JP2006054006A - Optical disk device, and optical pickup used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the S/N of a reproduced signal from being drastically reduced when removing an offset from a tracking error signal by a push-pull method. <P>SOLUTION: A grating is arranged in an optical path of reflected light from an optical pickup to obtain a main beam and a sub beam. A beam spot BS<SB>0</SB>by the main beam is formed on photodetection surfaces of quadrisected photodiode sections 161 M. The beam spots BS<SB>-1</SB>, BS<SB>+1</SB>by the side beams are formed on the photodetection surfaces of the photodiode sections 161 S<SB>-</SB>. P<SB>-</SB>. First and third dividing lines divide a region including interference regions P<SB>-</SB>and P<SB>+</SB>and regions other than the same are divided. The tracking error signal is determined by an operational expression S<SB>TE</SB>=ä(Sd+Sc)-(Sa+Sb)}-kä(Sb+Sh)-(Se+Sg)}, and the signal for removing the offset is obtaied by using the photodiode sections 161 S<SB>-</SB>and 161 S<SB>+</SB>, and thereby, the smaller number of the divisions of the photodiode sections 161 M for obtaining the reproduction signal is necessitated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a disc device suitable for application to, for example, a DVD device, a Blu-ray disc device, etc., and an optical pickup used therefor.

  Specifically, the present invention forms on the optical disc a signal for removing the offset accompanying the displacement of the light detection surface or the displacement of the objective lens in the radial direction included in the tracking error signal by the push-pull method. First to second divided by first, second, and third dividing lines in the direction corresponding to the radial direction of the optical disc are the light detecting means on which the beam spot by the reflected light from the beam spot is formed on the light detection surface. The second and third light detection units are configured to include a fourth light detection unit, and the second and third light detection units are configured so that a region that does not include the interference region of the zero-order light and the ± first-order light is located in the second and third light detection units. By using a configuration obtained by calculating the difference between the detection outputs of the third light detection units, the number of divisions of the light detection means can be made relatively small, and the reduction in the S / N of the reproduction signal can be suppressed. In addition, an optical disc capable of accurately obtaining a signal for removing the offset even when the beam spot formed on the light detection surface is shifted in a direction corresponding to the longitudinal direction (tangential direction) of the recording track. It relates to the device.

  The present invention also provides a signal on an optical disc for removing an offset associated with displacement of the light detection surface or displacement of the objective lens in the radial direction, which is included in the tracking error signal by the push-pull method. A diffraction means for obtaining the main beam and the side beam is provided in the optical path of the reflected light from the reflected beam spot, and the area not including the interference area of the 0th order light and ± 1st order light among the beam spots by the side beam is detected. There are provided second photodetection means having first and second photodetection units formed on the surface and divided by a dividing line in a direction corresponding to the radial direction of the optical disc, and the first and second photodetection units 1st light detection means by which the beam spot by a main beam is formed in a light detection surface by setting it as the structure obtained by performing the calculation which takes the difference of the detection output of this In addition to preventing an increase in the number of divisions and suppressing a decrease in the S / N of the reproduction signal, the beam spot formed on the light detection surface is also shifted in a direction corresponding to the longitudinal direction (tangential direction) of the recording track. The present invention relates to an optical disc apparatus or the like that can obtain a signal for removing an offset with high accuracy.

  2. Description of the Related Art Conventionally, a one-beam method called a push-pull method is known as a tracking error signal detection method in an optical disc apparatus handling an optical disc such as a DVD (Digital Versatile Disc). However, this method has a problem in that when the displacement of the light detection surface or the displacement (shift) of the objective lens in the radial direction occurs, an offset occurs in the tracking error signal and detracking occurs.

  Patent Document 1 describes an improved push-pull method (APP method) that reduces an offset generated in the tracking error signal by the above-described push-pull method. In this improved push-pull method (APP method), a light receiving element 9 in which a beam spot 7 by reflected light from a beam spot formed on an optical disk is formed on a light detection surface is divided as shown in FIG. A structure having light receiving cells A, B, C, and D divided by lines 10 and 11 is used to obtain a signal for removing an offset by performing an operation for obtaining a difference between detection outputs of light receiving cells A and B. . The dividing line 10 is a dividing line for dividing the light receiving element 9 in a direction corresponding to the longitudinal direction of the recording track, and the dividing line 11 is for the light receiving element 9 in the radial direction orthogonal to the longitudinal direction of the recording track. It is a dividing line that divides in a corresponding direction.

Japanese Patent No. 3491253 (see page 2, Fig. 9)

  According to the improved push-pull method (APP method) described in Patent Document 1, a light receiving element for obtaining a reproduction signal is divided into six only for obtaining a tracking error signal. When the light receiving element is divided into six in this way, the current signals obtained in the six light receiving cells are supplied to separate current / voltage converters, converted into voltage signals, amplified, and A reproduction signal is obtained by adding the output signals of the voltage converter by an adder. In this case, since the reproduction signal has undergone current / voltage conversion and amplification processing by six current / voltage converters, there is a problem that the S / N is greatly reduced.

  Further, the improved push-pull method (APP method) of Patent Document 1 has a light detection section that is divided in a direction corresponding to the longitudinal direction (tangential direction) of the recording track. When the beam spot formed on the detection surface deviates in a direction corresponding to the longitudinal direction of the recording track, the push-pull interference areas C and D receive a light detection unit (light reception) for obtaining a signal for removing the offset. There is a problem that it becomes impossible to accurately obtain a signal for entering the cells A and B and removing the offset.

  The object of the present invention is to prevent the S / N of the reproduction signal from greatly decreasing when the offset is removed from the tracking error signal by the push-pull method, and the beam spot formed on the light detection surface of the light receiving element is reduced. An object of the present invention is to make it possible to accurately obtain a signal for removing the offset even when the recording track is shifted in the direction corresponding to the longitudinal direction of the recording track.

  An optical disc apparatus according to the present invention is formed on a light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disc on which recording tracks are formed spirally or concentrically, and formed on the optical disc. An error signal generating means for generating a tracking error signal corresponding to the deviation of the beam spot from a predetermined recording track in the radial direction of the optical disk using reflected light from the beam spot, and based on the tracking error signal Tracking control means for controlling the beam spot to be positioned on a predetermined recording track.

  The error signal generation means includes first to fourth beam spots formed by reflected light on the light detection surface and divided by first, second, and third dividing lines in a direction corresponding to the radial direction of the optical disc. The light detection means having the light detection unit, and an arithmetic operation for calculating the difference between the sum of the detection outputs of the first and second light detection units and the sum of the detection outputs of the third and fourth light detection units, The first calculation means for obtaining a signal indicating the relative displacement between the recording track and the objective lens and the calculation for obtaining the difference between the detection outputs of the second light detection unit and the third light detection unit are performed on the light detection surface. Second calculating means for obtaining a signal indicating the relative displacement of the beam spot, multiplying means for multiplying the output signal of the second calculating means by a predetermined coefficient, the output signal of the first calculating means and the multiplying means Obtain the tracking error signal by calculating the difference between the output signals In which a third arithmetic means.

  The second dividing line is a straight line, and the first dividing line includes a region including the interference region of the 0th-order light and the −1st-order light of the beam spot formed on the light detection surface and other regions. This is a curve that is divided and is closest to the second dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track. The third dividing line is the zero-order light and +1 of the beam spot formed on the light detection surface This is a curve that divides the area including the interference area of the next light and the other areas and approaches the second dividing line closest to the center position in the direction corresponding to the longitudinal direction of the recording track.

  The optical pickup according to the present invention includes a light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are spirally or concentrically formed, and an optical disk. A beam spot formed by reflected light from the beam spot formed on the optical detection surface is formed on the light detection surface, and is formed by first, second, and third dividing lines in a direction corresponding to the radial direction of the optical disk perpendicular to the longitudinal direction of the recording track. And a light detection means having divided first to fourth light detection sections.

  The second dividing line is a straight line, and the first dividing line includes a region including the interference region of the 0th-order light and the −1st-order light of the beam spot formed on the light detection surface and other regions. This is a curve that is divided and is closest to the second dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track. The third dividing line is the zero-order light and +1 of the beam spot formed on the light detection surface This is a curve that divides the area including the interference area of the next light and the other areas and approaches the second dividing line closest to the center position in the direction corresponding to the longitudinal direction of the recording track.

  In the present invention, a light beam is condensed by an objective lens on an optical disk on which recording tracks are formed spirally or concentrically to form a beam spot. Then, using the reflected light from the beam spot, a tracking error signal corresponding to the deviation of the beam spot from a predetermined recording track in the radial direction of the optical disc is generated.

  In this case, a beam spot by reflected light is formed on the light detection surface of the light detection means. The light detection means includes first to fourth light detection units divided by first, second, and third division lines in a direction corresponding to the radial direction of the optical disc. Here, the second dividing line is a straight line. Further, the first dividing line divides the area including the interference area of the 0th-order light and the −1st-order light of the beam spot formed on the light detection surface and the other area, and corresponds to the longitudinal direction of the recording track. The curve is closest to the second dividing line at the center position in the direction to be. The third dividing line divides the area including the interference area of the 0th-order light and the + 1st-order light of the beam spot formed on the light detection surface and the other area, and corresponds to the longitudinal direction of the recording track. The curve is closest to the second dividing line at the center position in the direction.

  An operation is performed to take the difference between the sum of the detection outputs of the first and second light detection units and the sum of the detection outputs of the third and fourth light detection units, and indicates the relative displacement between the recording track and the objective lens. A signal is obtained. This signal corresponds to a tracking error signal by a simple push-pull method, and an offset is generated when the displacement of the light detection surface or the displacement of the objective lens in the radial direction occurs.

  The first dividing line is a curve that divides the region including the interference region of the 0th-order light and the −1st-order light of the beam spot formed on the light detection surface of the light detection means and the other region. A dividing line 3 is a curve that divides the region including the interference region of the 0th-order light and the + 1st-order light of the beam spot formed on the light detection surface of the light detection unit and the other region.

  For this reason, areas of the beam spots that do not include the interference areas of the 0th order light and the ± 1st order light are formed on the light detection surfaces of the second and third light detection units. As a result, by calculating the difference between the detection outputs of the second light detection unit and the third light detection unit, the beam spot on the light detection surface of the light detection unit is not affected by the interference region. A signal indicating the relative displacement of is obtained. By multiplying this signal by a predetermined coefficient, a signal corresponding to the offset is obtained. Then, a signal corresponding to the offset is subtracted from the signal indicating the relative displacement between the recording track and the objective lens, and a tracking error signal from which the offset is removed is obtained.

  Based on the tracking error signal acquired as described above, control is performed so that the beam spot formed on the optical disk is positioned on a predetermined recording track.

  As described above, the light detection means has the first to fourth light detection units in the direction corresponding to the radial direction of the optical disk in order to obtain the tracking error signal, and the number of divisions is relatively small. A decrease in the S / N of the reproduction signal obtained from the light detection means can be suppressed.

  In addition, the light detection means has a first to a fourth light detection unit in a direction corresponding to the radial direction of the optical disk in order to obtain a tracking error signal, and a beam spot formed on the light detection surface is recorded. Even in the case of a shift in the direction corresponding to the longitudinal direction (tangential direction) of the track, the push-pull interference region may enter the second and third light detection units for obtaining a signal corresponding to the offset. The signal corresponding to the offset (the signal for removing the offset) can be obtained with high accuracy.

  Each of the first and third dividing lines is a curve that is closest to the second dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track. For this reason, the second and third light detection portions have the narrowest width at the center position in the direction corresponding to the longitudinal direction of the recording track, and the width increases as the distance from the center position increases. Therefore, as described above, a signal indicating the relative displacement of the beam spot on the light detection surface of the light detection means can be obtained by performing the calculation for obtaining the difference between the detection outputs of the second and third light detection units. However, the detection sensitivity can be increased.

  An optical disc apparatus according to the present invention is formed on a light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disc on which recording tracks are formed spirally or concentrically, and formed on the optical disc. An error signal generating means for generating a tracking error signal corresponding to the deviation of the beam spot from a predetermined recording track in the radial direction of the optical disk using reflected light from the beam spot, and based on the tracking error signal Tracking control means for controlling the beam spot to be positioned on a predetermined recording track.

  Then, the error signal generation means includes first to fourth light beams formed by reflected light in the light detection surface and divided by the first, second, and third dividing lines in a direction corresponding to the radial direction. A recording track which performs a calculation to obtain a difference between a sum of detection outputs of the first and second light detection units and a sum of detection outputs of the third and fourth light detection units; A first calculation means for obtaining a signal indicating the relative displacement of the objective lens and the beam on the light detection surface by calculating a difference between detection outputs of the second light detection unit and the third light detection unit. Second computing means for obtaining a signal indicating the relative displacement of the spot; multiplication means for multiplying an output signal of the second computing means by a predetermined coefficient; output signal of the first computing means and output of the multiplying means A third operation for obtaining a tracking error signal by performing an operation for obtaining a difference between signals Those having a calculation unit.

  The second dividing line is a straight line. Further, the radius of the beam spot on the light detection surface of the light detection means is set to 1, and the maximum value of the displacement in the direction corresponding to the radial direction of the beam spot on the light detection surface is the radius of the beam spot. The first and third dividing lines correspond to the longitudinal direction of the recording track, where λ is the wavelength of the light beam, NA is the numerical aperture of the objective lens, and Tp is the recording track pitch. The distance w from the second dividing line at the center position in the direction is a line that satisfies the expression {(λ / NA) * (1 / Tp) −1} −d ≧ w> 0.

  The optical pickup according to the present invention includes a light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are spirally or concentrically formed, and an optical disk. A beam spot formed by reflected light from the beam spot formed on the optical detection surface is formed on the light detection surface, and is formed by first, second, and third dividing lines in a direction corresponding to the radial direction of the optical disk perpendicular to the longitudinal direction of the recording track. And a light detection means having divided first to fourth light detection sections.

  The second dividing line is a straight line. Further, the radius of the beam spot on the light detection surface of the light detection means is set to 1, and the maximum value of the displacement in the direction corresponding to the radial direction of the beam spot on the light detection surface is the radius of the beam spot. The first and third dividing lines correspond to the longitudinal direction of the recording track, where λ is the wavelength of the light beam, NA is the numerical aperture of the objective lens, and Tp is the recording track pitch. The distance w from the second dividing line at the center position in the direction is a line that satisfies the expression {(λ / NA) * (1 / Tp) −1} −d ≧ w> 0.

  In the present invention, a light beam is condensed by an objective lens on an optical disk on which recording tracks are formed spirally or concentrically to form a beam spot. Then, using the reflected light from the beam spot, a tracking error signal corresponding to the deviation of the beam spot from a predetermined recording track in the radial direction of the optical disc is generated.

  In this case, a beam spot by reflected light is formed on the light detection surface of the light detection means. The light detection means includes first to fourth light detection units divided by first, second, and third division lines in a direction corresponding to the radial direction of the optical disc.

  Here, the second dividing line is a straight line. The first and third dividing lines have a radius of the beam spot on the light detection surface of the light detection means of 1, and a displacement in a direction corresponding to the radial direction of the beam spot on the light detection surface. When the maximum value of the size is d times the radius of the beam spot, the distance w from the second dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track is {(λ / NA) * (1 / Tp) -1} -d ≧ w> 0. For example, each of the first and third dividing lines is a straight line. Further, for example, the first and third dividing lines are curves that are closest to the second dividing line at the center position. Note that (λ / NA) * (1 / Tp) is the distance between the center of the 0th order light and the center of the ± 1st order light.

  An operation is performed to take the difference between the sum of the detection outputs of the first and second light detection units and the sum of the detection outputs of the third and fourth light detection units, and indicates the relative displacement between the recording track and the objective lens. A signal is obtained. This signal corresponds to a tracking error signal by a simple push-pull method, and an offset occurs when the objective lens is displaced in the radial direction.

  In addition, a calculation is performed to obtain a difference between detection outputs of the second light detection unit and the third light detection unit, and a signal indicating the relative displacement of the beam spot on the light detection surface of the light detection unit is obtained. This signal is multiplied by a predetermined coefficient to obtain a signal corresponding to the offset. Then, a signal corresponding to the offset is subtracted from the signal indicating the relative displacement between the recording track and the objective lens, and a tracking error signal from which the offset is removed is obtained.

  Based on the tracking error signal acquired as described above, control is performed so that the beam spot formed on the optical disk is positioned on a predetermined recording track.

  As described above, the light detection means has the first to fourth light detection units in the direction corresponding to the radial direction of the optical disk in order to obtain the tracking error signal, and the number of divisions is relatively small. A decrease in the S / N of the reproduction signal obtained from the light detection means can be suppressed.

  In addition, the light detection means has a first to a fourth light detection unit in a direction corresponding to the radial direction of the optical disk in order to obtain a tracking error signal, and a beam spot formed on the light detection surface is recorded. Even in the case of a shift in the direction corresponding to the longitudinal direction (tangential direction) of the track, the push-pull interference region may enter the second and third light detection units for obtaining a signal corresponding to the offset. The signal corresponding to the offset (the signal for removing the offset) can be obtained with high accuracy.

  Each of the first and third dividing lines is a center position in the direction corresponding to the longitudinal direction of the recording track, and the distance w between the first dividing line and the second dividing line is {(λ / NA) * (1 / Tp) -1} -d ≧ w> 0. Therefore, even if the objective lens is displaced in the radial direction and the beam spot formed on the light detection surface of the light detection means is displaced in a direction corresponding to the radial direction, The state in which the region including the primary light interference region and the other regions are divided is maintained. Similarly, even if the objective lens is displaced in the radial direction and the beam spot formed on the light detection surface of the light detection means is displaced in a direction corresponding to this radial direction, The state in which the region including the interference region of the + 1st order light and the other region are divided is maintained.

  Therefore, even if the objective lens is displaced in the radial direction in the second and third light detection units, and the beam spot formed on the light detection surface of the light detection means is displaced in a direction corresponding to the radial direction, Of the beam spot, a region not including the interference region of the zero-order light and the ± first-order light is formed. As a result, the signal indicating the relative displacement of the beam spot on the light detection surface of the light detection means, which is obtained by performing the calculation for obtaining the difference between the detection outputs of the second and third light detection units, is the interference region. Therefore, a signal corresponding to the offset obtained based on this signal can always be obtained with high accuracy, and a tracking error signal can always be obtained with high accuracy.

