JP3754019B2 - Optical head and disk recording / reproducing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head in a disk recording / reproducing apparatus that is a system for optically recording / reproducing information by projecting a light spot onto a disk-shaped (or disk-shaped) information recording medium.
[0002]
[Prior art]
In recent years, optical heads and disk recording / reproducing apparatuses have been used for various purposes such as DVDs, MDs, CDs, and CD-Rs, and have become increasingly dense, high performance, high quality, and high added value. In particular, in a disk recording / reproducing apparatus using a recordable magneto-optical medium, the demand for portable devices is greatly increasing, and further miniaturization, thinning, high performance, and cost reduction are required.
[0003]
Conventionally, many reports have been made on the technology of the optical head of a disk recording / reproducing apparatus for a magneto-optical disk (see, for example, Patent Document 1). Hereinafter, an optical head of a disk recording / reproducing apparatus for a magneto-optical disk will be described as an example of a conventional optical head with reference to the drawings. FIG. 14, FIG. 15, FIG. 16, FIG. 17 and FIG. 18 are diagrams illustrating the schematic configuration of a conventional optical head and the principle of operation thereof.
[0004]
14, 15, 16, 17, and 18, 101 is a silicon substrate, 102 is a semiconductor laser that is a light source fixed on the silicon substrate 100, and 103 is formed on the silicon substrate 100 by an IC process. The multi-divided photodetector 104, a heat radiating plate for holding the silicon substrate 100 in a heat transfer state, 105 a terminal wired from the multi-divided photo detector by wire bonding, etc. 106, the silicon substrate 101, the radiating plate 104 and the terminal A resin package 105 holds, 107 is a hologram element (diffraction grating) formed of resin, 108 is a composite element composed of a beam splitter 108a, a folding mirror 108b, and a polarization separation element 108c.
[0005]
Further, an integrated unit 109 is defined as a structure in which the silicon substrate 101, the semiconductor laser 102, the multi-segment photodetector 103, the heat radiation plate 104, the terminal 105, the resin package 106, the hologram element 107, and the composite element 108 are integrated. 110 is a reflection mirror, 111 is an objective lens, 112 is an objective lens holder for fixing the objective lens 111, 113 is a magneto-optical recording medium which is an information recording medium having a magneto-optical effect, and 114 is a magneto-optical recording medium 113. Is an objective lens driving device that drives in a focusing direction (a direction substantially perpendicular to the magneto-optical recording medium 113) and a radial direction (a direction substantially parallel to the magneto-optical recording medium 113).
[0006]
The objective lens driving device 114 is a component of an objective lens 111, an objective lens holder 112, a base 115, a suspension 116, a magnetic circuit 117, and coils 118a and 118b that form a light spot on the magneto-optical disk using a light beam from the semiconductor laser 102. Consists of. By energizing the coil 118a, the objective lens 111 can be driven in the focus direction, and by energizing the coil 118b, the objective lens 111 can be driven in the radial direction. Reference numeral 119 denotes an optical bench, and the optical bench 119 fixes the reflection mirror 110.
[0007]
Further, the integrated unit 109 is fixed by adhering the optical bench 119 and the resin package 106. As a result, the position of the multi-split photodetector 103 in the Z-axis direction (optical axis direction) is the dimension of the optical bench 119 so that the focus error signal light-receiving region 124 is positioned approximately in the middle between the focal points 130 and 131 of the light spot. Is defined.
[0008]
On the other hand, in FIG. 18, 120 is a light spot for detecting a focus error signal formed on the multi-segment photodetector 103, 121 is a light spot for detecting a tracking error signal formed on the multi-segment photodetector 103, and 122. Is a main beam (P-polarized light) formed on the multi-split photodetector 103, 123 is a main beam (S-polarized light) formed on the multi-split photodetector 103, 124 is a focus error signal light receiving region, and 125 and 126. Is a tracking error signal light receiving area, 127 is an information signal light receiving area, 128 is a subtractor, and 129 is an adder.
[0009]
In FIG. 17, reference numerals 130 and 131 denote the focal points of a light spot for detecting a focus error signal, and 132 denotes a light spot formed on the magneto-optical recording medium 113. In FIG. 16, 133 is a cover, 134 is an adhesive, and 135 is a flexible circuit.
[0010]
Further, as shown in FIG. 14, the optical head feeding device for moving the optical head in the radial direction of the magneto-optical recording medium 113 is constituted by a feed screw 136, a countershaft 137, a feed motor 138, a gear 139a, a gear 139b, and a cover 133. The nut plate 140, the bearing 141, and the like are attached to the mechanical base 142 (details are not shown). At this time, the nut plate 140 and the feed screw 136 are engaged, and the optical head is rotated by the feed amount determined from the gear ratio of the gear 139a and the gear 139b and the reduction ratio calculated by the pitch of the feed screw 136 by the rotation of the feed motor 138. The whole moves in the radial direction.
[0011]
At this time, the relative position between the objective lens 111 and the optical bench 119 is shifted by the feed amount. Further, the maximum value of the movement amount of the objective lens 111 in the radial direction is a value immediately before the feed motor 138 rotates.
[0012]
As shown in FIG. 14, FIG. 15 and FIG. 20, the operation of the objective lens 111 at the time of recording or reproducing from the inner circumference to the outer circumference of the magneto-optical recording medium 113 is as follows. In order to move the objective lens 111 in the radial direction so as to follow the track of the magneto-optical recording medium 113, an electric current is applied to the coil 118b. A voltage corresponding to the current value applied to the coil 118b is applied to the feed motor 138, and when the predetermined voltage is reached, the feed motor 138 rotates, so that the gear ratio determined by the gears 139a and 139b and the feed screw 136 is reached. Is fed to the optical head to drive the entire optical bench 119 in the outer circumferential direction. At this time, the relative positional deviation between the objective lens 111 and the optical bench 119 (or the design optical axis) is a value obtained by subtracting the feed amount of the optical head from the movement amount of the objective lens 111.
