JP2000195091A - Optical head device - Google Patents

Abstract

(57) [Summary] [Problem] To reduce the offset amount of a focus error signal as compared with the related art, regardless of the magnitude of the birefringence of an information recording medium, to reduce the focus error signal detection sensitivity, and to detect a focus error signal. To prevent the linearity range from being narrowed. SOLUTION: A radiation light source for emitting a light beam, a first converging optical system for converging the light beam, and a light beam reflected by an information recording medium provided near a focal point of the first converging optical system are converged. A second converging optical system, a diffractive element disposed in an optical path of the light beam converged by the second converging optical system, and diffracting the light beam converged by the second converging optical system; With a photodetector having a plurality of light detection areas to detect the diffracted light,
An opening is provided between the photodetector and the diffraction element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical head device, an optical disk recording / reproducing device, and an optical disk recording / reproducing method.

[0002]

2. Description of the Related Art Optical memory technology using an optical disk having a pit pattern as a high-density and large-capacity storage medium includes digital audio disks, video disks,
Document file disk, data file, etc.
Its application range is expanding exponentially. In such an optical memory technology, information is recorded / reproduced on an optical recording medium such as an optical disk with high accuracy and reliability by passing a minutely focused light beam. This recording / reproducing operation depends solely on the optical system.

The basic functions of an optical head device, which is a main part of the optical system, are roughly classified into convergence for forming a diffraction-limited minute spot, focus control and tracking control of the optical system, and detection of a pit signal. . These functions are realized by a combination of various optical systems and photoelectric conversion detection methods according to the purpose and use.

On the other hand, in recent years, high-density, large-capacity optical disks called DVDs have been put into practical use, and have been spotlighted as information media capable of handling a large amount of information such as moving images. This DVD
The optical disk has a smaller pit size on the information recording surface in order to increase the recording density as compared with a conventional compact disk (hereinafter abbreviated as "CD"). Therefore, in an optical head device for recording / reproducing a DVD optical disk, the wavelength of a light source for determining the spot diameter and the numerical aperture (NumericalAperturing) of a converging lens are used.
e: Hereinafter, abbreviated as "NA". ) Is different from the case of CD. Incidentally, in the case of CD, the wavelength of the light source is approximately 0.7.
8 μm and NA are approximately 0.45, whereas in the case of a DVD optical disk, the wavelength of the light source is approximately 0.63 to 0.65 μm.
m and NA are approximately 0.6. Therefore, when two types of optical disks, CD and DVD, are recorded and reproduced by one optical disk drive, an optical head device having two optical systems is required.

On the other hand, there is a strong demand for downsizing, thinning, and cost reduction of the optical head device, and there is a tendency to share the optical system of CD and DVD as much as possible. For example, the light source is a DVD light source, and only the convergence lens is a DVD light source.
Use two types of convergence lenses for optical discs and CDs, or use a common convergence lens and change the NA mechanically or optically so that only NA is large for DVD optical discs and small for CDs. The fact is that the system is adopted.

Hereinafter, a method of optically changing the NA of the converging lens in the above-described optical head device will be described with reference to the drawings. In addition, x displayed at the lower left of each figure
In the yz coordinates, the same coordinate axis indicates the same direction on the drawing.

FIG. 4 is a configuration diagram of an optical system in a conventional optical head device. In FIG. 4, reference numeral 1 denotes a semiconductor laser having a wavelength of about 0.65 μm. The semiconductor laser 1 is arranged so as to emit a linearly polarized light beam having a plane of polarization in the xz plane of the xyz coordinates shown in the lower left of FIG.

Reference numeral 2 denotes a light beam, which is emitted from the semiconductor laser 1. Reference numeral 3 denotes a polarization anisotropic hologram, and x in FIG.
transmits about 70% of the polarized light having a plane of polarization in the z-plane, and yz
It is arranged to diffract about 100% of polarized light having a plane of polarization in the plane. The hologram pattern of the polarization anisotropic hologram 3 is formed so that the diffraction direction is different between the central portion and the outer peripheral portion, and the diffracted light from the central portion is converted into a plurality of light beams having different focal positions.

Reference numeral 4 denotes a quarter-wave plate, which converts linearly polarized light into circularly polarized light. Reference numeral 5 denotes a collimator lens, which converts the light beam 2 into parallel light. Reference numeral 6 denotes an objective lens, and the NA of the objective lens 6 is 0.6.

Reference numeral 7 denotes an optical disk. Reference numeral 9 denotes first diffracted light, which is light diffracted by the central portion of the polarization anisotropic hologram 3. Reference numeral 8 denotes second diffracted light, which is another light diffracted by the polarization anisotropic hologram 3.
Between the first diffracted light 9 and the second diffracted light 8, the first diffracted light 9 has a convergence position on the polarization anisotropic hologram 3 side. Reference numeral 10 denotes a photodetector, which comprises a plurality of photodetection areas.

