JPH0675312B2 - Pickup for magneto-optical recording medium - Google Patents

Description

The present invention relates to a pickup for reading a signal recorded on a magneto-optical recording medium such as a magneto-optical disk, and more particularly, it is small and lightweight using a light guide. The present invention relates to a pickup that can be formed in the.

(Prior Art) Recently, a magneto-optical recording medium such as a magneto-optical disk has been widely put into practical use as a recording medium for image signals and audio signals. A signal recorded in the direction of magnetization on this magneto-optical recording medium is read by an optical pickup. This pickup utilizes a phenomenon (a magnetic Kerr effect) in which the surface of a magneto-optical recording medium is irradiated with linearly polarized light such as laser light, and the plane of polarization of the light reflected by the recording medium rotates in accordance with the direction of magnetization. Then, the direction of magnetization on the recording medium is detected.

Specifically, in this magneto-optical recording medium pickup, by utilizing the fact that the reflected light from the recording medium is detected by a photodetector through an analyzer and the detected light amount changes according to the rotation of the polarization plane of the reflected light. The magnetization direction, that is, the recorded information is read. Further, in this pickup, the recording information is read as described above, and the light beam for tracking error detection, that is, for detecting the magnetized state is emitted while deviating to the left or right side from the center of the track along the predetermined groove. And a function for detecting focus error, that is, a function for detecting whether the focus of the light beam is closer or farther than the reflecting surface of the magneto-optical recording medium. To be That is, the tracking error and focus error detection signals are subjected to tracking control and focus control so that the signals are canceled so that the light beam is correctly irradiated to a predetermined track, and the light beam is applied to the magneto-optical recording medium. Used to focus properly on the reflective surface. Conventionally, push-pull method, heterodyne method, time difference detection method, etc. are known as tracking error detection methods, while astigmatism method, critical angle detection method, Foucault method, etc. are known as focus error detection methods. ing.

In order to have the above-described function in addition to the signal reading function, the conventional magneto-optical recording medium pickup separates the beam reflected by the magneto-optical recording medium from the light beam emitted toward the medium. Beam splitter, a lens for focusing the reflected beam in the vicinity of a photodetector such as a photodiode, the analyzer described above, and a prism for executing the tracking error detection method and the focus error detection method. And the like.

(Problems to be solved by the invention) However, the minute optical element as described above requires precise processing,
Further, since it is troublesome to adjust the mutual positions when assembling the pickup, a pickup using such an optical element is inevitably expensive. Furthermore, since the pickup with such a configuration is large and heavy,
It is disadvantageous in terms of downsizing and weight saving of the reading device and shortening of access time. In particular, when performing differential detection in order to improve the S / N of the read signal, a half mirror for splitting the reflected beam into two beams is required. Since it may require two photons, the pickup becomes even more complex, bulky and heavy.

In order to solve the above problems, various attempts have conventionally been made to simplify the structure of the pickup by using a special optical element such as an aspherical lens. However, since an optical element of this kind is particularly expensive, a pickup using such an element has a structure similar to that of the above-mentioned pickup in terms of cost.

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

(Means for Solving the Problems) The pickup for a magneto-optical recording medium of the present invention is achieved by the beam splitter, the lens, the prism, the analyzer, and the half mirror for performing the differential detection described above. The function is obtained by a light guide provided with a light-transmitting member made of a converging diffraction grating and a uniaxial anisotropic crystal. Specifically, linearly polarized light is applied to the surface of a magneto-optical recording medium such as an optical disk. A light source for irradiating the light beam, an objective lens for focusing the light beam on the reflecting surface of the magneto-optical recording medium, and a light arranged so that the reflected beam reflected by the magneto-optical recording medium is received on one surface. A guide is provided, and at the reflection beam irradiation position of the light guide, first and second converging diffraction gratings for respectively injecting the reflection beam into the light guide are arranged in parallel, The first and second converging diffraction gratings are arranged on both sides of an axis that passes through substantially the center of the reflected beam illuminating the light guide and extend on the surface of the light guide at a substantially right angle to the tracking direction. The reflected beam is made to enter the light guide in such a direction that the total reflection is repeated between the one surface and the other surface opposite to the one surface, and the light is guided to the end face side. The light guides are formed so as to be focused at positions separated from each other, while in the light guide, in the optical path portion of the reflected beam that repeats total reflection as described above, with respect to the traveling direction of the beam. A light-transmitting member made of a uniaxial anisotropic crystal that has an oblique beam passing surface and branches the P-polarized component and the S-polarized component of this reflected beam into different optical paths from each other is arranged. A photodetector for detecting the P-polarized component or the S-polarized component of each reflected beam focused by the first and second converging diffraction gratings is attached to the surface or end face of the photodetector. An error detection circuit for detecting a tracking error and a focus error based on the output, and a signal detection circuit for detecting recording information based on the output of the photodetector are provided.

