JPH0675313B2 - 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. In addition, in this pickup, the recording information is read as described above, and the light beam for tracking error detection, that is, for detecting the magnetization state is radiated to the left or right side of the track along the predetermined group. 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 has a light guide provided with a condensing diffraction grating to perform the functions of the above-mentioned beam splitter, lens, prism, analyzer and the like. Specifically, a light source for irradiating the surface of a magneto-optical recording medium such as an optical disk with a linearly polarized light beam, and focusing the light beam on the reflecting surface of the magneto-optical recording medium. An objective lens and a light guide arranged so as to receive the reflected beam reflected by the magneto-optical recording medium on one surface are provided, and the reflected beam is radiated at the reflected beam irradiation position of the light guide. The first and second converging diffraction gratings to be incident inside are arranged side by side, and these first and second converging diffraction gratings pass through substantially the center of the reflected beam that illuminates the light guide. In such a direction that the reflected beam repeats total reflection between the one surface and the other surface facing the same, and travels toward the end face side. Reflected beams that enter the light guide and travel in the light guide are formed so as to be focused at positions separated from each other with the axis interposed therebetween, while the light guide is totally reflected as described above. Is provided with an end face formed in the direction of incidence at the Brewster angle of the reflected beam that travels repeatedly, and at least two types of the reflected beam that has transmitted through this end face (that is, by the first and second converging diffraction gratings). (Reflected beam focused respectively), or 2 reflected by this end face
A plurality of photodetectors for detecting the reflected beam of the system are provided, and an error detection circuit for detecting tracking error and focus error based on the outputs of these photodetectors, and recording based on the output of the photodetector A signal detection circuit for detecting information is 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.

The Brewster angle is the refractive index of the light guide.
n _1, and the refractive index of the medium adjacent to the light guide the end face as the interface was n _2, an ^{_{α B = tan -1 (n 2}} / n 1) made an angle alpha _B, reflected linearly polarized When the beam is incident on the end face at this Brewster's angle, only a part of the S-polarized component is reflected at a predetermined reflectance, and the other S-polarized component and P-polarized component are transmitted through the end face. Therefore,
For example, if the amount of light of the reflected beam reflected by the end face is detected, the ratio of the S-polarized component in the reflected beam (that is, the direction of polarization) before separation at the end face, and thus the recorded information on the magneto-optical recording medium, can be read. become. That is, the light guide end face provides the beam splitting action performed by the half mirror and the like, and the action performed by the analyzer.

(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 example (track) along a predetermined groove, this block 12 uses a precision feed screw and an optical system feed motor or the like, for example, 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
Is repeatedly formed so as to travel toward the end face side and then converge at one point. First and second FG
31 and 32 are arranged side by side with the axis (y-axis in FIG. 2) on the light guide 29 that passes through the center of the reflected beam 15 'at right angles to the above-mentioned tracking direction, and these y It is formed so as to focus the reflected beams 15 'at positions spaced apart from each other by an axis.

The light guide 29 is arranged so that the direction of linear polarization of the reflected beam 15 '(direction of arrow H) and the x-axis form an angle φ (usually about 10 to 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 focusing position when there is no total reflection in 29) are (−Fx, Fy, Fz) and (Fx, Fy, Fz), the refractive index of the light guide 29 is n ₁ , and the reflected beam If the light wavelength of 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 it to a Si-N film by RIE. be able to.

