JPH05307764A - Method for detecting inclination of optical disk - Google Patents

Abstract

PURPOSE:To detect the inclination of an optical disk with high accuracy by converging the mixed beams of the high order diffracted beams of the laser beams of two wavelengths on an optical disk, separating the reflected beam to the beam of the wavelength by a wavelength selection mirror and being made incident on a quadripartite and a sexpartite photodiodes. CONSTITUTION:The diverging beam of a wavelength lambda1 outgoing from a laser diode 1 generates the high order diffracted beams in a diffraction grating 5 through a collimate lens 3. The diverging beam of a wavelength lambda2 outgoing from the laser diode 2 generates the high order diffracted beams in the diffraction grating 6 through a collimator lens 4 and passes through the diaphragm 9 and transmits a mirror 7. The mixed beams of the wavelengths lambda1, lambda2, pass through a half mirror 10 and converge on the optical disk 12 through the objective lens 11. The reflected beams reverse and are reflected by the mirror 10 and the beam of the wavelength lambda1 is reflected by the wavelength selection mirror 8 through a condenser lens 13, a cylindrical lens 14 and made incident on the sexpartite photodiode 15-17 and a focus and a tracking error signals are generated. The beam of the wavelength lambda2 is made incident on the quadripartite photodiodes 18-20 and the inclination of the optical disk is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc tilt detection method in an optical pickup device for reproducing information from an optical disc.

[0002]

2. Description of the Related Art With the progress of high density recording of optical discs, there has been a need for an optical pickup capable of forming a smaller beam spot on the optical disc. At present, research and development of a short-wavelength light source necessary for such an optical pickup are being conducted, and use of an objective lens having a large numerical aperture is considered. However, there is a problem that the aberration of the objective lens due to the tilt of the optical disk increases due to the increase in the numerical aperture. In general, the tilt detection that is generally performed at present is to attach a tilt detecting device that is a combination of the light emitting diode 41 and the photodiodes 42 and 43 at a position close to the objective lens 45 as shown in FIG. Has been adopted.

[0003]

In an optical pickup using an objective lens having a large numerical aperture, it is necessary to control the inclination of the objective lens with respect to the optical disc in order to suppress the aberration of the objective lens. A high-precision optical disc tilt detection method is required to meet the demand, but in the method detection method combining a light emitting diode and a light receiving element as described in the conventional art, the light source itself is large and the reading beam Since the position of the spot and the position irradiated by the light emitting diode do not match, it is difficult to read the tilt accurately. Then, the objective of this invention is providing the method of detecting the inclination of an optical disk with high precision.

[0004]

A diffraction grating is provided in the optical path of a light beam emitted from a second laser light source to generate a high-order diffracted beam. (In this description, for the sake of convenience, it is assumed that three diffracted beams of 0th order and ± 1st order, which generally have high light intensity, are used.) The orientation of the diffraction grating is that the three beam spots formed by the objective lens are on the optical disc. , And the line components are arranged so as to include the direction component for detecting the inclination. And
The return light reflected by the optical disc is condensed on the photodiode by a condensing optical system that generates astigmatism. The photodiode is divided into 4 vertically and horizontally and 3
Each of the three beam spots is arranged so as to be at the center of each photodiode. Then, the 0th-order beam spot is caused to follow the recording surface on the optical disk based on the signal from the photodiode that detects the 0th-order diffracted beam. At this time, the tilt of the optical disc is detected by detecting the focus error signal obtained from the photodiodes for the ± 1st-order diffracted beams.

[0005]

[Function] Generates high-order diffracted light by a diffraction grating,
When the beam is focused to the diffraction limit by the objective lens, a plurality of beam spots are formed on the focal plane. Then, the plurality of beam spots are arranged in a direction perpendicular to the direction of the grooves of the diffraction grating. Here, when the 0th-order diffracted beam spot is made to follow the recording surface of the optical disc, all the higher-order beam spots are formed on the recording surface of the optical disc if the focal plane and the optical disc are parallel. However, when the focal plane is not parallel to the optical disc, it is out of the recording surface of the optical disc. That is,
The tilt of the optical disc can be detected by detecting the focus state of the high-order diffracted beam spot. Further, by narrowing the diameter of the beam for tilt detection, the numerical aperture of the objective lens can be effectively reduced and the beam spot diameter can be increased, and the influence of diffraction due to the recording pits can be almost eliminated.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disc tilt detecting method according to the present invention will be described with reference to FIG. In this embodiment, the tilt of the optical disc in the radial direction is detected. The divergent beam of wavelength λ 1 emitted from the laser diode 1 is collimated by the collimator lens 3 and then is generated by the diffraction grating 5 to generate higher-order diffracted light, which is then reflected by the wavelength selection mirror 7. Further, the divergent beam of wavelength λ2 emitted from the laser diode 2 is collimated by the collimator lens 4, collimated light is generated by the diffraction grating 6, and the diameter thereof is reduced by the diaphragm 9. Through 7. Then, it becomes a mixed beam of wavelength λ1 and wavelength λ2, passes through the half mirror 10, and is condensed by the objective lens 11 to form a beam spot on the recording surface of the optical disc.