The condensing diffraction grating is a diffraction grating having a bend and a chirp, or a bend, diffracts incident light to enter the light guide, and focuses the diffracted light.

(Operation) The reflected beam from the magneto-optical recording medium is taken into the light guide by the converging diffraction grating, so that the reflected beam is separated from the optical path of the light beam traveling from the light source to the magneto-optical recording medium. This is the same as the function performed by the beam splitter described above. Also, the converging diffraction grating focuses the reflected beam in the light guide, which is the same function as the lens described above. Further first and second
Since the two condensing diffraction gratings are arranged at the positions as described above, the reflected beams from the magneto-optical recording medium are separated from each other in the tracking direction and converge at two positions. This is the same as the function of the prism described above.

Further, since the reflected beam is separated into the P-polarized component and the S-polarized component by the light-transmitting member made of the uniaxial anisotropic crystal, for example, the reflected beams focused by the first and second converging diffraction gratings are separated. First and second detection of P polarization component respectively
And the third and fourth photodetectors for detecting the S-polarized components of the reflected beams focused by the first and second condensing diffraction gratings, respectively, different polarizations can be obtained. The output of each of the first and third photodetectors for detecting the component beam changes complementarily depending on the polarization direction of the reflected beam. The same applies to the outputs of the second and fourth photodetectors. Therefore, for example, if the differential detection circuit detects the difference between the sum of the outputs of the first and second photodetectors and the sum of the outputs of the third and fourth photodetectors, the polarization of the reflected beam The direction, that is, the recorded information on the magneto-optical recording medium can be read. As a result, a read signal with a high S / N can be obtained as in the case where the differential detection optical system is provided and differential detection is performed. That is, the above-mentioned translucent member provides the beam splitting function achieved by the above-mentioned half mirror and the like,
The function of the analyzer described above is 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 a plan view of a light guide of this pickup and an electric circuit. As shown in FIG. 1, this pickup has a block 12 which is movable along rods 11 extending in a direction substantially perpendicular to the plane of the drawing. In order to follow the signal train (track) along a predetermined group, this block 12 is driven by, for example, a precision feed screw and an optical system feed motor, in a direction perpendicular to the direction of the track (direction of arrow U at the beam irradiation position). Or, it is designed to be moved in a direction close to it.

The block 12 includes a semiconductor laser 16 that emits a linearly polarized light beam (laser beam) 15 toward a reflecting surface 14 of a magneto-optical disk 13, and a collimator that converts a divergent beam emitted from the semiconductor laser 16 into a parallel beam. A lens 17 and an objective lens 18 that focuses a collimated light beam 15 on the reflecting surface 14 are attached. The objective lens 18 is movably supported in the tracking direction (direction perpendicular to the arrow U direction) and the focus direction (direction V) for tracking control and focus control, which will be described in detail later. 20
Are moved in the above directions respectively.

Between the collimator lens 17 and the objective lens 18, a flat light guide 29 made of, for example, optical glass is arranged so that the reflected beam 15 'reflected by the magneto-optical disk 13 is received by the surface 29a. ing. The surface 29a of the light guide 29 at the position irradiated with the reflected beam 15 'has first and second focusing diffraction gratings (Focusing Gr).
ating: hereinafter referred to as FG) 31, 32 are provided adjacent to each other (see FIG. 2). These FGs 31 and 32 are diffraction gratings having bends and chirps, or bends, and each diffracts the reflected beam 15 ′ and makes it enter the light guide 29, and inside the light guide 29, its one surface 29a and the other surface. 29b
The light guide 29 is formed so as to be repeatedly reflected to the end face side and then focused at one point in the light guide 29. The first and second FGs 31 and 32 are arranged side by side with an axis (y-axis in FIG. 2) on the light guide 29 that passes through the center of the reflected beam 15 'at a right angle to the tracking direction. Further, each is formed so as to focus the reflected beam 15 'at positions apart from each other across the y-axis.

