JP2009048725A - Optical pickup device and aberration correction system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device for properly correcting aberration even when displacement occurs between an objective lens and a coma aberration correction element and having a simple constitution for correcting the coma aberration in an optical pickup device including a coma aberration correction element. <P>SOLUTION: The coma aberration correction element 5 comprises a liquid crystal element. One of two transparent electrodes constituting the liquid crystal element is an electrode pattern divided into five regions A-E. On the basis of the phase of an optical beam passing through the region E, when correcting the coma aberration, the coma aberration correction element 5 generates, for optical beams passing through the regions A-D, phase differences satisfying A:B:C:D=1:-1:-0.4:0.4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup device that enables reading and writing of information by irradiating an optical disk with a light beam, and more particularly to a technique for correcting aberration by arranging an aberration correction element in an optical system of the optical pickup device.

  Optical disks such as compact disks (hereinafter referred to as CDs) and digital versatile disks (hereinafter referred to as DVDs) are in widespread use. Recently, optical discs capable of high-density recording, such as Blu-ray discs (hereinafter referred to as BD) with higher recording density than CDs and DVDs, have been put into practical use. Such reproduction of information on the optical disk and recording of information on the optical disk are performed using an optical pickup device that enables reading and writing of information by irradiating the optical disk with a light beam.

  By the way, when reading and writing information on an optical disk using an optical pickup device, it is caused by manufacturing variation of an objective lens provided for condensing a light beam on the recording surface of the optical disk, variation in assembly of the objective lens, or the like. Thus, it is known that coma aberration occurs. In particular, an optical pickup device compatible with a BD or the like that can record information with high density is susceptible to coma aberration because it uses a light beam with a short wavelength and an objective lens with a large numerical aperture.

  For this reason, many optical pickup apparatuses having a function of correcting coma aberration have been proposed. For example, a configuration for correcting coma aberration by mechanically tilting an optical pickup device itself or an objective lens provided in the optical pickup device has been proposed.

  As another configuration for correcting coma aberration, there is a configuration in which a coma aberration correcting element including a liquid crystal element is arranged in an optical system of an optical pickup device (see, for example, Patent Documents 1 and 2). In this configuration, the coma aberration correcting element gives a phase distribution to the passing light beam, thereby correcting the coma aberration. In the case of a configuration in which a liquid crystal element is used as a coma aberration correction element, a mechanical mechanism is not required unlike the case of tilting the optical pickup and the objective lens described above, and thus attention has been paid to the conventional technique.

  By the way, when the liquid crystal element is disposed in the optical system of the optical pickup device as the coma aberration correcting element, there are two cases: a case where the liquid crystal element is configured to be integrally driven with the objective lens, and a case where the liquid crystal element is configured not to be integrally driven. Has existed in the past.

  In the former case, the weight of the movable portion of the objective lens actuator provided for performing focus control and tracking control is increased, and there is a problem such as a decrease in sensitivity of the objective lens actuator. In addition, since the liquid crystal element is arranged in the movable portion, there is a problem that it is not easy to route wiring for supplying power to the liquid crystal element.

  On the other hand, in the latter case, the above-described problems relating to the sensitivity reduction of the objective lens actuator and the routing of the wiring to the liquid crystal element can be solved. However, when the objective lens moves in the tracking direction (direction parallel to the radial direction of the optical disc) for tracking control (hereinafter, such movement of the objective lens is expressed as a lens shift), the objective lens and the liquid crystal. There has been a problem that positional displacement occurs between the element and new coma and astigmatism.

In this regard, according to Patent Document 1, the optical reader detects the amount of discenter (positional displacement) and controls the voltage applied to the aberration correction element based on the amount of discenter. Yes. For this reason, the coma aberration caused by the positional deviation of the objective lens can be corrected.
JP 2002-358690 A JP 2002-342975 A

  However, in the case of the configuration of Patent Document 1, it is considered that the detection timing of the discent amount needs to be short in order to obtain high aberration correction performance by suppressing the influence of the lens shift. In this case, it is necessary to change the setting of the driving voltage of the liquid crystal element in a short time. However, the liquid crystal element takes time after the setting of the driving voltage is changed until a characteristic corresponding to the driving voltage is obtained. For this reason, in the case of the configuration of Patent Document 1, it is considered that the influence of the lens shift may not be sufficiently suppressed. Further, the configuration of Patent Document 1 is disadvantageous in terms of cost because the control mechanism is complicated and a lens position discriminator may be required.

