JP2002056565A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance optical pickup device that is free from deterioration in aberration compensating performance even at the time of tracking servo. SOLUTION: The optical pickup device is equipped with an optical unit including an objective lens and an aberration compensating element which is fixed on the objective lens and which corrects aberration generated in the optical system, with an actuator which transfers the optical unit in a tracking direction and/or a focusing direction, and with a detecting means which detects displacement of the optical unit in the tracking direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device used for an optical recording / reproducing apparatus, and more particularly to an optical pickup device having an aberration correction unit for correcting an aberration generated in an optical path.

[0002]

2. Description of the Related Art In recent years, various optical disks, such as a DVD (Digital Video Disc or Digital Versatile Disc), capable of recording a large amount of image / audio data and digital data have been developed. In addition, research and development of higher density for further increasing the capacity of such an optical disk are being promoted, and research and development of an optical pickup device and an information recording / reproducing device corresponding to the higher density are being promoted.

[0003] As a method for responding to the increase in the density of the optical disk, it is necessary to increase the numerical aperture (NA) of an objective lens provided in the optical pickup device or to use a short-wavelength light beam. May reduce the irradiation diameter of the light beam irradiated on the optical disc. However, when the numerical aperture NA of the objective lens is increased or a short-wavelength light beam is used, the influence of the aberration on the light beam by the optical disk increases, and it becomes difficult to improve the accuracy of information recording and information reproduction. The problem arises.

Further, as the density of an optical disk increases, the thickness of a transparent substrate through which a light beam passes has been reduced. However, even if a slight error in the thickness of the transparent substrate occurs during the manufacturing process, the influence of spherical aberration increases. The problem arises. In order to reduce the influence of such aberration, an optical pickup device including a liquid crystal element for correcting aberration has been conventionally proposed. As such a liquid crystal element, for example, Japanese Patent Application Laid-Open No. 10-269
No. 611 discloses this. This liquid crystal element has a plurality of electrodes formed concentrically on both sides, and adjusts the alignment state of the liquid crystal by applying different voltages to each electrode to correct aberrations generated in the optical path. It is.

In such an optical pickup device, generally, the objective lens is mounted on an actuator, and is constituted as a movable portion suspended and supported by an elastic member, and optical components other than the objective lens are mounted on the pickup body. For example, the actuator is a coil,
The objective lens is driven in a focusing direction and a tracking direction by a magnetic flux from a magnet fixed to the pickup body. For example, when the push-pull tracking error method is used, an offset occurs in the tracking error when the objective lens shifts in the tracking direction. To prevent this, the position of the objective lens during tracking is measured and subtracted from the push-pull tracking error. At this time, a light-shielding portion is added to the objective lens holder, the coil bobbin, and the like, and the displacement of the light-shielding portion is detected by a transmission sensor to measure the displacement of the objective lens during tracking.

[0006]

However, in the conventional optical pickup device, there is a problem that the aberration correction performance is deteriorated due to a shift between the objective lens and the liquid crystal element for aberration correction which occurs at the time of tracking servo. The present invention has been made in view of the above points, and it is an object of the present invention to provide a high-performance optical pickup device in which aberration correction performance does not deteriorate even during tracking servo. Is the purpose.

[0007]

An optical pickup device according to the present invention is an optical pickup device having an optical system for irradiating an optical disk with a light beam and guiding a reflected light beam from the optical disk. An optical unit fixedly including an aberration correction element for correcting an aberration generated in the optical system, an actuator for moving the optical unit in a tracking direction and / or a focusing direction, and detecting the displacement of the optical unit in the tracking direction Means.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings used in the following description, substantially the same components are denoted by the same reference numerals. [First Embodiment] FIG. 1 is a perspective view schematically showing a configuration of an optical unit 10 of an optical pickup device according to a first embodiment of the present invention. The optical unit 10 is incorporated in an optical pickup device of an optical recording / reproducing apparatus using an optical disk or the like as a recording medium, and is configured as a movable portion suspended and supported by an elastic member.

