JPH10214432A - Optical head device - Google Patents

Abstract

(57) [Problem] Since a distance between a substrate surface and an information recording surface is different between a DVD optical disc and a CD, aberration is generated when trying to record / reproduce a CD using a DVD optical disc objective lens. . Therefore, it has been difficult to control the position of the objective lens so that the jitter of the information signal is minimized. A minimum size of a light detection area for detecting a focus error signal in a light detector is set to a CD.
By making the diameter of the diffracted light spots 30 and 31 smaller than the minimum diameter at the time of recording / reproducing, light close to the optical axis greatly contributes to the focus error signal.

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.

[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,
Applications such as document file disks and data files are expanding. In this optical memory technology, information is recorded / reproduced on an optical disk with high precision and reliability via a light beam which is narrowed down. This recording / reproducing operation depends solely on the optical system.

The basic functions of the optical head device, which is the main part of the optical system, are roughly classified into convergence for forming a diffraction-limited small spot, focus control and tracking control of the optical system, and detection of a pit signal. You. 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 disc has a smaller pit size on the information recording surface in order to increase the recording density as compared with a conventional compact disc (hereinafter abbreviated as CD). Therefore, in an optical head device for recording / reproducing a DVD optical disk, a wavelength of a light source for determining a spot diameter,
Numerical Apert of the convergent lens
ure: abbreviated as NA) is different from the case of CD. Incidentally, in CD, the wavelength of the light source is approximately 0.78 μm.
Whereas m and NA are approximately 0.45, the wavelength of the light source of the DVD optical disk is approximately 0.63 to 0.65 μm, and NA is approximately 0.6. Therefore, CD and DVD optical disks
In order to record and reproduce various types of optical disks with one optical disk drive, an optical head device having two optical systems is required. On the other hand, miniaturization and thinning of optical head devices,
From the demand for cost reduction, the optical system for CD and DVD is being shared as much as possible.
Using a light source for convergence, only a convergence lens, two types of convergence lenses for DVD optical disk and CD, or a common convergence lens, and using only NA for DVD optical disk, large for DVD optical disk, and for CD A method of changing mechanically or optically so as to reduce the size 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. The xy displayed at the lower left of each figure
In the z coordinate, the same coordinate axis indicates the same direction on the drawing.

FIG. 8 shows a configuration of an optical system of a conventional optical head device. In FIG. 8, 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 light beam polarized in the x-axis direction of the xyz coordinate shown in the lower left of FIG. Reference numeral 2 denotes a light beam emitted from the semiconductor laser 1. A collimator lens 3 converts the light beam 2 into parallel light.
Reference numeral 4 denotes a polarization anisotropic hologram, which is arranged so as to transmit polarized light having a polarization plane in the xz plane of FIG. 8 and diffract polarized light having a polarization plane in the yz plane. The hologram pattern of the polarization anisotropic hologram 4 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 5 denotes a quarter-wave plate, which converts linearly polarized light into circularly polarized light. Reference numeral 6 denotes an objective lens.
A is 0.6. Reference numeral 7 denotes an optical disk. Reference numeral 9 denotes first diffracted light, which is light diffracted by the central part of the polarization anisotropic hologram 4. Reference numeral 8 denotes second diffracted light, which is another light diffracted by the polarization anisotropic hologram 4. In the first diffracted light 9 and the second diffracted light 8, the first
Has a converging position on the collimator lens 3 side. Reference numeral 10 denotes a photodetector, which includes a plurality of photodetection areas.

The operation of the optical head device configured as described above will be described below. 8, first, a light beam 2 emitted from a semiconductor laser 1 is a linearly polarized light having a polarization plane in an xz plane of xyz coordinates shown in the lower left part of FIG. After being converted into parallel light by the collimator lens 3, the light beam 2 enters the polarization anisotropic hologram 4. Since the polarization anisotropic hologram 4 transmits polarized light having a polarization plane in the xz plane and diffracts polarized light having a polarization plane in the yz plane, the light beam 2 passes through the polarization anisotropic hologram 4 as it is. Then, it is converted into circularly polarized light by the quarter-wave plate 5. This circularly polarized light is converged by the objective lens 6 and forms a minute spot on the information recording surface of the optical disk 7. However, since the thickness from the substrate surface to the information recording surface is different between CD and DVD optical disks,
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. It is known that, in the reproduction of a CD, aberrations are reduced and good spots can be obtained by using only light having an NA within about 0.38 of the light passing through the objective lens 6 out of the light passing through the objective lens 6. The light reflected on the information recording surface of the optical disk 7 passes through the objective lens 6 and the quarter-wave plate 5, and
It becomes linearly polarized light having a polarization plane in the z plane, and is diffracted by the polarization anisotropic hologram 4. The polarization anisotropy hologram is used to calculate the NA of the objective lens 6 out of the reflected light beam.
The diffraction direction is different between the central region and the outer peripheral region through which light within about 0.38 passes, and the light in the central region is converged by the collimator lens 3 as diffracted lights 9 and 8. . 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 collimator lens 3 than the diffracted light 8. The diffracted lights 9 and 8 are incident on the 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 4 in the case of a DVD optical disk, and is obtained from the polarization anisotropic hologram 4 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, of the light reflected from the information recording surface, a light beam having a small aberration within about 0.38 as the NA of the objective lens 6 is used for detecting the information signal, whereby a good signal can be obtained. Detection becomes possible.