In the optical head device configured as described above, first, the light beam 2 emitted from the semiconductor laser 1 is
This is linearly polarized light having a plane of polarization in the xz plane of the xyz coordinates. The light beam 2 enters the polarization anisotropic hologram 3. Since the polarization anisotropy hologram 3 transmits about 70% of the polarized light having the polarization plane in the xz plane and diffracts about 100% of the polarized light having the polarization plane in the yz plane, the light beam 2 remains unchanged. The light passes through the polarization anisotropic hologram 3 and is then converted into circularly polarized light by the quarter-wave plate 4. The light beam 2 converted into circularly polarized light is converted into parallel light by the collimator lens 5 and then converged by the objective lens 6 to form a minute spot on the information recording surface of the optical disk 7.

However, for CD and DVD optical discs,
Since the thickness from the substrate surface to the information recording surface is different, when the optical disk 7 is a DVD optical disk, a small spot with almost no aberration can be formed. However, when the optical disk 7 is a CD, aberration is generated, so that it is sufficient for CD reproduction. No spots are obtained. It is known that, in the reproduction of a CD, when only light having an NA of about 0.38 or less among the light passing through the objective lens 6 is used, aberration is reduced and a good spot can be obtained. The light reflected on the information recording surface of the optical disk 7 is converted into parallel light by the objective lens 6, converged by the collimator lens 5, and the converging light beam passes through the quarter-wave plate 4 and enters the polarization plane in the yz plane. And is diffracted about 100% by the polarization anisotropic hologram 3.

The polarization anisotropy hologram 3 has a diffraction direction in a central area and an outer peripheral area where light having an NA of the objective lens 6 of about 0.38 or less passes among the reflected light beams. In contrast, the light in the central region becomes diffracted lights 9 and 8 and enters the photodetector 10. At this time, the converging positions of the diffracted light 9 and the diffracted light 8 are different, and the diffracted light 9 converges to a position closer to the polarization anisotropic hologram 3 than the diffracted light 8.

The diffracted lights 9 and 8 are incident on a photodetector 10 and detected. By calculating the output of the photodetector 10, a focus error signal is obtained. The information signal is obtained from all the diffracted light diffracted from the central area and the outer peripheral area of the polarization anisotropic hologram 3 in the case of a DVD optical disc, and is obtained from the polarization anisotropic hologram 3 in the case of a CD. Are obtained from the diffracted lights 9 and 8 diffracted from the central part of.
As described above, in the case of a CD, among the light reflected from the information recording surface, a light beam having a small aberration with an NA of the objective lens 6 of about 0.38 or less is used for detecting an information signal, thereby providing a good signal. Detection becomes possible.

When the optical disk 7 has a birefringence corresponding to approximately one-half wavelength of the semiconductor laser 1 in the optical path of the disk substrate, the linearly polarized light having a polarization plane in the xz plane emitted from the semiconductor laser 1 is generated. About 70% is transmitted, and the transmitted light is 4%.
The light passing through the half-wave plate 4 becomes circularly polarized light, passes through the collimator lens 5, is condensed on the information recording surface of the optical disk 7 by the objective lens 6, and is reflected by the optical path of the disk substrate reciprocating light for approximately half. The light beam becomes a circularly polarized light whose phase is advanced by a half wavelength from the light before being reflected by the optical disk 7 due to the birefringence of one wavelength, passes through the objective lens 6, is converged by the collimator lens 5, and is being converged. Is a quarter
After passing through the wave plate 4, it becomes linearly polarized light having a polarization plane in the xz plane again, and 70% of the light passes through the polarization anisotropic hologram 3 and returns to the semiconductor laser 1, but has a polarization plane in the remaining xz plane. 30% of the linearly polarized light is diffracted by the polarization anisotropic hologram 3 into a plurality of lights, enters the photodetector 10, and is detected as a focus error signal. That is, approximately one-third of the reproduced signal can be detected as compared with the case where the optical disc has no birefringence, so that a sufficiently good signal can be obtained.

A method of detecting a focus error signal is, for example, a known SSD (spot size detection) method disclosed in Japanese Patent Application Laid-Open No. 2-185722, which will be described in detail with reference to FIGS.

FIG. 5 is a diagram for explaining a method of detecting a focus error signal. In FIG. 5, the same components as those in FIG. 4 are denoted by the same reference numerals and description thereof is omitted. 5 and 6, the arrangement of the polarization anisotropic hologram 3 and the quarter-wave plate 4 is different, but the operation is the same.

In FIG. 5A, the position of the information recording surface of the optical disk 7 is higher than the focal position of the objective lens 6.
The focal positions of the diffracted light 9 and the diffracted light 8 approach the collimator lens 5.