[0013]
The operation of the conventional example configured as described above will be described below with reference to FIGS. 14, 15, 16, 17, and 18. FIG. The light emitted from the semiconductor laser 102 is separated into a plurality of different light beams by the hologram element 107. A plurality of different light beams are transmitted through the beam splitter 108a of the composite element 108, reflected by the reflection mirror 110, and fixed to the objective lens holder 112 by the objective lens 111, and a light spot 132 having a diameter of about 1 micron on the magneto-optical recording medium 113. It is condensed as.
[0014]
Further, the light beam reflected by the beam splitter 108a of the composite element 108 enters a laser monitor light receiving element (not shown) and controls the drive current of the semiconductor laser 102. The reflected light from the magneto-optical recording medium 113 follows the reverse path, is reflected and separated by the beam splitter 108a of the composite element 108, and enters the folding mirror 108b and the polarization separation element 108c.
[0015]
The semiconductor laser 102 is installed so as to have a polarization direction parallel to the paper surface in FIG. 17A. The incident light is separated into two light beams of two polarization components orthogonal to each other by the polarization separation element 108c, and receives an information signal. The light enters the region 127.
[0016]
Of the reflected light from the magneto-optical recording medium 113, the light beam that has passed through the beam splitter 108 a is separated into a plurality of light beams by the hologram element 107 and is focused on the focus error signal light receiving region 124 and the tracking error signal light receiving regions 125 and 126. Focus servo is performed by the so-called SSD method, and tracking servo is performed by the so-called push-pull method.
[0017]
Further, by calculating the difference between the main beam 122 made of P-polarized light and the main beam 123 made of S-polarized light, the magneto-optical disk information signal can be detected by the differential detection method. Furthermore, the pre-pit signal can be detected by taking the sum of them.
[0018]
In the optical head configured as described above, the relative positions of the semiconductor laser 102, the objective lens 111, and the multi-segment photodetector 103 are adjusted at the time of assembly in order to obtain a desired detection signal by reflected light from the magneto-optical recording medium 113. Is done. Regarding these relative position adjustments, the initial position setting of the focus error signal is performed by setting the position of the multi-segment photodetector 103 in the Z-axis direction (optical axis direction), and the focus error signal light-receiving region 124 of the focal points 130 and 131 of the light spots. It is determined by defining the dimensions of the optical bench 119 and the resin package 106 of the integrated unit 109 so as to be positioned approximately in the middle.
[0019]
As shown in FIGS. 16A and 16B, the tracking error signal is adjusted by holding the base 115 with an external jig (not shown) and moving the objective lens driving device 114 in the Y and X directions. By moving, the output of the tracking error signal light receiving regions 125 and 126 is adjusted to be substantially uniform.
[0020]
As a result, this adjustment results in aligning the center of the objective lens 111 with the center of the emission axis of the semiconductor laser 2 in FIG. Further, the relative tilt adjustment between the magneto-optical recording medium 113 and the objective lens 111 is performed by holding the base 115 with an external jig (not shown), adjusting the skew in the radial direction (around the Y axis) θR, and the tangential direction (X axis). Around) Adjust by skew adjustment θT. After the adjustment, the base 115 is bonded and fixed to the optical bench 119 using an adhesive 134. Thus, the adjustment of the focus error signal and tracking error signal and the skew adjustment are completed, and the optical head is completed.
[0021]
On the other hand, FIG. 19 shows the focus servo of the optical head having the above-described conventional configuration. The focus error signal calculated and generated by the so-called SSD method is calculated according to the offset amount. The focus servo converges in the vicinity of GND by applying the measured current to the coil 118b.
[0022]
The focus error signal generates a so-called S-shaped signal due to the change in the focus direction position of the objective lens 111, and the focus point of the objective lens 111 converges in the vicinity of the GND of the focus error signal. At this time, the definition of the defocus amount is defined as the difference between the vicinity of the approximate center of the S-shaped signal and GND as shown in FIG.
[0023]
[Patent Document 1]
JP 2000-48374 A
[0024]
[Problems to be solved by the invention]
However, the optical system of the optical head having the above-described conventional configuration is a so-called finite system, and as the objective lens 111 moves in the radial direction of the magneto-optical recording medium 113 (particularly as it moves away from the design optical axis of the objective lens 111), the light An off-axis aberration occurs in the light spot 132 on the magnetic recording medium 113, and the shape of the light spot 120 for detecting the focus error signal on the focus error signal light receiving area 124 changes, so that FIGS. As shown in FIG. 5, the focus point of the light spot 132 with respect to the magneto-optical recording medium 113 is shifted and defocusing occurs.
[0025]
As shown in FIG. 21, the off-axis aberration (wavefront aberration) when the objective lens 111 moves in the radial direction is a breakdown of astigmatism, coma aberration, spherical aberration, higher order aberration, etc., most of which are astigmatism. The amount of defocus, which is an aberration and is generated when the objective lens 111 is moved in the radial direction, increases as the amount of movement of the objective lens 111 in the radial direction increases and the thickness of the objective lens 111 decreases. In particular, optical heads for portable disk recording / reproducing apparatuses are required to be small and thin, and off-axis aberrations increase as the objective lens 111 becomes smaller and thinner.
[0026]
Further, defocusing increases the spot diameter of the light spot 132 on the magneto-optical recording medium 113 and increases the ellipticity of the spot. At this time, astigmatism in the light spot 132 after emission from the objective lens 11 due to the astigmatic difference of the semiconductor laser 102 on the design optical axis (the radial shift amount of the objective lens 111 is 0 or the design optical axis of the objective lens 111). As for the direction of the aberration, the rear focal line of the light spot 132 coincides with the substantially radial direction, and off-axis aberrations (mainly astigmatism) increase as the objective lens 111 moves in the radial direction. In particular, when the objective lens 111 is made thin in order to make the optical head small and thin, the off-axis aberration (astigmatism) of the objective lens 111 increases.