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. 9 is a diagram for explaining a method of detecting a focus error signal. In FIG. 9, the same components as those in FIG. FIG.
5A, the position of the information recording surface of the optical disk 7 is farther from 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 closer to the collimator lens 3. In FIG. 3B, 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. 3C, the position of the information recording surface of the optical disc 7 is closer to the objective lens 6 than the focal position of the objective lens 6, and the diffracted light 9
The focal position of the diffracted light 8 moves away from the collimator lens 3. FIGS. 9A, 9B, and 9C show spots of the diffracted light on the photodetector 10 in the respective states shown in FIGS.
(B) and (c). In FIG. 10, reference numeral 10 denotes a photodetector, and reference numerals 8a to 8d and 9a to 9d denote diffracted light 9 and light obtained by dividing the diffracted light 8 in FIG. This division is performed by dividing the hologram element 4 into regions. Numerals 11 to 14 denote detection areas of a part of the photodetector 10. The sum of the outputs of the detection areas 11 and 14 is indicated by FE1, and the sum of the outputs of the detection areas 12 and 13 is indicated by FE2.
Indicated by FIG. 10A corresponds to FIG. 9A, and in FIG. 10A, the diffracted light spots 8a to 8d are shown.
Is smaller than the dimensions of the diffracted light spots 9a to 9d. FIG. 10B is a view corresponding to FIG. 9B, and in FIG. 10B, diffracted light spots 8a to 8
The dimension of d becomes equal to the dimensions of the diffracted light spots 9a to 9d. FIG. 10C is a diagram corresponding to FIG. 9C,
In FIG. 10C, 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. 11A is a view corresponding to FIG. 10A, wherein reference numerals 15 and 16 denote diffracted light spots,
Each of the diffracted light spots 8a to 8d shown in FIG.
9a to 9d. 17 to 22 are detection areas, and the detection area 17 is the detection area 11 shown in FIG.
The detection area 18 corresponds to the detection areas 12 and 13, and the detection area 1 corresponds to the detection area 1.
9 is the detection area 14, the detection area 20 is the detection area 13,
The detection area 21 corresponds to the detection areas 11 and 14, and the detection area 22 corresponds to the detection area 12. The focus error signal is the difference between the outputs FE1 and FE2 of the detection area (FE1-
FE2), becomes negative in FIG. 11A, becomes 0 in FIG. 11B, and becomes positive in FIG. 11C. Therefore, the objective lens 6 is moved by moving the objective lens 6 so that the focus error signal becomes zero.
And the position of the information recording surface of the optical disk 7 can be matched.

[0010]

However, in the above-mentioned conventional configuration, when recording / reproducing a CD optical disk, the position where the focus error signal is 0 and the position where the jitter (the value of the time axis fluctuation) of the information signal is minimized. There is a problem that does not always match. Hereinafter, this problem will be described with reference to the drawings. FIG. 12 is a schematic diagram of the convergence state of the objective lens. FIG. 12A shows a state where the light beam converges on a DVD optical disk, where 23 is a DVD optical disk substrate, and 24 is an information recording surface. For a DVD optical disc, the distance from the substrate surface to the information recording surface is 0.6
mm. Reference numeral 25 denotes a group of convergent light rays. FIG.
(B) shows a state when the light beam converges on a CD optical disk, 26 is a CD optical disk substrate, and 27 is an information recording surface. In a CD optical disk, the distance from the substrate surface to the information recording surface is 1.2 mm. Reference numeral 28 denotes a convergent light beam group. As shown in FIG. 12A, in the case of a DVD optical disk, the light beam group 25 of the convergent light is
And converges on the information recording surface 24 without aberration. However, when converging on a CD optical disk with the same objective lens, spherical aberration occurs because the distance from the substrate surface to the information recording surface is different from that of the DVD optical disk, and FIG.
As shown in (2), the light beams farther from the optical axis converge at a position farther from the objective lens, and the converged light beam group 28
Cannot be narrowed down to one point. As a result of the optical analysis, the present inventors
It has been found that the jitter of the information signal is minimized when the information recording surface is substantially at the position of the average focal length, that is, when the wavefront aberration of the convergent light spot on the information recording surface is substantially minimized. However, the sizes of the detection regions 18 and 21 of the photodetector 10 used for detecting the conventional focus error signal by the SSD method described above are the same in width, and as shown in FIG. Diffracted light spot 1
5 and 16 are set to be larger than the minimum possible diameter. Accordingly, in such a case, the focus error signal becomes 0 when the spot size of the light converged by the objective lens 6 (see FIG. 9B) becomes minimum on the information recording surface. , It is different from the position of the average focal length.

