JPH06119653A - Optical head device - Google Patents

Abstract

PURPOSE:To provide a method to form a minute spot on a medium and an optical head device in which the adjustment of an optical system having a servo stability is easy, in a recording and reproducing device of an optical recording medium. CONSTITUTION:In an optical system in which a disk 6 is irradiated with a small minute spot that is smaller than the value to be decided by the wavelength lambdaof a light source using a light shielding plate 2 and by the numerical aperture NA of an objective lens 5, the spot light receiving parts 13, 14 of a photodetector 7 are made conical. Consequently, in a tracking error detection system, a three beam optical system which is stable for tracking offset is adopted, side lobes are all eliminated, and in the optical head device in which signal deterioration due to cross talk noise is not generated, because pinholes 31 are not required, the optical adjustment is easily performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device of a recording / reproducing apparatus for an optical recording medium for recording / reproducing information such as an optical disc on which information is optically recorded, and more particularly to a side rope removing technique for the optical head device. Regarding

[0002]

2. Description of the Related Art A conventional optical head device will be described with reference to the drawings.

FIG. 4 is a block diagram of an optical system of a conventional optical head device and an optical recording medium, and FIG. 5 is a configuration diagram of the conventional optical head device.

In FIG. 4, the conventional optical head device is
The semiconductor laser 1, a collimator lens 21, a beam splitter 20, an objective lens 5, a condenser lens 22, and a photodetector 23 are used to form a minute spot on a disk 6 by a light beam. The disk 6 is an optical recording medium. 17
And a light transmissive substrate 18 and a disk surface 19.

Here, the light emitted from the semiconductor laser 1 is focused on the signal surface of the optical recording medium 17 laminated on the light transmissive substrate 18 via the collimator lens 21 and the beam splitter 20 from the disk surface 19 on the substrate side. While being condensed by the lens 5, the reflected light from the signal surface is incident on the light receiving surface of the photodetector 23 through the objective lens 5, the beam splitter 20, and the condensing lens 22, and is converted into an electric signal.

It is desired to increase the recording capacity by the optical information reproducing apparatus as described above, and in such an apparatus, it is indispensable to reduce the light spot irradiated on the medium for high density. ing.

The size of the minute spot on the medium depends on the wavelength λ of the laser and the numerical aperture NA of the condenser lens.
Therefore, to reduce the size of the irradiation spot,
Designs are made to reduce λ and increase NA.

In addition to λ and NA, there is a method of shielding the central portion of the beam from a light source to generate a minute spot exceeding the above diffraction limit. FIG. 5 shows a configuration diagram of the optical head device in this case.

In FIG. 5, the light emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 21. The parallel beam passes through the light blocking plate 2 and blocks the central portion of the parallel beam. Next, the beam other than the central portion passes through the beam splitter 25, enters the objective lens 5, and irradiates the disc 6 with a minute spot. Since the minute spot is condensed by the light whose central portion of the parallel beam is shielded by the shading plate 2, a spot smaller than the diffraction limit is created.

The light reflected by the disk 6 enters the objective lens 5 again, is converted into parallel light, and is reflected by the beam splitter 2.
The light is split into two optical path systems at 7, one of which is incident on the photodetector 30 and the other of which is incident on the photodetector 29 through the cylindrical lens 28. Astigmatism is created from the cylindrical lens 28, and the focusing error is detected by the photodetector 29.

The optical path system of the photodetector 29 performs tracking detection by the push-pull method.

In detecting the reproduction signal, crosstalk from adjacent pits on the disk 6 is mixed with the signal light due to the generation of side ropes (or diffraction rings) in addition to the spots formed by the light shielding plate 2 and the objective lens 5 described above. A phenomenon occurs and the reproduced signal is deteriorated as noise.

Therefore, a slit (or pinhole) 31 is installed in front of the photodetector 30, and an optical system is formed so as to remove the side rope.

[0014]

In the above-mentioned conventional optical head device, when the combination of only λ and NA is used, the size of the minute spot irradiated on the medium depends on the wavelength λ of the light source and the numerical aperture of the condenser lens. It has the drawback that it cannot be smaller than the value determined by.