As shown in FIG. 2, the light guide 29 is arranged so that the angle φ formed by the linear polarization direction (direction of arrow H) of the reflected beam 15 'and the x-axis becomes approximately 45 °. Since the direction of the linearly polarized light of the reflected beam 15 ′ rotates in correspondence with the direction of the magnetization of the magneto-optical disk 13, in this example, the direction of the linearly polarized light of the reflected beam 15 ′ reflected by the non-magnetized portion. With this as a reference, this direction and the x-axis form an angle of 45 °. The FGs 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 the FG31, 32, which performs the above-mentioned action, has the spatial coordinates of both axes passing through the x-axis (tracking direction axis) and the y-axis shown in FIG. 2 and the intersection of these axes. The beam focusing position by FG31,32 defined by the right-angled z-axis (as shown by point K in FIG.
The coordinates of the total reflection within 29 and the focusing position when there is no refraction due to the translucent member 22) are (−Fx, Fy, Fz),
(Fx, Fy, Fz), the refractive index of the light guide 29 is n ₁ ,
And if the light wavelength of the reflected beam 15 'is λ, Given in.

The FGs 31 and 32 are formed by a method such as forming a film of Si-N on the light guide 29 by PCVD, forming a resist pattern by electron beam direct writing, and then transferring the resist pattern to the Si-N film by RIE. be able to.

Inside the light guide 29, the translucent member 22 made of TiO ₂ which is a uniaxial anisotropic crystal is arranged. In addition, light guide
An antireflection coating is preferably applied to the interface between 29 and the uniaxially anisotropic crystal. This translucent member 22 is
The reflected beam 15 'condensed by the FG31 and the second FG32
It has, for example, a length that spans the entire width of the light guide 29 so that both reflected beams 15 'focused by can pass through. Further, the light transmitting member 22 is arranged so that its optical axis extends in a direction perpendicular to the paper surface of FIG. 1 (x-axis direction in FIG. 2). Further, this translucent member 22 is
It has a shape having beam passing surfaces 22a and 22b which are oblique with respect to the traveling direction of 15 '. Therefore, the reflected beam 15 'passing through the translucent member 22 is refracted as shown in FIG. 1, but in this example, the refractive index n _e for extraordinary light is larger than the refractive index n _o for ordinary light (light of wavelength 633 nm). Against n _e = 2.87
2, n _o = 2.584) Since the light-transmitting member 22 is formed of TiO ₂ , the S-polarized component 15S of the reflected beam 15 ′ is the P-polarized component 1
Refracting more than 5P, these components 15S, 15P separate and focus from each other. Further, the light guide 29 is provided with an end face 29c that is obliquely cut so as to spread along each focusing position of the reflected beam 15 'separated into four systems as described above. Then, on the end face 29c, the first and second photodetectors 24, which detect the P-polarized component 15P focused by the first and second FGs 31, 32 of the reflected beams 15 'of the above four systems, respectively. 25 and third and fourth photodetectors 26 and 27 for detecting the S-polarized component 15S focused by the first and second FGs 31 and 32, respectively, are attached. First photodetector 24
Is a photodiode PD1, which is divided into two by a gap that extends parallel to a plane that passes through the y-axis and is perpendicular to the light guide surface 29a.
It consists of PD2 and the other photodetectors 25, 26 and 27 are similar photodiodes PD3 and PD4, PD5 and PD6 and PD7, respectively.
And PD8.

As shown in detail in FIG. 3 as an example, the photodiode PD1 is formed by loading a lower transparent electrode 28a, a thin film photoconductive material 28b, and an upper electrode 28c on a light guide 29 in this order. Then, a predetermined electric field is applied from the power source 28d between the lower transparent electrode 28a and the upper electrode 28c. In the photodiode PD1 having this structure, when the photoconductive material 28b is irradiated with light, a photocurrent corresponding to the amount of light flows. Therefore, the amount of light received by the photoconductive material 28b can be detected by detecting the potential change at the terminal 28e. The photodiodes PD2 to 8 are also formed similarly to the photodiode PD1. The thin film photoconductive material 28b is, for example, Group IV Si, Ge, Group IV Se, III-V.
Group GaAs, II-VI group ZnO, CdS, IV-VI group PbS, etc. epitaxial films, polycrystalline films, amorphous films, etc. can be formed, and amorphous chalcogen film (a-Se , A-Se-As-Te, etc.), films containing amorphous Si as a main component and containing hydrogen and / or fluorine (a-Si: H, a-SiGe: H, a-SiC: H, etc.) in Group III, V
By adding a group atom (B, P, etc.), a pn junction,
A film that forms a photodiode by obtaining a pin junction, a film that forms a photodiode by using an electrode that forms a Schottky junction with the above-mentioned amorphous Si-based film that contains hydrogen and / or fluorine, etc. You can also