That is, in the conventional optical head device, when a DVD optical disk is used, the light converged by the objective lens is focused to one point, so that the jitter of the information signal is minimized regardless of the size of the detection area of the photodetector 10. Although the position can be detected, when a CD optical disk is used, the position of the focus error signal by the SSD method is 0 and the jitter of the information signal depend on the size of the detection area of the photodetector 10 due to the spherical aberration. There is a problem that the minimum position is different and the time axis fluctuation of the information signal cannot be reduced.

The present invention has been made in view of the above-mentioned problems of the conventional optical head device, and has as its object to provide an optical head device capable of reducing the time axis fluctuation of an information signal regardless of the type of information medium as compared with the conventional one. Aim.

[0013]

According to a first aspect of the present invention, there is provided a radiation source for emitting a light beam, a first converging optical system for converging the light beam, and a focal point of the first converging optical system. A diffractive element for diffracting a light beam reflected by an information medium provided in the vicinity, a second converging optical system for converging the diffracted diffracted light, and a plurality of light detectors for detecting the converged diffracted light A photodetector having an area,
An optical head device wherein a minimum dimension of a predetermined light detection area among the plurality of light detection areas is smaller than at least a minimum spot diameter of the diffracted light formed in the predetermined light detection area.

According to a second aspect of the present invention, there is provided a radiation source for emitting a light beam, a first converging optical system for converging the light beam, and an information medium provided near a focal point of the first converging optical system. A diffractive element for diffracting the light beam reflected by the light source, means for dividing the diffracted diffracted light, a second converging optical system for converging the split diffracted light, and detecting the converged diffracted light A light detector having a plurality of light detection regions, wherein the position of the principal ray of each of the divided diffracted light in one of the plurality of light detection regions in the light detection region and the one light An optical head device wherein an interval between a detection area and a boundary position between another detection area adjacent to the detection area is smaller than a radius of a minimum spot of diffracted light that can be formed when the division is not performed.

According to a ninth aspect of the present invention, there is provided a radiation source for emitting a light beam, a first converging optical system for converging the light beam, and an information medium provided near a focal point of the first converging optical system. Element for diffracting a light beam reflected by a light source, a second converging optical system for converging the diffracted diffracted light, and a photodetector having a plurality of light detection regions for detecting the converged diffracted light Wherein the diffraction element is divided into at least a first region and a second region in which respective convergence positions of diffracted light generated from the respective regions are different, and the plurality of light detection regions includes the first light detection region. A first light detection group for detecting a first diffracted light generated from the area and a second light detection group for detecting a second diffracted light generated from the second area; The first light detection group, The minimum dimension of the first light detection area including the principal ray of the first diffracted light is the second dimension of the second light detection area including the principal ray of the second diffracted light included in the second light detection group. An optical head device smaller than the minimum size.

According to a tenth aspect of the present invention, there is provided a radiation source for emitting a light beam, a first converging optical system for converging the light beam, and an information medium provided near a focal point of the first converging optical system. A diffractive element for diffracting the light beam reflected by the light source, means for dividing the diffracted diffracted light, a second converging optical system for converging the split diffracted light, and detecting the converged diffracted light And a photodetector having a plurality of photodetection regions, wherein the diffraction element is divided into at least a first region and a second region where respective convergence positions of diffracted light generated from the respective regions are different, The plurality of light detection areas include first and second light-emitting areas generated from the first and second areas.
A first light detection group that detects a part of the divided diffracted lights of the diffracted light, and a second light detection group that detects the remaining diffracted lights of the divided diffracted lights A position of a principal ray of the divided diffracted light of the first diffracted light in the first light detection group, and a boundary between light detection regions in the first light detection group. An interval between the principal ray and the boundary in the second light detection group is smaller than an interval between the principal ray position of the divided diffracted light of the second diffracted light and the boundary position. Are optical head devices having the same relationship as the positional relationship.

