JPH0191344A - Pickup for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To miniaturize the title pickup and to reduce the weight of the pickup by detecting an error and information by making a reflected beam going forward in a light guide detect P and S polarization components branched by a light transmittable member formed of a uniaxial anisotropic crystal material. CONSTITUTION:The light beam 15 emitted from a semiconductor laser 16 is transmitted through the light guide 29 and is converged by an objective lens 18 so as to be focused on the reflection surface 14 of an optical disk 13. The reflected beam 15 from the disk 13 is diffracted at FGs 31,32, and made incident on the guide 29 and is transmitted through the light transmitted member 22 formed of the uniaxial anisotropic crystal material and is separated into the P polarization component 15P and the S polarization component 15S. The P polarized component 15P is detected by photodectectors 24, 25, and the S polarization component 15s is detected by the photodetectors 26,27. By processing the outputs of the photodetectors 24-27 recorded information can be read by a read circuit and the lens 18 can be shifted through a tracking coil driving control circuit and a focus coil driving control circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is a pickup for reading signals recorded on a magneto-optical recording medium such as a magneto-optical disk. The present invention relates to a pickup that can be formed in the following manner.

(Prior Art) Recently, magneto-optical recording media such as magneto-optical disks have been widely used as recording media for image signals, audio signals, etc. Signals recorded in the magneto-optical recording medium in the form of magnetization directions are read by an optical pickup. This pickup utilizes a phenomenon (magnetic Kerr effect) in which the surface of a magneto-optical recording medium is irradiated with linearly polarized light such as a laser beam, and the plane of polarization of the light reflected on the recording medium rotates in accordance with the direction of magnetization. The direction of magnetization on the recording medium is detected.

Specifically, in this pickup for magneto-optical recording media, reflected light from the recording medium is detected by a photodetector through an analyzer, and the amount of detected light changes depending on the rotation of the polarization plane of the reflected light. The direction of the magnetization, that is, the recorded information is read. In addition, in this pickup, recorded information is read as described above, and a light beam for tracking error detection, that is, magnetization state detection, is irradiated with a deviation to the left or right from the center of the track along a predetermined group. and focus error detection, that is, a function to detect whether the focus of the light beam is closer or farther than the reflective surface of the magneto-optical recording medium. It will be done. In other words, this tracking error and focus error detection signal is used to apply tracking control and focus control so that the signal is canceled out, and in order to correctly irradiate the light beam onto a predetermined track, and to direct the light beam to the magneto-optical recording medium. Used for correct focusing on reflective surfaces. Conventionally, the push-pull method, heterogain method, time difference detection method, etc. have been known as tracking error detection methods, while the astigmatism method, critical angle detection method, Foucault method, etc. have been known as focus error detection methods. Are known.

In order to provide the above-mentioned functions in addition to the signal reading function, conventional pickups for magneto-optical recording media separate the beam reflected by the magneto-optical recording medium from the light beam directed toward the medium. a beam splitter, a lens for focusing this reflected beam near a photodetector such as a photodiode, the above-mentioned analyzer, and a prism for carrying out the above-mentioned tracking error detection method and focus error detection method. It was composed of micro optical elements such as.

(Problem to be solved by the invention) However, the above-mentioned microscopic optical elements require precise processing;
Further, since mutual position adjustment is troublesome when assembling the pickup, a pickup using such an optical element is necessarily expensive. Furthermore, a pickup with this configuration is large and heavy, so
This is disadvantageous in terms of making the reading device smaller and lighter and shortening the access time. In particular, when performing differential detection to improve the S/N of the read signal, the reflected beam is
A half mirror or the like is required to divide the book into books, and depending on the differential detection optical system, two analyzers may be required, making the pickup even more complex, large and heavy.

In order to solve the above-mentioned problems, various attempts have been made to simplify the configuration of the pickup by using special optical elements such as aspherical lenses. However, since this type of optical element is particularly expensive, a pickup using such an element is not much different from the above-mentioned pickup in terms of cost, even if the structure is simplified.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a pickup for a magneto-optical recording medium that is small, lightweight, and can be formed at extremely low cost.

