JP2008102998A - Optical head and optical disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an optical head which can obtain a stable servo signal in recording and reproducing of a multi-layer optical disk. <P>SOLUTION: The optical head is provided with a division element having a plurality of regions. The division element can divide luminous flux reflected by the optical disk into a plurality of luminous flux whose exiting directions are different. When focus is adjusted to the target information recording layer of the optical disk, the reflected luminous flux from the target information recording layer is focused on the light receiving part of a photodetector, then respective regions of the division element and the light receiving part of the photodetector are constituted so that the light receiving part of the photodetector is not irradiated with reflected luminous flux from the information recording layer other than the target information recording layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus for recording or reproducing information on an optical disc and an optical head used therefor, and more particularly to an optical disc apparatus for recording or reproducing information on an optical disc having a plurality of stacked information recording layers, and to the same. The present invention relates to an optical head used.

  As a method for increasing the recording capacity of an optical disk, a technique of a multi-layer optical disk in which information recording layers are stacked has been studied. In the DVD (Digital Versatile Disc), BD (Blu-ray Disc), and HD-DVD (High Density Digital Versatile Disc) standards, a dual-layer optical disc in which two information recording layers are stacked at an interval of about 20 to 55 μm is commercialized. ing. Further, as a further technology for increasing the capacity, an optical disc having three or more layers has been studied.

  When recording or reproducing such a multilayer optical disc, in order to accurately position the focal point of the laser beam on the target layer, servo signal offsets such as focus error signals and tracking error signals due to stray light from other layers are set. It must be eliminated as much as possible.

  As a method for eliminating the influence of stray light from other layers, for example, Non-Patent Document 1 describes that a tracking photo detector is arranged in a region without multilayer stray light (Non-Patent Document 1).

IEICE Technical Report CPM2005-149 (2005-10)

  However, Non-Patent Document 1 does not describe the influence of stray light on the focus error signal.

  Further, in Non-Patent Document 1, since it is necessary to dispose the light receiving part for tracking error signal outside the stray light from other layers generated around the light receiving part for focus error signal, the size of the photodetector is large. turn into.

  An object of the present invention is to provide an optical head capable of obtaining a stable servo signal in recording and reproduction of a multilayer optical disc, and an optical disc apparatus including the optical head.

In order to solve the above problems, an optical head according to the present invention includes a light source; an objective lens for condensing a light beam emitted from the light source on the optical disk; and a plurality of light beams reflected by the optical disk. A splitting element for splitting the light beam; a condensing lens for condensing the light beam reflected by the optical disk; and receiving the light beam collected by the condensing lens by a plurality of light receiving units and converting it into an electrical signal A photodetector for performing;
The dividing element is divided by a first dividing region disposed substantially at the center and a first dividing line, and is arranged so as to sandwich the first dividing region along the direction of the first dividing line. The first divided area is divided by a second divided area composed of the four divided areas and a second dividing line orthogonal to the first dividing line, and the first dividing line is formed along the direction of the second dividing line. A third divided region composed of four regions arranged so as to sandwich the divided region;
When each of the first to third divided areas is focused on the target information recording layer of the optical disc, the reflected light beam from the target information recording layer is reflected on the light receiving portion of the photodetector. A focused light beam is formed so that a reflected light beam from a recording / reproducing layer other than the target information recording layer is not irradiated to the light receiving portion of the photodetector.

  According to the present invention, a stable focus error signal and tracking error signal can be obtained by the one-beam tracking method.

  The optical head of the present invention, for example, divides the reflected light from the multilayer optical disk into a plurality of reflected light beams having different emission directions by the dividing element, and the divided light beams are focused at different positions on the photodetector. Configured. A focus error signal is detected by a knife edge method using a reflected light beam that has passed through a region that does not include the light beam center, and a reflected light beam that has passed through a region that does not include the light beam center is used. The tracking error signal is detected. Further, when the target layer is in focus, each region of the dividing element and the light receiving unit are arranged so that stray light from other layers does not enter the light receiving unit for the servo signal of the photodetector.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an optical head according to the present invention and an optical disk apparatus including the optical head will be described in detail below with reference to FIGS.

  FIG. 1 is a diagram showing a configuration of an optical head according to an embodiment of the present invention.

