JP2006228273A - Optical pickup and optical information processor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a good spot by removing residual astigmatism generated when a coma aberration caused by the tilting of an optical recording medium is corrected by tilting an objective lens. <P>SOLUTION: When a comma aberration caused by the tilting of an optical recording medium 108 is corrected by tilting an objective lens 107, astigmatism is generated in an optical beam emitted from a semiconductor laser 101 by the tilt correction of the objective lens 107. A phase correction element 105 for correcting the astigmatism is arranged. A phase difference is given to the optical beam according to a driving voltage applied to the phase correction element 105. The wave surface of a passing optical beam is not changed when reference phases are given to the optical beam in all the divided areas of the phase correction element 105. Positive and negative phase differences are given to the passing optical beam according to the applied driving voltage, and the occurrence of a coma aberration and astigmatism is suppressed to form a good spot on the optical recording medium 108. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup capable of easily and reliably correcting astigmatism of the entire optical pickup and an optical information processing apparatus using the same.

  As means for storing video information, audio information or data on a computer, optical recording media such as a CD having a recording capacity of 0.65 GB and a DVD having a recording capacity of 4.7 GB are becoming widespread. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity. As means for increasing the recording density of such an optical recording medium, in an optical pickup for writing or reading information on the optical recording medium, the numerical aperture (NA) of the objective lens is increased or the wavelength of the light source is shortened. Thus, it is effective to reduce the diameter of the beam spot condensed by the objective lens and formed on the optical recording medium.

  However, when the numerical aperture of the objective lens is increased or the wavelength of the light source is shortened, there is a problem that coma aberration generated due to the tilt of the optical recording medium increases. When coma occurs, a spot formed on the information recording surface of the optical recording medium deteriorates, so that normal recording / reproducing operation cannot be performed. The coma generated by the tilt of the optical recording medium is generally given by (Equation 1).

Here, n is the refractive index of the transparent substrate of the optical recording medium, d is the thickness of the transparent substrate, NA is the numerical aperture of the objective lens, λ is the wavelength of the light source, and θ is the tilt amount of the optical recording medium. From this (Equation 1), it can be seen that the shorter the wavelength and the higher the NA, the larger the aberration.

  Conventionally, in order to correct the aberration of the light beam caused by the tilt of the optical recording medium, the optical pickup or the carriage unit for moving the optical pickup is tilted so that the optical axis of the optical pickup is substantially perpendicular to the optical recording medium. The tilt of the optical recording medium is substantially corrected optically.

  As described above, when the optical pickup or the carriage unit that moves the optical pickup is tilted and the tilt of the optical recording medium is optically corrected, the tilt target is large and heavy, so that the response of the tilt correction operation is high. Unfortunately, it is difficult to tilt the optical pickup or carriage at high speed. Further, since a mechanism for tilting the optical pickup or the carriage is required, there is a problem that the optical pickup or the carriage becomes heavy and difficult to access at high speed.

  Accordingly, a tilt correction method in which only the objective lens is tilted has been proposed in order to eliminate these problems. FIG. 3 shows a main part of a general optical information processing apparatus provided with the tilt correction mechanism as described above. As shown in FIG. 3, the optical information processing apparatus includes an objective lens 107 that focuses a light beam on an information recording surface of an optical recording medium 108, and an objective lens holder 201 that holds the objective lens 107. The optical information processing apparatus includes a base portion 202 that supports the objective lens holder 201, and elastic support mechanisms 203 and 204 that are interposed between the base portion 202 and the objective lens holder 201. The objective lens holder 201 is elastically supported with respect to the base portion 202 so as to be movable in a total of three directions including a focus direction, a tracking direction, and a radial tilt direction.

Here, the focus direction refers to the Z-axis direction (optical axis direction of the objective lens 107) in FIG. 3, and the tracking direction refers to the X-axis direction (radial direction of the optical recording medium 108) in FIG. The radial tilt direction refers to the tilt direction around the Y axis in FIG. 3 (the direction of tilt relative to the radial direction of the optical recording medium 108). This optical information processing apparatus controls the input current to the drive coil of the lens actuator, and performs a focus servo and a tracking servo for following a predetermined light beam spot on the recording track on the information recording surface of the optical recording medium 108. In addition, the tilt servo is performed so that the incident direction of the light beam (that is, the optical axis of the objective lens 107) is perpendicular to the information recording surface of the optical recording medium 108.
JP 2003-338070 A JP 2000-67453 A

  FIG. 6A is a diagram showing the aberration characteristics generated by the tilt of the optical recording medium in a general objective lens. FIG. 6B is a diagram showing aberration characteristics generated by the tilt of the objective lens. The method of canceling out the coma aberration component generated by the tilt of the optical recording medium in FIG. 6A with the coma component generated by the tilt of the objective lens is the tilt correction described above, and FIG. 6C shows the light after the correction. It is a figure which shows the aberration characteristic by the tilt of a recording medium.

  However, in FIG. 6C, the corrected aberration characteristic is not zero but has residual aberration. This point will be described. As shown in FIG. 6B, when the objective lens is tilted, astigmatism occurs in addition to coma. This is because the coma component generated by the tilt of the optical recording medium can be canceled by the tilt correction, but the astigmatism component generated by the tilt of the objective lens is added. While coma increases linearly, astigmatism increases non-linearly, and as the tilt of the optical recording medium increases, the astigmatism component cannot be ignored.

  The present invention is directed to solving the above-described problems of the prior art, and in the method of correcting coma generated by the tilt of the optical recording medium by the tilt of the objective lens, the residual astigmatism component is also removed. An optical pickup capable of forming a good spot on an optical recording medium and an optical information processing apparatus using the same are provided.

  In order to achieve the above object, an optical pickup according to a first aspect of the present invention includes a light source, an objective lens for condensing a light beam emitted from the light source on an optical recording medium, an objective An objective lens driving means for tilting the lens in at least one of the radial direction and the tangential direction of the optical recording medium; and a phase correction element disposed between the light source and the objective lens for changing the amount of astigmatism of the light beam. The coma aberration generated due to the tilt of the optical recording medium is obtained by the configuration in which the direction in which the amount of astigmatism by the phase correction element is changed substantially coincides with the tilt direction of the objective lens. In the method of correcting by the inclination, astigmatism components remaining after correction can be removed.

  The optical pickup according to claims 2 and 3 is the optical pickup according to claim 1, wherein the phase correction element has an astigmatism amount in the light beam by the liquid crystal layer whose refractive index changes according to the applied voltage. And a tilt detection means for detecting the relative angle of the objective lens and the light beam incident on the objective lens, and the phase correction element reduces the amount of astigmatism according to the relative angle detected by the tilt detection means. By changing the configuration, the remaining astigmatism component can be easily driven by using a liquid crystal element with a small configuration, and the astigmatism can be corrected according to the tilt amount of the objective lens.

  The optical pickups according to claims 4 and 5 are the optical pickups according to claims 1 to 3, further comprising a beam shaping means between the light source and the objective lens, wherein the phase correction element is the tilt direction of the objective lens. And changing the amount of astigmatism in the direction rotated by 45 ° from the light beam shaping direction of the beam shaping means, or the direction in which the light beam shaping direction of the beam shaping means is rotated by 45 ° from the radial direction of the optical recording medium With this configuration, astigmatism after beam shaping, that is, astigmatism of the fixed optical system can be corrected, and astigmatism of the entire optical system can be corrected together with correction of residual astigmatism due to the tilt of the objective lens. The astigmatism correction can be easily performed by making the astigmatism correction mechanism easy by making the direction of residual astigmatism after beam shaping substantially coincide with the direction of occurrence of residual astigmatism after tilt correction of the objective lens. Can do.