  In view of the above problems, an object of the present invention is to appropriately correct aberration even if a positional deviation occurs between the objective lens and the coma aberration correcting element in the optical pickup device including the coma aberration correcting element, and An object of the present invention is to provide an optical pickup device capable of correcting coma with a simple configuration. Another object of the present invention is to provide an optical pickup apparatus including a coma aberration correcting element, which suppresses an increase in cost and appropriately corrects aberrations even if a positional deviation occurs between the objective lens and the coma aberration correcting element. It is to provide an aberration correction method that can be performed.

  In order to achieve the above object, the present invention provides a base, a light source fixedly disposed on the base, a light source that is displaceable with respect to the base, and collects a light beam emitted from the light source on a recording surface of an optical disc. A coma aberration correcting element that is disposed between the light source and the objective lens in a state of being fixed to the base, and that corrects coma aberration by giving a phase distribution to the passing light beam; In the optical pickup device, comprising: an actuator that displaces the objective lens in a focus direction that is in contact with and away from the optical disc and a tracking direction that is parallel to a radial direction of the optical disc. The element has first to fifth five regions, and the first region and the second region are an optical axis passing through the coma aberration correcting element and the first region. The third region and the fourth region are symmetrically arranged with reference to the symmetry line, and are symmetrically arranged with respect to a symmetry line substantially orthogonal to the direction parallel to the racking direction, and the first and The fifth region is disposed so as to sandwich the second region, and the fifth region is disposed at least at a position surrounded by the third and fourth regions and at a position surrounding the first and second regions. The first region and the third region, and the second region and the fourth region are provided on the same side with respect to the symmetry line, respectively. Based on the phase of the light beam that passes through, the first region and the second region are generated for a light beam that passes through a phase difference having substantially the same size and different signs, and The third region and the fourth region are substantially identical to each other. And a light beam that passes through a phase difference having a different sign and having a magnitude smaller than that of the phase difference generated in the first and second regions. The sign of the phase difference generated in the area and the fourth area and the sign of the phase difference generated in the second area and the third area are the same.

  According to this configuration, at the time of aberration correction, the influence of the lens shift of the objective lens can be suppressed by setting the phase difference generated in each region of the coma aberration correction element to a predetermined ratio. For this reason, the coma aberration correcting element can appropriately correct the aberration regardless of the lens shift. Further, since the configuration of the coma aberration correcting element is not changed according to the lens shift, the coma aberration can be corrected with a simple configuration.

  According to the present invention, in the optical pickup device configured as described above, the shape of the first and second regions is substantially elliptical in plan view, and the formation of the third and fourth regions is substantially circular in plan view. It may be arcuate. At this time, the ratio of the phase difference generated in the light beam passing through the first to fourth regions is expressed as follows: First region: Second region: Third region: Fourth region = It is good also as 1: -1: -0.4: 0.4. Thereby, it is possible to realize an optical pickup device that can appropriately correct aberrations even if a positional deviation occurs between the objective lens and the coma aberration correcting element.

  In the optical pickup device having the above-described configuration, the coma aberration correcting element may be a liquid crystal element having a liquid crystal and two transparent electrodes sandwiching the liquid crystal, and the first to fifth regions. May be formed by dividing at least one of the two transparent electrodes into five regions. Although a liquid crystal element can be used as an element that generates a phase distribution in the light beam, the above effect can also be obtained when this liquid crystal element is used as a coma aberration correcting element.