  An optical disc apparatus according to the present invention is formed on a light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disc on which recording tracks are formed spirally or concentrically, and formed on the optical disc. An error signal generating means for generating a tracking error signal corresponding to the deviation of the beam spot from a predetermined recording track in the radial direction of the optical disk using reflected light from the beam spot, and based on the tracking error signal Tracking control means for controlling the beam spot to be positioned on a predetermined recording track.

  Then, the error signal generating means is arranged in the optical path of the reflected light, a diffraction means for obtaining the main beam and the side beam, and a beam spot by the main beam is formed on the light detection surface, and in a direction corresponding to the radial direction, Of first-order light detection means having first and second light detection sections divided by a dividing line that is a straight line extending in a direction corresponding to the longitudinal direction of the recording track, and zero-order light among beam spots by side beams. And a region not including the ± 1st order light interference region is formed on the light detection surface, and is divided by a dividing line which is a straight line extending in a direction corresponding to the radial direction in a direction corresponding to the radial direction. The recording track is calculated by calculating the difference between the detection outputs of the second light detection unit having the second light detection unit and the first and second light detection units of the first light detection unit. The first light that obtains a signal indicating the relative displacement of the object lens and the first light that is detected by the first and second light detection units of the second light detection means are calculated to obtain the first light. Second computing means for obtaining a signal indicating the relative displacement of the beam spot on the light detection surface of the detecting means; multiplying means for multiplying an output signal of the second computing means by a predetermined coefficient; and first computing means And a third calculation means for obtaining a tracking error signal by calculating a difference between the output signal and the output signal of the multiplication means.

  The optical pickup according to the present invention includes a light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disc having a recording track formed in a spiral shape or a concentric shape, and a reflected light. Diffracting means for obtaining a main beam and a side beam and a beam spot by the main beam are formed on the light detection surface in a direction corresponding to the radial direction of the optical disc perpendicular to the longitudinal direction of the recording track, Of first-order light detection means having first and second light detection sections divided by a dividing line that is a straight line extending in a direction corresponding to the longitudinal direction of the recording track, and zero-order light among beam spots by side beams. An area that does not include the ± 1st order light interference area is formed on the light detection surface, and the recording track extends in a direction corresponding to the radial direction. First divided by the dividing line is a straight line extending in a direction corresponding to the longitudinal direction of the one in which and a second light detecting means having a second light detector.

  In the present invention, a light beam is condensed by an objective lens on an optical disk on which recording tracks are formed spirally or concentrically to form a beam spot. Then, using the reflected light from the beam spot, a tracking error signal corresponding to the deviation of the beam spot from a predetermined recording track in the radial direction of the optical disc is generated.

  In this case, a diffractive means is disposed in the optical path of the reflected light, and a main beam and a side beam are obtained. A beam spot by the main beam is formed on the light detection surface of the first light detection means. The first photodetecting means has first and second photodetecting sections divided in a direction corresponding to the radial direction of the optical disc by a dividing line that is a straight line extending in a direction corresponding to the longitudinal direction of the recording track. It is supposed to be. An operation for obtaining the difference between the detection outputs of the first and second light detection units is performed, and a signal indicating the relative displacement between the recording track and the objective lens is obtained. This signal corresponds to a tracking error signal by a simple push-pull method, and an offset occurs when the objective lens is displaced in the radial direction.

  Of the beam spot by the side beam, a region not including the interference region of the zero-order light and the ± first-order light is formed on the light detection surface of the second light detection means. The second photodetecting means has first and second photodetecting units divided in a direction corresponding to the radial direction of the optical disc by a dividing line that is a straight line extending in a direction corresponding to the longitudinal direction of the recording track. It is supposed to be. A calculation is performed to obtain a difference between the detection outputs of the first and second light detection units, and a signal indicating the relative displacement of the beam spot on the light detection surface of the first light detection means is obtained.

  A signal corresponding to the offset is obtained by multiplying the signal indicating the relative displacement of the beam spot by a predetermined coefficient. Then, a signal corresponding to the offset is subtracted from the signal indicating the relative displacement between the recording track and the objective lens, and a tracking error signal from which the offset is removed is obtained.

  Based on the tracking error signal acquired as described above, control is performed so that the beam spot formed on the optical disk is positioned on a predetermined recording track.

  Thus, a signal indicating the relative displacement of the beam spot on the light detection surface of the first light detection means is obtained by using the second light detection means, and the first light detection means has a tracking error. In order to obtain a signal, the first and second light detection units are provided in a direction corresponding to the radial direction of the optical disk, and the number of divisions is small. Therefore, the reproduction signal obtained from the first light detection means A decrease in S / N can be suppressed.

  The second photodetecting means is divided into first and second division lines that are straight lines extending in a direction corresponding to the longitudinal direction (tangential direction) of the recording track in a direction corresponding to the radial direction of the optical disc. Even if the beam spot formed on the light detection surface is shifted in the direction corresponding to the longitudinal direction of the recording track (tangential direction), the push-pull interference region is offset. The signal corresponding to the offset (signal for removing the offset) can be obtained with high accuracy without entering the second and third light detection units for obtaining the signal corresponding to.

  For example, the shape of the end of the second photodetecting means opposite to the dividing line of the first and second photodetecting parts is respectively the dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track. The curve shape is the closest. For this reason, the first and second photodetecting portions have the narrowest width at the center position in the direction corresponding to the longitudinal direction of the recording track, and the width increases as the distance from the center position increases. Therefore, as described above, a signal indicating the relative displacement of the beam spot on the photodetecting surface of the photodetecting means can be obtained by performing the calculation for obtaining the difference between the detection outputs of the first and second photodetecting units. However, the detection sensitivity can be increased.

  Further, for example, the radius of the beam spot on the light detection surface of the second light detection means is set to 1, and the maximum value of the magnitude of displacement in the direction corresponding to the radial direction of the beam spot on the light detection surface is When the radius of the beam spot is d times, the wavelength of the light beam is λ, the numerical aperture of the objective lens is NA, and the pitch of the recording track is Tp. The ends opposite to the dividing lines are center positions in the direction corresponding to the longitudinal direction of the recording track, and the distance w between the dividing lines is {(λ / NA) * (1 / Tp ) -1} -d ≧ w> 0.

  In this case, at the end of the first light detection unit, the objective lens is displaced in the radial direction, and the beam spot formed on the light detection surface of the second light detection unit is displaced in a direction corresponding to the radial direction. However, the state in which the region including the interference region of the 0th-order light and the −1st-order light and the other regions are divided is maintained. Similarly, at the end of the second light detection section, the objective lens is displaced in the radial direction, and the beam spot formed on the light detection surface of the second light detection means is displaced in a direction corresponding to this radial direction. However, the state in which the region including the interference region of the 0th-order light and the + 1st-order light and the other region are divided is maintained.

  Therefore, in the first and second light detection units, the objective lens is displaced in the radial direction, and the beam spot formed on the light detection surface of the second light detection means is displaced in a direction corresponding to the radial direction. However, a region that does not include the interference region of the zero-order light and the ± first-order light is formed in the beam spot. As a result, a signal indicating the relative displacement of the beam spot on the light detection surface of the first light detection means, which is obtained by calculating the difference between the detection outputs of the first and second light detection units, is Therefore, a signal corresponding to the offset obtained based on this signal can always be obtained with high accuracy, and a tracking error signal can always be obtained with high accuracy.

  According to the present invention, a beam spot formed on an optical disc is used to remove a signal included in a tracking error signal by the push-pull method to remove an offset accompanying displacement of the light detection surface or displacement of the objective lens in the radial direction. The first to fourth light beams divided by the first, second and third dividing lines in the direction corresponding to the radial direction of the optical disk are detected by the light detection means in which the beam spot by the reflected light from the light is formed on the light detection surface. The second and third light detectors are configured to have a detection unit, and the second and third light detection units are configured so that regions that do not include the interference region of the zero-order light and the ± first-order light are located in the second and third light detection units. This is obtained by calculating the difference between the detection outputs of the light detection units, and the number of divisions of the light detection means can be made relatively small, the S / N reduction of the reproduction signal can be suppressed, and light detection can be performed. It can be a beam spot formed to obtain good signal accuracy for removing longitudinally offset even when displaced in a direction corresponding to a (tangential direction) of the recording track.

  Further, according to the present invention, the signal for removing the offset accompanying the displacement of the light detection surface or the displacement of the objective lens in the radial direction included in the tracking error signal by the push-pull method is formed on the optical disc. A diffraction means for obtaining a main beam and a side beam is provided in the optical path of the reflected light from the beam spot, and the area not including the interference area of the 0th order light and ± 1st order light among the beam spots by the side beam is the light detection surface. And a second photodetection means having first and second photodetection units divided by a dividing line in a direction corresponding to the radial direction of the optical disc. This is obtained by calculating the difference between the detection outputs, and increasing the number of divisions of the first light detection means in which the beam spot by the main beam is formed on the light detection surface. In addition to being able to suppress a decrease in the S / N of the reproduction signal, an offset is also provided when the beam spot formed on the light detection surface is shifted in a direction corresponding to the longitudinal direction (tangential direction) of the recording track. A signal for removal can be obtained with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a DVD player 100 as an embodiment.

  The DVD player 100 has a system controller 101 including a microcomputer (not shown) that controls the operation of the entire player. The system controller 101 is connected to, for example, a display unit 102 that is configured by a liquid crystal display element and displays the state of the apparatus and the like, and an operation key unit 103 provided with a plurality of input keys for user operation. Yes.

  The DVD player 100 includes a spindle motor 105 for rotationally driving a DVD 104 as an optical disk, an optical pickup 106 including a laser diode, an objective lens, a photodetector, and the like, and the optical pickup 106 is arranged in the radial direction of the DVD 104 (radial). And a feed motor 107 for moving in the direction). In this case, the recording surface of the DVD 104 is irradiated with a laser beam from a laser diode that constitutes the optical pickup 106, and the reflected light is emitted to a photodetector that constitutes the optical pickup 106.

  Further, the DVD player 100 has a servo control circuit 108. The servo control circuit 108 controls tracking and focus in the optical pickup 106 and controls the operation of the feed motor 107. Further, the servo control circuit 108 controls the rotation of the spindle motor 105. Thereby, when the DVD 104 is reproduced, the DVD 104 is rotationally driven by CLV (Constant Linear Velocity).

Further, the DVD player 100 computes and amplifies the output signals of the plurality of photodetectors of the optical pickup 106, and reproduces the signal S _RF , the focus error signal S _FE by the astigmatism method, and the tracking error signal S _TE by the push-pull method. Has an RF amplifier unit 109. The RF amplifier 109 supplies the generated focus error signal _SFE and tracking error signal _STE to the servo control circuit 108. The servo control circuit 108 uses these error signals S _FE and S _TE to control tracking and focus in the optical pickup 106 as described above.

  Although not described above, a beam spot is formed on the DVD 104 by the optical pickup 106. Focus control is control for keeping the distance between the recording surface of the DVD 104 and the objective lens constant so that the light beam is condensed on the recording surface of the DVD 104. Tracking control is control for positioning the beam spot on a predetermined recording track of the DVD 104.

Also, the DVD player 100 is a read channel that performs a series of analog signal processing such as binarized slices of the reproduction signal S _RF generated by the RF amplifier unit 109 and generation of synchronous data by subsequent PLL (Phase-Locked Loop). Part 110. The read channel unit 110 also has functions such as generation of the CLV control signal S _CLV . The read channel unit 110 supplies the generated CLV control signal S _CLV to the servo control circuit 108. The servo control circuit 108 uses the CLV control signal S _CLV to control the rotation of the spindle motor 105 as described above.

  In addition, the DVD player 100 includes a demodulation / ECC unit 111 that performs processing such as demodulation of the synchronization data (8/16 modulation data) generated by the read channel unit 110 and subsequent error correction, and the demodulation / ECC unit 111. And a demultiplexer 112 that separates video data, audio data, sub-picture data, and the like from the output data stream.

  In addition, the DVD player 100 performs a data expansion process on the compressed video data separated by the demultiplexer 112 to obtain video data Va, and processes the sub-picture data separated by the demultiplexer 112. A sub-picture decoder 114 that obtains display data Sa for displaying subtitles and the like; and a synthesizer 115 that synthesizes the display data Sa obtained by the sub-picture decoder 114 with the video data Va obtained by the video decoder 113. ing.

  The DVD player 100 uses the video data output from the synthesizer 115 to generate, for example, an NTSC video data VD, a TV encoder 116, converts the video data VD into an analog signal, and converts the video signal SV into an analog signal. A DA converter 117 to be obtained, and an output terminal 118 for outputting the video signal SV.

  The DVD player 100 also performs an audio decoder 119 to obtain audio data AD by performing a data expansion process on the compressed audio data separated by the demultiplexer 112, and converts the audio data AD into an analog signal to convert the audio signal SA. A DA converter 120 for obtaining the sound signal SA, and an output terminal 121 for outputting the audio signal SA.

The operation of the DVD player 100 shown in FIG. 1 will be described.
When playback is instructed by the user operating the operation key unit 103, the spindle motor 105 starts to rotate under the control of the servo control circuit 108, the DVD 104 is driven to rotate at CLV, and playback starts.

The reproduction signal S _RF obtained from the RF amplifier unit 109 is supplied to the read channel unit 110, and the read channel unit 110 performs binarization slice processing, generation processing of synchronization data by PLL, and the like. The synchronization data output from the read channel unit 110 is supplied to the demodulation / ECC unit 111, and the demodulation / ECC unit 111 performs demodulation processing and error correction processing. The data stream from the demodulation / ECC unit 111 is supplied to the demultiplexer 112. In the demultiplexer 112, video data, audio data, and sub-picture data are separated from the data stream.

  The video data (MPEG2 video data) separated by the demultiplexer 112 is supplied to the video decoder 113 and subjected to data expansion processing. The sub picture data separated by the demultiplexer 112 is supplied to the sub picture decoder 114. Then, based on the operation of the operation key unit 103 by the user, the sub picture decoder 114 performs a decoding process to generate display data Sa for displaying subtitles and the like. This display data Sa is combined with the video data Va from the video decoder 113 by the combiner 115. As a result, subtitles and the like are superimposed on the reproduced image.

  The video data output from the synthesizer 115 is supplied to the TV encoder 116 and converted into, for example, NTSC video data VD. This video data VD is converted by the DA converter 117 into an analog video signal SV. The video signal SV is output to the output terminal 118. By supplying the video signal SV to a monitor (not shown), an image based on the video signal SV, that is, a reproduced image of the DVD 104 is displayed on the monitor screen.

  The audio data (AC3 data or the like) separated by the demultiplexer 112 is supplied to the audio decoder 119 and subjected to data expansion processing. The audio data AD obtained by the audio decoder 119 is converted into an analog audio signal SA by the DA converter 120. The audio signal SA is output to the output terminal 121. By amplifying this audio signal SA and supplying it to a speaker or the like (not shown), audio corresponding to the image displayed on the monitor described above is output.

Next, the optical system of the optical pickup 106 will be described. FIG. 2 shows the configuration of the optical system.
The optical pickup 106 includes a laser diode 151 that generates a laser beam as a light beam, a beam splitter 152, a collimator lens 153, and an objective lens 154. The beam splitter 152 transmits the laser beam from the laser diode 151 and reflects reflected light from the beam spot formed on the DVD 104. The collimator lens 153 shapes the laser beam from divergent light to parallel light. The objective lens 154 focuses the laser beam and forms a beam spot on the DVD 104.

The optical pickup 106 includes a cylindrical lens 155 and a photo detector 156. The cylindrical lens 155 is used to obtain a focus error signal by the astigmatism method. The photodetector 156 constitutes a light detection means for obtaining a reproduction signal S _RF , a focus error signal S _FE , and a tracking error signal S _TE .

  The operation of the optical system of the optical pickup 106 shown in FIG. 2 will be described. The laser beam as diverging light from the laser diode 151 passes through the beam splitter 152 and then shaped into parallel light by the collimator lens 153. The laser beam shaped into the parallel light is condensed on the DVD 104 by the objective lens 154, and a beam spot is formed on the DVD 104.

  Further, the laser beam as reflected light from the beam spot formed on the DVD 104 is reflected by the beam splitter 152 after passing through the objective lens 154 and the collimator lens 153, and further passed through the cylindrical lens 155 to the photodetector 156. Incident.

FIG. 3 shows the configuration of the photodetector 156. The photodetector 156 is composed of one 8-divided photodiode portion 161. On the light detection surface of the photodiode portion 161, a beam spot BS is formed by the laser beam as the reflected light described above. This beam spot BS has an interference region P ₋ where the 0th-order light and the −1st-order light overlap and an interference region P ₊ where the 0th-order light and the + 1st-order light overlap as shown by hatching in FIG.

The photodiode portion 161 is divided into a first dividing line L _D1 , a second dividing line L _D2, and a third dividing line L _D3 in the direction x corresponding to the radial direction of the DVD 104. It has a light detection part.

In this case, the second dividing line L _D2 is a straight line extending in the direction y corresponding to the longitudinal direction of the recording track formed on the DVD 104. The first dividing line L _D1 divides the region including the interference region P ₋ of the beam spot BS and the other region, and has a parabolic shape closest to the second dividing line L _D2 at the center position in the direction y. It is a curve. Similarly, the third dividing line L _D3 divides the area including the interference area P ₊ of the beam spot BS and the other area, and is closest to the second dividing line L _D2 at the center position in the direction y. It is a parabolic curve.

The photodiode unit 161 is divided into two in the direction y by a dividing line L _D4 that is a straight line extending in the direction x in order to obtain a focus error signal by the astigmatism method. Therefore, each of the first to fourth light detection units described above is composed of two photodiodes. That is, the first photodetection unit is composed of photodiodes Da1 and Db1, the second photodetection unit is composed of photodiodes Da2 and Db2, the third photodetection unit is composed of photodiodes Dd2 and Dc2, and the fourth The light detection unit is composed of photodiodes Dd1 and Dc1.

Here, as shown in FIG. 4, if the radius of the beam spot BS (the beam spot by the 0th order light) is 1, the center of the beam spot BS and the beam spot BS _{± 1} by the ± first order light (this radius is also 1) is given by equation (1). Here, λ is the wavelength of the laser beam, NA is the numerical aperture of the objective lens 154, and Tp is the pitch of the recording track formed on the DVD 104.
L = (λ / NA) * (1 / Tp) (1)

  When the objective lens 154 is displaced in the radial direction, the beam spot BS formed on the light detection surface of the photodiode portion 161 is displaced in the direction x corresponding to the radial direction. The maximum value of the displacement is uniquely determined by the maximum value of the displacement of the objective lens 154 in the radial direction. Here, the maximum value of the displacement in the direction x of the beam spot BS is set to d times the radius of the beam spot BS.

The above-described first and third dividing lines L _D1 and L _D3 are respectively the center positions in the above-described direction y, and the distance w (shown in FIG. 3) from the second dividing line L _D2 is (2). To satisfy the formula. As a result, even if the objective lens 154 is displaced in the radial direction and the beam spot BS is displaced in the direction x, the first and third dividing lines L _D1 and L _D3 have the interference regions P ₋ and P ₊ respectively. The state in which the including area and the other area are divided is maintained.
{(Λ / NA) * (1 / Tp) −1} −d ≧ w> 0 (2)

Next, generation processing of the reproduction signal S _RF , the focus error signal S _FE , and the tracking error signal S _{TE in} the RF amplifier unit 109 will be described.
In the optical pickup 106, detection outputs are obtained corresponding to the photodiodes of the photodiode unit 161, respectively. That is, incident light (optical signal) is converted into a current signal in the photodiode, and this current signal is further converted into a voltage signal by a current / voltage converter and amplified to be a detection output. From the optical pickup 106 to the RF amplifier unit 109, detection outputs Sa1, Sa2, Sb1, Sb2, eight photodiodes Da1, Da2, Db1, Db2, Dc1, Dc2, Dd1, Dd2 constituting the photodiode unit 161 are provided. Sc1, Sc2, Sd1, and Sd2 are supplied.

The RF amplifier unit 109, all the detection output Sa1, Sa2, Sb1, Sb2, Sc1, Sc2, Sd1, Sd2 is added, the added signal (Sa1 + Sa2 + Sb1 + Sb2 + Sc1 + Sc2 + Sd1 + Sd2) is amplified by reproduced signal S _RF is generated. In addition, the RF amplifier unit 109 generates a focus error signal _SFE based on the astigmatism method based on the equation (3).
S _FE = (Sa1 + Sa2 + Sc1 + Sc2) − (Sb1 + Sb2 + Sd1 + Sd2) (3)

In the RF amplifier unit 109, the tracking error signal _STE is generated based on the equation (4).
S _TE = {(Sd1 + Sd2 + Sc1 + Sc2) − (Sa1 + Sa2 + Sb1 + Sb2)}
-K {(Sd2 + Sc2)-(Sa2 + Sb2)} (4)

In this equation (4), the term {(Sd1 + Sd2 + Sc1 + Sc2) − (Sa1 + Sa2 + Sb1 + Sb2)} corresponds to a tracking error signal by a simple push-pull method, and the displacement of the light detection surface or the displacement of the objective lens 154 in the radial direction. When this occurs, an offset occurs. In the equation (4), the term k {(Sd2 + Sc2) − (Sa2 + Sb2)} is a signal {(Sd2 + Sc2) indicating the relative displacement of the beam spot BS on the light detection surface of the photodiode portion 161 in the direction x. ) − (Sa2 + Sb2)} multiplied by a coefficient k, which corresponds to the offset generated in the tracking error signal by the simple push-pull method described above. Accordingly, the tracking error signal S _TE is generated based on equation (4) is a tracking error signal offset is removed.

  Note that the coefficient k in the equation (4) is determined so that, for example, the objective lens 154 is intentionally displaced in the radial direction in the focused state at the time of manufacture so that no offset occurs in the tracking error signal. That's fine. This is the same as the DPP balance adjustment in the well-known DPP (Differential Push Pull) method.

In the RF amplifier unit 109, the tracking error signal _STE is generated by the circuit of FIG. That is, the detection outputs Sd1, Sd2, Sc1, and Sc2 are added by the adders 201 to 203, and the detection outputs Sa1, Sa2, Sb1, and Sb2 are added by the adders 204 to 206. The subtracter 207 subtracts the output of the adder 206 from the output of the adder 203 to obtain a tracking error signal S _TE ′ = {(Sd1 + Sd2 + Sc1 + Sc2) − (Sa1 + Sa2 + Sb1 + Sb2)} by a simple push-pull method.

The adder 208 adds the detection outputs Sd2 and Sc2, and the adder 209 adds the detection outputs Sa2 and Sb2. Then, the subtracter 210 subtracts the output of the adder 209 from the output of the adder 208, and further multiplies the subtracted output by a coefficient k in the multiplier 211, and the tracking error signal S _TE 'by the simple push-pull method described above. Thus, the offset S _OF = k {(Sd2 + Sc2)-(Sa2 + Sb2)} occurring in the above is obtained. Then, the subtractor 212 subtracts the offset S _OF which is the output of the multiplier 211 from the tracking error signal S _TE ′ by the simple push-pull method, which is the output of the subtractor 207, and the tracking error signal S from which the offset is removed. _TE is obtained.

In the above-described embodiment, the tracking error signal S _TE is basically obtained by the push-pull method. This tracking error signal S _TE is included in the tracking error signal S _TE ′ by the simple push-pull method. The offset S _OF is removed. Therefore, in the tracking control based on the tracking error signal _STE , the tracking control can be performed satisfactorily without detracking due to the offset.

Also, in the above-described embodiment, the photodiode section 161 which constitute the photodetector 156, in order to obtain a tracking error signal S _TE, the first to fourth light detection unit in a direction x which corresponds to the radial direction of the DVD104 It is the composition which has. Therefore, when the astigmatism method is not used for the focus error signal S _FE , the number of divisions of the photodiode portion 161 may be four, the number of divisions can be relatively small, and the S / N of the reproduction signal S _RF is reduced. Can be suppressed.

Also, in the above-described embodiment, the photodiode section 161 which constitute the photodetector 156, in order to obtain a tracking error signal S _TE, the first to fourth light detection unit in a direction x which corresponds to the radial direction of the DVD104 It is the composition which has. Therefore, even when the beam spot BS formed on the light detection surface is shifted in the direction y corresponding to the longitudinal direction (tangential direction) of the recording track, the push-pull interference region obtains a signal corresponding to the offset. Therefore, the signal corresponding to the offset (signal for removing the offset) can be obtained with high accuracy without entering the second and third light detection units.

Further, in the above-described embodiment, the first and third dividing lines L _D1 and L _D3 in the photodiode portion 161 are each at the center position in the direction y corresponding to the longitudinal direction of the recording track. The curve is closest to L _D2 . For this reason, the second photodetection section (consisting of photodiodes Da2 and Db2) and the third photodetection section (comprising photodiodes Dd2 and Dc2) are located at the center position in the direction y corresponding to the longitudinal direction of the recording track. The width is narrowest, and the width becomes wider as the distance from the center position increases. Therefore, as described above, a signal indicating the relative displacement of the beam spot BS on the light detection surface of the photodiode portion 161 is obtained by performing the calculation of the difference between the detection outputs of the second and third light detection portions. (Sd2 + Sc2)-(Sa2 + Sb2)} is obtained, but the detection sensitivity can be increased.

Further, in the above-described embodiment, the first and third dividing lines L _D1 and L _D3 of the photodiode portion 161 are respectively distances from the second dividing line L _D2 at the center position in the direction y described above. w is made to satisfy the equation (2). Therefore, even if the objective lens 154 is displaced in the radial direction and the beam spot BS is displaced in the direction x, the first and third dividing lines L _D1 and L _D3 include the interference regions P ₋ and P ₊ , respectively. The state where the area and the other area are divided is maintained.

Therefore, even if the objective lens 154 is displaced in the radial direction and the beam spot BS formed on the light detection surface of the photodiode portion 161 is displaced in the direction x, the beam spot is not detected in the second and third photodetectors. In the BS, a region not including the interference regions P ₋ and P ₊ of the 0th order light and the ± 1st order light is formed. As a result, a signal {() indicating the relative displacement of the beam spot BS on the light detection surface of the photodiode portion 161, which is obtained by performing a calculation of the difference between the detection outputs of the second and third light detection portions. Sd2 + Sc2) − (Sa2 + Sb2)} is not affected by the interference area interference areas P ₋ and P ₊ , and the offset S _OF based on this signal can always be obtained with high accuracy, and therefore the tracking error signal _STE is always high. It can be obtained with accuracy.

In the above embodiment, each of the first and third dividing lines L _D1 and L _D3 is a parabolic curve, but as shown in FIG. 6A, a straight line extending in the direction y, or As shown in FIG. 6B, it may be a polygonal curve in which the center position in the direction y is a break point.

Next, another embodiment of the present invention will be described. Although not shown, the DVD player as another embodiment differs in the configuration of the optical pickup 106 and the generation processing of the reproduction signal S _RF , the focus error signal S _FE , and the tracking error signal S _{TE in} the RF amplifier unit 109. The overall configuration is the same as that of the DVD player 100 shown in FIG.

  The optical system of the optical pickup 106 will be described. FIG. 7 shows the configuration of the optical system. In FIG. 7, parts corresponding to those in FIG.