Further, the external photodiode may be closely adhered to the end face 29c to be adhered thereto. In this case, it is desirable that the end face 29c be non-reflection coated.

As shown in FIG. 2, the outputs of the photodiodes PD1 and PD2, which detect the P-polarized component of the reflected beam 15 ', and the outputs of PD3 and PD4, are added by summing amplifiers 34 and 35, respectively, while the photodiodes that detect the S-polarized component are detected. Diodes PD5 and PD6, and PD7
And the outputs of PD8 are added by summing amplifiers 36 and 37, respectively, and the outputs of these summing amplifiers 34 and 35 and summing amplifiers 36 and 37 are added.
The outputs of are added by adding amplifiers 38 and 39, respectively. The outputs of these summing amplifiers 38 and 39 are differential amplifiers.
40, and the output D1 of the differential amplifier 40 is read by the reading circuit 41.
Entered in.

On the other hand, the outputs of the photodiodes PD1 and PD5 on the outside of each of the first and third photodetectors 24 and 26 for detecting the reflected beam 15 'focused by the first FG31 are added by the summing amplifier 42, and The outputs of the photodiodes PD2 and PD6 are added by the adding amplifier 43. The outputs of the photodiodes PD4 and PD8 on the outside of the second and fourth photodetectors 25 and 27 for detecting the reflected beam 15 'focused by the second FG 32 are added by the adding amplifier 45, and The outputs of the photodiodes PD3 and PD7 are added by the adding amplifier 44. The outputs of the addition amplifiers 42 and 43 are added by the addition amplifier 46, and the outputs of the addition amplifiers 44 and 45 are added by the addition amplifier 47. On the other hand, the outputs of the addition amplifiers 42 and 45 are added by the addition amplifier 48, and the outputs of the addition amplifiers 43 and 44 are added by the addition amplifier 49. Also, the above summing amplifier 46,4
The output of 7 is input to the differential amplifier 50, and the outputs of the summing amplifiers 48 and 49 are input to the differential amplifier 51. The outputs D2 and D3 of the differential amplifiers 50 and 51 are input to the tracking coil drive control circuit 52 and the focus coil drive control circuit 53, respectively.

Next, the operation of the pickup having the above structure will be described.
The light beam (laser beam) 15 emitted from the semiconductor laser 16 and converted into a parallel beam passes through the light guide 29 and is focused on the reflecting surface 14 of the magneto-optical disk 13 so as to be focused.
Focused by 18. The magneto-optical disk 13 is rotated by a rotation driving means (not shown) so that the track moves in the arrow U direction at the irradiation position of the light beam 15.
As is well known, the track is a train of image signals and audio signals recorded in the direction of magnetization (indicated by an arrow above the reflecting surface 14 in FIG. 1). The directions of linear polarization of 15 'rotate in opposite directions depending on the direction of magnetization as compared to the direction of linear polarization of the reflected beam 15' from the unmagnetized portion. That is, the reflected beam 15 'from the part magnetized in a certain direction
The direction of polarization of the reflected beam 15 'rotated from the polarization direction shown by the arrow H in FIG. 2 is clockwise, and the direction of polarization of the reflected beam 15' from the portion magnetized in the opposite direction is shown by the arrow H above. It rotates counterclockwise from the polarization direction.