The light guide 29 is provided with an obliquely cut end face 29f at a portion near the focus position of the reflected beam 15 '. A transparent member 22 made of a material having a lower refractive index than the material of the light guide 29 is closely fixed to the end surface 29f. That is, the end surface 29f serves as an interface between the light guide 29 and the translucent member 22. Also, the light guide end surface 29
f is formed at an angle at which the reflected beam 15 'is incident at Brewster's angle α _B. The Brewster angle alpha _B are as defined above, n ₁ the refractive index of the light guide 29, when the refractive index of the translucent member 22 and the n _2, alpha angle ^{_{B = tan -1 (n 2 /}} n 1) Is. As an example, FIG. 9 shows the relationship between the incident angle α of the reflected beam 15 ′ on the end face 29f and the transmission and reflectance at the end face 29f when n ₁ = 1.5 and n ₂ = 1.0. 2 is shown for each of the P-polarized component and the S-polarized component. T _p in the figure,
T _p indicates the transmittance and reflectance of the P-polarized component, respectively, and T _S ,
R _S indicates the transmittance and reflectance of the S-polarized component, respectively. As shown in the figure, when the reflected beam 15 'is incident on the end face 29f at the Brewster angle α _B , the reflectance R _p of the P-polarized component on the end face 29f becomes 0 (zero). Therefore, the reflected beam 15R reflected by the end face 29f is composed of only the S-polarized component, while the reflected beam 15T transmitted through the end face 29f.
Includes both the P-polarized component and the S-polarized component.
The light incident on the end face 29f is focused light, but since the light-collecting power of the light-collecting diffraction grating is small, it may be regarded as a substantially parallel light beam here. Therefore, the light analysis function based on the Brewster angle is achieved.

The translucent member 22 is provided with an end face 22a that is obliquely cut in the optical path portion of the reflected beam 15T that has passed through the light guide end face 29f, and on this end face 22a, the first and second FGs are provided.
First and second photodetectors 24 and 25 for respectively detecting the reflected beam 15T focused by the action of 31,32 are attached. Since the reflected beam 15 passes through a material having a refractive index n ₂ lower than the refractive index n ₁ of the light guide 29, the end face 22a is provided at the focal position reflecting the difference in these refractive indices. On the other hand, the surface 29b of the light guide 29 is provided with third and fourth photodetectors 26, 27 for detecting the reflected beam 15R reflected by the end face 29f. The third and fourth photodetectors 26 and 27 detect the reflected beam 15R focused by the action of the first and second FGs 31 and 32, respectively. The first photodetector 24 is composed of photodiodes PD1 and PD2 which are divided into two by a gap which extends parallel to a plane which passes through the y-axis and is perpendicular to the light guide surface 29a, and the other photodetectors 25, 26 and 27 are also included. The photodiodes PD3 and PD4, PD5 and PD6, and PD7 and PD8 are similar to each other.

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 transparent member 22 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, Si of the group IV, Ge, Se of the group IV, GaAs of the group III-V, ZnO of the group II-VI, CdS, an epitaxial film such as PbS of the group IV-VI, It can be formed from a polycrystalline film, an amorphous film, or the like, and also includes an amorphous chalcogen film (a-Se, a-Se-As-Te, etc.), amorphous Si as a main component, and hydrogen and / or fluorine. Group III, V in the film containing (a-Si: H, a-SiGe: H, a-SiC: H, etc.)
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 Also, an external photodiode may be adhered and adhered to the end face 22a and the light guide surface 29b. In this case, it is desirable to apply antireflection coating to each emission surface.

As shown in FIG. 2, the outputs of the photodiodes PD5 and PD6, which detect the reflected beam 15R, and PD7 and PD8 are added by adding amplifiers 34 and 35, respectively.
The respective outputs of are added by the adding amplifier 36. The output of the adding amplifier 36 is input to one input terminal of the differential amplifier 40, and the reference signal Dref is input to the other input terminal of the differential amplifier 40. The output of this differential amplifier 40
D1 is input to the reading circuit 41.

