JPS63261556A - Pickup for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enable a drastical cost down with the title pickup light and small sized by obtaining the action of an optical element by the converging diffraction grating (FGC) formed on an optical wave guide path. CONSTITUTION:A reflection beam is separated from the optical path of a light beam directing to a magneto-optical recording medium 13 from a light source by fetching the reflection beam from the magneto-optical recording medium 13 into an optical wave guide path 22 by FGC 31, 32. This is the same as the action fulfilled by a beam splitter. The FGC 31, 32 focus the reflection beam in the optical wave guide path 22 and this is the same as the action fulfilled by a lens. Since the 1st and 2nd FGC 31, 32 are arranged in two pieces the reflection beam from the magneto-optical recording medium 13 is separated in the tracking direction each other and focused at two places. This is the same as the action fulfilled by a prism. The light amt. of the reflection beam fetched into the optical wave guide path 22 by the 1st and 2nd FGC 31, 32 varies according to the direction of the polarized light of the reflection beam. In this case, an objective lens 18 is supported movable for the tracking and focusing directions.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application) The present invention relates to a pickup for reading signals recorded on a magneto-optical recording medium such as a magneto-optical disk, particularly a pickup using an optical waveguide. It is related to.

(Prior Art) Recently, magneto-optical recording media such as magneto-optical disks have been widely used as recording media for image signals, audio signals, etc. Signals recorded in the magneto-optical recording medium in the form of magnetization directions are read by an optical pickup. This pickup can be used for example with laser beams, etc. By irradiating the surface of a magneto-optical recording medium with polarized light and utilizing the phenomenon (magnetic Kerr effect) in which the plane of polarization of the light reflected on the recording medium rotates in accordance with the direction of magnetization, it is possible to change the magnetization on the recording medium. It is designed to detect the direction.

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

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

(Problem to be solved by the invention) However, the above-mentioned microscopic optical elements require precise processing;
Further, since it is troublesome to adjust the relative positions when assembling the pickup, a pickup using such an optical element has inevitably become expensive. Furthermore, a pickup with this configuration is large and heavy, so
This has disadvantages in terms of making the reading device smaller and lighter and shortening access time.

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

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

(Means for Solving the Problems) The pickup for magneto-optical recording media of the present invention performs the functions of the beam splitter, lens, prism, analyzer, etc. described above using a single device equipped with a light-converging diffraction grating. It is obtained by using an optical waveguide device, and specifically, it is directly applied to the surface of a magneto-optical recording medium such as an optical disk. a light source that emits a polarized light beam; an objective lens that focuses the light beam on the reflective surface of the magneto-optical recording medium; an optical waveguide, and at each reflected beam irradiation position on the surface of the optical waveguide, a first waveguide for making the reflected beam enter the leading waveguide.
A second condensing diffraction grating is arranged in parallel, and the first. The second light-collecting diffraction gratings are arranged with an axis passing through the approximate center of the reflected beam that irradiates the leading waveguide and extending approximately perpendicularly to the tracking direction on the surface of the optical waveguide, and each of them is a TE or a 1M guiding grating. The wave mode is excited and reflected beams guided in the optical waveguide are formed so as to be focused at mutually distant positions across the axis, and the first and second beams are formed on the surface or end face of the optical waveguide. A first and a second photodetector are installed to respectively detect the reflected beams focused by the two converging diffraction gratings, and the tracking error and focus are determined based on the outputs of the first and second photodetectors. The apparatus is provided with an error detection circuit that performs error detection, and a magneto-optical signal detection circuit that detects recorded information based on the outputs of the first and/or second photodetectors.

The above-mentioned light focusing diffraction grating (FGC: FocusinQ G
A rating coupler is a diffraction grating that has bends and chirps, or curves, and directly couples the spatial light wavefront outside the optical waveguide with the wavefront of the guided light traveling within the optical waveguide, and also couples the reflected beam within the optical waveguide. Focus.

(Function) By capturing the reflected beam from the magneto-optical recording medium into the optical waveguide by the above-mentioned condensing diffraction grating, the reflected beam is separated from the optical path of the light beam traveling from the light source toward the magneto-optical recording medium. This is the same effect as the beam splitter described above.