In FIG. 5B, the position of the information recording surface of the optical disk 7 coincides with the focal position of the objective lens 6. The focal positions of the diffracted light 9 and the diffracted light 8 are symmetrical with respect to the surface of the photodetector 10, and as a result, the beam sizes of the diffracted lights 9 and 8 on the photodetector 10 become the same.

In FIG. 5C, the position of the information recording surface of the optical disk 7 is closer to the objective lens 6 than the focal position of the objective lens 6, and the focal positions of the diffracted light 9 and the diffracted light 8 are from the collimator lens 5. Go away. 5 (a), (b),
(C) FIGS. 6A, 6B, and 6C show spots of diffracted light generated on the photodetector 10 in each state.

In FIG. 6, reference numeral 10 denotes a photodetector;
8d and 9a to 9d are the split light of the diffracted light 9 and the diffracted light 8 in FIG. This division is performed by dividing the hologram element 3 into regions. 11-1
Reference numeral 4 denotes a partial detection area of the photodetector 10;
1 and the output of the detection area 14 are indicated by FE1, and the sum of the outputs of the detection area 12 and the detection area 13 is indicated by FE2. FIG.
6A is a view corresponding to FIG. 6A, in which the dimensions of the diffracted light spots 8a to 8d are smaller than the dimensions of the diffracted light spots 9a to 9d.

FIG. 6 (b) is a view corresponding to FIG. 5 (b), and in FIG. 6 (b), the diffracted light spots 8a to 8
The dimension of d becomes equal to the dimensions of the diffracted light spots 9a to 9d. FIG. 6C is a view corresponding to FIG. 5C. In FIG. 5C, the dimensions of the diffracted light spots 8a to 8d are larger than the dimensions of the diffracted light spots 9a to 9d.

For ease of explanation, each quarter circle of the divided diffracted light spots 8a to 8d and 9a to 9d is virtually synthesized and shown in FIG. FIG. 7A is a view corresponding to FIG. 6A, wherein reference numerals 15 and 16 denote diffracted light spots, respectively, and diffracted light spots 8a to 8 shown in FIG.
d, 9a to 9d. 17 to 22 are detection areas, and the detection area 17 is the detection area 1 shown in FIG.
1, the detection area 18 is in the detection areas 12 and 13, the detection area 19 is in the detection area 14, and the detection area 20 is in the detection area 13
The detection area 21 corresponds to the detection areas 11 and 14, and the detection area 2 corresponds to the detection area 2.
Reference numerals 2 correspond to the detection areas 12, respectively.

The focus error signal is the output F of the detection area.
Obtained by the difference between E1 and FE2 (FE1-FE2),
It becomes negative in FIG. 6A, becomes 0 in FIG. 6B, and becomes positive in FIG. 6C. Therefore, by moving the objective lens 6 so that the focus error signal becomes 0, it becomes possible to make the focal position of the objective lens 6 coincide with the position of the information recording surface of the optical disk 7.

[0025]

However, in the above-described conventional configuration, when recording / reproducing an optical disc having birefringence, stray light which is unnecessary light due to diffracted light irrelevant to signal light is included in the focus error signal. Since the light is condensed on the photodetector, there is a problem that an offset is generated in the focus error signal and the detection sensitivity of the focus error signal is reduced.

Hereinafter, a mechanism for lowering the focus error signal detection sensitivity will be described with reference to the drawings.
The semiconductor laser 1 is applied to the optical disk 7 by using the optical path of the disk substrate.
, Approximately 70% of linearly polarized light having a polarization plane in the xz plane emitted from the semiconductor laser 1 is transmitted, and the transmitted light is a quarter-wave plate. 4, is converted into circularly polarized light, transmitted through the collimator lens 5, condensed on the information recording surface of the optical disk 7 by the objective lens 6, and reflected by the optical path of the disk substrate reciprocating light for approximately half wavelength. The light becomes circularly polarized light whose phase is advanced by a half wavelength from the light before being reflected by the optical disk 7 due to refraction, passes through the objective lens 6, is converged by the collimator lens 5, and the light beam being converged is a quarter. After passing through the wave plate 4, it becomes linearly polarized light having a polarization plane in the xz plane again.
0% transmits through the polarization anisotropic hologram 3 and returns to the semiconductor laser 1. However, the remaining 30% of linearly polarized light having a polarization plane in the xz plane is diffracted into a plurality of lights by the polarization anisotropy hologram 3, The light enters the photodetector 10 and is detected as a focus error signal. However, about 30% of linearly polarized light emitted from the semiconductor laser 1 and having a polarization plane in the xz plane which is not used as a focus error signal.
% Is diffracted and most of the diffracted light does not enter the collimator lens 5, but some diffracted light is reduced to a quarter.
The light passes through the wave plate 4 and becomes circularly polarized light.
Through the objective lens 6 and condensed and reflected on the information recording surface of the optical disk 7 by the objective lens 6, and the reflected light passes through the optical path of the disk substrate round trip.
Due to the birefringence of one-half wavelength, the light becomes circularly polarized light whose phase is advanced by one half wavelength from the light before being reflected by the optical disk 7, passes through the objective lens 6, is converged by the collimator lens 5, and is being converged. The light beam is a quarter wave plate 4
, Again becomes linearly polarized light having a polarization plane in the xz plane, so that 70% of the light passes through the polarization anisotropic hologram 3 and enters the photodetector 10.