  The optical pickup according to any one of claims 6 to 9 is the optical pickup according to claims 1 to 5, wherein the phase correction element changes the amount of spherical aberration of the light beam emitted from the objective lens, An optical recording medium that records or reproduces information by condensing a light beam is a plurality of optical recording media having different operating wavelengths, substrate thicknesses or numerical apertures used for recording or reproducing. One of the optical paths for condensing the light beam for performing recording is a finite system, and the objective lens for condensing the light beam has an objective according to the shift amount of the optical recording medium in the tracking direction. With the configuration in which the lens is tilted in the tracking direction, spherical aberration due to the substrate thickness of the optical recording medium can be corrected together with astigmatism by the phase correction element. And to have a gender, can correct astigmatism in the system of a finite system, further, the coma due to the shift of the objective lens can be canceled by the tilt correction of the objective lens, astigmatism generated by the tilt correction can be corrected.

  The optical information processing apparatus according to claim 10 is an optical information processing apparatus that performs at least one of recording, reproduction, and erasing of information on an optical recording medium. With the configuration using this optical pickup, it is possible to obtain an optical information processing apparatus in which the occurrence of coma and astigmatism is suppressed.

  According to the present invention, when the coma generated by the tilt of the optical recording medium is corrected by the tilt of the objective lens, the residual astigmatism generated by the tilt correction can be removed. An optical pickup capable of forming a good spot with suppressed astigmatism can be obtained, and an optical information processing apparatus using the same can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of an optical pickup capable of recording, reproducing, and erasing on an optical recording medium according to Embodiment 1 of the present invention. As shown in FIG. 1, the light beam from the fixed optical system 10 is condensed on the optical recording medium 108 by the objective lens 107, and the reflected light from the optical recording medium 108 is arranged in the fixed optical system 10. Information is recorded and reproduced based on a signal from a detection system (not shown). In addition to the fixed optical system 10, an actuator unit 20 for driving means for tilting the objective lens 107 and a tilt detecting means 30 for detecting the tilt of the optical recording medium 108 are installed. The actuator unit 20 is controlled to be tilted according to the tilt amount, and is always maintained so that the optical axis of the objective lens 107 is orthogonal to the surface of the optical recording medium 108. The configuration and operation of the fixed optical system 10, the actuator unit 20, and the tilt detection means 30 will be described below.

  FIG. 2 is a diagram showing a schematic configuration of a fixed optical system and an actuator unit that can be recorded on, reproduced from, or deleted from an optical recording medium. 2 includes a semiconductor laser 101, a collimating lens 102, a polarization beam splitter 103, a deflection mirror 104, a phase correction element 105, a quarter wavelength plate 106, an objective lens 107, a detection lens 109, and a cylindrical lens. 110 and a light receiving element 111.

  The linearly polarized divergent light emitted from the semiconductor laser 101 is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103, is deflected by 90 degrees in the optical path by the deflecting mirror 104, and is described later by the phase correction element 105. The astigmatism component is corrected to pass through the quarter-wave plate 106 to become circularly polarized light, which enters the objective lens 107 and is condensed as a minute spot on the optical recording medium 108. Information is reproduced, recorded or erased by this spot.

  Further, the light beam reflected from the optical recording medium 108 becomes circularly polarized light opposite to the outward path, becomes again substantially parallel light, passes through the quarter-wave plate 106 and becomes linearly polarized light orthogonal to the outward path, and is polarized. The light is reflected by the beam splitter 103, collected by the detection lens 109 and the cylindrical lens 110, and reaches the light receiving element 111.

  FIG. 3 is a perspective view showing a schematic configuration of the actuator unit. An objective lens 107 and an objective lens holder 201 that holds the objective lens 107 are provided. Further, a base portion 202 that supports the objective lens holder 201 and elastic support mechanisms 203 and 204 interposed between the base portion 202 and the objective lens holder 201 are provided. The elastic support mechanisms 203 and 204 elastically support the objective lens holder 201 with respect to the base portion 202 so that the objective lens holder 201 can move in a total of three directions including a focus direction, a tracking direction, and a radial tilt direction.

  Here, the focus direction refers to the Z-axis direction (optical axis direction of the objective lens 107) in FIG. 3, and the tracking direction refers to the X-axis direction (radial direction of the optical recording medium 108) in FIG. The radial tilt direction refers to a tilt direction around the Y axis in FIG. 3 (a tilt direction with respect to the radial direction of the optical recording medium 108). Further, driving means not shown in FIG. 3 is provided. The driving means includes, for example, a permanent magnet provided on the objective lens holder 201 and a driving coil fixed relatively to the base portion 202. It is comprised by what is called a voice coil motor.

  And this drive means drives the objective-lens holding body 201 to the said 3 direction according to the input current to a drive coil. Focus servo and tracking servo for controlling a current input to the drive coil of the drive means to follow a predetermined light beam spot on the recording track on the information recording surface of the optical recording medium 108 and the incident direction of the light beam ( That is, tilt servo is performed so that the optical axis of the objective lens 107 is perpendicular to the information recording surface of the optical recording medium 108.

  FIG. 4 is a diagram showing a schematic configuration of the tilt detection means. 4 includes a semiconductor laser 301, a collimating lens 302, a half mirror 303, a quarter wavelength plate 106, a polarization beam splitter 304, a first light receiving element 305, and a second light receiving element 306. Consists of. The linearly polarized divergent light emitted from the semiconductor laser 301 is deflected 90 degrees in the optical path by the half mirror 303 and is made substantially parallel light by the collimator lens 302.

  Subsequently, the surface on the light source side of the quarter-wave plate 106 is coated in a predetermined manner so that a part of the light beam from the half mirror 303 is reflected and the remaining components are transmitted. The light transmitted through the quarter-wave plate 106 passes through the quarter-wave plate 106 to become circularly polarized light and is reflected by the optical recording medium 108. The reflected light from the optical recording medium 108 becomes circularly polarized light opposite to the outward path, passes through the quarter-wave plate 106 again, and becomes linearly polarized light orthogonal to the outward path.

  That is, the light reflected from the surface of the quarter-wave plate 106 and the light reflected by the optical recording medium 108 after passing through the quarter-wave plate 106 are reflected as light reflected on the collimator lens 302 in a state where the polarization directions are orthogonal. Incident. Each reflected light follows substantially the same optical path, passes through the half mirror 303, and enters the polarization beam splitter 304. Here, the optical path of the reflected light from the surface of the quarter-wave plate 106 and the reflected light from the optical recording medium 108 are separated by the polarization beam splitter 304. The reflected light from the optical recording medium 108 is reflected by the polarizing beam splitter 304 and is transmitted to the first light receiving element 305, and the reflected light from the quarter wavelength plate 106 is transmitted through the polarizing beam splitter 304 to the second light receiving element 306. .

  In the configuration of FIG. 1 described above, the light beam from the fixed optical system 10 and the light beam from the tilt detecting means 30 both pass through the common quarter wavelength plate 106. A quarter-wave plate 106 that can convert light from each optical system from linearly polarized light to circularly polarized light or from circularly polarized light to linearly polarized light is provided. At this time, the phase difference between the ordinary ray (refractive index no) and the extraordinary ray (refractive index ne) at a certain thickness t as the quarter wavelength plate 106 is such that the wavelength λ1 of the fixed optical system 10 and the wavelength of the tilt detecting means 30 A quarter wavelength plate made of a crystal that is ¼ of λ2 may be employed. That is, the crystal satisfies the following (Equation 2) and (Equation 3).