The focusing grating also focuses the reflected beam within the optical waveguide, similar to the function performed by the lens described above. Furthermore, since the two first and second light-converging diffraction gratings are arranged at the positions described above, the reflected beams from the magneto-optical recording medium are separated from each other in the tracking direction, and the beams are separated from each other in the tracking direction.
Focus in one place.

This is the same effect as the prism described above.

The amount of light of the reflected beam taken into the optical waveguide by the condensing diffraction grating of the 19th rod 2 changes depending on the polarization direction of the reflected beam. Therefore, by measuring the output of the first or second photodetector, or both, it is possible to read the polarization direction of the reflected beam, that is, the information recorded on the magneto-optical recording medium. In this way, the first. The second light-collecting diffraction grating provides the effect of the analyzer described above.

Especially the first one. If the second light-collecting diffraction grating is formed to excite a common waveguide mode, the sum of the outputs of the first and second photodetectors will be constant regardless of tracking error or focus error. become. Therefore, based on the sum of these outputs, 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 a first embodiment of the present invention, and FIG. 2 shows a planar shape of an optical waveguide and an electric circuit of this pickup.

As shown in FIG. 1, this pickup has a block 12 that is movable along an O-rad 11.11 extending in a direction substantially perpendicular to the plane of the paper. This block 12
In order to follow a signal train (track) along a predetermined group, the signal is moved in a direction perpendicular to the direction of the track (in the direction of arrow U at the beam irradiation position) or in a direction perpendicular to the direction of the track (in the direction of arrow U at the beam irradiation position), for example, using a precision feed screw and an optical system feed motor. It will be moved in the near direction.

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

An optical waveguide 22 is disposed between the collimator lens 17 and the objective lens 18, oriented so that the reflected beam 15' reflected by the magneto-optical disk 13 is received by the surface 22a. This optical waveguide 22 is formed on a transparent substrate 23. Moreover, a first .
A second light-collecting diffraction grating (hereinafter referred to as FGC)>31.
32 are provided adjacent to each other.

These FGCs 31 and 32 are curved and chirped, or curved diffraction gratings, and each
5' into the optical waveguide 22, and
It is formed to focus at one point within. 1st. The second FGCs 31 and 32 are arranged in parallel with each other across an axis (y-axis in FIG. 2) on the optical waveguide 22 that is perpendicular to the above-mentioned tracking direction and passes approximately through the center of the reflected beam 15'. are formed so as to focus the reflected beams 15' at positions separated from each other across the y-axis. Also number 1. The grating pitch of each of the second FGCs 31 and 32 is set so as to receive the S wave linearly polarized in the X-axis direction shown in FIG. 2 and excite the TE waveguide mode. Furthermore, F
The GCs 31 and 32 may be provided on the surface of the optical waveguide 22 opposite to the surface 22a (the lower surface in FIG. 1).

The m-th lattice pattern shape formula of the FGCs 31 and 32 that performs the above-mentioned function is such that the position on the optical waveguide 22 is
defined by the axis and the X axis (tracking direction axis),
The coordinates of the beam focus positions by the FGCs 31 and 32 are (-FX, Fy) and (Fx, respectively).

Fy), the optical wavelength of the reflected beam 15' is λ, the incident angle of the beam 15' to the FGCs 31 and 32 is θ, and the effective refractive index of the optical waveguide 22 for TE mode light is N, then y 5inO×NT[ (x King Fx)2+ (y-Fy
)”=mλ+const.

[Double numbers are for FGC31 and - for FGC32.
It is given by 1.

As shown in FIG. 2, the optical waveguide 22 is arranged such that the X-axis is inclined at 45 degrees with respect to the direction of linearly polarized light of the reflected beam 15' (direction of arrow P). Note that the direction of the linearly polarized light of the reflected beam 15' rotates in accordance with the direction of magnetization in the magneto-optical disk 13, so in this example, the direction of the linearly polarized light of the reflected beam 15' is
′ is the direction of linearly polarized light, and this direction and the X axis are 4
They form an angle of 5°.

