc, a focus error signal called an S-curve is obtained, so that the objective lens 7 is brought closer to a position away from the incident surface D1. When moved, two focus error signals called S-shaped curves are obtained at the positions of the first signal recording layer L1 and the second signal recording layer L2.

  Thus, the first signal recording layer L1 and the second signal recording layer L2 can be identified by detecting the number of S-shaped curves obtained when the objective lens 7 is displaced. It can be recognized that the signal recording layer having the S-shaped curve is the second signal recording layer L2 which is a desired signal recording layer. Therefore, by performing the focus control operation and the tracking control operation for the second signal recording layer L2, it is possible to perform the read operation of the signal recorded on the second signal recording layer L2.

  Further, the read operation of the signals recorded in the third signal recording layer L3 and the fourth signal recording layer L4 is performed by the polarized light in the S direction as described above, but the fourth signal recording layer L4 has the third signal. Since the third signal recording layer L3 is disposed behind the recording layer L3 as viewed from the incident surface D1 and the amount of light is attenuated, it is necessary to increase the intensity of the laser light emitted from the laser diode 1. .

  As described above, the read operation of the signal recorded in the fourth signal recording layer L4 is the same as the read operation of the signal recorded in the third signal recording layer L3. This is performed by performing an operation of discriminating between the third signal recording layer L3 and the fourth signal recording layer L4 after performing a switching operation that is larger than the switching operation.

  Such a signal recording layer identification operation is performed by detecting a focus error signal obtained when the objective lens 7 is moved in a direction approaching from a position away from the incident surface D1 of the multilayer optical disc D as described above. Can be done. That is, when the objective lens 7 is displaced in the direction perpendicular to the signal surface of the optical disk, a focus error signal called an S-curve is obtained. Therefore, when the objective lens 7 is moved in a direction closer to the position away from the incident surface D1. Two focus error signals called S-shaped curves are obtained at the positions of the third signal recording layer L3 and the fourth signal recording layer L4.

  Thus, the third signal recording layer L3 and the fourth signal recording layer L4 can be distinguished by detecting the number of S-shaped curves obtained when the objective lens 7 is displaced. It can be recognized that the signal recording layer having the S-shaped curve is the fourth signal recording layer L4 which is a desired signal recording layer. Therefore, by performing the focus control operation and the tracking control operation for the fourth signal recording layer L4, it is possible to perform the read operation of the signal recorded on the fourth signal recording layer L4.

  As described above, the discriminating operation of the third signal recording layer L3 and the fourth signal recording layer L4 is obtained when the objective lens 7 is moved in a direction approaching from a position away from the incident surface D1 of the multilayer optical disc D. This can be done by detecting a focus error signal. When such an operation is performed, the focal position passes through the first signal recording layer L1 and the second signal recording layer L2 in accordance with the moving operation of the objective lens 7, and such an operation is applied to the laser beam of S-polarized light. Therefore, the laser light is not reflected by the first signal recording layer L1 and the second signal recording layer L2.

  Accordingly, when the focal position passes through the first signal recording layer L1 and the second signal recording layer L2, a focus error signal indicating an S-shaped curve characteristic is not generated. Therefore, the first S-curve characteristic is obtained when the focal position passes the position of the third signal recording layer L3, and the second S-curve characteristic is the position of the fourth signal recording layer L4. Since it is obtained when passing, the third signal recording layer L3 and the fourth signal recording layer L4 can be identified.

  In this embodiment, a multilayer optical disc having four signal recording layers is described. However, the present invention can be applied to a multilayer optical disc having three or more signal recording layers. In this embodiment, the multilayer type optical disc provided with four layers, that is, an even number of signal recording layers has been described. However, a multilayer type provided with an odd number of signal recording layers such as three or five layers. Of course, it is possible to implement on an optical disc.

  In addition, the half-wave plate 11 is provided for the operation of selectively changing the polarization direction of the laser beam for performing the reading operation of the signal recorded on the signal recording layer provided in the multilayer optical disc D of the present invention. The polarization direction control plate 10 is displaced by being displaced to the first operation position and the second operation position, but other configurations are of course possible.

It is sectional drawing which shows the relationship between the multilayer optical disk which concerns on this invention, and an objective lens. It is sectional drawing which shows the relationship between the multilayer optical disk which concerns on this invention, and an objective lens. It is sectional drawing which shows the relationship between the multilayer optical disk which concerns on this invention, and an objective lens. It is sectional drawing which shows the relationship between the multilayer optical disk which concerns on this invention, and an objective lens. 1 is a configuration diagram illustrating an embodiment of an optical pickup device that performs an operation of reading a signal recorded on a multilayer optical disc according to the present invention. FIG.

Explanation of symbols

L1 1st signal recording layer L2 2nd signal recording layer L3 3rd signal recording layer L4 4th signal recording layer P1 1st polarization reflection coat P2 2nd polarization reflection coat P3 3rd polarization reflection coat P4 4th polarization reflection coat 1 Laser Diode 3 Polarizing beam splitter 5 Collimating lens 7 Objective lens 9 Photo detector 10 Polarization direction control plate 11 1/2 wavelength plate 12 Through-hole

Claims (2)

It is a multilayer optical disc provided with at least three signal recording layers, and is attached to two signal recording layers arranged continuously from the side on which a laser beam for performing a signal reading operation is incident. A multilayer optical disk, wherein the polarization direction of the polarization reflection coat and the polarization direction of the polarization reflection coat applied to the adjacent signal recording layer are opposite to each other. A multi-layer type optical disc provided with at least four or more even numbered signal recording layers, and two signal recording layers arranged continuously from the side on which a laser beam for performing a signal reading operation is incident A multilayer type optical disc, wherein the polarization direction of the polarization reflection coat applied to the optical recording medium and the polarization direction of the polarization reflection coat applied to the two adjacent signal recording layers are opposite to each other.

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