By arranging the quarter wavelength plate 106 having such characteristics, a polarization separation optical system in which the polarization beam splitter 103 and the quarter wavelength plate 106 are combined with each other is realized for the fixed optical system 10. A sufficient amount of light can be obtained. In addition, the tilt detection unit 30 can detect the tilt of both the actuator unit 20 and the optical recording medium 108 with a light beam from one light source.

  Of course, the wavelength λ1 of the light beam of the fixed optical system 10 and the wavelength λ2 of the light beam of the tilt detecting means 30 may be the same. The material of the wave plate is not limited to crystals, and an organic material or the like may be used. In FIG. 1, the light beam from the fixed optical system 10 and the light beam from the tilt detecting means 30 both pass through the same quarter-wave plate 106, but separate quarter-wave plates are used. May be.

  In the first embodiment, the surface of the quarter-wave plate 106 is coated with a predetermined coat, and the tilt amount of the objective lens 107 that is integrally movable via the quarter-wave plate 106, that is, the actuator unit 20 is observed. is doing. At this time, it is desirable that the amount of incident light on the first and second light receiving elements 305 and 306 is substantially the same as the coating condition, and the reflectance of the coating is the optical recording medium for the wavelength λ2 of the tilt detecting means 30. The reflectance of 108 may be about ½. The coat is preferably formed outside the region where the light beam of the fixed optical system 10 passes through the objective lens 107.

  FIG. 5 is a block diagram showing a calculating means for the tilt signal detected from the first and second light receiving elements of the tilt detecting means shown in FIG. The configuration of the means for calculating output values from the first and second light receiving elements 305 and 306 will be described in detail with reference to FIGS. In order to detect the tilt amount of the optical recording medium 108, the first light receiving element 305 that detects the reflected light from the optical recording medium 108 includes a pair of light receiving portions 305a and 305b. The pair of light receiving portions 305 a and 305 b are arranged along the radial direction of the optical recording medium 108. Therefore, when the optical recording medium 108 is tilted in the radial tilt direction, the level of the detection signal from one of the pair of light receiving units 305a and 305b becomes higher than the other in accordance with the direction. The pair of light receiving units 305a and 305b are connected to preamplifiers 311 and 312, respectively, and further connected to a difference circuit 313 that outputs a difference between output signals from the preamplifiers 311 and 312 as a difference output signal. By calculating the difference output signal from the difference circuit 313, the amount of tilt (tilt) of the optical recording medium 108 is obtained. Although the reflectance of the optical recording medium 108 is changed or the light intensity of the light beam emitted from the semiconductor laser 301 is changed with time, the characteristics of the detection signals from the preamplifiers 311 and 312 are changed. This change in characteristics is corrected by a subsequent circuit. That is, the signals from the preamplifiers 311 and 312 are added by the adder circuit 314, and the added output is input to the divider circuit 315. In the division circuit 315, the difference output from the difference circuit 313 is normalized with the addition output as a reference, the fluctuation component included in the difference output is removed, and the tilt signal of the optical recording medium 108 is output from the division circuit 315. Is output.

  In addition, in order to detect the tilt amount of the actuator unit 20 on which the objective lens 107 and the quarter wavelength plate 106 are mounted, a light beam reflected from the quarter wavelength plate 106 installed in the actuator unit 20 is detected. The second light receiving element 306 includes a pair of light receiving portions 306a and 306b. When the objective lens 107 is tilted, the level of the detection signal generated from one of the pair of light receiving units 306a and 306b becomes larger than the signal level generated from the other according to the tilt direction. The pair of light receiving units 306a and 306b are connected to preamplifiers 316 and 317, respectively, and further connected to a difference circuit 318 that outputs a difference between output signals from the preamplifiers 316 and 317 as a difference output signal. By calculating the difference output signal from the difference circuit 318, the tilt amount of the actuator unit 20, that is, the objective lens 107 is obtained. The light intensity of the light beam emitted from the semiconductor laser 301 is changed with time to change the characteristics of the detection signals from the preamplifiers 316 and 317. This change in characteristics is corrected by a circuit in the subsequent stage. That is, the signals from the preamplifiers 316 and 317 are similarly added by the adder circuit 319, and the addition output is input to the divider circuit 320. In the division circuit 320, the difference output from the difference circuit 318 is normalized with the addition output as a reference, the fluctuation component included in the difference output is removed, and the tilt signal of the objective lens 107 is output from the division circuit 320. Is done.

  Dividing circuits 315 and 320 that output tilt signals corresponding to the tilt amounts of the optical recording medium 108 and the objective lens 107 are connected to a difference circuit 322, and a difference between the tilt signals is generated from the difference circuit 322. The difference output from the difference circuit 322 corresponds to the relative tilt amount of the objective lens 107 with respect to the optical recording medium 108. In addition, a switch 321 is installed in the previous stage of the difference circuit 322, and the tilt control is performed by selecting an objective lens tilt signal and a relative tilt signal according to a control procedure as will be described later.

  A state in which the coma aberration generated by the tilt of the optical recording medium is suppressed by using the means related to the tilt correction will be described with reference to FIGS. 6A to 6C and FIGS.

  6A is an aberration characteristic generated by tilting of an optical recording medium in a general objective lens, FIG. 6B is an aberration characteristic generated by tilting of the objective lens, and FIG. 6C is a graph after tilt correction. It is a figure which shows an aberration characteristic. Further, FIG. 7A is a diagram illustrating a wavefront shape of residual aberration after tilt correction in which the tilt of the optical recording medium, the tilt of the objective lens, and the tilt of the optical recording medium and the tilt of the objective lens are offset. FIG. 7-2 is a cross-sectional view of the wavefront shape of FIG. 7-1 in the radial direction and the tangential direction. In FIG. 7-2, “rad” is a radial component, and “tan” is a tangential component.

  In the first embodiment, a method of canceling the coma aberration component generated by the tilt of the optical recording medium shown in FIG. 6A with the coma component generated by the tilt of the objective lens shown in FIG. 6B is used. . That is, the coma aberration component of FIG. 6A and the coma aberration component of FIG. 6B have the same amount of aberration generated for the same tilt amount, and as shown in FIG. On the other hand, if the optical recording medium and the objective lens are parallel, the coma aberration component can be canceled. Since the relative tilt is detected in the first embodiment, the relative tilt amount may be controlled to be zero.

  However, as is apparent from FIG. 6C, FIG. 7-1, or FIG. 7-2, the corrected aberration does not become zero but has a residual aberration. This point will be described. When the objective lens is tilted as shown in FIG. 6B, astigmatism occurs in addition to coma. Therefore, the coma component generated by the tilt of the optical recording medium can be canceled by the tilt correction, but the astigmatism component generated by the tilt of the objective lens is added.