(Means for Solving the Problems) The magneto-optical recording medium pickup of the present invention includes the above-mentioned beam splitter, lens, prism, analyzer, and even a half mirror for performing differential detection. The effect is obtained by a light guide equipped with a light-transmitting member made of a light-converging diffraction grating and a uniaxially anisotropic crystal. a light source that irradiates a light beam, an objective lens that focuses the light beam on a reflective surface of a magneto-optical recording medium, and a light that is oriented such that one surface receives the reflected beam reflected by the magneto-optical recording medium. A first guide is provided at each of the reflected beam irradiation positions of the light guide, and a first guide for making the reflected beam enter the light guide.
A second condensing diffraction grating is arranged in parallel, and the first. The second light-concentrating diffraction gratings are arranged across an axis that passes approximately through the center of the reflected beam that illuminates the light guide and extends approximately perpendicularly to the tracking direction on the surface of the light guide, and each of the second condensing diffraction gratings focuses the reflected beam on the light guide. Total reflection is repeated between the one surface and the other surface facing it, and the reflected beam is made to enter the light guide in the direction of traveling toward the end face, and the reflected beam traveling inside the light guide is directed across the axis. On the other hand, inside the light guide, in the optical path portion of the reflected beam that travels through repeated total reflection as described above, a beam that is oblique to the traveling direction of the reflected beam is formed. A light-transmitting member made of a uniaxial anisotropic crystal having a passage surface and branching the P-polarized light component and the S-polarized light component of the reflected beam into different optical paths is disposed, and on the surface or end surface of the light guide, A photodetector is installed to detect the P-polarization component or the S-polarization component of each reflected beam focused by at least the first and second condensing gratings, and the tracking error is determined based on the outputs of these photodetectors. and an error detection circuit for detecting focus errors; and a signal detection circuit for detecting recorded information based on the output of the photodetector.

The light-converging diffraction grating is a diffraction grating having a curve and a chirve or a 6' curve, diffracts the incident light to enter the light guide, and focuses the diffracted light.

(Function) By capturing the reflected beam from the magneto-optical recording medium into the light guide using the above-mentioned condensing diffraction grating, the reflected beam is separated from the optical path of the light beam traveling from the light source toward the magneto-optical recording medium. This is the same effect as the beam splitter described above. The focusing grating also focuses the reflected beam within the light guide, similar to the function performed by the lenses described above. Furthermore, the first and second
Since the two light-converging diffraction gratings are arranged at the positions described above, the reflected beams from the magneto-optical recording medium are separated from each other in the tracking direction and focused at two points. This is the same effect as the prism described above.

In addition, since the reflected beam is separated into a P-polarized light component and an S-polarized light component by a light-transmitting member made of an axially anisotropic crystal, for example, each reflected beam is focused by the first and second condensing diffraction gratings. The first . If a second photodetector and third and fourth photodetectors each detect the S-polarized component of each reflected beam focused by the first and second condensing diffraction gratings are provided, it is possible to mutually 1. detecting beams of different polarization components; The output of each of the third photodetectors varies complementarily depending on the polarization direction of the reflected beam. Also, the second. The same applies to each output of the fourth photodetector. Therefore, for example, the above 1. the sum of the outputs of the second photodetector; and the sum of the outputs of the second photodetector; By detecting the difference from the sum of the outputs of the fourth photodetector using a differential detection circuit, the polarization direction of the reflected beam, that is, the information recorded on the magneto-optical recording medium can be read. Thereby, a read signal with a high S/N ratio can be obtained, similar to the case where a differential detection optical system is provided to perform differential detection. That is, by the above-mentioned light-transmitting member,
The beam splitting effect achieved by the above-mentioned half mirror etc. can be obtained, and the effect achieved by the above-mentioned analyzer can also be obtained.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a pickup for a magneto-optical recording medium according to a first embodiment of the present invention, and FIG. 2 shows the planar shape and electric circuit of a light guide of this pickup. As shown in FIG. 1, this pickup has a block 12 that is movable along a rod 11.11 extending in a direction substantially perpendicular to the plane of the paper. In order to follow a signal train (track) along a predetermined group, this block 12 is operated in a direction perpendicular to the direction of the track (in the direction of arrow U at the beam irradiation position) using, for example, a precision feed screw and an optical system feed motor. , or in a direction close to it.

The block 12 includes a reflective surface 1 of the magneto-optical disk 13.
Light beam (laser beam) linearly polarized toward 4 15
A semiconductor laser 16 that emits , a collimator lens 17 that converts the diverging beam emitted from the semiconductor laser 16 into parallel beats, and an objective lens 18 that focuses the parallel light beam 15 on the reflective surface 14 are attached. It is being This objective lens 18 is supported so as to be movable in the tracking direction (direction perpendicular to the direction of arrow U) and the focus direction (direction of arrow V) for tracking control and focus control, which will be described in detail later. 20, respectively, so as to be moved in the above-mentioned directions.

A flat light guide 29 made of, for example, optical glass is disposed between the collimator lens 17 and the objective lens 18 and is oriented such that its surface 29a receives the reflected beam 15' reflected by the magneto-optical disk 13. ing.