  In order to achieve the above object, the present invention provides a base, a light source fixedly disposed on the base, a light source that is displaceable with respect to the base, and collects a light beam emitted from the light source on a recording surface of an optical disc. A coma aberration correcting element that is disposed between the light source and the objective lens in a state of being fixed to the base, and that corrects coma aberration by giving a phase distribution to the passing light beam; An actuator for displacing the objective lens in a focus direction which is a direction in which the optical disk is in contact with and separated from the optical disk, and a tracking direction which is a direction parallel to the radial direction of the optical disk. 1 to 5 regions, and the first region and the second region are parallel to the optical axis passing through the coma aberration correcting element and the tracking direction. The third region and the fourth region are symmetrically arranged with respect to the symmetry line, and sandwich the first and second regions. The fifth region is at least a position surrounded by the third and fourth regions, and is disposed at a position surrounding the first and second regions, and the first region and The third region, and the second region and the fourth region are each an aberration correction method using the coma aberration correcting element in an optical pickup device provided on the same side with respect to the symmetry line. Based on the phase of the light beam that passes through the fifth region, the first region and the second region are light beams that pass through phase differences having substantially the same size and different signs. For the third region and the fourth region A region is a phase difference having substantially the same size and a different sign, and for a light beam that passes through a phase difference that is smaller than the phase difference generated in the first and second regions. The phase difference code generated in the first region and the fourth region, and the phase difference code generated in the second region and the third region are the same, It is characterized by correcting aberrations.

  According to this configuration, the influence of the lens shift of the objective lens can be suppressed by setting the phase difference generated in each region of the coma aberration correcting element to a predetermined ratio. For this reason, according to the aberration correction method of the present invention, it is possible to appropriately correct aberration regardless of the presence or absence of lens shift. Further, since the configuration of the coma aberration correction element is not changed according to the lens shift, the configuration for performing the coma aberration can be simplified by using the aberration correction method of the present invention, and the cost increase can be suppressed. .

  According to the present invention, in an optical pickup device including a coma aberration correcting element, even if a positional deviation occurs between the objective lens and the coma aberration correcting element, the aberration can be corrected appropriately, and the coma can be corrected with a simple configuration. An optical pickup device capable of performing Further, according to the present invention, in an optical pickup device including a coma aberration correcting element, an aberration that can appropriately correct aberration even if a positional deviation occurs between the objective lens and the coma aberration correcting element while suppressing an increase in cost. A correction method can be provided.

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

  First, the configuration of the optical pickup device of this embodiment will be described with reference to FIG. FIG. 1 is a diagram for explaining the configuration of the optical pickup device of the present embodiment. FIG. 1A is a schematic diagram showing the configuration of the optical system of the optical pickup device of the present embodiment, and FIG. These are the schematic plan views which show the relationship between the optical member which comprises the optical pick-up apparatus of this embodiment, and a slide base.

  The optical system of the optical pickup device 1 includes a light source 2, a beam splitter 3, a collimator lens 4, a coma aberration correction element 5, a rising mirror 6, an objective lens 7, a sensor lens 8, and a photodetector. 9 are provided. The optical members constituting these optical systems are mounted on the slide base 12. The slide base 12 is slidably attached to a slide shaft 13 extending in a direction (radial direction) parallel to the radial direction of the optical disc 20. Thereby, the optical pickup device 1 can move in the radial direction of the optical disc 20, and can read information recorded on the optical disc 20 and write information to the optical disc 20.

  The above-described optical member mounted on the slide base 12 is fixedly arranged with respect to the slat base 12 except for the objective lens 7.

  As the light source 2, a semiconductor laser is used. The wavelength of the laser light emitted from the semiconductor laser is determined as appropriate depending on which type of optical disk 20 the optical pickup apparatus 1 is compatible with. That is, for example, when the optical pickup apparatus 1 is compatible with BD, a semiconductor laser that emits laser light of 405 nm band is used, and when it is compatible with DVD, a semiconductor laser that emits laser light of 650 nm band is used. The configuration. Note that the optical pickup device 1 may be provided so as to be compatible with a plurality of types of optical discs 20. In this case, for example, a semiconductor laser capable of switching and emitting laser beams of a plurality of types of wavelengths is disposed in the light source 2. Or a plurality of semiconductor lasers may be arranged.

  The beam splitter 3 transmits the laser beam emitted from the light source 2 and guides it to the optical disc 20 side, and reflects the laser beam reflected by the optical disc 20 and guides it to the photodetector 9 side. The beam splitter 3 may be a polarizing beam splitter. In this case, a quarter wavelength plate is disposed in front of the objective lens 7.

  The collimating lens 4 converts the light transmitted from the beam splitter 3 into parallel light. The coma aberration correcting element 5 gives a phase distribution to the passing laser beam and corrects coma aberration generated in the optical system of the optical pickup device 1. The driver 11 controls the phase distribution. Details of the configuration of the coma aberration correcting element 5 will be described later.