[0027]
Accordingly, the shape of the light spot 132 on the magneto-optical recording medium 113 becomes an elliptical shape having a major axis in the radial direction due to defocus accompanying the movement of the objective lens 111 in the radial direction, and is adjacent to the groove to be reproduced. When a part of the light spot 132 is also radiated to the groove, the signal reading ability is reduced due to the increase in crosstalk at the time of reproducing the information signal recorded on the magneto-optical recording medium 113, or on the magneto-optical recording medium 113. There is a problem that the recording / reproducing ability deteriorates due to a decrease in reading ability due to crosstalk of the wobble signal (ADIP signal or ATIP signal) having the address information and the like formed in FIG.
[0028]
Further, as shown in FIG. 21, since the off-axis aberration tends to increase significantly in the small and thin lens, astigmatism, coma, spherical aberration and higher-order aberration increase accompanying off-axis aberration increase and Due to the inclination of the objective lens, the optical performance is significantly deteriorated with respect to the design axis, and the recording / reproducing performance is greatly deteriorated. In FIG. 21, the angle of view of 1 degree corresponds to the amount of movement of the objective lens 111.
[0029]
The present invention solves the above-described conventional problems, and realizes stable recording and reproduction with little crosstalk, and an optical head that can reduce the size and thickness of an apparatus by reducing the size and thickness of an objective lens. It is another object of the present invention to provide a disk recording / reproducing apparatus using the same.
[0030]
[Means for Solving the Problems]
In order to achieve the above object, an optical head according to the present invention is a finite or pseudo-finite optical system including a light source having astigmatism and an objective lens that forms a light spot on an information recording medium by a light beam from the light source. The optical spot has an initial astigmatism on the design optical axis, and the direction of the initial astigmatism is such that the rear focal line is substantially the radial direction of the information recording medium. An optical characteristic that generates astigmatism in a direction in which the initial astigmatism of the light spot decreases as the objective lens moves in a direction orthogonal to each other and moves away from the design optical axis in the radial direction. ,
Within the range of movement of the objective lens in the radial direction, the direction of astigmatism of the light spot formed by the objective lens is a direction in which the rear focal line is substantially orthogonal to the radial direction. Thus, the initial astigmatism is set so that the total astigmatism becomes zero at the position where the objective lens has moved by the maximum movement amount in the radial direction. It is characterized by that.
[0031]
Next, the disc recording / reproducing apparatus of the present invention includes the optical head of the present invention and an optical head feeding device that performs intermittent feeding so that the movement amount of the objective lens in the radial direction is within an allowable range. It is characterized by that.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
According to the optical head of the present invention, since the light spot at the time of defocusing can be made longitudinally long with respect to the track, a reproduction signal with little crosstalk can be realized, and the influence of off-axis aberration can be reduced. A lens can be realized, and the optical head can be made smaller and thinner.
[0033]
Also, according to the disk recording / reproducing apparatus of the present invention, since the optical head of the present invention is provided, the recording and reproducing performance can be improved, and a small and thin disk recording / reproducing apparatus can be realized.
[0034]
In the present optical head, it is preferable that astigmatism is added to the objective lens so as to obtain the initial astigmatism. According to this configuration, astigmatism can be added with a simple configuration without adding special parts.
[0035]
Further, it is preferable that astigmatism generating means is further provided between the light source and the objective lens, and the astigmatism generating means is added with astigmatism so as to obtain the initial astigmatism. According to this configuration, since the astigmatism generating means is provided separately from the objective lens, it is easy to adjust the amount of astigmatism to be added, and an optimal correction amount can be applied with high accuracy.
[0036]
The initial astigmatism is preferably in the range of 30 mλ to 100 mλ. According to this configuration, it is possible to use an ultra-thin objective lens that generates a large amount of astigmatism in the radial movement range.
[0037]
Moreover, it is preferable that the absolute value within the movement range of the radial direction of the objective lens is in a range of 200 μm or more and 500 μm or less.
In addition, it is preferable that a change amount of astigmatism generated by a movement amount of the objective lens in the radial movement range is in a range of 30 mλ to 100 mλ.
[0038]
The light source is preferably composed of a semiconductor laser, and the direction of astigmatism of the light spot generated by the semiconductor laser is preferably a direction in which the front focal line is substantially perpendicular to the radial direction.
The objective lens is a single lens formed of resin or glass, and the astigmatism direction of the light spot generated by the objective lens on the design optical axis is substantially the same as the radial direction of the rear focal line. It is preferable that it is the direction orthogonal to.
[0039]
The objective lens is a single lens made of resin or glass, and the astigmatism direction of the light spot generated by the astigmatism generating means on the design optical axis is such that the rear focal line is in the radial direction. It is preferable that the direction is substantially perpendicular to the direction.
[0040]
The astigmatism generating means is preferably a flat glass or a cylindrical lens. According to this configuration, the amount of astigmatism to be added can be adjusted simply by changing the angle of the flat glass or the cylindrical lens, and the optimum correction amount can be applied easily and accurately.
[0041]
The disc recording / reproducing apparatus of the present invention further includes a feed amount detection means in the radial direction of the objective lens, and the optical head feed device performs the intermittent feed when a predetermined movement amount is reached. preferable.
Further, it is preferable that a part of the tracking error signal is used for the calculation of the feed amount detecting means.