More specifically, the optical unit 10 has an objective lens 12 supported by a lens holder 11, a coil 14 wound on a bobbin as an actuator, and a liquid crystal element 16 supported by a liquid crystal holder 15. The lens holder 11, the coil bobbin, and the liquid crystal holder 15 have circular through holes at portions corresponding to the optical path diameter so as not to hinder the passage of the light beam. That is, an irradiation light beam from the optical system in the main body (pickup body) of the optical pickup device passes through the optical unit 10 and irradiates the optical disk, and a reflected light beam from the optical disk passes through the optical unit 10. It is supplied to the optical system in the pickup body.

[0010] Lens holder 11 and / or liquid crystal holder 1
5 is provided with a suspension spring 17 for supporting the optical unit 10 in a floating manner. In this embodiment, the suspension spring 17 also serves as a conductor for supplying electric power to the coil 14. The optical unit 10 is arranged between magnets (not shown) fixed to the pickup body, which function as magnetic flux applying means. Also, the coil 14
Includes a focusing coil and a tracking coil for focusing and tracking servo. Accordingly, the optical unit 10 is driven to be displaced in the focusing direction and the tracking direction relative to the pickup body by supplying current to the coil 14.

As will be described later, a strip-shaped light shielding portion 18 is provided on the liquid crystal element 16. On the other hand, an optical sensor 31 is provided on the pickup body, and detects a displacement of the light shielding portion 18 in the tracking direction. FIG. 2 is a perspective view schematically illustrating the configuration of the liquid crystal element 16. Also, an optical sensor 31 provided on the pickup body is shown. The liquid crystal element 16 has a liquid crystal 21 that changes birefringence with respect to light passing therethrough by an electric field generated according to the magnitude of the applied driving voltage. More specifically, FIG.
As shown in the cross-sectional view of FIG.
, Liquid crystal alignment films 23A and 23B, transparent insulating layers 24A and 24B, electrode layers 25A and 25B, and transparent substrates 26A and 26B made of glass or the like are formed respectively.

When a driving voltage is applied between the electrode layers 25A and 25B, the orientation of the liquid crystal molecules in the liquid crystal 21 changes according to the electric field generated by the driving voltage. As a result, the phase of the light passing through the liquid crystal 21 changes due to the birefringence of the liquid crystal 21. That is, the phase of the light passing through the liquid crystal 21 can be controlled by the driving voltage applied to the liquid crystal 21. Accordingly, it is possible to correct the aberration by forming the electrode layers 25A and 25B in a shape corresponding to the aberration distribution and applying a voltage corresponding to the magnitude of the aberration. In the present embodiment, an example is shown in which the electrode layer 25A is composed of a plurality of concentric (annular) electrodes in order to correct spherical aberration. The electrode layer 25B
The electrode is formed in an annular shape like the electrode layer 25A. The shape of the electrode layer 25B is not limited to an annular shape, and may be, for example, a full-surface electrode having a transparent conductor formed over the entire surface.

As shown in FIG. 2, on the liquid crystal 21, a wiring electrode 28 for supplying a drive voltage to each electrode of the electrode layer 25A and a strip-shaped light shielding portion 18 are formed. Shading part 1
8 is formed of the same material as the wiring electrode 28.
Alternatively, a part of the wiring electrode 28 can be used for the light shielding unit 18. The light-shielding portion 18 extends in the vertical direction of the tracking direction, and is electrically insulated from each element in the liquid crystal element 16 and protrudes from the liquid crystal element 16.
9 are formed. The protrusion 29 is provided for the liquid crystal element 16.
Of the transparent insulating layer 24B and the transparent substrate 26B
Have a protruding structure, or the liquid crystal element 16
Further, a similar structure may be provided by further providing a transparent substrate or the like below the bottom.