Further, on the surface 29a of the light guide 29 at the position where the reflected beam 15' is irradiated, there is a second focusing grating (hereinafter referred to as ml).
(referred to as FC) 31 and 32 are provided adjacent to each other (see Fig. 2). These FGs 31, 32 are curved and chirped or curved diffraction gratings, each of which diffracts the reflected beam 15' into the light guide 29.
the inside of the light guide 29 and one surface 29 of the light guide 29.
The light guide 29 is formed so that total reflection is repeated between the light guide 29a and the other surface 29b, the light propagates toward the end surface, and is focused at one point within the light guide 29. 1st. second FC31,
32 is a point (
They are arranged in parallel across the y-axis (in Figure 2), and each has a reflected beam of 15° at a position separated from each other across the y-axis.
It is formed to focus.

As shown in FIG. 2, the light guide 29 is arranged in such a direction that the angle φ between the linear polarization direction of the reflected beam 15° (direction of arrow H) and the X-axis is approximately 45°. Note that the direction of the linearly polarized light of the reflected beam 15' rotates in accordance with the direction of magnetization in the magneto-optical disk drive 3, so in this example, the direction of the linearly polarized light of the reflected beam 15' reflected from the non-magnetized portion is The direction is used as a reference, and this direction and the X axis form an angle of 45 degrees. Furthermore, FG
31 and 32 may be provided on the surface 29b of the light guide 29 opposite to the surface 29a.

The m-th lattice pattern shape formula of FG81.32, which performs the above-mentioned action, defines the spatial coordinates as shown in Figure 2 between the X-axis (tracking direction axis) and the y-axis, and the intersection of these axes with both axes. FG31.3 defined by the perpendicular z-axis
2 (as indicated by the dot in Fig. 1,
(-Fx, Fy, Fz), (Fx, Fy,
Fz), and the refractive index of the light guide 29 is 01,
If the optical wavelength of the 15° reflected beam is λ, it is given by -mλ+const (decoded in the same order with xJO).

The above FC31, 32 is 5L-N on the light guide 29.
It can be formed by a method such as forming a film by PCVD, forming a resist pattern by electron beam direct writing, and then transferring it to a 5i-N film by RIE.

Inside the light guide 29, there is a -axis anisotropic crystal T i
A transparent member 22 made of 02 is provided.

Note that it is desirable that an anti-reflection coating be applied to the interface between the light guide 29 and the uniaxially anisotropic crystal. This light-transmitting member 22 covers the entire width of the light guide 29, for example, so that both the reflected beam 15' focused by the first FG 31 and the reflected beam 15° focused by the second FG 32 can pass through. The length it spans is H. Further, the light-transmitting member 22 is arranged such that its optical axis extends in a direction perpendicular to the paper surface of FIG. 1 (X-axis direction in FIG. 2). Further, this light-transmitting member 22 allows the reflected beam 15゜
Beam passing surfaces 22a, 22b oblique to the traveling direction of
It is said that the shape has the following. Therefore, this transparent member 2
The reflected beam 15' passing through 2 is refracted as shown in FIG. , -2,872, no-2,584)
Since the transparent member 22 is formed of TiO2,
The S polarization component 15S of the reflected beam 15' is the P polarization component 1.
5P, and these components 15sS15P
separate from each other and converge. In addition, the light guide 29 includes the reflected beams 15 separated into four systems as described above.
An end face 29c is provided which is diagonally cut so as to extend along each focusing position. And this end face 29c
At the top, the first of the four reflected beams 15' is shown.
Pl-light component 1 focused by second FG31.32
．． The first and second photodetectors 24 detect 5P, respectively.
25 and 1st. The third. A fourth photodetector 26.27 is attached. The first photodetector 24 consists of photodiodes PD1 and PD2 divided into two by a gap extending parallel to a plane perpendicular to the light guide surface 29a through the y-axis, and the other photodetectors 25
．． 2ft and 27 are also similar photodiodes PD3 and PD4. PD5 and PD6 and PD7 and PD8
Consisting of

As shown in detail in FIG. 3, the photodiode PDI has a lower transparent electrode 28a on the light guide 29.
, a thin film photoconductive material 28b1 and an upper electrode 28c are loaded in this order. A power source 28d is connected between the lower transparent electrode 28a and the upper electrode 28c.
A predetermined electric field is applied from the

In the photodiode PDI having this configuration, when the photoconductive material 28b is irradiated with light, a photocurrent flows according to the amount of light. Therefore, by detecting the potential change at the terminal 28e, the amount of light received by the photoconductive material 28b can be detected. Photodiodes PD2 to PD8 are also formed similarly to photodiode PDI. Note that the thin film photoconductive material 28b is made of, for example, 5iSGe, I
Se of group V.