  The rising mirror 6 reflects the laser light emitted from the light source 2 so that the direction of the laser light is substantially perpendicular to the recording surface 20 a of the optical disc 20.

  The objective lens 7 condenses the laser beam sent from the rising mirror 6 on the recording surface 20 a of the optical disc 20. The objective lens 7 has a focus direction that is in contact with and away from the optical disc 20 by an objective lens actuator 10 that is fixedly arranged with respect to the slide base 12, and a tracking direction that is parallel to the radial direction of the optical disc 20. The same in the radial direction). Thereby, focus control and tracking control are possible.

  The configuration of the objective lens actuator 10 is a well-known configuration in which the objective lens 7 is moved using the electromagnetic action of the current flowing through the coil and the magnetic field generated by the permanent magnet, and therefore the description thereof is omitted here. To do.

  The sensor lens 8 is reflected by the optical disk 20, passes through the objective lens 7, the rising mirror 6, the coma aberration correcting element 5, and the collimating lens 4 in this order, and receives the laser light reflected by the beam splitter 3 by the photodetector 9. Condensate in an area (not shown).

  The photodetector 9 receives the laser beam that has passed through the sensor lens 8 and converts the optical information into an electrical signal. The electric signal output from the photodetector 9 is processed and used as reproduction information or servo information.

  Next, details of the configuration of the coma aberration correcting element 5 provided in the present embodiment will be described. FIG. 2 is a schematic side view showing the configuration of the coma aberration correcting element 5 provided in the optical pickup device 1 of the present embodiment. As shown in FIG. 2, the coma aberration correcting element 5 includes a liquid crystal 21, two transparent electrodes 22 and 23 disposed so as to sandwich the liquid crystal 21, and a glass substrate 24 that holds the transparent electrode 22 or the transparent electrode 23, respectively. , 25. That is, the coma aberration correcting element 5 of the present embodiment is a liquid crystal element configured using liquid crystal.

  FIG. 3 is a schematic plan view showing an electrode pattern of one of the two transparent electrodes 22 and 23 included in the coma aberration correcting element 5 of the present embodiment. As shown in FIG. 3, the transparent electrode 22 has an electrode pattern divided into five regions of region A, region B, region C, region D, and region E. Note that a gap is provided between different regions and is not electrically connected. Further, wiring (not shown) is independently drawn from these five areas A, B, C, D, and E, and each of the areas A to E is independently given a potential. The driver 11 controls the potential applied to each of the areas A to E.

  Of the five regions A to E formed on the transparent electrode 22, the region A and the region B are both formed in a substantially elliptical shape, and both are symmetrically arranged with respect to the symmetry line 26. The symmetry line 26 is a line orthogonal to both the tracking direction (left-right direction in FIG. 3) and the direction of the optical axis passing through the coma aberration correcting element 5 (paper surface direction in FIG. 3), and is provided for convenience of explanation. It is a drawn line.

  The region C and the region D are both formed in a substantially arc shape, and both are symmetrically arranged with respect to the symmetry line 26. In addition, the region C and the region D are arranged so as to sandwich the region A and the region B. A broken circle 27 in FIG. 3 indicates the pupil diameter of the objective lens 7, and the diameters of the outer peripheral sides of the regions C and D are configured to be slightly larger than the pupil diameter 27 of the objective lens 7.

  The region E is disposed in a portion where the region A, the region B, the region C, and the region D are not disposed, and surrounds the regions A to D.

  Moreover, the transparent electrode 23 which is the other transparent electrode of the two transparent electrodes 22 and 23 provided in the coma aberration correcting element 5 is a single solid electrode without being divided. When configured in this way, the refractive index of the liquid crystal 21 sandwiched between the regions A to E and the transparent electrode 23 can be adjusted by adjusting the potential applied to the regions A to E of the transparent electrode 22. it can. The laser light passing through the coma aberration correcting element 5 can be divided into five regions and given a phase distribution.

  Hereinafter, with respect to the liquid crystal 21, a portion sandwiched between the region A and the transparent electrode 23 is transparent to the first region A, and a portion sandwiched between the region B and the transparent electrode 23 is transparent to the second region B and region C. The portion sandwiched between the electrode 23 is the third region C, the portion sandwiched between the region D and the transparent electrode 23 is the fourth region D, the portion sandwiched between the region E and the transparent electrode 23 The fifth region E will be described.