  The laser beam 2 emitted from the semiconductor laser 1 is reflected by the polarization beam splitter 3 and becomes a parallel light beam by the collimator lens 4. The parallel light flux passes through the polarization diffraction grating 5 and the quarter-wave plate 6 and is condensed on the optical disk 8 by the objective lens 7. The optical disk 8 is provided with two recording / reproducing layers (information recording layers) of a first layer 9 and a second layer 10, and tracks (not shown) are formed in the directions of arrows 11, respectively.

  When one of the two recording / reproducing layers of the optical disc is in focus, the laser beam 2 reflected by the optical disc 8 is transmitted through the objective lens 7 and the quarter-wave plate 6 by the polarization diffraction grating 5. The luminous flux is divided into a plurality of regions and travels in different directions. Then, the light passes through the collimating lens 4 and the polarization beam splitter 3 and is focused on the photodetector 12.

  A plurality of light receiving portions 13 are formed on the photodetector 12, and each light receiving portion 13 is irradiated with a light beam divided by the polarization diffraction grating 5. An electrical signal is output from the photodetector 12 in accordance with the amount of light irradiated on the light receiving unit 13, and these outputs are calculated to generate a focus error signal and a tracking error signal.

  In the following description, when the optical head is opposed to the optical disk for recording or reproduction, the direction perpendicular to the surface of the optical disk 8 is the Z axis, the track direction is the Y axis, and the direction perpendicular to the track is It is defined as the X axis. The Z axis is substantially parallel to the optical axis of the light beam emitted from the objective lens 1.

  FIG. 2 shows the shape of the polarization diffraction grating 5 in FIG. The polarization diffraction grating 5 is divided into a plurality of regions, and in FIG. 2, the solid line indicates the boundary line between the regions. In FIG. 2, a two-dot chain line schematically shows the outer shape of the laser beam, and a hatched portion schematically shows a push-pull pattern generated by the track of the optical disk.

  In the polarization diffraction grating 5, a dividing line 15 is formed in the Y-axis direction passing through the light beam center 14, and a dividing line 16 is formed in the X-axis direction. In addition, the polarization diffraction grating 5 includes a divided region (first divided region) composed of four regions (regions C1 to C4) that are point-symmetric with respect to the light beam center 14 and include the light beam center 14, and a light beam center 14. A divided region (second divided region) composed of four regions (regions A1 to A4) including a part of the dividing line 16 in the X-axis direction, which is point-symmetric with respect to the light beam center 14, and the light beam A divided region (third divided region) composed of four regions (regions B1 to B4) that are point-symmetric with respect to the center 14, do not include the light beam center 14, and include a part of the dividing line 15 in the Y-axis direction; Is formed.

  When the optical head is opposed to the surface of the optical disc during recording or reproduction, the dividing line 15 is substantially perpendicular to the track direction of the optical disc, and the dividing line 16 is substantially parallel to the track direction of the optical disc.

  Regions A1 to A4 include an X-axis direction dividing line 16 passing through the light beam center 14, two Y-axis direction dividing lines 17 not passing through the light beam center 14, and four X-axis direction lines passing through the light beam center 14. The dividing line 18 and four dividing lines 19 having an angle of about 30 degrees with respect to the Y-axis direction with the light beam center 14 as the center. The interval u in the Y-axis direction of the four dividing lines 18 in the X-axis direction is set so as to include a push-pull pattern, and is set to a range of about 55 to 70% of the light beam diameter in the embodiment.

  Further, the areas A1 to A4 are arranged so as to sandwich the areas C1 to C4. The regions A1 to A4 are formed so that the regions A1 and A2 are line-symmetric with respect to the regions A4 and A3 and the dividing line 15, respectively.

  The regions B1 to B4 are also provided so as to sandwich the regions C1 to C4. The region B1 is symmetrical with respect to the region B2 and the dividing line 16, and the region B4 is symmetrical with respect to the region B3 and the dividing line 16.

  The interval w between the two dividing lines 17 in the Y-axis direction is as small as possible within the condition that the region A includes a push-pull pattern and stray light does not enter the light receiving unit according to the shape of the light receiving unit 13 of the photodetector 12. In the embodiment, it is set in a range of about 25 to 30% of the light beam diameter. The dividing line 19 that forms an angle of about 30 degrees with respect to the Y-axis direction is provided so that stray light does not enter the light receiving unit 13.