GaAs of m-v group, Zn0SCdS of U-Vl group.

It can be formed from an epitaxial film such as PbS of the IV-Vl group, a polycrystalline film, an amorphous film, etc., and an amorphous chalcogen film (a-8e, a-6e-As-Te, etc.),
A film mainly composed of amorphous Si and containing hydrogen and/or fluorine (a-8t:H, a-5iGe:HSa-5iC:
A film that forms a photodiode by obtaining a p-n junction or a p-1-n junction by adding atoms of group Ⅰ or group V (B, P, etc.) to (H, etc.); And/or it can also be formed from a film that forms a photodiode using a film containing fluorine and an electrode that forms a Schottky junction.

Further, an external photodiode may be brought into close contact with the end surface 29c. In this case, it is desirable to apply anti-reflection coating to the end face 29c.

As shown in FIG. 2, photodiodes PDI and PD2 detect the P-polarized component of the reflected beam 15'';
The outputs of PD 3 and PD 4 are added by adding amplifiers 34 and 35, respectively, while a photodiode P detecting the S polarization component
The outputs of D5 and PD6, and PD7 and PD8 are added by adding amplifiers 36 and 37, respectively.
The outputs of 4 and 35 and the outputs of summing amplifiers 36 and 37 are summed by summing amplifiers 38 and 39, respectively. Further, the outputs of these adding amplifiers 38 and 39 are outputted to the differential amplifier 4.
0, and the output D1 of this differential amplifier 40 is input to the reading circuit 41.

On the other hand, the first FG 31 detects the reflected beam 15' focused by the first FG 31. The outputs of the outer photodiodes PDI and PD5 of each of the third photodetectors 24 and 26 are connected to the summing amplifier 4.
2 and the inner photodiodes PD2 and PD6
The outputs of are added by an adding amplifier 43. Also the second FG
The second .32 detects the reflected beam 15° focused at 32. The outputs of the outer photodiodes PD4 and PD8 of each of the fourth photodetectors 25 and 27 are added by a summing amplifier 45,
The outputs of the inner photodiodes PD3 and PD7 are added together by a summing amplifier 44. And the above summing amplifier 42.4
The outputs of 3 are added by the addition amplifier 4B, and the outputs of the addition amplifier 44
．． The outputs of 45 are added by an adding amplifier 47. On the other hand, the outputs of the summing amplifiers 42 and 45 are added by the summing amplifier 48,
The outputs of the summing amplifiers 43 and 44 are added by the summing amplifier 49.

Furthermore, the output of the adding amplifiers 46 and 47 is the differential amplifier 50.
The outputs of the adder amplifiers 48 and 49 are input to the differential amplifier 51. And the output D2. of the differential amplifier 50.51. D3 is input to a tracking coil drive control circuit 52 and a focus coil drive control circuit 53, respectively.

Next, the operation of the pickup configured as described above will be explained. A parallel light beam (laser beam) 15 emitted from the semiconductor laser 16 passes through the light guide 29 and is focused by the objective lens 18 so as to be focused on the reflective surface 14 of the magneto-optical disk 13 . The magneto-optical disk 13 is driven by a rotational drive means (not shown) to drive the light beam 1.
At the irradiation position 5, the track is rotated to move in the direction of arrow U.

As is well known, the track is a row of image signals, audio signals, etc. recorded in the form of magnetization directions (indicated by arrows above the reflective surface 14 in FIG. The orientation of the 15° linear polarization rotates in opposite directions depending on the orientation of the magnetization compared to the orientation of the linear polarization of the reflected beam 15' from the unmagnetized portion. In other words, the polarization direction of the reflected beam 15' from a part magnetized in a certain direction rotates clockwise from the polarization direction shown by arrow H in Figure 2, and the direction of polarization of the reflected beam 15' from a part magnetized in the opposite direction rotates clockwise. The direction of polarization of the reflected beam 15° is
Rotate counterclockwise from the polarization direction indicated by arrow H above.
.

This reflected beam of 15° passes through the objective lens I8 and
The light is diffracted at points 31 and 32 and enters the light guide 29. Reflected beam 15° incident on light guide 29
The beam propagates through repeated total reflection between the one surface 29a and the other surface 29b, and is focused at a position across the y-axis due to the beam focusing action of each of the FGs 31 and 32. Here, as described above, each reflected beam 15° transmitted through the transparent member 22 is separated into a P polarization component 15P and an S polarization component 15S.