  FIG. 8A shows an aberration distribution due to astigmatism of the tilt “1 °” of the optical recording medium after correction shown in FIG. 6C, and represents an astigmatism occurrence region. FIG. 8B is a cross-sectional view of the aberration distribution in the radial direction of RG-R shown in FIG. 8A, that is, the tilt direction of the objective lens. It can be seen that the wavefront aberration distribution is small at the center of the pupil plane and increases in the positive direction toward the periphery. FIG. 8C is a cross-sectional view of the aberration distribution in the tangential direction of B-G-B shown in FIG. 8A, and is small at the center of the pupil plane, and the wavefront aberration becomes negative toward the periphery. It can be seen that the direction is larger. As described above, the aberration distribution mainly including astigmatism has a horseshoe shape and is symmetric with respect to the radial axis and the tangential axis. The coma increases linearly, while the astigmatism increases non-linearly. As the tilt of the optical recording medium increases, the astigmatism component cannot be ignored.

  In the first embodiment, a phase correction element for providing an astigmatism amount having a polarity opposite to the astigmatism amount is provided, and the phase correction element is arranged so as to generate astigmatism in the radial direction. Yes. 9 is a cross-sectional view of the phase correction element in FIG. 2 described above, and FIG. 10 is a diagram showing an electrode pattern of the phase correction element. The configuration and operating principle of the phase correction element will be described with reference to FIGS.

  First, the configuration of the phase correction element will be described with reference to FIG. The phase correction element 105 shown in FIG. 9 has a known configuration in Patent Document 1, Patent Document 2, and the like. Glass substrates 51a and 51b are bonded by a conductive spacer 52 to form a liquid crystal cell. On the inner surface of the glass substrate 51a, the transparent electrode 54a, the insulating film 55, and the alignment film 56 are arranged in this order from the inner surface. On the inner surface of the glass substrate 51b, the transparent electrode 54b, the insulating film 55, The alignment films 56 are coated in this order. The electrode 54a is wired in a pattern so that it can be connected to the control circuit by a connection line at the electrode lead-out portion 57.

  The electrode 54b is electrically connected to the electrode 54a formed on the glass substrate 51a through the conductive spacer 52. Therefore, the electrode 54 b can be connected to the control circuit by the connection line at the electrode lead-out portion 57. A liquid crystal 53 is filled inside the liquid crystal cell. The liquid crystal 53 has a so-called birefringence effect, and the refractive index is different between the optical axis direction of the liquid crystal molecules and the direction perpendicular thereto. Then, by changing the voltage applied between the electrode 54a and the electrode 54b, the direction of the liquid crystal molecules can be freely changed from the horizontal direction to the vertical direction. The applied voltage to the electrodes 54a and 54b is set by a control circuit (not shown), and by adjusting the voltage applied to each divided region of the electrodes 54a and 54b, a different phase difference is generated for each region formed by the divided electrodes. It is given.

  Next, FIG. 10 is an electrode pattern diagram showing a state in which the electrode 54a of the phase correction element 105 is divided so as to cancel astigmatism in the radial direction or tangential direction. The electrode 54a is divided into five pattern electrodes 58a to 58e as shown in FIG.

  In FIG. 10, a circular pattern electrode 58a is formed corresponding to the central portion of the light beam passage range. Further, four pattern electrodes 58b to 58e that are radially divided are formed on the outer peripheral portion, and are arranged symmetrically so as to divide the angle from the center of the light beam passage range at approximately equal intervals. Then, the pattern electrode 58b and the pattern electrode 58c, the pattern electrode 58d and the pattern electrode 58e face each other in a centrally symmetrical manner, and are in a direction in which the astigmatism component generated by the tilt of the objective lens can be corrected.

  Assume that the radial component of astigmatism remaining after correction of coma aberration due to the tilt of the objective lens is as shown by the solid line in the upper part of FIG. With respect to such wavefront aberration, the electrode pattern of the phase correction element is used so that the light beam incident on the objective lens from the light source side is given a phase difference as shown by the broken line in the lower part of FIG. When the applied phase difference is adjusted, the “wavefront aberration” can be canceled out by the wavefront delay at each part of the transmitted light beam. FIG. 11B shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay caused by the phase correction element) in FIG. 11A, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (solid line in the upper part of FIG. 11A).

  Similarly, it is assumed that the tangential direction component of astigmatism remaining after the coma aberration correction is as shown by the solid line in the lower part shown in FIG. For such wavefront aberration, the light beam incident on the objective lens from the light source side is given by the electrode pattern of the phase correction element so that a phase difference as shown by the broken line in the upper part of FIG. When the phase difference is adjusted, the “wavefront aberration” can be canceled by the advance of the wavefront at each part of the transmitted light beam. FIG. 11D shows the sum of the solid line (wavefront aberration) and the broken line (wavefront advance by the phase correction element) in FIG. 11C, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (solid line in the lower part of FIG. 11C).

FIG. 12 is a diagram showing the relationship between the driving voltage for the phase correction element and the phase difference applied to the light beam. Now, assuming that the reference voltage is V ₀ , a drive signal corresponding to V ₀ is applied, so that a reference phase φc is given to the light beam as shown in FIG. Here, when the reference phase φc is given to the light beam in all the divided regions of the phase correction element 105, the wavefront of the passing light beam does not change, and the phase correction element 105 is the same as a simple glass plate. .

As shown in FIG. 12, when a drive signal corresponding to a voltage V that satisfies the relationship of “V> V ₀ ” is applied, φa, which is a phase advanced from the reference phase φc, is given to the light beam. Therefore, the phase of the light beam that has passed through the region to which the drive signal corresponding to the voltage V is applied advances from the reference by φa−φc. That is, a positive phase difference φa−φc is generated in the light beam.

When a drive signal corresponding to the voltage V satisfying the relationship “V <V ₀ ” is applied, φb, which is a phase delayed from the reference phase φc, is given to the light beam. Therefore, the phase of the light beam that has passed through the region to which the drive signal corresponding to the voltage V is applied is delayed by φc−φb from the reference. That is, a negative phase difference φb−φc is generated in the light beam.

  Here, as can be seen from FIG. 12, the phase difference applied to the light beam with respect to the voltage change changes substantially linearly. For example, in order to correct the aberration distribution in which positive and negative are symmetric as in the first embodiment, the negative phase difference φb−φc and the positive phase difference φa−φc have the same absolute value but different signs. You can do it.

  Next, a control operation of the optical information processing apparatus for recording or reproducing information on an optical recording medium by mounting an optical pickup will be described with reference to the flowchart shown in FIG. 13 with reference to FIGS. It explains along.

  First, the objective lens tilt signal is selected, and a search signal is sent to tilt the actuator unit 20 with a constant amplitude in the radial tilt direction. Then, a tilt servo pull-in circuit (not shown) detects when the objective lens tilt signal becomes zero, and lens tilt servo is started (S1).

  Subsequently, focus servo is sequentially applied (S2) and tracking servo is applied (S3). After each servo is stabilized, the relative tilt signal is switched to the relative tilt signal when the relative tilt signal becomes zero, and the relative tilt servo is started in place of the lens tilt servo in the radial tilt direction (S4). Astigmatism is given according to the amount of lens tilt after the relative tilt servo.

  That is, the relationship between the tilt amount of the objective lens and the astigmatism amount to be applied shown in FIG. 6C is stored in advance, and the applied voltage of the phase correction element can be selected according to the movable amount of the tilt of the objective lens. That's fine.

  Instead of directly pulling the relative tilt servo as described above, the optical recording medium itself is obtained by performing the lens tilt servo once and starting the relative tilt servo after the value of the relative tilt angle is within a predetermined range. The relative tilt servo can be pulled in quickly and reliably without being affected by the dynamic tilt and disturbance.

