JPH0675308B2 - Pickup for magneto-optical recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 to a pickup using an optical waveguide. It is a thing.

(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. Has been.

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 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 according to the present invention has the function of the above-mentioned beam splitter, lens, prism, analyzer, etc. 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 the above-mentioned light beam on the reflecting surface of the magneto-optical recording medium. The objective lens for focusing on the optical waveguide and the optical waveguide arranged so as to receive the reflected beam reflected by the magneto-optical recording medium on one surface are provided. First and second converging diffraction gratings for making a beam incident on this optical waveguide are arranged side by side, and the first and second converging diffraction gratings are arranged at substantially the center of the reflected beam irradiating the optical waveguide. Pass and the Line the axes of the waveguide extending at right angles to the tracking direction on the surface of the waveguide, and each of them excites the TE or TM waveguide mode, and separates the reflected beams propagating in the optical waveguide from each other with the axes above. The first and second detection beams are formed so that they are respectively focused at different positions, and the reflected beams focused by the first and second converging diffraction gratings are respectively detected on the surface or the end face of the optical waveguide. A photodetector is attached, and an error detection circuit for detecting a tracking error and a focus error based on the outputs of the first and second photodetectors, and an output of the first and / or second photodetector. And a magneto-optical signal detection circuit for detecting recorded information based on the recorded information.

The above condensing diffraction grating (FGC: Focusing Grating Coupler)
Is a diffraction grating having a bend and a chirp or a bend, which directly couples the spatial light wavefront outside the optical waveguide and the wavefront of the guided light traveling inside the optical waveguide, and also focuses the reflected beam inside the optical waveguide.

(Operation) By taking the reflected beam from the magneto-optical recording medium into the optical waveguide by the above-mentioned converging diffraction grating, 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. The converging diffraction grating focuses the reflected beam in the optical waveguide, which is the same as the function of the lens described above. Furthermore, since two first and second converging 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 focused at two points. This is the same as the function of the prism described above.

The light amount of the reflected beam taken into the optical waveguide by the first and second converging diffraction gratings changes according to the polarization direction of the reflected beam. Therefore, by measuring the output of the first or second photodetector or both of them, the polarization direction of the reflected beam, that is, the recorded information on the magneto-optical recording medium can be read. In this way, the first and second condensing diffraction gratings provide the function of the analyzer described above.

In particular, if the first and second converging diffraction gratings are formed so as to excite the common waveguide mode, the sum of the outputs of the first and second photodetectors will be the tracking error and the focus error. It becomes constant regardless of Therefore, based on the sum of these outputs, the recorded information on the magneto-optical recording medium can be read more accurately.

(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 the first embodiment of the present invention, and FIG. 2 shows a plan view of an optical waveguide 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 groove, this block 12 uses, for example, a precision feed screw and an optical system feed motor,
The track is moved in a direction perpendicular to the direction of the track (direction of arrow U at the beam irradiation position) or a direction close thereto.

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 for focusing a parallel 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.

An optical waveguide 22 is arranged between the collimator lens 17 and the objective lens 18 in such a direction that the reflected beam 15 'reflected by the magneto-optical disk 13 is received by the surface 22a. The optical waveguide 22 is formed on a transparent substrate 23. Further, at the position where the reflected beam 15 ′ is irradiated, the surface 22a of the optical waveguide 22 is provided with first and second condensing diffraction gratings (hereinafter, referred to as FGC) 31, 32 adjacent to each other. There is. These FGCs 31 and 32 are diffraction gratings having bends and chirps, or bends, and each is formed so that the reflected beam 15 ′ is made incident on the optical waveguide 22 and is focused at one point in the optical waveguide 22. . First and second FGC 31,32
Is the reflected beam at a right angle to the aforementioned tracking direction
An axis on the optical waveguide 22 that passes through substantially the center of 15 '(y in FIG.
Are arranged side by side, and each is formed so as to focus the reflected beam 15 'at a position apart from each other with this y axis in between. The grating pitches of the first and second FGCs 31, 32 are set so as to excite the TE guided mode by receiving the S wave linearly polarized in the x-axis direction shown in FIG. The FGCs 31 and 32 may be provided on the surface of the optical waveguide 22 opposite to the surface 22a (lower surface in FIG. 1).