This P polarized light component 15P is detected by the first photodetector 24 (
photodiodes PDI and PD2), second photodetector 2
5 (photodiodes PD3 and PD4), while the S-polarized component 15s is detected by the third photodetector 2, respectively.
6 (photodiodes PD5 and PD6) and a fourth photodetector 27 (photodiodes PD7 and PD8). Here, if the direction of the linearly polarized light of the reflected beam 15° is rotated clockwise from the direction indicated by the arrow H, the P polarized light component 15P of the reflected beam 15' traveling in the light guide 29 increases, while the S polarized light Component 15S decreases. If the direction of the linearly polarized light of 15° of the reflected beam is rotated counterclockwise with respect to the direction of arrow H, the above will be reversed. If the P-polarized light component increases as described above, the output of the summing amplifier 38 increases, while the output of the summing amplifier 39 decreases.

The opposite is true when the S polarization component 15s increases. Therefore, for example, if the gains of the summing amplifiers 38 and 39 are appropriately set, when the direction of the linearly polarized light of the reflected beam 15' is rotated clockwise from the direction indicated by arrow H in FIG. The output of the differential amplifier 40 can be set as + (plus), and on the other hand, when the differential amplifier 40 is rotating counterclockwise, the output of the differential amplifier 40 can be set as - (minus). By determining the output D1 of the differential amplifier 40 in this manner, the direction of magnetization on the magneto-optical disk 13, that is, the recorded information can be read.

The photodetection signals output by the first to fourth photodetectors 24, 25, 26, and 27 include, for example, noise caused by fluctuations in the light intensity of the semiconductor laser 16, fluctuations in the reflectance of the recording magnetic film of the magneto-optical disk 13, etc. It often contains noise caused by crystal grains. These noise components are detected by the first to fourth photodetectors 2.
4.25, 28, and 27 are in phase with each other, so by differentially detecting the signal components as described above, these noise components are canceled and a read signal D1 with a high S/N is obtained. be able to.

Note that in the above example, the first and second photodetectors 24
．． The difference between the signal obtained by adding the outputs of the photodetectors 28 and 25 and the signal obtained by adding the outputs of the third and fourth photodetectors 28 and 27 is detected. Alternatively, it is also possible to read the signal by detecting the difference between the output signals of the photodetectors 25 and 27. Furthermore, it is also possible to detect the output fluctuation of one of the photodetectors 24 to 27 and read the signal. However, in that case, the output of the photodetector fluctuates due to tracking error, so in order to prevent signal detection errors due to this fluctuation, it is preferable to do as in the above embodiment.

In addition, in this example, the reflected beam 1 incident on FG31.32
5', the optical axis of the uniaxial anisotropic crystal forming the transparent member 22 is at an angle of approximately 45° with respect to the X axis.
Since it is parallel to the optical axis, the polarization direction of the reflected beam 15' incident on the light-transmitting member 22 is approximately 45° with respect to the optical axis. If the angle is like this,
Since the level of the differential output D1 outputted from the differential amplifier 40 is maximized, this is preferable for reading recording signals with high accuracy.

As described above, the block 12 is sent in a direction perpendicular to the direction of the arrow U or in a direction close to it by the drive of the optical system feed motor. position) is changed and the recorded signal is read continuously. Here, the light beam 15 must be correctly irradiated onto the center of a predetermined signal train (track). Hereinafter, control for maintaining the correct irradiation position of the light beam 15 in this manner, ie, tracking control, will be described. When the center of the reflected beam 15' is located exactly between FG31 and FG32, the amount of light detected by the first and third photodetectors 24.26 and the second and fourth photodetectors 25.27 The amount of light detected by Therefore, in this case, the outputs of the summing amplifiers 46 and 47 become equal, and the output D2 of the differential amplifier 50 becomes O (zero). On the other hand, if the irradiation position of the light beam 15 becomes incorrect and the light intensity distribution of the reflected beam I5° shifts upward in FIG. 2nd and 4th
exceeds the amount of light detected by the photodetectors 25 and 27. Therefore, the output D2 of the differential amplifier 50 becomes + (plus). On the other hand, when the light intensity distribution of the reflected beam 15° shifts downward in FIG. 2, the output D2 of the differential amplifier 50 becomes - (minus).
becomes.

In other words, the output D2 of the differential amplifier 40 indicates the direction of the tracking error (X-axis direction in FIG. 2). This output D2 is sent to the tracking coil drive control circuit 52 as a tracking error signal. Note that the method of detecting a tracking error by processing the outputs of the photodiodes PDI to 8 in this manner has been conventionally established as a push-pull method. The tracking coil drive control circuit 52 receives the tracking error signal D2, supplies a current It to the tracking coil 19 according to the direction of the tracking error indicated by the signal D2, and moves the objective lens 18 in the direction in which the tracking error is eliminated. move it. As a result, the light beam 15 is always correctly irradiated onto the center of the signal train.