On the other hand, the outputs of the outer photodiodes PD1 and PD5 of the first and third photodetectors 24 and 26 for detecting the reflected beams 15T and 15R focused by the first FG31 are added by the summing amplifier 42, The outputs of the photodiodes PD2 and PD6 are added by the adding amplifier 43. In addition, the reflected beam 15 focused by the second FG 32
The outputs of the outer photodiodes PD4 and PD8 of the second and fourth photodetectors 25 and 27 for detecting T and 15R are added by a summing amplifier 45, and the outputs of the inner photodiodes PD3 and PD7 are added. Added at 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. Meanwhile summing amplifier 42,45
Are added by the addition amplifier 48, and the outputs of the addition amplifiers 43 and 44 are added by the addition amplifier 49. In addition, the above addition amplifier
The outputs of 46 and 47 are input to the differential amplifier 50, and the summing amplifier 48,
The output of 49 is 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 made into a parallel beam passes through the light guide 29,
It is focused by the objective lens 18 so as to be focused on the reflecting surface 14 of the magneto-optical disk 13. 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 1 from the part magnetized in a certain direction
The polarization direction of 5'rotates clockwise from the polarization direction shown by the arrow H in FIG. 2, and the polarization direction of the reflected beam 15 'from the portion magnetized in the opposite direction is the same as that of the arrow H above.
It rotates counterclockwise from the polarization direction indicated by.

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. As described above, at the light guide end surface 29f, which is the interface with the translucent member 22,
Only the S-polarized component is reflected, and the reflected beam 15R is detected by the third photodetector 26 (photodiodes PD5 and PD6) and the fourth photodetector 27 (photodiodes PD7 and PD8). Here, the direction of the linearly polarized light of the reflected beam 15 'is the arrow H.
If you rotate it clockwise than the direction shown by,
The P-polarized component of the reflected beam 15 'traveling in 29 increases, while the S-polarized component decreases. If the direction of the linearly polarized light of the reflected beam 15 'rotates counterclockwise than the direction of arrow H,
The opposite is true. If the S-polarized component decreases as described above, the output of the summing amplifier 36 decreases. The opposite is true when the S polarization component increases. Therefore, the reference signal Dref
If the value of is properly set, the output of the differential amplifier 40 is set to- (minus) when the direction of the linearly polarized light of the reflected beam 15 'is rotated clockwise from the direction shown by the arrow H in FIG. , On the contrary, when rotating counterclockwise, a differential amplifier
40 outputs can be + (plus). 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.

In the above example, the third and fourth photodetectors 26, 2
Although the recording signal is detected based on the signal obtained by adding the outputs of 7 signals, it is also possible to detect the output fluctuation of one of the photodetectors 26 and 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.

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, 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 15 focused by the FG 31
T is focused at an intermediate position between the photodiodes PD1 and PD2,
Further, the reflected beam 15R is focused at an intermediate position between the photodiodes PD5 and PD6. At this time, similarly, the reflected beam 15T focused by the FG32 is focused at an intermediate position between the photodiodes PD3 and PD4, and the reflected beam 15R is reflected by the photodiode P.
Focus at an intermediate position between D7 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, FG
The reflected beam 15 'incident on 31,32 becomes a convergent beam,
The irradiation position of the reflected beam 15 'on each of the photodetectors 24, 25, 26, 27 is displaced inward (to the photodiode PD2, PD6 side and photodiode PD3, PD7 side). Therefore, in this case, the output of the adding amplifier 48 is lower than the output of the adding amplifier 49, and the output D3 of the differential amplifier 51 is-(minus).
Becomes On the contrary, when the light beam 15 is focused at a position farther than the reflecting surface 14, the reflected beam 1 incident on the FGs 31 and 32
5'becomes a divergent beam, and photodetectors 24 and 25 and photodetectors 26 and 2
The irradiation positions of the reflected beams 15T and 15R in each of 7 are displaced to the outside (on the side of the photodiodes PD1 and PD5 and on the side of the photodiodes PD4 and PD8). 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 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. The focus coil drive control circuit 53 receives the focus error signal D3, and supplies a current If depending on the direction of the focus error indicated by the signal D3 to the focus coil 20.
And the objective lens 18 is moved in a direction in which this focus error is eliminated. As a result, the light beam 15 is always correctly focused on the reflecting surface 14 of the magneto-optical disk 13.

To detect the tracking error and the focus error described above, at least the reflected beam 15T or the reflected beam 15R focused by the first and second FGs 31 and 32 may be detected. Also, in the reflected beam 15T including both the P-polarized component and the S-polarized component, the increase rate of the light amount differs when the P-polarized component increases and when the S-polarized component increases. It is also possible to read the recording signal by detecting. Therefore, in the device of the present invention, the photodetector is at least the aforementioned photodetector 24.
25, or 26 and 27 may be provided.

