JP2009032369A - Optical pickup and optical recording medium driving unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup and optical recording medium driving unit with a simple and compact configuration for detecting a proper track error signal in which effect of a stray light between layers is reduced. <P>SOLUTION: The optical pickup comprises photo detectors 9 and 10, and generates the track error signal Tr according to (A-D)-ma((B1+B2)-(C1+C2)) (ma is a coefficient set based on a ratio of tilt of a DC offset corresponding to a lens shift in the radial direction) based on a differential signal (A-D) of light receiving signals A and D from a split light receiving element of the photo detector and a differential signal ä(B1+B2)-(C1+C2)} of each sum signal of the light receiving element signals B1 and B2 and C1 and C2. Especially when recording or reproducing one of the recording layers of a double layer disk, the coefficient ma is corrected to be smaller than the correction coefficient set based on the ratio of the tilt of the DC offset corresponding to the lens shift in the radial direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup, for example, and more particularly to an optical pickup and an optical recording medium driving apparatus that can accurately detect a track error signal or the like.

  Conventionally, a DVD (Digital Versatile Disc), which is an optical disk, is widely used as a recording medium for recording content with a large amount of information such as moving images. In the DVD, the content is recorded on a recording layer whose capacity is increased by multilayering.

  In an optical pickup employed in an optical disk apparatus as an optical recording medium driving apparatus that reads / writes information from / to this optical disk, the reflected light of the irradiated light on the information recording surface of the optical disk is divided into a plurality of areas. The light detection unit receives the light and detects a track error signal by a push-pull method or the like. Here, the “push-pull method” refers to an objective lens when the distribution of reflected light from the surface of an optical disc such as a DVD changes depending on the positional relationship between the light spot and the guide groove or pit row, and a track shift occurs. This is a technique characterized in that a track error signal is obtained using the difference in the amount of light by making use of the asymmetry above.

  By the way, in an optical disk apparatus that employs a tracking servo system based on the push-pull method that detects a track error signal with one beam, when the objective lens moves in the radial direction (perpendicular to the track) of the optical disk and the optical axis shifts, light detection is performed. The spot on the vessel translates, resulting in a DC offset in the detected push-pull signal itself.

In order to avoid this, in the prior art, for example, as shown in FIG. 16, the light receiving element A of the photodetector 100 is divided into a plurality of regions, and the light receiving outputs A and B1 from the regions that receive the light spot 101 are received. , B2, C1, C2, D based on the track error signal Tr
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
And the coefficient ma is set based on the ratio of the slope of the DC offset according to the lens shift.

  Here, for example, in Patent Document 1, when the track error signal is obtained by the push-pull method, the DC in the track error signal is set particularly when the spot diameter is set so that the primary light contacts or overlaps at the center of the spot. An optical disc apparatus that effectively avoids the offset and performs tracking servo is disclosed.

JP 2006-059417 A

  However, when recording or reproducing is performed on a two-layer optical disk using the optical pickup according to the conventional technique as described above, return light (interlayer stray light) from a recording layer other than the target recording layer is generated, and this is the track error signal. Causes deterioration.

  In particular, when interlayer stray light is generated from the boundary between the recorded part and the unrecorded part (boundary stray light), the recorded part and the unrecorded part have different reflectivities, so that there is a difference in the intensity of the light returned in the radial direction by the photodetector. As a result, a DC offset occurs in the light receiving outputs A and D and (B1 + B2) and (C1 + C2) in the light receiving element shown in FIG.

  In addition, while the interlayer stray light is substantially uniform over the entire light receiving element, the return light from the target recording layer has an intensity distribution, and the light intensity increases at the center of the light receiving element. The influence of interlayer stray light on the differential signal {(B1 + B2)-(C1 + C2)} is relatively greater than that on (AD). Therefore, the DC offset due to the boundary stray light increases as the value of the coefficient ma increases. As a result, a DC offset occurs in the track error signal, and there is a possibility that the tracking servo characteristics such as off-tracking and off-tracking may be seriously hindered.

  Therefore, an object of the present invention is to enable detection of an appropriate track error signal with reduced influence of boundary stray light with a simple and small configuration.

  The optical pickup according to the first aspect of the present invention is divided into at least two parts in a predetermined direction on the optical recording medium, and both divided end parts are further divided into at least three parts in a direction perpendicular to the predetermined direction. A case where a divided light receiving element is provided, and a light detecting means for detecting return light from the optical recording medium by the divided light receiving element, and recording or reproduction on a predetermined recording layer of the optical recording medium having a plurality of layers The first difference signal that is the difference between the light receiving element signals of the central divided light receiving element among the three divided light receiving elements and the end portion in the vertical direction of the three divided light receiving elements. Than the coefficient set based on the ratio of the second difference signal, which is the difference between the sum signals of the light receiving element signals of the two divided light receiving elements, and the slope of the DC offset according to the lens shift with respect to the predetermined direction. Small value And a signal processing means for generating a tracking error signal based on a constant coefficient.

  Therefore, by using the above coefficient, it is possible to generate an appropriate track error signal that eliminates the influence of boundary stray light.