  The optical pickup 106 includes a laser diode 151 that generates a laser beam as a light beam, a beam splitter 152, a collimator lens 153, and an objective lens 154. The beam splitter 152 transmits the laser beam from the laser diode 151 and reflects reflected light from the beam spot formed on the DVD 104. The collimator lens 153 shapes the laser beam from divergent light to parallel light. The objective lens 154 focuses the laser beam and forms a beam spot on the DVD 104.

Further, the optical pickup 106 includes a grating (diffraction grating) 157 as a diffraction means, a cylindrical lens 155, and a photodetector 156A. The grating 157 is disposed in the optical path of the reflected light of the beam spot formed on the DVD 104, and is used to obtain a main beam composed of 0th order light and a side beam composed of ± 1st order light. The split light quantity ratio of the grating 157 is, for example, 85% for 0th order light and 6% for ± 1st order light. The cylindrical lens 155 is used to obtain a focus error signal by the astigmatism method. The photodetector 156A constitutes a light detection means for obtaining a reproduction signal S _RF , a focus error signal S _FE , and a tracking error signal S _TE .

  The operation of the optical system of the optical pickup 106 shown in FIG. 7 will be described. The laser beam as diverging light from the laser diode 151 passes through the beam splitter 152 and then shaped into parallel light by the collimator lens 153. The laser beam shaped into the parallel light is condensed on the DVD 104 by the objective lens 154, and a beam spot is formed on the DVD 104.

  The laser beam as reflected light from the beam spot formed on the DVD 104 is reflected by the beam splitter 152 after passing through the objective lens 154 and the collimator lens 153, and is input to the grating 157. The grating 157 provides a main beam of 0th order light and a side beam of ± 1st order light. The main beam and the side beam are incident on the photodetector 156A via the cylindrical lens 155.

FIG. 8 shows the configuration of the photodetector 156A. The photodetector 156A includes three quadrant photodiode portions 161M, 161S ₋ and 161S ₊ . Here, the photodiode portion 161M constitutes a first light detection means, and the photodiode portions 161S _- and 161S ₊ constitute a second light detection means.

The light detecting surface of the photodiode section 161 M, the beam spot BS ₀ is formed by the main beam of the 0 order light described above. This beam spot BS ₀ has an interference region P _{− in} which the 0th-order light and the −first-order light overlap and an interference region P _{+ in} which the 0th-order light and the + 1st-order light overlap are shown by hatching in FIG. . Note that the 0th-order light and ± 1st-order light here are not caused by the grating 157 but are caused by diffraction by pits formed on the recording track of the DVD 104.

Photodiode section 161M in the direction x which corresponds to the radial direction of the DVD 104, along with being divided into two by a straight line L _D11 extending in a direction y which corresponds to the longitudinal direction of the recording tracks formed on the DVD 104, in the direction y, direction x It is divided into two by a straight line L _D12 extending in the direction of 4 and has four photodiodes Da, Db, Dc, Dd. Here, the photodiodes Da and Db constitute a first photodetection unit, and the photodiodes Dc and Dd constitute a second photodetection unit. These first and second light detection units are used to obtain a push-pull signal.

On the light detection surface of the photodiode portion 161S _−, the beam spot BS ₋₁ by the side beam of the −1st order light described above is formed. Similarly to the beam spot BS ₀ by the main beam described above, the beam spot BS _{-1 is} also shown by hatching in FIG. 8, the interference region P ₋ where the 0th order light and the −first order light overlap, the 0th order light and It has an interference region P ₊ where + 1st order light overlaps.

The photodiode portion 161S ₋ has four photodiodes De ′, De, Df divided in the direction x by the first dividing line L _D21 , the second dividing line L _D22, and the third dividing line L _D23 . , Df ′. In this case, the second dividing line L _D22 is a straight line extending in the direction y. The first dividing line L _D21 divides the area including the interference area P ₋ of the beam spot BS ₋₁ and the other areas, and is a parabola closest to the second dividing line L _D22 at the center position in the direction y. It is a curved line. Similarly, the third dividing line L _D23 divides the area including the interference area P ₊ of the beam spot BS ₋₁ and the other areas, and at the center position in the direction y, the third dividing line L _D23 becomes the second dividing line L _D22 . It is the parabolic curve that is closest.

Here, the photodiodes De and Df constitute first and second light detection units, respectively, and using the detection outputs of the first and second light detection units, as will be described later, the photodiode unit. A signal indicating the relative displacement of the beam spot BS ₀ on the 161M light detection surface is generated. In this case, regions of the beam spot BS _-1 that do not include the interference regions P ₋ and P ₊ are formed on the light detection surfaces of the first and second light detection units (photodiodes De and Df). Further, the shapes of the end portions of the first and second light detection portions (photodiodes De, Df) on the side opposite to the second dividing line L _D22 are the center positions in the direction y, respectively. The curve shape is closest to the dividing line L _D22 . Note that the photodiodes De ′ and Df ′ are not actually required and therefore may not be necessary.

Further, the first and third dividing lines L _D21 and L _D23 are respectively in the same direction y as the first and third dividing lines L _D1 and L _{D3 of the} photodiode portion 161 (see FIG. 3). The distance w (shown in FIG. 8) with the second dividing line L _D22 is set so as to satisfy the above-described expression (2). As a result, even if the objective lens 154 is displaced in the radial direction and the beam spot BS- ₁ is displaced in the direction x, the first and third dividing lines L _D21 and L _D23 are respectively in the interference regions P ₋ and P D. _The state where the area including ₊ and the other area are divided is maintained.

On the light detection surface of the photodiode portion 161S _+, the beam spot BS _{+ 1} by the side beam of the ₊ 1st order light described above is formed. Similarly to the beam spot BS ₀ by the main beam described above, the beam spot BS _{+1 is} also shown by hatching in FIG. 8, the interference region P ₋ where the 0th order light and the −first order light overlap, the 0th order light and It has an interference region P ₊ where + 1st order light overlaps.

The photodiode portion 161S ₊ includes four photodiodes Dg ′, Dg, Dh divided in the direction x by the first dividing line L _D31 , the second dividing line L _D32, and the third dividing line L _D33 . , Dh ′. In this case, the second dividing line L _D32 is a straight line extending in the direction y. The first dividing line L _D31 divides the area including the interference area P ₋ of the beam spot BS ₊₁ and the other area, and a parabola that is closest to the second dividing line L _D32 at the center position in the direction y. It is a curved line. Similarly, the third dividing line L _D33 divides the area including the interference area P ₊ of the beam spot BS ₊₁ and the other areas, and at the center position in the direction y, the third dividing line L _D33 becomes the second dividing line L _D32 . It is the parabolic curve that is closest.

Here, the photodiodes Dg and Dh constitute first and second light detection units, respectively, and using the detection outputs of the first and second light detection units, as will be described later, the photodiode unit. A signal indicating the relative displacement of the beam spot BS ₀ on the 161M light detection surface is generated. In this case, in this case, regions that do not include the interference regions P ₋ and P ₊ out of the beam spot BS ₊₁ are formed on the light detection surfaces of the first and second light detection units (photodiodes Dg and Dh). Is done. In addition, the shape of the end of the first and second light detection units (photodiodes Dg, Dh) on the opposite side to the second dividing line L _D32 is the center position in the direction y, respectively. The curve shape is closest to the dividing line L _D32 . Note that the photodiodes Dg ′ and Dh ′ are not actually required and therefore may not be necessary.

Further, the first and third dividing lines L _D31 and L _D33 are respectively in the direction y similarly to the first and third dividing lines L _D1 and L _{D3 of the} photodiode portion 161 (see FIG. 3). The distance w (shown in FIG. 8) with the second dividing line L _D32 is set so as to satisfy the above-described expression (2). Thereby, even if the objective lens 154 is displaced in the radial direction and the beam spot BS _{+ 1} is displaced in the direction x, the first and third dividing lines L _D31 and L _D33 are respectively in the interference regions P ₋ and P D. _The state where the area including ₊ and the other area are divided is maintained.

Next, generation processing of the reproduction signal S _RF , the focus error signal S _FE , and the tracking error signal S _{TE in} the RF amplifier unit 109 will be described.

In the optical pickup 106, detection outputs are obtained corresponding to the photodiodes of the photodiode portions 161M, 161S ₋ and 161S ₊ . That is, incident light (optical signal) is converted into a current signal in the photodiode, and this current signal is further converted into a voltage signal by a current / voltage converter and amplified to be a detection output. From the optical pickup 106 to the RF amplifier unit 109, detection outputs Sa, eight photodiodes Da, Db, Dc, Dd, De, Df, Dg, Dh constituting the photodiode units 161M, 161S ₋ , 161S ₊ , Sb, Sc, Sd, Se, Sf, Sg, Sh are supplied.

In the RF amplifier unit 109, all of the detection outputs Sa, Sb, Sc, Sd, Se, Sf, Sg, Sh are added, and the added signal (Sa + Sb + Sc + Sd + Se + Sf + Sg + Sh) is amplified to generate a reproduction signal _SRF . Further, the RF amplifier unit 109 generates a focus error signal _SFE based on the astigmatism method based on the equation (5).
S _FE = (Sa + Sc) − (Sb + Sd) (5)

Further, in the RF amplifier unit 109, the tracking error signal _STE is generated based on the equation (6).
S _TE = {(Sd + Sc) − (Sa + Sb)} − k {(Sf + Sh) − (Se + Sg)}
... (6)

In this equation (6), the term {(Sd + Sc) − (Sa + Sb)} corresponds to a tracking error signal by a simple push-pull method, and the displacement of the light detection surface or the displacement of the objective lens 154 in the radial direction. When this occurs, an offset occurs. Further, in the equation (6), the term k {(Sf + Sh) − (Se + Sg)} is a signal indicating the relative displacement of the beam spot BS ₀ on the light detection surface of the photodiode portion 161M in the direction x {( Sf + Sh) − (Se + Sg)} is multiplied by a coefficient k, and corresponds to the offset generated in the tracking error signal by the simple push-pull method described above. Accordingly, the tracking error signal S _TE is generated based on equation (6) is a tracking error signal offset is removed.

  Note that the coefficient k in the equation (6) is the same as the coefficient k in the equation (4) described above. For example, the objective lens 154 is intentionally displaced in the radial direction in the focused state at the time of manufacturing. The tracking error signal may be determined so that no offset occurs.

In the RF amplifier unit 109, the tracking error signal _STE is generated by the circuit of FIG. That is, the adder 221 adds the detection outputs Sd and Sc, and the adder 222 adds the detection outputs Sa and Sb. Then, the subtracter 223 subtracts the output of the adder 222 from the output of the adder 221 to obtain a tracking error signal S _TE ′ = {(Sd + Sc) − (Sa + Sb)} by a simple push-pull method.

The adder 224 adds the detection outputs Sf and Sh, and the adder 225 adds the detection outputs Se and Sg. Then, the subtractor 226 subtracts the output of the adder 225 from the output of the adder 224, and further multiplies the subtracted output by the coefficient k by the multiplier 227. The tracking error signal S _TE 'by the simple push-pull method described above. The offset S _OF = k {(Sf + Sh) − (Se + Sg)} occurring in FIG. Then, the subtracter 228 subtracts the offset S _OF which is the output of the multiplier 227 from the tracking error signal S _TE ′, which is the output of the subtractor 223, which is simply the push-pull method, and the tracking error signal S from which the offset is removed. _TE is obtained.

In the other embodiments described above, the tracking error signal S _TE is basically obtained by the push-pull method. This tracking error signal S _TE is obtained from a tracking error signal S _TE ′ obtained by a simple push-pull method. The offset S _OF included is removed. Therefore, in the tracking control based on the tracking error signal _STE , the tracking control can be performed satisfactorily without detracking due to the offset.

In the other embodiments described above, a signal indicating the relative displacement of the beam spot BS ₀ on the light detection surface of the photodiode portion 161M is obtained using the photodiode portions 161S ₋ , 161S ₊ . The photodiode unit 161M is configured to have first and second light detection units in a direction x corresponding to the radial direction of the DVD 104 in order to obtain a tracking error signal, and the number of divisions is small, and the reproduction signal S _RF S / N can be suppressed from decreasing.

In the other embodiments described above, the photodiodes 161S ₋ and 161S ₊ are straight lines extending in the direction x corresponding to the radial direction of the DVD 104 and in the direction y corresponding to the longitudinal direction (tangential direction) of the recording track. And a beam formed on the light detection surface, having a first light detection unit (De, Dg) and a second light detection unit (Df, Dh) divided by the division lines L _D22 and L _D32 . Even when the spots BS ₋₁ and BS ₊₁ are shifted in the direction y corresponding to the longitudinal direction of the recording track, the push-pull interference areas P ₋ and P ₊ are used to obtain a signal corresponding to the offset. The signal corresponding to the offset (signal for removing the offset) can be obtained with high accuracy without entering the first and second light detection units.

In the other embodiments described above, the first dividing lines L _D21 and L _D31 and the third dividing lines L _D23 and L _D33 in the photodiode portions 161S ₋ and 161 ₊ are respectively in the longitudinal direction of the recording track. The curve is closest to the second dividing lines L _D22 and L _D32 at the center position in the direction y corresponding to. For this reason, the first photodetection section (photodiode De, Dg) and the second photodetection section (photodiode Df, Dh) are the narrowest at the center position in the direction y corresponding to the longitudinal direction of the recording track. The shape becomes wider as the distance from the center position increases. Therefore, as described above, the signal indicating the relative displacement of the beam spot BS ₀ on the light detection surface of the photodiode portion 161M is obtained by performing the calculation of the difference between the detection outputs of the first and second light detection portions. {(Sf + Sh) − (Se + Sg)} is obtained, but its detection sensitivity can be increased.

In the other embodiments described above, the first dividing lines L _D21 and L _D31 and the third dividing lines L _D23 and L _D33 in the photodiode portions 161S ₋ and 161 ₊ are respectively in the direction y described above. At the center position, the distance w between the second dividing lines L _D22 and L _D32 is set to satisfy the expression (2). Therefore, even if the objective lens 154 is displaced in the radial direction and the beam spots BS ₋₁ and BS ₊₁ are displaced in the direction x, the first dividing lines L _D21 and L _D31 , the third dividing lines L _D23 and L _{D D33} maintains a state in which the region including the interference regions P ₋ and P ₊ and the other region are divided.

Therefore, the first light detector (photodiode De, Dg), the second optical detector (photodiode Df, Dh), the objective lens 154 is displaced in the radial direction, the photodiode section 161S _-, 161S ₊ Even if the beam spots BS _-1 and BS ₊₁ formed on the light detection surface of the beam spot are displaced in the direction x, the interference region P of the zero-order light and the ± first-order light among the beam spots BS _-1 and BS _{+1 -} an area that does not include the P ₊ is formed. As a result, a signal indicating the relative displacement of the beam spot BS ₀ on the light detection surface of the photodiode portion 161M, which is obtained by performing a calculation for obtaining the difference between the detection outputs of the first and second light detection portions { (Sf + Sh) − (Se + Sg)} is not affected by the interference region interference regions P ₋ and P ₊ , and the offset S _OF based on this signal can always be obtained with high accuracy, and therefore the tracking error signal _STE is always obtained. It can be obtained with high accuracy.

In the other embodiments described above, the grating 157 acquires the 0th-order main beam and the ± 1st-order side beam, and the beam spots BS ₋₁ and BS ₊₁ by the two side beams are _converted into photo diode section 161S _-, 161 ₊ of forming on the photodetection surface, these photodiode section 161S _-, 161 ₊ first, on the light detecting surface of the photodiode section 161M using the detection output of the second light detector A signal indicating the relative displacement of the beam spot BS ₀ is obtained. However, the grating 157 is blazed to obtain a −1st order side beam or a + 1st order light side beam by the grating 157, and only the obtained side beam is used on the light detection surface of the photodiode portion 161M. A signal indicating the relative displacement of the beam spot BS ₀ may be obtained. In this case, the photodiode section 161S _- or any of the photodiode portion 161S ₊ is unnecessary, even a circuit for obtaining a tracking error signal S _TE is simplified (the adder 224 of Figure 9 is not necessary).

Also in the other embodiments described above, the first dividing lines L _D21 and L _D31 and the third dividing lines L _D23 and L _D33 in the photodiode portions 161S ₋ and 161 ₊ are parabolic curves, respectively. However, it may be a straight line extending in the direction y (see FIG. 6A) or a broken line-like curve (see FIG. 6B) having a center position in the direction y as a break point.

  In the above embodiment, the present invention is applied to a DVD player. However, the present invention can be similarly applied to other optical disk apparatuses such as a Blu-ray disk apparatus.

  According to the present invention, when the offset is removed from the tracking error signal by the push-pull method, it is possible to prevent the S / N of the reproduction signal from being significantly reduced, and the beam spot formed on the light detection surface is the length of the recording track. The signal for removing the offset can be obtained with high accuracy even when the direction is shifted to the direction corresponding to the direction (tangential direction), and can be applied to an optical disc device such as a DVD device or a Blu-ray disc device.

It is a block diagram which shows the structure of the DVD player as embodiment. It is a figure which shows the structure of the optical system of an optical pick-up. It is a figure which shows the structure of a photodetector. It is a figure for demonstrating the distance between the center of the beam spot of 0th order light and +/- 1st order light. It is a block diagram which shows the circuit which produces | generates a tracking error signal. It is a figure which shows the other structure of a photodetector. It is a figure which shows the structure of the optical system of the optical pick-up in other embodiment. It is a figure which shows the structure of the photodetector in other embodiment. It is a block diagram which shows the circuit which produces | generates the tracking error signal in another actual form. It is a figure for demonstrating the example of a division | segmentation of the light receiving element for obtaining the tracking error signal in the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... DVD player, 101 ... System controller, 102 ... Display part, 103 ... Operation key part, 104 ... DVD, 105 ... Spindle motor, 106 ... Optical pick-up, 107 ... Feeding motor, 108 ... Servo control circuit, 109 ... RF amplifier section, 110 ... Read channel section, 111 ... Demodulation / ECC section, 112 ... Demultiplexer, 113 ... Video decoder, 114 ... sub-picture decoder, 115 ... synthesizer, 116 ... TV encoder, 117,120 ... DA converter, 118,121 ... output terminal, 119 ... audio decoder, 151 ... Laser diode, 152 ... Beam splitter, 153 ... Collimator lens, 154 ... Objective 'S, 155 ... cylindrical lens, 156,156A ... photodetector, 157 ... _{grating, 161,161M, 161S -, 161S +} ··· photodiode portion