This reflected beam 15 'passes through the objective lens 18 and
The light is diffracted at and enters the light guide 29. The reflected beam 15 'incident on the light guide 29 has one surface 29
Repeats total reflection between a and the other surface 29b to proceed to FG3
The beam focusing action of each of 1,32 causes the beam to be focused at a position sandwiching the y axis. Here, as described above, each reflected beam 15 'transmitted through the translucent member 22 is separated into a P-polarized component 15P and an S-polarized component 15S. This P polarization component
15P is the first photodetector 24 (photodiode PD1
And PD2), the second photodetector 25 (photodiodes PD3 and PD
4), while the S-polarized component 15S is detected by the third photodetector 26 (photodiodes PD5 and PD6) and the fourth photodetector 27 (photodiodes PD7 and PD8), respectively. Here, if the direction of the linearly polarized light of the reflected beam 15 'rotates clockwise relative to the direction indicated by the arrow H, the P-polarized component 15P of the reflected beam 15' traveling in the light guide 29 increases, while the S-polarized component of the S-polarized light increases. The component 15S is reduced. Reflected beam 1
If the direction of the linearly polarized light of 5'rotates counterclockwise as compared with the direction of arrow H, the above is reversed. When the P-polarized component increases as described above, the output of the adding amplifier 38 increases,
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 set appropriately, the reflected beam 1
When the direction of the 5'linearly polarized light is rotating clockwise from the direction shown by the arrow H in FIG. 2, the output of the differential amplifier 40 is +
When the counterclockwise rotation is made, the output of the differential amplifier 40 can be made negative (-). By discriminating the output D1 of the differential amplifier 40 in this way, the direction of magnetization on the magneto-optical disk 13, that is, the recorded information can be read.

The photodetection signals output from the first to fourth photodetectors 24, 25, 26, 27 include, for example, noise due to variations in the light intensity of the semiconductor laser 16, variations in the reflectance of the recording magnetic film of the magneto-optical disk 13, and Noise and the like due to crystal grains are often included. Since these noise components are in phase with each other at the outputs of the first to fourth photodetectors 24, 25, 26, 27, by performing differential detection of the signal components as described above, these noise components Are canceled out, and a read signal D1 having a high S / N can be obtained.

In the above example, the first and second photodetectors 24,2
The signal obtained by adding the outputs of 5 and the third and fourth photodetectors 2
Although the difference between the output signals of 6 and 27 is detected, the signal is detected by detecting the difference between the output signals of photodetectors 24 and 26 or the difference between the output signals of photodetectors 25 and 27. It is also possible to read. Further, it is possible to detect the output fluctuation of one of the photodetectors 24-27 and read the signal. However, in that case, the output of the photodetector fluctuates due to the tracking error. Therefore, in order to prevent erroneous signal detection due to this fluctuation, it is preferable to adopt the above-mentioned embodiment.

Also, in this example, the polarization direction of the reflected beam 15 'incident on the FGs 31 and 32 forms an angle of about 45 ° with respect to the x-axis, and
Since the optic axis of the uniaxial anisotropic crystal forming the is parallel to the x-axis, the polarization direction of the reflected beam 15 'incident on the translucent member 22 is approximately 45 ° with respect to the optic axis. Become.
With such an angle, the level of the differential output D1 output from the differential amplifier 40 is maximized, which is preferable for accurately reading the recording signal.

As described above, the block 12 is fed by the drive of the optical system feed motor in the direction perpendicular to the direction of the arrow U or in the direction close thereto, whereby the irradiation position of the light beam 15 on the magneto-optical disc 13 (the disc radial direction). Position) is changed,
The recording signal is continuously read. Where the above light beam
15 must be correctly illuminated in the center of a given signal train (track). Hereinafter, the control for properly maintaining the irradiation position of the light beam 15 in this way, that is, the tracking control will be described. The center of the reflected beam 15 'is just
When located between FG31 and FG32, the amount of light detected by the first and third photodetectors 24, 26 matches the amount of light detected by the second and fourth photodetectors 25, 27. To do. 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 0 (zero).
On the other hand, the irradiation position of the light beam 15 becomes incorrect and the reflected beam
When the light intensity distribution of 15 'is displaced to the upper side in FIG.
The amount of light detected by the third and third photodetectors 24, 26 exceeds the amount of light detected by the second and fourth photodetectors 25, 27. Therefore, the output D2 of the differential amplifier 50 becomes + (plus). On the contrary, when the light intensity distribution of the reflected beam 15 'is displaced downward in FIG. 2, the output D2 of the differential amplifier 50 becomes-(minus). That is, the output D2 of the differential amplifier 40 indicates the tracking error direction (x-axis direction in FIG. 2). This output D2
Is sent to the tracking coil drive control circuit 52 as a tracking error signal. The method of processing the outputs of the photodiodes PD1 to PD8 to detect the tracking error is conventionally established as a push-pull method. Tracking coil drive control circuit 52
Receives the tracking error signal D2, supplies a current It according to the direction of the tracking error indicated by the signal D2 to the tracking coil 19, and moves the objective lens 18 in the direction in which the tracking error is eliminated. As a result, the light beam 15 is always radiated correctly to the center of the signal train.

