JP2010049750A - Multilayer optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that unnecessary light reflected by a signal recording layer gives evil effect to focusing control operation when reproducing operation of a signal recorded in the signal recording layer is performed. <P>SOLUTION: Provided is a multilayer optical disk provided with a plurality of signal recording layers, wherein intervals between the signal recording layers are set so that the quantity of stray light reflected by the signal recording layers provided in the inner part of a signal recording layer is made minimum when read-out operation of a signal recorded in the signal recording layer provided on the side of a surface on which a laser beam for performing read-out operation of the signal is made incident is performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multilayer optical disc in which a signal reading operation is performed by laser light and a plurality of signal recording layers are provided.

  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.

  As an optical disk, a disk called CD or DVD is widely used. Recently, an optical disk called BD (Blu-ray disk) having a large recording capacity is spreading. Such an optical disc of the BD standard is specified to use a blue-violet laser beam having a wavelength of 405 nm and perform a signal condensing operation with an objective lens having a numerical aperture of 0.85.

  Recently, a multi-layer 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. An optical pickup device capable of performing the above has also been 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 due to stray light, a light detector having a shape that eliminates the influence of stray light has been developed. (See Patent Document 1.)
JP 2007-42236 A

  The prior art disclosed in Patent Document 1 described above is configured to suppress the influence of stray light on a multilayer optical disc provided with a plurality of signal recording layers.

  The focusing control operation in the optical disc apparatus is performed by first moving the objective lens incorporated in the optical pickup device to the operating position, that is, the position for condensing the laser beam on the signal recording layer, and then performing planar vibration of the optical disc. In order to correct the shift in focusing due to this, the operation is performed in combination with an operation of finely displacing the position of the objective lens.

  When the objective lens is displaced to the operating position in order to perform a focusing control operation on a desired signal recording layer, the laser spot irradiated to the sub beam light receiving unit and the main beam light receiving unit provided in the photodetector is greatly expanded. Therefore, unnecessary laser light reflected from the signal recording layer disposed in the back of the desired signal recording layer, particularly stray light that is a spot of the main beam having a high light intensity, is applied to the light receiving unit for the sub beam, and the focusing control operation The problem of adversely affecting the system occurs.

  The present invention is intended to provide a multilayer optical disc that can solve the problem that the focusing control operation becomes unstable due to stray light or unnecessary laser light.

  The multilayer optical disc according to the present invention has a signal recording layer in the back of the signal recording layer when the signal recording operation is performed on the signal recording layer provided on the side on which the laser beam that performs the signal reading operation is incident. The distance between the signal recording layers is set so that the amount of stray light reflected from the provided signal recording layer is minimized.

  The multilayer optical disc of the present invention is characterized in that it is an optical disc defined so as to perform a signal reading operation with a laser beam having a wavelength of 405 nm.

  The multilayer optical disk according to the present invention is characterized in that the optical disk is defined so as to perform a signal reading operation with a laser beam condensed by an objective lens having a numerical aperture of 0.85. is there.

  In addition, the multilayer optical disk of the present invention is defined by a laser beam that is regulated to perform a signal read operation with a laser beam having a wavelength of 405 nm and is focused by an objective lens having a numerical aperture of 0.85. The optical disk is defined to perform a signal reading operation.

  The multilayer optical disc of the present invention is characterized in that the interval between signal recording layers is set to 20 μm to 25 μm.

The multilayer optical disc according to the present invention has a signal recording layer in the back of the signal recording layer when the signal recording operation is performed on the signal recording layer provided on the side on which the laser beam that performs the signal reading operation is incident. Since the interval between the signal recording layers is set so that the amount of stray light reflected from the provided signal recording layer is minimized, the control operation such as the focus control operation in the optical pickup device can be accurately performed. As a result, there is an advantage that the signal reading operation can be performed accurately.

  FIG. 1 is a diagram for explaining the relationship between a multilayer optical disk according to the present invention and a laser beam condensed by an objective lens, and FIG. 2 shows a read operation of a signal recorded on the multilayer optical disk of the present invention. FIG. 3 is a diagram for explaining the relationship between a photodetector incorporated in the optical pickup device and laser light, and FIGS. 4 and 5 are incorporated in a conventional optical pickup device. FIG. 6 is a characteristic diagram for explaining the characteristics of the multilayer optical disk according to the present invention.

  First, the configuration of the optical pickup device will be described with reference to FIG. In FIG. 2, reference numeral 1 denotes a laser diode that emits an output laser beam L1 corresponding to a drive signal supplied from a laser drive circuit. The laser beam L1 is a blue-violet laser beam having a wavelength of 405 nm and has a cross section. It is an elliptical laser beam.