The m-th lattice pattern shape formula of the FGCs 31, 32 that perform the above-described action defines the position on the optical waveguide 22 by the y-axis and the x-axis (tracking direction axis), and
The coordinates of the beam focusing position by (−Fx, Fy),
(Fx, Fy), the optical wavelength of the reflected beam 15 ′ is λ, the incident angle of the beam 15 ′ to the FGCs 31, 32 is θ, and the effective refractive index of the optical waveguide 22 for TE mode light is N, [Compounds are given as + for FGC31 and-for FGC32].

And the optical waveguide 22 is, as shown in FIG.
The x-axis is 4 with respect to the 5'direction of the linearly polarized light (direction of arrow P).
It is placed so that it tilts 5 °. The reflected beam 1
The 5'direction of the linearly polarized light rotates in accordance with the direction of the magnetization in the magneto-optical disk 13, so in this example, the direction of the linearly polarized light of the reflected beam 15 'reflected by the non-magnetized portion is used as a reference. , This direction and the x-axis form an angle of 45 °.

The optical waveguide 22 as described above can be formed, for example, by sputtering # 7059 glass on the Pyrex glass substrate 23, while the FGCs 31 and 32 use Si-N PCVD on the optical waveguide 22.
The film can be formed by a method such as forming a film by, forming a resist pattern by electron beam direct writing, and then transferring to a Si-N film by RIE. By the way, when the optical waveguide 22 (thickness 0.76 μm) and the FGCs 31 and 32 are formed of the above materials, the FGC3 whose lattice pattern is defined by the above-mentioned shape formulas is used.
The center period of 1,32 (TE mode excitation) is 0.782 μm.

On the other hand, on the surface 22a of the optical waveguide 22, the first reflected beam 15 ', which is focused as described above, is detected so as to be respectively detected.
The photodetector 24 and the second photodetector 25 are provided. As an example, the first photodetector 24 is composed of photodiodes PD1 and PD2 divided into two by a gap extending in parallel with the y-axis, and the second photodetector 25 is also the same photodiode PD.
It consists of 3, PD4. As shown in detail in FIG. 3, for example, these photodiodes PD1 to PD4 are formed by loading a lower transparent electrode 27a, a thin film photoconductive material 27b, and an upper electrode 27c on the optical waveguide 22 in this order. It is a thing. A power supply 27d is provided between the lower transparent electrode 27a and the upper electrode 27c.
, A predetermined electric field is applied. In the photodiodes PD1 to PD4 of this configuration, when the photoconductive material 27b is irradiated with light, a photocurrent corresponding to the amount of light flows. Therefore,
If the potential change at the terminal 27e is detected, the photoconductive material 2
The amount of light received by 7b can be detected. The thin-film photoconductive material 27b 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 for forming a photodiode by obtaining a pin junction, a film for forming a photodiode by using an electrode forming a Schottky junction with a film containing hydrogen and / or fluorine mainly containing the amorphous Si. You can also

As shown in FIG. 2, the outputs of the photodiodes PD1 and PD2 are added by the adding amplifier 34, and the photodiodes PD3 and PD2 are also added.
The outputs of 4 are likewise summed by the summing amplifier 37, and
The outputs of the outer photodiodes PD1 and PD4 of the second photodetectors 24 and 25 are added by the adding amplifier 35, and the outputs of the inner photodiodes PD2 and PD3 are added by the adding amplifier 36. The outputs of the summing amplifiers 34 and 37 are the summing amplifier 38.
Input to differential amplifier 40, and summing amplifier 35,3
The output of 6 is input to the differential amplifier 39. Above summing amplifier 3
The output of 8 is input to the differential amplifier 41. At the same time, the reference signal Sref is input to the differential amplifier 41, and the amplifier 41 outputs the output S1 according to the difference between these inputs. The output S1 of the differential amplifier 41, the output S2 of the differential amplifier 39, and the output S3 of the differential amplifier 40 are input to the reading circuit 42, the focus coil drive control circuit 43, and the tracking coil drive control circuit 44, respectively.

Next, the operation of the pickup having the above structure will be described. A light beam (laser beam) 15 emitted from a semiconductor laser 16 and made into a parallel beam is transmitted through a substrate 23 and an optical director 22, and focused by an objective lens 18 so as to be focused on a reflecting surface 14 of a magneto-optical disk 13. To be done. 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 direction of polarization of the reflected beam 15 'from the part magnetized in a certain direction rotates clockwise from the polarization direction shown by the arrow P in FIG. 2 and from the part magnetized in the opposite direction. The polarization direction of the reflected beam 15 'rotates counterclockwise from the polarization direction indicated by the arrow P.

This reflected beam 15 'passes through the objective lens 18 and
Are taken into the optical waveguide 22. The reflected beam 15 'guided in the optical waveguide 22 is focused at two points across the y axis by the beam focusing action of each of the FGCs 31 and 32. Here, as described above, the first and second FGCs 31, 32
Is formed so as to combine with the S-polarized component of the reflected beam 15 '(polarized component having an electric field perpendicular to the paper surface in FIG. 1) to excite the TE guided mode, and the electric field in the direction indicated by arrow E in FIG. Light having a vector is guided in the optical waveguide 22. Therefore, if the direction of the linearly polarized light of the reflected beam 15 'rotates clockwise relative to the direction indicated by the arrow P, the first and second
The FGCs 31 and 32 reduce the light amount of the reflected beam 15 'taken into the optical waveguide 22. If the direction of the linearly polarized light of the reflected beam 15 'rotates counterclockwise as compared with the direction of arrow P, the above is reversed. More specifically, assuming that the angle formed by the direction of the linearly polarized light of the reflected beam 15 'and the x axis in FIG. 2 is φ, the light quantity I ₁ taken into the optical waveguide 22 by the FGCs 31 and 32 is shown in FIG. As shown by the curve, it changes in proportion to cos ² φ. Therefore, if the reference signal Sref input to the differential amplifier 41 is set to a value corresponding to the light amount P ₀ (see FIG. 9) when the angle φ is 45 °, the linearly polarized light of the reflected beam 15 ′ is When the direction is clockwise from the direction indicated by arrow P in FIG. 2, the output of the differential amplifier 41 is-(minus), and when the direction is counterclockwise, the differential amplifier 41 is opposite. The output of can be + (plus).
By determining the output S1 of the differential amplifier 41 in this way,
The direction of magnetization on the magneto-optical disk 13, that is, recorded information can be read.

As is clear from FIG. 9, if the change width of the angle φ is constant, the change amount of the light amount I ₁ becomes maximum when the change center is φ = 45 °, and the differential output S 1 also becomes maximum. . Therefore, even if the linear polarization plane rotation angle (Kerr rotation angle) of the reflected beam 15 'due to the difference in the direction of magnetization on the magneto-optical disk 13 is extremely small (generally about 0.3 to 0.5 °), Rotation can be detected with high accuracy. However, the amount of light detected by the photodetectors 24 and 25, that is, the sum of their outputs, is
Since the maximum is obtained when the polarization angle φ is 0 °, S / of the differential output S1
From the point of N, the change center point of the polarization angle φ is 45 ° above.
It is preferable to set the angle smaller than the above (for example, 15 °).

In the above embodiment, both the first and second FGCs 31, 32 are formed so as to excite the TE guided mode, but they may be formed so as to excite the TE guided mode. In that case, the amount of light I ₂ taken into the optical waveguide 22 is
As shown by the curve in FIG. 9, it changes in proportion to sin ² φ. Even in this case, the amount of light I _2, that is, the output of the adding amplifier 38 changes according to the polarization angle φ, so that the recorded information can be read in the same manner as described above.

In the above example, the first and second photodetectors 24,2
Although the signal reading is performed based on the signal obtained by adding the outputs of 5, it is also possible to perform the signal reading based on the output signal of one of the photodetectors 24 and 25. In that case, the first and second FGCs 31 and 32 may excite different waveguide modes. However, in that case, the output of the photodetector 24 or 25 fluctuates due to a tracking error. Therefore, in order to prevent signal erroneous 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 FGC31 and FGC32, the first photodetector 24
The amount of light detected by (photodiodes PD1 and PD2) and the amount of light detected by the second photodetector 25 (photodiodes PD2 and PD4) match. Therefore, in this case, the output S3 of the differential amplifier 40 becomes 0 (zero). On the other hand, when the irradiation position of the light beam 15 becomes incorrect and the light intensity distribution of the reflected beam 15 'is displaced to the upper side in FIG. 2, the amount of light detected by the first photodetector 24 is changed to the second photodetector 25. Exceeds the detected light intensity of. Therefore, the output S3 of the differential amplifier 40 becomes + (plus). On the contrary, when the light intensity distribution of the reflected beam 15 'is displaced to the lower side in FIG. 2, the output of the differential amplifier 40 is S3- (minus). That is, the output S3 of the differential amplifier 40 indicates the direction of tracking error (direction of arrow x in FIG. 2). This output S3 is sent to the tracking coil drive control circuit 44 as a tracking error signal. The method of processing the outputs of the photodiodes PD1 to PD4 to detect the tracking error in this way is conventionally established as a push-pull method. The tracking coil drive control circuit 44 receives the tracking error signal S3, supplies a current It corresponding to the direction of the tracking error indicated by the signal S3 to the tracking coil 19, and moves the objective lens 18 in the direction in which the tracking error is eliminated. To move. 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 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 FGC 31
5'is focused at an intermediate position between the photodiodes PD1 and PD2. At this time, the reflected beam 1 similarly focused by the FGC 32
5'is focused at an intermediate position between the photodiodes PD3 and PD4. Therefore, the output of the adding amplifier 35 and the output of the adding amplifier 36 become equal, and the output S2 of the differential amplifier 39 is 0 (zero).
Becomes On the other hand, when the light beam 15 is focused at a position closer than the reflecting surface 14, the reflected beam incident on the FGC 31, 32
15 'becomes a convergent beam, and the irradiation position of the reflected beam 15' on each of the photodetectors 24 and 25 is displaced inward (to the photodiode PD2 side and the photodiode PD3 side). Therefore, in this case, the output of the addition amplifier 35 becomes lower than the output of the addition amplifier 36, and the output S2 of the differential amplifier 39 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 FGCs 31, 32 becomes a divergent beam, and the reflected beam 15 ′ at each of the photodetectors 24, 25 becomes The irradiation positions are respectively displaced to the outside (the photodiode PD1 side and the photodiode PD4 side). Therefore, in this case, the output of the adding amplifier 35 exceeds the output of the adding amplifier 36, and the output S2 of the differential amplifier 39 becomes + (plus). Thus, the output S2 of the differential amplifier 39
Indicates the direction of the focus error. This output S2 is sent to the focus coil drive control circuit 43 as a focus error signal. The method of processing the outputs of the photodiodes PD1 to PD4 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 43 uses the focus error signal S2
In response to this, a current If corresponding to the direction of the focus error indicated by the signal S2 is supplied to the focus coil 20, and the objective lens 18 is moved in the 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.

It should be noted that the light beam 15 emitted from the semiconductor laser 16 is generated by the FGC 31, when traveling from the collimator lens 17 to the objective lens 18.
Since a part of the light beam 15 is taken into the optical waveguide 22 by 32, the light beam 15 is reflected by the end face 22c of the optical waveguide 22 and the photodetector 2
It is desirable that a light absorbing member 45 be attached to the end face 22c or that the end face 22c be roughened so that the end face 22c is not received by the light.

Further, in this embodiment, the two FGCs 31 and 32 are formed in a state where their respective lattices are continuous and in close contact with each other, but these FGCs 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 which is respectively focused by FGC31, 32
5'cross each other, that is, FGC if explained in FIG.
FGC31, 32 so that the beam focusing position by 31 is below the y-axis and the beam focusing position by FGC32 is above the y-axis.
May be formed.

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 optical waveguide 22 in a converged beam state. It has become. Also in this case, the optical waveguide 22
Two reflected beams 15 'that converge in the inside are detected by the first and second photodetectors 24 and 25 as shown in FIG. 2, and the detected signals are processed as described above to record. Signals, tracking errors and focus errors can be detected.

The m-th grating pattern shape formula of the FGCs 31 and 32 in this embodiment defines the position on the optical waveguide 22 and the coordinates of the beam focusing position by the FGCs 31 and 32 in the same manner as in the first embodiment, and the reflected beam 15 ′ Is the wavelength of light, λ is the angle between the central axis of the beam 15 ′ and the optical waveguide 22, and θ is the beam divergence point.
The distance of the beam center axis to 1,32 is L (see Fig. 4), TE
Let N _TE be the effective refractive index of the optical waveguide 22 for mode light, [Compounds are given as + for FGC31 and-for FGC32].

Next, a third embodiment of the present invention will be described with reference to FIG. In the pickup of the third embodiment, the substrate
50 is formed of a material having a sufficiently high refractive index, and the light beam 15
Is reflected at the interface between the substrate 50 and the buffer layer 51 and travels toward the magneto-optical disk 13 side. A reflective thin film such as metal may be provided between the buffer layer 51 and the substrate 50. Also in this case, the reflected beam 1 from the magneto-optical disk 13
5'is taken into the optical waveguide 22 by the three FGCs 31 and 32.

In the case of the above configuration, it is not necessary to form the substrate 50 from a transparent member. Therefore, in this case, the substrate 50 is formed of, for example, an n-type Si substrate, and the reflected beam is guided.
A buffer layer 51 for preventing the leaked light (evanescent light) of 15 'from entering the substrate 50 is provided, and a p-type Si layer 52 and an electrode 53 as shown in FIG. It is possible to integrate PD4. The photodiodes PD1 to PD4 integrated in this way are particularly preferable because they can respond at high speed.

FIG. 7 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 used as a divergent beam on the substrate.
It is reflected at the interface between the buffer layer 50 and the buffer layer 51, 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 optical waveguide 22 and the objective lens
18 and 18 are fixed and integrated with one head 60, and this head 60 is supported on the block 12 so as to be movable in the tracking direction and the focus direction. The head 60 includes a tracking coil 19 and a focus coil.
Moved by 20. In other words, in this example, the optical waveguide 22 is the objective lens for tracking control and focus control.
Moved with 18. By doing this, the objective lens
Since the objective lens 18 is not offset from the optical waveguide 22 by the tracking control as in the case of moving only 18, the tracking control can be performed more accurately.

In the example of FIG. 8, the substrate 50 and the buffer layer 51 are
Although the light beam 15 reflected at the interface of is irradiated onto the magneto-optical disk 13, even when the optical waveguide 22 and the objective lens 18 are integrally moved as described above, the light transmitted through the optical waveguide 22 is It is of course possible to irradiate the magneto-optical disk 13 with the beam 15, and of course, the light beam 15 may be transmitted through the optical waveguide 22 or reflected at the interface in the state of a divergent beam. Further, the semiconductor laser 16 and the collimator lens 17 can also be fixed to the head 60 and moved integrally with the optical waveguide 22 and the objective lens 18.

In the five embodiments described above, the first and second photodetectors 24 and 25 are loaded or integrated on the surface 22a of the optical waveguide 22, but these photodetectors 24 and 25 are It is also possible to attach to the optical waveguide 22 in a form. That is, for example, as shown in FIG. 10, the photodetectors 24 and 25 can be arranged close to the surface 22a of the optical waveguide 22. Further, when the photodetectors 24 and 25 are arranged close to the surface 22a of the optical waveguide 22 as described above, as shown in FIG.
It is also possible to increase the light receiving efficiency of the photodetectors 24 and 25 by providing a diffraction grating 80 for emitting the reflected beam 15 '(guided light) to the outside of the optical waveguide 22 on the surface 22a of the. Further, as shown in FIG. 12, after polishing the end face 22b of the optical waveguide 22, the end face 22b is polished.
The photodetectors 24 and 25 can be closely fixed to each other.

Further, the FGCs 31 and 32 are not limited to the above-described manufacturing method, and can be formed by the planar technique by a well-known photolithography method, 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 magneto-optical recording medium of the present invention, the action that optical elements such as a beam splitter, a lens, a prism, and an analyzer in the conventional pickup play is formed on the optical waveguide. It can be obtained by the light condensing diffraction grating. 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.

Furthermore, 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 optical waveguide. 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. FIG. 4 is a side view showing the photodetector of the device in detail, FIGS. 4 and 5 are respectively a second embodiment device of the present invention,
FIG. 6 is a side view showing the third embodiment device, FIG. 6 is a side view showing the photodetector of the third embodiment device in detail, and FIGS. 7 and 8 are the fourth and fifth embodiment devices of the present invention, respectively. FIG. 9 is a side view showing the relationship between the linear polarization plane angle of the reflected beam according to the present invention and the amount of light taken into the optical waveguide by the converging diffraction grating, and FIGS. It is a side view which shows the other example of the photodetector used for the apparatus of this invention. 13 ... Magneto-optical disc, 14 ... Reflecting 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 ... Optical waveguide 22a ... surface of optical waveguide, 22b ... end face of optical waveguide 23,50 ... substrate, 24 ... first photodetector 25 ... second photodetector, 31 ... first FGC 32 ... second FGC 34,35 , 36, 37, 38 ... Addition amplifier 39, 40, 41 ... Differential amplifier, 42 ... Reading circuit 43 ... Focus coil drive control circuit 44 ... Tracking coil drive control circuit 51 ... Buffer layer, 60 ... Head PD1-4 ... Photo diode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-237245 (JP, A) JP-A 63-148448 (JP, A) JP-A 63-200348 (JP, A) JP-A 63- 247939 (JP, A) Actual development Sho 63-188844 (JP, U)

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. An optical waveguide arranged so as to receive the reflected beam on one surface, and an axis extending substantially at the center of the beam and extending substantially perpendicular to the tracking direction on the surface at the reflected beam irradiation position on the surface of the optical waveguide. Side by side, each
A TE or TM waveguide mode is excited to cause the reflected beam to enter the optical waveguide, and the reflected beams guided in the optical waveguide are each focused at positions separated from each other with the axis interposed therebetween. And a second converging diffraction grating, and first and second detection beams attached to the surface or the end face of the optical waveguide for detecting each reflected beam focused by the first and second converging diffraction gratings. A photodetector, an error detection circuit for detecting a tracking error and a focus error based on outputs of the first and second photodetectors, and an output of the first and / or second photodetector A pickup for a magneto-optical recording medium, which comprises a magneto-optical signal detection circuit for detecting information recorded on the recording medium. 2. The first and second converging diffraction gratings are formed so as to excite a common waveguide mode, and the magneto-optical signal detection circuit is provided in the first and second photodetectors. The pickup for a magneto-optical recording medium according to claim 1, wherein the pickup is configured to detect the information based on a sum of outputs. 3. A plane including the axis and the central axis of the reflected beam, and the polarization direction of the reflected beam are inclined by approximately 0 ° to 45 °,
The magneto-optical recording medium pickup according to claim 1, wherein the optical waveguide is arranged. 4. The first and second photodetectors are divided by a gap extending substantially parallel to the axis so that tracking error detection and focus error detection can be performed by the push-pull method and Foucault method, respectively. A magneto-optical recording medium pickup according to any one of claims 1 to 3, wherein the pickup comprises a two-divided photodetector. 5. The substrate of the optical waveguide comprises a transparent member,
The optical waveguide is arranged between the light source and the objective lens.
Item 7. A pickup for a magneto-optical recording medium according to any one of items. 6. A buffer layer is provided between the optical waveguide and the substrate thereof, and the optical waveguide reflects the light beam emitted from the light source at an interface between the buffer layer and the substrate, and The pickup for a magneto-optical recording medium according to any one of claims 1 to 4, wherein the pickup is arranged so as to advance toward the recording medium. 7. The optical waveguide 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 claims 1 to 6. 8. The optical waveguide according to claim 1, wherein the optical waveguide is integrated with the objective lens, and is moved together with the objective lens for tracking control and focus control. Item 6 any 1
A pickup for a magneto-optical recording medium according to the item.