An optical pickup according to a second aspect of the present invention is an optical pickup that is applied to recording or reproducing information on an optical recording medium, and is divided into at least two parts in a predetermined direction on the optical recording medium. A photodetector having a divided light receiving element divided into at least three parts in a direction perpendicular to the predetermined direction and detecting return light from the optical recording medium by the divided light receiving element; A difference signal (A−D) that is a difference between the light receiving element signals A and D of the central divided light receiving element among the divided light receiving elements divided at least in the vertical direction at both ends, and the vertical at the both ends. Difference signal {(B1) which is the difference between the sum signals of the light receiving element signals B1 and B2, C1 and C2 of the two divided light receiving elements at the end in the vertical direction among the divided light receiving elements divided into at least three in a certain direction. B2) - and (C1 + C2)}, based on the coefficient ma that is set based on the ratio of the slope of the DC offset corresponding to the lens shift for said predetermined direction, a track error signal Tr,
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
A signal processing unit that executes a process generated according to the above-mentioned coefficient, and when the signal processing unit records or reproduces data on a predetermined recording layer of an optical recording medium having a plurality of layers, the coefficient ma is corrected and set to a value smaller than a correction coefficient set based on the ratio of the slope of the DC offset corresponding to the lens shift with respect to the predetermined direction.

  Therefore, when recording or reproducing on one recording layer of an optical recording medium having a plurality of layers, it is possible to generate an appropriate track error signal that eliminates the influence of boundary stray light using the correction coefficient.

  The optical recording medium driving apparatus according to the third aspect of the present invention is divided into at least two in a predetermined direction on the optical recording medium, and the divided end portions are further at least 3 in a direction perpendicular to the predetermined direction. A divided light-receiving element having a divided light-receiving element that detects return light from the optical recording medium by the divided light-receiving element, and recording or reproduction on a predetermined recording layer of the optical recording medium having a plurality of layers The first difference signal, which is the difference between the light receiving element signals of the central divided light receiving element among the three divided light receiving elements, and the vertical direction of the three divided light receiving elements. Set based on the ratio of the second difference signal, which is the difference between the sum signals of the two light receiving element signals of the two divided light receiving elements at the end of the, and the slope of the DC offset according to the lens shift with respect to the predetermined direction. Smaller than the coefficient An optical pickup having a signal processing means for generating a tracking error signal based on the set coefficients.

  Therefore, by using the above coefficient, it is possible to generate an appropriate track error signal that eliminates the influence of boundary stray light, and to realize an appropriate track servo.

An optical recording medium driving apparatus according to a fourth aspect of the present invention is an optical recording medium driving apparatus for recording or reproducing information on an optical recording medium, and is divided into at least two in a predetermined direction on the optical recording medium. The divided end portions have a divided light receiving element divided into at least three in a direction perpendicular to the predetermined direction, and the return light from the optical recording medium is detected by the divided light receiving element. And a differential signal (A−D) that is a difference between the light receiving element signals A and D of the central divided light receiving element among the divided light receiving elements divided into at least three in the vertical direction at both ends. The difference between the sum signals of the light receiving element signals B1 and B2 and C1 and C2 of the two divided light receiving elements at the ends in the vertical direction among the divided light receiving elements divided at least in the vertical direction at both ends. The difference signal {( 1 + B2) - and (C1 + C2)}, based on the coefficient ma that is set based on the ratio of the slope of the DC offset corresponding to the lens shift for said predetermined direction, a track error signal Tr,
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
An optical pickup having a signal processing unit that executes processing generated according to the method, and the signal processing unit records or reproduces data on a predetermined recording layer of an optical recording medium having a plurality of layers in the above processing In addition, the coefficient ma is corrected and set to a value smaller than a correction coefficient set based on the ratio of the slope of the DC offset corresponding to the lens shift with respect to the predetermined direction.

  Therefore, when recording or reproducing on one recording layer of an optical recording medium having multiple layers, a correct tracking error signal is generated using the correction coefficient to eliminate the influence of interlayer stray light, and an appropriate track servo is realized. can do.

  According to the present invention, it is possible to provide an optical pickup and an optical recording medium driving device that can detect an appropriate track error signal with reduced influence of boundary stray light with a simple and small configuration.

  The best mode for carrying out the present invention (hereinafter simply referred to as an embodiment) will be described below in detail with reference to the drawings.

  FIG. 1 shows and describes the configuration of an optical pickup according to an embodiment of the present invention.

  This can be applied to an optical disk device or the like as an optical recording medium driving device.

  As shown in FIG. 1, a collimator lens 2 and a polarizing beam splitter (PBS) 3 are sequentially arranged on the optical path of the light emitted from the semiconductor laser 1. A quarter-wave plate 4 and an objective lens 5 are sequentially disposed on the light transmission side of the PBS 3. An optical disk 6 which is an example of an optical recording medium is positioned on the laser beam output side of the objective lens 5. On the return light side optical path in the return path of the PBS 3, a condenser lens 7, a half mirror 8, two photodetectors (PD 1) 9 for detecting return light separated by the half mirror 8, and a photodetector. (PD2) 10 is provided. Detection signals from the two photodetectors (PD1) 9 and (PD2) 10 are input to the signal processing unit 11. In the signal processing unit 11, a track error signal Tr and a focus error signal Fo are generated, the signals Tr and Fo are output to a servo control system (not shown), and tracking servo and focus servo are executed by picking up or driving a lens. . The signal processing unit 11 may be disposed inside or outside the optical pickup 100. In the above configuration, the photodetectors 9 and 10 function as, for example, light detection means, and the signal processing unit 11 functions as, for example, signal processing means. As the optical recording medium, a data recording medium using light interference fringes can also be employed.