  In the present embodiment, of the two transparent electrodes 22 and 23, only the transparent electrode 22 is formed with an electrode pattern that is divided into a plurality of regions. However, the present invention is not limited to this. That is, of the two transparent electrodes 22 and 23, only the transparent electrode 23 (opposite to the case of the present embodiment) may be configured to form an electrode pattern divided into a plurality of regions. In addition, an electrode pattern divided into a plurality of regions may be formed on both of the two transparent electrodes 22 and 23.

  Next, a method for correcting coma using the coma aberration correcting element 5 thus provided will be described. In the optical pickup device 1 of the present embodiment, the coma aberration correcting element 5 is fixed to the slide base 12, and the objective lens 7 is moved relative to the slide base 12 by the objective lens actuator 10. In the case of this configuration, when the objective lens 7 is moved in the tracking direction (same as the radial direction) for tracking control (that is, when the lens is shifted), as described above, the coma aberration correcting element 5 and the objective lens 7 May cause misalignment and extra aberrations. However, in the present embodiment, the coma aberration can be corrected by suppressing the extra aberration as much as possible by appropriately determining the setting conditions when the coma aberration correcting element 5 corrects the aberration.

  Hereinafter, how the setting conditions of the coma aberration correcting element 5 are determined in the present embodiment will be described. In the present embodiment, the coma aberration correcting element is used during the aberration correction after the phase distribution generated by the coma aberration correcting element 5 is once determined so that the coma aberration can be corrected with a simple configuration. It is assumed that the phase distribution generated in step 5 is not changed (in principle, the setting is not changed).

  4, 5 and 6 are diagrams for explaining how the setting conditions at the time of aberration correction are determined in the coma aberration correcting element 5 of the present embodiment. 4A to 6B, FIG. 4A shows the amount of astigmatism generated with respect to the amount of lens shift, and FIG. 4B shows the amount of coma generated with respect to the amount of lens shift. 4, 5, and 6 is the phase distribution given to the laser light that passes through the coma aberration correcting element 5.

  Specifically, in FIG. 4, the ratio of the phase difference generated in the laser light in each region on the basis of the phase of the laser light passing through the fifth region E is expressed as first region A: second region B. : Third region C: Fourth region D = 1: -1: -1: 1. In FIG. 5, the ratio of the phase difference generated in the laser light in each region on the basis of the phase of the laser light passing through the fifth region E is expressed as follows: first region A: second region B: third Region C: Fourth region D = 1: −1: −0.4: 0.4. In FIG. 6, the ratio of the phase difference generated in the laser light in each region on the basis of the phase of the laser light passing through the fifth region E is expressed as follows: first region A: second region B: third region C: The case where the fourth region D = 1: −1: 0: 0 is shown.

  When the phase distribution is given to the laser light passing through the coma aberration correction element 5 at such a ratio and the position of the pupil of the objective lens 7 is shifted (shifted in the tracking direction), the laser beam is condensed by the objective lens 7. The graphs of FIGS. 4 to 6 show the results obtained by calculating each aberration generated in the laser spot.

  4A, FIG. 5A, and FIG. 6A, the third region C and the fourth region are compared with the phase difference generated in the first region A and the second region B. As the magnitude (absolute value) of the phase difference generated in the region D is reduced, the amount of astigmatism generated by the lens shift tends to be reduced.

  Further, by comparing FIG. 4B, FIG. 5B, and FIG. 6B, the amount of third-order coma aberration generated is a phase difference generated in the first region A and the second region B. On the other hand, when the magnitude (absolute value) of the phase difference generated in the third region C and the fourth region D is reduced, the generation amount tends to be suppressed (FIG. 4B and FIG. 5). Compared with (b), especially when the lens shift amount is small). However, if the magnitude of the phase difference generated in the third area C and the fourth area D is too small with respect to the phase difference generated in the first area A and the second area B, the lens shift will occur. There is a tendency for the amount of third-order coma aberration to increase when the value of becomes large (FIG. 6B).