However, as in this embodiment, if the tracking error and the focus error are detected based on the signal indicating the sum of both the P-polarized component and the S-polarized component, the error detection signal is
It is more preferable because the high frequency component modulated by the recording signal 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 embodiment, the light transmitting member 2 is provided on the end face 29f of the light guide.
2 is fixed in close contact with the transparent member 22.
Alternatively, the reflected beam 15T transmitted through the end face 29f may be directly emitted into the air for detection.

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 has become. 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.

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

In the five embodiments described above, the first and second photodetectors 24, 25 are loaded on the obliquely cut end face 22a of the translucent member 22, but these photodetectors 24, 25 Can be attached to the translucent member 22 in other forms. That is, for example, as shown in FIG.
The photodetectors 24 and 25 are arranged in close proximity to, and a diffraction grating 80 for emitting the reflected beam 15T is provided on the surface 22b.
The reflected beam 15T emitted therefrom may be received by the photodetectors 24 and 25. This also applies to mounting the photodetectors 26 and 27 on the surface 29b of the light guide 29.

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 is obtained by the converging diffraction grating formed on the guide and the end surface of the light guide formed so that the reflected beam is incident at the Brewster angle. 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.
And FIG. 8 is a side view showing the fifth embodiment device, FIG. 8 is a side view showing another example of the photodetector used in the device of the present invention, and FIG. 7 is a graph showing the relationship between the incident angle on the end face of the light guide and its transmittance and reflectance. 13 ... Magneto-optical disk, 14 ... Reflective surface of disk 15 ... Light beam, 15 '... Reflected beam 15R ... Reflected beam reflected by light guide end surface 15T ... Reflected beam transmitted through light guide end surface 16 ... Semiconductor laser, 17 ... Collimator Lens 18 ... Objective lens, 19 ... Tracking coil 20 ... Focus coil, 22 ... Transparent member 22a ... End face of transparent member, 22b ... Surface of transparent member 29 ... Light guide, 29a ... One surface of light guide 29b ... Light Other surface of guide 29d, 29f ... End surface of light guide 31 ... First FG, 32 ... Second FG 34,35,36,42,43,44,45,46,47,48,49 ... 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 (7)

[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 reflected beam irradiation position on the one surface of the light guide and extending on the surface substantially at a right angle to the tracking direction. 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. A light guide end face formed in a direction in which the reflected beam that travels back by traveling enters at a Brewster angle, and two reflected beams transmitted through at least this end face, or two reflected beams reflected by this end face A plurality of photodetectors for detecting the error, an error detection circuit for detecting a tracking error and a focus error based on the outputs of these photodetectors, and an output of the photodetectors, recorded on the recording medium. A pickup for a magneto-optical recording medium, which comprises a signal detection circuit for detecting information. 2. A first photodetector and a second photodetector respectively detecting the two reflected beams transmitted through the end face of the light guide are provided, and the two reflected beams reflected by the end face are detected. First
Third and fourth photodetectors are provided, and the error detection circuit performs the tracking error detection and the focus error detection based on the outputs of the first, second, third, and fourth photodetectors. 3. The signal detection circuit according to claim 1, wherein the signal detection circuit is formed so as to detect the information based on a sum of outputs of the third and fourth photodetectors. A pickup for the magneto-optical recording medium described. 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 magneto-optical recording medium as claimed in claim 1, wherein the light guide is arranged between the light source and the objective lens. pick up. 5. The light guide is arranged so as to reflect a light beam emitted from the light source and to advance the light beam toward a reflecting surface of the magneto-optical recording medium. A pickup for a magneto-optical recording medium according to any one of claims 1 to 3. 6. 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 5th
Item 7. A pickup for a magneto-optical recording medium according to any one of items. 7. 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 5. The pickup for magneto-optical recording medium according to any one of items 5.