  In such a configuration, the light emitted from the semiconductor laser 1 is collimated (that is, converted into parallel light) by the collimator lens 2 and then enters the PBS 3. PBS3 has a polarizing mirror. The incident light beam passes through the PBS 3, is converted into circularly polarized light by the quarter wavelength plate 4, and is collected on the optical disk 6 by the objective lens 5. On the other hand, the light reflected by the optical disk 6 passes through the objective lens 5 and the quarter-wave plate 4, is converted into linearly polarized light orthogonal to the forward polarized light, and is reflected by the PBS 3. The light reflected by the PBS 3 is condensed by the condenser lens 7 and separated into two by the half mirror 8, and then one light is received at a position close to L from the condensing point S1 to the half mirror 8 side. The light is received by a photodetector (PD1) 9 having a surface, and the other light is received by a photodetector (PD2) 10 having a light receiving surface at a position L away from the condensing point S2 to the half mirror 8 side. Is done.

  Here, the configuration of the photodetectors (PD1) 9 and (PD2) 10 is, for example, as shown in FIG. That is, the photodetector (PD1) 9 and the photodetector (PD2) 10 are divided into three in the radial direction (disc radial direction) in a symmetrical pattern with respect to the center line.

  As shown in FIG. 2A, the photodetector (PD1) 9 is divided into three parts in a radial direction (disk radial direction) which is a predetermined direction in a symmetrical pattern with respect to the center line. The light receiving portions at both ends in the radial direction other than are divided into three in the direction perpendicular to the radial direction, that is, the track direction (B1, A, B2, C1, D, C2), for a total of seven divided light receiving elements A, It consists of B1, B2, C1, C2, D, and I. Further, as shown in FIG. 2B, the photodetector (PD2) 10 has a total of three divided light receptions, which are divided into three in the radial direction (disk radial direction) in a symmetrical pattern with respect to the center line. It consists of elements E, H and J.

  Under such a configuration, the photodetector (PD1) 9 receives the light spot at a position close to the half mirror by L from the light condensing point S1, and the photodetector (PD2) 10 condenses the light. A light spot at a position L away from the half mirror from the point S2 is received.

  The signal processing unit 11 inputs a light receiving element signal detected by the photodetector (PD1) 9 and calculates a track error signal Tr by the following equation. Here, the light receiving element signals from a total of seven divided light receiving elements are A, B1, B2, C1, C2, D, and I.

Tr = (A−D) −ma {(B1 + B2) − (C1 + C2)} (1)
Here, ma is a correction coefficient for correcting the influence of the lens error of the track error signal Tr.

  Hereinafter, a case where the objective lens 5 is shifted in the radial direction as the disk radial direction will be considered.

  FIG. 3 shows the correspondence between the shift amount of the objective lens 5 in the radial direction and the track error signal Tr calculated by the equation (1), and the shift amount of the objective lens 5 and the equation (1). A graph relating to a correspondence relationship with each signal value of (AD) and {(B1 + B2) − (C1 + C2)} as components will be described.

  In FIG. 3, the lens shift [mm] indicates a change in each signal when the central portion is 0 and a lens shift occurs in a range of −0.25 to +0.25 from the central portion.

  The position of the lens shift 0 in the center is a state in which the objective lens 5 is disposed at the correct track position of the optical disc 6. FIG. 3 shows changes in each signal when the objective lens 5 has a lens shift in the range of −0.25 to +0.25 in the radial direction.

  As the objective lens 5 is shifted, the DC level of the (AD) signal is offset. The (AD) signal is a signal with a relatively large slope, and the (AD) signal is large when the lens shift is in the-direction, and the (AD) signal is large when the lens shift is in the + direction. Get smaller. That is, it can be seen that the (AD) signal has a DC level offset as a direct current component with a relatively large slope.

  On the other hand, the DC level of the {(B1 + B2)-(C1 + C2)} signal is offset with a slope different from that of the (AD) signal. That is, as shown in FIG. 3, the {(B1 + B2) − (C1 + C2)} signal is a signal having a relatively small slope and has a relatively small slope. When the lens shift is in the −direction, {(B1 + B2) − (C1 + C2)} The signal becomes large, and the {(B1 + B2)-(C1 + C2)} signal becomes small when the lens shift is in the + direction. That is, the {(B1 + B2)-(C1 + C2)} signal has a DC level offset as a direct current component with a relatively small slope, which is different from the (AD) signal.

  Therefore, in this embodiment, first, the coefficient ma set in the calculation formula (1) of the track error signal Tr is set to the slope of the DC offset of the (AD) signal that can be calculated from the graph shown in FIG. (B1 + B2) − (C1 + C2)} The DC offset slope ratio of the signal is set. When the track error signal Tr is calculated by setting the coefficients in this way, only a pure track error signal with no DC level offset is obtained from the track error signal Tr even if a lens shift occurs.

  In addition to the above, in this embodiment, in the case of using a multilayer type optical disc (hereinafter, a two-layer disc is taken as an example) as an optical recording medium having a plurality of layers, the objective lens is made to follow the tracking. Focusing on the fact that an offset variation that cannot be corrected only by the above method occurs in the track error signal when the lens is shifted, the feature is that the influence of interlayer stray light is also reduced.

  Hereinafter, the influence of interlayer stray light and boundary stray light focused on by the present embodiment will be described in detail.

  FIG. 4 shows and describes the laminated structure of the two-layer disc 12.

  As shown in FIG. 4, the dual-layer disc 12 has a first recording layer (L0 layer) 12b laminated on a substrate 12a, and an intermediate layer 12c as a bonding layer is formed on the L0 layer. A second recording layer (L1 layer) 12d is laminated. A protective layer 12e is formed on the second recording layer 12d. The laser light emitted from the optical pickup 100 is incident on the first recording layer 12b or the second recording layer 12d from the substrate 12a side.