  Similarly, by comparing FIG. 4B, FIG. 5B, and FIG. 6B, the fifth-order coma aberration is related to the phase difference generated in the first region A and the second region B. Thus, when the magnitude (absolute value) of the phase difference generated in the third region C and the fourth region D is reduced, the generation amount tends to be reduced. On the other hand, with respect to the seventh-order coma aberration, the magnitude of the phase difference generated in the third region C and the fourth region D with respect to the phase difference generated in the first region A and the second region B ( When the absolute value is made too small (FIG. 6B), there is a tendency that the amount of aberration generated due to lens shift increases.

  In determining the setting conditions at the time of correcting the aberration of the coma aberration correcting element 5, it is desirable to suppress the generation of the third-order coma aberration as much as possible and suppress the generation of other aberrations as much as possible even when there is a lens shift. . Therefore, from the above result, the magnitude (absolute value) of the phase difference generated in the third region C and the fourth region D with respect to the phase difference generated in the first region A and the second region B. It is understood that it is desirable that the size is small, and that the size is not too small (not zero). Then, considering the overall balance, the ratio of the phase difference generated in the first region A, the second region B, the third region D, and the fourth region D on the basis of the phase in the fifth region E It is understood that 1: -1: -0.4: 0.4 (corresponding to the case of FIG. 5) is more preferable.

  In addition, about the ratio of the phase difference produced | generated to a laser beam in 1st-4th area | region AD, the result of the conditions between FIG. 4 and FIG. 5 and between FIG. 5 and FIG. 6 is not shown. This is because, between FIGS. 4 and 5 and between FIGS. 5 and 6, an approximate value can be predicted by the first-order approximation with respect to the tendency of the change in the amount of aberration generated with the change in conditions. .

  When the optical pickup device 1 corrects coma aberration, the coma aberration correcting element 5 is set so that the ratio of the phase difference generated in the first to fourth regions A to D is as described above. However, the phase difference value to be specifically generated may be determined, for example, by an experiment in the manufacturing stage and stored in a memory (not shown). Then, when the coma aberration correcting element 5 is actually driven, the conditions stored in the memory may be read and driven.

  In addition, coma aberration occurs due to warpage of the optical disk. The coma aberration generated by the optical disc differs from one optical disc to another, and cannot be determined by experiment at the time of manufacture as described above. For this reason, when correcting the coma generated by the warp of the optical disk, for example, after the optical disk is mounted, the tilt sensor is used to check the tilt of the laser beam with respect to the optical disk. Thus, the phase difference generated in the first to fourth regions A to D of the coma aberration correcting element 5 may be determined. Also in this case, the ratio of the phase difference to be generated is the above-described constant ratio.

  The embodiment described above is an example, and the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, the first to fifth regions A to E provided in the transparent electrode 22 are not limited to the shape of the present embodiment, and various changes can be made. For example, the first and second regions may be semicircular. For the third and fourth regions, for example, in the present embodiment, the outer peripheral side is not a complete arc, but this portion may also be an arc. The fifth region may be provided only in a portion surrounded by the third and fourth regions, for example.

  When the shape is changed from the first region to the fifth region in this way, the ratio (1: -1) described above is used as the ratio of the phase difference generated in the laser light in the first to fourth regions. : -0.4: 0.4) may be a preferred value. However, even in this case, the magnitude (absolute value) of the phase difference generated in the third region and the fourth region is smaller than the phase difference generated in the first region and the second region, and If the phase difference larger than zero is generated, the influence of the aberration caused by the lens shift can be suppressed.

  According to the present invention, there is provided an optical pickup device that can appropriately correct aberrations even when a positional deviation occurs between the objective lens and the coma aberration correcting element and that has a simple configuration for correcting coma aberration. it can. Therefore, the present invention is useful in the field of optical pickup devices.

These are figures for demonstrating the structure of the optical pick-up apparatus of this embodiment. These are the schematic side views which show the structure of the coma aberration correction element with which the optical pick-up apparatus of this embodiment is provided. These are the schematic plan views which showed the electrode pattern of one transparent electrode among the two transparent electrodes with which the coma aberration correction element of this embodiment is provided. These are the figures for demonstrating how the setting conditions at the time of an aberration correction are determined in the coma aberration correction element of this embodiment. These are the figures for demonstrating how the setting conditions at the time of an aberration correction are determined in the coma aberration correction element of this embodiment. These are the figures for demonstrating how the setting conditions at the time of an aberration correction are determined in the coma aberration correction element of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Light source 5 Coma aberration correction element 7 Objective lens 10 Objective lens actuator 12 Slide base 20 Optical disk 20a Recording surface 21 Liquid crystal 22, 23 Transparent electrode 26 Symmetric line

