JPH09138967A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read out information from optical disks having different thicknesses by using one piece of an objective lens. SOLUTION: This optical pickup has first and second hologram laser units 1, 4 emitting laser beams whose wavelengths are different with each other. Then, in the case a substrate 5 is a thick optical disk, the first hologram laser unit 1 is selected and in the case the substrate 5 is thin optical disk, the second hologram laser unit 4 is selected. The laser beams emitted from the first and second hologram laser units 1, 4 are condensed on recording surfaces of optical disks by respectively being passed through a polarizing beam splitter 2 and an objective lens 3.

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 for reproducing information by irradiating an optical disc with laser light.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional optical pickup device includes a hologram laser unit 51 for emitting a laser beam and an objective lens for condensing the laser beam on a surface of a recording layer formed on a substrate 55 of an optical disc. And 53. The hologram laser unit 51 includes a laser light source 51a that emits laser light, a hologram element 51b that diffracts reflected light from an optical disc, and a photodetector 51c that detects the reflected light.

According to the above construction, the light beam emitted from the laser light source 51a passes through the hologram element 51b and is focused on the recording track of the optical disc through the objective lens 53. The condensed light flux is reflected by the optical disc, passes through the objective lens 53 again, and the hologram element 51
The light is diffracted by b and received by the photodetector 51c. In this way, according to the output signal from the photodetector 51c,
Reads information from the optical disk.

However, since the objective lens 53 of the above conventional optical pickup device is designed to read information on an optical disc having a thick substrate 55, it is possible to reproduce optical discs having different substrate thicknesses. There was a problem that I could not.

That is, as shown in FIG. 4A, in the case of an optical disc having a thick substrate 55, the light beam is condensed at a point O on the surface of the recording layer without aberration. On the other hand, as shown in FIG. 4B, when the substrate 56 is a thin optical disc, the point where light is condensed from the peripheral edge of the objective lens 53 and the point where light is condensed from near the optical axis are displaced. This is a spherical aberration, and when this aberration occurs, it becomes impossible to focus the laser light to the diffraction limit. In this way, the objective lens 53 whose aberration is corrected for the optical disc having the thick substrate 55 cannot focus light on the optical disc having the thin substrate 56 without aberration.

In order to solve such a problem, two optical pickup devices having an optical system design corresponding to the thickness of the substrate, that is, an optical disc device having two objective lenses are disclosed in Japanese Patent Laid-Open No. 4-281232. Gazette and Japanese Patent Laid-Open No. 4-2
It is disclosed in Japanese Patent Publication No. 89530.

Further, in Japanese Unexamined Patent Publication No. 6-259804, laser beams from a semiconductor laser for CD and a semiconductor laser for thin optical disc are combined on a substantially same path by using a half mirror to be condensed on an optical disc. The reflected light is split into two beams again by passing through the wavelength selection mirror,
An optical pickup device is disclosed in which each photodetector receives light.

[0008]

However, when the two optical pickup devices are equipped as described above,
There is a problem that the size of the optical disk device increases and the cost increases.

Further, in the optical pickup device disclosed in Japanese Patent Laid-Open No. 6-259804, the laser power is lost because the half mirror is used. Further, since it is necessary to provide a wavelength selection mirror in front of the photodetector for CD and the photodetector for thin optical disc, there is a problem that the number of parts increases and the optical system becomes complicated.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to read information from optical disks having different substrate thicknesses by using one objective lens. An object is to provide an optical pickup device.

[0011]

In order to achieve the above object, an optical pickup device according to claim 1 of the present invention comprises:
In an optical pickup device having a condensing unit (for example, an objective lens) for condensing a laser beam on the recording layer surface of an optical disc, a plurality of hologram laser units each emitting a laser beam of a different wavelength, and a substrate thickness of the optical disc. An optical system (for example, a polarization beam splitter) that irradiates the condensing means with the laser light from the hologram laser unit when one hologram laser unit is selected according to And a photodetector for detecting reflected light from the optical disc.

