JP3788962B2 - Optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device that records information on an optical recording medium with light or reproduces information from the optical recording medium.
[0002]
[Prior art]
Optical discs such as compact discs (CD), digital versatile discs (DVD) and mini discs (MD) are used as optical recording media in many fields such as audio video and computers. In accordance with the demand for increasing the storage capacity that is the amount of information recorded on the optical recording medium as described above, along with the narrowing of the track pitch that is the interval between the tracks formed on the optical recording medium, It has been used as an information storage area until the lap.
[0003]
In an information recording / reproducing apparatus using such an optical recording medium, a light spot is condensed on the information recording surface of the optical recording medium, and the information is recorded or reproduced by following the light spot to a track formed on the optical recording medium. I do. The control for causing the light spot to follow the track is called tracking control. In tracking control, the light reflected by the optical recording medium is detected by the light receiving element, and the detection signal from the light receiving element is collected to collect the light on the optical recording medium. This is performed by feeding back to an actuator that drives an objective lens that is an optical means. A signal used for feedback control of driving of the actuator is called a tracking error signal (hereinafter sometimes referred to as TES), and a differential push-pull (one of the signal generation methods used as the tracking error signal) DPP) method.
[0004]
The DPP method is disclosed, for example, in JP-A-7-93764. FIG. 17 is a system diagram showing a simplified configuration of a conventional optical pickup device 1 in which the DPP method is used. The conventional optical pickup device 1 is configured as follows, for example. An optical pickup device 1 includes a semiconductor laser 2, which is a light source, a collimator lens 3, a diffraction grating 4, a beam splitter 5, a quarter wave plate 6, an objective lens 7, a cylindrical lens 8, and a photodetector 9 including a light receiving element. Including.
[0005]
In the optical pickup device 1, the light emitted from the semiconductor laser 2 is made into substantially parallel light by the collimator lens 3, and diffracted by the diffraction grating 4 into at least zero-order diffracted light, + 1st-order diffracted light, and −1st-order diffracted light. And is converted into circularly polarized light by the quarter-wave plate 6, condensed by the objective lens 7, and irradiated onto the optical recording medium 10.
[0006]
FIG. 18 is a diagram illustrating a state of zero-order diffracted light and ± first-order diffracted light irradiated on the optical recording medium 10. FIG. 18A shows the arrangement of zero-order diffracted light and ± first-order diffracted light irradiated on a track formed on the optical recording medium 10, and FIG. 18B shows the cross-sectional shape of the optical recording medium 10. Indicates. A main beam (hereinafter abbreviated as MB) constituting the zero-order diffracted light is a center in the width direction of a track on which information is to be recorded or a track 11 on which information to be reproduced is recorded (hereinafter referred to as an information track). The tracking is controlled so as to be irradiated. At this time, the first sub-beam that is + 1st order diffracted light (hereinafter abbreviated as SB1) and the second subbeam that is -1st order diffracted light (hereinafter abbreviated as SB2) are both sides of the information track 11 irradiated with MB. The adjacent tracks 12 and 13 are irradiated at positions shifted by a half of the track pitch TP.
[0007]
MB, SB1 and SB2 irradiated on the optical recording medium 10 are reflected by the optical recording medium 10, pass through the objective lens 7 and the quarter-wave plate 6 again, are reflected by the beam splitter 5, and are cylindrical lenses 8. Astigmatism is given by, and the photodetector 9 receives the light.
[0008]
FIG. 19 is a diagram showing an outline of a circuit for obtaining a DPP signal based on a detection signal from the photodetector 9. The aforementioned photodetector 9 is divided into two so as to have a dividing line in a direction parallel to the direction in which the track formed on the optical recording medium 10 extends in a state where the optical recording medium 10 is mounted facing the optical pickup device 1. Photodetectors 9b and 9c made up of the received light receiving elements, and light detectors 9a made up of light receiving elements divided into four so as to have a dividing line in a direction parallel to and orthogonal to the track extending direction.
[0009]
The MB push-pull signal obtained by the MB light reception signal detected by the photodetector 9a and the subtractor 14 is referred to as MPP (Main Push Pull), and the SB1 light reception signal detected by the photodetector 9b and the subtractor 15 are used. The push-pull signal of SB1 obtained by the above is SPP1 (Sub Push Pull-1), and the SB2 push-pull signal obtained by the light reception signal of SB2 detected by the photodetector 9c and the subtractor 16 is SPP2 (Sub Push Pull). Pull-2), the adder 17 calculates the addition signal SPP (= SPP1 + SPP2) obtained by the SPP1 and SPP2 and the adder 17 and the subtractor 19 based on the above-described MPP. The DPP signal is given by the following equation (1).
DPP = MPP-k (SPP1 + SPP2) (1)
[0010]
Here, k which is an amplification factor in the amplifier 18 is a coefficient used for correcting a difference in light intensity between the zero-order diffracted light and the ± first-order diffracted light. When the light intensity ratio of each diffracted light is as follows: light intensity of zero-order diffracted light: light intensity of + 1st-order diffracted light: light intensity of −1st-order diffracted light = a: b: b, k = a / (2b ).
[0011]
As described above, since SB1 and SB2 are irradiated to positions adjacent to the adjacent tracks on both sides from the information track irradiated with MB by a half of the track pitch TP, the phases of SPP1 and SPP2 are The phase is 180 degrees shifted from the MPP phase. FIG. 20 is a diagram illustrating an example of a push-pull signal. FIG. 20 illustrates a case where the above-described diffracted lights have the same light intensity and a = b, that is, the coefficient k = 0.5. Since SPP1 and SPP2 have the same light intensity, SPP1 and SPP2 overlap, and SPP obtained by further multiplying the sum of SPP1 and SPP2 by 0.5 is identical to SPP1 and SPP2, and thus overlaps SPP1 and SPP2. . Since MPP and SPP have opposite phases that are 180 degrees out of phase, a signal obtained by adding absolute values of the amplitudes of MPP and SPP is obtained as a DPP signal.
[0012]
FIG. 21 is a diagram illustrating an example of the push-pull signal in a state where the offset ΔP is generated. Even in a state where each diffracted light is applied to a predetermined track position on the optical recording medium 10, an offset ΔP may occur due to a shift of the objective lens or an inclination of the optical recording medium 10. However, even when such an offset ΔP occurs, the MPP and the SPP are in opposite phases as described above, so that it is possible to obtain a DPP signal in which the offset ΔP is canceled.
[0013]
Another prior art of the DPP method is disclosed in JP-A-11-296875. In this prior art, the phase of SB1 and SB2 is inverted with respect to the phase of MB, and MB and SB1 and SB2 are irradiated on the same track, thereby reducing the offset.
[0014]
The other optical pickup device used in the prior art is substantially the same as the optical pickup device 1 used in the above-described prior art, and is not shown in the figure. That is. FIG. 22 is a plan view showing a simplified configuration of the diffraction grating 20 provided in an optical pickup device used in another conventional technique. The diffraction grating 20 is a grating called a phase inversion diffraction grating, and is divided at a predetermined interval GW in a direction orthogonal to the extending direction of the grating grooves, and each divided grating is a direction orthogonal to the extending direction of the grating grooves. Are provided so as to be shifted from each other by a half of the pitch at which the lattice grooves are formed. The predetermined interval GW is such that the track pitch formed on the optical recording medium 10 is TP, the numerical aperture of the objective lens 7 is NA, the effective beam diameter of light at the position where the diffraction grating 20 is inserted in the optical path is D, and the light Is given by equation (2).