The guide waveguide 22 as described above can be formed by sputtering #7059 glass on the Pyrex glass substrate 23, for example, while the FGCs 31 and 32 can be formed by sputtering 5i-N on the optical waveguide 22. After forming a resist pattern by electron beam direct writing, R
It can be formed by a method such as transferring to a 5i-N film using IE. By the way, the optical waveguide 22 is made of the above material.
(thickness: 0.76 μm), and when the FGCs 31 and 32 are formed, the center period of the FGCs 31 and 32 (TE mode excitation) whose grating patterns are defined by each of the above-mentioned shape formulas is 0.782 μm.

On the other hand, on the surface 22a of the optical waveguide 22, first photodetectors 24. A second photodetector 25 is provided. The first photodetector 24 is, for example, a photodiode P divided into two by a gap extending parallel to the y-axis.
D1. PD2, and the second photodetector 25 is also a similar photodiode PD3. PD4 roars. These photodiodes PD1 to PD4 have a lower transparent electrode 27a on the optical waveguide 22, as shown in detail in FIG.
It is formed by loading a film-like photoconductive material 27b and an upper electrode 27c in this order. A predetermined electric field is applied from a power source 27d between the lower transparent electrode 27a and the upper electrode 27c. In the photodiodes PD1 to PD4 having this configuration, when the photoconductive material 27b is irradiated with light, a photocurrent flows according to the amount of light. Therefore, by detecting the potential change at the terminal 27e, the amount of light received by the photoconductive material 27b can be detected. Note that the thin film photoconductive material 27bGt, for example 3i of the HalV group,
Ge, 3e of group IV.

■-V group GaAs1n-VI group ZnO1CdS11
It can be formed from epitaxial films such as V-VI group PbS, polycrystalline films, amorphous films, etc. It can also be formed from amorphous chalcogen films (a-8e1a-8e-AS-Te, etc.), amorphous Si A film containing mainly hydrogen and/or 77 elements (a
-8i: H, a-8iGe:H, a-8iC:H, etc.) by adding group II, group V atoms < B, P, etc.) to obtain p-n junctions and p-1-n junctions, and photo It can also be formed from a film that forms a diode, a film that forms a photodiode using a film that is mainly composed of the amorphous material 3i and contains hydrogen and/or fluorine, and an electrode that forms a Schottky junction.

As shown in FIG. 2, the outputs of the photodiodes PD1°PO2 are summed by the summing amplifier 34, and the outputs of the photodiodes PD3. The outputs of PD4 are similarly added by the adding amplifier 37, and the outputs of the first . The outputs of the outer photodiodes P01 and PO4 of each of the second photodetectors 24 and 25 are added by the summing amplifier 35, and the outputs of the inner photodiode PD2
．． The outputs of the PDs 3 are added by an adding amplifier 36. Further, the outputs of the summing amplifiers 34 and 37 are inputted to an summing amplifier 38 and a differential amplifier 40, and the summing amplifiers 35.3
The output of 6 is input to a differential amplifier 39. The output of the adder 138 is input to the differential amplifier 41. At the same time, the reference signal 3ref is input to the differential amplifier 41, and the amplifier 41 generates an 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 a reading circuit 42, a focus coil drive control circuit 43, and a tracking coil drive control circuit 44, respectively.
is input.

Next, the operation of the pickup configured as described above will be explained. A parallel light beam (laser beam) 15 emitted from the semiconductor laser 16 passes through the substrate 23 and the optical waveguide 22, and is focused by the objective lens 18 so as to be focused on the reflective surface 14 of the magneto-optical disk 13. Ru. The magneto-optical disk 13 is rotated by a rotation drive means (not shown) so that the track moves in the direction of arrow U at the irradiation position of the light beam 15. 1. As is well known, the track is a row of image signals, audio signals, etc. recorded in the form of magnetization directions (indicated by arrows above the reflective surface 14 in FIG. 15
The directions of the linearly polarized light of ' are rotated in opposite directions depending on the direction of magnetization compared to the direction of the linearly polarized light of the reflected beam 15' from the unmagnetized part. In other words, the polarization direction of the reflected beam 15' from the part magnetized in a certain direction rotates clockwise from the polarization direction - indicated by arrow P in FIG. 2, and from the part magnetized in the opposite direction. The polarization direction of the reflected beam 15' is rotated counterclockwise from the polarization direction indicated by the above arrow P.

This reflected beam 15' passes through the objective lens 18 and
The light is taken into the optical waveguide 22 by C31 and C32. The reflected beam 15' guided in the optical waveguide 22 is F
Due to the beam focusing action of each of the GCs 31 and 32, the beams are focused at two points across the y-axis. Here, as mentioned earlier, the first. The second FGCs 31 and 32 are formed so as to combine with the S-polarized component of the reflected beam 15' (the polarized component having an electric field perpendicular to the plane of the paper in FIG. 1) to excite the TE waveguide mode, and Light having an electric field vector in the direction E is guided within the optical waveguide 22. Therefore, the direction of the linearly polarized light of the reflected beam 15' is
If the rotation is more clockwise than the direction indicated by , the first rotation will occur. The amount of reflected beam 15' taken into optical waveguide 22 by the second FGCs 31 and 32 is reduced. If the direction of the linearly polarized light of the reflected beam 15' is rotated counterclockwise with respect to the direction of arrow P, the above will be reversed. To explain in more detail, if the angle between the direction of the linearly polarized light of the reflected beam 15' and the X axis in FIG. As shown by (2), it changes in proportion to CO32φ. Therefore, if the reference signal 5ref input to the differential amplifier 41 is set to a value corresponding to the light ff1Po (see FIG. 9) when the angle φ is 45°, the direction of the linearly polarized light of the reflected beam 15' is rotating clockwise from the direction indicated by arrow P in Fig. 2, the output of the differential amplifier 41 is - (minus).
On the other hand, when the rotation is counterclockwise, the output of the differential amplifier 41 can be set to + (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, the recorded information can be read.

As is clear from FIG. 9, if the range of change in angle φ is constant, the light amount Is is when the center of change is at φ=45°.
The amount of change in is the maximum, and the differential output S1 is also the maximum. Therefore, even if the rotation angle (Kerr rotation angle) of the linear polarization plane of the reflected beam 15' due to the difference in the direction of magnetization on the magneto-optical disk 13 is extremely small, <generally 0-13~
(approximately 0.5°), this rotation of the plane of polarization can be detected with high precision. However, since the amount of light detected by the photodetectors 24 and 25, that is, the sum of their outputs, is maximum when the polarization angle φ is O''', considering the S/N of the differential output S1, the polarization angle φ It is preferable to set the center point of change at an angle smaller than the above-mentioned 45° (for example, 15°, etc.).

Note that in the above embodiment, the first and second F G C31
, 32 are both formed to excite the TE waveguide mode, but they may also be formed to excite the TM waveguide mode. In that case, the amount of light 12 taken into the leading waveguide 22 is as shown by the curve ■ in FIG.
It changes in proportion to sin 2φ.

Even if this is done, the optical fJ I 2, that is, the addition amplifier 3
Since the output of 8 changes according to the polarization angle φ, it becomes possible to read recorded information using the same sphere as above.

Further, in the above example, the first and second photodetectors 24
．． Although the signal is read based on the signal obtained by adding the outputs of the photodetectors 24 and 25, it is also possible to read the signal based on the output signal of one of the photodetectors 24 and 25. When doing so, the first and second FGC31, 3
2 may excite mutually different waveguide modes. However, in that case, the output of the photodetector 24 or 25 fluctuates due to the tracking error, so it is preferable to use the method described in the above embodiment in order to prevent errors in detection due to this fluctuation.

As described above, the block 12 is sent in a direction perpendicular to the direction of the arrow U or in a direction close to it by the drive of the optical system feed motor. position) is changed and the recorded signal is read continuously. Here, the light beam 15 must be correctly irradiated onto the center of a predetermined signal train (track). Hereinafter, control for maintaining the correct irradiation position of the light beam 15 in this manner, ie, tracking control, will be described. When the center of the reflected beam 15' is located exactly between the FGC 31 and the FGC 32, the amount of light detected by the first photodetector 24 (photodiodes PD1 and PO2>) and the second photodetector 2
5 (photodiodes P'D2 and PO2) coincide with each other. Therefore, in this case, the output S3 of the differential amplifier 40 becomes O (zero). On the other hand, if the irradiation position of the light beam 15 becomes incorrect and the light intensity distribution of the reflected beam 15' shifts upward in FIG. exceeds the detected light amount. Therefore, the output S3 of the differential amplifier 40 becomes + (plus).

On the other hand, when the light intensity distribution of the reflected beam 15' shifts downward in FIG. 2, the output S3 of the differential amplifier 40 becomes - (minus). In other words, the output S3 of the differential amplifier 40 indicates the direction of the tracking error (arrow Ep x direction in FIG. 2). This output S3 is sent to the tracking coil drive control circuit 44 as a tracking error signal. Note that the method of detecting tracking errors by processing the outputs of the photodiodes PD1 to PD4 in this manner has been conventionally established as a push-pull method. The tracking coil drive control circuit 44 receives the tracking error signal S3 and supplies a current 1t to the tracking coil 1 according to the direction of the tracking error indicated by the signal S3.
9 and moves the objective lens 18 in the direction in which this tracking error is eliminated.

As a result, the light beam 15 is always correctly irradiated onto the center of the signal train.

Next, focus control, that is, control for correctly focusing the light beam 15 on the reflective surface 14 of the magneto-optical disk 13 will be explained. When the light beam 15 is focused on the reflective surface 14 of the magneto-optical disk 13, the reflected beam 15' focused by the FGC 31 is reflected by the photodiodes PD1 and P.
Focuses at an intermediate position with O2.

At this time, the reflected beam 15', which is similarly focused by the FGC 32, is focused at an intermediate position between the photodiodes PD3 and PO2. Therefore, the output of the summing amplifier 35 and the output of the summing amplifier 36 become equal, and the output S2 of the differential amplifier 39 becomes 0 (zero). On the other hand, when the light beam 15 is focused at a position closer than the reflecting surface 14, the FGC 3
The reflected beam 15' incident on each of the photodetectors 24.
’ irradiation position is inside (photodiode PD2
side and photodiode PD3 side). Therefore, in this case, the output of the summing amplifier 35 is the output of the summing amplifier 3
6, and the output S2 of the differential amplifier 39 becomes - (minus). On the other hand, 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 and 32 becomes a diverging beam, and the reflected beam 15' at each of the photodetectors 24 and 25 becomes a divergent beam. The irradiation positions are respectively displaced to the outside (to the photodiode PDI side and the photodiode PD4 side).

Therefore, in this case, the output of the summing amplifier 35 exceeds the output of the summing amplifier 36, and the output S2 of the differential amplifier 39 is +
It becomes 〈plus〉. In this way, the output S2 of the q17J 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. Note that the method of detecting focus errors by processing the outputs of the photodiodes PD1 to PD4 in this way has been conventionally implemented in the Foucault method using a Foucault prism.

The focus coil drive control circuit 43 receives the focus error signal S2, supplies a current 1f to the focus coil 20 according to the direction of the focus error indicated by the signal S2, and moves the objective lens 18 in the direction in which the focus error is eliminated. move it. Thereby, the light beam 15 is always correctly focused on the reflective surface 14 of the magneto-optical disk 13.

Note that a portion of the light beam 15 emitted from the semiconductor laser 16 is taken into the optical waveguide 22 by the FGCs 31 and 32 when heading from the collimator lens 17 to the objective lens 18. To prevent light from being reflected by the end surface 22c and received by the photodetector 24.25, it is recommended to attach a light absorbing member 45 to the end surface 22c or to roughen the end surface 22c. desirable.

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

This also applies to the embodiments described below.

In addition, the reflected beams 15' focused by the FGCs 31 and 32 are made to intersect with each other. In other words, as shown in FIG. The FGCs 31 and 32 may be formed so as to be located at the same position.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that in FIG. 4, elements that are equivalent to those in FIG. 1 are given the same numbers, and explanations thereof will be omitted unless necessary (the same applies hereinafter). In the pickup of this second embodiment, the collimator lens 17 provided in the apparatus shown in FIG.
It is designed to be incorporated into 2. In this case as well, the two systems of reflected beams 15 converged within the optical waveguide 22
' as shown in FIG. By detecting with the second photodetector 24 and 25 and processing the detection signals as described above, the recording signal, tracking error, and focus error can be detected.

The m-th grating pattern shape formula of FGCs 31 and 32 in this example is based on the position on the optical waveguide 22 and the FGC
The coordinates of the beam focusing position by 31 and 32 are defined in the same way as in the first embodiment, the optical wavelength of the reflected beam 15' is λ, the angle between the central axis of the beam 15' and the optical waveguide 22 is θ, and the beam If the distance of the beam center axis from the divergence point to FGC 31°32 is L (see Fig. 4), and the effective refractive index of the optical waveguide 22 for TE mode light is Nt E, then +mλ+const.

[Designs are given in + for FGC31 and in part for FGC32.

Next, a third embodiment of the present invention will be described with reference to FIG. In the pickup of this third embodiment, the substrate 50 is made of a material with 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. It has become. Note that a reflective thin film made of metal or the like may be provided between the buffer layer 51 and the substrate 50.

In this case as well, the reflected beam 15' from the magneto-optical disk 13 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 from, for example, an n-type 3i substrate, and a buffer layer 51 is provided to prevent the evanescent light (evanescent light) of the guided reflected beam 15' from entering the substrate 50. By providing a p-type Si layer 52 and an electrode 53 as shown in FIG. 6, it becomes possible to integrate the photodiodes PD1 to PD4.

Photodiodes PD1~ integrated in this way
PD4 is particularly preferable because it allows high-speed response.

FIG. 7 shows a pickup according to a fourth embodiment of the present invention. In this embodiment, the semiconductor laser 16
The light beam 15 emitted from the substrate 50 is reflected as a diverging beam at the interface between the substrate 50 and the buffer layer 51, and is caused to travel 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 are fixed to one head 60 and integrated,
This head 60 is supported by the block 12 so as to be movable in the tracking direction and the focusing direction.

This head 60 is moved by a tracking coil 19 and a focusing coil 20. That is, in this example, the optical waveguide 22 is moved together with the objective lens 18 for tracking control and focus control. In this way, the objective lens 18 will not be offset with respect to the optical waveguide 22 due to tracking control, unlike when only the objective lens 18 is moved, and tracking control can be performed with higher accuracy.

In the example shown in FIG.
However, even when the optical waveguide 22 and the objective lens 18 are moved integrally as described above, the light beam 15 that has passed through the optical waveguide 22 is irradiated onto the magneto-optical disk 13. Of course, the light beam 15 may be transmitted through the optical waveguide 22 in a diverging beam state or may be reflected at the interface. Further, it is also possible to fix the semiconductor laser 16 and the collimator lens 17 to the head 60 and move them together with the optical waveguide 22 and the objective lens 18.

In the five embodiments described above, the first and second photodetectors 24.25 are loaded or integrated on the surface 22a of the optical waveguide 22, but these photodetectors 24.2
5 can also be attached to the optical waveguide 22 in other forms. That is, for example, as shown in FIG.
You can also place . Also, in this way, the optical waveguide 22
When the photodetectors 24 and 25 are placed close to the surface 22a of the optical waveguide 22, as shown in FIG.
2a is provided with a diffraction grating 80 for emitting the reflected beam 15' (guided light) to the outside of the optical waveguide 22, and a photodetector 24.25 is provided.
It is also possible to increase the light reception efficiency of Furthermore, as shown in FIG. 12, the end surface 22b of the optical waveguide 22 may be polished and the photodetectors 24 and 25 may be closely fixed to the end surface 22b.

In addition, FGC31 and 32 can be formed not only by the above-mentioned manufacturing method but also by the well-known 7-otolithography method, holographic transfer method, etc. using the Brenna technology, and can be easily mass-produced. (Effects of the invention) As explained in detail above, in the pickup for magneto-optical recording media of the present invention, the function played by optical elements such as beam splitters, lenses, prisms, and analyzers in conventional pickups is that the condensing diffraction formed on the optical waveguide It can be obtained by using a lattice. Therefore, since the pickup of the present invention has an extremely small number of parts and is made small and lightweight, it is possible to significantly reduce costs and shorten access time compared to conventional devices.

Further, since the main parts of the pickup of the present invention can be easily mass-produced using brainer technology, significant cost reductions can also be achieved from this point of view as well.

Furthermore, in the pickup of the present invention, there is no need to adjust the position of the optical element as described above, and since the photodetector is coupled to the optical waveguide, there is no need to adjust the position W1 between the optical element and the photodetector. , cost reduction can also be achieved in this respect.

[Brief explanation of drawings]

FIG. 1 is a side view showing a device according to a first embodiment of the present invention, FIG. 2 is a schematic diagram showing the planar shape of an optical waveguide and an electric circuit of the device according to the first embodiment, and FIG. 3 is a side view showing the device according to the first embodiment. FIGS. 4 and 5 are side views showing details of the photodetector of the device, respectively;
A side view showing the device of the third embodiment, FIG. 6 is the third embodiment 1! 7 and 8 are side views showing the fourth and fifth embodiments of the present invention, respectively. FIG. 9 is a side view showing the reflected beam linear polarization plane angle according to the present invention, A graph showing the relationship between the tip metal taken into the optical waveguide by the condensing diffraction grating, and Figures 10.11 and 12 are side views showing other examples of the photodetector used in the device of the present invention, respectively. . 13... Magneto-optical disk 14... Reflective surface of disk 15... Light beam 15'... Reflected beam 16... Semiconductor laser 17... Collimator lens 18... Objective lens 19... Tracking coil 2o0.・Focus coil 22...
- Optical waveguide 22a...Surface of optical waveguide 22b...
End faces 23, 50 of the optical waveguide...Substrate 24.
...First photodetector 25...Second photodetector 31
...First FGC32...Second FGC 34, 35, 36, 37, 38...Summing amplifier 39,
40.41...Differential amplifier 42...Reading circuit 4
3... Focus coil drive burial circuit 44... Tracking coil drive control circuit 51... Buffer layer
60...Head PD1-4...Photodiode Figure 1 Figure 3 - Figure 6 Figure 7 Figure 10 Figure 11 Figure 12

Claims (7)

[Claims] (1) A light source that irradiates a linearly polarized light beam onto the surface of a magneto-optical recording medium, an objective lens that focuses the light beam on a reflective surface of the magneto-optical recording medium, and a reflection reflected by the magneto-optical recording medium. An optical waveguide arranged to receive the beam on one surface, and an axis passing through the approximate center of the beam and extending approximately perpendicular to the tracking direction on this surface at the reflected beam irradiation position on the surface of this optical waveguide. are arranged in parallel, each excites the TE or TM waveguide mode to make the reflected beam enter the optical waveguide, and the reflected beam guided in the optical waveguide is spaced apart from each other across the axis. first and second condensing diffraction gratings that are respectively focused on positions; and each reflected beam that is attached to the surface or end face of the optical waveguide and that is focused by the first and second condensing diffraction gratings is detected. an error detection circuit that detects a tracking error and a focus error based on the outputs of the first and second photodetectors; A pickup for a magneto-optical recording medium, comprising a magneto-optical signal detection circuit that detects information recorded on the recording medium based on the output of a detector. (2) The first and second light-collecting diffraction gratings are formed to excite a common waveguide mode, and the magneto-optical signal detection circuit is configured to detect outputs of the first and second photodetectors. 2. 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. (3) The optical waveguide is arranged such that the polarization direction of the reflected beam is inclined by approximately 0° to 45° with respect to a plane including the axis and the central axis of the reflected beam. The pickup for a magneto-optical recording medium according to item 1 or 2. (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 using the push-pull method and the Foucault method, respectively. A pickup for a magneto-optical recording medium according to any one of claims 1 to 3, characterized in that it comprises a split photodetector. (5) The substrate of the optical waveguide is made of a transparent member, and the optical waveguide is disposed between the light source and the objective lens. A pickup for magneto-optical recording media as described in Section 1. (6) A buffer layer is provided between the optical waveguide and its substrate, and the optical waveguide reflects the light beam emitted from the light source at an interface between the buffer layer and the substrate,
Claims 1 to 4 are arranged to advance toward the magneto-optical recording medium.
A pickup for a magneto-optical recording medium according to any one of the items. (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 Items 1 to 6. (8) Claims 1 to 6, characterized in that the optical waveguide is integrated with the objective lens and is moved together with the objective lens for tracking control and focus control. A pickup for a magneto-optical recording medium according to any one of the items.