Further, in the method using the light shielding plate, particularly in the tracking error detection system, when the three-beam optical system having stability against the tracking offset is adopted, the generated side ropes generate all three beams. , It is difficult to remove the side rope on the photo detector.

Further, when the side rope is removed by the pinhole, it is very difficult to adjust the photodetector of the pinhole.

An object of the present invention is to remove a light-shielding plate that shields the central portion of the semiconductor laser from light, a diffraction grating for creating three beams for detecting a tracking error, and side ropes generated in all three beams. By providing a cone-shaped inclination on the photodetector cover part, the above-mentioned drawbacks are eliminated, and a method for generating a minute spot on the medium and an optical head device for easily adjusting an optical system with servo stability are provided. To provide.

[0018]

The optical head device according to the first aspect of the present invention is a phase shifter for shifting the phase of the central portion of the light beam or the light shielding plate for shielding the central portion of the light beam emitted from the semiconductor laser. A minute spot forming optical system composed of a plate and a three-beam optical system using a diffraction grating are combined.

The optical head device according to the second aspect of the present invention includes a light shield plate for shielding the central portion of the light beam emitted from the semiconductor laser, a phase shift plate for shifting the phase of the central portion of the light beam, and the light shield plate or Diffraction grating is generated in the light beam emitted from the phase shift plate and at the same time creates three beams for tracking error detection, and all three beams created by the diffraction grating are generated by the light shield plate or the phase shift plate It has a photodetector cover part for removing the side rope of the signal detection optical system, and creates a minute spot on the optical recording medium optically by the light passing through the light shielding plate or the phase shift plate and the diffraction grating. In the optical head device for recording / reproducing information, the surface of the photodetector cover is inclined to remove the side rope.

[0020]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram of an optical system of an optical head device according to an embodiment of the present invention and an optical recording medium, and FIG. 2 shows a relationship between a light receiving element and a spot on a photodetector of the optical head device according to the present embodiment. FIG. 2A is a diagram showing the relationship between the light receiving element and the spot on the photodetector when the objective lens and the disk of the optical head device of this embodiment are at predetermined positions, and FIG. 2B is the present embodiment. FIG. 2C is a diagram showing the relationship between the light receiving element on the photodetector and the spot when the disk is close to the objective lens of the optical head device of the example, and FIG. 2C shows that the disk is away from the objective lens of the optical head device of the present embodiment. It is a figure which shows the relationship between the light receiving element and the spot on a photodetector in the case.

In FIG. 1, the optical head device of the present embodiment is roughly composed of a semiconductor laser 1, a light shielding plate 2, a diffraction grating 3, a half mirror 4, an objective lens 5 and a photodetector 7, and an optical recording medium of a disk 6. A small spot is created by the light beam on the top.

The light emitted from the semiconductor laser 1 passes through the light blocking plate 2 to block the central portion of the light beam and enters the diffraction grating 3. Then, the light is reflected by the half mirror 4 and the objective lens 5
To form a minute spot on the disk 6. Since the minute spot shields the central part of the incident light beam, a diffraction phenomenon occurs and the spot becomes smaller than the spot diameter determined by the wavelength λ of the light source and the numerical aperture NA of the objective lens 5.

The signal recorded on the disk 6 is reflected, enters the objective lens 5 again, passes through the half mirror 4, and enters the photodetector 7. In the photo detector 7, the focus error signal, the track error signal,
Detect the playback signal.

FIG. 2 shows the relationship between the light receiving element on the photodetector and the spot. FIG. 2A shows the case where the disk 6 and the objective lens 5 are arranged at predetermined positions, and the spot on the photodetector at this time is irradiated with a predetermined spot diameter. The main beam 9 is incident on the light receiving element 8, and the light receiving element 8 is divided into four parts. Further, side lobes 10 are generated around the main beam 9. This is due to the diffraction spot by the light shield plate 2, and is also generated for the sub beam 11 generated by the diffraction grating.

The sub beam 11 is incident on the light receiving element 12,
It is configured with a side rope 10.

2B and 2C show a case where the disk 6 approaches the objective lens 5 and a case where the disk 6 moves away from it. In this case, since astigmatism occurs when passing through the half mirror 4, the beams 9 and 11 have elliptic diameters. In the case of the main beam 9, the focus error signal is detected by combining the respective elements of the four-divided light receiving element 8, and the tracking error signal is detected from each light receiving element 12 of the sub beam 11.

