JPH11161998A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small optical pickup device capable of preventing the generation of unwanted stray light. SOLUTION: A second diffraction element 3 is divided into a first area 3a and a second area 3b by a dividing line DL passing through the optical axis, a part diffracted by the first area 3a among the main beams reflected by a disk is converged on the boundary between photodetectors 7b, 7c and a part diffracted by the second area 3a is converged on a photodetector 7d. By representing two sub-beams by a first and second sub-beams, a diffracted part of the first sub-beam in the first area 3a is converged on the photodetector 7a and the remainder is converged between photodetectors 7c and 7d. Similarly, a diffracted part of the second sub-beam in the second area is converged on the photodetector 7e and the remainder is converged between photodetectors 7c and 7d. A radial error signal based on a three beam method is generated by comparing the outputs of the photodetector 7a and the photodetector 7e with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to, for example, a disc,
The present invention relates to an optical information recording / reproducing apparatus for recording information on a recording medium such as a magneto-optical disk or reproducing the recorded information, and particularly to an optical pickup apparatus.

[0002]

2. Description of the Related Art Introducing a diffractive element into an optical system of an optical pickup device requires reducing the size and weight of the optical pickup device.
It is effective in reducing the cost and improving the reliability. Currently, an optical pickup device using a diffraction grating is becoming mainstream.

FIG. 4 shows an optical pickup device showing one example. The light emitted from the semiconductor laser 101 is the first
Is divided into a main beam and two sub-beams by the diffraction grating 102, and the light that has passed through the second diffraction grating 103 as the 0th-order diffracted light passes through the collimating lens 104 and the objective lens 105 to form a disk 106 as a recording medium. Focused on top. The light reflected by the disk 106 passes through the objective lens 105 and the collimator lens 104 again to enter the second diffraction grating 103.

[0004] The second diffraction grating 103 is divided into two regions, and the three light beams reflected by the disk 106 are each divided into two, and are detected by a predetermined light detection device 107 as a total of six light beams. You. This light detection device 1
07 has five photodetectors 107a to 107e, and if the outputs of the photodetectors 107a to 107e are S1 to S5, the focus error signal FES is FES = S2−S3, and the tracking error signal RES is RES = S1. -S5, The reproduction information signal RF is given by RF = S2 + S3 + S4.

[0005]

The essential problem of the above-described optical pickup device using a diffraction grating is that light emitted from a semiconductor laser 101 as a light source is generated when passing through a second diffraction grating 103. The first-order diffracted light enters the collimator lens 104, is reflected by the disk 106 and enters the photodetector 107, and generates a false signal.
Failures such as instability of the servo system may occur.

In order to solve this problem, the applicant of the present application has disclosed in Japanese Patent Application Laid-Open No. 2-273336 that the formation area of the second diffraction grating 103 can be suppressed by setting the area to a predetermined range.

However, in order to record information on a write-once disc, a magneto-optical disc, or the like, the main beam is 4 m above the disc.
Since it is necessary to have an output of about W, the numerical aperture NA of the collimating lens must be increased to about 0.18. When the NA of the collimating lens is increased, the area of the second diffraction grating 103 also increases in proportion to the numerical aperture. Therefore, in order to keep the formation range of the diffraction grating 103 within the above-described predetermined range, six light beams are required. The focal points need to be arranged in parallel. Then, the sub-beam detection photodetector 1
Since 07a and 107e need to be further divided into two, a total of seven photodetectors are arranged in parallel.
This is difficult considering assembly tolerances. Further, as the number of photodetectors increases, the number of output pins of a package containing the photodetectors and the like also increases, which causes a problem that the package becomes large.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art, and has as its object to provide a small-sized optical pickup device capable of preventing generation of unnecessary stray light.

[0009]

According to a first aspect of the present invention, there is provided an optical pickup device comprising: a light source; a first diffraction grating for dividing a light beam from the light source into a main beam and two sub-beams; An optical system for condensing a light beam of a beam on a recording medium, a second diffraction grating for diffracting reflected light from the recording medium, and a plurality of light detectors for detecting light diffracted by the second diffraction grating An optical pickup device comprising:
The second diffractive element is divided into a first area and a second area, and of the two sub-beams, the intensity of one of the sub-beams diffracted in the first area and the second Is configured to obtain a tracking signal by comparing the intensity of the other sub-beam diffracted in the region with, thereby achieving the above object.