  If the optical pickup 100 having the above-described configuration shown in FIG. 1 is simply applied to the two-layer disc 12 having the above structure, the return light from the recording layer other than the target recording layer other than the original reflected light, that is, “Interlayer stray light” is also generated, which may cause deterioration of the detection signal.

  In the dual-layer disc 12, recording is normally performed on the L0 layer 12b from the inner periphery toward the outer periphery, and after recording to the outermost periphery, the light spot jumps to the L1 layer 12d, and the L1 layer 12d moves from the outer periphery toward the inner periphery. Record. Based on this recording situation, interlayer stray light will be further described.

  FIG. 5 shows and describes the state of interlayer stray light from the L0 layer 12b during recording on the L1 layer 12d. FIG. 5A shows a state in which laser light is irradiated to the second recording layer (L1 layer) through the first recording layer (L0 layer) 12b through the objective lens 5, and FIG. ) Shows how the light spots 30 and 31 of the reflected light due to the irradiation are received by the photodetector (PD1) 9. As shown in FIGS. 5A and 5B, since the recording light beam is focused on the L1 layer 12d and is not condensed on the L0 layer 12b, the return light from the L1 layer 12d is detected by the photodetector. A predetermined light spot 30 is formed on (PD1) 9, but the return light from the L0 layer 12b becomes a light spot 31 of a spread pattern which is not in focus. Accordingly, the interlayer stray light from the uniformly recorded layer is canceled by the track error signals A and D, (B1 + B2) and (C1 + C2) in the above equation (1), and (AD), {(B1 + B2) − (C1 + C2)} is not offset, and in this case, no offset occurs in the track error signal Tr of the above-described equation (1).

  Next, FIG. 6 illustrates a case where recording on the L0 layer 12b is completed and recording on the L1 layer 12d is started on the outermost periphery of the disc. In this case, since the outer side of the outermost track of the L0 layer 12b is unrecorded, stray light from the L0 layer 12b includes a mixture of light reflected from the recording portion and light reflected from the unrecorded portion. That is, in FIG. 6A, laser light is transmitted to the second recording layer (L1 layer) through the boundary between the recording portion and the unrecorded portion of the first recording layer (L0 layer) 12b via the objective lens 5. FIG. 6B shows a state in which the light spots 30 and 31 of the reflected light due to the irradiation are received by the photodetector (PD1) 9. FIG.

  As shown in FIGS. 6A and 6B, the stray light from the recording portion of the L0 layer 12b forms a light spot 30 on the inner side in the disc radial direction of the photodetector (PD1) 9, and the photodetector The stray light from the unrecorded portion of the L0 layer 12b forms a light spot 32 outside the (PD1) 9 in the disc radial direction. 6A and 6B, since a recording mark is already formed in the recording portion of the double-layer disc 12, the reflectance at the recording portion is smaller than that of the unrecorded portion. Therefore, the intensity of the stray light component (light spot 32) received by the photodetector (PD1) 9 is not uniform, stray light is relatively large inside the radial direction, and stray light is relatively small outside. Become.

  That is, stray light intensity differs between A and D, (B1 + B2) and (C1 + C2), and DC offsets occur in (AD) and {(B1 + B2)-(C1 + C2)}, respectively. As a result, the track error signal is DC offset. Since the return light from the L1 layer 12d is concentrated in the center of the photodetector (PD1) 9, the light intensity of the A and D portions is larger than the light intensity of the B1, B2, C1, and C2 portions. Since the stray light from the L0 layer 12b extends over the entire photodetector (PD1) 9, the A and D portions and the B1, B2, C1, and C2 portions have substantially the same light intensity.

  For this reason, in the above-described equation (1), the influence of stray light is relatively greater in the {(B1 + B2) − (C1 + C2)} term than in the (AD) term. Further, from equation (1), as the value of the coefficient ma increases, the contribution of the {(B1 + B2) − (C1 + C2)} term increases, and the DC offset of the track error due to stray light increases.

  In view of the above points, the present embodiment adopts a one-beam push-pull tracking servo system, and in particular, tracks error offset due to interlayer stray light when recording on a two-layer disc as an optical recording medium having a plurality of layers. Reduce. More specifically, the coefficient ma in Expression (1) is set to a value that is smaller by a predetermined value than the value that compensates for the track error offset due to lens shift.

  Hereinafter, the relationship between the coefficient ma and the track error offset will be described.

1. As described above, the signal processing unit 11 receives the light receiving element signal detected by the photodetector (PD1) 9 and calculates the track error signal Tr by the following equation.

Tr = (AD) -ma {(B1 + B2)-(C1 + C2)} (1)
Accordingly, the track error signal Tr in the equation (1) becomes 0 with the coefficient ma (ma1) satisfying the relationship of the equation (1), and the track offset is minimized. When the coefficient ma is different from the value ma1, the ma {(B1 + B2)-(C1 + C2)} term in the equation (1) varies depending on the ma value, so that the track offset is proportional to | ma-ma1 |. To increase. This situation is as shown in FIG. 7. In FIG. 7, the vertical axis represents the track offset and the horizontal axis represents the value of the coefficient ma, showing the relationship between the two.