  Reference numeral 2 denotes a diffraction grating on which the laser beam L1 emitted from the laser diode 1 is incident, and generates and emits a laser beam L2 composed of a 0th-order light as a main beam and a + 1st order light and a −1st order light as sub beams. It works.

  Reference numeral 3 denotes a polarization beam splitter on which the laser beam L2 emitted from the diffraction grating 2 is incident. The polarization beam splitter 3 is provided for transmitting the laser beam L3 irradiated to the optical disc and controlling the output of the laser beam. A control film 3a for reflecting the monitor laser light L4 irradiated to the diode 4 is provided. The control film 3a is also configured to reflect the return light reflected from the optical disc as control laser light, as will be described later.

  Reference numeral 5 denotes a collimator lens to which the laser beam L3 transmitted through the control film 3a of the polarizing beam splitter 3 is incident. The collimator lens 5 changes the incident laser beam L3 to a laser beam L5 that is a parallel beam and has an optical axis direction. It has the effect | action which correct | amends spherical aberration by the displacement to. Reference numeral 6 denotes a reflection mirror on which the laser beam L5 is incident, and serves to reflect all of the laser beam L5 in the direction of the optical disc as the laser beam L6. Such a reflection mirror 6 is generally called a raising mirror.

  Reference numeral 7 denotes a quarter-wave plate on which the laser beam L6 reflected from the reflection mirror 6 is incident, and functions to shift the phase of the laser beam L6 by a quarter wavelength. Reference numeral 8 denotes an objective lens in which the laser beam L7 transmitted through the quarter-wave plate 7 is incident and the numerical aperture is set to 0.85. The laser beam focused on the signal recording layer provided on the optical disc The light is condensed as L8. The objective lens 8 is configured to perform a focusing control operation by a displacement operation in a direction perpendicular to the signal surface of the optical disc and to perform a tracking control operation by a displacement operation in the radial direction of the optical disc. The objective lens that performs such an operation is fixed to a member called a lens holder that is displaceable in the focusing control direction and the tracking control direction by, for example, four support wires. Such a configuration is well known. Since there is, explanation is omitted.

Laser light L8 irradiated to the signal recording layer of the optical disc by the objective lens 8 is incident on the objective lens 8 as return light reflected from the signal recording layer. Return light incident on the objective lens 8 is incident on the polarization beam splitter 3 through the quarter-wave plate 7, the reflection mirror 6, and the collimator lens 5.

  In this way, the phase of the return light incident on the polarization beam splitter 3 is reciprocally transmitted through the quarter-wave plate 7, that is, transmitted twice. become. When the return light whose phase is shifted in this way is incident on the polarizing beam splitter 3, it is reflected as control laser light L9 by the control film 3a formed on the polarizing beam splitter 3.

  Reference numeral 9 denotes a sensor lens on which the control laser light L9 reflected by the control film 3a of the polarization beam splitter 3 is incident. The control laser light L9 is received by a light detector 10 called a PDIC. It has the effect | action which irradiates to a part as the condensing laser beam L10. The sensor lens 9 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.

  In the optical pickup device shown in FIG. 2, the laser light L 1 emitted from the laser diode 1 passes through the diffraction grating 2, the polarization beam splitter 3, the collimator lens 5, the reflection mirror 6 and the quarter wavelength plate 7 to the objective lens 8. Incident light is applied to the signal recording layer of the optical disk by the focusing operation of the objective lens 8.

  The laser beam L8 applied to the signal recording layer is reflected from the signal recording layer and is incident on the objective lens 8 from the optical disc side as return light. The return light incident on the objective lens 8 is incident on the polarization beam splitter 3 via the quarter-wave plate 7, the reflection mirror 6 and the collimator lens 5.

  The return light incident on the polarization beam splitter 3 is reflected as control laser light L9 by the control film 3a provided on the polarization beam splitter 3. The control laser beam L9 obtained in this way is incident on the sensor lens 9 and is irradiated as a condensed laser beam L10 on a light receiving portion provided in the photodetector 10.

  As the light receiving section provided in the photodetector 10, as shown in FIG. 3, a main beam light receiving section used for signal reproduction operation and focusing control operation while being irradiated with a 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 unit SD1 that is used for the tracking control operation and the subsequent subbeam S2 that is the −1st order light is irradiated and used for the tracking control operation. The rear sub-beam light receiving portion SD2 is configured.