According to the above structure, first, the hologram laser unit is selected according to the thickness of the substrate of the optical disk. The laser light emitted from the laser light source in the selected hologram laser unit is incident on the condensing means by the optical system. Then, the laser light is condensed and reflected on the surface of the recording layer of the optical disc by the condensing means. The reflected light is received by the photodetector in the hologram laser unit, and the information on the optical disc is read.

At this time, since the hologram laser unit is selected according to the thickness of the substrate of the optical disc, one optical pickup device can read information from optical discs having different substrate thicknesses. That is, it is possible to focus the laser light on the surface of the recording layer for each optical disk without aberration.

According to the optical pickup device of a second aspect, in addition to the configuration of the first aspect, the optical system is a polarization beam splitter, and the polarization beam splitter is one laser from two hologram laser units. It is characterized in that light is transmitted and the other is reflected to irradiate the condensing means.

According to the above construction, in the case of an optical disc having a thick substrate, the polarization beam splitter transmits (or reflects) the laser light from the selected hologram laser unit and irradiates it onto the condensing means. On the other hand, in the case of an optical disc having a thin substrate, the polarization beam splitter reflects (or transmits) the laser light from the selected hologram laser unit and irradiates the converging means.

At this time, since one polarization beam splitter is used for the two hologram laser units, the device can be downsized. Further, since the polarization beam splitter is used as the optical system, the laser power can be effectively used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the optical pickup device includes a first hologram laser unit 1, a second hologram laser unit 4, a polarization beam splitter (optical system).
2 and an objective lens (condensing means) 3.

The first hologram laser unit 1 is so constructed as to emit a laser beam corresponding to the case where the substrate 5 of the optical disc is thick, a laser light source 1a for emitting the laser beam, a hologram element 1b for diffracting the reflected light from the optical disc,
And a photodetector 1c for detecting its reflected light.

The second hologram laser unit 4 emits a laser beam corresponding to the case where the substrate 5 of the optical disc is thin. Like the first hologram laser unit 1, the second hologram laser unit 4 emits a laser beam from a laser light source 4a and an optical disc. It has a hologram element 4b for diffracting the reflected light and a photodetector 4c for detecting the reflected light. The wavelengths of the laser light source 4a and the laser light source 1a are different.

The polarization beam splitter 2 transmits the laser light from the first hologram laser unit 1 and irradiates it to the objective lens 3, while reflecting the laser light from the second hologram laser unit 4 to the objective lens 3. Irradiate.

The objective lens 3 focuses the laser light transmitted or reflected by the polarization beam splitter 2 on the surface of the recording layer formed on the substrate 5 of the optical disk. The objective lens 3 is designed so that the laser light from the first hologram laser unit 1 and the laser light from the second hologram laser unit 4 are focused on an arbitrary point without any aberration.
That is, the refractive index of the objective lens 3 is formed to change depending on the wavelength difference between the laser light source 1a and the laser light source 4a.

According to the above configuration, when reading information from an optical disc having a thick substrate 5, the laser light source 1a of the first hologram laser unit 1 is selected. Then, the light flux A emitted from the laser light source 1a is the hologram element 1
b through the polarization beam splitter 2 and the objective lens 3
The light is focused on the recording track of the recording layer via. The condensed light flux A is reflected by the optical disk, again transmitted through the objective lens 3 and the polarization beam splitter 2, diffracted by the hologram element 1b, and received by the photodetector 1c. Thus, by the output signal from the photodetector 1c,
The information on the optical disc is read.

On the other hand, when reading information from an optical disc having a thin substrate 5, the laser light source 4a of the second hologram laser unit 4 is selected. Then, the light beam B emitted from the laser light source 4 a passes through the hologram element 4 b, is reflected by the polarization beam splitter 2, and is condensed on the recording track of the optical disc through the objective lens 3. The condensed light beam B is reflected by the optical disk and is irradiated onto the hologram element 4b following the path opposite to the above.
After that, the reflected light is diffracted by the hologram element 4b and received by the photodetector 4c. Thus, the photodetector 4c
The information on the optical disc is read by the output signal from the optical disc.