  The interval v between the two dividing lines 20 in the X-axis direction at the boundary between the region B and the region C is as much as possible within the condition that stray light does not enter the light receiving unit 13 according to the shape of the light receiving unit 13 of the photodetector 12. It is decided to be smaller.

  The diffraction grating formed in each region has the same shape for the regions C1 and C3 and C2 and C4, but the other regions have different shapes. In each diffraction grating, the light beam is separated into ± first-order diffracted light and irradiated to the photodetector 12.

  FIG. 3 shows the shape of the light receiving unit 13 of the photodetector 12 and the shape of the light pattern irradiated on the photodetector. FIG. 3 shows an optical pattern of only reflected light from the recording / reproducing layer, and does not show an optical pattern of stray light from other layers.

  When focused on the recording / reproducing layer, the laser beam 2 reflected by the recording / reproducing layer forms a focal point 21 on the photodetector 12, and these are the eighteen A to T formed on the photodetector 12. The light receiving unit 13 is irradiated.

The light receiving portions M, N, O, and P are light receiving portions for detecting a focus error signal by a double knife edge method. When ± 1st-order diffracted light beams diffracted in the region A1 and irradiated on the photodetector 12 are expressed as a1 + and a1-, the light beam a1- is received at the boundary between the light receiving parts M and N, and the light beam a2- is received. At the boundary between the parts P and O, the light beam a3- is irradiated onto the boundary between the light receiving parts P and N, and the light beam a4- is irradiated onto the boundary between the light receiving parts M and O. When the outputs of the light receiving parts A to J are respectively represented by a to j and the outputs of the light receiving parts M to T are represented by m to t, respectively, the focus error signal (FES) is
(FES) = (m + p) − (n + o)
Is obtained by the arithmetic expression.

  The light receiving parts E, F, G, H and the light receiving parts Q, R, S, T are arranged outside the light receiving parts A, B, C, D and the light receiving parts M, N, O, P, respectively. The light receiving portions A, B, C, and D have light beams a1 +, a2 +, a3 +, and a4 +, and the light receiving portions E, F, G, and H have light beams b1 +, b2 +, b3 +, and b4 +, and the light receiving portions Q, R, and S. , T are irradiated with light beams b1-, b2-, b3-, b4-, which are used to detect tracking error signals.

Tracking error signal (TES) by push-pull method is
(TES) = ((a + e + b + f) − (c + g + d + h)) − K ((q + r) − (s + t))
Is obtained by the arithmetic expression. K is a constant, and the value of K is determined so that no offset occurs in (TES) when the objective lens 7 moves in the X-axis direction by the tracking operation.

  The tracking error signal (DPD) by the DPD method is obtained by detecting the phase difference between (a + e, c + g) and (b + f, d + h).

The light receiving portions I and J are disposed outside the light receiving portions E, F, G, and H. The light receiving portion I is irradiated with light beams c1 + and c3 +, and the light receiving portion J is irradiated with light beams c2 + and c4 +. These are used together with other signals to detect the playback signal (RF)
(RF) = a + b + c + d + e + f + g + h + i + j
Is obtained by the arithmetic expression.

  Further, the light beams c1-, c2-, c3-, and c4- are irradiated to a portion where the light receiving unit 13 is not provided, and these are not used for signal detection.

  FIG. 4 shows the change of the light pattern of each light beam irradiated on the photodetector 12 during defocusing and the waveform of the focus error signal (FES).

  The light pattern of the + 1st order diffracted light 22 is indicated by a lattice pattern, and the light pattern of the −1st order diffracted light 23 is indicated by oblique lines. At the in-focus position (c), the light pattern is focused on the boundary line between the light receiving parts M to P. At this time, the focus error signal becomes zero. The light pattern becomes larger as defocusing is performed, and the focus error signal takes the maximum and minimum values when (b) and (d). When the light pattern further increases (a) and (e), the light receiving unit 13 is not irradiated with light, and the focus error signal becomes zero.

  As the defocusing is performed, the light pattern is expanded centering on the condensing point (c). At this time, the light pattern in the area C1 to C4 is also enlarged, but the area C1 is other than the areas of the light receiving portions I and J. Since the light pattern in the vicinity of the light beam center of C4 is not included, the light pattern is deviated from the light receiving unit 13. In the light receiving portions M to P that detect the focus error signal, the light patterns deviate from the light receiving portions M to P in accordance with the expansion of the light patterns in the regions B1 to B4 and the regions C1 to C4.

  The change of the light pattern in the light receiving parts M to P that detect the focus error signal will be described in detail with reference to FIG. FIG. 5 shows a change in the light pattern 25 of the light beam a2- condensed at the boundary between the light receiving surfaces O and P at the time of focusing. (B), (c), and (d) correspond to the states in FIG. 4, and (a ′) and (e ′) indicate intermediate states between (a) and (b), and (d) and (e), respectively. In (c), the light is condensed at a position corresponding to the light beam center 16, and the light pattern 25 expands around the light condensing point (light beam center) in (c) as it is defocused. At this time, since the virtual light patterns 26 and 27 corresponding to the light beams b2- and c2- irradiated to the other light receiving portions are enlarged, the light pattern 25 is moved away from the light receiving portions MP, and (a ') (e In '), the light is completely removed from the light receiving parts M to P and is not irradiated.

  In FIG. 4, the interval Wp in the X-axis direction of the light pattern in the areas A1 to A4 at the time of defocusing is determined corresponding to the width w of the dividing line 17 of the polarization diffraction grating 5, so that the light pattern is irradiated to the light receiving unit 13 at the time of defocusing. The relationship between the shape of the light receiving unit 13 and the width w of the dividing line 17 is determined so as not to be performed.

  Further, since the light receiving unit 13 is arranged between the intervals Wp, it is possible to arrange the light receiving units closer to each other as compared with the case where the light receiving unit 13 is arranged outside the light pattern at the time of defocusing. Can be miniaturized.

  Further, when the light pattern is enlarged as the defocusing is performed, if the light patterns of other regions are irradiated to the light receiving parts M to P, the focus error signal waveform is distorted, causing an error at the time of focus pull-in. . The hatched portion 24 of the region A formed by the dividing line 19 that forms an angle of about 30 degrees with the Y-axis direction of the polarization diffraction grating 5 is when the light pattern irradiated to the light receiving portions A to D expands with defocusing. Are provided so as not to be incident on the light receiving parts M to P. Depending on the arrangement of the light receiving portion, the shaded portion is not necessary.

  FIG. 6 shows the shape of the optical pattern on the photodetector 12 and the waveform of the focus error signal (FES) in the double-layer disc. The light pattern 28 of the reflected light from the first layer 9 is indicated by a lattice pattern, and the light pattern 29 of the reflected light from the second layer 10 is indicated by oblique lines.

  The focus error signal waveform (FE) of the two-layer disc is obtained as a synthesis of the focus error signal waveform (FE1) generated in the first layer 9 and the focus error waveform (FE2) generated in the second layer 10. 6A shows a state of the light patterns 28 and 29 when the first layer 9 is in focus, and the light pattern 28 is focused on the photodetector 12, and at this time, the light pattern 29 (stray light) is irradiated outside the light receiving unit 13.

  As the focal point moves from the first layer 9 to the second layer 10, the light pattern 28 increases and the light pattern 29 decreases. At the intermediate point (b) between the first layer 9 and the second layer 10, The size of the light pattern 29 is substantially the same, and the light receiving parts M to P are hardly irradiated. In (c) focused on the second layer 10, the light pattern 29 is focused on the photodetector 12, and the light pattern 28 (stray light) is irradiated outside the light receiving unit 13.

  Although the focus error signal is obtained by calculating the outputs of the light receiving parts M to P, stray light is not applied to the light receiving parts M to P at the focal point, so that no offset due to stray light occurs, and the intensity distribution of the laser light 2 An offset due to stray light does not occur even with respect to variations or misalignment between the light receiving unit 13 and the light pattern, so that a stable focus error signal can be obtained.

  Further, the focus error signal waveform (FE) of the two-layer disc is distorted when the overlap between the waveform (FE1) generated in the first layer 9 and the waveform (FE2) generated in the second layer 10 is large, and the focus is pulled in. Although an error may occur, in this embodiment, the light pattern is hardly irradiated to the light receiving parts M to P in the vicinity of the intermediate point (b) between the first layer 9 and the second layer 10, so that (FE1) and (FE2) The output is small and the distortion of the focus error signal waveform (FE) is also small.

  Similarly, the tracking error signal is obtained by calculating the outputs of the light receiving portions A to H and Q to T. However, since the stray light is not applied to the light receiving portions A to H and Q to T at the focal point, an offset due to stray light occurs. A stable tracking error signal can be obtained.

  Since the light receiving portions I and J include the center of the light beam, even if the light pattern becomes large, the light beam near the center of the light beam remains in the light receiving portion and becomes stray light, but this portion is used to detect the focus error signal and tracking error signal. Therefore, even if there is stray light, it is not a problem in practice.

  Since it is not affected by stray light as described above, it is possible to change the balance of the amount of ± first-order diffracted light diffracted by the polarization diffraction grating 5. It is possible to improve the SN of the reproduction signal by increasing the light amount of the + 1st order diffracted light 22 so that the light amount of the light receiving unit for detecting the reproduction signal is increased. At this time, the light amount of the −1st order diffracted light 23 is reduced. Since the offset due to the stray light does not increase due to the decrease in, it is only necessary to consider electrical restrictions.

  In the above embodiment, the polarization diffraction grating 5 and the quarter wave plate may be fixed together so as to move together with the objective lens 7, or may be fixed separately so as not to move together with the objective lens 7. . When the objective lens 7 is fixed separately from the objective lens 7, when the objective lens 7 moves in the X-axis direction by the tracking operation, the outer shape of the light beam indicated by a two-dot chain line in FIG. Although shifted from the center 14, the position and size of the interval Wp of the light pattern appearing on the photodetector 12 corresponding to the width w of the dividing line 17 does not change. There is nothing. Since the outer shape of the light beam moves in the X direction, the value of K in the calculation formula of the tracking error signal (TES) by the push-pull method is different from that in the case of being fixed integrally.

  The polarization diffraction grating 5 is not limited to the shape of the above embodiment. Hereinafter, other embodiments of the polarization diffraction grating will be described.

  7 and 8 show the shape of the divided region of the second embodiment of the polarization diffraction grating 5 and the shape of the light pattern irradiated onto the photodetector 12 at that time. The light pattern 28 of the reflected light from the first layer 9 is focused on the photodetector 12, and the light pattern 29 (stray light) of the reflected light from the second layer 10 at that time is indicated by diagonal lines. The difference from the first embodiment is that the width Wc in the X-axis direction of the regions C1 to C4 is narrow. The regions B1 to B4 are enlarged by the amount that the width is reduced. The shapes of the regions A1 to A4 are the same as in the first embodiment. Since the regions B1 to B4 are enlarged, stray light tends to enter the light receiving portions E to F and Q to T with respect to the positional deviation of the photodetector 12, but an effect of increasing the output of the tracking error signal can be expected.

  9 and 10 show the shape of the divided region of the third embodiment of the polarization diffraction grating 5 and the shape of the light pattern irradiated on the photodetector 12 at that time. The light pattern 28 of the reflected light from the first layer 9 is focused on the photodetector, and the light pattern 29 (stray light) of the reflected light from the second layer 10 at that time is indicated by diagonal lines.

The difference from the first embodiment is that there are no four dividing lines 18 in the X-axis direction that do not pass through the light beam center 14, and four that form an angle of about 30 degrees with respect to the Y-axis direction around the light beam center 14. The dividing line 19 is extended. For this reason, since the areas of the regions B1 to B4 are reduced, the outputs q to t of the light receiving portions Q to T are reduced, and the tracking error signal calculation formula by the push-pull method
(TES) = ((a + e + b + f) − (c + g + d + h)) − K ((q + r) − (s + t))
However, since the area of A1 to A4 increases, the effect of increasing the output of the focus error signal can be expected.

  In the above embodiment, a polarization diffraction grating is used as a beam splitting element and is arranged between the collimating lens and the quarter wave plate. However, a normal diffraction grating is arranged between the polarization beam splitter and the photodetector. May be.

  It can be expected to be applied to an optical disc apparatus that records and reproduces information on an optical disc.

  When the target layer of the optical disc is in focus, the stray light from the other layer is out of the light receiving part for the servo signal of the photodetector, so that only the reflected light of the target layer is received to obtain the servo signal. It is possible to obtain a stable focus error signal and tracking error signal that do not cause an offset due to stray light from other layers.

  Next, an optical disc apparatus provided with the optical head according to the present invention will be described.