  As described above, the photodetector 10 is provided with the light receiving part MD for the main beam, the light receiving part SD1 for the preceding sub beam, and the light receiving part SD2 for the succeeding sub beam, and the arrangement direction thereof is the tracking control direction, that is, the objective. When the spot condensed by the lens 8 is displaced in the radial direction of the optical disk, the main beam M, the preceding sub-beam S1, and the main beam M, the preceding sub-beam receiving unit SD1, and the subsequent sub-beam receiving unit SD2 are irradiated. The trailing sub-beam S2 is configured to coincide with the displacement direction.

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 four divided sensors as shown in the figure. Then, a signal corresponding to the light quantity of the main beam irradiated to all the sensors A, B, C, and D constituting the main beam light receiving part MD is added to read out as a reproduction signal from the signal recorded on the optical disc. However, such an operation is well known, and a description thereof will be omitted.

  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, a diagonal sensor among the four-divided sensors constituting the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 is added, and the other signal is added from this addition signal. Sub-focus error signals are generated by subtracting signals obtained by adding signals obtained from the diagonal sensors, and the sub-focus error signals and the four-divided sensors constituting the main beam light receiving unit MD are obtained. A focus error signal is calculated and generated from the main focus error signal to perform a focusing control operation. 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 generation operation will be described with reference to the reference numerals of the illustrated sensor unit. 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 tracking control operation is performed by the irradiation operation of the preceding sub beam S1 and the irradiation operation of the subsequent sub beam S2 to the light receiving unit SD1 for the preceding 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 configured to perform a tracking control operation combining a sub beam and a main beam has been developed.

  The laser beam L1 emitted from the laser diode 1 is incident on the polarization beam splitter 3 as the laser beam L2 diffracted by the diffraction grating 2. A part of the laser beam L1 is reflected by the control film 3a and is monitored by the monitoring laser. The light is irradiated to the front monitor diode 4 as light L4.

The monitoring laser light L4 irradiated to the front monitoring diode 4 changes according to the output level of the laser light L1 emitted from the laser diode 1. Therefore, the monitor signal generated by the front monitor diode 4 is fed back to a drive circuit provided to supply a drive signal to the laser diode 1, whereby the output of the laser light L1 emitted from the laser diode 1 is predetermined. 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 8 in a direction perpendicular to the signal surface of the optical disk, and the tracking control operation is performed by moving the objective lens 8 to the optical disk. It is carried out by displacing in the radial direction.

  FIG. 1 shows the relationship between the first signal recording layer L0, the second signal recording layer L1, and the objective lens 8 provided in the multilayer optical disk D of the present invention. The state shown in the figure is the first signal recording layer. This shows a state in which the laser beam L8 is condensed on L0 by the focusing control operation. That is, in such a state, the laser beam L8 is focused on the first signal recording layer L0, and the tracking control operation is performed on the signal track provided on the first signal recording layer L0, so that the first signal is recorded. The read operation of the signal recorded in the recording layer L0 is performed.

  When performing the read operation of the signal recorded on the second signal recording layer L1, the laser light L8 is moved to the second signal recording layer L1 by displacing the objective lens 8 upward from the position shown in FIG. The focusing control operation for each signal recording layer is well known, and the description thereof is omitted.

  As described above, the multilayer optical disk D according to the present invention and the optical pickup device that performs the read operation of the signal recorded on the optical disk D are configured. A configuration related to D stray light countermeasures will be described.

  First, an adverse effect caused by stray light in a conventional optical pickup device will be described. As shown in FIG. 1, when a signal recorded on the first signal recording layer L0 is being read out, the first signal recording layer L0 includes a main beam M generated by the diffraction grating 2, and a preceding signal. The laser beam L8 composed of the sub beam S1 and the succeeding sub beam S2 is irradiated.

  Then, the main beam M, the preceding sub beam S1, and the subsequent sub beam S2 are reflected from the first signal recording layer L0, respectively, and then the objective lens 8, the quarter wavelength plate 7, the reflection mirror 6, and the collimator lens 5 are reflected. And enters the control film 3 a of the polarization beam splitter 3. The laser beam thus entered is reflected by the control film 3a of the polarization beam splitter 3 as described above, and is incident on the sensor lens 9 as the control laser beam L9.

  The control laser light L9 incident on the sensor lens 9 is applied to the light receiving portion provided in the photodetector 10 as the condensed laser light L10 by the condensing action of the sensor lens 9. FIG. 3 shows the relationship between the focused laser beam L10 irradiated in this way and the light receiving unit. As is clear from FIG. 3, the main beam M, the preceding sub beam S1, and the subsequent sub beam S2 are respectively main. The light is irradiated onto the beam light receiving part MD, the preceding sub-beam light receiving part SD1, and the subsequent sub-beam light receiving part SD2.

  As described above, the main beam M, the preceding sub-beam S1, and the subsequent sub-beam S2 are respectively irradiated on the main beam light-receiving part MD, the preceding sub-beam light-receiving part SD1, and the subsequent sub-beam light-receiving part SD2. A focusing control operation for L0 and a tracking control operation for a signal track provided in the first signal recording layer L0 are performed. Therefore, it is possible to perform a read operation of the signal recorded in the first signal recording layer L0.

  As described above, the laser beam L8 is irradiated to the first signal recording layer L0 of the optical disc by the focusing operation of the objective lens 8, and the main beam M in the laser beam L8 is emitted from the second signal recording layer L1 as stray light. As shown by the broken line in FIG. In this way, the stray light reflected from the second signal recording layer L1 is the objective lens 8, the quarter wavelength plate 7, the reflection mirror 6, and the collimator lens in the same manner as the laser light reflected from the first signal recording layer L0. 5 is incident on the control film 3 a of the polarization beam splitter 3.

  The stray light incident on the control film 3 a of the polarization beam splitter 3 in this manner is reflected by the control film 3 a and then irradiated to the light receiving unit provided in the photodetector 10 through the sensor lens 9. Such stray light is not condensed laser light like the reflected light from the first signal recording layer L0, and therefore is not condensed on the light receiving portion by the sensor lens 9.

  FIG. 4 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 portion inside the ring P indicated by the broken line is the stray light beam. This is the irradiated part.

  As is apparent from this figure, the stray light beam 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 10.

  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, the light amount of the sub beam reflected as stray light from the second signal recording layer L1 is sufficiently smaller than the light amount of the main beam reflected as stray light, so that the influence on the focusing control operation and the like can be ignored. .

  Further, since the light quantity of the main beam M irradiated to the main beam light receiving part MD is sufficiently larger than the light quantity of the stray light beam, it is recorded in the signal generating operation by the main beam light receiving part MD, that is, the first signal recording layer L0. This does not adversely affect the read operation of the current signal and the generation operation of 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. It is set to be higher than the gain of the amplifier.

  As a result, the influence of stray light generated from the main beam M reflected from the second signal recording layer L1 on the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 increases. 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.

As a method for solving such a problem, as shown in FIG. 3, the areas of the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 are made smaller than the area of the main beam light-receiving part MD and are formed in an octagonal shape. A method has been proposed. As a method for further improving the problem caused by stray light, a technique has been proposed in which the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 are elongated in the tracking control direction, that is, the arrow N1 direction as shown in the figure. ing. That is, when the shapes of the preceding sub-beam light receiving part SD1 and the succeeding sub-beam light receiving part SD2 are long in the tracking control direction, the preceding sub-beam light receiving part SD1 and Even if the preceding sub-beam S1 and the succeeding sub-beam S2 irradiated to the succeeding sub-beam light receiving unit SD2 are displaced in the direction of the arrow N1, the preceding sub-beam S1 and the succeeding sub-beam S2 are received by the preceding sub-beam receiving unit SD1 and the succeeding sub-beam, respectively. It is possible to prevent protrusion from the part SD2.

  According to such a configuration, even if the laser spot is displaced in the tracking direction, the preceding sub-beam S1 and the succeeding sub-beam S2 can be positioned on the preceding sub-beam light receiving part SD1 and the succeeding sub-beam light receiving part SD2. The control operation can be performed accurately.

  In the photodetector configured as described above, the preceding sub-beam light-receiving unit SD1 and the subsequent sub-beam light-receiving unit SD2 have a length in the direction perpendicular to the tracking control direction, that is, in the direction of the arrow N2, as illustrated. It is comprised so that it may become substantially the same as a diameter. According to such a configuration, the areas of the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 can be minimized, so that the influence of stray light can be avoided as much as possible, and the focusing control operation is accurately performed. I can do it.

  As described above, the shapes of the preceding sub-beam light receiving part SD1 and the succeeding sub-beam light receiving part SD2 are octagonal, but are generated by irradiating the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2. If the shape is approximate to the shape of the preceding sub-beam S1 and the following sub-beam S2, the influence of stray light can be further improved.

  FIG. 5 shows the relationship between the unnecessary light and the main beam light receiving part MD, the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 incorporated in the photodetector used in the conventional optical pickup device. Is. In a state where the focusing operation by the objective lens 8 is not performed, the main beam M, the preceding sub beam S1, and the subsequent sub beam S2 are on the main beam light receiving unit MD, the preceding sub beam light receiving unit SD1, and the subsequent sub beam light receiving unit SD2. The light receiving portions are irradiated in a spread state such as the main beam PM, the preceding sub-beam PS1, and the subsequent sub-beam PS2.