  As another example of the first embodiment, a servo signal or an RF signal from an optical recording medium may be used as the drive signal for the actuator unit or the phase correction element instead of the output value of the tilt detection means. It is known that when there is coma or astigmatism, the amplitude of the tracking error signal or RF signal is attenuated. Therefore, the position where the tracking error signal and the RF signal are maximized may be searched by changing the movable amount of the actuator unit and the applied voltage value of the phase correction element within an appropriate range. According to this method, since it is not necessary to provide a tilt detection means, it is possible to reduce the size of the optical pickup and reduce the number of assembling steps.

  In addition, the tilt direction of the actuator unit may be not only the radial direction but also four-axis tilting in the tangential direction. The configuration of the actuator section at this time is shown in FIG. The tangential tilt direction refers to a tilt direction around the X axis (a tilt direction with respect to a tangential direction of the optical recording medium 108). As the tilt detection means at this time, as shown in FIG. 15, instead of the light receiving element having the light receiving portion divided into two in FIG. 5 described above, the light is divided into four parts including light receiving parts 305 c to f and light receiving parts 306 c to 306 f. These light receiving elements may be used as the first and second light receiving elements 305 and 306. With this configuration, it is possible to perform tilt correction not only in the radial direction of the optical recording medium but also in the tangential direction, and it is possible to realize stable recording and reproduction operations with various margins.

  FIG. 16 is a diagram showing a schematic configuration of a fixed optical system and an actuator unit that can be recorded on, reproduced from, or deleted from the optical recording medium according to Embodiment 2 of the present invention. The difference from the first embodiment described above is that the beam shaping prism 112 is used as the beam shaping means and the phase correction element 105a corresponding to the beam shaping prism 112 is used, and the other configurations are the same.

  16 includes a semiconductor laser 101, a collimating lens 102, a beam shaping prism 112, a polarizing beam splitter 103, a deflecting mirror 104, a phase correcting element 105a, a ¼ wavelength plate 106, an objective lens 107, and detection. The lens 109, the cylindrical lens 110, and the light receiving element 111 are included. The linearly polarized divergent light emitted from the semiconductor laser 101 is converted into substantially parallel light by the collimator lens 102, and the elliptical light beam is converted into a substantially circular light beam by the beam shaping prism 112, and transmitted through the polarization beam splitter 103. Then, the optical path is deflected by 90 degrees by the deflecting mirror 104, the astigmatism component is corrected by the phase correction element 105a as will be described later, passes through the quarter-wave plate 106, becomes circularly polarized light, and enters the objective lens 107. Then, it is condensed as a minute spot on the optical recording medium 108. Information is reproduced, recorded or erased by this spot.

  The light reflected from the optical recording medium 108 becomes circularly polarized light in the opposite direction to the forward path, becomes again substantially parallel light, passes through the quarter-wave plate 106 and becomes linearly polarized light orthogonal to the forward path, and the polarization beam splitter 103. And is collected by the detection lens 109 and the cylindrical lens 110 and reaches the light receiving element 111.

  The semiconductor laser emits light beams having different divergence angles depending on an axis parallel to the active layer and an axis perpendicular to the axis. Therefore, the intensity distribution in the cross section perpendicular to the optical axis of the light beam made parallel by the collimator lens is elliptical, and the ratio of the light beams emitted from many semiconductor lasers is 1: 2 or more. A beam shaping prism is known as means for shaping the elliptical intensity distribution into a substantially circular shape. FIG. 17 shows an example of a beam shaping prism. When the radial direction and the tangential direction are defined as shown in FIG. 17, an elliptical beam having a short radial direction is incident on the surface 112a inclined in the radial direction of the beam shaping prism 112, and the surface 112a The radial direction is expanded by refracting.

  Refraction on the surface 112a does not change the width of the light beam in the tangential direction, so that the intensity distribution of the elliptical light beam is shaped, and a substantially circular intensity distribution can be obtained. The light beam whose intensity distribution is substantially circular is condensed by the objective lens. In this configuration, since the optical recording medium can be irradiated with a light beam shaped into a substantially circular shape, the spot diameter can be reduced and a more circular spot can be obtained, so that recording and reproduction of a high recording density optical recording medium can be achieved. Can be realized.

  In an optical system using such a beam shaping prism, it is known that the astigmatism of the light beam incident on the objective lens changes by changing the divergence degree of the light beam incident on the beam shaping prism. For this reason, in the assembly process of the optical pickup, the distance between the collimating lens and the semiconductor laser is changed, and the distance at which astigmatism is minimized is fixed while varying the divergence degree of the light incident on the beam shaping prism.

  On the other hand, in the optical system, the component itself has astigmatism. By using the collimating lens adjustment described above, astigmatism possessed by the components arranged in the optical path can be suppressed. However, it has been confirmed that the astigmatism component that can be suppressed at this time is limited to the component in the beam shaping direction. This will be described below with reference to FIG. The right column shown in FIG. 18 shows the wavefront distribution when the astigmatism amount is 0.045 λrms and the generation direction is different. As shown in the scale of FIG. 18, G to R are positive directions, G to B are negative directions, and the shading in each direction represents the magnitude of the aberration change. The astigmatism amount and the direction of astigmatism are shown below the wavefront distribution diagram in FIG. For each state in the right column of FIG. 18, a state in which the astigmatism is adjusted to be minimum in the optical system arranged so as to perform beam shaping in the radial direction is shown in the left column.

  As can be seen from FIG. 18, the correction effect decreases as the astigmatism before correction deviates from the radial axis. FIG. 19 is a graph showing the situation. It can also be seen that the astigmatism remaining after correction is a component of astigmatism in a direction rotated by 45 ° from the radial direction which is the beam shaping direction.

  From the above results, it can be said that the astigmatism remaining when the collimating lens is adjusted in the system including the beam shaping prism is a specific direction, and the direction is a direction rotated by 45 ° from the beam shaping direction. Therefore, the phase correction element according to the second embodiment generates astigmatism in the radial direction and in the direction of 45 ° with respect to the radial axis. Thereby, in addition to the astigmatism after the tilt correction of the objective lens, an astigmatism amount having a reverse polarity to the astigmatism amount after the collimating lens adjustment can be provided.

  The electrode pattern of the phase correction element that provides the astigmatism amount having the opposite polarity will be described with reference to FIG. FIG. 20 is an electrode pattern diagram showing a state in which the astigmatism with respect to the radial direction and the direction of 45 ° from the radial axis can be canceled out. As shown in FIG. 20, it is divided into nine pattern electrodes 58a to 58i.

  In FIG. 20, a circular pattern electrode 58a is formed corresponding to the central portion of the light beam passage range. Further, eight pattern electrodes 58b to 58i that are radially divided are formed on the outer peripheral portion, and are arranged symmetrically so as to divide the angle from the center of the light beam passage range at approximately equal intervals. Then, the pattern electrode 58b and the pattern electrode 58c, the pattern electrode 58d and the pattern electrode 58e, the pattern electrode 58f and the pattern electrode 58g, the pattern electrode 58h and the pattern electrode 58i face each other and are arranged symmetrically, and the pattern electrodes 58b to 58e are used. Astigmatism components generated by the objective lens tilt can be corrected, and residual astigmatism components can be corrected by adjusting the distance between the semiconductor laser and the collimating lens with respect to the beam shaping prism using the pattern electrodes 58f to 58i. The correction principle is the same as that described in FIG. 12 of the first embodiment.