GW = D · λ / (2NA · TP) (2)
[0015]
The diffraction grating 20 formed in this way is a grating whose phase is inverted by 180 degrees with the interval GW as a cycle, and this interval GW is ± 0th order diffracted light diffracted by the tracks formed on the optical recording medium 10 and ± It is set so as to correspond to the deviation of the reflected light from the first-order diffracted light. As described above, the light emitted from the light source passes through the diffraction grating 20 and, before being irradiated onto the optical recording medium 10, the phases of SB1 and SB2 with respect to the phase of MB so as to correspond to the deviation. Is inverted and irradiated onto the optical recording medium 10, so that the zero-order diffracted light and the ± first-order diffracted light can be irradiated onto the same track. FIG. 23 is a diagram showing a state where MB and SB1 and SB2 are irradiated on the same track 11. In FIG. Based on the detection signals of the zero-order diffracted light and the ± first-order diffracted light reflected on the same track 11 as shown in FIG. 23, the influence of the offset is affected in the same manner as the DPP signal shown in FIG. An excluded DPP signal can be obtained.
[0016]
[Problems to be solved by the invention]
However, the above-described prior art has the following problems. In the prior art disclosed in Japanese Patent Laid-Open No. 7-93764, SB1 and SB2 must be shifted on the optical recording medium 10 with respect to the MB by a half of the track pitch. In the technique disclosed in Japanese Patent Laid-Open No. 11-296875, MB, SB1, and SB2 must be arranged on the same track on the optical recording medium 10. Therefore, in any of the above-described conventional techniques, there is a problem that the diffraction gratings 4 and 20 must be positioned and adjusted with high accuracy when the apparatus is assembled.
[0017]
In any prior art, the influence of the curvature of the track formed on the optical recording medium 10 is not taken into consideration. As described above, the signal from the track formed near the center of the optical recording medium is used because it is used for information storage and reproduction up to the vicinity of the center of the optical recording medium in response to a request for increasing the storage capacity. In detection, the influence of the curvature of the track must be taken into account.
[0018]
FIG. 24 is a diagram illustrating a state in which MB, SB1, and SB2 are irradiated onto a track having a curvature on the optical recording medium 10. In FIG. As shown in FIG. 24, when the track has a curvature, if SB1 that is the preceding beam of the sub-beam is arranged at the center of the track, SB2 that is the subsequent beam cannot be arranged at the center of the track. In the servo control system using three beams (MB, SB1, SB2) using zero-order diffracted light and ± first-order diffracted light, SB1 and SB2 are arranged on adjacent tracks on both sides of the track on which MB is arranged, respectively. However, if the track has a curvature as shown in FIG. 24 and the MB is arranged in the land portion 21 of the track, the SB1 is placed in the groove portion 22a which is a track adjacent to the land portion 21. At the same time, and at the same time, SB2 cannot be arranged in the groove portion 22b which is a track adjacent to the land portion 21.
[0019]
FIG. 25 is a diagram illustrating an example of a DPP signal obtained based on detection signals of MB, SB1, and SB2 irradiated on a track having a curvature. As shown in FIG. 25, when MB is placed in the land portion 21 and SB1 and SB2 cannot be placed in the groove portions 22a and 22b adjacent to the land portion 21 at the same time, the SPP has a phase difference with respect to the MPP. Therefore, a phase difference also occurs between DPP and MPP obtained by the above equation (1), and this phase difference becomes a track offset.
[0020]
Even when three beams of MB and SB1 and SB2 are arranged on the same track as in another conventional technique, if the track has curvature, the three beams can be arranged on the same track at the same time. Since either one of the beams is shifted from the adjacent track, a track offset occurs as described above.
[0021]
Further, as a factor causing the track offset due to the curvature of the track formed on the optical recording medium, there is a relationship between the beam interval B and the track pitch TP. Here, the beam interval B is a linear distance connecting the spot center of MB irradiated on the optical recording medium and the spot center of SB1 or SB2.
[0022]
FIG. 26 shows the relationship between the beam interval B and the track offset when information is reproduced from an optical recording medium having a track pitch TP of 1.2 μm. FIG. 26 shows a result obtained by arranging SB1 and SB2 in the track direction adjacent to the track on which MB is arranged, instead of arranging the three beams on the same track. The line 23 in FIG. 26 shows the relationship between the beam interval B and the track offset, and it can be seen that the track offset amount increases as the beam interval B increases from the line 23.
[0023]
Therefore, when the beam interval B is set wide, in order to reduce the track offset amount, the position where the three beams are arranged, that is, MB is arranged at the center of the track, and SB1 and SB2 are adjacent to the track, respectively. The position of the diffraction grating that determines the irradiation position of the MB, SB1, and SB2 on the optical recording medium becomes strict.
[0024]
FIG. 26 illustrates a case where the track pitch TP is 1.2 μm, but it is known that when the beam interval B is constant, a track offset is likely to occur when the track pitch TP becomes small. Since the value of the track pitch TP is determined according to each optical disc that is an optical recording medium, a large value cannot be used freely. However, the beam interval B can be determined according to the configuration of the optical system used in the optical pickup device, and the design value is determined according to the processing accuracy of the groove pitch of the diffraction grating, thereby suppressing a certain amount of track offset. It is possible. For example, in MD, the track pitch TP is 1.2 μm, and the beam interval B is set to 21 μm.
[0025]
The cause of the occurrence of the track offset is not only the relationship between the track pitch TP and the beam interval B, but also the difference in light intensity between the sub beams SB1 and SB2, for example. SB1 and SB2 are affected by a difference in spectral ratio, a difference in aperture limit of an objective lens, a difference in sensitivity of a photodetector, and the like when diffracted by a diffraction grating, and thus their light intensity is not always the same. In addition, the light intensity is not always constant. A track offset also occurs due to such a difference (unbalance) in light intensity between SB1 and SB2.
[0026]
FIG. 27 is a diagram showing a state in which MBs are arranged on the straight line 24 that extends in the radial direction through the center of the optical recording medium 10. A desirable arrangement of the three beams in the servo control method using the three beams is that the MBs are arranged on a straight line 24 extending in the radial direction through the center of the optical recording medium 10. However, in the actual assembly adjustment, it is difficult to accurately arrange the MB on the straight line 24 by adjusting the position of the diffraction grating. Often, as shown in FIG. The direction shifts to a position indicated by, for example, MB ′. At this time, the sub-beams are naturally shifted to the positions SB1 'and SB2'. Even when such a three-beam position shift occurs, a track offset occurs.
[0027]
Such a track offset is required to be further suppressed with an increase in the storage capacity of the optical recording medium, in other words, with an improvement in recording density. There is a problem that the offset in the track portion is not sufficiently suppressed, and the quality of the reproduction information near the center of the optical recording medium deteriorates.
[0028]
An object of the present invention is to provide an optical pickup device that can cancel a track offset generated in tracking control using the DPP method with a simple configuration and can simplify assembly adjustment of the device. .
[0029]
[Means for Solving the Problems]
The present invention is an optical pickup device for recording information on an optical recording medium by light or reproducing information from the optical recording medium,
A light source that emits light;
The light emitted from the light source is diffracted into at least zero-order diffracted light, plus (+) first-order diffracted light, and minus (−) first-order diffracted light, and gives a phase difference to a part of the + and − (±) first-order diffracted lights. A diffraction grating,
Condensing means for condensing zero-order diffracted light and ± first-order diffracted light on the optical recording medium;
A light branching unit disposed between the light source and the light collecting unit and transmitting and reflecting zero-order diffracted light and ± first-order diffracted light;
Photodetection means comprising a plurality of light receiving elements for receiving zero-order diffracted light and ± first-order diffracted light reflected by the optical recording medium,
A beam interval B, which is a distance between a beam spot center of zero-order diffracted light focused on the optical recording medium and a beam spot center of + 1st-order diffracted light or −1st-order diffracted light, and a track formed on the optical recording medium In a state where the ratio (B / TP) to the pitch TP is 40 or more,
The diffraction grating is
The ratio (SPP1 / SPP2) of the push-pull signal SPP1 obtained based on the + 1st order diffracted light detected by the plurality of light receiving elements and the push-pull signal SPP2 obtained based on the -1st order diffracted light exceeds 2 or 2 When it is less than 1 /
The area ratio (S1 / S0) is given, where S0 is the beam area of the + 1st order or −1st order diffracted light irradiated to the diffraction grating, and S1 is the area of the diffraction grating that gives a phase difference to the + 1st order or −1st order diffracted light. , 0.45 or more and 0.53 or less.