[0017]

Embodiments of the present invention will be described below. (Embodiment 1) FIG. 1 is a diagram showing a configuration of an optical system of an optical head device according to a first embodiment of the present invention. The configuration shown in FIG. 9 is the same as the configuration of the optical head device shown in the conventional example except for the points described below, and the same components as those in FIG. Here, FIG.
Are different from the photodetector 29 and the polarization anisotropic hologram 1
8, the photodetector 29 differs from the photodetector 10 in FIG. 8 in the pattern size of the photodetection area. Further, the hologram pattern of the polarization anisotropic hologram 100 is also different from the hologram pattern of the polarization anisotropic hologram 4 of FIG.

The wavelength of the semiconductor laser 1 is 0.65 μm, and the light beam 2 emitted from the semiconductor laser 1 is a linearly polarized light having a polarization plane in the xz plane of the xyz coordinates shown in the lower left part of FIG. After the light beam 2 is converted into parallel light by the collimator lens 3, the polarization anisotropic hologram 100
Incident on. The polarization anisotropic hologram is produced, for example, by using lithium niobate as a substrate and exchanging some lithium for protons. The polarization anisotropy hologram 100 is x
It is arranged to transmit polarized light having a plane of polarization in the z plane and diffract polarized light having a plane of polarization in the yz plane,
The light beam 2 passes through the polarization anisotropic hologram 100 as it is, and is then converted into circularly polarized light by the quarter-wave plate 5. This circularly polarized light is converged by the objective lens 6 and forms a minute spot on the information recording surface of the optical disk 7.
The NA of the objective lens 6 was 0.6. Optical disk 7 is C
In the case of D, aberration occurs as described in the section of the problem to be solved by the invention. The circularly polarized light reflected on the information recording surface of the optical disk 7 passes through the objective lens 6 and the quarter-wave plate 5 to become linearly polarized light having a polarization plane in the yz plane, and is diffracted by the polarization anisotropic hologram 100. You. The polarization anisotropic hologram 100 is one of the reflected light beams.
The diffraction direction is different between the central region and the outer peripheral region through which light having a numerical aperture of about 0.38 or less as the NA of the objective lens 6 passes.
8 and converged by the collimator lens 3. At this time, the diffracted light 9 and the diffracted light 8 have different convergence positions,
The diffracted light 9 converges to a position closer to the collimator lens 3 than the diffracted light 8. The diffracted lights 9 and 8 are incident on the photodetector 29 and detected. By calculating the output of the photodetector 29, a focus error signal is obtained. In the case of a DVD optical disc, 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 100. Light 9, 8 diffracted from the center of
Obtained from As described above, in the case of a CD, of the light reflected from the information recording surface, a light beam having a small aberration within about 0.38 as the NA of the objective lens 6 is used for detecting the information signal, whereby a good signal can be obtained. Detection becomes possible. FIG. 2 shows an example of a pattern of a light detection area of the light detector 29 and a diffracted light spot when the optical disk 7 is a CD. FIG. 2 shows a case where the distance between the objective lens 6 and the optical disk 7 is larger than the average focal length of the objective lens 6, where 30 and 31 are diffracted light spots, and the diffracted lights 9 and 8 shown in FIG. It is a spot that did. 32 to 37 are detection areas,
The focus error signal is obtained by the difference (FE1-FE2) between the output FE1 of the detection areas 32, 34, 36 and the output FE2 of the detection areas 33, 35, 37. When the optical disk 7 in FIG. 1 is a CD, the convergent light by the objective lens 6 has a spherical aberration, so that the convergent position of light near the optical axis and the convergent position of light far from the optical axis are different. The amount of spherical aberration is generally indicated as a shift amount (longitudinal aberration) of an imaging point of another light ray from a position of an imaging point (paraxial image point) of paraxial light (light close to the optical axis). The generation amount of this longitudinal aberration increases as the height of the light beam passing through the objective lens 6 from the optical axis increases. This is because the radius of curvature of the lens surface increases. Therefore, the average focal position described in the section of the problem to be solved by the invention is not the center of the position of the paraxial image point and the position where the light beam farthest from the optical axis is imaged, but the paraxial image point. Become more.