FIG. 3 is a perspective view of the photodetector of the optical head device of this embodiment.

In FIG. 3, the photodetector 15 has a light receiving element packaged in a transparent resin, the main beam light receiving portion 13 and the sub beam light receiving portion 14 are formed in a conical shape, and the side rope 10 shown in FIG. A reflective film is applied to the periphery so that the light is reflected by the inclination of the periphery. Thereby, the side ropes 10 can be configured so as not to be incident on the light receiving element by being reflected by the inclination around each light receiving portion.
Conventionally, the pinhole which has been arranged in front of the photodetector is not required, the adjustment becomes easy, and it becomes possible to employ a stable three-beam optical system in the tracking detection method.

The same effect can be obtained by using a phase shift plate that shifts the phase of the central portion of the light beam, instead of the light shielding plate 2 described above.

[0031]

As described above, in the optical head device of the present invention, the size of the spot that can be irradiated on the medium can be made smaller than that of the conventional one, and the recording density can be increased.

In the tracking error detection system,
A stable beam optical system can be adopted, noise due to crosstalk can be removed, and reproduction characteristics can be improved.

Further, as one of the conventional methods for removing noise due to crosstalk, it is difficult to perform adjustment by disposing a pinhole in front of the photodetector, but the adjustment is easy because the pinhole is unnecessary. There is an effect that a high-density optical head device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical system including an optical head device and an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a light receiving element and a spot on a photodetector of the optical head device of this embodiment. Figure 2
FIG. 9A is a diagram showing a relationship between a light receiving element and a spot on the photodetector when the objective lens and the disk of the optical head device of the present embodiment are at predetermined positions. FIG. 2B is a diagram showing the relationship between the light receiving elements and the spots on the photodetector when the disk approaches the objective lens of the optical head device of this embodiment. FIG. 2C is a diagram showing the relationship between the light receiving elements and the spots on the photodetector when the disk moves away from the objective lens of the optical head device of this embodiment.

FIG. 3 is a perspective view of a photodetector of the optical head device according to the present embodiment.

FIG. 4 is a block diagram of an optical system of an optical head device and an optical recording medium of a conventional example.

FIG. 5 is a configuration diagram of a conventional optical head device.

[Explanation of reference numerals] 1 semiconductor laser 2 light-shielding plate 3 diffraction grating 4 half mirror 5 objective lens 6 disk 7 photodetector 8 4-split light receiving element 9 main beam 10 side rope 11 sub beam 12 sub light receiving element 13 main beam light receiving section 14 sub beam light receiving section 15 Photodetector 16 Connection Terminal 17 Optical Recording Medium 18 Optical Transmissive Substrate 19 Disk Surface 20 Beam Splitter 21 Collimator Lens 22 Condensing Lens 23 Photodetector 25 Beam Splitter 26 Convex Lens 27 Beam Splitter 28 Cylindrical Lens 29 Focusing Photodiode 30 For Track Photodiode 31 Pinhole (or slit)

Claims (2)

[Claims] 1. A minute spot forming optical system comprising a light shielding plate for shielding the central portion of a light beam emitted from a semiconductor laser or a phase shift plate for shifting the phase of the central portion of the light beam, and a diffraction grating. An optical head device characterized by being combined with a three-beam optical system using. 2. A light shielding plate for shielding the central portion of a light beam emitted from a semiconductor laser, or a phase shift plate for shifting the phase of the central portion of the light beam, and the light shielding plate or the phase shift plate for emitting light. A diffraction grating for generating a diffraction phenomenon in a light beam and simultaneously generating three beams for tracking error detection, and a signal detection generated by the light shielding plate or the phase shift plate for all three beams generated by the diffraction grating And a photodetector cover portion for removing side ropes of the optical system, and optically creates a minute spot on the optical recording medium by light passing through the light shielding plate or the phase shift plate and the diffraction grating. Recording of information
An optical head device for reproducing, wherein the surface of the photodetector cover is provided with an inclination in order to remove the side ropes.