[0030]
In the present invention, the diffraction grating may be
When the ratio of the push-pull signals SSP1 and SSP2 (SPP1 / SPP2) is greater than 3 or less than 1/3,
The area ratio (S1 / S0) is formed to be 0.47 or more and 0.52 or less.
[0031]
According to the present invention, in the state where the ratio (B / TP) between the beam interval B and the track pitch TP of the optical recording medium is 40 or more, the diffraction grating has a ratio between the push-pull signal SPP1 and the push-pull signal SPP2. When (SPP1 / SPP2) is greater than 2 or less than half, the area ratio (S1 / S0) of the diffraction grating is formed to be 0.45 or more and 0.53 or less, and SPP1 / When SPP2 is greater than 3 or less than 1/3, the area ratio (S1 / S0) is formed to be 0.47 or more and 0.52 or less. As a result, the amplitudes of SPP1 and SPP2 can be made smaller than the amplitude of the push-pull signal MPP obtained on the basis of the zeroth-order diffracted light, so that the curvature of the track is large and the ± first-order diffracted light deviates from the center of the track. Even in such a case, the amount of occurrence of track offset can be reduced.
[0032]
The present invention also provides an optical pickup device for recording information on an optical recording medium with light or reproducing information from the optical recording medium,
A light source that emits light;
The light emitted from the light source is diffracted into at least zero-order diffracted light, plus (+) first-order diffracted light, and minus (−) first-order diffracted light, and gives a phase difference to a part of the + and − (±) first-order diffracted lights. A diffraction grating,
Condensing means for condensing zero-order diffracted light and ± first-order diffracted light on the optical recording medium;
A light branching unit disposed between the light source and the light collecting unit and transmitting and reflecting zero-order diffracted light and ± first-order diffracted light;
Photodetection means comprising a plurality of light receiving elements for receiving zero-order diffracted light and ± first-order diffracted light reflected by the optical recording medium,
A beam interval B, which is a distance between a beam spot center of zero-order diffracted light focused on the optical recording medium and a beam spot center of + 1st-order diffracted light or −1st-order diffracted light, and a track formed on the optical recording medium In a state where the ratio (B / TP) to the pitch TP is less than 40,
The diffraction grating is
The ratio (SPP1 / SPP2) of the push-pull signal SPP1 obtained based on the + 1st order diffracted light detected by the plurality of light receiving elements and the push-pull signal SPP2 obtained based on the -1st order diffracted light exceeds 2 or 2 When it is less than 1 /
The area ratio (S1 / S0) is given, where S0 is the beam area of the + 1st order or −1st order diffracted light irradiated to the diffraction grating, and S1 is the area of the diffraction grating that gives a phase difference to the + 1st order or −1st order diffracted light. , 0.40 or more and 0.56 or less.
[0033]
In the present invention, the diffraction grating may be
When the ratio of the push-pull signals SSP1 and SSP2 (SPP1 / SPP2) is greater than 3 or less than 1/3,
The area ratio (S1 / S0) is formed to be 0.45 or more and 0.53 or less.
[0034]
According to the present invention, in a state where the ratio (B / TP) between the beam interval B and the track pitch TP of the optical recording medium is less than 40, the diffraction grating has an SPP1 / SPP2 of greater than 2 or 2 minutes. When the area ratio (S1 / S0) is less than 1, the area ratio (S1 / S0) is 0.40 or more and 0.56 or less, and when SPP1 / SPP2 is more than 3 or less than 1/3, the area The ratio (S1 / S0) is formed to be 0.45 or more and 0.53 or less. As a result, the amplitudes of SPP1 and SPP2 can be made smaller than the amplitude of the push-pull signal MPP obtained on the basis of the zeroth-order diffracted light, so that the curvature of the track is large and the ± first-order diffracted light deviates from the center of the track. Even in such a case, the amount of occurrence of track offset can be reduced.
[0035]
The present invention further includes a holding member for holding the diffraction grating,
The holding member is provided to be movable in a direction parallel to a direction in which a grating groove formed in the diffraction grating extends.
[0036]
According to the present invention, it is possible to adjust the insertion position of the diffraction grating relative to the light beam by moving the holding member that holds the diffraction grating in a direction parallel to the direction in which the grating groove formed in the diffraction grating extends. By such a simple adjustment operation, the area ratio (S1 / S0) can be adjusted to be within a suitable range, so that the amplitude of SPP1 and SPP2 with respect to the amplitude of MPP is reduced, and the amount of generated track offset can be easily suppressed. Can be realized.
[0037]
In the invention, it is preferable that a length of the holding member is smaller than a length of the diffraction grating in a direction orthogonal to a direction in which the grating groove of the diffraction grating extends.
[0038]
According to the present invention, the area ratio (S1 / S0) can be adjusted within a suitable range simply by moving the holding member in a uniaxial direction parallel to the direction in which the grating grooves formed in the diffraction grating extend. When configured, the holding member does not need to be held so as to cover the entire diffraction grating, so that the length in the direction orthogonal to the one-axis direction can be reduced. Thus, by reducing the dimensions of the members, it is possible to contribute to downsizing of the optical pickup device.
[0039]
The present invention further includes a holding member for holding the diffraction grating,
The holding member is provided so that the diffraction grating can be angularly displaced in a virtual plane including the diffraction grating and perpendicular to the optical axis.
[0040]
According to the present invention, the holding member for holding the diffraction grating can be angularly displaced in a virtual plane including the diffraction grating and perpendicular to the optical axis to adjust the insertion position of the diffraction grating with respect to the light beam. it can. By such a simple adjustment operation, the area ratio (S1 / S0) can be adjusted to be within a suitable range, so that the amplitude of SPP1 and SPP2 with respect to the amplitude of MPP is reduced, and the amount of generated track offset can be easily suppressed. Can be realized.
[0041]
The present invention further includes a holding member for holding the diffraction grating, and the holding member is provided to be movable in a direction parallel to the optical axis direction.
[0042]
According to the present invention, it is possible to adjust the insertion position of the diffraction grating with respect to the light beam by moving the holding member that holds the diffraction grating in the direction parallel to the optical axis direction. By such a simple adjustment operation, the area ratio (S1 / S0) can be adjusted to be within a suitable range, so that the amplitude of SPP1 and SPP2 with respect to the amplitude of MPP is reduced, and the amount of generated track offset can be easily suppressed. Can be realized.
[0043]
In the present invention, the light branching means is a beam splitter,
The diffraction grating is attached to the beam splitter near the light source of the beam splitter.
[0044]
According to the present invention, by attaching the diffraction grating to the beam splitter, a holding member for holding the diffraction grating can be eliminated. Further, since the insertion positions of the diffraction grating and the beam splitter with respect to the light beam can be adjusted at the same time, the efficiency of the adjustment work can be realized.
[0045]
In the present invention, the light branching means is a beam splitter,
The diffraction grating is formed near the light source of the beam splitter, and is integrated with the beam splitter as a single component.
[0046]
According to the present invention, since the diffraction grating is integrated with the beam splitter into a single component, the number of components can be reduced. As a result, it is possible to reduce the number of assembling steps at the time of assembling the apparatus, reduce the adjustment work between the parts, and improve the production efficiency.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a system diagram showing a simplified configuration of an optical pickup device 30 according to an embodiment of the present invention. The optical pickup device 30 radiates from a semiconductor laser 31 that is a light source, a collimator lens 32, a diffraction grating 33, a holding member 34 that holds the diffraction grating 33, a beam splitter that is an optical branching unit 35, and the semiconductor laser 31. An objective lens that is a condensing means 36 that condenses the light to be reflected on the optical recording medium 40, a reflected light condensing lens 37 that condenses the light reflected by the optical recording medium 40, a cylindrical lens 38, and a plurality of And a light detection means 39 composed of a light receiving element.