Next, focus control, that is, control for correctly focusing the light beam 15 on the reflective surface 14 of the magneto-optical disk 13 will be explained. When the light beam 15 is focused on the reflective surface 14 of the magneto-optical disk 13, the P-polarized component of the reflected beam 15° focused by the FG31 is focused at an intermediate position between the photodiodes PDI and PD2, and the S The polarized light components are focused at an intermediate position between photodiodes PD5 and PD6. At this time, the P-polarized component of the reflected beam 15', which is similarly focused by FG32, is focused at an intermediate position between photodiodes PD3 and PD4, and the S-polarized component is focused at an intermediate position between photodiodes PD7 and PD8.

Therefore, the output of the summing amplifier 48 and the output of the summing amplifier 49 become equal, and the output D3 of the differential amplifier 51 becomes 0 (zero). On the other hand, when the light beam 15 is focused at a position closer than the reflecting surface 14, the reflected beam 15° incident on the FC 31° 32 becomes a convergent beam, and the photodetector 24
．． Reflected beam 15' in each of 25.28.27
The irradiation positions are inside (photodiode PD2.
PD6 side and photodiode PD3. PD7 side). Therefore, in this case, the output of the summing amplifier 48 is lower than the output of the summing amplifier 49, and the output D3 of the differential amplifier 51 becomes - (minus). On the other hand, when the light beam 15 is focused at a position farther than the reflecting surface 14, the FG
The reflected beam 15° incident on the photodetectors 24, 25, 26, and 27 becomes a diverging beam, and the irradiation positions of the reflected beam 15' on each of the photodetectors 24, 25, 26, and 27 are outside (the photodiodes PD1 and PD5 sides and the photodiode P
D4. PDS side). Therefore, in this case, the output of the summing amplifier 48 exceeds the output of the summing amplifier 49,
The output D3 of the differential amplifier 51 becomes + (plus).

In this way, the output D3 of the differential amplifier 51 indicates the direction of the focus error. This output D3 is sent to the focus coil drive control circuit 5 as a focus error signal.
Sent to 3. In this way, the photodiode PDI
The method of detecting focus errors by processing the outputs of 8 to 8 is conventionally carried out in the Foucault method using a Foucault prism. The focus coil drive control circuit 53 receives the focus error signal D3, supplies the focus coil 2o with a current II' corresponding to the direction of the focus error indicated by the signal D3, and moves the objective lens 18 in the direction in which the focus error is eliminated. move. Thereby, the light beam 15 is always correctly focused on the reflective surface 14 of the magneto-optical disk 13.

In order to detect the tracking error and focus error described above, it is sufficient to detect at least the P polarized light component or the S polarized light component focused by the first and second POs 31 and 32. Furthermore, if the differential detection of the recording signal described above is not performed, the recording signal can be read by detecting the component focused by one of the P polarized light components or the S polarized light components by one of the POs 31 or 32. Therefore, in the apparatus of the present invention, at least two sets of photodetectors 24 and 25 or 26 and 27 described above may be provided. Further, the P-polarized light component and the S-polarized light component of the reflected beam 15' focused by one of the first PO 31 and the second PO 32 are detected to perform the above-mentioned differential detection, and the first
When detecting only one of the P-polarized light component and the S-polarized light component focused by the second PO 31 and 32 to detect tracking error and focus error, the photodetectors 24 to 2
It is sufficient if three of the numbers 7 and 7 are provided.

However, as in this embodiment, if tracking errors and focus errors are detected based on a signal that is a combination of a signal that detects a P-polarized light component and a signal that detects an S-polarized light component, the error detection signal can include a recording signal. This is more preferable because the high frequency components modulated by the above do not overlap.

Note that a portion of the front beam 15 emitted from the semiconductor laser 16 is taken into the light guide 29 by the POs 31 and 32 when heading from the collimator lens 17 to the objective lens 18.
is reflected at the end surface 29d of the photodetector 24.25°28,2
7, a light absorbing member 55 is attached to the end surface 29d, or the end surface 29d is
It is desirable to roughen the surface.

Further, in this embodiment, the two POs 31 and 32 are formed so that their respective lattices are continuous and close to each other, but these POs 31 and 32 may be formed independently from each other with a short distance between them. . This also applies to the embodiments described below.