Here, using FIG. 6 and FIG. 8, about 30% of the diffracted light of the linearly polarized light having a polarization plane in the xz plane which is not used as a focus error signal and emitted from the semiconductor laser 1, which is a problem, is the light. The detailed description up to the incidence on the detector 10 will be described below.

FIG. 8 shows the components shown in FIG. 4 simply by dots or planes, and the same components as those in FIG. 4 are denoted by the same reference numerals. 3a is an effective light use area of the polarization anisotropic hologram 3, 3b is a diffraction area of the polarization anisotropic hologram, 2
a is one ray of diffracted light passing through the effective light use area 3a of the polarization anisotropic hologram, and 2b is one ray of diffracted light passing through the diffraction area 3b of the polarization anisotropic hologram. One ray 2a of the diffracted light emitted from the semiconductor laser 1 and passing through the effective light use area 3a of the polarization anisotropic hologram 3 is diffracted because of the linearly polarized light having the polarization plane in the xz plane as described above. The light that has passed through the quarter-wave plate 4 to become circularly polarized light, transmitted through the collimator lens 5, condensed and reflected on the information recording surface of the optical disk 7 by the objective lens 6, is reflected by the reciprocating optical path of the disk base material for approximately half. Optical disc 7 by birefringence for one wavelength
The light becomes circularly polarized light whose phase is advanced by a half wavelength from the light before being reflected, passes through the objective lens 6, does not enter the collimator lens 5, and is not condensed on the photodetector 10. That is, the diffracted light that has passed through the effective light use region 3a of the polarization anisotropic hologram does not return to the photodetector 10 and does not pose a problem.

However, one ray 2b of the diffracted light emitted from the semiconductor laser 1 and passing through the diffraction region 3b of the polarization anisotropic hologram 3 is diffracted because of the linearly polarized light having a polarization plane in the xz plane as described above. The light passes through the quarter-wave plate 4 to become circularly polarized light, passes through the collimator lens 5, and is condensed and reflected on the information recording surface of the optical disk 7 by the objective lens 6. Due to the birefringence of one-half wavelength, the light becomes circularly polarized light whose phase is advanced by one half wavelength from the light before being reflected by the optical disk 7, passes through the objective lens 6, is converged by the collimator lens 5, and is being converged. Since the light beam passes through the quarter-wave plate 4 and becomes linearly polarized light having a polarization plane in the xz plane again, the effective light use area 3a of the polarization anisotropic hologram 3 and the polarization anisotropic hologram 3 70% area between the folding region 3b is transmitted, it will be incident on the optical detector 10. That is,
The light incident on the photodetector 10 described above is formed by the difference between FE1 and FE2 because it is incident on any of the detection areas 11, 12, 13, and 14 on the photodetector 10 described above with reference to FIG. An offset is generated in the focus error signal, and the detection sensitivity of the focus error signal is reduced or fluctuated.

As a result, there is a problem that an offset is added to the focus error signal, the focus position is deviated from the best jitter point, the detection sensitivity of the focus error signal is reduced, and the linearity range of the detection is narrowed, and the vibration resistance is reduced. Had.

According to the present invention, in order to overcome the above-mentioned problems, the offset amount of the focus error signal is made smaller than before, regardless of the magnitude of the birefringence of the information recording medium, and the detection sensitivity of the focus error signal is reduced. And to prevent the linearity range of focus error signal detection from being narrowed.

[0032]

In order to achieve the above object, an optical head device according to the present invention comprises a radiation light source for emitting a light beam, a first converging optical system for converging the light beam, and a first converging optical system. A second converging optical system for converging the light beam reflected by the information recording medium disposed near the focal point of the converging optical system; and a second converging optical system disposed in the optical path of the light beam converged by the second converging optical system. A diffractive element for diffracting the light beam converged by the convergent optical system, and a photodetector having a plurality of light detection regions for detecting the diffracted light diffracted by the diffractive element. It is characterized in that a circular opening is provided between them.

By providing such an aperture, of the diffracted light, one that causes an offset in the focus error signal is shielded, so that it does not enter the photodetector.
It is possible to suppress a decrease or fluctuation in the detection sensitivity of the focus error signal.

Further, in the optical head device according to the present invention, the diameter of the opening is determined based on the effective diameter of the first converging optical system from the focal length of the second converging optical system and the position where the opening is arranged. It is preferable that the diameter be equal to or larger than a value proportionally calculated based on the distance in the optical axis direction to the detector. If the value is smaller than such a value, even the diffracted light that should be treated as effective light is blocked.