The optical pickup device according to a second aspect of the present invention is characterized in that a boundary between the first area and the second area in the second diffraction element is a straight line passing through an optical axis.

The optical pickup device according to a third aspect of the present invention is characterized in that the plurality of photodetectors are arranged at substantially the same distance from the light source.

According to a fourth aspect of the present invention, in the optical pickup device, one of the two sub-beams has an optical axis passing through the first region as a first sub-beam, and the optical axis thereof corresponds to the first sub-beam. When the other sub-beam passing through the second region is defined as a second sub-beam, the intensity of the first sub-beam diffracted in the first region and the second sub-beam diffracted in the second region are determined. The tracking signal is obtained by comparing the intensity of the sub beam.

According to a fifth aspect of the present invention, there is provided an optical pickup device, comprising: a light splitting means for splitting a part of the reflected light from the recording medium; and a light beam split by the light splitting means into two polarization components. It is characterized by further comprising a polarized light separating means and a polarized light detecting photodetector for detecting the two separated polarized light components.

According to a sixth aspect of the present invention, in the optical pickup device, the light source, the plurality of light detectors, and the polarization detection light detector are housed in the same package.

The operation of the present invention will be described below.

According to the first aspect of the present invention, the second diffractive element is divided into first and second regions, and one of the two sub beams diffracted in the first region. Since the tracking signal is obtained by comparing the intensities of the sub-beam and the other sub-beam diffracted in the second region, the number of photodetectors can be reduced, and even if a collimating lens having a large numerical aperture is employed. It is easy to prevent the generation of unnecessary stray light due to its small size. Further, a stable tracking signal by the three-beam method can be obtained with a small number of photodetectors.

In the case of claim 2 of the present invention,
Since the boundary between the first and second regions in the second diffraction element is a straight line passing through the optical axis, unnecessary offset components are not superimposed on the tracking signal.

According to the third aspect of the present invention,
Since the photodetectors are located at approximately the same distance from the light source,
Generation of unnecessary stray light can be more easily suppressed, and the degree of freedom in design increases.

In the case of claim 4 of the present invention,
Of the two sub-beams, one sub-beam whose optical axis passes through the first region is referred to as a first sub-beam, and the optical axis thereof is the second sub-beam.
When the other sub-beam passing through the area is a second sub-beam, the intensity of the first sub-beam diffracted in the first area and the second sub-beam diffracted in the second area Since the tracking signal is obtained by comparing the intensities of the tracking signals, it is possible to alleviate a decrease in the tracking signal output.

In the case of claim 5 of the present invention,
Light splitting means for splitting a part of the reflected light from the recording medium, polarization splitting means for splitting the light beam split by the light splitting means into two polarized light components, and polarized light for detecting the two split polarized light components Since it has the photodetector for detection, information recorded on the magneto-optical recording medium can also be reproduced.

According to the sixth aspect of the present invention,
Since the light source, the plurality of light detectors, and the polarization detection light detector are housed in the same package, the mutual positional relationship between the elements is kept stable, and the environmental resistance is improved. .

[0022]

(First Embodiment) A first embodiment of the present invention.
An optical pickup device according to the embodiment will be described with reference to FIGS.

The light emitted from the semiconductor laser 1 is split by the first diffraction grating 2 into a main beam and two sub-beams, passes through the second diffraction grating 3 as zero-order diffracted light, and has a collimating lens 4 and an objective lens. The light is condensed on a disk 6 as a recording medium by 5. The light reflected by the disk 6 again passes through the objective lens 5 and the collimator lens 4 and enters the second diffraction grating 3.

The second diffraction element 3 has a dividing line D passing through the optical axis.
L is divided into a first area 3a and a second area 3b, and a portion of the main beam reflected by the disk 6 that is diffracted by the first area 3a is a photodetector 7b of the photodetector 7
The light is condensed on the boundary between the second region 3c and the light diffracted by the second region 3b is condensed on the photodetector 7d of the photodetector 7.
Therefore, the focus error signal FES and the reproduction information signal R
F is given by FES = S2-S3 and RF = S2 + S3 + S4, where the outputs of the photodetectors 7b to 7d are S2 to S4.