2. Relationship between the coefficient ma and the track offset due to the boundary stray light As described above, when recording on the L1 layer 12d includes stray light from the L0 layer 12b, both from the recorded portion and from the unrecorded portion, a photodetector ( PD1) 9 stray light from the recording portion of the L0 layer 12b on the inner side in the disc radial direction, and stray light from the unrecorded portion of the L0 layer 12b on the outer side in the disc radial direction of the photodetector (PD1) 9. Each pattern is formed (see FIG. 6). Since the reflectance of the recording part is lower than that of the unrecorded part, the intensity of the stray light component received by the photodetector has a difference in the radial direction. That is, (A−D) and {(B1 + B2) − (C1 + C2)} are not zero, respectively, and cause a DC offset in the track error signal.

  Since the return light from the L1 layer 12d is concentrated at the center of the photodetector (PD1) 9, the light intensity of the A and D portions is larger than the light intensity of the B1, B2, C1, and C2 portions, whereas L0 Since the stray light from the layer 12b covers the entire photodetector (PD1) 9, the A and D portions and the B1, B2, C1, and C2 portions have substantially the same light intensity. For this reason, in the expression (1), the influence of stray light becomes relatively larger in the {(B1 + B2) − (C1 + C2)} term than in the (AD) term.

  Also, according to equation (1), when the value of the coefficient ma is changed, the (AD) term is constant, whereas the {(B1 + B2)-(C1 + C2)} term is proportional to the value of the coefficient ma. Change. The track offset due to the boundary stray light is the sum of the (AD) term and the {(B1 + B2)-(C1 + C2)} term. This state is as shown in FIG. 8, and the vertical axis of FIG. 8 shows the track offset and the horizontal axis shows the value of the coefficient ma to show the above relationship.

3. Track offset by lens shift when there is boundary stray light And 2. Accordingly, the track offset due to lens shift in the presence of boundary stray light is the sum of the track offset due to lens shift and the track offset due to boundary stray light. When the value of the coefficient ma is changed, the track offset varies as shown in FIG. It became clear to do. That is, in FIG. 9, when the value of the coefficient ma is larger than ma1, the track offset increases monotonously. On the other hand, when the value of the coefficient ma is made smaller than ma1, the track offset is reduced by the amount that the stray light contributes less. However, when the value is less than the predetermined value ma2, the contribution of the lens shift becomes dominant and further increases. It became clear that when the value is smaller than ma3, the track offset becomes larger than the value at the optimum value ma1 obtained based only on the lens shift.

  1 above. To 3. From this consideration, in the present embodiment, when the value of the coefficient ma in the equation (1) is set to an intermediate value between ma1 and ma3 in FIG. 9, only the lens shift is optimized as in the prior art. In comparison, the track offset was reduced.

  Next, FIG. 10 shows an example of measurement of the track error offset due to stray light at the boundary between the recorded area and the unrecorded area when the coefficient ma is changed.

  In the figure, the vertical axis represents the track error offset, and the horizontal axis represents the value of the coefficient ma with respect to the lens shift. Although the value of the coefficient ma with respect to this lens shift differs depending on the individual optical pickups, the relationship between the coefficient ma and the track error offset is substantially uniquely determined regardless of the optical pickup. That is, as the coefficient ma increases, the track error offset increases monotonously. For example, in an optical pickup having a coefficient ma for compensating lens shift of 4 dB, tracking is offset by about 10% at the outermost periphery of the L1 layer. In an optical pickup having a coefficient ma for compensating lens shift of 6 dB, the L1 layer is used. The offset at the outermost periphery is about 15%. In this embodiment, the coefficient ma is set small by a predetermined value in order to reduce the DC offset of the track error due to stray light at the boundary between the recording part and the unrecorded part of the optical disk 15. However, if the coefficient ma is excessively decreased, a track error due to lens shift increases, and the reduction amount is classified according to the value of the coefficient ma.

  More specifically, for example, when the coefficient ma is 4.2 dB or less, 0.6 dB is reduced, and when it is 4.2 dB or more, 1.2 dB is subtracted.

  From FIG. 7, the change rate of the track error offset with respect to the coefficient ma differs at the boundary of the coefficient ma = 4.2 dB (± 0.3) dB, and the relationship between the coefficient ma and the track error offset TEoffset is approximately: It has been found that the following relationship is true (ie this boundary is in the range of 3.9 dB to 4.5 dB, preferably 4.2 dB):

For example, if the boundary value is 4.2 dB,
When [ma] ≧ 4.2 dB: [TE off] = 4.1 × [ma] −7.5
When [ma] ≦ 4.2 dB: [TE off] = 1.6 × [ma] +3.2
The relationship is established.

  From this relationship, when the coefficient ma is 4.2 dB or less, the improvement amount of the track error offset by reducing 0.6 dB is about 1%, and when the coefficient ma is 4.2 dB or more, 1.2 dB is subtracted. Therefore, the improvement amount of the track error offset is about 5%.

  On the other hand, by making the coefficient ma smaller than a value that minimizes the track error due to the lens shift, a DC offset of the track error due to the lens shift occurs.

  Next, FIG. 11 illustrates an actual measurement example of the track error offset due to the lens shift when the value of the coefficient ma is changed from a value (0 dB) at which the track error is minimized.

  As shown in FIG. 11, the increase in the track error offset when the coefficient ma is reduced by 0.6 dB is 0.7%, and the increase in the track error offset when the coefficient ma is reduced by 1.2 dB is 2. It can be seen that it is 1%, which is smaller than the improvement in track error offset due to the interlayer stray light described above with reference to FIG.

  That is, the sum of the track offset due to the interlayer stray light and the track offset due to the lens shift is 0.6 dB when the coefficient ma is 4.2 dB or less from the value of the coefficient ma that minimizes the track error due to the lens shift. It can be seen that the improvement is obtained by subtracting 1.2 dB when the value is 4.2 dB or more.

  Hereinafter, the calculation process sequence of the coefficient ma will be described in detail with reference to the flowchart of FIG. As described above, it is assumed that the track error signal is obtained by Tr = (A−D) −ma {(B1 + B2) − (C1 + C2)}.

First, when an optical disk is inserted into the drive (step S101), the focus servo is turned on (step S102). Next, a DC driving current is supplied to the objective lens actuator to shift the lens by a certain amount (step S103). This is a process of shifting the objective lens of the pickup shown in FIG. 1 by a certain distance in the radial direction of the disc. The shift distance may be any predetermined distance. Subsequently, ave ((A−D)) that is the average value of the A−D signals and ave ((B1 + B2) − that is the average value of the (B1 + B2) − (C1 + C2) signals at the time of executing the shift processing of the constant distance. (C1 + C2)) ratio, ie
[Ave (AD)] / [ave ((B1 + B2)-(C1 + C2))]
Is calculated (step S104).

Next, the correction coefficient [ma] is
ma = [ave (AD)] / [ave ((B1 + B2)-(C1 + C2))]
(Step S105).

  Here, a specific processing example of each step executed in the calculation processing flow of the correction coefficient ma in FIG. 12 will be described with reference to FIGS. 13 and 14.

  That is, a supplementary description will be given of the processing in steps S103 and S104 in FIG.

FIG. 13 shows the relationship between the shift amount of the objective lens 5 of the optical pickup 2 and the track error signal (Tr), as in FIG.
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
And [A−D] and [(B1 + B2) − (C1 + C2)] corresponding to each signal value as a component of the equation.

It is assumed that a certain amount of lens shift in step S103 in FIG. 12 is executed up to [−0.1] in the left direction in the graph shown in FIG. After this lens shift process, in step S104, the average value of the AVE (AD) and (B1 + B2) − (C1 + C2) signals, which are the average values of the A−D signals, when the fixed distance shift process is executed. The ratio of a certain ave ((B1 + B2)-(C1 + C2)), that is,
[Ave (AD)] / [ave ((B1 + B2)-(C1 + C2))]
Is calculated. The average value of the A-D signal ave (AD) corresponds to the height of the triangle [a] shown in FIG. 10, and the average value of the (B1 + B2)-(C1 + C2) signal ave ((( B1 + B2) − (C1 + C2)) corresponds to the height of the triangle [b] shown in FIG.

  Here, FIG. 14 shows and explains a diagram in which these triangles are extracted.

  The height h1 of the triangle [a] shown in FIG. 14 is an average value of the A-D signal when the lens shift is performed up to [−0.1] in the left direction in the graph shown in FIG. It corresponds to a certain ave (AD). Further, the height h2 of the triangle [b] shown in FIG. 14 is (B1 + B2) − (C1 + C2) when the lens shift is performed up to [−0.1] in the left direction in the graph shown in FIG. This corresponds to ave ((B1 + B2) − (C1 + C2)), which is an average value of the signals. Thus, each average value corresponds to the slope of the DC level of each signal.

In step S104, the ratio of the slopes of these two signals (h1 / h2) is
[Ave (AD)] / [ave ((B1 + B2)-(C1 + C2))]
In step S105, the correction coefficient [ma] is calculated as
ma = [ave (AD)] / [ave ((B1 + B2)-(C1 + C2))]
The process to set as is executed.

  Returning to the description of FIG. 12 again, the value of the correction coefficient ma is compared with 4.2 dB (step S6). If smaller than the value, 0.6 dB is calculated from ma previously calculated in step S105. The subtracted value is used as the final correction coefficient ma (step S107).

On the other hand, when the value of the correction coefficient ma is larger than 4.2 dB in step S6, a value obtained by subtracting 1.2 dB from ma previously calculated in step S105 is set as the final correction coefficient ma ( Step S108). By setting such a correction coefficient ma, the following track error signal calculation formula, that is,
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
Even if a lens shift occurs when there is stray light at the boundary between the recorded area and the unrecorded area, the track error signal detection to which is applied reduces the influence of the DC level offset, and the track servo is detected with good track error detection. Is executed.

  By the way, the calculation processing of the track error signal Tr based on the processing of the above-described embodiment can be applied to pickups having various configurations.

  Accordingly, FIG. 15 shows a pickup structure that realizes a reduction in size, and the detection processing of the track error signal Tr by this structure will be described in detail.

  As shown in FIG. 15, a prism 52 is disposed on the optical path of the laser light of the semiconductor laser 51, and the light reflected by the PBS film 53 formed on the 45-degree inclined surface 64 of the prism 52. On the road, a quarter-wave plate 54, a collimating lens 55, and an objective lens 56 are arranged in this order. On the prism bottom surface 61 of the prism 52, photodetectors (PD1) 59 and (PD2) 60 are arranged. The light detector (PD1) 59 is disposed so that the light receiving surface is positioned on the light transmission path of the PBS film 53 of the prism 52 of the reflected light 52 from the optical disc 57, and the light detector (PD2) 60 is reflected by the light detector (PD2) 60. The light receiving surface is disposed on the reflection optical path of the half mirror film 59 of the light prism 52 and the mirror coat of the prism upper surface 63.