Further, in the optical head device according to the present invention, the effective diameter of the first converging optical system is 3.96 mm, the focal length of the second converging optical system is 18 mm or more and 20 mm or less, and the opening is formed from the photodetector. It is desirable that the aperture is arranged at a distance of 3.9 mm or more and 4.3 mm or less in the optical axis direction and the diameter of the opening is 0.79 mm or more. Within the practical range, when the focal length of the second converging optical system is 20 mm and the aperture is located at a distance of 4.0 mm from the photodetector in the optical axis direction, the diameter of the aperture is 0.1 mm.
If it is not more than 79 mm, even the diffracted light which should be treated as effective light is blocked.

In the optical head device according to the present invention, it is preferable that the shape of the opening is elliptical or elliptical. This is because an effect equivalent to the case where the shape of the opening is circular can be expected.

Further, in the optical head device according to the present invention, the opening has an elliptical shape or an elliptical shape, and the length of the major axis of the elliptical shape or the elliptical shape is set to the first effective diameter of the first converging optics. From the effective diameter of the first converging optical system to the focal length of the second converging optical system and the arrangement of the apertures according to the value obtained by adding the maximum amount of movement of the converging optical system across the information sequence recorded on the information recording medium. And a value calculated in proportion to the distance in the optical axis direction from the photodetector, and the direction of the major axis in the elliptical or elliptical opening is determined according to the direction traversing the information sequence recorded on the information recording medium. It is preferable to make them substantially coincide with the direction. This is for blocking the diffracted light that causes the offset of the focus error signal.

Also, in the optical head device according to the present invention, it is preferable that the first converging optical system also functions as the second converging optical system. This is because the integrated type can be expected to reduce the manufacturing cost due to the reduction in the number of parts.

Further, in the optical head device according to the present invention, it is preferable that the diffraction element is a hologram element having polarization anisotropy of diffraction efficiency. This is because effective diffracted light can be easily controlled.

Further, it is preferable that the optical head device according to the present invention includes means for detecting a focus error signal from the diffracted light. This is because the detection of the focus error signal makes it easy to move the objective lens or the like to make the focal length of the objective lens coincide with the position of the information recording surface of the information recording medium.

In the optical head device according to the present invention, it is preferable that an opening is formed integrally with the diffraction element. This is because the integrated type can be expected to reduce the manufacturing cost due to the reduction in the number of parts.

Next, in order to achieve the above object, an optical head device according to the present invention comprises a radiation light source for emitting a light beam, a first converging optical system for converging the light beam, and a first converging optical system. A second converging optical system for converging a light beam reflected by the information recording medium provided near the focal point of
A diffractive element arranged in the optical path of the light beam converged by the second converging optical system, diffracting the light being converged, and being divided into a plurality of regions in the radial direction of the light beam luminous flux; A light detector having a plurality of light detection regions for detecting light, wherein a circular floating light removal opening is provided between the second converging optical system and the diffraction element.

By providing such a circular floating light removing aperture, not only the diffracted light that causes an offset in the focus error signal can be shielded, but also the diffracted light can be stably incident on the photodetector. Therefore, it is possible to suppress the generation of noise with respect to the signal component of the floating light, and it is possible to suppress the deterioration of the jitter and the offset.

Further, in the optical head device according to the present invention, the diameter of the floating light removing opening is set to be smaller than the effective diameter of the first converging optical system and the focal length of the second focusing optical system and the floating light removing opening are arranged. It is preferable that the diameter be equal to or greater than a value proportionally calculated from the distance in the optical axis direction from the position to the photodetector. If the value is smaller than such a value, even the diffracted light that should be treated as effective light is blocked.

In the optical head device according to the present invention, it is preferable that a floating light removing opening is formed integrally with the diffraction element. This is because the integrated type can be expected to reduce the manufacturing cost due to the reduction in the number of parts.

[0046]

Embodiment 1 Hereinafter, an optical head device according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an optical system in the optical head device according to the first embodiment of the present invention. Note that the same components as those of the conventional optical head device shown in FIG. FIG. 1 differs from FIG. 4 in that it has a circular opening.

In FIG. 1, reference numeral 1 denotes a semiconductor laser,
The wavelength is approximately 0.65 μm. The semiconductor laser 1 is arranged so as to emit a linearly polarized light beam having a plane of polarization in the xz plane of the xyz coordinates shown in the lower left of FIG.