Next, FIG. 3 shows a detailed view of the spots of the first diffracted light 9 and the second diffracted light 8 in the photodetector 29.
FIG. 3 shows a case where the information recording surface of the optical disc 7 is located at the average focal position of the objective lens 6, and 30a to 30c and
31a to 31c are spots formed by specific light beams, respectively. The spot 30b and the spot 31b are spots formed on the photodetector 29 by reflecting and diffracting a light beam converged at one point on the information recording surface of the light beam converged by the objective lens 6, and having the same size. is there. Spot 30a
And a spot 31a are formed on the photodetector 29 by reflecting and diffracting a light ray closer to the optical axis than a light ray converged on one point on the information recording surface.
Is larger than the spot 30b, and the spot 31a is smaller than the spot 31b. As described above, since the average focal position is located at a position closer to the paraxial image point, the spot 30
The size of a, 31a is not much different from the size of spots 30b, 31b. Spot 30c and spot 31c
Is a spot formed on the photodetector 29 by reflecting and diffracting a light ray farther from the optical axis than a light ray converged on one point on the information recording surface. Spot 30c because it converges to a position far from the focal point
And the spot 31c, a spot larger than the spots 30b and 31b is formed, and the spot 31c is larger than the spot 30c. Therefore, spot 30a
The light intensity distribution of the spots 31a to 31c has a higher intensity at the central portion than the light intensity distribution (light amount distribution) of the spots 30a to 30c. As a result, the output of the light detection area 33 is smaller than the output of the light detection area 36. On the other hand, the light detection area 32,
Since the output of the light detection areas 35 and 37 is smaller than the output of the light detection areas 35 and 37, the minimum dimensions (length in the x-axis direction in FIG. 3) of the light detection areas 33 and 36 are set within a range smaller than the diameter of the minimum spot. By properly selecting, FE1-FE2 can be set to zero.

In the experiment by the inventor of the present application, the photodetector 2
The minimum spot diameter of the diffracted lights 9 and 8 on the surface 9 is approximately 40 μm
In this case, when the minimum size of the detection regions 33 and 36 was set to 20 μm, the jitter of the information signal could be minimized when the focus error signal was 0. (Embodiment 2) Next, an optical head device according to a second embodiment of the present invention will be described. FIG. 4 is a diagram showing the configuration of the optical head device according to the second embodiment. In FIG. 4, the same components as those in FIG. The difference from the optical head device of the first embodiment is that
Of the polarization anisotropy hologram and the photodetector 39. The polarization anisotropy hologram 38 and the photodetector 39 will be described in detail below. FIG. 5 is a diagram showing a hologram pattern of the polarization anisotropic hologram 38. In FIG. 5, reference numeral 40 denotes a hologram pattern. The hologram pattern 40 is the first
A lithium niobate substrate was produced by proton exchange in the same manner as described in the first embodiment. Hologram pattern 4
0 indicates areas A1 to A3, areas B1 to B3,
It is divided into areas C1 to C3 and areas D1 to D3. Light rays in the area of 0.38 to 0.6 as the NA of the objective lens 6 pass through the areas A3, B3, C3, and D3, and the areas A1, A3
The size and arrangement of the hologram pattern were determined so that light rays within 0.38 of the NA of the objective lens 6 passed through 2, B1, B2, C1, C2, D1, and D2. The region A1 and the region A2 are designed so that two diffracted lights having focal points on the front side and the rear side of the photodetector 39 are diffracted as + 1st-order diffracted light, respectively. The front side of the photodetector 39 refers to the side on which the optical disc 7 is set with reference to the position of the photodetector 39, and the rear side of the photodetector 39 refers to the opposite side. Areas B1, B2, C1, C2,
The same applies to D1 and D2. These A1, A2
The areas D1 and D2 are on the hologram pattern,
A to D are divided into four groups, and each group is divided into 1 /
With the four-circle shape, the following polarization anisotropy can be realized. That is, the diffracted light that has passed through the four-divided hologram pattern is formed on the photodetector 39 in a state where the image due to the diffracted light is divided into quarter circles (see FIG. 6A). .