When the objective lens 12 shifts in accordance with the tracking servo operation, the sensor light (arrow in the figure) of the transmission type optical sensor 31 provided on the pickup body is blocked by the light shielding portion 18, and the displacement in the tracking direction is measured. Is done. As described above, the liquid crystal element 16 is connected to the objective lens 12.
, And is integrally driven, the displacement of the objective lens 12 in the tracking direction can be measured by the optical sensor 31 and the light shielding unit 18. Accordingly, the position of the objective lens 12 and the position of the liquid crystal element 16 do not shift during tracking servo, so that the aberration correction performance of the liquid crystal element 16 does not deteriorate.

Therefore, as described above, the position of the objective lens 12 can be measured without adding an extra part as a target (detected portion) of the optical sensor 31. In the above embodiment, the projection 29 is provided on the liquid crystal element 16.
The case where the light shielding portion 18 on the projection 29 is used as the detected portion has been described. However, as shown in FIG. May be provided. [Second Embodiment] FIG. 5 is a perspective view schematically showing a structure of a liquid crystal element 16 according to a second embodiment of the present invention. Also, an optical sensor 31 provided on the pickup body is shown.

In the present embodiment, the light-shielding portion 18 is composed of a plurality of stripe-shaped light-shielding bands. Other configurations are the same as those in the first embodiment. The plurality of stripe-shaped light shielding portions 18 are formed using the same electrode material as the wiring electrodes 28. The optical sensor 31 is of a transmission type. Objective lens 1 with tracking servo operation
When 2 shifts, the sensor light of the optical sensor 31 is intermittently blocked. Therefore, a pulse signal is obtained in a sensor light receiving unit (not shown). By calculating the pulse signal detected by the sensor light receiving section, the amount of movement of the objective lens 12 can be accurately measured, and operates as an optical position sensor. Third Embodiment FIG. 6 is a perspective view schematically showing a structure of a liquid crystal element 16 according to a third embodiment of the present invention. Further, an optical sensor 32 provided on the pickup body is also shown. In the present embodiment, a reflection type optical sensor 32 is used. Further, the light shielding portion 18 is configured by a plurality of stripe-shaped light shielding bands. It is preferable that a plurality of light-shielding bands are made of a high reflectance material. Other configurations are the same as those in the first embodiment.

The sensor light of the optical sensor 32 is transmitted to the liquid crystal element 16.
The sensor light that has passed through the protruding portion 29 and is reflected by the light-shielding band of the light-shielding portion 18 is detected by the light-receiving portion of the optical sensor 32. As in the case of the second embodiment, the optical sensor 3
The amount of movement of the objective lens 12 can be accurately measured by calculating the pulse signals detected by the two light receiving units. Fourth Embodiment FIG. 7 is a perspective view schematically showing a structure of a liquid crystal element 16 according to a fourth embodiment of the present invention. In this embodiment, the liquid crystal element 16 is provided with reflection-type hologram elements 33A and 33B, and the pickup body is provided with two-divided detectors 34A and 34B for receiving reflected light from the hologram elements 33A and 33B. ing.

As schematically shown in the sectional views of FIGS. 7 and 8, the hologram elements 33A and 33B are arranged outside the effective diameter 35 of the liquid crystal element 16 and inside the irradiation light beam diameter 36, and are divided into two parts. The detectors 34A and 34B are arranged outside the irradiation light beam diameter 36. In this embodiment, a part of the irradiation light beam is reflected by the hologram elements 33A and 33B, and the reflected light beam is received by the two-divided detectors 34A and 34B. When the objective lens 12 shifts with the tracking servo operation, the spot of the reflected light beam on the two-divided detectors 34A and 34B moves. More specifically, as shown in FIG. 9, when the shift of the objective lens 12 is zero, the spots on the two-divided detectors 34A and 34B (indicated by A and B in FIG. 9) are located at the center of the detector. I do. When the objective lens 12 shifts in the plus (+) direction due to the tracking servo operation, the spot shifts from the center of the detector, and when the objective lens 12 shifts in the minus (-) direction, the spot shifts in the opposite direction.