  In such a configuration, light emitted from the semiconductor laser 51 is reflected 45 degrees by the PBS film 53 formed on the 45-degree inclined surface 64 of the prism 52 and converted into circularly polarized light by the quarter-wave plate 54. After that, the light is collimated by the collimating lens 55 and condensed on the optical disk 57 by the objective lens 56. The light reflected by the optical disk 57 passes through the objective lens 56, the collimating lens 55, and the quarter wavelength plate 54 and is converted into linearly polarized light orthogonal to the forward polarized light. The light converted into the linearly polarized light is divided into light that is transmitted through the PBS film 53 on the 45-degree inclined surface 64 of the prism 52, 50% transmitted through the half mirror film 58 on the prism bottom surface 61, and light that is reflected 50%. The light transmitted through the half mirror film 58 is received by the photodetector (PD1) 59 disposed on the prism bottom surface 61.

  On the other hand, the light reflected by the half mirror film 58 is reflected by the mirror coat 62 on the prism upper surface 63 and enters the prism bottom surface 61 again. The light incident on the prism bottom surface 61 is received by a photodetector (PD2) 60 disposed on the prism bottom surface 61.

  In this pickup configuration, the photodetector (PD1) 59 and the photodetector (PD2) 60 have the photodetector configurations shown in FIGS. 2 (a) and 2 (b), respectively.

  That is, as shown in FIG. 2A, the photodetector (PD1) 59 is divided into three in the radial direction (disk radial direction) in a symmetrical pattern with respect to the center line, and further, other than the central portion (I). A total of seven divided light receiving elements (A, B1, B2, C1, C2, D, I) in which the light receiving portions at both ends are divided into three in the track direction (B1, A, B2, and C1, D, C2), respectively. It is set as a photodetector composed of Further, as shown in FIG. 2 (b), the photodetector (PD2) 60 has a total of three divided light receiving elements divided into three in the radial direction (disk radial direction) in a symmetrical pattern with respect to the center line. It is set as a photodetector composed of (E, H, J).

  Even in such a downsized pickup configuration, control using the track error signal Tr according to the above-described embodiment is realized.

  As described above, according to one embodiment of the present invention, for example, the light receiving portions at both ends divided into three in the radial direction (predetermined direction) corresponding to the disk radial direction are perpendicular to the radial direction. The first photodetector (PD1) 9 divided into three in the track direction and the second photodetector (PD2) 10 divided into three in the radial direction are applied, and the first photodetector (PD1) is mainly used. The track error signal is generated by the input signal from 9. Therefore, according to the optical pickup according to the present embodiment, when recording or reproducing is performed on a two-layer optical disc as an optical recording medium having a plurality of layers, stray light at the boundary between the recording unit and the non-recording unit is used. Track error offset can be reduced.

  The embodiment of the present invention has been described above, but the present invention is not limited to this, and it is needless to say that various improvements and changes can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, the influence of the interlayer stray light has been described by taking the situation as shown in FIGS. 5 and 6 as an example. However, when there is a boundary between the unrecorded area and the recorded area of the L0 layer 12b, the L1 layer When recording or reproduction is performed on 12d, the same boundary stray light phenomenon occurs, but the problem can be solved by adjusting the value of the coefficient ma by a similar method. Further, when the boundary between the unrecorded area and the recorded area of the L1 layer 12d exists, the same boundary stray light phenomenon occurs even when recording or reproduction is performed on the L0 layer 12b. The problem can be solved by adjusting the value of.

1 is a configuration diagram of an optical pickup according to an embodiment of the present invention. The block diagram of the photodetector of the optical pick-up which concerns on one embodiment of this invention. The figure which shows the graph which concerns on the change with respect to a lens shift about a track error signal and its element signal. The figure which shows the laminated structure of a two-layer disc. (A), (b) is a figure which shows the mode of the interlayer stray light from the L0 layer during recording to the L1 layer. (A), (b) is a figure which shows the mode of the interlayer stray light from the L0 layer during recording to the L1 layer. The figure which shows the relationship between the coefficient ma and the track offset by lens shift. The figure which shows the relationship between the coefficient ma and the track offset by boundary stray light. The figure which shows the relationship between the track offset by the lens shift in case there exists a boundary stray light, and the coefficient ma. The figure which shows the relationship between coefficient ma and track error offset. The figure which shows the relationship between the variation | change_quantity of coefficient ma, and the track error offset by a lens shift. The flowchart which shows the sequence of the determination process of the coefficient ma. The figure which shows the graph which shows the correspondence of the shift amount of an objective lens, and each signal value as a component of a track error signal. The figure for demonstrating the specific process example which calculates the correction coefficient ma of a track error signal. The figure which shows the structural example of the pickup which can apply this invention. The figure which shows the structural example of the light-receiving part of the photodetector applied to the optical pick-up concerning a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Collimating lens, 3 ... Polarizing beam splitter, 4 ... 1/4 wavelength plate, 5 ... Objective lens, 6 ... Optical disk, 7 ... Condensing lens, 8 ... Half mirror, 9 ... Photodetector, DESCRIPTION OF SYMBOLS 10 ... Photodetector, 11 ... Signal processing part, 12 ... Optical disk, 12b ... 1st recording layer, 12d ... 2nd recording layer

Claims (8)