Next, focus control, that is, control for correctly focusing the light beam 15 on the reflecting surface 14 of the magneto-optical disk 13 will be described. When the light beam 15 is focused on the reflecting surface 14 of the magneto-optical disk 13, the reflected beam 1 focused by the FG 31
The 5 ′ P-polarized component is focused at an intermediate position between the photodiodes PD1 and PD2, and the S-polarized component is the photodiode PD5.
Focus at an intermediate position between and PD6. At this time, similarly, the P-polarized component of the reflected beam 15 'focused by the FG32 is focused at the intermediate position between the photodiodes PD3 and PD4, and the S-polarized component is focused at the intermediate position between the photodiodes PD7 and PD8. Therefore, the output of the addition amplifier 48 and the output of the addition 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 1 incident on the FG 31, 32
5'becomes a convergent beam, and the irradiation position of the reflected beam 15 'on each of the photodetectors 24, 25, 26, 27 is inside (photodiode PD2, PD6 side and photodiode PD3, PD7
Side). Therefore, in this case, the output of the adding amplifier 48 becomes lower than the output of the adding amplifier 49, and the output D3 of the differential amplifier 51 becomes-(minus). On the contrary, when the light beam 15 is focused at a position farther than the reflecting surface 14, the reflected beam 15 'incident on the FGs 31 and 32 becomes a divergent beam and the photodetector
The irradiation position of the reflected beam 15 'on each of 24, 25, 26, 27 is displaced to the outside (the photodiode PD1, PD5 side and the photodiodes PD4, PD8 side). Therefore, in this case, the output of the addition amplifier 48 exceeds the output of the addition amplifier 49, and 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 focus error. This output D3 is sent to the focus coil drive control circuit 53 as a focus error signal. The method of processing the outputs of the photodiodes PD1 to PD8 to detect the focus error in this way is conventionally executed in the Foucault method using a Foucault prism. Focus coil drive control circuit
53 receives the focus error signal D3, supplies a current If according to the direction of the focus error indicated by the signal D3 to the focus coil 20, and moves the objective lens 18 in a direction in which this focus error is eliminated. Thereby the light beam
15 will always be correctly focused on the reflecting surface 14 of the magneto-optical disk 13.

In order to detect the tracking error and the focus error described above, at least the P-polarized light component or the S-polarized light component focused by the first and second FGs 31 and 32 may be detected. If the differential detection of the recording signal is not performed, the recording signal can be read only by detecting the component of the P-polarized component or the S-polarized component focused by one of the FGs 31 or 32. Therefore, in the device of the present invention, the photodetector is at least the aforementioned photodetectors 24 and 25,
Alternatively, two sets of 26 and 27 may be provided. Also, the reflected beam 1 focused on one of the first FG31 and the second FG32
The 5'P-polarized light component and S-polarized light component are detected to perform the differential detection described above, and only one of the P-polarized light component and the S-polarized light component focused by the first and second FGs 31 and 32 is detected. When detecting a tracking error and a focus error, three of the photodetectors 24 to 27 may be provided.

However, as in the present embodiment, if the tracking error and the focus error are detected based on the signal obtained by adding the signal in which the P-polarized component is detected and the signal in which the S-polarized component is detected, the recording signal becomes the error detection signal. It is more preferable because the high frequency component modulated by does not overlap.

The light beam 15 emitted from the semiconductor laser 16 is FG31,3 when traveling from the collimator lens 17 to the objective lens 18.
Part 2 is taken into the light guide 29 by 2, so
This light beam 15 is not reflected by the end surface 29d of the light guide 29 and received by the photodetectors 24, 25, 26, 27,
It is desirable to attach a light absorbing member 55 to the end surface 29d or to roughen the end surface 29d.

Further, in this embodiment, the two FGs 31 and 32 are formed such that their respective grids are continuous and in close contact with each other, but these FGs 31 and 32 may be formed independently of each other with a small distance. . This also applies to the embodiments described below.