Reference numeral 2 denotes a light beam, which is emitted from the semiconductor laser 1. Reference numeral 31 denotes a circular opening for restricting only the effective light of the light beam 2 emitted from the semiconductor laser 1. Reference numeral 3 denotes a polarization anisotropic hologram, which is arranged so as to transmit about 70% of polarized light having a plane of polarization in the xz plane and diffract about 100% of polarized light having a plane of polarization in the yz plane in FIG. ing. Polarized anisotropic holograms are, for example, those made by proton exchange of some lithium with lithium niobate as a substrate, or those made by applying a resin containing liquid crystal to a glass substrate and dry-etching. is there. The hologram pattern of the polarization anisotropic hologram 3 is formed so that the diffraction direction is different between the central portion and the outer peripheral portion, and the diffracted light from the central portion is converted into a plurality of light beams having different focal positions.

Reference numeral 4 denotes a quarter-wave plate, which converts linearly polarized light into circularly polarized light. Reference numeral 5 denotes a collimator lens, which converts the light beam 2 into parallel light. Reference numeral 6 denotes an objective lens, and the NA of the objective lens 6 is 0.6.

Reference numeral 7 denotes an optical disk. Reference numeral 9 denotes first diffracted light, which is light diffracted by the central portion of the polarization anisotropic hologram 3. Reference numeral 8 denotes second diffracted light, which is another light diffracted by the polarization anisotropic hologram 3. In the first diffracted light 9 and the second diffracted light 8, the first
Has a converging position on the side of the polarization anisotropic hologram 3. Reference numeral 10 denotes a photodetector, which comprises a plurality of photodetection areas.

In the case where the optical disk 7 has birefringence corresponding to approximately a half wavelength of the semiconductor laser 1 in the optical path of the disk substrate,
Aperture 31 of light beam 2 emitted from semiconductor laser 1
Allows only the effective light to pass through, and the polarization anisotropic hologram 3
Of linearly polarized light having a plane of polarization in the xz plane
% Is transmitted.

The transmitted light passes through the quarter-wave plate 4 to become circularly polarized light, passes through the collimator lens 5, is condensed on the information recording surface of the optical disk 7 by the objective lens 6, and is reflected.

The reflected light becomes circularly polarized light whose phase is advanced by a half wavelength from the light before being reflected by the optical disk 7 due to birefringence of approximately a half wavelength in the optical path of the disk base material reciprocation. The light passes through the objective lens 6 and passes through the collimator lens 5
Converged by

The converging light beam passes through the quarter-wave plate 4 and becomes linearly polarized light having a polarization plane in the xz plane again, and 70% of the light beam is transmitted through the polarization anisotropic hologram 3 to the semiconductor. Return to laser 1.

However, 30% of the linearly polarized light having a polarization plane in the remaining xz plane is diffracted into a plurality of lights by the polarization anisotropy hologram 3 and is incident on the photodetector 10.
Is detected as the focus error signal described above.

Next, FIG. 2 is a simplified view of each component shown in FIG. 1 by dots or planes, and the same components as those in FIG. 1 are denoted by the same reference numerals. In FIG. 2, reference numeral 2a denotes a light beam that passes through the opening 31 and enters the polarization anisotropic hologram 3 and one light beam of effective diffracted light that passes through the opening 31.
b denotes one ray of virtual diffracted light that passes through the opening 31 and assumes no aperture 31.

One ray 2a of the effective diffracted light passing through the aperture 31 emitted from the semiconductor laser 1 enters the polarization anisotropic hologram 3 and is diffracted because of the linearly polarized light having a polarization plane in the xz plane. The light passes through the quarter-wave plate 4 to become circularly polarized light, passes through the collimator lens 5, and is condensed and reflected on the information recording surface of the optical disk 7 by the objective lens 6. The reflected light becomes circularly polarized light whose phase is advanced by a half wavelength with respect to the light before being reflected by the optical disk 7 by birefringence of approximately a half wavelength in the optical path of the disk substrate reciprocation. , Does not enter the collimator lens 5, and does not converge on the photodetector 10.

Here, one ray 2b of the virtual diffracted light passing through the polarization anisotropic hologram 3 emitted from the semiconductor laser 1 assuming the case without the opening 31 is a linearly polarized light having a polarization plane in the xz plane. The light is diffracted, passes through the quarter-wave plate 4, becomes circularly polarized light, passes through the collimator lens 5, and is condensed and reflected on the information recording surface of the optical disk 7 by the objective lens 6. The reflected light becomes a circularly polarized light whose phase is advanced by a half wavelength from the light before being reflected by the optical disk 7 by birefringence of approximately a half wavelength in the optical path of the disk substrate reciprocating. The transmitted light beam is converged by the collimator lens 5, and the converging light beam passes through the quarter-wave plate 4 again to become linearly polarized light having a polarization plane in the xz plane. 70% of the light is transmitted and enters the photodetector 10.

However, one light beam 2b of the virtual diffracted light assuming that there is no opening 31 is blocked without passing through the opening by providing the opening 31 between the photodetector 10 and the polarization anisotropic hologram. And does not enter the photodetector 10.