  Further, as shown in FIG. 20, the phase correction element is not limited to the configuration for correcting the astigmatism component due to the objective lens tilt and the residual astigmatism after the collimating lens adjustment with one electrode pattern. You may correct | amend correction | amendment of a point aberration by an individual electrode pattern. That is, as shown in FIG. 21, a pattern for correcting astigmatism in the radial direction on each surface of the opposing electrodes 54a and 54b of the phase correction element 105a (pattern of the upper electrode 54b in FIG. 21) and 45 ° from the radial direction. A configuration in which a pattern for correcting astigmatism in the rotated direction (a pattern of the lower electrode 54a in FIG. 21) is provided.

  Further, the beam shaping direction is not limited to the radial direction, and may be a tangential direction. That is, the beam shaping prism 112 of FIG. 16 and the active layer of the semiconductor laser 101 are rotated by 90 ° about the optical axis. In this case, the same pattern as in FIGS. 20 and 21 may be used.

  Further, beam shaping may be performed in a direction deviating from the radial direction or the tangential direction. In this case, the electrode pattern corresponding to the collimating lens adjustment in FIG. 21 is rotated by 45 ° in the beam shaping direction as shown in FIG. What is necessary is just to do together (pattern of the lower electrode 57a of FIG. 22). This case corresponds to the case where the beam shaping prism 112 and the semiconductor laser 101 in FIG. 16 are rotated by an arbitrary angle around the optical axis.

  Furthermore, as shown in FIG. 23, it is desirable that the beam shaping direction is in a direction rotated by 45 ° from the radial direction. In this case, since the astigmatism that occurs after correction of coma due to the tilt of the objective lens matches the astigmatism that occurs after adjustment of the collimating lens, the electrode pattern is the same as that shown in FIG. 10 of the first embodiment. It may be composed of the same five patterns, and can simplify the electrode pattern and facilitate the driving method.

  Further, the beam shaping means is not limited to a method using a prism, and may be a method using a lens. That is, a toroidal lens or an anamorphic lens having different lens powers in the direction perpendicular to the optical axis vertical plane may be used.

  As the phase correction element according to the third embodiment of the present invention, in addition to the electrode pattern for correcting astigmatism described in the first and second embodiments, an electrode pattern for correcting spherical aberration may be provided. In general, it is known that variation due to substrate thickness error of an optical recording medium generates spherical aberration. For example, in the “Blu-ray standard of blue wavelength, numerical aperture: NA 0.85”, a spherical aberration correction element is installed. Products that have been released are on sale. The function of correcting this spherical aberration can be provided as the phase correction element of the third embodiment without increasing the number of parts.

  The electrode pattern in that case will be described below with reference to FIG. As shown in FIG. 24, any electrode pattern that corrects residual astigmatism after tilt correction and electrode pattern that corrects spherical aberration are provided on each surface of opposing electrodes 54b and 54c of the phase correction element 105b. Good.

  The pattern of the upper electrode 54b in FIG. 24 is an electrode pattern diagram showing a state in which the astigmatism with respect to the radial direction or the tangential direction can be canceled. It is divided into five pattern electrodes 58a to 58e. A circular pattern electrode 58a is formed corresponding to the central portion of the light beam passage range. Further, four pattern electrodes 58b to 58c that are radially divided are formed on the outer peripheral portion, and are arranged symmetrically so that the angles are divided at approximately equal intervals from the center of the light beam passage range. The pattern electrode 58b and the pattern electrode 58c, and the pattern electrode 58d and the pattern electrode 58e are arranged so as to face each other and be symmetrical with respect to the center, so that astigmatism components generated by the objective lens tilt can be corrected.

  Further, the pattern of the lower electrode 54c in FIG. 24 is an electrode pattern diagram showing a state where the pattern is divided so that spherical aberration can be canceled. It is divided into three pattern electrodes 59a, 59b, 59c. It is divided concentrically from the central part of the light beam passage range, and is configured to be able to correct the spherical aberration component caused by the substrate thickness error of the optical recording medium.

  Now, it is assumed that the spherical aberration component due to the substrate thickness of the optical recording medium is as shown by the solid line in the upper portion shown in FIG. With respect to such wavefront aberration, an electrode pattern of the phase correction element is used so that a phase difference as shown by a broken line in the lower part of FIG. When the applied phase difference is adjusted, the “wavefront aberration” can be canceled out by the wavefront delay at each part of the transmitted light beam. FIG. 25B shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay by the phase correction element) in FIG. 25A, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (solid line in the upper part of FIG. 25A).

  Further, when the phase correction element is disposed in the fixed optical system, coma aberration occurs due to the optical axis shift accompanying the tracking operation of the objective lens. FIGS. 26A and 26B are diagrams for explaining the outline. FIG. 26A is a diagram showing a case where the optical axis of the objective lens and the optical axis of the fixed optical system coincide with each other. The spherical aberration having the opposite polarity to the spherical aberration caused by the substrate thickness error of the optical recording medium is phase-shifted. It cancels by being generated by the correction element. On the other hand, FIG. 26B is a diagram showing a case where the optical axes of the objective lens and the fixed optical system are deviated from each other. The deviation between the spherical aberration caused by the substrate thickness error of the optical recording medium and the spherical aberration of the phase correction element. Coma occurs. In practice, the phase difference added from the phase correction element is stepped as described with reference to FIGS. 11A to 11D and FIGS. 25A and 25B. Explained with a continuous wavefront.

  In contrast to the coma caused by the optical axis shift as shown in FIG. 26B, in the third embodiment, coma can be generated by the tilt of the objective lens, which can be canceled out. For example, a sensor that can detect the position of the objective lens is provided in the actuator unit, and the objective lens may be tilted according to the amount of optical axis deviation from the fixed optical system of the objective lens based on the output of the sensor.

  Further, if the above-mentioned problem is taken in reverse, it can be seen that if the phase correction element is provided in the actuator portion, the coma due to the optical axis deviation does not occur.

  FIG. 27 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing on an optical recording medium in Embodiment 4 of the present invention.

  The system for correcting the residual astigmatism after the objective lens tilt correction described in the first, second, and third embodiments, or the residual astigmatism after adjusting the collimating lens, has a wavelength used, a substrate thickness, or a numerical aperture. The present invention may be applied to an optical pickup that performs recording or reproduction on a plurality of different optical recording media. In this case, the phase correction element may be arranged in a common optical path having a plurality of wavelengths, and the configuration of the optical pickup shown in FIG.

  A specific example will be described with reference to an optical pickup as shown in FIG. That is, FIG. 27 shows a “blue optical recording medium having a working wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” and a “DVD system having a working wavelength of 660 nm, NA of 0.65 and a light irradiation side substrate of 0.6 mm. An optical pickup capable of recording, reproducing, and erasing the “optical recording medium” together will be described as an example.

  27 includes a semiconductor laser 101 having a wavelength of 405 nm, a collimating lens 102, a polarizing beam splitter 103, a dichroic prism 123, a deflecting mirror 104, a phase correcting element 105, a quarter-wave plate 106, and an objective lens 107. , A detection lens 109, a beam splitting means 110a, a light receiving element 111, an infinite blue optical system through which a light beam having a wavelength of 405 nm passes, a hologram unit 121, a coupling lens 122, a dichroic prism 123, a deflection mirror 104, It is composed of a finite DVD optical system through which a light beam having a wavelength of 660 nm, which is composed of a phase correction element 105, a quarter wavelength plate 106, and an objective lens 107, passes.