[0048]
Here, in the state where the optical pickup device 30 is operating facing the optical recording medium 40, the directions of the X, Y, and Z axes constituting the three-dimensional coordinates are defined. The direction of the cross-sectional line passing through the center of the optical recording medium 40 in FIG. 1, that is, the radial direction of the optical recording medium 40 is taken as the X axis, and the direction perpendicular to the X axis in the plane including the optical recording medium 40 is shown. The direction in which the track formed in 40 extends is the Y axis, and the optical axis direction orthogonal to both the X and Y axes is the Z axis direction. The optical axis is used to mean the axis of light emitted from the semiconductor laser 31 toward the optical recording medium 40 unless otherwise specified.
[0049]
The semiconductor laser 31 is a compound semiconductor containing, for example, a group III element and a group V element defined in the periodic table of elements, and can oscillate laser light. The collimator lens 32 makes light emitted from the semiconductor laser 31 substantially parallel.
[0050]
The diffraction grating 33 diffracts into at least zero-order diffracted light, + 1st-order diffracted light, and −1st-order diffracted light by passing the light beam 43 emitted from the semiconductor laser 31. FIG. 2 is a plan view showing the configuration of the diffraction grating 33 provided in the optical pickup device 30. The configuration of the diffraction grating 33 will be described with reference to FIG. The diffraction grating 33 is a planar grating in which a plurality of grooves 41 extending in the X-axis direction are formed, and light is diffracted by being reflected and interfered when passing through the grooves 41. In the diffraction grating 33, it should be noted that the groove 41 is divided into three in the extending direction, that is, the X-axis direction, the length of the central region 42b in the X-axis direction is W, and each region 42a, 42b, 42c. Is configured to be shifted from each other in the Y-axis direction by a half of the lattice constant d, which is the pitch at which the grooves 41 are formed. The length in the X-axis direction of each of the three regions 42a, 42b and 42c divided into three is based on the pitch TP of the track formed on the optical recording medium 40 and the beam interval B. The phase of the ± 1st order diffracted light that is diffracted when passing through is set to a value that makes a phase difference of 180 degrees with respect to the phase of the zeroth order diffracted light.
[0051]
Returning to FIG. 1 again, the beam splitter 35 is, for example, a polarization beam splitter, which transmits light emitted from the semiconductor laser 31 and reflects reflected light reflected by the optical recording medium 40. Arranged between the semiconductor laser 31 and the optical recording medium 40.
[0052]
The objective lens 36 condenses the zero-order diffracted light and the ± first-order diffracted light transmitted through the beam splitter 35 on a track formed on the information recording surface of the optical recording medium 40. In the present embodiment, zero-order diffracted light is irradiated onto an information track as a main beam (MB), + 1st-order diffracted light is a first sub-beam (SB1), and −1st-order diffracted light is a second sub-beam (SB2) on the information track. Irradiate on adjacent tracks.
[0053]
MB, SB1 and SB2 reflected by the optical recording medium 40 pass through the objective lens 36 again, are reflected by the beam splitter 35, and enter the reflected light collecting lens 37. MB, SB1 and SB2 collected through the reflected light condensing lens 37 are given astigmatism for defocus detection by the cylindrical lens 38 and received and detected by the light detecting means 39.
[0054]
The light detection means 39 is a light detector constituted by a plurality of light receiving elements made of photodiodes. The light detection means 39 includes a first photodetector 39a configured by four light receiving elements divided by a dividing line parallel to the X-axis direction and a dividing line parallel to the Y-axis direction, and the Y-axis direction. That is, it includes the second and third photodetectors 39b and 39c configured by two light receiving elements divided by a dividing line parallel to the track extending direction.
[0055]
The first photodetector 39a detects MB, and the push-pull signal obtained based on the light reception signal of MB detected by the first photodetector 39a is MPP. The second photodetector 39b detects SB1, and a push-pull signal obtained based on the light reception signal of SB1 detected by the second photodetector 39b is SPP1. The third photodetector 39c detects SB2, and a push-pull signal obtained based on the light reception signal of SB2 detected by the third photodetector 39c is SPP2.
[0056]
The DPP signal used as the TES can be obtained by Expression (1) in the same manner as described above by MPP, SPP1, and SPP2. FIG. 3 is a diagram illustrating a push-pull signal obtained in the optical pickup device 30 of the present embodiment, and FIG. 4 shows a push in a state where the offset ΔP required in the optical pickup device 30 of the present embodiment is generated. It is a figure which illustrates a pull signal.
[0057]
As shown in FIG. 3, the SPP obtained based on SB1 and SB2 has a smaller amplitude than the MPP obtained based on MB. This is because the phase of MB does not change when passing through the diffraction grating 33, whereas the phase of SB1 and SB2 is inverted by 180 degrees when passing through the region 42a and the region 42c of the diffraction grating 33. . As shown in FIG. 4, even when the offset ΔP is generated, the offsets generated in the MPP and SPP1 and SPP2 have the same phase, so that the offset ΔP is canceled as described above.
[0058]
In this embodiment, since the amplitude of the SPP can be reduced by passing the light beam 43 through the diffraction grating 33 in this manner, the influence of the track offsets of SB1 and SB2 can be mitigated. However, if the track offset amounts of SB1 and SB2 become undesirably large, it is difficult to avoid a deterioration in the quality of the recording / reproducing signal due to the influence of the residual track offset. Therefore, in order to avoid the deterioration of the quality of the recording / reproducing signal due to the track shift of SB1 and SB2, the SPP signal amplitude amount is set to be equal to or smaller than the amplitude amount determined corresponding to the allowable maximum track offset amount. There must be.
[0059]
The maximum track offset amount (hereinafter referred to as the allowable track offset amount) that can be allowed in order to avoid a deterioration in the quality of the recording / reproducing signal is not uniquely determined. For example, edited by Yoshito Tsunoda, edited by the Institute of Electronics, Information and Communication Engineers In “Basics and Applications of Optical Storage”, p. 98 to 104 (1995, Corona), 8% or less of the track pitch TP is proposed as one standard. When 8% of the track pitch TP is used as the allowable track offset amount, the area ratio (S1 / S0) of the diffraction grating 33 that is set so that the amplitude amount of the SPP can be 8% or less of the track pitch TP. The reason for limiting the range will be described below.
[0060]
FIG. 5 is a diagram illustrating a state in which SB1 is detected by the photodetector 39b. FIG. 5 shows a beam spot of the sub beam SB1 in a state where it is received by the photodetector 39b. Arcs 62 and 63 in the beam spot of SB1 are patterns of light diffracted by the irregularities on the surface of the optical recording medium when SB1 is irradiated onto the optical recording medium 40. In the beam spot of SB1, a region where the phase of SB1 is inverted by the diffraction grating 33 is hatched and projected onto the photodetector 39b. The hatched region is a region where the light beam 43 is diffracted and the phase is reversed when passing through the diffraction grating 33, that is, a region that has passed through the region 42a and the region 42c shown in FIG. In FIG. 5, an area obtained by adding all the areas of the hatched area is defined as S1. The ratio of this area S1 to the beam spot area S0 of SB1 is the area ratio (S1 / S0). Although FIG. 5 illustrates SB1, the area ratio (S1 / S0) is similarly defined for SB2.
[0061]
FIG. 6 is a diagram showing the relationship between the area ratio (S1 / S0) and the amplitude ratio (SPP / MPP). FIG. 6 shows the ratio (SPP) of the amplitude of the push-pull signal SPP by SB1 and SB2 detected when the area ratio (S1 / S0) of the diffraction grating 33 is changed and the amplitude of the push-pull signal MPP by MB. / MPP: hereinafter referred to as amplitude ratio). A line 44 in FIG. 6 shows the relationship between the area ratio (S1 / S0) and the amplitude ratio (SPP / MPP). As shown in FIG. 6, when the area ratio (S1 / S0) is 0.5, that is, when the area S1 that gives the phase difference to the sub-beams is equal to the area that does not give the phase difference (= S0−S1), the amplitude The ratio (SPP / MPP) becomes almost zero. Even if the area ratio (S1 / S0) increases from 0.5 or decreases, the amplitude ratio (SPP / MPP) increases.