Claims (12)

A light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are formed in a spiral shape or a concentric shape;
Error signal generating means for generating a tracking error signal corresponding to a deviation of the beam spot from a predetermined recording track in a radial direction of the optical disk using reflected light from the beam spot formed on the optical disk; ,
Tracking control means for controlling the beam spot to be positioned on the predetermined recording track based on the tracking error signal;
The error signal generating means is
A light spot having a beam spot formed by the reflected light on a light detection surface and having first to fourth light detection parts divided by first, second and third dividing lines in a direction corresponding to the radial direction. Means,
A calculation is performed to obtain a difference between the sum of the detection outputs of the first and second light detection units and the sum of the detection outputs of the third and fourth light detection units, and the relative relationship between the recording track and the objective lens is calculated. First computing means for obtaining a signal indicative of a general displacement;
Second computing means for obtaining a signal indicating a relative displacement of the beam spot on the light detection surface by performing a calculation for obtaining a difference between detection outputs of the second light detection unit and the third light detection unit. When,
Multiplying means for multiplying the output signal of the second computing means by a predetermined coefficient;
Third arithmetic means for obtaining the tracking error signal by performing an arithmetic operation for obtaining a difference between the output signal of the first arithmetic means and the output signal of the multiplier means;
The second dividing line is a straight line,
The first dividing line divides a region including the interference region of the 0th-order light and the −1st-order light of the beam spot formed on the light detection surface and the other region, and extends in the longitudinal direction of the recording track. A curve closest to the second dividing line at a central position in a corresponding direction;
The third dividing line divides a region including the interference region of the 0th-order light and the + 1st-order light of the beam spot formed on the light detection surface and the other region, and corresponds to the longitudinal direction of the recording track. An optical disc device characterized by being a curve that is closest to the second dividing line at a central position in the direction in which the optical disc is moved. A light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are formed in a spiral shape or a concentric shape;
A beam spot by reflected light from the beam spot formed on the optical disc is formed on the light detection surface, and the first, second and second directions in the direction corresponding to the radial direction of the optical disc perpendicular to the longitudinal direction of the recording track. Photodetecting means having first to fourth photodetecting units divided by three dividing lines,
The second dividing line is a straight line,
The first dividing line divides a region including the interference region of the 0th-order light and the −1st-order light of the beam spot formed on the light detection surface and the other region, and extends in the longitudinal direction of the recording track. A curve closest to the second dividing line at a central position in a corresponding direction;
The third dividing line divides a region including the interference region of the 0th-order light and the + 1st-order light of the beam spot formed on the light detection surface and the other region, and corresponds to the longitudinal direction of the recording track. An optical pickup characterized by being a curve that is closest to the second dividing line at a central position in the direction in which the light picks up. A light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are formed in a spiral shape or a concentric shape;
Error signal generating means for generating a tracking error signal corresponding to a deviation of the beam spot from a predetermined recording track in a radial direction of the optical disk using reflected light from the beam spot formed on the optical disk; ,
Tracking control means for controlling the beam spot to be positioned on the predetermined recording track based on the tracking error signal;
The error signal generating means is
A light spot having a beam spot formed by the reflected light on a light detection surface and having first to fourth light detection parts divided by first, second and third dividing lines in a direction corresponding to the radial direction. Means,
A calculation is performed to obtain a difference between the sum of the detection outputs of the first and second light detection units and the sum of the detection outputs of the third and fourth light detection units, and the relative relationship between the recording track and the objective lens is calculated. First computing means for obtaining a signal indicative of a general displacement;
Second computing means for obtaining a signal indicating a relative displacement of the beam spot on the light detection surface by performing a calculation for obtaining a difference between detection outputs of the second light detection unit and the third light detection unit. When,
Multiplying means for multiplying the output signal of the second computing means by a predetermined coefficient;
Third arithmetic means for obtaining the tracking error signal by performing an arithmetic operation for obtaining a difference between the output signal of the first arithmetic means and the output signal of the multiplier means;
The second dividing line is a straight line,
The radius of the beam spot on the light detection surface of the light detection means is 1, and the maximum value of the displacement of the beam spot in the direction corresponding to the radial direction on the light detection surface is the beam. When the radius of the spot is d times, the wavelength of the light beam is λ, the numerical aperture of the objective lens is NA, the pitch of the recording track is Tp, and the first and third dividing lines are respectively The distance w from the second dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track is {(λ / NA) * (1 / Tp) −1} −d ≧ w> 0. An optical disc device characterized by being a line that satisfies the equation. The optical disc apparatus according to claim 3, wherein the first and third dividing lines are straight lines. The optical disc apparatus according to claim 3, wherein the first and third dividing lines are curves that are closest to the second dividing line at the center position, respectively. A light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are formed in a spiral shape or a concentric shape;
A beam spot by reflected light from the beam spot formed on the optical disc is formed on the light detection surface, and the first, second and second directions in the direction corresponding to the radial direction of the optical disc perpendicular to the longitudinal direction of the recording track. Photodetecting means having first to fourth photodetecting units divided by three dividing lines,
The second dividing line is a straight line,
The radius of the beam spot on the light detection surface of the light detection means is 1, and the maximum value of the displacement of the beam spot in the direction corresponding to the radial direction on the light detection surface is the beam. When the radius of the spot is d times, the wavelength of the light beam is λ, the numerical aperture of the objective lens is NA, the pitch of the recording track is Tp, and the first and third dividing lines are respectively The distance w from the second dividing line at the center position in the direction corresponding to the longitudinal direction of the recording track is {(λ / NA) * (1 / Tp) −1} −d ≧ w> 0. An optical pickup characterized by being a line that satisfies the equation. A light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are formed in a spiral shape or a concentric shape;
Error signal generating means for generating a tracking error signal corresponding to a deviation of the beam spot from a predetermined recording track in a radial direction of the optical disk using reflected light from the beam spot formed on the optical disk; ,
Tracking control means for controlling the beam spot to be positioned on the predetermined recording track based on the tracking error signal;
The error signal generating means is
A diffractive means disposed in the optical path of the reflected light to obtain a main beam and a side beam;
A beam spot by the main beam is formed on the light detection surface, and is divided into first and second division lines that are straight lines extending in a direction corresponding to the radial direction of the recording track in a direction corresponding to the radial direction. First light detection means having a light detection unit;
Of the beam spot by the side beam, a region not including the interference region of the 0th order light and ± 1st order light is formed on the light detection surface, and corresponds to the longitudinal direction of the recording track in the direction corresponding to the radial direction. A second photodetecting means having first and second photodetection units divided by a dividing line that is a straight line extending in the direction;
A first calculation for obtaining a signal indicating a relative displacement between the recording track and the objective lens by calculating a difference between detection outputs of the first and second light detection units of the first light detection means. Means,
Relative displacement of the beam spot on the light detection surface of the first light detection means by calculating the difference between the detection outputs of the first and second light detection units of the second light detection means Second calculating means for obtaining a signal indicating
Multiplying means for multiplying the output signal of the second computing means by a predetermined coefficient;
An optical disc apparatus comprising: a third computing unit that obtains the tracking error signal by performing a computation that obtains a difference between the output signal of the first computing unit and the output signal of the multiplication unit. The shapes of the ends of the first and second light detection portions of the second light detection means on the side opposite to the dividing line are the center positions in the direction corresponding to the longitudinal direction of the recording track, respectively. The optical disc device according to claim 7, wherein the optical disc device has a curved shape that is closest to the dividing line. The radius of the beam spot on the light detection surface of the second light detection means is 1, and the maximum value of the displacement of the beam spot in the direction corresponding to the radial direction on the light detection surface Is d times the radius of the beam spot, the wavelength of the light beam is λ, the numerical aperture of the objective lens is NA, and the pitch of the recording track is Tp. The end of the second light detection unit opposite to the dividing line is the center position in the direction corresponding to the longitudinal direction of the recording track, and the distance w from the dividing line is {( The optical disk apparatus according to claim 7, wherein the optical disk apparatus has a linear shape satisfying an expression of λ / NA) * (1 / Tp) −1} −d ≧ w> 0. The shape of the edge part on the opposite side to the said dividing line of the 1st, 2nd light detection part of the said 2nd light detection means is respectively a linear shape. Optical disk device. The shapes of the ends of the first and second light detection portions of the second light detection means opposite to the dividing line are curved shapes that are closest to the dividing line at the central position. The optical disc apparatus according to claim 9. A light beam irradiating means for condensing a light beam by an objective lens to form a beam spot on an optical disk on which recording tracks are formed in a spiral shape or a concentric shape;
A diffractive means disposed in the optical path of the reflected light to obtain a main beam and a side beam;
A beam spot formed by the main beam is formed on a light detection surface and is a straight line extending in a direction corresponding to the radial direction of the optical disc perpendicular to the longitudinal direction of the recording track and extending in a direction corresponding to the longitudinal direction of the recording track First light detection means having first and second light detection units divided by a line;
Of the beam spot by the side beam, a region not including the interference region of the 0th order light and ± 1st order light is formed on the light detection surface, and corresponds to the longitudinal direction of the recording track in the direction corresponding to the radial direction. An optical pickup comprising: a second photodetecting unit having first and second photodetecting units divided by a dividing line that is a straight line extending in the direction.

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