On the other hand, the two sub-beams are also reflected by the disk 6 and enter the second diffraction grating 3. Of the two sub-beams, one whose optical axis passes through the first region 3a is a first sub-beam, and one whose optical axis passes through the second region 3a is a second sub-beam. Of the first sub-beam, the portion diffracted in the first region 3a is condensed on the photodetector 7a, and the rest is condensed between the photodetectors 7c and 7d. Similarly, of the second sub-beam, a portion diffracted in the second region is focused on the photodetector 7e, and the rest is collected between the photodetectors 7c and 7d. The tracking signal RES is given by RES = S1-S5, where the outputs of the photodetectors 7a and 7e are S1 and S5.

In the optical pickup device according to this embodiment, since the number of light spots whose light intensity is to be detected is four, all the photodetectors 7a to 7e are connected to the semiconductor laser 1
It is possible to arrange at a position sufficiently distant from the camera. As a result, it is possible to realize a configuration in which the diffracted light generated by the second diffraction grating 3 does not enter the collimator lens 4.
Also, it is possible to avoid an increase in the size of the package due to an increase in the number of pins. In addition, all the photodetectors 7a to 7e can be provided so as to be located on a certain straight line as shown in FIG. 7e can be arranged.

Since only a part of the reflected light from the disk 6 is used for detection, the output of the sub-beam is about 1 /
2, but by using the portion diffracted in the region where the optical axis passes as described above for detection, the rate of reduction can be reduced somewhat. For example, the focal length and numerical aperture of the objective lens 5 are respectively 3 mm and 0.45, those of the collimating lens 4 are 9 mm and 0.18, the distance from the semiconductor laser 1 to the second diffraction grating 3 is 3 mm, and the disk 6 Assuming that the distance between the main beam and the sub beam is 20 μm, the distance between the optical axis of the main beam and the optical axis of the sub beam on the second diffraction grating is 40 μm, and the beam diameter is 0.9 mm. Therefore, when viewed with the first sub-beam, 56% of the total light amount
Therefore, the output can be improved by about 12% on the basis of 50%.

Preferably, the dividing line DL is set so that the optical axis of the main beam passes. Because the dividing line D
If L deviates from the optical axis of the main beam, there will be a difference between the outputs of the photodetectors 7a and 7e even if the main beam is correctly focused on the track.

(Second Embodiment) FIG. 3 shows an optical pickup device according to a second embodiment.

The basic structure of this optical pickup device is the same as that of the first embodiment, but the polarization beam splitter 8
, A mirror 9 and an optical waveguide element 10 are added. For simplicity, the same members as those in FIG. 1 are denoted by the same reference numerals.

The polarization beam splitter 8 is disposed between the first diffraction grating 3 and the second diffraction grating 2. Part of the reflected light from the disk 6 is reflected by the polarization beam splitter 8, reflected again by the mirror 9, and enters the optical waveguide element 10.

The optical waveguide element 10 has a polarization separating means 11 for separating the reflected light into two polarized light components, and a polarization detecting light detector 12 for detecting two polarized lights. By comparing the intensities of the two polarized lights emitted by the detector 12, the rotation of the polarization plane of the reflected light can be detected. Therefore, in the second embodiment, a magneto-optical disk can be used as a recording medium.

The optical waveguide element 10 uses a thin film technology to separate the polarization separating means 11 and the polarization detecting photodetector 12 by 1 mm ×
Since it can be integrated on a chip of about 2 mm, it is suitable for downsizing an optical pickup device. Further, among the optical waveguide elements 10, at least the polarization detection photodetector 12, the semiconductor laser 1 and the servo signal detection photodetector 7 are housed in the same package (not shown) so that each Is kept stable, and the environmental resistance is improved.

The optical waveguide device 10 and an optical pickup device using the same are disclosed in Japanese Patent Application No. 8-179970.
5, which is described in detail in Japanese Patent Application No. 9-040517.