[0062]
FIG. 7 is a diagram showing the value of the amplitude ratio (SPP / MPP) at which the track offset amount satisfies 8% or less of the track pitch TP. Since the shift amount of SB1 and SB2 with respect to the track is related to the track pitch TP and the beam interval B, in FIG. 7, the horizontal axis represents the ratio (B / TP) of the beam interval B to the track pitch TP, and the vertical axis represents Amplitude ratio (SPP / MPP) is shown. Further, as described above, the track offset is also generated due to a difference in light intensity between SB1 and SB2, that is, a light amount difference, so that the light amount of one beam is twice as large as the light amount of the other beam. The amplitude ratio was obtained for the case of. In FIG. 7, the ratio of the beam light quantity is expressed by β (= SB1 light quantity / SB2 light quantity or SB2 light quantity / SB1 light quantity may be used), the result when the line 45 is β: 2, and the line 46 is shown. The results for β: 3 are shown.
[0063]
As shown in FIG. 7, when the beam light quantity ratio β is 2 or 3, the amplitude ratio (SPP / MPP) changes greatly when the ratio (B / TP) is 40. That is, when the ratio (B / TP) is 40 or more and less than 40, the amplitude ratio (SPP / MPP) for satisfying the track offset amount of 8% or less of the track pitch TP is different.
[0064]
When the ratio (B / TP) is 40 or more, when the beam light quantity ratio β is 2, the amplitude ratio (SPP / MPP) must be 0.2 or less, and when the beam light quantity ratio β is 3. The amplitude ratio (SPP / MPP) must be less than or equal to 0.1. The area ratio (S1 / S0) of the diffraction grating 33 formed so as to satisfy the requirements of these amplitude ratios (SPP / MPP) can be obtained from FIG. By forming the diffraction grating 33 so that the area ratio (S1 / S0) is 0.45 or more and 0.53 or less, the beam light quantity ratio β = 2 and the amplitude ratio (SPP / MPP) ≦ 0.2 is satisfied. can do. Further, by forming the diffraction grating 33 so that the area ratio (S1 / S0) is 0.47 or more and 0.52 or less, the beam light quantity ratio β = 3 and the amplitude ratio (SPP / MPP) ≦ 0.1. Can be satisfied.
[0065]
When the ratio (B / TP) is less than 40, when the beam light quantity ratio β is 2, the amplitude ratio (SPP / MPP) must be 0.4 or less, and when the beam light quantity ratio β is 3. The amplitude ratio (SPP / MPP) must be less than 0.18. The area ratio (S1 / S0) of the diffraction grating 33 formed so as to satisfy the requirements of these amplitude ratios (SPP / MPP) can be obtained from FIG. By forming the diffraction grating 33 so that the area ratio (S1 / S0) is 0.40 or more and 0.56 or less, the beam light quantity ratio β = 2 and the amplitude ratio (SPP / MPP) ≦ 0.4 is satisfied. can do. Further, by forming the diffraction grating 33 so that the area ratio (S1 / S0) is 0.45 or more and 0.53 or less, the beam light quantity ratio β = 3 and the amplitude ratio (SPP / MPP) ≦ 0.18. Can be satisfied.
[0066]
The length W of the region 42b in the X-axis direction is within the above-described predetermined range in which the area ratio (S1 / S0) of the diffraction grating 33 is determined corresponding to the value of the amplitude ratio (SPP / MPP) to be satisfied. Is set to be The area ratio (S1 / S0) of the diffraction grating 33 is set to be within the above-mentioned predetermined range, and the amplitude ratio (SPP / MPP) is defined according to the ratio (B / TP) and the beam light quantity ratio β. By setting the value to be equal to or smaller than the value, the track offset can be suppressed to be equal to or smaller than the allowable track offset amount.
[0067]
FIG. 8 is a perspective view showing a simplified configuration of the holding member 34 that holds the diffraction grating 33 provided in the optical pickup device 30. The holding member 34 includes a fixing member 47 to which the diffraction grating 33 is fixed, and a guide member 48 to which the fixing member 47 is slidably mounted.
[0068]
The fixing member 47 is a frame-like member whose outer shape is formed in a substantially rectangular parallelepiped shape, and is formed so as not to shield the light beam passing through the diffraction grating 33 in a state where the diffraction grating 33 is fixed. . As shown in FIG. 8, in the state where the diffraction grating 33 is fixed to the fixing member 47, the first and second side portions 49, 49 of the fixing member 47 extend in the direction in which the groove 41 of the diffraction grating 33 extends, that is, the X-axis direction. First and second projecting portions 51 and 52 are formed so as to project outward from 50.
[0069]
The guide member 48 is a member having a flat U-shape, and includes a base portion 53 with which the fixing member 47 to which the diffraction grating 33 is fixed comes into contact, and a first vertically rising from both longitudinal ends of the base portion 53. 1 and second upright portions 54 and 55 are provided. First and second groove portions 56 and 57 are formed on the first and second raised portions 54 and 55 so as to face the fixing member 47. The first and second protrusions 51 and 52 of the fixing member 47 are fitted into the first and second groove portions 56 and 57, respectively, so that the fixing member 47 is mounted on the guide member 48. The fixing member 47 is such that the first and second projecting portions 51 and 52 slide with the first and second groove portions 56 and 57 of the guide member 48 so that the lattice groove 41 extends, that is, the guide member in the X-axis direction. It can be moved by being guided by 48.
[0070]
The movement of the fixing member 47 is realized as follows, for example. A female thread portion penetrating in the X-axis direction is formed in the first upright portion 54. A screw member (not shown) is screwed into the female screw portion, and the tip of the screw member is attached to the first projecting portion 51 so as to be rotatable. The guide member 48 is fixed to a casing (not shown) of the optical pickup device 30, and the screw member is rotated to adjust the forward or backward movement amount in the X-axis direction, whereby the diffraction grating 33 fixed to the fixed member 47 is X The relative position of the diffraction grating 33 with respect to the beam of light emitted from the semiconductor laser 31 can be adjusted by moving in the axial direction.
[0071]
FIG. 9 is a diagram showing an outline of position adjustment of the diffraction grating 33 in the X-axis direction. The length W in the X-axis direction of the region 42b formed in the diffraction grating 33 is set so that the area ratio (S1 / S0) of the diffraction grating 33 satisfies a predetermined amplitude ratio (SPP / MPP). Depending on the irradiation position of the beam 43 emitted from the semiconductor laser 31 and applied to the diffraction grating 33, a state in which the predetermined amplitude ratio (SPP / MPP) is not satisfied appears.
[0072]
FIG. 9A shows a state in which the center 58 of the beam 43 has a shift G1 in the X-axis direction with respect to the center line 59 in the X-axis direction of the region 42b. That is, FIG. 9A illustrates a state in which the beam 43 irradiates the region 42a and the region 42b but does not irradiate the region 42c. When the center 58 of the beam 43 has the above-described deviation G1, the beam 43 passes through the diffraction grating 33, is reflected by the optical recording medium 40, and is received by the light detection means 39. Since the area ratio (S1 / S0) of the diffraction grating projected onto a plurality of divided light receiving elements constituting each photodetector 39a, 39b, 39c is different in each light receiving element, it is based on the sub beams SB1 and SB2. The signal amplitude remains in the push-pull signal SPP obtained in this way.
[0073]
FIG. 10 is a diagram illustrating a state in which the center of the beam 43 has a deviation G1 in the X-axis direction and a signal amplitude remains in the SPP. SPP0 in FIG. 10 indicates a push-pull signal in a state where the center 58 of the beam 43 exists on the center line 59 of the region 42b, and almost no signal amplitude is generated. On the other hand, SPP150 in FIG. 10 indicates a push-pull signal in a state where the center 58 of the beam 43 has a deviation G1 = 150 μm with respect to the center line 59 of the region 42b, and the signal amplitude is larger than that of SPP0. As described above, since the track offset occurs when the signal amplitude of the push-pull signal SPP increases, the relative position between the beam 43 and the diffraction grating 33 must be adjusted so as to reduce the deviation G1.