[0042]
Moreover, it is preferable that the calculation of the feed amount detection means uses an applied current of an objective lens driving device that drives the objective lens in a radial direction.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0043]
(Embodiment 1)
1 to 6, 1 is a silicon substrate, 2 is a semiconductor laser which is a light source fixed on the silicon substrate 1, 3 is a multi-segment photodetector on the silicon substrate 1, and the multi-segment photodetector 3 is For example, it is formed by an IC process or the like. 4 is a heat dissipation plate for holding the silicon substrate 1 in a heat transfer state, 5 is a terminal wired from the multi-divided photodetector by wire bonding or the like, 6 is a resin package for holding the silicon substrate 1, the heat dissipation plate 4 and the terminal 5, 7 is a hologram element (diffraction grating) formed of resin, and 8 is a composite element composed of a beam splitter 8a, a folding mirror 8b, and a polarization separation element 8c.
[0044]
Reference numeral 9 denotes an integrated unit in which the silicon substrate 1, the semiconductor laser 2, the multi-divided photodetector 3, the heat radiating plate 4, the terminal 5, the resin package 6, the hologram element 7 and the composite element 8 are integrated.
[0045]
Reference numeral 10 denotes a reflection mirror, 12 denotes an objective lens holder, 11 denotes an objective lens, and 12 denotes an objective lens holder for fixing the objective lens 11. The objective lens 11 is described later on a magneto-optical disk using a light beam from the semiconductor laser 1. The light spot 32 is formed. Reference numeral 13 denotes a magneto-optical recording medium having a magneto-optical effect.
[0046]
The semiconductor laser 2 has an astigmatic difference, and the amount of this astigmatic difference is referred to as A. Reference numeral 14 denotes an objective lens driving device that drives the objective lens 11 in the focus direction and radial direction of the magneto-optical recording medium 13.
[0047]
As shown in FIG. 3, the objective lens driving device 14 shown in FIG. 4 includes an objective lens 11, an objective lens holder 12, a base 15, a suspension 16, a magnetic circuit 17, and coils 18a and 18b. By energizing the coil 18a, the objective lens 11 can be driven in the focus direction, and by energizing the coil 18b, the objective lens 11 can be driven in the radial direction.
[0048]
Reference numeral 19 denotes an optical bench, and the reflection mirror 10 is fixed to the optical bench 19. Further, the integrated unit 9 is fixed by bonding the optical bench 19 and the resin package 6 together. As a result, the position of the multi-split photodetector 3 in the Z-axis direction (optical axis direction) is the dimension of the optical bench 19 so that the focus error signal light receiving region 24 is positioned approximately in the middle between the focal points 30 and 31 of the light spot. Is defined.
[0049]
On the other hand, 20 is a light spot for detecting a focus error signal formed on the multi-split photodetector 3, 21 is a light spot for detecting a tracking error signal formed on the multi-split photodetector 3, and 22 is a multi-split. The main beam (P-polarized light) formed on the photodetector 3, 23 is the main beam (S-polarized light) formed on the multi-split photodetector 3, 24 is a focus error signal light receiving area, and 25 and 26 are tracking errors. Signal receiving area 27, information signal receiving area 27, subtractor 28, adder 29, 30 and 31 are focal points of the light spot for detecting the focus error signal, 32 is a light spot formed on the magneto-optical recording medium 13 , 33 is a cover, 34 is an adhesive, and 35 is a flexible circuit.
[0050]
Further, the optical head feeding device for moving the optical head in the radial direction of the magneto-optical recording medium 13 includes a feed screw 36, a countershaft 37, a feed motor 38, a gear 39a, a gear 39b, and a cover 33 as shown in FIG. The nut plate 40, the bearing 41, and the like are attached to the mechanical base 42 (details are not shown).
[0051]
At this time, the nut plate 40 and the feed screw 36 are engaged, and by rotation of the feed motor 38, the optical head is fed by a feed amount determined from the gear ratio between the gears 39a and 39b and the reduction ratio calculated from the pitch of the feed screw 36. The whole moves in the radial direction. At this time, the relative position between the objective lens 11 and the optical bench 19 is shifted by the feed amount. Further, the maximum value of the movement amount of the objective lens 11 in the radial direction is a value immediately before the feed motor 38 rotates.
[0052]
As shown in FIG. 2, FIG. 3 and FIG. 9, the operation of the objective lens 11 at the time of recording or reproducing from the inner circumference to the outer circumference of the magneto-optical recording medium 13 is as follows. In order to move the objective lens 11 in the radial direction so as to follow the track of the magneto-optical recording medium 13, a current is applied to the coil 18b. A voltage corresponding to the current value applied to the coil 18b is applied to the feed motor 38, and when the voltage reaches a predetermined voltage, the feed motor 38 rotates to determine the gear determined by the gears 39a and 39b and the feed screw 36. A feed amount corresponding to the ratio is applied to the optical head to drive the entire optical bench 19 in the outer circumferential direction.
[0053]
At this time, the relative positional deviation between the objective lens 11 and the optical bench 19 (or the design optical axis or the central axis of the objective lens) is a value obtained by subtracting the feed amount of the optical head from the movement amount of the objective lens 11. At this time, from the viewpoint of power consumption, the objective lens 11 is moved in the radial direction by following the track of the magneto-optical recording medium 13 by moving only the objective lens driving device 14 as much as possible without operating the feed motor 38 as far as possible. It is preferable to move it.
[0054]
The operation of the first embodiment configured as described above will be described below with reference to FIGS. 1, 2, 3, 4, 5, and 6. The light emitted from the semiconductor laser 2 is separated into a plurality of different light beams by the hologram element 7. A plurality of different light beams are transmitted through the beam splitter 8a of the composite element 8, reflected by the reflecting mirror 10, and fixed to the objective lens holder 12 by the objective lens 11 on the magneto-optical recording medium 13 so as to have a light spot 32 having a diameter of about 1 micron. It is condensed as.
