JPH05234114A - Optical pickup - Google Patents

Abstract

PURPOSE:To detect the inclination of an optical disk to the light axis of an optical pickup with high accuracy by eliminating the lens action of the central area of an objective and detecting a reflected beam from the optical disk of parallel rays passing through the area. CONSTITUTION:A through hole is provided on the central area of the objective 8 and the beam passing through the through hole is not subjected to the lens action and is left to be parallel rays as it is. Reflected parallel rays of the parallel rays from the optical disk 9 is reflected by a half mirror 7 and incident on a photodetector 11 and the inclination of the disk 9 to the light axis of the lens 8 is detected with high accuracy without using an optical disk inclination detecting device constituted of an exclusive LED and the photodetector.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used for reproducing an optical disc.

[0002]

2. Description of the Related Art In an optical disc recording / reproducing apparatus, a laser beam (hereinafter referred to as a light beam) of an optical pickup is focused by an objective lens to form a minute spot to trace a pit on the optical disc and detect its reflected light. By doing so, the desired signal is obtained. The light beam emitted from the objective lens passes through a transparent plate portion of about 1.2 mm which constitutes an optical disk and reaches a signal recording surface. In the objective lens, the transparent plate is also designed as a part of the lens. is there. Therefore, at the time of reproducing the optical disk, if the optical disk is tilted with respect to the optical axis of the objective lens, an aberration occurs, and an offset occurs in the reproduction signal, and in an extreme case, the S / N of the signal deteriorates and recording / reproduction becomes impossible. There is no state.

In order to eliminate this, it is necessary to provide a device for detecting the inclination of the optical disc with respect to the optical axis of the optical pickup, control the attitude of the optical pickup by this detection signal, and always keep the inclination between the optical axis of the optical pickup and the optical disc constant. There is. FIG. 7 shows an example of a conventional optical disc tilt detection device, in which a photodetector 11 receives reflected light from the optical disc 9 of a light beam emitted from an LED 12, and the photodetector 1 receives the reflected light.
The tilt of the optical disc is detected based on the output difference between the light receivers A and B constituting the optical disc 1.

[0004]

Conventionally, it is necessary to provide the optical disc tilt detecting device separately from the optical pickup, and there is a problem of alignment of the optical axes of the both, and since the optical axes of the both are separated from each other, the correct optical pickup is provided. There is a problem that the tilt of the optical disk with respect to the optical axis cannot be detected.

[0005]

In an optical pickup for focusing a light beam on an optical disk and reading bit information on the optical disk, the light beam is focused through a predetermined area in the center of an objective lens for focusing the light beam. The parallel light is not reflected, and the tilt of the optical disk is detected by the reflected light of the parallel light from the optical disk.

[0006]

Among the light beams directed to the optical disc of the optical pickup, the light beam passing through the predetermined area in the central part of the objective lens is
Since it is not focused by the objective lens and therefore has no ability to read pit information of the optical disc, the reflected light beam of the above light beam changes only by the tilt of the optical disc. The direction and amount of the tilt of the optical disk can be detected by differentially extracting the detection signal by the photodetector configured by the four-division photodetector.

[0007]

1 is an embodiment of an optical pickup according to the present invention, which is a lens holder including a pickup 1, a collimating lens 2, a beam splitter 3 and a mirror 4, and a half mirror 7 and an objective lens 8. 10
And an actuator 6 having a movable part to which the photodetector 11 is attached. The light beam emitted from the laser 1 is collimated by the collimator lens 2, passes through the beam splitter 3, and then is raised by the mirror 4 to the actuator 6. The light beam entering the actuator 6 passes through the half mirror 7 and reaches the objective lens 8.

Of the light beam passing through the objective lens 8,
The light beam that passes through a region having no lens effect in the predetermined region in the center of the objective lens 8 reaches the optical disc 9 without being focused, becomes reflected light, passes through the objective lens 8 again, and is reflected by the half mirror 7. It is guided to the detector 11. The light beam obtained by the photodetector 11 passes through a portion of the objective lens 8 which does not have a lens effect, and does not include pit information of the optical disc 9 but has inclination information of the optical disc 9 with respect to the optical axis of the optical pickup. It becomes an ingredient.

2 and 3 each show an example of the objective lens 8 used in the present invention. FIG. 2 is a sectional view of the objective lens 8 in which a predetermined region in the central portion is formed by a through hole 81, and FIG. A concave lens is attached to a predetermined area of the central portion of the lens 8 to cancel the lens action in the above area. In addition, the area of the objective lens 8 may be formed in a flat plate shape to eliminate the lens effect. Although FIG. 4 shows the half mirror 7, a mirror coating 71 is applied to a predetermined area in the central portion, but the entire surface may be mirror coated.

FIG. 5 shows a photodetector 11 which is divided into four photodetectors A, B, C and D. For example, (A + B)-(C + D) and (A + D)-(B + C) from the output signals of the photodetectors. It is possible to detect the tilt of the optical disc in two directions by obtaining the output signal. Although the reading of the pit information recorded on the optical disc 9 is well known and is not shown, it is focused by the objective lens, reflected by the optical disc 9, again collimated through the objective lens, and not reflected by the half mirror 7. The component returned to is separated by the beam splitter 3 to obtain the servo signal and the HF signal.

Regarding the tracking error in the servo signal, the detector 11 surrounded by the four-divided light receivers E and F shown in FIG. 6 is provided around the four-divided light receiver shown in FIG.
Can be detected by the output signal (EF).
In the above-described embodiment, the photodetector 11 is a 4-divided photodetector to obtain the tilt detection signals of the optical disc in two directions.
It is also possible to obtain a tilt detection signal of the optical disc in one direction by a two-divided light receiver.

[0012]

As described above, according to the present invention, the predetermined region in the central portion of the objective lens forming the optical pickup does not have a lens action, and the reflected light from the optical disk of the light beam passing through the region is detected. The tilt of the optical disc with respect to the optical axis of the optical pickup is detected by a device, so that it is not necessary to separately provide an optical disc tilt detection device, and the tilt of the optical disc can be detected at the position of the objective lens.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an optical pickup of the present invention.

2 and 3 are diagrams showing a configuration of an embodiment of an objective lens of the present invention.

FIG. 4 is a diagram showing a configuration of an embodiment of a half mirror of the present invention.

5 and 6 are diagrams showing the configuration of a photodetection embodiment of the present invention.

FIG. 7 is a diagram showing an example of a conventional optical disc tilt detection device.

[Explanation of symbols]

 1 Laser 2 Collimator Lens 3 Beam Splitter 4 Mirror 5 Pickup Base 6 Actuator 7 Half Mirror 8 Objective Lens 9 Optical Disk 10 Lens Holder 11 Photodetector 12 LED 71 Mirror Coating 81 Through Hole 82 Concave Lens

Claims (1)

[Claims] 1. An optical pickup for focusing laser light to read bit information on an optical disc, wherein the laser light passing through a predetermined central area of an objective lens for focusing the laser light is not focused and becomes parallel light. An optical pickup characterized by detecting the tilt of the optical disc by the reflected light of the parallel light from the optical disc.