JP2000215505A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reproducing different optical disk recording media with one object lens by making drivable a liquid crystal panel and an optical lens as a single unit. SOLUTION: A laser beam 11 emitted form a semiconductor laser 1 is converted to a parallel beam by a collimator lens 2, passed through a Fresnel zone plate using a transmission type liquid crystal panel 3 and an object lens 4, and focused on a disk substrate 5. The liquid crystal panel 3 generates electrically a ring band pattern having a transparent part and an opaque part in a concentric circle state, and forms an optical system in which a focal point can be varied by varying its spatial frequency. Spherical aberration compensating information caused by the difference in the thickness of a DVD and thickness of a CD is added to the ring band pattern, and playing of a DVD and a CD is performed with one object lens 4. An appropriate beam spot can be formed without deviating an optical axis at tracking servo, by integrating the liquid crystal panel 3 and the object lens 4 with a holder 6 and moving them in the direction shown by the arrow A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device for an optical pickup in an optical disk device.

[0002]

2. Description of the Related Art In recent years, digital video disks (DVDs) have become widespread as high-density, large-capacity recording media. In a DVD player, compatibility with a compact disk (CD) or a CD recordable (CD-R), which is the same optical disk, is an important technical issue.

For example, the DVD disk thickness is 0.6 mm, which is half that of a CD, and the same condensing optical system causes aberrations such as spherical aberration due to differences in the disk thickness, making recording and reproduction impossible. For this reason, a normal player uses a DVD
It is common practice to prepare an optical pickup having separate light collecting optical systems for the optical pickup and the CD.

However, if two optical pickups for DVD and CD are separately prepared, the size of the player is increased and the price is increased. Therefore, a mechanism that can reproduce both DVD and CD with one optical pickup as shown in FIG. 2 has been considered. As shown in FIG. 2, by switching the two objective lenses of the DVD objective lens 21 and the CD objective lens 22 so as to change the focal length according to the disk thickness, both the DVD and the CD can be connected to one optical pickup. To make it reproducible.

[0005] As shown in FIG. 2, objective lenses 21 and 22 and a tracking coil 23 are attached to a lens holder 25. The tracking coil 23 is energized, and the magnetic force generated by the tracking magnet 24 causes
Tracking servo is performed by quickly moving the objective lenses 21 and 22 in the horizontal direction. Normally, when the tracking servo operates, the objective lens is stabilized at the optimum position, but can be switched to another objective lens by applying a large pulse to the tracking coil 23.

Another example is disclosed in JP-A-63-249.
125, there is an optical system using an optical system in which a liquid crystal panel that generates an image pattern electrically and an optical lens are combined.

This technique uses an optical system in which a transparent liquid crystal panel that electrically generates an image pattern and an optical lens are combined, a pattern of a Fresnel zone plate is generated in the transmission liquid crystal panel, and a focus position shift detection signal is generated. In this case, the spatial frequency of the Fresnel zone plate is electrically controlled, and the focus servo is performed by changing the combined focal length of the optical system combining the transmission type liquid crystal panel and the optical lens.

[0008]

However, the method of switching between the two objective lenses cannot reduce the size of the optical pickup to a sufficient size and increases the cost. In the method of combining a transmission type liquid crystal and an optical lens, it is possible to electrically control the Fresnel zone plate to make the focus variable, but to control the position in the track direction at high speed, the response of the liquid crystal is high. Is not enough. For this reason, it is difficult to control the focus to the optimum position in the track direction.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical device capable of reproducing different optical disk recording media with one objective lens by integrally driving a liquid crystal panel and an objective lens.

[0010]

According to the present invention, a liquid crystal panel for electrically generating an image pattern and an optical lens are integrated with each other, and a tracking servo mechanism such as a tracking coil or a tracking magnet is combined with the optical lens. A DVD and a CD can be reproduced by an objective lens.

[0011]

FIG. 1 shows an embodiment of the present invention. Laser light 11 emitted from the semiconductor laser 1 is converted into parallel light by a collimator lens 2, passes through a Fresnel zone plate using a transmission type liquid crystal panel 3 and an objective lens 4, and is focused on a disk substrate 5.

The transmissive liquid crystal 3 is a Fresnel zone plate in which an annular pattern having a transparent portion and an opaque portion in a concentric circle is electrically generated, and an optical system capable of changing the focus by changing the spatial frequency of the annular pattern. Form.

At this time, the thickness of the DVD and the CD
By incorporating spherical aberration correction information generated due to the difference from the thickness of
And CD playback becomes possible.

In the tracking servo, the objective lens 4 is quickly moved on a plane parallel to the disk surface by the tracking coil 7 and a tracking magnet (not shown) to form a stable beam spot at an optimum position.

Usually, in an optical disk device, the tracking servo is performed by swinging the objective lens 4 right and left by about 0.3 mm. At this time, if the transmissive liquid crystal 3 is fixed to the optical pickup main body, an appropriate beam spot cannot be formed on the disk surface 5 because the optical axes of the objective lens 4 and the transmissive liquid crystal 3 are shifted.

In order to solve this problem, as shown in FIG. 1, the transmission type liquid crystal 3 and the objective lens 4 are integrated by a holder 6, and this is moved by a tracking coil 7 in a direction indicated by an arrow A. This makes it possible to form an appropriate beam spot on the disk surface without shifting the optical axis even during tracking servo.

Here, the transmission type liquid crystal 3 has a thickness of 0.5 mm.
Were produced by laminating two glass plates. Objective lens 4
In the case where the objective lens 4 is integrated, the inertial mass is increased as compared with the case where only the objective lens 4 is driven.
A method such as plasticizing a glass plate is advantageous for a tracking servo system.

In this embodiment, the transmission type liquid crystal is shown as a variable focus type optical system using a Fresnel zone plate.
The present invention is also effective in an optical system compatible with optical discs having different recording densities by switching the numerical aperture by using a liquid crystal as disclosed in International Publication No. WO98 / 15952.

[0019]

According to the present invention having such features, by driving the liquid crystal panel and the objective lens integrally, it is possible to form an optical pickup capable of reproducing different optical disk recording media with one objective lens. For this reason, there is an effect that the size and the price of the optical pickup can be reduced.

In addition, by driving the liquid crystal panel and the objective lens integrally, it is possible to manufacture a high-precision optical pickup having no optical axis shift.

[Brief description of the drawings]

FIG. 1 is a side view of an optical device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an optical pickup according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Liquid crystal panel 4 Objective lens 5 Disk substrate 6 Holder 7 Tracking coil

Claims (2)

[Claims] 1. An optical apparatus comprising: a liquid crystal panel that electrically generates an image pattern; and an optical system in which an optical lens is combined with the liquid crystal panel and the optical lens. 2. A liquid crystal display comprising: a semiconductor laser; a collimator lens; a liquid crystal panel for electrically generating an image pattern; and an objective lens, wherein the liquid crystal panel and the objective lens can be driven integrally. Optical pickup device.