JP2884960B2 - Optical head and optical information device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for reproducing or recording / reproducing an information signal on a magneto-optical information recording medium, and more particularly to a focus error signal by an astigmatism method and a tracking error signal by a push-pull method. And an optical information apparatus using the optical head, which collectively detects the trajectory by a single optical system, and reduces mixing of a track crossing signal into a focus error signal.

[0002]

2. Description of the Related Art FIG. 19 is a configuration diagram showing a configuration of a conventional optical head for detecting a magneto-optical signal by a differential detection method, a focus error signal by an astigmatism method, and a tracking error signal by a push-pull method. is there.

A light beam emitted from a semiconductor laser 1 is converted into a parallel light by a collimating lens 2, and after a beam shaping prism 3 converts anisotropic laser light intensity into isotropic light. After being transmitted through the first beam splitter 4 and changed its traveling direction by the reflection mirror 5, it is irradiated by an objective lens 6 onto a disk 7 (hereinafter referred to as a magneto-optical disk 7) as a magneto-optical information recording medium. You.

[0004] The reflected light from the magneto-optical disk 7 is reflected by the beam splitter 4 via the objective lens 6 and the reflection mirror 5 and travels to the second beam splitter 8. The reflection surface of the beam splitter 8 has a predetermined light transmittance and a predetermined reflectance, and the incident light flux is divided into transmitted light and reflected light.

[0005] Of these, the transmitted light enters the third beam splitter 9 and is split into two parts: transmitted light and reflected light. The transmitted light passes through the detection lens 10 and is given astigmatism through the cylindrical lens 11, enters the photodetector 12 and is used for focus error detection by the astigmatism method. The reflected light enters the photodetector 13 and is used for tracking error detection by the push-pull method.

On the other hand, the reflected light reflected by the second beam splitter 8 is rotated by 45 degrees by passing through a half-wave plate 14, and then turned into convergent light by a lens 15 to be a polarized beam. The light enters the splitter 16 and is split into two light beams whose polarizations are orthogonal to each other.
8 is incident. Then, the magneto-optical signal recorded on the magneto-optical disk 7 can be reproduced by a detection method that takes the difference between the detection signals of the photodetectors 17 and 18, that is, a differential detection method.

In this configuration, the positions of the photodetectors 12 and 13 can be adjusted independently of each other. However, since the optical systems for detecting the focus error and the tracking error are separate,
There is a problem that it is difficult to reduce the size and weight of the optical head.

On the other hand, for example, Japanese Patent Laid-Open No.
In the optical head described in Japanese Patent Publication No. 41, the polarizing beam splitter is a parallel plate type having a grating (a polarizing film is provided on the incident surface side and a grating is provided on the emitting surface side), and the polarizing beam splitter is inclined by 45 degrees during convergent light. Are arranged. As a result, the light incident on the parallel plate type is separated into two light beams whose polarizations are orthogonal to each other, that is, reflected light (S-polarized light) and transmitted light (P-polarized light) by the polarizing film on the incident surface side. Here, the transmitted light is incident on an emission surface having two grating regions. Then, ± 1st-order diffracted lights from the two grating regions are respectively detected, and their intensities are compared to obtain a tracking error signal by the push-pull method. Further, it is possible to detect a focus error signal by the astigmatism method using the zero-order diffracted light of the diffraction grating, that is, directly transmitted light. Further, the magneto-optical signal is to differentially detect a light beam reflected by the parallel plate type polarizing beam splitter and a transmitted light beam (the sum of ± 1st-order diffracted light for a tracking error signal and 0th-order diffracted light for a focus error signal). Has been gained. Thus, the number of parts is reduced.

[0009]

However, in the optical head in the above-mentioned proposed example, high-order diffracted light other than the 0th-order diffracted light and the ± 1st-order diffracted light is generated on the exit surface having two grating regions. Therefore, the polarization-separated P
All of the transmitted light, which is a polarized light component, is not detected, and the amount of light is reduced, resulting in a problem that a magneto-optical signal is deteriorated. In addition, a focus error signal is obtained by inclining the parallel plate during the convergent light to generate astigmatism. However, since the direction of inclination of the parallel plate is the same as the direction of the information track of the magneto-optical disk (although the configuration is possible even in the direction perpendicular to the direction of the information track, it is not described), the direction of the focus error signal There is a problem that a track crossing signal is largely mixed and a normal focus error signal cannot be obtained as a result. That is, as shown in FIG. 2, when the spot moves from the center of the information track of the disk to the inner and outer circumferences (off-track) in a state where the spot is irradiated on the disk, the spot is focused on the disk. That is, regardless of the just focus, a focus error signal is generated as shown in FIG. 3 (this is referred to as mixing of a track crossing signal into the focus error signal). Therefore, the spot is defocused by the focus servo (the position of the objective lens is controlled so that the focus error signal becomes zero). Actually, some off-track is allowed due to various errors (optical head, circuit system, etc.). Therefore, in an optical head in which a track crossing signal is mixed into the focus error signal, defocus occurs when the spot is off-track. However, there is no description regarding such mixing of the track crossing signal into the focus error signal. In the above optical head, if the parallel plate is arranged to be rotated by 45 degrees around the optical axis, mixing of the track crossing signal into the focus error signal can be reduced, but aberrations of the optical system (for example, coma aberration, astigmatism, etc.) ) And positioning errors (for example, a photodetector or the like) of optical components or the like. This was not taken into account. The two grating regions provided in the parallel-plate polarizing beam splitter interfere with the 0th-order diffraction light and the + 1st-order diffraction light and the 0th-order diffraction light and the -1st-order diffraction light in the information track in the reflected light from the magneto-optical disk. It is provided only in a portion corresponding to the portion where the two meet. Therefore, in order to adjust the tracking error signal, it is necessary to adjust the parallel plate in two axial directions (the information track direction and the direction perpendicular to the information track direction, that is, the direction corresponding to the disk radial direction). The movement of the parallel plate causes the displacement (especially the change of the inclination) in conjunction with the movement of the parallel plate, and it is necessary to readjust (the amount of astigmatism generated and the direction change, so the readjustment is required) There was a problem that occurs.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a one-system optical system in which a focus error signal by an astigmatism method and a tracking error signal by a push-pull method are degraded without deteriorating a magneto-optical signal. It is an object of the present invention to provide an optical head which can collectively detect signals by a system and reduce mixing of a track crossing signal into a focus error signal.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magneto-optical signal detection system and a servo signal (focus error signal and tracking error signal) detection of reflected light from a magneto-optical disk by using a beam splitter. Separately, and a magneto-optical signal is detected from the magneto-optical signal detection system. The servo signal detection system includes a band-shaped region having no grating between the beam splitter and the photodetector, and A push-pull method using ± 1st-order diffracted light from each region is provided with a diffraction grating having two grating regions having different diffraction directions or diffraction angles from each other across the region and a means for generating astigmatism. To detect a tracking error signal by using the zeroth-order diffracted light that is directly transmitted through the diffraction grating.

[0012]

According to the present invention, a magneto-optical signal is detected by a differential detection method from a light beam separated by the beam splitter and guided to a magneto-optical signal detection system. The light beam guided to the servo signal detection system passes through the diffraction grating, is given astigmatism for focus error detection by the astigmatism generation means, and then enters the photodetector. Here, the diffraction grating has a band-shaped region having no grating, and two grating regions having different grating line directions with respect to the region. In other words, the two boundaries between the band-shaped region having no grating and the grating region are parallel, and the direction of the image projected on the diffraction grating of the information track of the disc coincides with the center of the two boundaries. It is arranged to be. Therefore,
Of the incident light flux, the light at the center is incident on a region without a band-like lattice, and a substantially semicircle substantially including a portion where the 0th-order diffracted light and the + 1st-order diffracted light in the information track interfere is incident on one lattice region, A substantially semicircle substantially including a portion where the 0th-order diffracted light and the -1st-order diffracted light interfere in the information track enters the other grating region. By detecting the ± 1st-order diffracted lights from these two grating regions and comparing the intensities, a tracking error signal by the push-pull method can be obtained. Further, it is possible to detect a focus error signal by an astigmatism method using the light at the center of the diffraction grating and the zero-order diffracted light of the two grating regions, that is, directly transmitted light. Here, the intensity of the transmitted light used for the focus error signal at the portion where the 0th-order diffracted light and the ± 1st-order diffracted light interfere with each other in the information track decreases.
Mixing of the track crossing signal into the focus error signal can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical head according to the present invention will be described in detail with reference to the drawings.

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

In FIG. 1, a semiconductor laser 1 as a light source is shown.
A light beam 100 emitted from a semiconductor laser (with a high-frequency superimposing circuit 1a for reducing noise of a semiconductor laser) is converted into a parallel light beam 101 by a collimating lens 2, and the intensity of the laser light is reduced by a beam shaping prism 3. The isotropic light is corrected and converted into an isotropic parallel light flux 102.

The light beam 102 emitted from the beam shaping prism 3
Is deflected by 90 degrees in the optical path by the reflection mirror 19, and is incident on the first reflection surface 4a of the first beam splitter 4. The first reflection surface 4a of the beam splitter 4 has different reflectance and transmittance between the P-polarized light and the S-polarized light.
It has polarization characteristics of p ≒ 0.7, P polarized light reflectance Rp ≒ 0.3, S polarized light transmittance Ts ≒ 0, and S polarized light reflectance Rs ≒ 1.
The light beam 102 (P-polarized light) incident on the first reflection surface 4a is split into a transmitted light 103 and a reflected light 104.

The reflected light 104 enters the light shielding member 30 having an opening (a circular opening, not shown in this embodiment), and the light beam 105 transmitted through the opening enters the light detector 32. The light shielding member 30 is not always necessary, and the light beam 10
4 may be led directly to the photodetector 32. Photodetector 3
Numeral 2 is arranged to be inclined with respect to the light beam 105 as a countermeasure against stray light (a countermeasure to prevent light not required to be reflected at the incident surface, that is, stray light from entering a semiconductor laser or another photodetector). I have. The light intensity of the light beam 100 emitted from the semiconductor laser 1 is controlled using the photodetector 32. This will be described in detail later.

On the other hand, the light beam 103 transmitted through the first reflecting surface 4a of the first beam splitter 4 is changed its traveling direction by the reflecting mirror 5, and then is rotated by the objective lens 6 into the disk rotating system 20 (spindle motor). Etc.) to the magneto-optical disk 7 mounted on the disk. The optical head of this embodiment drives the reflecting mirror 5, the objective lens 6, and the objective lens in two directions, a focus direction (Z axis in the figure) and a track direction (Y axis in the figure). Only the two-dimensional actuators 159 and the carriage 160 on which they are mounted are accessed by an access system (mechanism system, control system,
(Not shown), it is movable from the inner peripheral position to the outer peripheral position in the access direction of the magneto-optical disk 7 (Y axis in the figure), and other optical components and the like are fixed (hereinafter, this optical system is referred to as a fixed optical system). )).

The reflected light 106 from the magneto-optical disk 7 is
Beam splitter 4 passes through objective lens 6 and reflection mirror 5
Is reflected by the first reflecting surface 4a and travels toward the second reflecting surface 4b. The second reflection surface 4b of the beam splitter 4 has different reflectance and transmittance between the P-polarized light and the S-polarized light. For example, the P-polarized light transmittance TpＴ0.6, the P-polarized light reflectance Rp ≒ 0.4, S
It has polarization characteristics of a polarization transmittance Ts ≒ 0 and an S polarization reflectance Rs ≒ 1. The light flux 106 incident on the second reflection surface 4b is split into a transmitted light 107 and a reflected light 108.

The light beam 108 reflected from the second reflecting surface 4b of the beam splitter 4 is converted into convergent light 109 by a lens 15, and is separated by a polarization splitting means for splitting an incident light beam into two polarized light beams whose polarization directions are orthogonal to each other. Certain polarizing beam splitter 2
1 and are polarized and separated into two light beams P-polarized light 109p (not shown) and S-polarized light 109s (not shown) whose polarizations are orthogonal to each other. Then, a detection method for obtaining the difference between the detection signals of the light receiving region 22a (not shown) for receiving the P-polarized light 107p and the light receiving region 22b (not shown) for receiving the S-polarized light 107s in the photodetector 22, that is, differential detection By the method, the magneto-optical signal recorded on the magneto-optical disk 7 can be reproduced.

On the other hand, the light beam 107 transmitted through the second reflecting surface 4b of the beam splitter 4 is converged by the detection lens 29 via the diffraction grating 27, and is focused by the cylindrical lens 40 (astigmatism generating means). After being given astigmatism for detection, the light enters the photodetector 30. Detection of a servo signal (a focus error signal and a tracking error signal) using the photodetector 30 will be described later in detail.

Next, characteristic optical components of the optical head having the above-described configuration will be described in detail with reference to the drawings.

FIG. 4 is a diagram showing the configuration of the beam shaping prism 3 used in the optical head of this embodiment. The beam shaping prism 3 of this embodiment is designed to prevent stray light (light that is not required to be reflected at the incident / exit surface, that is, stray light is prevented from entering the semiconductor laser 1, the photodetectors 32, 22, and 30). As a countermeasure, as shown in FIG. 4, the luminous flux is always refracted at each of the entrance / exit surfaces A1, A2, B1, and B2 of the prism A and the prism B constituting the beam shaping prism 3 to enter or exit. And the optical axis 101a of the light beam 101 incident on the beam shaping prism 3 and the light beam 10
The two optical axes 102a are configured to be parallel.
Therefore, since the incident light on each of the incident surfaces A1, A2, B1, and B2 is not perpendicularly incident, the reflected light (stray light) is reflected at an angle to the incident light.
It does not enter the photodetectors 32, 22, 30.

FIG. 5 shows a semiconductor laser using the photodetector 32.
FIG. 3 is a diagram showing a method for controlling the light intensity of the laser light of laser 1; As shown in the figure, the photodetector 32 has two light receiving regions 32a and 32b, and the light receiving regions 32a and 32b
33a and 33b output from the current-voltage converter 3
The laser driving circuit 35 inputs the laser driving circuit 35 through 4a and 34b.
The laser drive circuit 35 has a light intensity control function 35a for controlling the light intensity of the light beam 100 emitted from the semiconductor laser 1.
(Generally Auto Power Control),
It has at least a protection function 35b for detecting abnormal light emission of the semiconductor laser 1 (light intensity that causes thermal destruction of an information signal on the magneto-optical disk) and stopping light emission of the semiconductor laser 1. The output 33a is used as the light intensity control function 35a, the output 33b is used as the protection function 35b, the sum signal of the outputs 33a and 35a is generated and used as the light intensity control function 35a and the protection function 35b. For 35b, there is a configuration using both the output 33a and the output 33b. As described above, if this configuration for detecting the light beam 105 which is a part of the light beam 100 emitted from the semiconductor laser 1 is used, a light intensity detecting light receiving element conventionally provided in the semiconductor laser can be used. Can be removed.
In this embodiment, the photodetectors are connected to the two light receiving areas 32a, 32a.
Although 2b is used, one light receiving area may be used. The light intensity of the light beam 100 emitted from the semiconductor laser 1 is controlled by a drive signal 36 from a laser drive circuit 35, and protection is performed when abnormal light emission of the semiconductor laser 1 is actually detected. The function 35b operates to stop the light emission of the semiconductor laser 1, and outputs a control signal 37 to the system control circuit 38.
Similarly, when the light emission of the semiconductor laser 1 cannot be confirmed, or when a decrease in the output due to the deterioration of the semiconductor laser (the necessary drive current increases) is detected, the system control circuit 38 is similarly controlled. A signal is output. Although not shown in the present embodiment, such a semiconductor laser 1
When an abnormality related to the light emission of the optical information device is detected, the system main body has a function for displaying the abnormality, and the user of the optical information device can confirm the abnormality.

FIG. 6 is a view for explaining a method of mounting the beam splitter 4 used in the optical head of the present embodiment. Here, as shown in FIG. 6, the beam splitter 4 is provided on each incident surface (4 in FIG. 6) to prevent the above-mentioned stray light.
c) and a cubic beam splitter 4 whose output surfaces (4d in the figure) are parallel or perpendicular to each other are arranged by rotating about 1.5 degrees about the X axis in the figure. At this time, the luminous flux (the luminous fluxes 102 and 106 in the figure) incident on the beam splitter 4 and the outgoing luminous flux (the luminous flux 103 in the figure) have a parallel relationship, and the optical axis of the luminous flux after being emitted (transmitted or reflected) is Never lean.

Each optical component of the fixed optical system of the optical head of the embodiment is provided on the lower surface 210a side of the mounting member 210 (hereinafter, referred to as a fixed optical system chassis 210) (the objective lens 6 with respect to the magneto-optical disk 7). On the side where is located). In the beam splitter 4, the mounting surface 4e
Is opposite to the surface 4f in the direction of gravity, so that dust or other dust can be prevented from adhering to the surface 4f due to gravity. Therefore, in the optical information device equipped with the optical head of the present embodiment,
It is possible to prevent deterioration of the optical performance (for example, a decrease in the light utilization rate) due to adhesion of the mixed dust and the like to the optical components.

FIG. 7 is a diagram for explaining the configuration and operation of the polarization beam splitter 21 which is a polarization splitting means used in the optical head of this embodiment. In FIG. 7, the polarization beam
The splitter 21 includes a parallelogram prism 21a and a parallel plate 21b made of a transparent optical medium such as glass, a polarizing film 21c formed on a joint surface between the parallelogram prism 21a and the parallel plate 21b, and a parallel film parallel to the parallelogram prism 21a. Total reflection films 21d and 21 formed on the flat plate 21b, respectively.
e. The polarization beam splitter 21
The light beam 109 emitted from the lens 15 is disposed by being rotated about 45 degrees around the optical axis of the light beam 109. Light beam 10 emitted from lens 15
Reference numeral 9 denotes a polarized light component, in which the S-polarized light component (polarized light having a vibration perpendicular to the paper surface in the drawing) is reflected by the polarizing film 21c, and the P-polarized light component (polarized light having a vibration parallel to the paper surface in the drawing) is reflected. The light passes through the polarizing film 21c, travels straight, is reflected by the total reflection film 21e, and transmits through the polarizing film 21c again.
The light beam 109s reflected by the polarizing film 21c and the polarizing film 21c
Are reflected by the total reflection film 21d and enter the photodetectors 22, respectively.

Next, the photodetector 22 will be described with reference to FIG. FIG. 8 is a view of the light receiving surface side of the photodetector 22 of the present embodiment viewed from the direction of the polarization beam splitter 21 of FIG. The photodetector 22 has two light receiving areas 22a and 22b, and a conversion circuit 24 that processes the output (current) from the light receiving areas 22a and 22b. The light flux 109p and the light flux 109s enter the light receiving regions 22a and 22b, respectively, and form light spots 110p and 110s, respectively. Light receiving area 22
Output currents 23a and 23b of a and 22b are guided to a conversion circuit 24. In the conversion circuit 24, electric elements 24a and 24b for converting a current into a voltage and electric elements 24c and 24d for performing addition or subtraction are integrated (integrated). Therefore, the output currents 23a and 23b are converted by the conversion circuit 24 into a magneto-optical signal 25, which is a subtraction signal, and an addition signal 26 (an uneven pit signal formed in advance on the magneto-optical disk 7; for example, an information signal such as an address signal; Signal 26) is output. It should be noted that the conversion circuit 24 of the photodetector 22 according to the present embodiment includes electrical elements 24a and 24 that convert a current into a voltage.
Only b may be integrated.

The polarizing beam splitter 21 and the photodetector 22 are once mounted on a mounting member 28 as shown in FIG. The mounting member 28 is fixed to the fixed optical system chassis 210 with, for example, screws.

Next, the diffraction grating 27 used in the optical head of this embodiment and the detection of each error signal will be described in detail.