The divided light receiving element is divided into at least two parts in a predetermined direction on the optical recording medium, and both divided end parts are further divided into at least three parts in a direction perpendicular to the predetermined direction. Light detecting means for detecting return light from the optical recording medium;
When recording or reproduction is performed on a predetermined recording layer of an optical recording medium having a plurality of layers, a first difference which is a difference between light receiving element signals of a central divided light receiving element among the three divided light receiving elements. A second difference signal that is the difference between the sum signals of the light receiving element signals of the two divided light receiving elements at the end in the vertical direction among the three divided light receiving elements, and the predetermined signal Signal processing means for generating a tracking error signal based on a coefficient set to a value smaller than a coefficient set based on the ratio of the slope of the DC offset according to the lens shift with respect to the direction,
An optical pickup characterized by that. In an optical pickup applied to recording or reproducing information on an optical recording medium,
The optical recording medium is divided into at least two parts in a predetermined direction, and the divided light receiving elements are divided into at least three parts in a direction perpendicular to the predetermined direction at both ends. A photodetector for detecting return light from the optical recording medium by the divided light receiving element;
A difference signal (A−D) that is a difference between the light receiving element signals A and D of the central divided light receiving element among the divided light receiving elements divided into at least three in the vertical direction of the both end parts, and the above-mentioned Of the divided light receiving elements divided into at least three in the vertical direction, the difference signal {() is the difference between the sum signals of the light receiving element signals B1 and B2, C1 and C2 of the two divided light receiving elements at the end in the vertical direction. B1 + B2) − (C1 + C2)} and a coefficient ma set based on the ratio of the slope of the DC offset corresponding to the lens shift with respect to the predetermined direction, the track error signal Tr is
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
A signal processing unit that executes processing to be generated according to
When the signal processing unit performs recording or reproduction on a predetermined recording layer of an optical recording medium having a plurality of layers at the time of the processing, the signal ma is set to the DC corresponding to the lens shift with respect to the predetermined direction. An optical pickup, wherein the optical pickup is corrected and set to a value smaller than a correction coefficient set based on a ratio of an offset slope. The correction amount for the coefficient ma is
A DC offset taking into account boundary stray light from recording layers other than the recording layer that performs recording or reproduction of the optical recording medium having the plurality of layers is set based on a slope ratio of the DC offset corresponding to only the lens shift. The optical pickup according to claim 2, wherein the optical pickup is set in a range not exceeding a DC offset corresponding to the corrected correction coefficient. The correction amount for the coefficient ma is:
When the coefficient set based on the ratio of the slope of the DC offset according to the lens shift with respect to the predetermined direction is 4.2 ± 0.3 dB or less, the coefficient is 0.6 dB, and the coefficient is 4.2 ± The optical pickup according to claim 2, wherein the optical pickup is 1.2 dB when 0.3 dB or more. The divided light receiving element is divided into at least two parts in a predetermined direction on the optical recording medium, and both divided end parts are further divided into at least three parts in a direction perpendicular to the predetermined direction. Light detecting means for detecting return light from the optical recording medium;
When recording or reproduction is performed on a predetermined recording layer of an optical recording medium having a plurality of layers, a first difference which is a difference between light receiving element signals of a central divided light receiving element among the three divided light receiving elements. A second difference signal that is the difference between the sum signals of the light receiving element signals of the two divided light receiving elements at the end in the vertical direction among the three divided light receiving elements, and the predetermined signal And an optical pickup having a signal processing means for generating a tracking error signal based on a coefficient set to a value smaller than a coefficient set based on the ratio of the slope of the DC offset corresponding to the lens shift with respect to the direction. The
An optical recording medium driving device. In an optical recording medium driving apparatus for recording or reproducing information on an optical recording medium,
The optical recording medium is divided into at least two parts in a predetermined direction, and the divided light receiving elements are divided into at least three parts in a direction perpendicular to the predetermined direction at both ends. A photodetector for detecting return light from the optical recording medium by the divided light receiving element;
A difference signal (A−D) that is a difference between the light receiving element signals A and D of the central divided light receiving element among the divided light receiving elements divided into at least three in the vertical direction of the both end parts, and the above-mentioned Of the divided light receiving elements divided into at least three in the vertical direction, the difference signal {() is the difference between the sum signals of the light receiving element signals B1 and B2, C1 and C2 of the two divided light receiving elements at the end in the vertical direction. B1 + B2) − (C1 + C2)} and a coefficient ma set based on the ratio of the slope of the DC offset corresponding to the lens shift with respect to the predetermined direction, the track error signal Tr is
Tr = (AD) -ma {(B1 + B2)-(C1 + C2)}
An optical pickup having a signal processing unit that executes processing to be generated according to
When the signal processing unit performs recording or reproduction on a predetermined recording layer of an optical recording medium having a plurality of layers at the time of the processing, the signal ma is set to the DC corresponding to the lens shift with respect to the predetermined direction. An optical recording medium driving device, wherein the optical recording medium driving device is corrected and set to a value smaller than a correction coefficient set based on a ratio of the slope of the offset. The correction amount for the coefficient ma is
A DC offset taking into account boundary stray light from recording layers other than the recording layer that performs recording or reproduction of the optical recording medium having the plurality of layers is set based on a slope ratio of the DC offset corresponding to only the lens shift. The optical recording medium driving device according to claim 6, wherein the optical recording medium driving device is set in a range not exceeding a DC offset corresponding to the corrected correction coefficient. The correction amount for the coefficient ma is:
When the coefficient set based on the ratio of the slope of the DC offset according to the lens shift with respect to the predetermined direction is 4.2 ± 0.3 dB or less, the coefficient is 0.6 dB, and the coefficient is 4.2 ± The optical recording medium driving device according to claim 6, wherein when it is 0.3 dB or more, it is 1.2 dB.

Images