The amount of movement of the objective lens 12 can be determined from the above-mentioned spot shift amount. That is, 2
The received light amounts of the detector elements of the split detector (A) 34A are A1 and A2, respectively. Similarly, the received light amounts of the detector elements of the two-divided detector (B) 34B are B1 and B2.
Then, for example, the movement amount δ of the objective lens 12 is calculated by the following equation. δ = ((A1 + B1)-(A2 + B2)) / (A1 + A2 + B1 + B2) (1) In the above equation, the two-part detectors 34A and 34
The reason why the light quantity is divided by the sum (A1 + A2 + B1 + B2) of the light quantities incident on both B is to reduce errors due to changes in the light quantity distribution.

Therefore, as described above, the position of the objective lens 12 can be measured by providing the hologram element as a portion to be detected of the optical sensor outside the effective diameter of the liquid crystal element 16. [Fifth Embodiment] FIG. 10 is a perspective view schematically showing a structure of a liquid crystal element 16 according to a fifth embodiment of the present invention. In this embodiment, the optical pickup is a polarization beam system. That is, a polarized beam is used as the irradiation light beam. Further, tracking servo is performed by a push-pull tracking error method.

As shown in FIGS. 10 and 11, the liquid crystal element 16 is provided with reflection type hologram elements 33A and 33B and λ / 4 wavelength plates 38A and 38B. Further, two-divided detectors 34A and 34B for receiving the reflected light from the hologram elements 33A and 33B are provided on the same plane as the four-divided light-receiving element 39 for detecting the reflected light from the optical disk. As in the case of the fourth embodiment, the hologram elements 33A, 33B and λ / 4
The wave plates 38A and 38B are arranged outside the effective diameter of the liquid crystal element 16 and inside the irradiation light beam diameter.

In this embodiment, the hologram element 33
A part of the irradiation light beam is reflected by A and 33B, and the reflected light beam is received by the two-divided detectors 34A and 34B. Objective lens 12 with tracking servo operation
Is shifted, the light receiving element 39 and the two-segment detector 3
The spot of the reflected light beam on 4A, 34B moves.
More specifically, as shown in FIG. 12, when the shift of the objective lens 12 is zero, the two-divided detectors 34A, 34A,
4B and the light receiving element 39 (in FIG. 12, A,
The upper spot (indicated by B and C) is located at the center of the detector. When the objective lens 12 shifts in the plus (+) direction due to the tracking servo operation, the spot shifts from the center of the detector, and the objective lens 12 moves in the minus (-) direction.
Shifting in one direction shifts the spot in the opposite direction.

The amount of movement of the objective lens 12 can be determined from the above-mentioned spot shift amount. That is, 2
Using the received light amounts A1, A2, B1, and B2 of the detector elements of the divided detectors 34A and 34B and the received light amounts C1, C2, C3, and C4 of the light receiving element 39, for example, the moving amount ( δ), a push-pull tracking error (ε) is calculated. δ = ((A1 + B1)-(A2 + B2)) / (A1 + A2 + B1 + B2) (2) ε = ((C1 + C4)-(C2 + C3) (3) After offset correction Tracking error (ε ')
Is given by ε ′ = ε−G × δ (4) where G is a predetermined gain.

In the above equation, the two-part detector 3
The sum of the amounts of light incident on both 4A and 34B (A1 + A2 + B1
The reason for dividing by + B2) is to reduce errors due to changes in the light amount distribution. The normal push-pull signal cannot separate the light and dark due to the track diffraction effect and the offset due to the shift of the objective lens, but according to the above configuration,
Since the light beam for measuring the shift of the objective lens is not affected by the track, an offset corresponding to the lens shift can be measured.

In the above embodiment, a case where a liquid crystal element is used as an aberration correction element has been described as an example.
An element that performs aberration correction based on another operation principle may be used.