[0074]
Returning to FIG. 9 again, in FIG. 9B, the fixing member 47 provided in the holding member 34 is slid to move the diffraction grating 33 in the X-axis direction, and the center 58 of the beam 43 is moved to the diffraction grating 33. The state adjusted so that it may be located on the centerline 59 of the area | region 42b is shown. In this way, by adjusting the relative positions of the beam 43 and the diffraction grating 33, the deviation G1 is reduced, and the amplitude ratio (SPP / MPP) is set within a predetermined range to prevent the occurrence of track offset. Can do. In the present embodiment, the movement of the beam 43 with respect to the Y-axis direction does not affect the area ratio (S1 / S0) of the diffraction grating 33, so that the position adjustment of only one axis in the X-axis direction is simple. The operation can prevent the occurrence of a track offset. In FIG. 9, the illustration of the holding member 34 is omitted in order to facilitate understanding of the position adjustment of the diffraction grating 33.
[0075]
As described above, in the optical pickup device 30 according to the present embodiment, the area ratio (S1 / S0) of the diffraction grating 33 is adjusted within a suitable range simply by moving the fixing member 47 of the holding member 34 in the X-axis uniaxial direction. Configured to be able to. Therefore, since the holding member 34 does not need to be held so as to cover the entire diffraction grating 33, the length h1 of the holding member 34 in the direction orthogonal to the X-axis direction is orthogonal to the X-axis direction as shown in FIG. It can be made smaller than the length h2 of the diffraction grating 33 in the direction to be. By reducing the size of the holding member 34, the optical pickup device 30 can be reduced in size.
[0076]
FIG. 11 is a diagram showing an outline of position adjustment of the diffraction grating 33 provided in the optical pickup device according to the second embodiment of the present invention. Since the optical pickup device of the present embodiment is similar to the optical pickup device 30 of the first embodiment, a diagram showing the configuration is omitted.
[0077]
It should be noted that the diffraction grating 33 is configured to be angularly displaceable in a virtual plane including the diffraction grating 33 and orthogonal to the optical axis. The diffraction grating 33 is angularly displaced to adjust the position of the diffraction grating 33 relative to the beam 43, and the area ratio (S1 / S0) of the diffraction grating 33 is adjusted.
[0078]
In FIG. 11A, the center 58 of the beam 43 has a deviation G2 from the center line 59 in the X-axis direction of the region 42b, and further has a deviation G3 from the center line 60 in the Y-axis direction of the diffraction grating 33. Indicates. Thus, the center 58 of the beam 43 has a deviation G2 in the X-axis direction from the intersection 61 of the center line 59 and the center line 60, that is, the center 61 on the plan view of the diffraction grating 33, and a deviation G3 in the Y-axis direction. , It is difficult to move the diffraction grating 33 with high precision in both X and Y axial directions so that the center 58 of the beam 43 and the center 61 of the diffraction grating 33 coincide with each other. This is because the movement direction of the diffraction grating 33 is biaxial, so that a movement error is superimposed as compared with a case where the diffraction grating 33 is moved only in one axial direction.
[0079]
In the present embodiment, the diffraction grating 33 is held by a holding member that can be angularly displaced about an axis that passes through the center 61 of the diffraction grating 33 and extends in a direction perpendicular to the paper surface of FIG. As shown in FIG. 11 (b), the holding member holding the diffraction grating 33 is angularly displaced by an angle θ around the axis in a virtual plane that includes the diffraction grating and is perpendicular to the optical axis. The insertion position of can be adjusted.
[0080]
Although the illustration of the holding member is omitted in FIG. 11, the angularly displaceable holding member is a cylindrical member that shares the axis with the axis passing through the center 61 of the diffraction grating 33. The diffraction grating 33 is held inside the cylinder so that the grating plane is included in a virtual plane orthogonal to the optical axis. The cylindrical holding member is inserted into a columnar opening formed in the housing so as to correspond to the cylindrical shape of the holding member. At this time, the holding member is slidably mounted along the inner peripheral surface of the housing forming the opening. By angularly displacing such a cylindrical holding member around the aforementioned axis, the diffraction grating 33 held by the holding member is angularly displaced around the axis in the plane, and the insertion position with respect to the beam 43 is adjusted. .
[0081]
As described above, the area ratio (S1 / S0) of the diffraction grating 33 is accurately set within a suitable range by a simple adjustment operation in one direction in which the holding member that holds the diffraction grating 33 is angularly displaced about the axis. Therefore, it is possible to easily reduce the amplitude ratio (SPP / MPP) and suppress the amount of generated track offset.
[0082]
FIG. 12 is a system diagram showing a simplified configuration of an optical pickup device 65 according to the third embodiment of the present invention. The optical pickup device 65 of the present embodiment is similar to the optical pickup device 30 of the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.
[0083]
It should be noted in the optical pickup device 65 of the present embodiment that the collimator lens 32 is disposed between the beam splitter 35 and the objective lens 36, so that the light emitted from the semiconductor laser 31 is diffused while diffusing. 33 is irradiated. Therefore, the area of the beam 43 irradiated to the diffraction grating 33 is varied depending on the variation in the distance between the diffraction grating 33 and the semiconductor laser 31 as the light source, that is, the position where the diffraction grating 33 is arranged in the Z-axis direction, which is the optical axis direction. fluctuate.
[0084]
FIG. 13 is a diagram illustrating a state in which the irradiation area of the beam 43 on the diffraction grating 33 varies as the distance between the diffraction grating 33 and the semiconductor laser 31 varies. FIG. 13A is a plan view of the diffraction grating 33 in a state in which the diffraction grating 33 is farthest from the semiconductor laser 31. Hereinafter, the diffraction grating 33 will be described in the order of FIGS. 13B and 13C. FIG. 3 is a plan view of the semiconductor laser 31 in the state where the laser beam is close to the semiconductor laser 31.
[0085]
As shown in FIG. 13, the area S <b> 1 of the region that gives the phase difference in the irradiation area of the beam 43 increases as the diffraction grating 33 moves away from the semiconductor laser 31. That is, the area ratio (S1 / S0) of the diffraction grating 33 increases as the diffraction grating 33 is moved away from the semiconductor laser 31, and decreases as the diffraction grating 33 is brought closer to the semiconductor laser 31. In the present embodiment, the holding member 66 that holds the diffraction grating 33 is provided so as to be movable in the optical axis direction, that is, the Z-axis direction.
[0086]
FIG. 14 is a perspective view showing a simplified configuration of the holding member 66 that holds the diffraction grating 33 provided in the optical pickup device 65. FIG. 14 is a perspective view showing a state in which the irradiation surface of the beam 43 of the diffraction grating 33 is viewed from the side of the semiconductor laser 31 that is a light source. The diffraction grating 33 is fixed to the holding member 66, and the holding member 66 is slidably attached to the housing 68. The housing 68 is a member having a substantially U-shaped cross section perpendicular to the Z-axis direction. The housing 68 is connected to both ends of the base portion 69 and the base portion 69 and rises vertically from both ends of the base portion 69. And second upright portions 70 and 71. A guide groove 72 extending in the Z-axis direction is formed in the base portion 69 so as to face the inside of the housing. An elongated hole 73 that extends through the first upright portion 70 and extends in the Z-axis direction is formed at the approximate center of the first upright portion 70.
[0087]
The holding member 66 has a substantially rectangular parallelepiped shape, and an opening 74 through which light can pass is formed. The diffraction grating 33 is fixed to the opening 74. With the diffraction grating 33 fixed, the holding member 66 is formed with a guide protrusion 75 that protrudes in a direction perpendicular to the direction in which the grating groove of the diffraction grating 33 extends. The holding protrusion 66 and the diffraction grating 33 fixed to the holding member 66 are mounted on the housing 68 so that the guide protrusion 75 engages with the guide groove 72 formed on the base 69 of the housing 68. The The guide protrusion 75 is slidable with a guide groove 72 formed in the base 69, and both end surfaces in the X-axis direction of the holding member 66 in the state of being mounted on the housing 68 are first and second. The surfaces of the upright portions 70 and 71 facing the inner side of the housing are configured to be slidable. Since the housing 68 is fixed to a casing (not shown) of the optical pickup device 65, the diffraction grating 33 held by the holding member 66 moves together with the holding member 66 to move the optical pickup device 65. The position can be changed relative to other optical members.
[0088]
The movement of the diffraction grating 33 relative to the housing 68 is realized as follows, for example. A fitting hole is formed in advance on the sliding surface of the holding member 66 with respect to the first upright portion 70 at a position aligned with the aforementioned long hole 73. A rod-shaped adjustment jig that can be fitted into the fitting hole is prepared, the adjustment jig is fitted into the fitting hole of the holding member 66 through the elongated hole 73, and the adjustment jig is attached in the Z-axis direction. By moving the holding member 66 to, the position of the holding member 66 and the diffraction grating 33 fixed to the holding member 66 can be moved and adjusted in the Z-axis direction.
[0089]
The insertion position of the diffraction grating 33 with respect to the beam 43 is adjusted by a simple adjustment operation of moving the holding member 66 that holds the diffraction grating 33 in one axis direction of the Z axis, and the area ratio (S1 / S0) is preferably set. Since the adjustment can be made to be within the range, the amplitude ratio (SPP / MPP) can be reduced, and the suppression of the track offset generation amount can be easily realized.
[0090]
FIG. 15 is a simplified perspective view showing the configuration of the diffraction grating 33 and the beam splitter 35 provided in the optical pickup device according to the fourth embodiment of the present invention. Since the optical pickup device of the present embodiment is similar to the optical pickup device 30 of the first embodiment, a diagram showing the configuration is omitted.
[0091]
It should be noted in the optical pickup device of the present embodiment that the diffraction grating 33 is attached to the beam splitter 35 near the semiconductor laser 31 of the beam splitter 35. As shown in FIG. 15, by attaching the diffraction grating 33 to the beam splitter 35, a holding member for holding the diffraction grating 33 can be made unnecessary. In addition, since the insertion positions of the diffraction grating 33 and the beam splitter 35 with respect to the light beam can be adjusted at the same time, the efficiency of the adjustment work can be realized.
[0092]
FIG. 16 is a perspective view showing a simplified configuration of the diffraction grating 33 and the beam splitter 35 provided in the optical pickup device according to the fifth embodiment of the present invention. Since the optical pickup device of the present embodiment is similar to the optical pickup device 30 of the first embodiment, a diagram showing the configuration is omitted.
[0093]
It should be noted in the optical pickup device of the present embodiment that the diffraction grating 33 is formed near the semiconductor laser 31 of the beam splitter 35 and is integrated with the beam splitter 35 into a single component. As shown in FIG. 16, since the diffraction grating 33 is integrated with the beam splitter 35 into a single component, the number of components can be reduced. As a result, it is possible to reduce the number of assembling steps at the time of assembling the apparatus, reduce the adjustment work between the parts, and improve the production efficiency.
[0094]
【The invention's effect】
According to the present invention, in the state where the ratio (B / TP) between the beam interval B and the track pitch TP of the optical recording medium is 40 or more, the diffraction grating has a ratio between the push-pull signal SPP1 and the push-pull signal SPP2. When (SPP1 / SPP2) is greater than 2 or less than half, the phase difference with respect to the + 1st order or −1st order diffracted light with respect to the beam area S0 of the + 1st order or −1st order diffracted light irradiated to the diffraction grating Is formed so that the area ratio (S1 / S0) of the area S1 of the diffraction grating giving 0.4 is 0.45 or more and 0.53 or less, and SPP1 / SPP2 is more than 3 or less than 1/3 The area ratio (S1 / S0) is 0.47 or more and 0.52 or less. As a result, the amplitudes of SPP1 and SPP2 can be made smaller than the amplitude of the push-pull signal MPP obtained on the basis of the zeroth-order diffracted light, so that the curvature of the track is large and the ± first-order diffracted light deviates from the center of the track. Even in such a case, the amount of occurrence of track offset can be reduced.
[0095]
Further, according to the present invention, in the state where the ratio (B / TP) between the beam interval B and the track pitch TP of the optical recording medium is less than 40, the diffraction grating has an SPP1 / SPP2 of more than 2 or 2 minutes. When the area ratio (S1 / S0) is 0.40 or more and 0.56 or less, and SPP1 / SPP2 is more than 3 or less than 1/3, The area ratio (S1 / S0) is formed to be 0.45 or more and 0.53 or less. As a result, the amplitudes of SPP1 and SPP2 can be made smaller than the amplitude of the push-pull signal MPP obtained on the basis of the zeroth-order diffracted light, so that the curvature of the track is large and the ± first-order diffracted light deviates from the center of the track. Even in such a case, the amount of occurrence of track offset can be reduced.
[0096]
Further, according to the present invention, it is possible to adjust the insertion position of the diffraction grating with respect to the light beam by moving the holding member that holds the diffraction grating in a direction parallel to the direction in which the grating groove formed in the diffraction grating extends. By such a simple adjustment operation, the area ratio (S1 / S0) can be adjusted to be within a suitable range, so that the amplitude of SPP1 and SPP2 with respect to the amplitude of MPP is reduced, and the amount of generated track offset can be easily suppressed. Can be realized.
[0097]
Further, according to the present invention, the area ratio (S1 / S0) can be adjusted within a suitable range simply by moving the holding member in a uniaxial direction parallel to the direction in which the grating grooves formed in the diffraction grating extend. Since the holding member does not need to be held so as to cover the entire diffraction grating, the length in the direction orthogonal to the one-axis direction can be reduced. Thus, by reducing the dimensions of the members, it is possible to contribute to downsizing of the optical pickup device.
[0098]
According to the invention, the holding member that holds the diffraction grating is angularly displaced in a virtual plane including the diffraction grating and perpendicular to the optical axis to adjust the insertion position of the diffraction grating with respect to the light beam. Can do. By such a simple adjustment operation, the area ratio (S1 / S0) can be adjusted to be within a suitable range, so that the amplitude of SPP1 and SPP2 with respect to the amplitude of MPP is reduced, and the amount of generated track offset can be easily suppressed. Can be realized.
[0099]
Further, according to the present invention, it is possible to adjust the insertion position of the diffraction grating with respect to the light beam by moving the holding member that holds the diffraction grating in the direction parallel to the optical axis direction. By such a simple adjustment operation, the area ratio (S1 / S0) can be adjusted to be within a suitable range, so that the amplitude of SPP1 and SPP2 with respect to the amplitude of MPP is reduced, and the amount of generated track offset can be easily suppressed. Can be realized.
[0100]
According to the present invention, the holding member for holding the diffraction grating can be made unnecessary by mounting the diffraction grating on the beam splitter. Further, since the insertion positions of the diffraction grating and the beam splitter with respect to the light beam can be adjusted at the same time, the efficiency of the adjustment work can be realized.
[0101]
According to the present invention, since the diffraction grating is integrated with the beam splitter into a single component, the number of components can be reduced. As a result, it is possible to reduce the number of assembling steps at the time of assembling the apparatus, reduce the adjustment work between the parts, and improve the production efficiency.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a simplified configuration of an optical pickup device 30 according to an embodiment of the present invention.
2 is a plan view showing a configuration of a diffraction grating 33 provided in the optical pickup device 30. FIG.
FIG. 3 is a diagram illustrating a push-pull signal required in the optical pickup device 30 of the present embodiment.
FIG. 4 is a diagram illustrating a push-pull signal in a state where an offset ΔP required in the optical pickup device 30 of the present embodiment is generated.
FIG. 5 is a diagram illustrating a state in which SB1 is detected by a photodetector 39b.
FIG. 6 is a diagram showing a relationship between an area ratio (S1 / S0) and an amplitude ratio (SPP / MPP).