In addition, the reflected beams 15' focused by PO31 and 32 are made to intersect with each other. In other words, referring to FIG. 2, the beam focusing position by PO31 is placed below the y-axis.
The POs 31 and 32 may be formed so that the beam focusing position by the PO 32 is located above the y-axis.

Further, in the above embodiment, the light-transmitting member 22 is formed from the opening, T i 02, which is >n□;
may be formed from other materials, including materials where n e < n □. For example, n a > n.

Examples of abrasive materials with n, < n (1) include L LTa03, ZnO, etc., while materials with n, < n (1) include LiNb0
a, ADP (NHA H2PO4), KDP (K
H2POa ), quartz (S 102 ), calcite (
CaCO3) and the like.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 4, elements that are equivalent to those in FIG. 1 are given the same numbers, and explanations thereof will be omitted unless necessary (the same applies hereinafter). In the pickup of this second embodiment, the collimator lens 17 provided in the apparatus of FIG. 1 is omitted, and the magneto-optical disk 13 is
The reflected beam 15' is taken into the light guide 29 in the form of a convergent beam. In this case as well, the four systems of reflected beams 15' converged within the light guide 29 are connected to the first beam 15' as shown in FIG.
Second, third and fourth photodetector 24.25.28.2
7 and process these detection signals as described above, it is possible to detect recording signals, tracking errors, and focus errors.

In this case, the m-th grating pattern shape equation of FG31.32 defines the spatial coordinates and the coordinates of the beam focusing position by FC31, 32 in the same way as in the first embodiment, and also defines the refractive index of the light guide 29. n! And if the coordinates of the light source are defined as (0, 0, Lz), it is given by -mλ+const, (decoding in the same order when x<0).

Next, a third embodiment of the present invention will be described with reference to FIG. In the pickup of this third embodiment, the light guide 29 is made of a material with a sufficiently high refractive index,
The light beam 15 is reflected by the surface 29a of the light guide 29 and travels toward the magneto-optical disk 13. In this case as well, the reflected beam 1 from the magneto-optical disk 13
5' is diffracted and focused by two FC31°32.

FIG. 6 shows a pickup according to a fourth embodiment of the present invention. In this embodiment, the semiconductor laser 16
The light beam 15 emitted from the light guide 29 is reflected in a diverging beam state at the surface 29a of the light guide 29, and is caused to proceed toward the magneto-optical disk 13.

Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, the light guide 29 and the objective lens 18 are fixed and integrated into one head 60, and this head 60 is supported with respect to the block 12 so as to be movable in the tracking direction and the focusing direction. This head 60 has a tracking coil 19
, are moved by the focus coil 20. That is, in this example, the light guide 29 is moved together with the objective lens 18 for tracking control and focus control.

In this way, the objective lens 18 will not be offset with respect to the light guide 29 due to tracking control, unlike when only the objective lens 18 is moved, and tracking control can be performed with higher accuracy.

Note that it is also possible to fix the semiconductor laser 16 and the collimator lens 17 to the head 60 and move them together with the light guide 29 and the objective lens 18.

In the five embodiments described above, the first, second, and third embodiments are different from each other. Third and fourth photodetectors 24, 25, 26 and 27 are loaded on the obliquely cut end face 29c of the light guide 29, but these photodetectors 24, 25, 28 and 27 are It is also possible to attach it to the light guide 29 in this form. That is, as shown in FIG. 8, for example, the photodetectors 24, 25, 28, 27 are arranged close to the surface 29a of the light guide 29, and the reflected beam 15'' is emitted from the surface 29a to the outside of the light guide 29. A diffraction grating 80 may be provided to allow the photodetectors 24 to 27 to receive a reflected beam of 15° emitted therefrom.

In addition, FC31 and 32 are not limited to the manufacturing method described above.
It can be formed using the Brehner technique using known photolithography, holographic transfer, etc., and can be easily reproduced in large quantities.

(Effects of the Invention) As explained in detail above, in the magneto-optical recording medium pickup of the present invention, the functions played by optical elements such as beam splitters, lenses, prisms, half mirrors, and analyzers in conventional pickups are This is achieved by a light-concentrating diffraction grating formed on a guide and a light-transmitting member made of a uniaxially anisotropic crystal. Therefore, since the pickup of the present invention has an extremely small number of parts and is made small and lightweight, it is possible to significantly reduce costs and shorten access time compared to conventional devices.

Since the main parts of the pickup of the present invention can be easily mass-produced using planar technology, significant cost reductions can also be achieved from this point of view.