  Of the above-described configuration, the dichroic prism 123, the deflection mirror 104, the phase correction element 105, the quarter wavelength plate 106, and the objective lens 107 are common parts of the two optical systems. Here, the objective lens 107 is designed to have a minimum wavefront aberration in an infinite system with respect to “a blue light recording medium having a working wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm”. This is because the objective lens generally has a tighter tolerance as the NA is higher and the wavelength is shorter, and thus it is more difficult to obtain desirable characteristics with a blue NA of 0.65.

  The optical recording media 108a and 108b are optical recording media having different substrate thicknesses or different operating wavelengths. The optical recording medium 108a is a blue optical recording medium having a substrate thickness of 0.6 mm, and the optical recording medium 108b is a substrate. This is a DVD optical recording medium having a thickness of 0.6 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a blue optical recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is made substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103 and the dichroic prism 123, and is deflected by 90 degrees in the optical path by the deflecting mirror 104. The astigmatism component is corrected by the correction element 105, passes through the quarter-wave plate 106, becomes circularly polarized light, enters the objective lens 107, and is condensed as a minute spot on the optical recording medium 108a. Information is reproduced, recorded or erased by this spot.

  The light reflected from the optical recording medium 108a becomes circularly polarized light in the opposite direction to the outward path, becomes again substantially parallel light, passes through the quarter wavelength plate 106, and becomes linearly polarized light orthogonal to the forward path, and the polarization beam splitter 103 And is converged by the detection lens 109, deflected and divided into a plurality of optical paths by the light beam splitting means 110 a, and reaches the light receiving element 111. An information signal and a servo signal are detected from the light receiving element 111.

  Next, a description will be given of a case where “DVD optical recording medium having a used wavelength of 660 nm, NA of 0.65, and light irradiation side substrate thickness of 0.6 mm” is recorded, reproduced or erased. In recent years, a hologram unit in which a light receiving and emitting element is installed in one can and a light beam is separated using a hologram has come to be generally used for a DVD pickup. In FIG. 27, reference numeral 121 denotes a hologram unit formed by integrating a semiconductor laser 121a, a hologram 121b, and a light receiving element 121c of a laser chip. The light beam of 660 nm emitted from the semiconductor laser 121a of the hologram unit 121 is transmitted through the hologram 121b, is converted into predetermined finite light by the coupling lens 122, the light beam in the blue wavelength band is transmitted, and the light beam in the red wavelength band is transmitted. The light beam is reflected by the reflecting dichroic prism 123 in the direction of the deflecting mirror 104, the optical path is deflected by 90 degrees by the deflecting mirror 104, and the astigmatism component is corrected by the phase correcting element 105 as will be described later. The light passes through the wave plate 106, becomes substantially circularly polarized light, enters the objective lens 107, and is condensed as a minute spot on the optical recording medium 108b. Information is reproduced, recorded or erased by this spot.

  The light beam reflected from the optical recording medium 108b is reflected by the deflecting mirror 104 and the dichroic prism 123, converged by the coupling lens 122, and diffracted by the hologram 121b toward the light receiving element 121c in the same can as the semiconductor laser 121a. And is received by the light receiving element 121c. An information signal and a servo signal are detected from the light receiving element 121c.

  The astigmatism that is corrected by the tilt of the objective lens and the astigmatism component that remains after the tilt correction is corrected by the phase correction element. The point of applying and canceling is the same as in the first, second, and third embodiments. Since the phase correction element is arranged in the common optical path, the above-described correction method can be performed on the optical paths of the blue and DVD optical systems in the fourth embodiment. However, since the amount of aberration that occurs differs for each optical path, it is necessary to control the objective lens drive amount or the drive voltage of the phase correction element in accordance with the type of optical recording medium.

  Next, a case where the generated aberration is different will be described. First, when the DVD optical system is used as a finite optical path with the objective lens having the characteristics described in FIGS. 6A, 6B, and 6C of Embodiment 1 as a blue light recording medium. The wavefront distribution is shown in FIGS. In the optical path of the blue optical system shown in FIGS. 6A, 6B, and 6C, the coma aberration amount generated by the tilt of the optical recording medium and the coma aberration amount generated by the tilt of the objective lens are the same tilt. The amount was equivalent. For this reason, it has been described that the objective lens and the optical recording medium may be controlled to be parallel (relative tilt amount is zero).

  However, when compared with the aberration characteristics shown in FIGS. 28A and 28B, the coma component due to the tilt of the objective lens is about 1/5 of the coma generated by the tilt of the optical recording medium. In this case, in order to cancel the coma caused by the tilt of the optical recording medium with the coma due to the tilt of the objective lens, the objective lens is about five times as large as the tilt of the optical recording medium as shown in FIG. It is necessary to drive with a tilt amount. However, in FIG. 28B, when the objective lens is tilted, the astigmatism changes more greatly than the coma aberration. When the coma aberration is corrected, the astigmatism increases as shown in FIG. It will remain.

  Since the phase correction element 105 is provided in the fourth embodiment, this can be suppressed by the method described in the first, second, and third embodiments.

  Note that spherical aberration occurs when the wavelength used and the thickness of the optical recording medium change. In this embodiment, since the blue objective lens is used after being focused on the DVD, spherical aberration occurs in the DVD optical recording medium. In contrast, the fourth embodiment solves this problem by arranging the optical path of the DVD optical system in a finite system.

  Since this finite system, that is, changing the degree of divergence of the light beam incident on the objective lens is equivalent to changing the spherical aberration, it can be canceled out.

  As in the third embodiment, coma aberration is also generated in this case due to the shift of the objective lens. However, this coma aberration may be canceled by the tilt of the objective lens.

  FIG. 29 is a transparent perspective view schematically showing the configuration of the optical information processing apparatus according to Embodiment 5 of the present invention. As shown in FIG. 29, the optical information processing apparatus 40 is an apparatus that performs one or more of recording, reproducing, and erasing information with respect to an optical recording medium 45 by using an optical pickup 41. In the fifth embodiment, the optical recording medium 45 has a disk shape and is stored in the protective case 46. The optical recording medium 45, together with the protective case 46, is inserted into the optical information processing device 40 from the insertion port 42 in the direction of the arrow “in”, is rotated by the spindle motor 43, and is recorded by the optical pickup 41 moved by the carriage 44. Playback or deletion is performed. The optical recording medium 45 does not need to be placed in the protective case 46 and may be in a bare state. As the optical pickup 41 used in the optical information processing apparatus 40, the optical pickup described in the above embodiments can be used as appropriate.

  The optical pickup and the optical information processing apparatus using the same according to the present invention remove residual astigmatism caused by tilt correction when correcting coma generated by tilt of the optical recording medium by tilt of the objective lens. It is possible to form a good spot with suppressed coma and astigmatism on the optical recording medium, and to easily and reliably correct astigmatism in the optical information processing apparatus and the entire optical pickup used therefor. Useful for.

1 is a schematic diagram showing a configuration of an optical pickup capable of recording, reproducing, and erasing an optical recording medium in Embodiment 1 of the present invention. The figure which shows schematic structure of the fixed optical system and actuator part which can be recorded on or reproduced from and erased from the optical recording medium in the first embodiment The perspective view which shows schematic structure of the actuator part in this Embodiment 1. FIG. The figure which shows schematic structure of the tilt detection means in this Embodiment 1. 4 is a block diagram showing a calculation means for tilt signals detected from the first and second light receiving elements of the tilt detection means shown in FIG. 4 in the first embodiment. In a general objective lens, (a) shows aberration characteristics caused by tilting of the optical recording medium, (b) shows aberration characteristics caused by tilt of the objective lens, and (c) shows aberration characteristics after tilt correction. The figure which shows the wavefront shape of the residual aberration after the tilt correction which canceled the tilt of the optical recording medium, the tilt of the objective lens, and the tilt of the optical recording medium and the tilt of the objective lens The figure which shows the cross-sectional shape of a radial direction and a tangential direction among the wavefront shapes of FIGS. (A) is an astigmatism distribution of the tilt “1 °” of the optical recording medium after correction shown in FIG. 6C, (b) is a cross-sectional view of the radial aberration distribution shown in (a), and (c). Is a sectional view of the aberration distribution in the tangential direction shown in FIG. Sectional drawing of the phase correction element in this Embodiment 1 The figure which shows the electrode pattern of the phase correction element in this Embodiment 1. Astigmatism (a) remaining after correction of coma due to the tilt of the objective lens is a radial component, (b) is a radial component after correction, (c) is a tangential component, and (d) is a corrected component. Diagram showing the tangential direction component The figure which shows the relationship between the drive voltage with respect to the phase correction element in this Embodiment 1, and the phase difference provided to a light beam. 7 is a flowchart showing a control operation of the optical information processing apparatus for recording or reproducing information on the optical recording medium in the first embodiment. The perspective view which shows schematic structure of the 4-axis actuator part which tilts in the radial direction and the tangential direction in this Embodiment 1. FIG. The figure which shows the light receiving element divided into 4 for the 4-axis actuator parts in this Embodiment 1. The figure which shows schematic structure of the fixed optical system and actuator part which can be recorded on or reproduced from, and erase | eliminated to the optical recording medium in Embodiment 2 of this invention The figure which shows the beam shaping prism in this Embodiment 2. The figure which shows the aberration distribution before and behind collimating lens adjustment in this Embodiment 2. The figure which shows the relationship between the amount of astigmatism before and behind collimating lens adjustment in Embodiment 2, and an angle. The figure which shows the electrode pattern of the phase correction element which provides the astigmatism amount of reverse polarity in this Embodiment 2. The figure which shows the phase correction element which has the pattern which corrects the astigmatism of the radial direction in this Embodiment 2, and the pattern which corrects the astigmatism rotated by 45 degrees from the radial direction. The figure which shows the phase correction element which made the electrode pattern corresponding to the collimating lens adjustment in this Embodiment 2 the pattern match | combined with the beam shaping direction. The figure explaining the beam shaping direction which makes the direction of the remaining astigmatism in this Embodiment 2 and a light beam correspond. The figure which shows the phase correction element which has the pattern which cancels astigmatism in this Embodiment 3, and the pattern which cancels spherical aberration FIG. 4A is a diagram illustrating a spherical aberration wavefront, and FIG. 4B is a diagram illustrating a corrected spherical aberration wavefront generated in a light beam incident on the objective lens from the light source side according to the third embodiment. In the spherical aberration in the third embodiment, (a) shows the case where the optical axes of the objective lens and the fixed optical system are coincident, and (b) shows the case where the optical axes of the objective lens and the fixed optical system are shifted and coma aberration occurs. Diagram showing each wavefront The figure which shows schematic structure of the optical pick-up which can be recorded on or reproduced from and erased in the optical recording medium in Embodiment 4 of this invention When the DVD optical system is used in the optical path of the finite system by the blue optical system objective lens in the fourth embodiment, (a) is the tilt aberration characteristic of the DVD optical recording medium, and (b) is the tilt aberration of the objective lens. (C) is an aberration characteristic after coma aberration correction due to the tilt of the DVD optical recording medium, and (d) is a diagram showing the drive tilt amount of the objective lens with respect to the tilt of the DVD optical recording medium. A transparent perspective view schematically showing a configuration of an optical information processing device according to a fifth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fixed optical system 20 Actuator part 30 Tilt detection means 40 Optical information processing apparatus 41 Optical pick-up 42 Insertion port 43 Spindle motor 44 Carriage 45,108,108a, 108b Optical recording medium 46 Protective case 51a, 51b Glass substrate 52 Conductive spacer 53 Liquid crystal 54a, 54b, 54c Electrode 55 Insulating film 56 Alignment film 57 Electrode extraction portions 58a, 58b, 58c, 58d, 58e, 58f, 58g, 58h, 58i, 59a, 59b, 59c Pattern electrodes 101, 121a, 301 Semiconductor laser 102 , 302 Collimate lenses 103, 304 Polarizing beam splitter 104 Deflection mirrors 105, 105a, 105b Phase correction element 106 1/4 wavelength plate 107 Objective lens 109 Detection lens 110 Cylindrical lens 110a Beam splitting means 11 1, 121 c Light receiving element 112 Beam shaping prism 112 a Surface 121 Hologram unit 121 b Hologram 122 Coupling lens 123 Dichroic prism 201 Objective lens holder 202 Base portion 203, 204 Elastic support mechanism 303 Half mirror 305 First light receiving element 306 Second Light receiving elements 305a, 305b, 306a, 306b Light receiving units 311, 312, 316, 317 Preamplifiers 313, 318, 322 Difference circuits 314, 319 Adder circuits 315, 320 Arithmetic circuit 321 Switch

Claims (10)

A light source, an objective lens for condensing the light beam emitted from the light source on the optical recording medium, and the objective lens tilted in at least one of a radial direction and a tangential direction of the optical recording medium An optical pickup comprising objective lens driving means, and a phase correction element that is disposed between the light source and the objective lens and changes the amount of astigmatism of the light beam,
An optical pickup characterized in that a direction in which an amount of astigmatism by the phase correction element is changed substantially coincides with a tilt direction of the objective lens.   2. The optical pickup according to claim 1, wherein the phase correction element imparts an astigmatism amount to the light beam by a liquid crystal layer whose refractive index changes according to an applied voltage.   A tilt detection unit that detects a relative angle between the objective lens and a light beam incident on the objective lens is provided, and the phase correction element changes the amount of astigmatism according to the relative angle detected by the tilt detection unit. The optical pickup according to claim 1 or 2.   A beam shaping unit is provided between the light source and the objective lens, and the phase correction element changes an astigmatism amount in a direction rotated by 45 ° from the tilt direction of the objective lens and the light beam shaping direction of the beam shaping unit. The optical pickup according to any one of claims 1 to 3, wherein the optical pickup is used.   2. A beam shaping unit is provided between the light source and the objective lens, and a light beam shaping direction by the beam shaping unit is a direction rotated by 45 ° from a radial direction of the optical recording medium. 4. The optical pickup according to any one of items 3.   The optical pickup according to claim 1, wherein the phase correction element changes a spherical aberration amount of a light beam emitted from the objective lens.   7. The optical recording medium for recording or reproducing information by condensing the light beam is a plurality of optical recording media having different operating wavelengths, substrate thicknesses or used numerical apertures. The optical pickup according to claim 1.   8. The optical pickup according to claim 7, wherein any one of optical paths for condensing a light beam for performing recording or reproduction on the plurality of optical recording media is a finite system.   9. The optical pickup according to claim 6, wherein the objective lens for condensing the light beam tilts the objective lens in the tracking direction according to a shift amount of the optical recording medium in the tracking direction.   An optical information processing apparatus that performs at least one of recording, reproduction, and erasing of information on an optical recording medium, wherein the optical pickup according to any one of claims 1 to 9 is used.