FIG. 7 is a diagram illustrating an amplitude ratio (SPP / MPP) value at which the track offset amount satisfies 8% or less of the track pitch TP.
8 is a perspective view showing a simplified configuration of a holding member 34 that holds a diffraction grating 33 provided in the optical pickup device 30. FIG.
FIG. 9 is a diagram showing an outline of position adjustment of the diffraction grating 33 in the X-axis direction.
FIG. 10 is a diagram illustrating a state in which the center of a beam 43 has a deviation G1 in the X-axis direction and a signal amplitude remains in the SPP.
FIG. 11 is a diagram showing an outline of position adjustment of a diffraction grating 33 provided in an optical pickup device according to a second embodiment of the present invention.
FIG. 12 is a system diagram showing a simplified configuration of an optical pickup device 65 according to a third embodiment of the present invention.
FIG. 13 is a diagram showing a state where the irradiation area of the beam 43 on the diffraction grating 33 varies as the distance between the diffraction grating 33 and the semiconductor laser 31 varies.
14 is a perspective view showing a simplified configuration of a holding member 66 that holds the diffraction grating 33 provided in the optical pickup device 65. FIG.
FIG. 15 is a perspective view showing a simplified configuration of a diffraction grating 33 and a beam splitter 35 provided in an optical pickup device according to a fourth embodiment of the present invention.
FIG. 16 is a perspective view showing a simplified configuration of a diffraction grating 33 and a beam splitter 35 provided in an optical pickup device according to a fifth embodiment of the present invention.
FIG. 17 is a system diagram schematically showing a configuration of a conventional optical pickup device 1 in which the DPP method is used.
18 is a diagram showing a state of zero-order diffracted light and ± first-order diffracted light irradiated on the optical recording medium 10. FIG.
19 is a diagram showing an outline of a circuit for obtaining a DPP signal based on a detection signal from a photodetector 9. FIG.
FIG. 20 is a diagram illustrating an example of a push-pull signal.
FIG. 21 is a diagram illustrating an example of a push-pull signal in a state where an offset ΔP is generated.
FIG. 22 is a plan view showing a simplified configuration of a diffraction grating 20 provided in an optical pickup device used in another conventional technique.
FIG. 23 is a diagram showing a state in which MB and SB1 and SB2 are irradiated on the same track 1;
24 is a diagram showing a state in which MB, SB1, and SB2 are irradiated on a track having a curvature on the optical recording medium 10. FIG.
FIG. 25 is a diagram illustrating an example of a DPP signal obtained based on detection signals of MB, SB1, and SB2 irradiated on a track having a curvature.
FIG. 26 shows a relationship between a beam interval B and a track offset when information is reproduced from an optical recording medium having a track pitch TP of 1.2 μm.
FIG. 27 is a diagram showing a state where MBs are displaced from a straight line 24 that extends in the radial direction through the center of the optical recording medium 10;
[Explanation of symbols]
30, 65 Optical pickup device
31 Semiconductor laser
32 Collimator lens
33 Diffraction grating
34, 66 holding member
35 Beam splitter
36 Objective lens
37 Reflected light condensing lens
38 Cylindrical lens
39 Light detection means
40 Optical recording media

Claims (10)

An optical pickup device for recording information on an optical recording medium by light or reproducing information from the optical recording medium,
A light source that emits light;
The light emitted from the light source is diffracted into at least zero-order diffracted light, plus (+) first-order diffracted light, and minus (−) first-order diffracted light, and gives a phase difference to a part of the + and − (±) first-order diffracted lights. A diffraction grating,
Condensing means for condensing zero-order diffracted light and ± first-order diffracted light on the optical recording medium;
A light branching unit disposed between the light source and the light collecting unit and transmitting and reflecting zero-order diffracted light and ± first-order diffracted light;
Photodetection means comprising a plurality of light receiving elements for receiving zero-order diffracted light and ± first-order diffracted light reflected by the optical recording medium,
A beam interval B, which is a distance between a beam spot center of zero-order diffracted light focused on the optical recording medium and a beam spot center of + 1st-order diffracted light or −1st-order diffracted light, and a track formed on the optical recording medium In a state where the ratio (B / TP) to the pitch TP is 40 or more,
The diffraction grating is
The ratio (SPP1 / SPP2) of the push-pull signal SPP1 obtained based on the + 1st order diffracted light detected by the plurality of light receiving elements and the push-pull signal SPP2 obtained based on the -1st order diffracted light exceeds 2 or 2 When it is less than 1 /
The area ratio (S1 / S0) is given, where S0 is the beam area of the + 1st order or −1st order diffracted light irradiated to the diffraction grating, and S1 is the area of the diffraction grating that gives a phase difference to the + 1st order or −1st order diffracted light. , 0.45 or more and 0.53 or less. The diffraction grating is
When the ratio of the push-pull signals SSP1 and SSP2 (SPP1 / SPP2) is greater than 3 or less than 1/3,
2. The optical pickup device according to claim 1, wherein the area ratio (S1 / S0) is formed to be 0.47 or more and 0.52 or less. An optical pickup device for recording information on an optical recording medium by light or reproducing information from the optical recording medium,
A light source that emits light;
The light emitted from the light source is diffracted into at least zero-order diffracted light, plus (+) first-order diffracted light, and minus (−) first-order diffracted light, and gives a phase difference to a part of the + and − (±) first-order diffracted lights. A diffraction grating,
Condensing means for condensing zero-order diffracted light and ± first-order diffracted light on the optical recording medium;
A light branching unit disposed between the light source and the light collecting unit and transmitting and reflecting zero-order diffracted light and ± first-order diffracted light;
Photodetection means comprising a plurality of light receiving elements for receiving zero-order diffracted light and ± first-order diffracted light reflected by the optical recording medium,
A beam interval B, which is a distance between a beam spot center of zero-order diffracted light focused on the optical recording medium and a beam spot center of + 1st-order diffracted light or −1st-order diffracted light, and a track formed on the optical recording medium In a state where the ratio (B / TP) to the pitch TP is less than 40,
The diffraction grating is
The ratio (SPP1 / SPP2) of the push-pull signal SPP1 obtained based on the + 1st order diffracted light detected by the plurality of light receiving elements and the push-pull signal SPP2 obtained based on the -1st order diffracted light exceeds 2 or 2 When it is less than 1 /
The area ratio (S1 / S0) is given, where S0 is the beam area of the + 1st order or −1st order diffracted light irradiated to the diffraction grating, and S1 is the area of the diffraction grating that gives a phase difference to the + 1st order or −1st order diffracted light. , 0.40 or more and 0.56 or less. The diffraction grating is
When the ratio of the push-pull signals SSP1 and SSP2 (SPP1 / SPP2) is greater than 3 or less than 1/3,
The optical pickup device according to claim 3, wherein the area ratio (S1 / S0) is formed to be 0.45 or more and 0.53 or less. A holding member for holding the diffraction grating;
The holding member is
The optical pickup device according to claim 1, wherein the optical pickup device is provided so as to be movable in a direction parallel to a direction in which a grating groove formed in the diffraction grating extends. In a direction orthogonal to the direction in which the grating grooves of the diffraction grating extend,
6. The optical pickup device according to claim 5, wherein a length of the holding member is smaller than a length of the diffraction grating. A holding member for holding the diffraction grating;
The holding member is
5. The optical pickup device according to claim 1, wherein the optical pickup device is provided so that the diffraction grating can be angularly displaced in a virtual plane that includes the diffraction grating and is perpendicular to the optical axis. A holding member for holding the diffraction grating;
The optical pickup device according to claim 1, wherein the holding member is provided so as to be movable in a direction parallel to the optical axis direction. The light branching means is a beam splitter,
The diffraction grating is
The optical pickup device according to claim 1, wherein the optical pickup device is attached to the beam splitter near the light source of the beam splitter. The light branching means is a beam splitter,
The diffraction grating is
5. The optical pickup device according to claim 1, wherein the optical pickup device is formed near the light source of the beam splitter and integrated with the beam splitter as a single component.

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