In addition, in the pickup of the present invention, the position adjustment of the optical element as described above is of course unnecessary, and since the photodetector is coupled to the light guide, the position adjustment of the optical element and the photodetector is also unnecessary. Cost reduction can also be achieved in this respect.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a device according to a first embodiment of the present invention, FIG. 2 is a schematic diagram showing a planar shape of a leading waveguide and an electric circuit of the device according to the first embodiment, and FIG. 3 is a schematic diagram showing the electrical circuit of the first embodiment. 4.5.6 and 7, respectively, are side views detailing the photodetector of the device. Third. FIG. 8 is a side view showing another example of the photodetector used in the device of the present invention. 13... Magneto-optical disk 14... Reflective surface of disk 15... Light beam 15''... Reflected beam 16... Semiconductor laser 17... Collimator lens IB... Objective lens 19... Tracking coil 20...Focusing coil 22.
...Transparent members 22a, 22b...Light passing surface 29 of transparent ML material...Light guide 29a...One surface of the light guide 29b...Other surfaces of the light guide 29c, 29d...Light Guide end face 31... first FG 32... second FG 34, 35.
3B, 37.38.39.42.43.44.45.
4B. 47, 48.49... Adding amplifier 40, 50.51... Differential amplifier 41... Reading circuit 52... Tracking coil drive control circuit 53.
... Focus coil drive control circuit 60 ... Head
PD1-8...Photodiode, Fig. 1 Fig. 3 Fig. 4

Claims (1)

[Scope of Claims] (1) A light source that irradiates a linearly polarized light beam onto the surface of a magneto-optical recording medium, an objective lens that focuses the light beam on a reflective surface of the magneto-optical recording medium, and the magneto-optical recording medium. A light guide is arranged to receive the reflected beam reflected by the recording medium on one surface, and at the reflected beam irradiation position on one surface of this light guide, the beam passes approximately through the center of the beam and approximately runs on the surface in the tracking direction. They are arranged in parallel across axes extending at right angles, and each makes the reflected beam repeat total reflection between the one surface and the other surface opposing it, and enter the light guide in a direction in which it travels toward the end face side. and first and second light-converging diffraction gratings that respectively focus the reflected beam traveling within the light guide at positions separated from each other across the axis; A uniaxial anisotropic device that is disposed in the optical path of the reflected beam, has a beam passing surface oblique to the traveling direction of the beam, and branches the P-polarized component and the S-polarized component of the reflected beam into separate optical paths. a light-transmitting member made of synthetic crystal; attached to the surface or end face of the light guide;
a photodetector for detecting a P-polarized component or an S-polarized component of each reflected beam focused by at least the first and second condensing diffraction gratings; and a tracking error and a focus error based on the output of the photodetector. A pickup for a magneto-optical recording medium, comprising: an error detection circuit that performs detection; and a signal detection circuit that detects information recorded on the recording medium based on the output of the photodetector. (2) first and second photodetectors are provided for detecting the P-polarized light components of the respective reflected beams focused by the first and second condensing diffraction gratings; third and fourth photodetectors are provided for detecting the S-polarized light component of each reflected beam focused by the condensing diffraction grating, and the signal detection circuit is connected to the first and second photodetectors. Claim 1 characterized in that the information is differentially detected based on the difference between the sum of the outputs of the third and fourth photodetectors and the sum of the outputs of the third and fourth photodetectors. A pickup for magneto-optical recording media as described in Section 1. (3) The light guide passes through the axis so that the first, second, third, and fourth photodetectors can detect tracking errors and focus errors using the push-pull method and the Foucault method, respectively. 3. The pickup for a magneto-optical recording medium according to claim 2, comprising a two-split photodetector divided by a gap extending substantially parallel to a plane perpendicular to the one surface. (4) The polarization direction of the reflected beam incident on the light-transmitting member is approximately 45 degrees with respect to the optical axis of the uniaxially anisotropic crystal of the light-transmitting member.
4. A pickup for a magneto-optical recording medium according to any one of claims 1 to 3, wherein the light guide is arranged so as to be tilted at an angle of .degree. (5) The pickup for a magneto-optical recording medium according to any one of claims 1 to 4, wherein the light guide is arranged between the light source and the objective lens. (6) The light guide is arranged so as to reflect the light beam emitted from the light source and make it travel toward the reflective surface of the magneto-optical recording medium. The pickup for a magneto-optical recording medium according to any one of items 1 to 4. (7) The light guide and the objective lens are arranged independently of each other, and only the objective lens is moved for tracking control and focus control. A pickup for a magneto-optical recording medium according to any one of Items 1 to 6. (8) Claims 1 to 6, characterized in that the light guide is integrated with the objective lens and is moved together with the objective lens for tracking control and focus control. A pickup for a magneto-optical recording medium according to any one of the items.