  FIG. 11 is a schematic diagram showing a specific example of an optical disc apparatus on which the optical head shown in FIG. 1 is mounted. The semiconductor laser 1, the polarization beam splitter 3, the polarization diffraction grating 5, the quarter wavelength plate 6, the photodetector 12 shown in FIG. 1 and a mirror 27 (not shown in FIG. 1) for changing the direction of the laser light. Is adhesively fixed to the case 28. The collimating lens 4 is fixed to the case 28 so as to be movable along the optical axis by the moving mechanism 29. Each of the cases where recording / reproduction is performed on the first layer 9 and recording / reproduction on the second layer 10 of the optical disc 8 is performed. Thus, the laser beam 2 focused on the optical disk 8 can be moved to a position where the spherical aberration is minimized.

  The objective lens 7 is attached to a holder 31 in which a coil 30 is incorporated, and is combined with a magnet (not shown) to form an actuator. The objective lens 7 can follow the surface blur and eccentricity of the optical disk 8. .

  The case 28 can be moved in the radial direction of the optical disk 8 by the motor 32 and the lead screw 33. The optical disk 8 is fixed to the spindle motor 34.

  The operation of each component is controlled by the system control circuit. When recording / reproducing is performed, first, the spindle motor drive circuit is operated to drive the spindle motor 34 and rotate the optical disc 8.

  Next, the laser drive circuit is operated to cause the semiconductor laser 1 to emit light.

  A focus error signal is generated from the output of the light detector 12 by a servo signal generation circuit, and the actuator is driven by an actuator drive circuit based on the signal to match the focal point of the laser light 2 by the objective lens 7 with the recording / reproducing layer. Focusing control is performed as follows.

  When the condensing point of the laser beam 2 is aligned with the first layer 9, the focus error signal is detected after the collimating lens 5 is moved to a position corresponding to the first layer 9. Since the waveform shown in FIG. 6 is obtained as the focus error signal, focusing control is performed at the first layer in-focus position.

  Next, the access control circuit is operated to rotate the motor 32 and move the case 28 to a desired position on the inner or outer periphery of the optical disc 8 via the lead screw 33.

  After that, tracking control for driving the actuator by the actuator driving circuit based on the tracking error signal generated from the output of the photodetector 12 by the servo signal generating circuit to follow the condensing point of the laser beam 2 on the track of the optical disk 8. To do.

  Next, the data signal on the track of the optical disk 8 is reproduced from the output of the photodetector 12 by the information signal reproducing circuit.

  When recording information on the optical disk 8, the system control circuit operates a laser driving circuit corresponding to the recording information, and modulates the output of the semiconductor laser 1 to form a recording mark on the track.

  When the recording / reproducing layer is moved from the first layer 9 to the second layer 10, after the tracking control is stopped by the system control circuit, the focusing control is stopped, and at the same time, the actuator drive circuit is operated to collect the laser beam 2. Move the point towards the second layer. Next, focusing control is performed so that the actuator is driven at the timing when the focus position of the second layer of the focus error signal is detected, and the laser beam is focused on the second layer. Next, after the collimating lens 4 is moved to a position corresponding to the second layer 10, the actuator is driven based on the tracking error signal to perform tracking control for following the condensing point of the laser light 2 on the track. The reproduction operation and the recording operation in the second layer 10 are performed in the same manner as in the first layer 9.

  In the above embodiment, the polarization diffraction grating 5 and the quarter-wave plate 6 are fixed to the case 28, but may be fixed to the same holder 31 as the objective lens 7 and moved together with the objective lens 7.

  As described above, the embodiments of the optical head according to the present invention and the optical disk apparatus including the optical head have been described in detail. However, the present invention is not limited to the above-described embodiments, and the scope of the present invention is not deviated. Various modifications and improvements may be included.

  For example, in the above embodiment, the recording or reproduction of an optical disc in which two recording / reproducing layers (information recording layers) are laminated has been described. However, the recording or reproduction of an optical disc in which three or more recording / reproducing layers are laminated is described. The present invention can also be applied to reproduction.

  Further, the arrangement pattern of the light receiving portions of the photodetector is not limited to the above example, and when the target information recording layer of the optical disc is focused, the reflected light beam from the recording / reproducing layer other than the target recording / reproducing layer is reflected. As long as the light receiving part of the photodetector is not irradiated, the light receiving part may be arranged in any way.

  Moreover, in the said embodiment, although the 1st division area was comprised from four area | regions C1 to C4, this invention is not limited to this, You may comprise a 1st division area only by one area | region, You may comprise from 2 area | regions, and also you may comprise from 4 or more area | regions.

The figure which shows the structure of the optical head which is an Example of this invention. The figure which shows the shape of the polarizing diffraction grating in the Example of this invention The figure which shows the shape of the photodetector and optical pattern in the Example of this invention The figure which shows the mode of the change of the light pattern in the Example of this invention The figure which shows the mode of the change of the light pattern in the Example of this invention The figure which shows the shape of the optical pattern in the double layer disc in the Example of this invention The figure which shows the 2nd Example of the polarizing diffraction grating in this invention. The figure which shows the shape of the optical pattern in 2nd Example of the polarizing diffraction grating in this invention The figure which shows the 3rd Example of the polarization diffraction grating in this invention The figure which shows the shape of the optical pattern in the 3rd Example of the polarizing diffraction grating in this invention Schematic diagram of an optical disc apparatus mounting an optical head according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Laser beam, 3 ... Polarizing beam splitter, 4 ... Collimating lens, 5 ... Polarization diffraction grating, 6 ... 1/4 wavelength plate, 7 ... Objective lens, 8 ... Optical disk, 9 ... 1st layer, DESCRIPTION OF SYMBOLS 10 ... 2nd layer, 11 ... Arrow, 12 ... Photodetector, 13 ... Light receiving part, 14 ... Light beam center, 15-21 ... Dividing line, 22 ... + 1st order diffracted light, 23 ...- 1st order diffracted light, 24 ... Shaded part 25-29 ... light pattern, 27 ... mirror, 28 ... case, 29 ... moving mechanism, 30 ... coil, 31 ... holder, 32 ... motor, 33 ... lead screw, 34 ... spindle motor

Claims (5)

An optical head for irradiating a light beam to an optical disk having a plurality of information recording layers stacked at a predetermined interval from each other, and detecting a reflected light beam from the optical disk,
With a light source;
An objective lens for condensing the light beam emitted from the light source onto the optical disc;
A splitting element for splitting the light beam reflected by the optical disc into a plurality of light beams;
A condensing lens for condensing the light beam reflected by the optical disc;
A photodetector for receiving the light beam collected by the condenser lens by a plurality of light receiving sections and converting the received light into an electrical signal;
The dividing element is
A first divided region disposed substantially in the center;
A second divided region composed of four regions that are divided by the first dividing line and arranged so as to sandwich the first divided region along the direction of the first dividing line;
It is divided by a second dividing line orthogonal to the first dividing line, and is composed of four regions arranged so as to sandwich the first dividing region along the direction of the second dividing line. A third divided region;
When each of the first to third divided areas is focused on the target information recording layer of the optical disc, the reflected light beam from the target information recording layer is reflected on the light receiving portion of the photodetector. An optical head that is focused and configured so that a reflected light beam from a recording / reproducing layer other than the target information recording layer is not irradiated to the light receiving portion of the photodetector. A focus error signal by a knife edge method is detected with the light beam that has passed through the second divided region,
A tracking error signal is detected by the light flux that has passed through the second divided region and the third divided region;
Detecting the offset correction signal of the tracking error signal with the light beam that has passed through the third divided region;
2. The optical head according to claim 1, wherein a reproduction signal is detected by a light beam that has passed through the first, second, and third divided regions. A diffraction grating is formed in each region of the dividing element,
A focus error signal is detected by -1st order diffracted light diffracted in the second divided region;
A tracking error signal is detected using + 1st order diffracted light diffracted in the second and third divided regions;
Detecting an offset correction signal of the tracking error signal from the −1st order diffracted light diffracted in the third divided region;
3. The optical head according to claim 1, wherein a reproduction signal is detected by a sum of + 1st order diffracted light diffracted in the first, second, and third divided regions.   4. The optical head according to claim 3, wherein the diffraction grating is formed so that the light amount of the + 1st order diffracted light diffracted in each region of the dividing element is larger than the light amount of the −1st order diffracted light. An optical head according to any one of claims 1 to 4,
A laser drive circuit for driving the light source;
A servo signal generation circuit for generating a servo signal from the output signal of the photodetector of the optical head;
An information signal reproducing circuit for reproducing information recorded on the optical disc from an output signal of a photodetector of the optical head;
An optical disk apparatus comprising: a system control circuit for controlling the laser drive circuit, the servo signal generation circuit, and the information signal reproduction circuit.

Images