Further, four diffracted lights having a focal point on the surface of the photodetector 39 are designed to be diffracted as + 1st-order diffracted lights from the regions A3, B3, C3, and D3. In FIG. 4, the light beam reflected from the optical disk 7 passes through the quarter-wave plate 5 to become linearly polarized light having a polarization plane in the YZ plane, so that the polarization anisotropic hologram 3
8 is incident. A plurality of diffracted lights are generated from the polarization anisotropic hologram 38 as described above, and these diffracted lights are converged by the collimator lens 3. In FIG.
For simplicity, regions A1 and B of polarization anisotropy hologram 38
1, the diffracted lights generated from C1, D1 and having a focus on the front side of the photodetector 39 are collectively referred to as diffracted light 41, and the rear side of the photodetector 39 generated from the areas A2, B2, C2, D2. The diffracted light having the focal point is collectively described as a diffracted light. FIG. 6 shows a light detection area of the light detector 39 and a diffracted light spot. In the figure, reference numerals 43 to 46 denote light detection regions, and reference numerals 41a to 41d denote diffracted light spots formed by diffracted light generated from the regions A1, B1, C1, and D1 of the polarization anisotropic hologram 38, respectively. 42a-42d
Are the areas A2 of the polarization anisotropic hologram 38, respectively.
These are spots of diffracted light generated from B2, C2, and D2. The sum of the outputs of the light detection area 43 and the light detection area 46 is FE
1, the sum of the outputs of the light detection area 44 and the light detection area 45 is indicated by FE2. The diffracted lights 41 and 42 in FIG. 4 are divided into the diffracted light spots 41a to 41 shown in FIG.
d, 42a to 42d. FIG. 6A shows a case where the position of the information recording surface of the optical disk 7 is farther from the objective lens 6 than the focal position of the objective lens 6, and FIG. Shows a case where the position substantially coincides with the average focal position of the objective lens 6. FIG. 3C shows a case where 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. In FIG. 6, the center of a quarter circle formed by the diffracted light spots 41a to 41d and 42a to 42d, that is, the position where the principal ray of each diffracted light is incident on the photodetector 39 is defined as the light detection areas 43 and 44.
10 from the boundary of the light detection areas 45 and 46.
Polarized anisotropic holograms were designed to be separated by μm.
Diffracted light spot 41 divided for ease of explanation
Each quarter circle of a to 41d and 42a to 42d is virtually synthesized and shown in FIG. FIG. 7 is a view corresponding to FIG. 6A, wherein 47 and 48 are diffracted light spots, respectively, which are the diffracted light spots 42a to 42 shown in FIG.
d, 41a to 41d. In FIG. 7, reference numerals 49 to 54 denote detection areas.
The detection area 50 is different from the detection area 43 shown in FIG.
And 45, the detection area 51 is in the detection area 46, and the detection area 5 is in
2 is the detection area 45, and the detection area 53 is the detection areas 43 and 4.
6, the detection area 54 corresponds to the detection area 44, respectively. Focus error signals are detected in detection areas 49, 51, 5
3 and the output F of the detection areas 50, 52, 54
Obtained by the difference of E2 (FE1-FE2). Needless to say, the value of FE1-FE2 calculated as described above using the output of each detection area shown in FIG. 7 and the value of FE1 and FE2 shown in FIG. 6 using the output of each detection area shown in FIG. The calculated values of FE1-FE2 are equivalent.

When a CD is used as the optical disk 7, the diameter of a circle obtained by virtually combining the diffracted light spots on the surface of the photodetector 38 is about 40 μm as in the first embodiment.
m. In FIG. 7, since the minimum size of the virtual light detection area 50 is 20 μm, as described in the first embodiment of the present invention, the focus error signal becomes zero.
At the time, the jitter of the information signal could be minimized.

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, the present invention relates to an optical head device for recording / reproducing or erasing information on an optical medium or a magneto-optical medium such as an optical disk or an optical card. The present invention relates to an optical head device capable of recording / reproducing or erasing information on various optical media or magneto-optical media having different dimensions up to an information recording surface, and has the following effects.

That is, according to the first aspect of the present invention, by making the minimum size of the light detection area smaller than the minimum diameter of the diffracted light spot, the distance from the substrate surface to the information recording surface can be varied. On the other hand, a remarkable effect of controlling the focal position of the recording / reproducing spot so as to minimize the jitter of the information signal can be obtained.

Further, according to the second aspect of the present invention, the position of the principal ray of the divided diffracted light spot is made closer to the boundary of the light detection area, thereby reducing the size of the light detection area without reducing the size of the light detection area. Since the same effect as the first invention can be obtained,
A remarkable effect is obtained when the photodetection area cannot be made very small in order not to deteriorate the frequency characteristics of the gain of the information signal.

The first light detection group and the second light detection group of the present invention
In the first embodiment, the light detection groups correspond to the detection areas 32 to 34 and the detection areas 35 to 37, respectively. However, the light detection groups are not limited thereto, and may have a different number of detection areas. good.

In the first embodiment, the first light detection region and the second light detection region of the present invention correspond to the detection region 33 and the detection region 36, respectively. This corresponds to the shorter width dimension of each of the rectangular detection areas 33 and 36.

Further, the first region and the second region of the diffraction element of the present invention are provided.
In the second embodiment, for example, the region
Group of B1, C1, D1 and areas A2, B2, C
2 and D2.