[0026]

As is evident from the above, according to the present invention, a high-performance optical pickup device in which the aberration correction performance does not deteriorate even during tracking servo can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration of an optical unit according to a first embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a configuration of a liquid crystal element.
Also, an optical sensor provided on the pickup body is shown.

FIG. 3 is a cross-sectional view of the liquid crystal device shown in FIG.

FIG. 4 is a perspective view schematically showing a modified example of the liquid crystal element, which has no protrusion.

FIG. 5 is a perspective view schematically showing a configuration of a liquid crystal element according to a second embodiment of the present invention. Also, an optical sensor provided on the pickup body is shown.

FIG. 6 is a perspective view schematically showing a configuration of a liquid crystal element according to a third embodiment of the present invention.

FIG. 7 is a perspective view schematically showing a configuration of a liquid crystal element according to a fourth embodiment of the present invention.

8 is a diagram showing an arrangement of a hologram element and a detector shown in FIG.

FIG. 9 is a diagram illustrating a movement of a spot on a two-segment detector when an objective lens is shifted with a tracking servo operation.

FIG. 10 is a perspective view schematically showing a configuration of a liquid crystal element according to a fifth embodiment of the present invention.

11 is a diagram showing an arrangement of a hologram element, a λ / 4 wavelength plate, and a detector shown in FIG.

FIG. 12 is a diagram showing a movement of a spot on the two-segment detector and a spot on the signal detection light-receiving element when the objective lens is shifted due to the tracking servo operation.

[Explanation of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 10 Optical unit 12 Objective lens 14 Actuator 16 Aberration correction element 17 Suspension spring 18 Light shielding part 31, 32, 34A, 34B Sensor 33A, 33B Hologram element 38A, 38B λ / 4 wavelength plate

Continued on the front page F term (reference) 2H049 BA06 CA07 CA20 2H088 EA45 HA02 HA03 HA14 HA17 HA21 JA04 MA20 5D118 AA18 BA01 BB02 BF02 BF03 CD02 CD03 CD08 CD11 CF30 DA40 DC03 5D119 AA09 AA21 AA29 BA01 DA01 DA05 EA02 JA03 EC03

Claims (10)

[Claims] 1. An optical pickup device having an optical system that irradiates an optical disk with a light beam and guides a reflected light beam from the optical disk, comprising: an objective lens; and an aberration fixed to the objective lens and generated by the optical system. An optical unit including an aberration correction element that corrects the optical unit, an actuator that moves the optical unit in a tracking direction and / or a focusing direction, and a detection unit that detects a displacement of the optical unit in the tracking direction. Optical pickup device. 2. The apparatus according to claim 1, wherein said detecting means includes a light-shielding portion formed on said aberration correcting element, and an optical sensor for optically detecting a displacement of said light-shielding portion. Optical pickup device. 3. The optical pickup device according to claim 2, wherein the light shielding portion is a part of an electrode of the aberration correction element. 4. The optical pickup device according to claim 2, wherein the light-shielding portion comprises a plurality of stripe-shaped light-shielding bands. 5. The optical pickup device according to claim 2, wherein the optical sensor is a reflection type sensor. 6. A reflection means formed outside an effective area of the aberration correction element to reflect a part of a light beam irradiated to the optical disk, and a detector for detecting reflected light from the reflection means. The optical pickup device according to claim 1, comprising: 7. The optical pickup device according to claim 6, wherein said reflection means includes a hologram element. 8. The irradiation light beam is a polarized beam,
7. The optical pickup device according to claim 6, wherein said reflection means comprises a λ / 4 wavelength plate and a hologram element. 9. The optical pickup device according to claim 8, wherein said detector is provided on the same plane as a light receiving element for detecting light reflected from said optical disk. 10. The optical pickup according to claim 1, wherein the actuator includes a coil attached to the optical unit, and a magnetic flux applying unit that applies a magnetic flux to the coil. apparatus.