Claims (5)

Base and
A light source fixedly disposed on the base;
An objective lens provided so as to be displaceable with respect to the base and condensing a light beam emitted from the light source on a recording surface of an optical disc;
A coma aberration correction element that is disposed between the light source and the objective lens in a state of being fixed to the base, and corrects coma aberration by giving a phase distribution to the passing light beam;
An actuator for displacing the objective lens in a focus direction, which is a direction in which the optical disk is in contact with or separated from the optical disk, and a tracking direction, which is a direction parallel to a radial direction of the optical disk,
In an optical pickup device comprising:
The coma aberration correcting element has first to fifth regions,
The first region and the second region are symmetrically arranged with respect to an optical axis passing through the coma aberration correcting element and a symmetry line substantially orthogonal to a direction parallel to the tracking direction,
The third region and the fourth region are arranged symmetrically with respect to the symmetry line, and are arranged so as to sandwich the first and second regions,
The fifth region is at least a position surrounded by the third and fourth regions, and is disposed at a position surrounding the first and second regions,
The first region and the third region, and the second region and the fourth region are provided on the same side with respect to the symmetry line, respectively.
At the time of aberration correction, based on the phase of the light beam passing through the fifth region,
The first region and the second region are generated with respect to a light beam that passes through a phase difference having substantially the same size and different signs.
The third region and the fourth region are phase differences having substantially the same size and different signs, and are larger than the phase difference generated in the first and second regions. Is generated for a light beam passing through a small phase difference,
The sign of the phase difference generated in the first area and the fourth area and the sign of the phase difference generated in the second area and the third area are the same. A characteristic optical pickup device.   The shape of the said 1st and 2nd area | region is planar view substantially elliptical shape, and formation of the said 3rd and 4th area | region is planar view substantially circular arc shape, The shape of Claim 1 characterized by the above-mentioned. Optical pickup device. 3. The optical pickup device according to claim 2, wherein a ratio of the phase difference generated in the light beam passing through the first to fourth regions is expressed by the following equation.
1st area | region: 2nd area | region: 3rd area | region: 4th area | region = 1: -1: -0.4: 0.4 The coma aberration correcting element is a liquid crystal element having a liquid crystal and two transparent electrodes sandwiching the liquid crystal,
4. The optical pickup according to claim 1, wherein the first to fifth regions are formed by dividing at least one of the two transparent electrodes into five regions. 5. apparatus. Base and
A light source fixedly disposed on the base;
An objective lens provided so as to be displaceable with respect to the base and condensing a light beam emitted from the light source on a recording surface of an optical disc;
A coma aberration correction element that is disposed between the light source and the objective lens in a state of being fixed to the base, and corrects coma aberration by giving a phase distribution to the passing light beam;
An actuator that displaces the objective lens in a focus direction that is a direction in which the optical disk is in contact with or separated from, and a tracking direction that is a direction parallel to a radial direction of the optical disk,
The coma aberration correcting element has first to fifth regions,
The first region and the second region are arranged symmetrically with respect to an optical axis passing through the coma aberration correcting element and a symmetry line substantially orthogonal to a direction parallel to the tracking direction, and the third region The region and the fourth region are disposed symmetrically with respect to the symmetry line, and are disposed so as to sandwich the first and second regions, and the fifth region includes at least the third and third regions. 4 is disposed at a position surrounded by the area of 4 and surrounding the first and second areas,
The coma aberration correcting element in the optical pickup device provided on the same side with respect to the symmetry line is used for the first region and the third region, and the second region and the fourth region, respectively. An aberration correction method,
Based on the phase of the light beam passing through the fifth region,
The first region and the second region are generated for a light beam that passes through a phase difference having substantially the same size and different signs,
The third region and the fourth region are phase differences having substantially the same size and different signs, and the size is larger than the phase difference generated in the first and second regions. Generated for a light beam passing through a small phase difference,
The phase difference code generated in the first area and the fourth area is the same as the phase difference code generated in the second area and the third area, and aberration correction is performed. An aberration correction method characterized by being performed.

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