The diffractive element and the means for splitting the diffracted light according to the present invention are not limited to the case where they are integrally formed in the polarization anisotropic hologram 38 in the second embodiment. , May be configured separately.

The split diffracted light of the first diffracted light and the split diffracted light of the second diffracted light according to the present invention are, for example, diffracted light spots 41a and 41 Although it corresponds to the diffracted light spot 42a of a one-half circle, the invention is not limited to this. For example, the light may be further finely divided, and the number of divisions of the diffracted light is not limited.

The boundary positions of the first and second photodetection groups of the present invention are determined by the detection areas 43 and 4 of the second embodiment.
4 and the boundary between the detection areas 45 and 46.

Further, in the above-described embodiment, the case where the focus control is performed using the light quantity distribution has been described. However, the present invention is not limited to this, and for example, the following configuration may be adopted. That is, the optical head device in this case includes a radiation light source that emits a light beam, a first converging optical system that converges the light beam, and an information medium that is provided near a focal point of the first converging optical system. A diffractive element for diffracting the diffracted light beam, a second converging optical system for converging the diffracted diffracted light, and a photodetector having a plurality of light detection regions for detecting the converged diffracted light. Wherein the diffraction element is divided into at least a first region and a second region in which respective convergence positions of diffracted light generated from the respective regions are different, and the plurality of light detection regions are separated from the first region. A first light detection group for detecting the generated first diffracted light, and a second light detection group for detecting the second diffracted light generated from the second region; The first group included in the photodetection group of The minimum dimension of the first light detection area including the principal ray of the diffracted light is the minimum dimension of the second light detection area including the principal ray of the second diffracted light, which is included in the second light detection group. Is smaller than That is, FIG.
In the above, the shorter dimension of the region 33 is configured to be smaller than the corresponding dimension of the region 36. In this case, the same effect as above can be obtained. However, in this case, in order to achieve the same effect as described above when using a DVD, it is necessary to perform switching control of weighting so that the output of the area 33 and the output of the area 36 are weighted differently. There is. As another example that does not use the light amount distribution, the following configuration may be used. That is, the optical head device in this case includes a radiation light source that emits a light beam, a first converging optical system that converges the light beam, and an information medium that is provided near a focal point of the first converging optical system. A diffractive element for diffracting the diffracted light beam, means for dividing the diffracted diffracted light, a second converging optical system for converging the split diffracted light, and detecting the converged diffracted light, A light detector having a plurality of light detection regions, wherein the diffraction element is divided into at least a first region and a second region where respective convergence positions of diffracted light generated from the respective regions are different from each other; A first light detecting area for detecting a part of the plurality of divided diffracted lights of the first and second diffracted lights generated from the first and second areas; Detect light detection group and remaining split diffracted light And the position of the principal ray of the divided diffracted light of the first diffracted light in the first light detection group, and the light detection in the first light detection group. The distance between the boundary position between the regions is smaller than the distance between the position of the principal ray of the divided diffracted light of the second diffracted light and the boundary position, and the distance in the second light detection group is smaller than the distance between the boundary positions. The light beam and the boundary have the same relationship as the positional relationship. That is, in FIG. 6, for example, the distance between the principal ray of the quarter circle spot 42a and the boundary between the regions 43 and 44 is larger than the distance between the principal ray of the quarter circle spot 41a and the regions 43 and 44. The distance is smaller than the distance from the boundary. In this case, the same effect as above can be obtained. However, in this case, in order to achieve the same effect as described above when using a DVD, it is necessary to perform switching control of weighting so that the output of the area 33 and the output of the area 36 are weighted differently. There is.

[0034]

As is apparent from the above description, the present invention has an advantage that the fluctuation of the information signal on the time axis can be reduced as compared with the related art regardless of the type of the information medium.

[Brief description of the drawings]

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

FIG. 2 is a view showing an example of a pattern of a light detection area of the photodetector of the embodiment and a diffracted light spot;

FIG. 3 is a detailed view of a diffracted light spot on the photodetector of the embodiment.

FIG. 4 is a diagram showing a configuration of an optical head device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a hologram pattern of the polarization anisotropic hologram of the embodiment.

FIGS. 6A to 6C are diagrams showing a light detection area and a diffracted light spot of the photodetector according to the embodiment, respectively.

FIG. 7 is a diagram showing a virtually synthesized diffracted light spot according to the embodiment;

FIG. 8 is a diagram showing a configuration of an optical system of a conventional optical head device.

FIGS. 9A to 9C are diagrams for explaining a method of detecting a focus error signal.

FIGS. 10A to 10C are diagrams showing a light detection area and a diffracted light spot of a photodetector, respectively.