FIG. 2 shows such a state. The small beam spots 21, 22, 23 are of wavelength λ1 and the large beam spots 24, 25, 26 are of wavelength λ2.
belongs to. Use an objective lens without chromatic aberration so that the beams of wavelength λ1 and wavelength λ2 have the same focal plane. The beam diffracted and reflected by the recording surface returns to the objective lens again, is reflected by the half mirror 10, and passes through a synthetic lens system of a condensing lens 13 and a cylindrical lens 14 which is a return optical system for generating astigmatism. After the light becomes convergent, it is separated by the wavelength selection mirror 8 due to the difference in wavelength. The beam of wavelength λ1 is reflected and guided to the six-division photodiodes 15, 16 and 17, and the focus error signal and tracking error signal of the beam for reproducing the recording pit are detected, and the beam spot follows the recording surface of the optical disk based on these signals. Control to do.

On the other hand, the beam of wavelength λ2 is transmitted through the wavelength selection mirror, and the three quadrant photodiodes 18, 19,
A beam spot is formed on 20. FIG. 3 is an enlarged view of the 4-division photodiode. The beam spot on the photodiode 18 is a 0th-order diffracted beam, which is focused on the recording surface during reproduction. Therefore,
The zero-cross point of the S-shaped curve of the focus error signal ((sum signal of 18a and 18c)-(sum signal of 18b and 18d)) obtained from the photodiode 18 and the focus error signal obtained from the photodiode 15 should match. When the position of the photodiode 18 is adjusted in the vertical direction of the photodiode, the 4-division photodiode 1
Signals from 9 and 20 ((19a and 19c and 20b and 20
The tilt of the optical disc can be detected based on (sum signal of d)-(sum signal of 19b, 19d, 20a, and 20c)).

Further, in the previous embodiment, another diffraction grating is placed so as to be orthogonal to the groove at the diffraction grating 6 so as to form a cross-shaped beam spot on the optical disk, and these beams are also formed. If five 4-division photodiodes are installed on the cross so as to detect the focus error signal of, the tilt in the tangential direction as well as in the radial direction can be detected.

[0010]

According to the present invention, it is possible to detect the tilt of the optical disk at the position where the reading beam spot is irradiated, and it is possible to detect even a slight tilt. Therefore, by controlling the tilt of the optical disc or the optical pickup based on the tilt information, a good reproduction signal can be obtained even when an objective lens having a large numerical aperture is used.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system of an optical pickup device showing an embodiment of the present invention.

FIG. 2 is an enlarged view showing a state of a beam spot on an optical disc.

FIG. 3 is an enlarged view showing a 4-split photodiode and a beam spot.

FIG. 4 is a perspective view showing a conventional inclination detection method.

[Explanation of symbols]

1,2 Laser diode 3,4 Collimator lens 5,6 Diffraction grating 7,8 Wavelength selection mirror 9 Aperture stop 10 Half mirror 11,45 Objective lens 12,44 Optical disk 13 Condensing lens 14 Cylindrical lens 15,18,19,20 4-division photodiode 16,17,42,43 Photo diode 21,22,23,24,25,26 Beam spot 41 Light emitting diode

Claims (4)

[Claims] 1. Information is recorded by converging a laser beam onto an optical disk on which information is recorded concentrically or spirally, and detecting a change in intensity of reflected return light affected by diffraction by a recording pit. In an optical pickup device for reading the same, a first laser light source for reading the recording pit and a second laser light source having a different wavelength from the first laser light source for detecting the inclination of the optical disc having the recording pit And a diffraction grating for generating high-order diffracted light of the second laser light source, and condensing the diffracted light to form three diffracted beam spots of 0th order and ± nth order on the optical disc. A detection means is provided for detecting the focus error signals of the three diffracted beam spots of the 0th order and the ± nth order in the optical path of the reflected return light Inclination detecting method of an optical disk according to this and features. 2. A converging optical system for generating astigmatism is provided in the optical path of the reflected return light, and each of the three beam spots of the 0th-order and ± nth-order diffracted beams is formed by three 4-division photodiodes. The optical disc tilt detection method according to claim 1, wherein the focus error signal is detected by receiving light and using an astigmatism method. 3. A diameter of the light beam is narrowed by providing a diaphragm in the optical path of the light beam emitted from the second laser light source for detecting the tilt of the optical disk, and the beam spot on the optical disk is used for reading recording pits. The tilt detecting method for an optical disk according to claim 1, wherein the tilt is larger than the beam spot. 4. A dead zone is provided at the center of a four-division photodiode for receiving ± n-order diffracted beams, and the diameter of the dead zone is made substantially equal to the minimum diameter of a beam spot for irradiation. Of optical disk tilt detection.