  In such a light receiving state, since the light amount of the sub beam is smaller than the light amount of the main beam as described above, the influence of the sub beams PS1 and PS2 applied to the main beam light receiving part MD can be ignored. The influence of the main beam PM irradiated on the preceding sub-beam light receiving part SD1 and the subsequent sub-beam light receiving part SD2 cannot be ignored.

  In the photodetector shown in FIG. 3, the area of the preceding sub-beam light receiving part SD1 and the succeeding sub-beam light receiving part SD2 is made smaller than the area of the main beam light-receiving part MD, or the preceding sub-beam light receiving part SD1 and the rear Since the shape and length of the row sub-beam light receiving portion SD2 are devised as described above, the influence of the main beam PM can be reduced, and as a result, the focusing control operation can be performed accurately.

As described above, according to the photodetector having the configuration shown in FIG. 3, the first signal recording layer L0 provided in the multilayer optical disc D, that is, the signal recording layer provided on the side where the laser beam is incident is provided. When a recorded signal is read out, the influence of stray light reflected from the second signal recording layer L1 provided at the back of the signal recording layer can be suppressed, but such a countermeasure has been taken. An optical pickup device incorporating a non-photodetector is greatly affected by stray light.

  The multilayer optical disc of the present invention is characterized in that the distance between the first signal recording layer L0 and the second signal recording layer L1, that is, the interval is set so that the amount of stray light is minimized. The characteristic diagram shown in FIG. 6 shows the relationship between the distance between the first signal recording layer L0 and the second signal recording layer L1 and the ratio of the stray light amount to the signal light amount in the sub-beam light receiving section.

  As is clear from the characteristic diagram shown in FIG. 6, when the interval is 20 μm to 25 μm, the light quantity ratio is about 4%, the amount of stray light is the smallest, and the amount of stray light is large even if the interval is narrowed or widened. I understand that It has been confirmed through experiments that the same characteristics can be obtained even when the configuration of the light receiving portion of the photodetector is configured as in the embodiment shown in FIG. 3 or when no modification is made.

  In this embodiment, the two-layer type optical disc having two signal recording layers, the first signal recording layer L0 and the second signal recording layer L1, has been described. However, three or more signal recording layers are provided. Needless to say, the present invention can be applied to a multilayer optical disk. In this embodiment, a standard optical disc using a laser beam having a wavelength of 405 nm and an objective lens having a numerical aperture of 0.85 has been described. Of course, the present invention can be applied to an optical disc of another standard. is there.

It is a figure for demonstrating the relationship between the multilayer optical disk of this invention, and the laser beam condensed with an objective lens. It is a perspective view of the principal part which shows the optical pick-up apparatus which performs the read-out operation | movement of the signal recorded on the multilayer type optical disk of this invention. It is a figure for demonstrating the relationship between the photodetector incorporated in an optical pick-up apparatus, and a laser beam. It is a figure for demonstrating the relationship between the photodetector incorporated in an optical pick-up apparatus, and a laser beam. It is a figure for demonstrating the relationship between the photodetector incorporated in an optical pick-up apparatus, and a laser beam. It is a characteristic view for demonstrating the characteristic of the multilayer type optical disk based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Diffraction grating 3 Polarizing beam splitter 8 Objective lens 9 Sensor lens 10 Photodetector MD Main beam light receiving part SD1 Previous beam light receiving part SD2 Subsequent beam light receiving part

Claims (5)

A multi-layer type optical disc provided with a plurality of signal recording layers, and performing a signal reading operation recorded on a signal recording layer provided on the side on which a laser beam for performing the signal reading operation is incident A multilayer optical disc characterized in that the interval between the signal recording layers is set so that the amount of stray light reflected from the signal recording layer provided in the back of the signal recording layer is minimized. 2. The multilayer optical disk according to claim 1, wherein the multilayer optical disk is an optical disk specified to perform a signal reading operation with a laser beam having a wavelength of 405 nm. 2. The multi-layer type optical disk according to claim 1, wherein the multi-layer type optical disk is an optical disk specified to perform a signal reading operation with a laser beam condensed by an objective lens having a numerical aperture of 0.85. optical disk. The multilayer optical disc is regulated to perform a signal readout operation with a laser beam having a wavelength of 405 nm, and performs a signal readout operation with a laser beam condensed by an objective lens having a numerical aperture of 0.85. 2. The multilayer optical disk according to claim 1, wherein the optical disk is defined as follows. 5. The multilayer optical disk according to claim 4, wherein the interval between the signal recording layers is set to 20 μm to 25 μm.

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