FIGS. 11A to 11C are diagrams each showing virtually diffracted light spots synthesized;

FIGS. 12A and 12B are schematic diagrams showing a convergence state of an objective lens, respectively.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 light beam 3 collimator lens 5 quarter-wave plate 6 objective lens 7 optical disk 39 photodetector 40 diffracted light 42 diffracted light 100 polarization anisotropic hologram

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Nishino 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] A 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 medium provided near a focal point of the first converging optical system. A diffractive element that diffracts, a second converging optical system that converges the diffracted diffracted light, and a photodetector that has a plurality of light detection regions that detects the converged diffracted light; An optical head device, wherein a minimum dimension of a predetermined light detection area among the light detection areas is smaller than at least a minimum spot diameter of the diffracted light formed in the predetermined light detection area. 2. A 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 medium provided near a focal point of the first converging optical system. A diffractive element that diffracts the light, a unit that divides the diffracted diffracted light, a second converging optical system that converges the divided diffracted light, and a plurality of light detection areas that detect the converged diffracted light. A light detector having: a position of a principal ray of each of the divided diffracted lights in one of the plurality of light detection areas in a light detection area, and adjacent to the one light detection area and the area. An optical head device, wherein the distance from the boundary position to another light detection area is smaller than the radius of the minimum spot of diffracted light that can be formed if the division is not performed. 3. The optical system according to claim 1, wherein the first converging optical system also serves as the second converging optical system.
The optical head device as described in the above. 4. The optical head device according to claim 1, wherein the diffraction element is a hologram element having polarization anisotropy. 5. The diffraction element according to claim 1, wherein the diffraction element is divided into a plurality of regions, and diffracted light from a region near the optical axis is used for detecting a focus error signal. An optical head device according to item 1. 6. A convergence position of a first diffracted light generated from a partial area of the diffraction element and a convergence position of a second diffraction light generated from another partial area of the diffraction element are different from each other. 2. A focus error signal is obtained based on a difference between a light quantity distribution of the spot of the first diffracted light and a light quantity distribution of the spot of the second diffracted light on the photodetector. 6. The optical head device according to any one of items 1 to 5. 7. The diffractive element is divided into at least a first region and a second region where convergence positions of diffracted light generated from the respective regions are different from each other. A first light detection group for detecting a first diffracted light generated from the area, and a second light detecting group for detecting a second diffracted light generated from the second area.
Wherein the predetermined light detection areas are first and second minimum size light detection areas having substantially the same minimum dimension, and the first minimum size light detection area An area is provided in the first light detection group, and a second minimum size light detection area is provided in the second light detection group. 2. The optical head device according to claim 1, wherein a focus error signal is detected by utilizing a difference in a light amount distribution of the spot. 8. 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 medium provided near a focal point of the first converging optical system. A diffractive element that diffracts, a second converging optical system that converges the diffracted diffracted light, and a photodetector that detects the converged diffracted light, wherein the diffracted light on the photodetector is An optical head device for detecting a focus error signal by utilizing a difference in light amount distribution of a plurality of images formed. 9. A 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 medium provided near a focal point of the first converging optical system. A diffractive element that diffracts the light, a second converging optical system that converges the diffracted diffracted light, and a photodetector that detects the converged diffracted light and has a plurality of light detection regions. Is divided into at least a first region and a second region where the respective converging positions of the diffracted light generated from the respective regions are different, and the plurality of light detection regions is a first region generated from the first region. The first light detection group is divided into a first light detection group for detecting diffracted light and a second light detection group for detecting second diffracted light generated from the second region. A principal ray of the first diffracted light included Is smaller than the minimum size of the second photodetection region included in the second photodetection group and including the principal ray of the second diffracted light. Characteristic optical head device. 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 medium provided near a focal point of the first converging optical system. A diffractive element that diffracts the light, a unit that divides the diffracted diffracted light, a second converging optical system that converges the divided diffracted light, and a plurality of light detection areas that detect the converged diffracted light. Wherein the diffractive element is divided into at least a first region and a second region where respective convergence positions of diffracted light generated from each region are different, and the plurality of light detection regions are A first light detection group that detects a part of the plurality of divided diffracted lights of the first and second diffracted lights generated from the first and second regions, Second light detection group for detecting the remaining split diffracted light A position of a principal ray of the divided diffracted light of the first diffracted light in the first light detection group, and a boundary between light detection regions in the first light detection group. An interval between the principal ray and the boundary in the second light detection group is smaller than an interval between the principal ray position of the divided diffracted light of the second diffracted light and the boundary position. Are in the same relationship as the positional relationship.