Here, when the substrate 5 of the optical disk is thick, as shown in FIG. 2 (a), the light flux A transmitted through the objective lens 3 is condensed at a point O on the surface of the recording layer on the substrate 5a without aberration. Therefore, the information can be read accurately.

When the substrate 5 of the optical disc is thick, the light beam B transmitted through the objective lens 3 is condensed at a point O'on the surface of the recording layer on the substrate 5b without aberration as shown in FIG. 2 (b). Therefore, the information can be read accurately.

As described above, in the optical pickup device according to the present embodiment, the first and second hologram laser units 1 and 4 are selected according to the thickness of the substrate 5 of the optical disc, so that one optical pickup is used. The device can support optical disks having different substrate thicknesses. That is, by correcting the spherical aberration of the objective lens 3, it is possible to focus the laser light on the surface of the recording layer of each optical disk without aberration.

Further, since it is possible to have a simple structure in which one polarization beam splitter 2 is provided for two hologram laser units, the optical pickup device can be miniaturized. Further, since the polarization beam splitter 2 is used as an optical system for irradiating the objective lens 3 with the light flux,
It is possible to effectively use the laser power.

In this embodiment, the first hologram laser unit 1 corresponds to the case where the substrate 5 of the optical disc is thick, and the second hologram laser unit 4 corresponds to the case where the substrate 5 is thin. It goes without saying that it is good.

In this embodiment, the hologram laser unit is two, but the number is not limited to this.
However, when there are three or more hologram laser units, an optical system corresponding to them is required.

[0031]

As described above, in the optical pickup device according to the first aspect of the present invention, a plurality of hologram laser units each emitting a laser beam of a different wavelength and one hologram laser unit depending on the thickness of the substrate of the optical disk are provided. An optical system for irradiating the condensing means with laser light from the hologram laser unit when a hologram laser unit is selected is provided, and each hologram laser unit is provided with a laser light source for emitting laser light and reflected light from an optical disk. This is a configuration in which a photodetector for detection is incorporated.

Since the hologram laser unit is selected according to the thickness of the substrate of the optical disk,
One optical pickup device can be used to read information from optical disks having different substrate thicknesses. That is, it is possible to focus the laser light on the surface of the recording layer for each optical disk without aberration.

In addition to the structure of claim 1, the optical pickup device according to claim 2 is a polarization beam splitter having one optical system, and the polarization beam splitter is one laser from two hologram laser units. The light is transmitted and the other is reflected to irradiate the condensing means.

As a result, since one polarization beam splitter is used for the two hologram laser units, the size of the device can be reduced. Further, since the polarization beam splitter is used as the optical system, the laser power can be effectively utilized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of an optical pickup device according to the present invention.

FIG. 2A shows a state in which laser light is focused on an optical disc having a thick substrate by the optical pickup device,
(B) is an explanatory view showing a state where laser light is focused on an optical disc having a thin substrate.

FIG. 3 is a schematic configuration diagram showing a configuration of a conventional optical pickup device.

FIG. 4A shows a state in which laser light is focused on an optical disc having a thick substrate by the optical pickup device,
(B) is an explanatory view showing a state where laser light is focused on an optical disc having a thin substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st hologram laser unit 1a * 4a Laser light source 1c * 4c Photodetector 2 Polarization beam splitter (optical system) 3 Objective lens (condensing means) 4 2nd hologram laser unit 5 Substrate

Claims (2)

[Claims] 1. An optical pickup device having a condensing means for condensing a laser beam on a recording layer surface of an optical disc, wherein a plurality of hologram laser units each emitting a laser beam of a different wavelength, and a thickness of a substrate of the optical disc. An optical system for irradiating the condensing means with the laser light from the hologram laser unit when one hologram laser unit is selected accordingly. Each hologram laser unit is provided with a laser light source for emitting laser light and an optical disc. An optical pickup device having a built-in photodetector for detecting the reflected light of. 2. The optical system is one polarization beam splitter, and the polarization beam splitter transmits one laser beam from two hologram laser units and reflects the other laser beam to irradiate a condensing means. An optical pickup device according to claim 1, wherein: