JPH06162527A - Optical head and optical information device using it - Google Patents

Abstract

PURPOSE:To obtain an optical head by which a focus error signal on an astigma tism method and a tracking error signal on a push/pull method are detected in one lot by means of one optical system without deteriorating magneto-optical signals, also by which the adjustment of the tracking error signal is made in dependently from the focus error signal, and further by which the mixing of a track crossing signal into the focus error signal is reduced. CONSTITUTION:The device is provided with, between a beam splitter 4 by which a servo signal is separated from a magneto-optical signal and a photodetector 30 for servo signal, a belt-like area without grating, a diffraction grating 27 which is provided with two grating areas having mutually different grating lines across the belt-like area, a detecting lens 29 and a cylinder lens 40. Also, the diffracted rays of the diffraction grating including 0th-order diffracted light (direct transmitted light) are guided to the photodetector 30, the focus error signal by the astigmatism method is detected by means of the 0th-order diffracted light, and the tracking error signal is detected by means of a + or -1st- order diffracted light.

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 and 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. The present invention relates to a configuration of an optical head for collectively detecting the above-mentioned optical system with one optical system and reducing mixing of a track crossing signal into a focus error signal, and an optical information device using the same.

[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.

The light beam emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2 and is converted from the anisotropy of the intensity of the laser light into isotropic light by the beam shaping prism 3. After passing through the first beam splitter 4 and having its traveling direction changed by a reflection mirror 5, the objective lens 6 irradiates a disk 7 (hereinafter referred to as a magneto-optical disk 7) which is a magneto-optical information recording medium. It

The reflected light from the magneto-optical disk 7 passes through the objective lens 6 and the reflection mirror 5 and is reflected by the beam splitter 4 toward the second beam splitter 8. The reflecting surface of the beam splitter 8 has a predetermined light transmittance and reflectance, and the incident light flux is divided into transmitted light and reflected light.

Of these, the transmitted light is incident on the third beam splitter 9, and is divided into transmitted light and reflected light. After passing through the detection lens 10, the transmitted light 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 the half-wave plate 14 and is then converted into a converged light by the lens 15 to be a polarized beam. The light enters the splitter 16 and is split into two light beams whose polarization is orthogonal to each other.
It is incident on 8. Then, the magneto-optical signal recorded on the magneto-optical disk 7 can be reproduced by the detection method that takes the difference between the detection signals of the photo detectors 17 and 18, that is, the differential detection method.

In this structure, the positions of the photodetectors 12 and 13 can be adjusted independently, but since the focus error and tracking error detection optical systems 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. 2-1016
In the optical head described in Japanese Patent 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 this is tilted at 45 degrees in converging light. Are arranged. As a result, the light incident on the parallel plate type is separated by the polarizing film on the incident surface side into two light beams whose polarizations are orthogonal to each other, that is, reflected light (S polarized light) and transmitted light (P polarized light). Here, the transmitted light is incident on the emission surface having two grating regions. Then, the ± 1st-order diffracted lights from the two grating regions are detected, and their intensities are compared to obtain a tracking error signal by the push-pull method. Further, the focus error signal by the astigmatism method can be detected by using the 0th-order diffracted light of the diffraction grating, that is, the direct transmitted light. Further, the magneto-optical signal is subjected to differential detection of a light beam reflected by the parallel plate type polarization beam splitter and a light beam transmitted (sum of ± 1st order diffracted light for tracking error signal and 0th order diffracted light for focus error signal). Is gained by. As a result, the number of parts is reduced.

[0009]

However, in the optical head in the above-mentioned proposed example, high-order diffracted light other than 0th-order diffracted light and ± 1st-order diffracted light is generated at the exit surface having two grating regions. Therefore, P separated by the polarizing film
There is a problem that the transmitted light, which is a polarized component, is not entirely detected and the amount of light is reduced, resulting in deterioration of the magneto-optical signal. Further, the parallel plate is tilted in the convergent light to generate astigmatism, and the focus error signal is obtained. However, since the tilt direction of the parallel plate is the same as the direction of the information track of the magneto-optical disk (although it is possible to configure the structure even in the direction perpendicular to the direction of the information track, it is not described), the focus error signal There is a problem that a track crossing signal is mixed in large, and as a result, a normal focus error signal cannot be obtained. That is, as shown in FIG. 2, when the spot is moved from the center of the information track of the disc to the inner and outer circumferences (off-track) while the spot is illuminated on the disc, the spot is focused on the disc. 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 the track crossing signal into the focus error signal). Therefore, the spot is defocused by the focus servo (the objective lens position is controlled so that the focus error signal becomes zero). In practice, off-track to some extent is allowed due to various errors (optical head, circuit system, etc.). Therefore, in the optical head in which the cross-track signal is mixed with the focus error signal, defocus occurs when the spot is off-track. However, there is no description about the mixing of the track crossing signal into the focus error signal. Further, in the above optical head, if the parallel flat plate is 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.) can be reduced. ) Or a positioning error (such as a photodetector) of an optical component or the like causes the mixing. This point was not taken into consideration. Further, the two grating areas provided in the parallel plate type polarization beam splitter interfere with the 0th-order diffracted light and the + 1st-order diffracted light and the 0th-order diffracted light and the -1st-order diffracted light in the information track in the reflected light from the magneto-optical disk. It is provided only in the portion corresponding to the intersecting portion. 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 orthogonal thereto, that is, the direction corresponding to the disk radial direction), and the focus error signal adjusted in advance is used. The adjustment of (1) causes a positional shift (especially the change of the inclination) in conjunction with the movement of the parallel plate, and it is necessary to readjust (the amount of generated astigmatism and the direction change, so readjustment is required). There was a problem that occurs.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a focus error signal by the astigmatism method and a tracking error signal by the push-pull method in one system without degrading the magneto-optical signal. An object of the present invention is to provide an optical head that can be collectively detected by a system and can reduce the mixture of track crossing signals into a focus error signal.

[0011]

The above object is to detect the reflected light from the magneto-optical disk using a beam splitter and detect the magneto-optical signal and the servo signal (focus error signal and tracking error signal). Separately leading to the system, and detecting the magneto-optical signal from the magneto-optical signal detection system, the servo signal detection system is a strip-shaped region having no grating between the beam splitter and the photo detector, A push-pull method using a ± 1st-order diffracted light from each area is provided by providing a diffraction grating having two grating areas having gratings with different diffraction directions or diffraction angles across the area, and using ± 1st-order diffracted light from each area. The tracking error signal is detected by the method described above, and the focus error signal is detected by the astigmatism method using the 0th-order diffracted light that is the directly transmitted light of the diffraction grating.

[0012]

In the present invention, the magneto-optical signal is detected by the differential detection method from the luminous flux separated by the beam splitter and guided to the magneto-optical signal detection system. Further, 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 sandwiching the region and having mutually different directions of grating lines. That is, the two boundary lines of the band-shaped region having no grating and the grating region are parallel, and the direction of the image projected onto the diffraction grating of the information track of the disk coincides with the center of the two boundary lines. Are arranged as follows. Therefore,
Of the incident light flux, the light in the central portion is incident on a region without a band-shaped grating, and a substantially semicircle that substantially includes a portion where the 0th-order diffracted light and the + 1st-order diffracted light in the information track interfere is incident on one grating region A substantially semicircle that substantially includes a portion where the 0th-order diffracted light and the −1st-order diffracted light on the information track interfere with each other enters the other grating region. Tracking error signals by the push-pull method can be obtained by detecting the ± first-order diffracted lights from these two grating regions and comparing their intensities. Further, the focus error signal by the astigmatism method can be detected by using the light at the center of the diffraction grating and the 0th-order diffracted light of the two grating regions, that is, the directly transmitted light. In the transmitted light used for the focus error signal, the intensity of the portion where the 0th-order diffracted light and the ± 1st-order diffracted light in the information track interfere with each other is reduced.
Mixing of the track crossing signal into the focus error signal can be reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical head of the present invention will be described in detail below with reference to the drawings.

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

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

Light flux 102 emitted from the beam shaping prism 3
Is deflected by 90 degrees on 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 reflecting surface 4a of the beam splitter 4 has different reflectance and transmittance between P-polarized light and S-polarized light.
The polarization characteristics are p≈0.7, P-polarized reflectance Rp≈0.3, S-polarized transmittance Ts≈0, and S-polarized reflectance Rs≈1.
The light flux 102 (P-polarized light) incident on the first reflecting surface 4a is divided into a transmitted light 103 and a reflected light 104.

Of these, the reflected light 104 enters a light shielding member 30 having an opening (a circular opening in this embodiment, not shown), and a light beam 105 transmitted through the opening enters a photodetector 32. The light blocking member 30 is not always necessary, and the light flux 10
4 may be directly led to the photodetector 32. Also the photodetector 3
Reference numeral 2 denotes a stray light measure (a measure that prevents light that does not need to be reflected on the incident surface, that is, stray light from entering the semiconductor laser and other photodetectors), and is arranged obliquely with respect to the light beam 105. There is. The light intensity of the light beam 100 emitted from the semiconductor laser 1 is controlled by 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 in its traveling direction by the reflecting mirror 5, and then the objective lens 6 is used to rotate the disc rotating system 20 (spindle motor). And the like) is irradiated onto the magneto-optical disk 7 mounted on the same. The optical head of this embodiment drives the reflecting mirror 5, the objective lens 6, and the objective lens to the objective lens position in two axes of the focus direction (Z axis in the drawing) and the track direction (Y axis in the drawing). Only the two-dimensional actuator 159 and the carriage 160 carrying them are provided with an access system (mechanism system and control system,
(Not shown) is used to move the magneto-optical disk 7 in the access direction (Y-axis in the drawing) from the inner peripheral position to the outer peripheral position, and other optical components are fixed (hereinafter, this optical system is referred to as a fixed optical system). It is a separate type optical head.

The reflected light 106 from the magneto-optical disk 7 is
Beam splitter 4 through objective lens 6 and reflection mirror 5
It is reflected by the first reflecting surface 4a of the above and goes toward the second reflecting surface 4b. The second reflecting surface 4b of the beam splitter 4 has different reflectances and transmittances between P-polarized light and S-polarized light, for example, P-polarized light transmittance Tp≈0.6, P-polarized light reflectance Rp≈0.4, S.
It has polarization characteristics of polarization transmittance Ts≈0 and S polarization reflectance Rs≈1. The light flux 106 incident on the second reflecting surface 4b is divided into a transmitted light 107 and a reflected light 108.

The light beam 108 reflected by the second reflecting surface 4b of the beam splitter 4 is converted by the lens 15 into a converged light beam 109, which is polarized light separating means for separating the incident light beam into two polarized light beams whose polarization directions are orthogonal to each other. A certain polarizing beam splitter 2
1, and the polarized light beams 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, and respectively enter the photodetector 22. Then, a detection method for obtaining a difference between detection signals of a light receiving region 22a (not shown) that receives the P-polarized light 107p and a light receiving region 22b (not shown) that receives 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 which has passed through the second reflecting surface 4b of the beam splitter 4 passes through the diffraction grating 27 and becomes a convergent light by the detection lens 29, and the cylindrical lens 40 (astigmatism generating means) produces a focus error. After being given astigmatism for detection, the light enters the photodetector 30. The detection of the servo signals (focus error signal and tracking error signal) using the photodetector 30 will be described in detail later.

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

FIG. 4 is a configuration diagram of the beam shaping prism 3 used in the optical head of this embodiment. The beam shaping prism 3 of this embodiment is a measure against stray light (light which is not required to be reflected on the entrance / exit surface, that is, stray light is prevented from entering the semiconductor laser 1 and the photodetectors 32, 22, 30. As a countermeasure, as shown in FIG. 4, the light beam is always refracted and enters or exits on each of the entrance / exit surfaces A1, A2, B1 and B2 of the prism A and the prism B which form the beam shaping prism 3. In addition, the optical axis 101a of the incident light beam 101 to the beam shaping prism 3 and the outgoing 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, B2 is not vertically incident, the reflected light (stray light) is reflected with an inclination with respect to the incident light, so that the semiconductor laser 1,
It does not enter the photodetectors 32, 22, 30.

FIG. 5 shows a semiconductor laser using the photodetector 32.
It is the figure which showed the control method of the light intensity of the laser light of the laser 1. As shown in the figure, the photodetector 32 has two light receiving regions 32a and 32b.
Outputs 33a and 33b from the current-voltage converter 3 respectively
It is input to the laser drive circuit 35 via 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),
The semiconductor laser 1 has at least a protective function 35b for detecting abnormal light emission (light intensity that causes thermal destruction of the information signal on the magneto-optical disk) and stopping the 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, and 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 in which both the output 33a and the output 33b are used. As described above, by using the present configuration for detecting the light beam 105 which is a part of the light beam 100 emitted from the semiconductor laser 1, the light receiving element for detecting the light intensity provided in the conventional semiconductor laser can be used. Can be removed.
In this embodiment, the photodetector has two light receiving regions 32a, 3a.
Although it is 2b, it may be one light receiving region. The light intensity of the luminous flux 100 emitted from the semiconductor laser 1 is controlled by the drive signal 36 from the laser drive circuit 35, and is protected 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 the control signal 37 to the system control circuit 38.
Further, when it is not possible to confirm the light emission of the semiconductor laser 1 or when a decrease in the output due to the deterioration of the semiconductor laser (the required drive current increases at this time) is detected, the system control circuit 38 is similarly controlled. The signal is output. Although not shown in the present embodiment, such a semiconductor laser 1
When an abnormality relating to the light emission of is detected, the system main body has a function of displaying the abnormality, which can be confirmed by the user of the optical information device.

FIG. 6 is a diagram for explaining a method of mounting the beam splitter 4 used in the optical head of this embodiment. Here, as a measure against the above-mentioned stray light, the beam splitter 4 is provided on each incident surface (4 in the figure) as shown in FIG.
A cubic beam splitter 4 in which c) and each output surface (4d in the figure) are parallel or perpendicular to each other is arranged by rotating about 1.5 degrees around the X axis in the figure. At this time, the light fluxes entering the beam splitter 4 (light fluxes 102 and 106 in the figure) and the light flux exiting (the light flux 103 in the figure) are in a parallel relationship, and the optical axis of the light flux after emission (transmission or reflection) is There is no inclination.

Further, each optical component of the fixed optical system of the optical head of the embodiment is attached to the lower surface 210a of the mounting member 210 (hereinafter referred to as the fixed optical system chassis 210) (the objective lens 6 with respect to the magneto-optical disk 7). Is installed 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, and it is possible to prevent dust such as dust from adhering to the surface 4f due to gravity. Therefore, in the optical information device equipped with the optical head of this embodiment,
It is possible to prevent deterioration of optical performance (for example, reduction of light utilization rate) due to adhesion of mixed dust and the like to optical components.

FIG. 7 is a diagram for explaining the construction and operation of the polarization beam splitter 21 which is the polarization separation 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 parallelogram prism 21a. Total reflection films 21d, 21 respectively formed on the flat plate 21b
e and. The polarization beam splitter 21 is
The light beam 109 emitted from the lens 15 is rotated about 45 degrees around the optical axis and arranged. Light flux 10 emitted from the lens 15
Of the polarized light components, the S-polarized light component (polarized light having a vibration perpendicular to the paper surface in the figure) component 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) component perpendicular thereto is reflected. The light passes through the polarizing film 21c, goes straight, is reflected by the total reflection film 21e, and again passes through the polarizing film 21c.
The luminous flux 109s reflected by the polarizing film 21c and the polarizing film 21c
109p transmitted through is reflected by the total reflection film 21d and is incident on the photodetector 22.

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 this embodiment as seen from the direction of the polarization beam splitter 21 of FIG. The photodetector 22 has two light receiving regions 22a and 22b and a conversion circuit 24 that processes the output (current) from the light receiving regions 22a and 22b. The luminous flux 109p and the luminous flux 109s respectively enter the light receiving regions 22a and 22b, and form light spots 110p and 110s, respectively. Light receiving area 22
Output currents 23a and 23b of a and 22b are guided to the conversion circuit 24. The conversion circuit 24 is integrated (integrated into an IC) with electric elements 24a and 24b for converting current into voltage, and electric elements 24c and 24d for addition or subtraction. 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, and the following information). Signal 26) is output. The conversion circuit 24 of the photodetector 22 according to the present exemplary embodiment includes electrical elements 24a and 24 that convert current into voltage.
Only b may be integrated.

The polarization beam splitter 21 and the photodetector 22 are once attached to the attachment member 28 as shown in FIG. Then, 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 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 includes a band-shaped region 27a having no grating and two grating regions 27b and 27c (grating line direction 27d of the present embodiment that sandwich the region 27a and have different grating line directions 27d and 27e). And 27
The angle formed by e is approximately 90 degrees). That is, the band-shaped area 27a and the grid area 27 which do not have a grid
b or the two boundary lines 27f and 27 with the lattice area 27c.
g is parallel, and is arranged so that the direction 27 of the image projected onto 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, in the incident light flux 107, the light in the central portion is incident on the area 27a without the band-shaped grating, and the area 107a where the 0th-order diffracted light and the + 1st-order diffracted light on the information track 7a interfere with each other is almost A substantially semicircle including the light enters the one grating region 27b, and a substantially semicircle including substantially the portion 107b where the 0th-order diffracted light and the −1st-order diffracted light on the information track 7a interfere with each other enters the other grating region 27c. A tracking error signal by the push-pull method can be obtained by detecting the ± first-order diffracted lights from the two grating regions 27b and 27c and comparing the intensities thereof. Also,
The light of the central portion 27a of the diffraction grating and the 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 direct transmitted light.
Further, as shown in the figure, the transmittance of the directly transmitted light of the diffraction grating 27 is high in the central area 27a of the diffraction grating 27 (approximately 1.0 in this embodiment), and the two grating areas 27b, 27 are provided.
c is low (approximately 0.5 in this embodiment). Therefore, as a result, the directly transmitted light is equal to or less than ± 1 with the 0th-order diffracted light on the information track 7a.
Since the intensity of the portions 107a and 107b where the next-order diffracted light interferes is reduced, it is possible to reduce mixing of the track crossing signal into the focus error signal.

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

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

The photodetector 30 has four light-receiving regions 30a to 30d at the center and independent light-receiving regions 30e to 30h around it.

The light of the central portion 27a of the diffraction grating 30 and the 0th-order diffracted light of the two grating regions 27b and 27c, that is, the directly transmitted light are incident on the four-division light receiving regions 30a to 30d of the photodetector 30 as a light spot 31. To do. Therefore, the light receiving area 30
By converting the photocurrents from a and 30c and the photocurrents from the light receiving regions 30b and 30d into voltages with a current-voltage converter (not shown), and inputting them into the differential amplifier 42, astigmatism is obtained. It is possible to obtain a focus error signal according to the method.

On the other hand, the ± first-order diffracted lights diffracted by the grating region 27b are respectively the light receiving regions 30f and 3f of the photodetector 30.
The light spots 41f and 41h are incident on 0h. The ± first-order diffracted light diffracted by the grating region 27c is reflected by the light spots 41 on the light receiving regions 30e and 30g of the photodetector 30, respectively.
It is incident as e, 41 g. Therefore, the light receiving region 30e,
The photocurrent from 30g and the photocurrents 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 to perform tracking by the push-pull method. An error signal can be obtained. At this time, the tracking error signal is received by the light receiving area 30.
The difference between the incident light intensity signals of h and 30 g, or the light receiving region 30
It can also be obtained from the difference between the incident light intensity signals of e and 30f.

In FIG. 12, the light receiving areas 30e to 30h.
The substantially semicircular shape of the images of the upper light spots 41e to 41h is rotated 90 degrees with respect to the shape on the diffraction grating 27, because the cylindrical lens 40 imparts astigmatism. Since it is not the shape of the image that is detected by the light receiving regions 30e to 30h 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 has a light receiving region 30.
The sum of the incident light intensity signals of e to 30h, or the light receiving region 30
The sum of the incident light intensity signals of e and 30f, or the light receiving area 3
It is also obtained from the sum of the incident light intensity signals of 0a to 30d and the sum of the total light receiving regions 30a to 30h.

By the way, the adjustment of the so-called focus error signal, that is, the adjustment of the focus error signal to a predetermined value when in focus on the disc, is performed by the detection lens 29 and the cylindrical lens 40 in FIG. Can be carried out by integrally moving in the direction 117 of the incident light axis of the incident light 107. Alternatively, the photodetector 30 may be moved in the optical axis direction. Further, in the just tracking state on the disk, the adjustment is performed so that the tracking error signal becomes a predetermined value, that is, the so-called tracking error signal is adjusted by setting the diffraction gratings 27 in parallel with each other in FIGS. This is done by moving in a direction 118 perpendicular to the two boundary lines 27f and 27g. Since this adjustment is performed on the light beam 107 that is parallel light, no tilt occurs in the light beam that has passed through the diffraction grating 27 as in the conventional example. There is also no amount of aberration such as astigmatism. Therefore, the focus error signal adjusted in advance does not come into the adjusted state due to the adjustment of the tracking error signal by moving the diffraction grating 27. As described above, focus adjustment and tracking adjustment can be performed independently.

As described above in detail, the optical head of this embodiment has one system of the focus error signal by the astigmatism method and the tracking error signal by the push-pull method without degrading the magneto-optical signal. In this case, it is possible to detect all of them at once and reduce the mixture 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 the light source changes, the light spot 31 on the four-divided light receiving regions 30a to 30d does not move, and a correct focus error signal can be obtained.

Since the ± 1st-order diffracted light from the diffraction grating 27 is used to detect the tracking error signal, the light spots 41e to 41h on the light receiving regions 30e to 30h move due to the wavelength fluctuation of the semiconductor laser 1. Light receiving area 3
In 0e to 30h, the amount of light incident on each area is detected. Therefore, the size of the light receiving areas 30e to 30h is set to the light spot 41.
There is no problem if it is designed in consideration of the movement of e to 41h. In the detection of tracking error signal by push-pull method,
When the objective lens moves following the information track of the disc, the reflected light from the disc also moves accordingly, causing an offset in the detected tracking error signal. However, in the present embodiment, as the tracking error signal, in the incident light flux 107 of the diffraction grating 27, the central light is the area 2 without the band-shaped grating in FIG.
The light incident on 7a is not used, but the light incident on the grating regions 27b and 27c, that is, the light on the portions 107a and 107b where the 0th-order diffracted light and the ± 1st-order diffracted light on the information track 7a interfere is detected. Therefore, it also has an advantage that the offset of the tracking error signal due to the movement of the objective lens can be reduced.

Next, referring to FIG. 13, a method of aligning the intensity center Ic of the light beam 103 incident on the objective lens 6 and the objective lens center Oc will be described. In the separable optical head as in the present embodiment, the position is located at the intensity center Ic of the incident light beam 103 and the objective lens center Oc due to the inclination of the light emitting portion of the semiconductor laser 1 or the mounting error of the optical components and the access system. There will be a shift. This misalignment adversely affects the focus error signal and the tracking error signal (for example, the offset of the focus error signal caused by the misalignment of the optical components due to temperature or the like increases). Therefore, in this embodiment, as shown in FIG.
, The tangential direction (X axis) of the objective lens center Oc and the intensity center Ic of the incident light beam 103 to the magneto-optical disk 7.
The positional deviation dX 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 this embodiment, the reference surface 3 of the mechanical chassis 350 is arranged so that the fixed optical system chassis 210 does not move in the Z-axis direction in the drawing.
The fixed optical system chassis 210 is moved in parallel with reference to 50a (a plane parallel to the tangential direction (X axis) of the disk 7 and perpendicular to the Y axis in the radial direction). On the other hand, the center O of the objective lens
The radial displacement (Y axis) of the magneto-optical disk 7 between the c and the intensity center Ic of the incident light beam 103 is dY. As shown in FIG. 14, the mounting position of the two-dimensional actuator 159 is set to the reflection mirror-5. On the other hand, in the radial direction of the disk 7 (Y axis)-
It is adjusted by moving dY. Ie 2
Dimensional actuator 159 is attached to member 158 and reflective mirror 5 is attached to carriage 160, where member 15 is attached.
By attaching 8 to the carriage 160, the two-dimensional actuator 159 is fixed 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 constitutional view showing the constitution of an optical head as a second embodiment of the present invention.

In FIG. 15, the same reference numerals as those in FIG. 1 showing the structure of the optical head of the first embodiment indicate the same parts. In the optical head of this embodiment, a light beam 100 (S-polarized) emitted from a semiconductor laser 1 (with a high frequency superposition circuit 1a) as a light source is collimated by a collimating lens 49 into a parallel light beam 130.
And the polarization direction is 90 degrees after passing through the half-wave plate 50.
It becomes a light beam 131 (P-polarized light) that has been rotated, and the reflection mirror
The light path is deflected by 90 degrees at 19 and enters the first beam splitter 4 to form a light spot 170 on the magneto-optical disk 7. FIG. 16 shows the information track 7 of the magneto-optical disk 7.
The relationship between a, the intensity of the light spot 170, and the polarization direction is shown.
The light spot 170 is an oval spot that is long in the direction perpendicular to the information track 7a (disk radial direction), and the 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 photo detector 22 and as a servo signal by the photo detector 30 is the same as that of the optical head of the first embodiment. Omitted because it is the same. In addition, in the optical head of this embodiment, as shown in FIG.
The beam shaping prism 3 for correcting the light intensity of the semiconductor laser 1 used in the above optical head is removed. However, the configuration is not limited to this. An example of another configuration is shown below.

FIG. 17 is a structural diagram showing the structure of an optical head as a third embodiment of the present invention.

In FIG. 17, the first and second aspects of the present invention
1 and 15 showing the configuration of the optical head of the embodiment of FIG.
The same reference numerals as in FIG. In the optical head of this embodiment, the light beam 100 (S-polarized) emitted from the semiconductor laser 1 (with the high-frequency superimposing circuit 1a) as a light source is collimated.
The parallel light flux 130 is formed by the lens 49 and enters the first reflecting surface 55 a of the first beam splitter 55.
The first reflecting surface 55a of the beam splitter 55 has different reflectance and transmittance between P-polarized light and S-polarized light, for example, P-polarized light transmittance Tp≈1, P-polarized light reflectance Rp≈0, S-polarized light transmittance Ts≈. It has a polarization characteristic of 0.2 and S-polarized light reflectance Rs≈0.8. The light flux 130 (S
Polarized light is divided into transmitted light 131 (not shown) and reflected light 132.
Be divided.

Of these, the reflected light 132 is incident on the second reflecting surface 55b of the first beam splitter 55. The second reflection surface 55b of the beam splitter 55 has different reflectances and transmittances between P-polarized light and S-polarized light, for example, P-polarized light transmittance Tp≈1, P-polarized light reflectance Rp≈0, S-polarized light transmittance Ts≈.
It has a polarization characteristic of 0.2 and S-polarized light reflectance Rs≈0.8. The light flux 132 (S-polarized) incident on the second reflecting surface 55b is divided 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 beam 135 (P-polarized light) rotated by 90 degrees, and is emitted from 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, 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 to prevent dust and the like from entering. 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.
Is detected as a magneto-optical signal by the beam splitter 55, transmitted through the second reflecting surface 55b and the first reflecting surface 55a of the beam splitter 55, and detected by the photodetector 22 as a servo signal. The process up to the detection is the same as that of the optical head of the first embodiment, and 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 polarization direction of the information track 7a and the light spot 170 of the magneto-optical disk 7 shown in FIG. 16 is obtained. be able to. When 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 is used.
0 may be made transparent or removed.

The diffraction grating 27 used in the optical head of the above-mentioned embodiment has different diffraction directions, but the diffraction direction is not limited to this, and as shown in FIG. 18, the spacing between the lattice lines (lattice pitch).
May be different from each other. FIG. 18 is a front view showing the structure of the diffraction grating 57. The diffraction grating 57 includes a band-shaped area 57a having no grating and the area 57a.
With two grid regions 57b and 57c having different grid pitches P1 and P2. That is, the belt-shaped region 57a and the lattice region 57b having no lattice
Or two boundary lines 57f and 57g with the lattice area 57c
Are parallel to each other and are arranged so that the directions 57 of the images projected onto the diffraction grating 57 of the information track 7a of the magneto-optical disk 7 coincide with each other at the center 57h of the two boundary lines.
Therefore, in the optical head of FIG. 1, as shown in FIG. 11, the light in the central portion of the incident light beam 107 is incident on the region 57a having no band-shaped grating, and the 0th-order diffracted light on the information track 7a is equal to +1. A substantially semicircle that substantially includes a portion 107a where the second-order diffracted light interferes is incident on one grating region 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 including almost 07b is incident on the other lattice region 57c. A tracking error signal by the push-pull method can be obtained by detecting the ± first-order diffracted lights from the two grating regions 57b and 57c and comparing the intensities thereof. Further, the focus error signal by the astigmatism method can be detected using the light of the central portion 57a of the diffraction grating and the 0th-order diffracted light of the two grating regions 57b and 57c, that is, the direct transmitted light. Also, as shown in FIG. 11,
The transmittance of the directly transmitted light of the diffraction grating 57 is higher in the inner central area 57a of the diffraction grating 57, and the two grating areas 57 are higher.
b and 57c are low. Therefore, as a result, the intensity of the directly transmitted light in 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 reduced, so that mixing 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 uses a single optical system for the focus error signal by the astigmatism method and the tracking error signal by the push-pull method without degrading the magneto-optical signal. It is possible to collectively detect and reduce the mixture 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 on / from a magneto-optical information recording medium, a focus error signal by an astigmatism method can be obtained without degrading the magneto-optical signal. The tracking error signal by the push-pull method can be collectively detected 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 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 illustrating 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 diagram illustrating the intensity detection of the 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 for mounting a beam splitter used in the optical head according to the first embodiment of the present invention.

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

FIG. 8 is a diagram illustrating a method of mounting the polarization beam splitter.

FIG. 9 is a front view showing the 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 the configuration of the diffraction grating used in the optical head as the first embodiment of the present invention.

FIG. 11 is a diagram illustrating the light utilization rate of the 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 diagram for explaining position adjustment of the center of the objective lens and the center of light intensity (in the disc tangential direction) in the optical head as the first embodiment of the present invention.

FIG. 14 is a diagram for explaining position adjustment (in the disc 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 showing 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 as 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 ... Polarization beam splitter, 22 ... Photodetector for magneto-optical signals, 27 ... Diffraction grating, 29 ... Detection lens, 40 ... Cylindrical lens, 30 ... Ser
BO signal photo detector

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuo Kitada 2880 Kunizu Jinzu, Odawara, Kanagawa Stock Company Hitachi Storage Systems Division (72) Inventor Kuniichi Onishi 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Inside Hitachi Media Media Research Laboratories

Claims (8)

[Claims] 1. A semiconductor laser for emitting a laser beam, a collimating lens for converting divergent light emitted from the semiconductor laser into parallel light, and a laser beam for condensing the laser beam to produce an optical beam. An objective lens that irradiates a recording surface on which a track is formed in an information recording medium as a light spot and focuses a laser beam reflected on the recording surface, and guides the laser light to the objective lens at the same time. A first beam splitter for separating a part of the laser light and for separating a reflected light beam from the recording surface from an optical path connecting the semiconductor laser and the magneto-optical information recording medium; A diffraction grating that is composed of a plurality of regions having different directions or different diffraction angles, diffracts the reflected light beam (or transmitted light beam) separated by the first beam splitter, and emits it as diffracted light, and the diffracted light from the diffraction grating. 0 first for receiving, including order diffracted light
And the astigmatism that gives astigmatism to the reflected light beam (or transmitted light beam) from the first beam splitter to the diffraction grating or the diffracted light from the diffraction grating to the first photodetector. A focus error signal according to the size of the spot diameter of the light spot irradiated on the optical information recording medium, from the 0th-order diffracted light received by the first photodetector. A tracking error according to the amount of positional deviation from the track of the light spot irradiated on the optical information recording medium from the ± first-order diffracted light detected by the astigmatism method and received by the first photodetector. In the optical head for detecting the information signal and the information signal on the recording surface from the 0th order diffracted light or the ± 1st order diffracted light, the diffraction grating does not have a grating. The band-shaped region and a grating region sandwiching the region and having different diffraction directions or angles from each other, and the two boundary lines of the belt-shaped region having no grating and the grating region are parallel to each other. Optical head to do. 2. A semiconductor laser for emitting a laser beam, a collimating lens for converting divergent light emitted from the semiconductor laser into parallel light, and a laser beam for condensing the laser beam. When an objective lens for irradiating a recording surface on which a track is formed in a physical information recording medium as a light spot and for condensing a laser beam reflected on the recording surface, and for guiding the laser light to the objective lens At the same time, a first beam splitter which separates a part of the laser light and separates a reflected light beam from the recording surface from an optical path connecting the semiconductor laser and the magneto-optical information recording medium, The laser beam separated (reflected or transmitted) by the first beam splitter is reflected and transmitted by the reflected beam from the recording surface,
A second beam splitter that splits a reflected light beam and a transmitted light beam into two light beams, and a transmitted light beam (or a reflected light beam) split by the second beam splitter into two polarized light beams whose polarization directions are orthogonal to each other. The polarization beam splitting means, a first photodetector for receiving the two polarized light beams split by the polarization beam splitting means, a plurality of regions having different diffraction directions or diffraction angles, and the second beam splitter A diffraction grating that diffracts the separated reflected light flux (or transmitted light flux) and emits it as diffracted light,
A second photodetector for receiving the diffracted light from the diffraction grating including the 0th-order diffracted light, and a reflected light beam (or a transmitted light beam) from the second beam splitter to the diffraction grating or the diffraction grating to the first light beam. At least astigmatism generating means for giving astigmatism to the diffracted light reaching the second photodetector, and detecting the information signal on the recording surface by the first photodetector, From the 0th-order diffracted light received by the photodetector, a focus error signal corresponding to the size of the spot diameter of the light spot applied to the magneto-optical information recording medium is detected by the astigmatism method, and the second error is detected. An optical head for detecting a tracking error signal according to the amount of positional deviation of the light spot applied to the magneto-optical information recording medium from the track from the ± 1st-order diffracted light received by the photodetector. The diffraction grating is a band-shaped region having no grating, and a grating region sandwiching the region and having diffraction directions or angles different from each other, and a band-shaped region having no grating and a grating region. An optical head characterized in that the two boundary lines of are parallel. 3. A semiconductor laser that emits a laser beam, a collimating lens that converts divergent light emitted from the semiconductor laser into parallel light, and anisotropy of the laser light. A beam-shaping prism that converts the light into a direction and a laser beam are condensed and irradiated as a light spot on the recording surface of the magneto-optical information recording medium on which tracks are formed, and on the recording surface. An objective lens for condensing the reflected laser beam and a laser beam that has passed through the beam shaping prism are guided to the objective lens and at the same time a part of the laser beam is separated, and on the recording surface. From a first beam splitter for separating the reflected light beam from the optical path connecting the semiconductor laser and the magneto-optical information recording medium, and the semiconductor laser separated by the first beam splitter. Detecting a part of the emitted laser light And a second beam for reflecting and transmitting the laser light flux separated by the first beam splitter by the reflected light flux from the recording surface and separating it into two light fluxes, a reflected light flux and a transmitted light flux. The splitter and the transmitted light beam (or reflected light beam) separated by the second beam splitter have their polarization directions orthogonal to each other.
And a second photodetector for respectively receiving the two polarized light beams separated by the polarized light separation unit, and a plurality of regions having different diffraction directions or angles. A diffraction grating that diffracts the reflected light beam (or transmitted light beam) separated by the second beam splitter and emits it as diffracted light, and third light detection that receives the diffracted light from this diffraction grating including the 0th-order diffracted light. And an astigmatism generating means for giving astigmatism to the reflected light beam (or transmitted light beam) from the second beam splitter to the diffraction grating or the diffracted light from the diffraction grating to the third photodetector. At least, the information signal on the recording surface is detected by the second photodetector, and the magneto-optical information recording is performed from the 0th-order diffracted light received by the third photodetector. A focus error signal corresponding to the size of the spot diameter of the light spot irradiated on the recording medium is detected by the astigmatism method, and the ± 1st-order diffracted light received by the third photodetector is used to detect the magneto-optical signal. In an optical head for detecting a tracking error signal according to a positional deviation amount of a light spot irradiated on an information recording medium from the track, the diffraction grating includes a belt-shaped area having no grating, and the area. Therefore, the optical head is characterized in that the gratings have different diffraction directions or diffraction angles from each other, and two boundary lines of the band-shaped area having no grating and the grating area are parallel to each other. 4. A beam of light that enters or exits the beam shaping prism is refracted at each of the incident surface and the exit surface and is incident on the beam shaping prism. 4. The optical axis and the optical axis of the emitted light beam are configured to be parallel or perpendicular to each other.
The optical head described in 1. 5. The polarization separating means and the first or second photodetector for detecting the light beams polarized and separated by the polarization separating means are provided on the same mounting member, and the mounting member is an optical chassis. The optical head according to any one of claims 2 to 4, wherein the optical head is attached to and fixed to. 6. The first and second beam splitters have a cubic shape in which the outer shape of the beam splitter is an incident surface on which light enters or exits, or an outgoing surface is parallel or vertical, and The optical head according to claim 1, wherein the optical head is rotated around an incident optical axis or an axis perpendicular to the incident optical axis. 7. A semiconductor laser for emitting a laser beam, a collimating lens for converting divergent light emitted from the semiconductor laser into parallel light, a reflection mirror for deflecting an optical path, and a laser. An objective lens which collects a light beam and irradiates it as a light spot on a recording surface on which a track is formed in an optical information recording medium, and collects a laser light beam reflected on the recording surface; First, the laser light is guided to the objective lens, and at the same time, a part of the laser light is separated, and the reflected light flux from the recording surface is separated from an optical path connecting the semiconductor laser and the optical information recording medium. Beam splitter and a photodetector for detecting reflected light from the optical information recording medium, and the objective lens, an actuator for driving the objective lens to at least the focus, and a reflection mirror. Only less An optical head mounted on the same carriage and movable in the access direction of the optical information recording medium, the reflection mirror is mounted on the carriage, and the objective lens and the actuator mounting the objective lens are mounted on a member. 7. The member is fixed by being attached to the carriage.
The optical head described in 1. 8. An optical information recording medium, a rotating system for rotating the optical information recording medium, an optical head for reproducing or recording an information signal on a recording surface of the optical information recording medium, and an optical head. An optical information device comprising at least an access system movable in an access direction of the optical information recording medium and a system control circuit for controlling the entire device, wherein the optical head is the optical head according to any one of claims 1 to 7. An optical information device characterized in that