As a result, no offset is generated in the focus error signal generated from a part of the detection area formed on the photodetector 10, and the detection sensitivity of the focus error signal is reduced or the fluctuation is suppressed. It is possible to do.

In the first embodiment of the present invention, the polarization anisotropic hologram and the quarter-wave plate are formed separately, but there is no particular problem even if they are formed integrally. Absent.

In Embodiment 1 of the present invention,
Although the polarization anisotropy hologram and the aperture are configured separately and independently, the same effect can be expected even if the aperture is integrally formed on one surface of the polarization anisotropy hologram.

Further, in Embodiment 1 of the present invention,
The shape of the opening is not limited to a circle, but may be an ellipse or an ellipse, and the direction of the major axis of the ellipse or the ellipse substantially coincides with the direction traversing the information sequence recorded on the information recording medium. A similar effect can be expected by setting a value calculated by a predetermined proportional expression according to a value obtained by adding the amount of movement of the objective lens and the effective diameter of the objective lens to the major axis length of the aperture.

(Embodiment 2) Hereinafter, an optical head device according to Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 3 is a configuration diagram of an optical system in the optical head device according to the first embodiment of the present invention. FIG. 3 is the same as the configuration of the optical head device according to the first embodiment shown in FIG. 1 except for the points described below, and the same components as those in FIG. I do. FIG. 3 differs from FIG. 1 in that a floating light removing opening 32 is provided.

In FIG. 3, the light beam 2 emitted from the semiconductor laser 1 is a linearly polarized light having a polarization plane in the xz plane. The light beam 2 enters the polarization anisotropic hologram 3. The polarization anisotropy hologram 3 transmits about 70% of the polarized light having the polarization plane in the xz plane and diffracts about 100% of the polarized light having the polarization plane in the yz plane.
Is transmitted through the polarization anisotropic hologram 3 as it is,
The light is converted into circularly polarized light by the half-wave plate 4. The light beam 2 converted into circularly polarized light passes through the floating light removing opening 32 and is converted into parallel light by the collimator lens 5.
It is converged by the objective lens 6 and forms a minute spot on the information recording surface of the optical disk 7.

However, in the case of a CD and a DVD optical disc,
Since the thickness from the substrate surface to the information recording surface is different, when the optical disk 7 is a DVD optical disk, a small spot with almost no aberration can be formed.
In the case of (1), an aberration occurs, so that a spot sufficient for CD reproduction cannot be obtained. The objective lens 6 is used for CD playback.
It is known that when only the light having an NA of about 0.38 or less is used among the light passing through, the aberration is reduced and a good spot is obtained.

The light reflected by the information recording surface of the optical disk 7 is converted into parallel light by the objective lens 6, converged by the collimator lens 5, passes through the floating light removal opening 32, and is converged by a quarter of the light beam. The light passes through the wave plate 4 to become linearly polarized light having a polarization plane in the yz plane, and is diffracted by the polarization anisotropic hologram 3 by about 100%. The polarization anisotropy hologram 3 has a different diffraction direction between the central region and the outer peripheral region through which the light of which the NA of the objective lens 6 is about 0.38 or less among the reflected light beams passes,
The light in the central region becomes diffracted lights 9 and 8 and becomes a photodetector 10.
Incident on. At this time, the converging positions of the diffracted light 9 and the diffracted light 8 are different, and the diffracted light 9 converges to a position closer to the polarization anisotropic hologram 3 than the diffracted light 8. Diffracted light 9, 8
Is incident on the photodetector 10 and detected.

Here, the floating light removing opening 32 will be described. Although not shown in the drawings, the above components are
In an actual optical head, the optical head is held by a casing made of metal or resin. Floating light, which is reflected light from the inner surface of the housing, the surface of the polarization anisotropic hologram 3, the surface of the collimator 5 on which the light beam 2 is incident, the surface of the objective lens 6 on which the light beam 2 is incident, etc., is detected. Unstable input to the vessel 10 can be prevented by providing the floating light removing opening 32. Therefore, it is possible to suppress noise caused by the floating light on the signal component detected from the photodetector 10, and it is possible to expect an effect of suppressing the deterioration of the jitter and the offset to the focus error signal.

In the second embodiment of the present invention, the polarization anisotropic hologram and the floating light removing aperture are configured as separate and independent ones. However, they may be configured integrally. . The same effect can be expected even if it is formed integrally with the quarter wavelength plate.

In the above description, an example in which a polarization anisotropic hologram is used as a hologram element has been described. However, a hologram element having no polarization anisotropy can be similarly used. Further, although the description has been given mainly of the optical disk, the present invention can be similarly applied to a magneto-optical disk.

As described above, according to the second embodiment, it is possible to prevent the floating light from entering the photodetector in an unstable manner, and to generate noise for the signal component of the floating light detected from the photodetector. Can be suppressed, and it is possible to suppress the deterioration of the jitter and the offset to the focus error signal.

[0072]

As described above, according to the optical disk apparatus of the present invention, when the optical disk has birefringence, light is shielded by providing an opening between the photodetector and the polarization anisotropic hologram. Since the stray light diffracted by the polarization anisotropy hologram outside the effective diameter does not enter the photodetector, an offset is generated in a focus error signal generated from a partial detection area formed on the photodetector. In addition, the detection sensitivity of the focus error signal can be reduced or the fluctuation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system in an optical head device according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram of an optical system in the optical head device according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical system in an optical head device according to a second embodiment of the present invention;

FIG. 4 is a configuration diagram of an optical system in a conventional optical head device.

FIG. 5 is an explanatory diagram of a method of detecting a focus error signal.

FIG. 6 is a diagram showing the relationship between a light detection area of a photodetector and a diffracted light spot.

FIG. 7 is an explanatory diagram of a diffracted light spot.

FIG. 8 is a schematic view of an optical system in a conventional optical head device.

[Explanation of symbols]

Reference Signs List 1 semiconductor laser 2 light beam 3 polarization anisotropy hologram 4 quarter wave plate 5 collimator lens 6 objective lens 7 optical disk 8, 9 diffracted light 8a, 8b, 8c, 8d, 9a, 9b, 9c, 9d, 1
5, 16 Diffracted light spot 10 Photodetector 11, 12, 13, 14, 17, 18, 19, 20, 2
1, 22 detection area 31 opening 32 floating light removal opening

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuo Ito 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Hideki Hayashi 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Seiji Nishino 1006 Kazuma Kazuma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference)

Claims (12)

[Claims] A light source for emitting a light beam; a first converging optical system for converging the light beam; and a light reflected by an information recording medium disposed near a focal point of the first converging optical system. A second converging optical system for converging the beam, and a diffractive element arranged in an optical path of the light beam converged by the second converging optical system, for diffracting the light beam converged by the second converging optical system And a photodetector having a plurality of photodetection regions for detecting diffracted light diffracted by the diffraction element, wherein a circular opening is provided between the photodetector and the diffraction element. Head device. 2. The method according to claim 1, wherein a diameter of the opening is based on an effective diameter of the first converging optical system and a distance between a focal length of the second converging optical system and a position where the opening is disposed to the photodetector. 2. The optical head device according to claim 1, wherein the diameter is equal to or larger than a value calculated in proportion to the distance in the optical axis direction. 3. An effective diameter of the first converging optical system is 3.9.
6 mm, the focal length of the second converging optical system is 18 mm or more and 20 mm or less, and the aperture is arranged at a distance of 3.9 mm or more and 4.3 mm or less from the photodetector in the optical axis direction,
3. The optical head device according to claim 1, wherein the diameter of the opening is 0.79 mm or more. 4. The optical head device according to claim 1, wherein the shape of the opening is an ellipse or an ellipse. 5. An elliptical or elliptical shape of the opening,
And the maximum movement amount of the first converging optical system which traverses the information sequence recorded on the information recording medium to the length of the major axis of the elliptical or elliptical shape to the effective diameter of the first converging optical. Is calculated from the effective diameter of the first converging optical system in accordance with the value obtained by adding the focal length of the second converging optical system and the distance in the optical axis direction from the photodetector where the aperture is disposed. 5. The optical head device according to claim 4, wherein the direction of the major axis of the elliptical or elliptical opening substantially coincides with the direction corresponding to the direction crossing the information sequence recorded on the information recording medium. 6. The optical head device according to claim 1, wherein the first converging optical system also functions as the second converging optical system. 7. The optical head device according to claim 1, wherein the diffraction element is a hologram element having polarization anisotropy of diffraction efficiency. 8. The optical head device according to claim 1, further comprising: means for detecting a focus error signal from the diffracted light. 9. The optical head device according to claim 1, wherein the opening is formed integrally with the diffraction element. 10. A radiation source for emitting a light beam, a first converging optical system for converging the light beam, and a light beam reflected by an information recording medium provided near a focal point of the first converging optical system. A second converging optical system that converges the light beam; a second converging optical system disposed in an optical path of a light beam converged by the second converging optical system; And a photodetector having a plurality of light detection areas for detecting the converged diffracted light, wherein a circular floating element is provided between the second converging optical system and the diffraction element. An optical head device comprising a light removing opening. 11. The light from the floating light removing opening is arranged such that the diameter of the floating light removing opening is smaller than the effective diameter of the first converging optical system from the focal length of the second converging optical system and the position where the floating light removing opening is arranged. 11. The optical head device according to claim 10, wherein the diameter is equal to or larger than a value calculated in proportion to the distance in the optical axis direction to the detector. 12. The optical head device according to claim 10, wherein the floating light removing opening is formed integrally with the diffraction element.