[0055]
The light beam reflected by the beam splitter 8a of the composite element 8 is incident on a laser monitor light receiving element (not shown) and controls the drive current of the semiconductor laser 2. The reflected light from the magneto-optical recording medium 13 follows the reverse path, is reflected and separated by the beam splitter 8a of the composite element 8, and enters the folding mirror 8b and the polarization separation element 8c.
[0056]
The semiconductor laser 2 is installed so as to have a polarization direction parallel to the paper surface in FIG. 5A, and incident light is separated into two light beams of two polarization components orthogonal to each other by the polarization separation element 8c. It enters the information signal light receiving area 27 shown.
[0057]
Of the reflected light from the magneto-optical recording medium 13, the light beam that has passed through the beam splitter 8 a is separated into a plurality of light beams by the hologram element 7 and condensed into the focus error signal light receiving region 24 and the tracking error signal light receiving regions 25 and 26. To do. Focus servo is performed by the so-called SSD method, and tracking servo is performed by the so-called push-pull method.
[0058]
Further, by calculating the difference between the main beam 22 made of P-polarized light and the main beam 23 made of S-polarized light, the magneto-optical disk information signal can be detected by the differential detection method. Furthermore, the pre-pit signal can be detected by taking the sum of them.
[0059]
In the optical head configured as described above, relative position adjustment of the semiconductor laser 2, the objective lens 11, and the multi-segment photodetector 3 is performed at the time of assembly in order to obtain a desired detection signal by reflected light from the magneto-optical recording medium 13. Is done. Regarding these relative position adjustments, the initial position setting of the focus error signal is performed by setting the position of the multi-segment photodetector 3 in the Z-axis direction (optical axis direction) and the focus error signal light-receiving area 24 of the focal points 30 and 31 of the light spots. It is determined by defining the dimensions of the optical bench 19 and the resin package 6 of the integrated unit 9 so as to be positioned approximately in the middle.
[0060]
As shown in FIGS. 4A and 4B, the tracking error signal is adjusted by holding the base 15 with an external jig (not shown) and moving the objective lens driving device 14 in the Y direction and the X direction. By doing so, the outputs of the tracking error signal light receiving regions 25 and 26 are adjusted to be substantially uniform. As a result, this adjustment results in aligning the optical axis center of the objective lens 11 with the emission axis center of the semiconductor laser 2 in FIG.
[0061]
Further, the relative inclination adjustment between the magneto-optical recording medium 13 and the objective lens 11 is performed by holding the base 15 with an external jig (not shown), adjusting the skew in the radial direction (around the Y axis) θR, and the tangential direction (X axis). Around) Adjust by skew adjustment θT. After the adjustment, the base 15 is bonded and fixed to the optical bench 19 using an adhesive 34. Thus, the adjustment of the focus error signal and tracking error signal and the skew adjustment are completed, and the optical head is completed.
[0062]
On the other hand, FIGS. 7A and 7B show the focus servo of the optical head according to the first embodiment, and the offset amount with respect to the focus error signal calculated and generated by the so-called SSD method is calculated. The focus servo is configured to converge near GND by applying a current corresponding to the offset amount to the coil 18b. The focus error signal generates a so-called S-shaped signal due to a change in the focus direction position of the objective lens 11, and the focus point of the objective lens 11 converges in the vicinity of the GND of the focus error signal. At this time, the defocus amount is defined as the difference between the vicinity of the approximate center of the S-shaped signal and GND as shown in FIG. 7B.
[0063]
As the objective lens 11 moves in the radial direction, the amount of astigmatism of the light spot 32 changes and the shape of the light spot 20 on the focus error signal light receiving region 24 changes, so that a defocus difference occurs. The defocus amount at this time is the largest when the feed motor 38 starts to move as shown in FIGS. 9A, 9B, and 9C, and the defocus direction at this time is the minus direction (magneto-optical recording medium). 13 and the direction in which the objective lens 11 moves away).
[0064]
FIGS. 8A and 8B are schematic views of the shape of the light spot 32 on the magneto-optical recording medium 13 at the time of defocusing. FIG. 8A relates to the present embodiment, and FIG. 8B relates to a comparative example.
Although details will be described later, in this embodiment, the light spot has initial astigmatism on the design optical axis, and the direction of the initial astigmatism is the rear focal line in the radial direction of the magneto-optical recording medium 13. The direction is substantially perpendicular to the direction. The design optical axis here is an axis that is equal to the optical axis of the objective lens 11 when the radial shift amount of the objective lens 11 is 0, and the objective lens 11 on the design optical axis is If it deviates, the optical axis of the objective lens 11 will also deviate from the design optical axis. The same applies to the following description.
[0065]
In this embodiment, because of such initial astigmatism, when defocused in the-direction, the light spot is elongated in the track direction as shown in FIG. (I.e., the major axis of the elliptical light spot is along the track direction), making it difficult for the light spot to illuminate the track adjacent to the desired track to be illuminated, thereby reducing the effects of crosstalk. It becomes difficult to receive. Therefore, stable recording and reproduction can be realized even when defocusing (particularly, defocusing in the negative direction) occurs in the radial direction movement region of the objective lens 11 shown in FIG.
[0066]
On the other hand, in the comparative example having no initial astigmatism as described above, as shown in FIG. 8B, when defocused in the negative direction, the light spot is elongated in the radial direction. (I.e., the major axis of the elliptical light spot is along the radial direction), and the light spot is likely to irradiate adjacent tracks.
[0067]
FIG. 10 shows the direction of astigmatism and astigmatism of the first embodiment with respect to the magneto-optical recording medium 13. FIG. 1 shows a schematic diagram of an optical path. In the illustration of FIG. 1, two sets of combinations of the objective lens 11 and the semiconductor laser 2 are illustrated, but the left side is illustrated in the XY plane (horizontal side), and the right side is illustrated in the XZ plane (vertical side). FIG. The disk 13 is shown to indicate the track direction and the radial direction, and the positional relationship with respect to the optical path is different from the actual one. The Z axis is also the direction of the optical axis between the semiconductor laser 2 and the disk 13.