In addition, the reflected beam 1 focused by FG31 and 32, respectively
5'intersect each other, that is, FG3 if explained in FIG.
The FGs 31 and 32 may be formed such that the beam focusing position by 1 is below the y axis and the beam focusing position by FG 32 is above the y axis.

Further, in the above-mentioned embodiment, the translucent member 22 is made of TiO ₂ with n _e > n _o , but the translucent member 22 is made of other materials including the material with n _e <n _o. May be. For example, materials having n _e > n _o include LiTaO ₃ and ZnO, while materials having n _e <n _o include LiNbO ₃ and ADP (NH ₄ H ₂ P
O ₄ ), KDP (KH ₂ PO ₄ ), quartz (SiO ₂ ), calcite (CaCO ₃ ), and the like.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 4, elements that are the same as the elements in FIG. 1 are given the same numbers, and explanations thereof are omitted unless necessary (the same applies below). In the pickup of the second embodiment, the collimator lens 17 provided in the apparatus of FIG. 1 is omitted, and the reflected beam 15 'from the magneto-optical disk 13 is taken into the light guide 29 in a converged beam state. It is like this. In this case also, the four reflected beams 15 'that are focused in the light guide 29 are used.
For example, as shown in FIG. 2, the first, second, third and fourth
If the photodetectors 24, 25, 26, and 27 detect the signals and process the detection signals as described above, the recording signal, the tracking error, and the focus error can be detected.

In this case, the m-th grid pattern shape formula of FG31, 32 is
The spatial coordinates and the coordinates of the beam focusing position by FG31, 32 are defined as in the case of the first embodiment, the refractive index of the light guide 29 is n _1, and the coordinates of the light source are (0, 0, L _Z ), Given in.

Next, a third embodiment of the present invention will be described with reference to FIG. In the pickup of the third embodiment, the light guide 29 is made of a material having a sufficiently large refractive index, and the light beam 15 is reflected by the surface 29a of the light guide 29 and travels toward the magneto-optical disk 13 side. ing. In this case as well, the reflected beam 15 'from the magneto-optical disk 13 has two
Diffracted and focused by FG31 and 32.

FIG. 6 shows a pickup according to the fourth embodiment of the present invention. In this embodiment, the light beam 15 emitted from the semiconductor laser 16 is reflected on the surface 29a of the light guide 29 in the state of a divergent beam, and travels 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 to and integrated with one head 60, and this head 60 is supported movably in the tracking direction and the focus direction with respect to the block 12. The head 60 is moved by the tracking coil 19 and 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. By doing so, the objective lens 18 does not offset with respect to the light guide 29 due to the tracking control as in the case of moving only the objective lens 18, and the tracking control can be performed more accurately.

The semiconductor laser 16 and the collimator lens 17 are also heads.
It is also possible to fix it to 60 and move it integrally with the light guide 29 and the objective lens 18.

In the five embodiments described above, the first, second, third and fourth photodetectors 24, 25, 26 and 27 are light guides 29.
Although mounted on the obliquely cut end face 29c of, the photodetectors 24, 25, 26 and 27 can be attached to the light guide 29 in other forms. That is, for example, as shown in FIG. 8, while arranging the photodetectors 24, 25, 26, 27 close to the surface 29a of the light guide 29,
The surface 29a is provided with a diffraction grating 80 for emitting the reflected beam 15 'to the outside of the light guide 29, and the reflected beam is emitted from the diffraction grating 80.
15 'should be received by the photodetectors 24-27.

Further, the FGs 31 and 32 are not limited to the manufacturing method described above, and can be formed by the planar technology by a known photolithography method, a holographic transfer method, or the like, and can be easily mass copied.

(Effects of the Invention) As described in detail above, in the pickup for a magneto-optical recording medium of the present invention, the action performed by the optical elements such as the beam splitter, the lens, the prism, the half mirror and the analyzer in the conventional pickup is It can be obtained by a light-transmitting member made of a converging diffraction grating and a uniaxial anisotropic crystal formed on a guide. Therefore, since the pickup of the present invention has a very small number of parts and is formed in a small size and light weight, the cost can be significantly reduced as compared with the conventional device, and the access time can be shortened.

Since the main part of the pickup of the present invention can be easily mass-produced by the planar technique, a significant cost reduction can be realized from this point as well.

Further, in the pickup of the present invention, it is of course unnecessary to adjust the position of the optical element as described above, and it is also unnecessary to adjust the position of the optical element and the photodetector by coupling the photodetector to the light guide, Also in this respect, cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a side view showing the first embodiment device of the present invention, FIG. 2 is a schematic view showing the planar shape of an optical waveguide and an electric circuit of the first embodiment device, and FIG. 3 is the first embodiment. The side view showing the photodetector of the device in detail, FIGS. 4, 5, 6 and 7 are respectively the second, third and fourth of the present invention.
FIG. 8 is a side view showing the device of the fifth embodiment, and FIG. 8 is a side view showing another example of the photodetector used in the device of the present invention. 13 ... Magneto-optical disc, 14 ... Reflective surface of disc 15 ... Light beam, 15 '... Reflected beam 16 ... Semiconductor laser, 17 ... Collimator lens 18 ... Objective lens, 19 ... Tracking coil 20 ... Focus coil, 22 ... Translucent member 22a, 22b ... Light passing surface of translucent member 29 ... Light guide, 29a ... One surface of light guide 29b ... Other surface of light guide 29c, 29d ... End surface of light guide 31 ... First FG, 32 ... Second FG 34,35,36,37,38,39,42,43,44,45,46,47,48,49… Summing 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,

Claims (8)

[Claims] 1. A light source for irradiating a surface of a magneto-optical recording medium with a linearly polarized light beam, an objective lens for converging the light beam on a reflecting surface of the magneto-optical recording medium, and a reflection on the magneto-optical recording medium. A light guide arranged so as to receive the reflected beam on one surface thereof, and an axis extending substantially through the center of the beam at the irradiation position of the reflected beam on the one surface of the light guide and substantially perpendicular to the tracking direction on the surface. The light beams are arranged in parallel with each other and are incident on the light guide in a direction in which the reflected beam repeats total reflection between the one surface and the other surface facing the one surface and advances toward the end face side. First and second converging diffraction gratings for converging the reflected beams traveling in the guide at positions separated from each other with the axis in between, and total reflection in the light guide. It is arranged in the optical path of the reflected beam that travels back by returning, has a beam passage surface that is oblique to the traveling direction of the beam, and splits the P-polarized component and the S-polarized component of this reflected beam into mutually different optical paths. A translucent member made of a uniaxial anisotropic crystal, and attached to the surface or end face of the light guide,
A photodetector that detects at least the P-polarized component or the S-polarized component of each reflected beam focused by the first and second converging 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. A first photodetector and a second photodetector for detecting the P-polarized components of the respective reflected beams focused by the first and second converging diffraction gratings are provided, and the first and second photodetectors are provided. Third and fourth detecting the S-polarized component of each reflected beam focused by the second converging diffraction grating
The photodetector is provided, and the signal detection circuit is configured to detect the signal based on a difference between a sum of outputs of the first and second photodetectors and a sum of outputs of the third and fourth photodetectors. The pickup for a magneto-optical recording medium according to claim 1, which is formed so as to perform differential detection of information. 3. The light is passed through the axis so that the first, second, third and fourth photodetectors can perform tracking error detection and focus error detection by the push-pull method and Foucault method, respectively. The magneto-optical recording medium pickup according to claim 2, comprising a two-division photodetector divided by a gap extending substantially parallel to a plane perpendicular to the one surface of the guide. 4. The light guide is arranged so that a polarization direction of a reflected beam incident on the light transmitting member is inclined by about 45 ° with respect to an optical axis of a uniaxial anisotropic crystal of the light transmitting member. The pickup for a magneto-optical recording medium according to any one of claims 1 to 3, wherein: 5. The magneto-optical recording medium according to claim 1, wherein the light guide is arranged between the light source and the objective lens. pick up. 6. The light guide is arranged so as to reflect a light beam emitted from the light source and advance the light beam toward a reflecting surface of the magneto-optical recording medium. The pickup for a magneto-optical recording medium according to any one of claims 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. Range 1st to 6th
Item 7. A pickup for a magneto-optical recording medium according to any one of items. 8. The light guide according to claim 1, wherein the light guide is integrated with the objective lens and is moved together with the objective lens for tracking control and focus control. Item 7. The pickup for magneto-optical recording medium according to any one of items 6.