[0035]

According to the first aspect of the present invention, the second
Is divided into first and second regions, and
Since the tracking signal is obtained by comparing the intensities of one sub-beam diffracted in the first region and the other sub-beam diffracted in the second region, the number of photodetectors Therefore, even if a collimating lens having a large numerical aperture is employed, it is easy to prevent the generation of unnecessary stray light which is small and unnecessary. Further, a stable tracking signal by the three-beam method can be obtained with a small number of photodetectors.

According to the second aspect of the present invention,
Since the boundary between the first and second regions in the second diffraction element is a straight line passing through the optical axis, unnecessary offset components are not superimposed on the tracking signal.

According to the third aspect of the present invention,
Since the photodetectors are located at approximately the same distance from the light source,
Generation of unnecessary stray light can be more easily suppressed, and the degree of freedom in design increases.

Further, in the case of claim 4 of the present invention,
Of the two sub-beams, one sub-beam whose optical axis passes through the first region is referred to as a first sub-beam, and the optical axis thereof is the second sub-beam.
When the other sub-beam passing through the region is defined as a second sub-beam, the intensity of the first sub-beam diffracted in the first region and the second sub-beam diffracted in the second region Since the tracking signal is obtained by comparing the intensities of the tracking signals, it is possible to alleviate a decrease in the tracking signal output.

According to the fifth aspect of the present invention,
Light splitting means for splitting a part of the reflected light from the recording medium, polarization splitting means for splitting the light beam split by the light splitting means into two polarized light components, and polarized light for detecting the two split polarized light components Since it has the photodetector for detection, information recorded on the magneto-optical recording medium can also be reproduced.

According to the sixth aspect of the present invention,
Since the light source, the plurality of light detectors, and the polarization detection light detector are housed in the same package, the mutual positional relationship between the elements is kept stable, and the environmental resistance is improved. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram (perspective view) showing an optical pickup device according to a first embodiment of the present invention.

FIG. 2 is a plan view illustrating a relationship between a second diffraction grating and a photodetector used in the optical pickup device according to the first embodiment of the present invention.

FIG. 3 is a schematic configuration diagram (perspective view) showing an optical pickup device according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram (perspective view) showing a conventional optical pickup device.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 first diffraction grating 3 second diffraction grating DL dividing line 3a first area 3b second area 4 collimating lens 5 objective lens 6 disk 7 photodetector 7a, 7b, 7c, 7d, 7e light Detector 8 Polarizing beam splitter 9 Mirror 10 Optical waveguide element

Claims (6)

[Claims] A light source; a first diffraction grating for dividing a light beam from the light source into a main beam and two sub-beams;
An optical system that focuses the light beams of the two beams on a recording medium,
An optical pickup device comprising: a second diffraction grating that diffracts light reflected from the recording medium; and a plurality of photodetectors that detect light diffracted by the second diffraction grating. Is divided into a first region and a second region. Of the two sub-beams, the intensity of one sub-beam diffracted in the first region and the intensity of one of the two An optical pickup device configured to compare with the intensity of the other diffracted sub-beam to obtain a tracking signal. 2. The optical pickup device according to claim 1, wherein a boundary between the first region and the second region in the second diffraction element is a straight line passing through an optical axis. 3. The optical pickup device according to claim 1, wherein said plurality of photodetectors are arranged at substantially equal distances from said light source. 4. A sub-beam of one of the two sub-beams whose optical axis passes through the first region is a first sub-beam, and the other sub-beam whose optical axis passes through the second region. Is a second sub-beam, comparing the intensity of the first sub-beam diffracted in the first region with the intensity of the second sub-beam diffracted in the second region, 3. The optical pickup device according to claim 2, wherein a tracking signal is obtained. 5. A light splitting means for splitting a part of the reflected light from the recording medium, a polarization splitting means for splitting a light beam split by the light splitting means into two polarized light components, 2. The optical pickup device according to claim 1, further comprising a polarization detection photodetector for detecting a polarization component. 6. The optical pickup device according to claim 5, wherein the light source, the plurality of light detectors, and the polarization detection light detector are housed in the same package.