[0068]
As shown in FIG. 1, the semiconductor laser 2 has a difference between a light emitting point on the XY plane (horizontal side) and a light emitting point on the XZ plane (vertical side) (light emitting point on the semiconductor end face). It has a point difference A. The direction of the astigmatic difference of the semiconductor laser 2 in the optical head is the direction shown in FIG. At this time, the light emitting point on the XZ plane is close to the objective lens 11 side. When the light spot 32 is in the direction in which the distance between the magneto-optical recording medium 13 and the objective lens 11 is away, the elliptical shape of the light spot 32 is obtained. The major axis direction is substantially perpendicular to the radial direction.
[0069]
The astigmatic difference A is compressed by an amount converted by the longitudinal magnification β2 of the optical system and becomes astigmatism of the light spot 32 after passing through the objective lens 11. At this time, the focal line at the focal position in the direction in which the objective lens 11 and the magneto-optical recording medium 13 approach is defined as the front focal line, and the focal line in the focal position in the direction away from the objective lens 11 is defined as the rear focal line.
[0070]
FIG. 11 is a diagram showing the concept of wavefront aberration (or total aberration) of the light spot 32. The wavefront aberration is a sum of astigmatism, coma aberration, spherical aberration, high order aberration, and the like, and the objective lens 11 deviates from the design optical axis (the optical axis of the objective lens 11 and the design optical axis become different). Off-axis aberrations occur in the light spot 32 (as it deviates).
[0071]
Here, in the present embodiment, as shown in FIGS. 10 and 11, initial astigmatism is given on the design optical axis. The direction of this initial astigmatism is a direction in which the rear focal line is substantially orthogonal to the radial direction of the magneto-optical recording medium 13 (coincident with the substantially tangential direction), and as the objective lens 11 moves in the radial direction. Astigmatism occurs in the direction in which the initial astigmatism decreases.
[0072]
Since astigmatism is dominant in the off-axis aberration, as shown in FIG. 11, if the astigmatism is reduced with the movement in the radial direction, the objective lens 11 is not moved in the radial direction. Although coma, spherical aberration, and higher-order aberrations increase, total aberrations decrease. In the first embodiment, the radial movement range of the objective lens 11 in which the astigmatism is 0 mλ is set to 200 μm or more and 500 μm or less.
[0073]
Further, as described above, the light spot 32 has initial astigmatism, but its value is astigmatism on the design optical axis of the objective lens 11, the astigmatism of the semiconductor laser 2, the mirror 10, etc. Is determined by the astigmatism in the optical path (mainly the objective lens 11 and the semiconductor laser 2 are dominant), the amount of astigmatism generated in the radial movement range of the objective lens 11, and the radial of the objective lens 11 The amount of directional movement is determined by the astigmatism direction of the light spot 32 in the radial direction movement range of the objective lens 11.
[0074]
Astigmatism correction in the present embodiment, that is, as shown in FIG. 10, the rear focal line has an initial astigmatism in the direction that coincides with the substantially tangential direction of the magneto-optical recording medium 13 on the design optical axis. The characteristic can be obtained by the shape of the objective lens 11, for example. Specifically, the astigmatism is corrected (added) by increasing the focal position due to the notch by adding a groove-shaped notch with a constant width in the radial direction of the disk side surface of the objective lens. is there. In this objective lens configuration, when the objective lens is viewed from the optical axis direction, one groove passing through the optical axis is formed so as to cross one side of the lens.
[0075]
At this time, when the objective lens 11 is shifted in the radial direction, the focal position in the radial direction moves to a position away from the disk due to normal image plane distortion. As a result, the astigmatism becomes the initial astigmatism as it moves in the radial direction. As a result, the astigmatism of the light spot is reduced, and the astigmatism is zero as shown in FIG. 10 with a preset radial movement amount.
[0076]
In the first embodiment, since the objective lens 11 is ultra-thin, the amount of generated astigmatism in the radial direction moving range is large, and the initial astigmatism of the light spot 32 is taken into consideration in consideration of the astigmatism A of the semiconductor laser 2. Is 30 mλ or more and 100 mλ or less, and the amount of astigmatism of the objective lens 11 in the radial direction moving range is also 30 mλ or more and 100 mλ or less.
[0077]
Furthermore, the direction of astigmatism (the initial astigmatism is reduced by off-axis aberration) in the radial direction moving range is always the direction aa in FIG. That is, regardless of whether the objective lens 11 moves in the outer circumferential direction or the inner circumferential direction, the astigmatism direction is such that the rear focal line is substantially perpendicular to the radial direction (the rear focal line is substantially tangential). The initial astigmatism of the light spot is reduced regardless of whether it moves in the outer peripheral direction or the inner peripheral direction.
[0078]
Here, the astigmatism direction aa in which the rear focal line is substantially orthogonal to the radial direction makes the direction of astigmatism of the light spot 32 away from the magneto-optical recording medium 13 and the objective lens 11 ( − Direction), the minor axis direction of the ellipse of the light spot 32 is set to a direction substantially coincident with the radial direction.
[0079]
Thus, when the objective lens 11 moves in the radial direction during recording or reproduction, when the astigmatism is in the direction aa, the minor axis direction of the light spot 32 is substantially radial even when defocused in the-direction. Since it coincides with the direction, it is possible to accurately detect the crosstalk of the reproduction signal and the Adip signal as the address signal without being affected by the crosstalk.
[0080]
Accordingly, since the direction of astigmatism is aa in the radial movement range of the objective lens 11 during recording and reproduction, the initial astigmatism amount is larger than the amount of off-axis aberration (astigmatism) generated by the objective lens 11. It is determined. In addition, when moving in the radial direction, bad conditions such as an increase in off-axis aberration and tilt of the objective lens 11 increase, recording and reproduction conditions deteriorate, and reproduction signal reading ability and Adip signal detection ability deteriorate greatly. .
From the viewpoint of power consumption, it is desirable to move the objective lens 11 as much as possible in the radial direction, and the amount of movement in the radial direction is determined by the performance of the optical head when moving in the radial direction. Therefore, by setting the initial astigmatism and the astigmatism generation direction of the objective lens 11 in the direction in which the astigmatism is reduced off-axis, it is possible to increase the amount of movement in the radial direction.
[0081]
Furthermore, by setting the direction of astigmatism on the design axis to be the direction aa, a light spot 32 whose tangential direction is narrowed due to the influence of rim intensity and astigmatism is formed, and recorded on the information recording medium. The signal detection capability is improved, and the reproduction jitter and Adip signal detection capability are greatly improved.
[0082]
As described above, according to the first embodiment, by defining the direction of astigmatism, the amount of aberration, and the radial direction range (movement amount) of the light spot 32 after exiting the objective lens 11, Even in the case of a large movement in the direction, stable recording and reproduction signals can be obtained, and stable detection of the Adip signal can be realized.
[0083]
In addition, since the objective lens 11 can be further reduced in size and thickness, the optical head can be further reduced in size and thickness, and the recording and playback performance in the disk recording and playback apparatus can be greatly improved and the size and thickness can be reduced. realizable.
[0084]
In addition, since the influence of astigmatism (off-axis aberration) when moving in the radial direction can be reduced, the maximum amount of movement of the objective lens in the radial direction can be increased and the amount of movement in the radial direction can be increased. Since the intermittent rate (stop ratio) of the feed motor 38 is improved, the power consumption is reduced and the battery life is greatly improved.
[0085]
Furthermore, recording as well as recording and reproducing conditions and power due to tilt of the objective lens 11 or off-axis aberration are provided at the expense of recording and reproducing performance and power margin on the designed optical axis by providing initial astigmatism on the designed optical axis. Even when shifting in the radial direction where the margin deteriorates, recording and playback are performed while reducing astigmatism (off-axis aberration), so that stable recording / playback performance and power margin are ensured over the entire radial movement range. This makes it possible to realize a stable disc recording / reproducing device, and further, the objective lens can be made smaller and thinner, so that the optical head can be significantly reduced in size and thickness. Can be realized.
[0086]
In the first embodiment, the direction of astigmatism of the semiconductor laser 2 is the direction of bb. However, if the amount and direction of the initial astigmatism of the light spot 32 are taken into consideration, the direction of 0 or aa Needless to say, there is no problem.
[0087]
In the first embodiment, the astigmatism aberration of the objective lens 11 is set to aa and the astigmatism direction of the semiconductor laser 2 is set to bb on the design optical axis, but the light spot 32 on the design optical axis. It goes without saying that the direction and amount of astigmatism of the objective lens 11 and the semiconductor laser 2 may be any amount as long as the amount and direction of the initial astigmatism coincide with a predetermined set value. In the present embodiment, when the read-only semiconductor laser 2 is used, the value of bb reaches about 25 mλ, so that the astigmatism amount of the light spot 32 is 30 mλ or more, the astigmatism added to the objective lens 11. The amount of aberration is 50 mλ or more in the direction aa. When the high-power recording / reproducing semiconductor laser 2 is used, the value of bb is almost 0 mλ.
[0088]
In addition, the optical head feeding device may be configured to drive the feeding motor 38 and perform intermittent feeding so that the movement amount of the objective lens 11 in the radial direction is within a predetermined value or a preset range.
[0089]
At this time, the moving amount detecting means in the radial direction may be calculated from the current value of the coil 18b or may be calculated using a part of the tracking error signal.
Moreover, although the optical system has been described with a finite example, it may be quasi-finite.
[0090]
(Embodiment 2)
Next, a second embodiment will be described with reference to FIG. This embodiment is different from the first embodiment in that the initial astigmatism is given by the flat glass 43. Astigmatism is generated by arranging the flat glass 43 obliquely in the light flux. By applying astigmatism correction of the correction amount cc to P that becomes the focal point of the XY plane due to this astigmatism and moving the focal point to the R position, the astigmatism becomes QR astigmatism direction. Changes.
[0091]
By this method, it is possible to easily and accurately apply the optimum correction amount cc simply by changing the angle of the flat glass 43 as compared with the case where astigmatism is given to the objective lens 11.
[0092]
In the second embodiment, the initial astigmatism is not applied to the objective lens 11, but it may be applied by the flat glass 43 and the objective lens 11.
[0093]
In the second embodiment, the flat glass 43 is used as a method for applying astigmatism, but it goes without saying that a lens composed of a cylindrical surface having a lens effect only in one direction may be used.
[0094]
【The invention's effect】
As described above, according to the present invention, even when the objective lens is shifted in the radial direction and defocused, the light spot on the magneto-optical recording medium is always vertically elongated with respect to the information track (the radial direction is short). Therefore, a reproduced signal with little crosstalk can be realized. In addition, since the influence of off-axis aberration can be reduced, a small and thin objective lens can be realized, and the optical head can be made small and thin.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an optical path diagram of an optical head according to a first embodiment.
2 is a perspective view of an optical head and an optical head feeding device according to Embodiment 1. FIG.
FIG. 3 is an exploded perspective view showing the configuration of the optical head according to the first embodiment.
4 is a perspective view showing an optical head adjustment method according to Embodiment 1. FIG.
FIG. 5 is a diagram showing an optical path diagram of the optical head according to the first embodiment.
6 is a schematic diagram of a light emitting / receiving element of the optical head according to Embodiment 1. FIG.
FIG. 7 is a diagram showing a configuration of focus servo of the optical head according to the first embodiment.
8A is a schematic diagram illustrating the shape of a light spot according to Embodiment 1. FIG. 8B is a schematic diagram illustrating the shape of a light spot according to a comparative example.
FIG. 9 is a schematic diagram showing the relationship between the operation of the optical head and the optical head feeding device according to the first embodiment.
FIG. 10 is a schematic diagram showing the relationship between the direction of astigmatism and the radial shift of the optical head according to the first embodiment.
11 is a schematic diagram showing the relationship between astigmatism and wavefront aberration of the optical head according to Embodiment 1. FIG.
12 is a schematic diagram showing a radial direction moving region of the optical head according to Embodiment 1. FIG.
13 is a schematic diagram of an optical path diagram of an optical head according to Embodiment 2. FIG.
FIG. 14 is a schematic perspective view of a conventional optical head and an optical head feeding device.
FIG. 15 is an exploded perspective view showing a configuration of a conventional optical head.
FIG. 16 is a perspective view showing a conventional method of adjusting an optical head.
FIG. 17 shows an optical path diagram of a conventional optical head.
FIG. 18 is a schematic diagram of a light receiving and emitting element of a conventional optical head.
FIG. 19 is a schematic diagram showing the configuration of a focus servo of a conventional optical head.
FIG. 20 is a schematic diagram showing the relationship between operations of a conventional optical head and an optical head feeding device.
FIG. 21 is a schematic diagram showing the relationship between astigmatism and wavefront aberration of a conventional optical head.
[Explanation of symbols]
1 Silicon substrate
2 Semiconductor laser
3 Multi-segment photodetector
4 Heat dissipation plate
5 terminals
6 Resin package
7 Hologram element (diffraction grating)
8 Composite elements
8a Beam splitter
8b Folding mirror
8c Polarization separation element
9 Integrated unit
10 reflection mirror
11 Objective lens
12 Objective lens holder
13 Magneto-optical recording medium
14 Objective lens drive
15 base
16 Suspension
17 Magnetic circuit
18a, 18b coil
19 Optical stand
20 Light spot for focus error signal detection
21 Light spot for tracking error signal detection
22 Main beam (P-polarized light)
23 Main beam (S-polarized light)
24 Focus error signal light receiving area
25, 26 Tracking error signal light receiving area
27 Information signal light receiving area
28 Subtractor
29 Adder
30, 31 Focus of light spot for focus error signal detection
32 light spots
33 Cover
34 Adhesive
35 Flexible circuit
36 Lead screw
37 Secondary shaft
38 Feed motor
39a Gear
39b gear
40 Nut plate
41 Bearing
42 Mechanical base
43 Flat glass

Claims (14)

A finite or pseudo-finite optical system including a light source having an astigmatic difference and an objective lens that forms a light spot on an information recording medium by a light beam from the light source;
In the optical system, the light spot has initial astigmatism on the design optical axis, and the direction of the initial astigmatism is a direction in which the rear focal line is substantially perpendicular to the radial direction of the information recording medium. And an optical characteristic that generates astigmatism in a direction in which the initial astigmatism of the light spot decreases as the objective lens moves in the radial direction away from the design optical axis,
Wherein in the movement range of the radial direction of the objective lens, the astigmatism direction of the light spot formed by the objective lens, the direction der the rear side focal line is perpendicular the in radial direction substantially is,
The optical head according to claim 1 , wherein the initial astigmatism is set so that total astigmatism becomes zero at a position where the objective lens has moved by a maximum amount of movement in the radial direction .   The optical head according to claim 1, wherein the objective lens is provided with astigmatism so as to obtain the initial astigmatism.   The astigmatism generation unit is further provided between the light source and the objective lens, and the astigmatism generation unit adds astigmatism so as to obtain the initial astigmatism. Optical head.   The optical head according to claim 1, wherein the initial astigmatism is in a range of 30 mλ to 100 mλ.   2. The optical head according to claim 1, wherein an absolute value of the objective lens in a radial movement range is in a range of 200 μm to 500 μm.   2. The optical head according to claim 1, wherein a change amount of astigmatism generated by a movement amount of the objective lens within a movement range in the radial direction is in a range of 30 mλ to 100 mλ.   The light source is composed of a semiconductor laser, and the direction of astigmatism of the light spot generated by the semiconductor laser is a direction in which the front focal line is substantially perpendicular to the radial direction. The optical head described.   The objective lens is a single lens made of resin or glass, and the astigmatism direction of the light spot generated by the objective lens on the design optical axis is such that the rear focal line is substantially orthogonal to the radial direction. The optical head according to claim 1, wherein the optical head is in a direction to travel.   The objective lens is a single lens made of resin or glass, and the direction of the astigmatism of the light spot generated by the astigmatism generating means on the design optical axis is substantially the same as the radial direction of the rear focal line. The optical head according to claim 2, wherein the directions are perpendicular to each other.   The optical head according to claim 2, wherein the astigmatism generating means is a flat glass or a cylindrical lens.   An optical head according to any one of claims 1 to 10, and an optical head feeding device that performs intermittent feeding so that a movement amount of the objective lens in the radial direction is within an allowable range. Disc recording / playback device.   12. The disc recording / reproducing apparatus according to claim 11, further comprising a radial feed amount detection means for the objective lens, wherein the optical head feed device performs the intermittent feed when a predetermined movement amount is reached.   The disk recording / reproducing apparatus according to claim 12, wherein the calculation of the feed amount detection means uses a part of a tracking error signal.   13. The disc recording / reproducing apparatus according to claim 12, wherein the calculation of the feed amount detecting means uses an applied current of an objective lens driving device that drives the objective lens in a radial direction.

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