First, the diffraction grating 27 will be described with reference to FIGS. FIG. 10 is a front view showing the configuration of the diffraction grating 27. The diffraction grating 27 has a band-like region 27a having no grating, and two grating regions 27b and 27c having different grating line directions 27d and 27e across the region 27a (the grating line direction 27d in this embodiment). And 27
The angle formed by e is approximately 90 degrees). That is, the band-like region 27a having no lattice and the lattice region 27
b or two boundary lines 27f and 27 with the grid region 27c
g is parallel, and is disposed such that the direction 220 of the image projected on the diffraction grating 27 of the information track 7a of the magneto-optical disk 7 coincides with the center 27h of the two boundary lines. Therefore, as shown in FIG. 11, the light at the center of the incident light flux 107 is incident on the region 27a having no band-like lattice, and the part 107a where the 0th-order diffracted light and the + 1st-order diffracted light in the information track 7a interfere is almost changed. A substantially semicircle including the portion 107b is incident on one grating region 27b, and a substantially semicircle substantially including a portion 107b where the 0th-order diffracted light and the -1st-order diffracted light interfere with each other on the information track 7a is incident on the other grating region 27c. By detecting ± first-order diffracted lights from the two grating regions 27b and 27c and comparing the intensities, a tracking error signal by the push-pull method can be obtained. Also,
Light at the central portion 27a of the diffraction grating and two grating regions 27
The focus error signal by the astigmatism method can be detected using the 0th-order diffracted light of b and 27c, that is, the directly transmitted light.
As shown in the figure, the transmittance of the directly transmitted light of the diffraction grating 27 is high in the central region 27a of the grating of the diffraction grating 27 (approximately 1.0 in this embodiment), and the two grating regions 27b and 27
c is low (approximately 0.5 in this embodiment). Accordingly, the directly transmitted light is consequently ± 0 order diffracted light at the information track 7a ± 1.
Since the intensity of the portions 107a and 107b where the next-order diffracted light interferes is reduced, mixing of the track crossing signal into the focus error signal can be reduced.

Next, the photodetector 30 will be described in detail with reference to FIG.

FIG. 12 shows a front view showing the structure of the photodetector 30 in detail and an arithmetic circuit for obtaining each signal.

The photodetector 30 has four divided light receiving areas 30a to 30d at the center, and has independent light receiving areas 30e to 30h around the light receiving areas 30a to 30d.

The light at the central portion 27a of the diffraction grating 30 and the zero-order diffracted light of the two grating regions 27b and 27c, that is, the directly transmitted light, enter the four-divided light receiving regions 30a to 30d of the photodetector 30 as light spots 31. I do. Therefore, the light receiving area 30
a, 30c and the photocurrents from the light receiving areas 30b, 30d are converted into voltages by a current-voltage converter (not shown), and then input to the differential amplifier 42, whereby astigmatism is obtained. A focus error signal by the method can be obtained.

On the other hand, the ± 1st-order diffracted lights diffracted by the grating area 27b are received by the light receiving areas 30f, 3f of the photodetector 30, respectively.
The light is incident on 0h as light spots 41f and 41h. The ± 1st-order diffracted lights diffracted by the grating area 27c are respectively applied to the light spots 41e and 30g of the photodetector 30 in the light spots 41e and 30g.
e, 41 g. Therefore, the light receiving area 30e,
The photocurrent from 30g and the photocurrent from the light receiving regions 30f and 30h are converted into a voltage by a current-voltage converter (not shown), and then input to the differential amplifier 44, whereby tracking by the push-pull method is performed. An error signal can be obtained. At this time, the tracking error signal is
h and the difference between the incident light intensity signals of 30 g or the light receiving area 30
It can also be obtained from the difference between the incident light intensity signals e and 30f.

In FIG. 12, light receiving areas 30e to 30h
The substantially semicircular shapes of the images of the upper light spots 41e to 41h are rotated by 90 degrees with respect to the shape on the diffraction grating 27, because the cylindrical lens 40 gives astigmatism. Since what is detected by the light receiving regions 30e to 30h is not the shape of the image but the amount of light incident on each region,
There is no problem even if the shape of the image changes.

The information signal 26 is transmitted to the light receiving area 30.
e to 30h, the sum of the incident light intensity signals, or the light receiving area 30
e and the sum of the incident light intensity signals of 30f, or the light receiving area 3
It can be obtained from the sum of the incident light intensity signals of 0a to 30d and the sum of all the light receiving areas 30a to 30h.

By the way, the adjustment of the focus error signal, that is, the adjustment of the focus error signal to a predetermined value in the focused state on the disk, that is, the adjustment of the detection lens 29 and the cylindrical lens 40 in FIG. Can be integrally moved in the direction 117 of the incident optical axis of the incident light 107. Alternatively, the light detector 30 may be moved in the optical axis direction. The adjustment of the tracking error signal to adjust the tracking error signal to a predetermined value in the just tracking state on the disk, that is, the adjustment of the tracking error signal is performed by using the diffraction grating 27 in FIG. 1 and FIG. It is performed by moving in a direction 118 perpendicular to two boundary lines 27f and 27g. Since this adjustment is performed on the light beam 107 that is a parallel light, the light beam transmitted through the diffraction grating 27 does not have an inclination unlike the conventional example. Further, there is no generation of aberration such as astigmatism. Therefore, the focus error signal adjusted in advance does not come and go due to the adjustment of the tracking error signal by moving the diffraction grating 27. As described above, the focus adjustment and the tracking adjustment can be performed independently.

As described above in detail, the optical head of the present embodiment is capable of transmitting the focus error signal by the astigmatism method and the tracking error signal by the push-pull method to one system without deteriorating the magneto-optical signal. Thus, it is possible to detect all at once, and reduce mixing of the track crossing signal into the focus error signal. In this embodiment, since the 0th-order diffracted light of the diffraction grating 27 is used for detecting the focus error signal,
Even when the wavelength of the semiconductor laser 1 as a light source changes, the light spot 31 on the four-divided light receiving areas 30a to 30d does not move, and a correct focus error signal can be obtained.

Further, since the ± 1st-order diffracted light by the diffraction grating 27 is used for detecting the tracking error signal, the light spots 41e to 41h on the light receiving regions 30e to 30h move due to the fluctuation of the wavelength of the semiconductor laser 1. Light receiving area 3
0e to 30h, the size of the light receiving areas 30e to 30h is changed to the light spot 41 to detect the amount of light incident on each area.
There is no problem if it is designed in consideration of the movement of e to 41h. In the detection of the tracking error signal by the push-pull method,
When the objective lens moves following the information track of the disc, the reflected light from the disc also moves with the movement, and there is a problem that an offset occurs in the detected tracking error signal. However, in the present embodiment, as the tracking error signal, in the incident light beam 107 of the diffraction grating 27 in FIG.
The light incident on the grating regions 27b and 27c, that is, the light of the portions 107a and 107b where the 0th-order diffracted light and the ± 1st-order diffracted light in the information track 7a interfere with each other is detected without using the light incident on the beam 7a. Therefore, there is an advantage that the offset of the tracking error signal due to the movement of the objective lens can be reduced.

Next, a method for aligning the center Ic of the light beam 103 incident on the objective lens 6 with the center Oc of the objective lens will be described with reference to FIG. In the separation type optical head as in this embodiment, due to the inclination of the light emitting portion of the semiconductor laser 1 or the mounting error of the optical parts and the access system, the position is located between the intensity center Ic of the incident light beam 103 and the center Oc of the objective lens. Deviation occurs. This positional shift adversely affects the focus error signal and the tracking error signal (for example, the offset of the focus error signal caused by the positional shift of the optical component or the like due to temperature or the like becomes large). Therefore, in this embodiment, FIG.
As shown in the figure, the tangential direction (X-axis) of the magneto-optical disk 7 between the center Oc of the objective lens and the intensity center Ic of the incident light beam 103
Is adjusted by moving the mounting position of the fixed optical system chassis 210 to the mechanical chassis 350 by -dX in the tangential direction. That is, in the present embodiment, the fixed optical system chassis 210 is moved in the Z-axis direction in the drawing so that the reference surface 3 of the mechanical chassis 350 is not moved.
The fixed optical system chassis 210 is translated with reference to 50a (a plane parallel to the tangential direction (X axis) of the disk 7 and perpendicular to the radial Y axis). On the other hand, the center O of the objective lens
The displacement dY in the radial direction (Y-axis) of the magneto-optical disk 7 between c and the intensity center Ic of the incident light beam 103 causes the attachment position of the two-dimensional actuator 159 to the reflection mirror 5 as shown in FIG. On the other hand, in the radial direction (Y axis) of the disk 7,
It is adjusted by moving dY. That is, 2
The three-dimensional actuator 159 is mounted on a member 158 and the reflective mirror 5 is mounted on a carriage 160 where the member 15 is mounted.
8 is attached to the carriage 160 to fix the two-dimensional actuator 159 to the carriage 160.
The adjustment is performed by moving the member 158 in parallel with the carriage 160 in the radial direction of the disk 7.

FIG. 15 is a configuration diagram showing the configuration of an optical head according to a second embodiment of the present invention.

In FIG. 15, the same reference numerals as in FIG. 1 showing the structure of the optical head of the first embodiment denote the same parts. In the optical head of this embodiment, a light beam 100 (S-polarized light) emitted from a semiconductor laser 1 (with a high-frequency superimposing circuit 1a) as a light source is converted into a parallel light beam 130 by a collimating lens 49.
And passes through the half-wave plate 50 to change the polarization direction to 90.
Deflected light beam 131 (P-polarized light) becomes a reflection mirror.
At 19, the optical path is deflected by 90 degrees, and enters the first beam splitter 4 to form a light spot 170 on the magneto-optical disk 7. FIG. 16 shows information tracks 7 on the magneto-optical disk 7.
The relation between a and the intensity of the light spot 170 and the polarization direction is shown.
The light spot 170 is an elliptical spot that is long in a direction perpendicular to the information track 7a (in the radial direction of the disc), and its polarization direction matches the information track 7a. The process until the reflected light 106 of the light spot 170 of the magneto-optical disk is detected as a magneto-optical signal by the photodetector 22 and as a servo signal by the photodetector 30 is the same as that of the optical head of the first embodiment. It is omitted because it is the same. In the optical head of the present embodiment, FIG.
The beam shaping prism 3 for correcting the light intensity of the semiconductor laser 1 used in the optical head of FIG. However, the configuration is not limited to this. An example of another configuration is shown below.

FIG. 17 is a configuration diagram showing the configuration of an optical head according to a third embodiment of the present invention.

In FIG. 17, the first and second embodiments of the present invention are shown.
1 and 15 showing the configuration of the optical head according to the third embodiment.
The same reference numerals indicate the same parts. In the optical head of this embodiment, a light beam 100 (S-polarized light) emitted from a semiconductor laser 1 (with a high-frequency superimposing circuit 1a) as a light source is collimated.
The light beam is converted into a parallel light beam 130 by the torens 49 and is incident on the first reflection surface 55 a of the first beam splitter 55.
The first reflection surface 55a of the beam splitter 55 has different reflectance and transmittance between the P-polarized light and the S-polarized light. For example, the P-polarized light transmittance Tp {1, the P-polarized light reflectance Rp {0, the S-polarized light transmittance Ts}. It has a polarization characteristic of 0.2, S polarization reflectance Rs 反射 0.8. The light flux 130 (S
(Polarized light) is transmitted light 131 (not shown) and reflected light 132
Divided.

The reflected light 132 is incident on the second reflection surface 55b of the first beam splitter 55. The second reflection surface 55b of the beam splitter 55 has different reflectance and transmittance between the P-polarized light and the S-polarized light. For example, the P-polarized light transmittance Tp {1, the P-polarized light reflectance Rp {0, the S-polarized light transmittance Ts}.
It has a polarization characteristic of 0.2, S polarization reflectance Rs 反射 0.8. The light beam 132 (S-polarized light) incident on the second reflection surface 55b is split into a transmitted light 133 and a reflected light 134.

Here, the transmitted light 133 enters the photodetector 32, and the reflected light 134 (S-polarized light) passes through the half-wave plate 50 provided at the exit of the fixed optical system and the polarization direction. Becomes a light flux 135 (P-polarized light) rotated by 90 degrees, and exits the fixed optical system. Then, a light spot 170 is formed on the magneto-optical disk 7. Information track 7 of magneto-optical disk 7
FIG. 16 shows the relationship between a and the intensity of the light spot 170 and the polarization direction.
Will be the same as Further, in this embodiment, the transparent member 56 is provided at the entrance of the movable optical system in order to prevent the entry of dust and the like. The reflected light 106 from the magneto-optical disk passes through the second reflecting surface 55b of the beam splitter 55 and passes through the photodetector 22.
Are transmitted through the second reflection surface 55b and the first reflection surface 55a of the beam splitter 55, and are detected by the photodetector 22 as a servo signal. The process up to the detection is the same as that of the optical head according to the first embodiment, and a description thereof will be omitted. Even if the half-wave plate 50 and the transparent member 56 are replaced with quarter-wave plates, the relationship between the intensity and the polarization direction of the information track 7a of the magneto-optical disk 7 and the light spot 170 shown in FIG. be able to. If the polarization direction of the light spot 170 is the same as the radial direction of the magneto-optical disk (Y axis in the figure), the half-wave plate 5
It is sufficient to make 0 transparent and non-material or remove it.

The diffraction grating 27 used in the optical head of the above embodiment changes the diffraction direction, but is not limited to this. As shown in FIG. 18, the interval between the grating lines (grating pitch)
May be different from each other. FIG. 18 is a front view showing the configuration of the diffraction grating 57. The diffraction grating 57 includes a band-like region 57a having no grating and the region 57a
And two grating regions 57b and 57c having different grating pitches P1 and P2 from each other. That is, the band-like region 57a having no lattice and the lattice region 57b
Or two boundary lines 57f and 57g with the lattice area 57c
Are arranged in such a manner that the direction 220 of the image projected on the diffraction grating 57 of the information track 7a of the magneto-optical disk 7 coincides with the center 57h of the two boundary lines.
Therefore, in the optical head of FIG. 1, as shown in FIG. 11, the light at the center of the incident light beam 107 enters the region 57a without the strip-like grating, and the 0th-order diffracted light at the information track 7a and the +1 A substantially semicircle substantially including a portion 107a where the next-order diffracted light interferes enters one of the grating regions 57b, and a portion 1 where the 0th-order diffracted light and the -1st-order diffracted light at the information track 7a interfere with each other.
A substantially semicircle substantially including 07b enters the other grating region 57c. By detecting ± first-order diffracted lights from the two grating regions 57b and 57c, respectively, and comparing the intensities, a tracking error signal by the push-pull method can be obtained. Further, it is possible to detect a focus error signal by the astigmatism method using the light of the central portion 57a of the diffraction grating and the zero-order diffracted light of the two grating regions 57b and 57c, that is, the directly transmitted light. Also, as shown in FIG.
The transmittance of the directly transmitted light of the diffraction grating 57 is high in the central region 57 a of the grating of the diffraction grating 57, and the two grating regions 57.
b, 57c are low. Therefore, as a result, the intensity of the directly transmitted light at the portions 107a and 107b where the 0th-order diffracted light and the ± 1st-order diffracted light at the information track 7a interfere is reduced, so that the intrusion of the track crossing signal into the focus error signal can be reduced.

As described in detail above, the optical head of the present invention can use a single optical system to convert the focus error signal by the astigmatism method and the tracking error signal by the push-pull method without deteriorating the magneto-optical signal. It is possible to collectively detect and reduce the intrusion of the track crossing signal into the focus error signal.

[0051]

According to the present invention, in an optical head for reproducing or recording / reproducing an information signal with respect to a magneto-optical information recording medium, a focus error signal by an astigmatism method can be obtained without deteriorating a magneto-optical signal. The tracking error signal by the push-pull method can be detected collectively by one optical system, and the tracking error signal can be adjusted independently of the focus error signal. Mixing can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of an optical head as a first embodiment of the present invention.

FIG. 2 is a diagram illustrating mixing of a track crossing signal into a focus error signal.

FIG. 3 is a diagram for explaining mixing of a track crossing signal into a focus error signal.

FIG. 4 is a diagram illustrating a beam shaping prism used in the optical head according to the first embodiment of the present invention.

FIG. 5 is a view for explaining intensity detection of a semiconductor laser element used in the optical head according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a method of mounting a beam splitter used in an optical head according to a first embodiment of the present invention.

FIG. 7 is a diagram illustrating a polarization beam splitter used in an optical head according to a first embodiment of the present invention.

FIG. 8 is a diagram for explaining a method of attaching a polarizing beam splitter.

FIG. 9 is a front view showing a configuration of a photodetector for a magneto-optical signal used in the optical head according to the first embodiment of the present invention.

FIG. 10 is a front view showing a configuration of a diffraction grating used in the optical head according to the first embodiment of the present invention.

FIG. 11 is a diagram illustrating the light utilization rate of a diffraction grating used in the optical head according to the first embodiment of the present invention.

FIG. 12 is a front view showing the configuration of a servo signal photodetector and an arithmetic circuit used in the optical head according to the first embodiment of the present invention.

FIG. 13 is a view for explaining the position adjustment (disc tangent direction) of the center of the objective lens and the center of the light intensity in the optical head as the first embodiment of the present invention.

FIG. 14 is a view for explaining the position adjustment (in the disk radial direction) of the center of the objective lens and the center of the light intensity in the optical head as the first embodiment of the present invention.

FIG. 15 is a configuration diagram showing a configuration of an optical head as a second embodiment of the present invention.

FIG. 16 is a diagram illustrating a relationship between a spot on a magneto-optical disk and a polarization direction of an optical head according to a second embodiment of the present invention.

FIG. 17 is a configuration diagram showing a configuration of an optical head according to a third embodiment of the present invention.

FIG. 18 is a front view showing the configuration of another embodiment of the diffraction grating used in the optical head of the present invention.

FIG. 19 is a configuration diagram showing a configuration of a conventional optical head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 3 ... Beam shaping prism, 4 ... Beam splitter, 6 ... Objective lens, 21 ... Polarized beam splitter, 22 ... Photodetector for magneto-optical signals, 27 ... Diffraction grating, 29 ... Detection lens, 40: cylindrical lens, 30: server
Photodetector for signal

──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yasuo Kitada 2880 Kozu Kozu, Odawara City, Kanagawa Prefecture, Japan Storage System Division, Hitachi, Ltd. (72) Inventor Kuniichi Onishi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture (56) References JP-A-1-241028 (JP, A) JP-A-63-71938 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB G11B 7/09-7/095 G11B 7/135

Claims (3)

(57) [Claims] 1. A semiconductor laser for emitting a laser beam, and a light beam from the semiconductor laser is condensed and irradiated as a light spot on a recording surface of an optical information recording medium on which a track is formed. An objective lens for condensing the reflected laser beam, and a beam splitter for separating the laser beam reflected on the recording surface and condensed by the objective lens from an optical path connecting the semiconductor laser and the optical information recording medium. A diffraction grating composed of a plurality of regions having different diffraction directions or diffraction angles and diffracting a light beam separated by the beam splitter to emit as a zero-order light and a first-order diffraction light; A photodetector for receiving next-order diffracted light, and an optical path in the optical path from the beam splitter to the diffraction grating or from the diffraction grating to the photodetector Astigmatism generating means disposed,
And detecting a focus error signal corresponding to the size of the spot diameter of a light spot applied to the optical information recording medium by the astigmatism method from the zero-order diffracted light received by the photodetector. An optical head for detecting a tracking error signal corresponding to a positional shift amount of a light spot irradiated on the optical information recording medium from the track, from the first-order diffracted light received by the photodetector; The grating has a band-shaped region where no grating is formed, and a region where gratings having different diffraction directions or diffraction angles are formed on both sides of the band-shaped region.
Unshaped strips and the grids on both sides of the strips
The two boundary lines with the area where the optical recording medium is formed
The optical head is parallel to each other in a direction optically corresponding to the track . 2. The apparatus according to claim 1, wherein the diffraction grating is arranged in a longitudinal direction of the band-shaped region.
The direction optically corresponds to the track of the optical information recording medium
The optical head according to claim 1, wherein the direction is a direction. (3) Optical information recording medium and optical information recording
Rotating system for rotating a medium, and recording of the optical information recording medium
Plays information signal on the surface or records the recording signal on the recording surface
The optical head according to claim 1 or 2,
Moving means for moving the optical disk in the radial direction of the optical information recording medium
And at least a system control circuit for controlling the device. You
An optical information device, comprising: