JPH0675309B2 - 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 particular, when performing differential detection in order to improve the S / N of the read signal, a half mirror for splitting the reflected beam into two beams is required. Since it may require two photons, the pickup becomes even more complex, bulky and heavy.

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

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

(Means for Solving the Problems) The pickup for a magneto-optical recording medium of the present invention is achieved by the beam splitter, the lens, the prism, the analyzer, and the half mirror for performing the differential detection described above. The function is obtained by two optical waveguide elements having a converging diffraction grating. Specifically, a light source for irradiating a surface of a magneto-optical recording medium such as an optical disk with a linearly polarized light beam is used. An objective lens that focuses the light beam on the reflecting surface of the magneto-optical recording medium and is integrated in a state of overlapping with each other, and is oriented so that the reflected beam reflected by the magneto-optical recording medium is received on one surface. The first and second optical waveguides are provided, and the first and second light-converging properties for causing the reflected beam to enter the first optical waveguide are provided at the reflected beam irradiation positions on the surface of the first optical waveguide. Folded gratings are arranged side by side, and on the other hand, at the position where the surface of the second optical waveguide is irradiated with the reflected beam, that is, at the position where it overlaps with the first and second converging diffraction gratings, the reflected beam is guided inside the second optical waveguide. Incident on the third
Is provided, and the first and second converging diffraction gratings pass through substantially the center of the reflected beam irradiating the first optical waveguide and on the surface of the optical waveguide in the tracking direction. Lined up with axes extending at right angles, each of which excites either TE or TM guided mode, and the reflected beams guided in the same waveguide mode in this optical waveguide are sandwiched by the axes described above. The third converging diffraction grating is formed so as to be focused at distant positions, while the third converging diffraction grating is different from the guided mode (that is, the first and second converging modes, for example, by the first and second converging diffraction gratings). When the second converging diffraction grating excites the TE waveguide mode, the TM waveguide mode is excited to cause the above-mentioned reflected beam to enter the second optical waveguide, and the reflection is guided in this optical waveguide. The beam is formed so as to be focused, and the first or second light guide is formed. First, second and third photodetectors for detecting the respective reflected beams focused by the first, second and third converging diffraction gratings are attached to the surface or the end face of the path, and further An error detection circuit for detecting a tracking error and a focus error based on outputs of the first and second photodetectors; an output of the first and / or second photodetector;
And a differential detection circuit for detecting recorded information based on the difference between the outputs of the photodetectors.

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 first and second condensing diffraction gratings are formed so as to excite the TE (TM) guided mode, while the third condensing diffraction grating is formed so as to excite the TM (TE) guided mode. As a result, the output of the first and / or second photodetector and the output of the third photodetector will change in a complementary manner according to the direction of polarization of the reflected beam. If the difference in output is detected by the differential detection circuit, the direction of polarization of the reflected beam, that is, the recorded information on the magneto-optical recording medium can be read. As a result, a read signal with a high S / N can be obtained as in the case where the differential detection optical system is provided and differential detection is performed. That is, by providing the third converging diffraction grating in addition to the first and second converging diffraction gratings, the beam splitting function achieved by the above-mentioned half mirror or the like can be obtained, and each converging diffraction grating can be obtained. By setting the excitation waveguide mode by the above, the action achieved by the above two analyzers can be obtained.

It is possible to arrange the above-mentioned first, second and third converging diffraction gratings side by side on the surface of one optical waveguide, but it is possible to use TE (TM) by the first and second converging diffraction gratings. In some cases, the S (P) polarization component of the reflected beam that is coupled with the mode-guided light cannot enter the optical waveguide due to the third converging diffraction grating. The portion of the S (P) polarization component of irradiating the portion of the third condensing diffraction grating cannot be used at all. And, of course, the opposite can happen. However, if the first and second converging diffraction gratings and the third converging diffraction grating are provided so as to overlap each other as in the device of the present invention, the first and second (third) The polarization component of the reflected beam that did not enter the first (second) optical waveguide due to the condensing diffraction grating also passes through this diffraction grating, and the third (first, second) converging diffraction Since the grating allows the light to enter the second (first) optical waveguide, the detection efficiency of the reflected beam and thus the light utilization efficiency are improved as compared with the above case.

(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.

A second optical waveguide 29 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 29a. The second optical waveguide 29 is integrated with the first optical waveguide 22 formed on the transparent substrate 23 via the buffer layer 28. The buffer layer 28 is formed of a transparent material having a lower refractive index than the optical waveguides 22 and 29. Further, at the position where the reflected beam 15 'is irradiated, the first and second converging diffraction gratings (hereinafter, referred to as FGC) 31, 32 are adjacent to each other on the surface 22a of the first optical waveguide 22. It is provided (see FIG. 3). These FGCs 31 and 32 are diffraction gratings having bends and chirps, or bends, and each of them makes the reflected beam 15 ′ enter the first optical waveguide 22,
The optical waveguide 22 is formed so as to be focused at one point. The first and second FGCs 31 and 32 are arranged side by side with an axis (y-axis in FIG. 2) on the optical waveguide 22 which is orthogonal to the above-mentioned tracking direction and which passes through substantially the center of the reflected beam 15 '. Further, each is formed so as to focus the reflected beam 15 'at positions apart from each other across the y-axis.

On the other hand, the third FGC 33 is provided on the surface 29a of the second optical waveguide 29. The third FGC 33 is basically the same as the first and second FGCs 31 and 32, and has an opening area substantially equal to the opening areas of these FGCs 31 and 32, and is provided at a position overlapping with the FGCs 31 and 32. Has been.

Here, the grating pitch is set so that the first and second FGCs 31 and 32 excite the TE waveguide mode, while the third FGC 33 excites the TM waveguide mode. And optical waveguide 22,29
As shown in FIG. 2, is arranged such that the x axis is inclined by 45 ° with respect to the direction of the linearly polarized light of the reflected beam 15 '(direction of arrow P). Since the direction of the linearly polarized light of the reflected beam 15 ′ rotates in correspondence with the direction of the magnetization of the magneto-optical disk 13, in this example, the direction of the linearly polarized light of the reflected beam 15 ′ reflected by the non-magnetized portion. With this as a reference, this direction and the x-axis form an angle of 45 °. The 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). Also
The same applies to FGC33.

The m-th lattice pattern shape formula of the FGCs 31 and 32 that performs the above-described action defines the position on the optical waveguide 22 by the x-axis (tracking direction axis) and the y-axis shown in FIG.
The coordinates of the beam focus position by 1,32 are (-Fx, F
y), (Fx, Fy), and the optical wavelength of the reflected beam 15 ′ is λ, the incident angle of the beam 15 ′ on the FGCs 31, 32 is θ, and the effective refractive index of the first optical waveguide 22 for TE mode light. _Is N _TE , [Compounds are given as + for FGC31 and-for FGC32].

On the other hand, the m-th grating pattern shape formula of FGC33 is the coordinates of the beam focusing position by FGC33 (0, Fy), the effective refractive index of the second optical waveguide 29 for TM mode light is N _TM , and others are the same as above. If you specify Given in.

The first optical waveguide 22 is, for example, a Pyrex glass substrate
# 7059 glass can be sputtered onto the 23. The second optical waveguide 29 can also be formed by providing the transparent buffer layer 28 made of, for example, SiO ₂ on the first optical waveguide 22, and then sputtering # 7059 glass on the transparent buffer layer 28. On the other hand, the FGC 31, 32, and 33 are S on the optical waveguide 22 or 29.
It can be formed by a method of forming a film of iN by PCVD, forming a resist pattern by direct writing with an electron beam, and then transferring it to a Si-N film by RIE. By the way, when the optical waveguides 22 and 29 (thickness 0.76 μm) and FGCs 31, 32 and 33 are formed from the above materials, the FGC31 and 32 (TE mode excitation) in which the lattice pattern is defined by the above-mentioned shape formulas
Center period of 0.782 μm, FGC33 (TM mode excitation)
The center period of is 0.786 μm.

On the other hand, as shown in FIG. 3 showing only the first optical waveguide 22, the reflected beams 15 'focused as described above are respectively detected on the surface 22a of the optical waveguide 22. Further, a first photodetector 24 and a second photodetector 25 are provided. A third photodetector 26 is similarly provided on the surface 29a of the second optical waveguide 29. As an example, the first photodetector 24 has a gap extending in parallel with the y-axis.
It is composed of divided photodiodes PD1 and PD2, and the second photodetector 25 is also composed of similar photodiodes PD3 and PD4. On the other hand, the third photodetector 26 is a photodiode
It consists of PD5. The photodiode PD5 is, for example, as shown in detail in FIG. 4, a lower transparent electrode 27 on the optical waveguide 29.
It is formed by loading a, a thin film photoconductive material 27b, and an upper electrode 27c in this order. Then, a predetermined electric field is applied from the power source 27d between the lower transparent electrode 27a and the upper electrode 27c. In the photodiode PD5 having this configuration, when the photoconductive material 27b is irradiated with light, a photocurrent corresponding to the amount of light flows. Therefore, the amount of received light of the photoconductive material 27b can be detected by detecting the potential change at the terminal 27e. Photodiodes PD1-4
Is also formed similarly to the photodiode PD5. The thin film photoconductive material 27b is, for example, a group IV Si, Ge, IV
Group Se, III-V group GaAs, II-VI group ZnO, CdS, IV-VI group PbS, etc. epitaxial films, polycrystalline films, amorphous films, etc. Chalcogen film (a-Se,
a-Se-As-Te, etc.), mainly amorphous Si and hydrogen and /
Alternatively, a pn junction or a pin junction can be formed by adding a Group III or V group atom (B, P, etc.) to a film containing fluorine (a-Si: H, a-SiGe: H, a-SiC: H, etc.). It can also be formed from a film that forms a photodiode, a film that forms a photodiode using an electrode that forms a Schottky junction with the film that mainly contains amorphous Si and contains hydrogen and / or fluorine.

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 and the output of the photodiode PD5 are input to the differential amplifier 41. The output S1 of this differential amplifier 41, the differential amplifier 39
Of the differential amplifier 40 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 the semiconductor laser 16 and made into a parallel beam is a substrate 23, a first optical director 22,
The objective lens 18 passes through the buffer layer 28 and the second optical waveguide 29 and is focused on the reflecting surface 14 of the magneto-optical disk 13.
Be focused by. 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 direction of linear polarization of 15 'is compared with the direction of linear polarization of the reflected beam 15' from the unmagnetized part,
They rotate in opposite directions depending on the direction of magnetization. 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.

The S-polarized component of the reflected beam 15 'passes through the objective lens 18 and is taken into the second optical waveguide 29 by the FGC 33. The P-polarized light component of the reflected beam 15 ′ that has passed through the optical waveguide 29 is taken into the first optical waveguide 22 by the FGCs 31 and 32. The reflected beam 15 ′ guided in the second optical waveguide 29 is 1 on the y axis due to the beam focusing action of the FGC 33.
Focus on points. On the other hand, the reflected beam 15 'guided in the first 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 and 32 are formed so as to excite the TE waveguide mode, and the light having the electric field vector in the direction indicated by the arrow E in FIG. On the other hand, the third FGC 33 is formed so as to excite the TM waveguide mode, and guides light having an electric field vector in a direction perpendicular to the paper surface in FIG. Therefore, if the direction of the linearly polarized light of the reflected beam 15 'rotates clockwise relative to the direction shown by the arrow P, the light amount of the reflected beam 15' taken into the optical waveguide 29 by the third FGC 33 increases, while The first and second 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, the angle between the direction of the linearly polarized light of the reflected beam 15 ′ and the x-axis of FIG. 2 is φ, and the aperture areas of FGC31 and 32 and FGC33 are
Assuming that the aperture areas of the two are equal, the light quantity I ₁ taken into the first optical waveguide 22 by the FGCs 31 and 32 and the light quantity I ₂ taken into the second optical waveguide 29 by the FGC 33 are shown in FIG. , Cos ² φ, sin ² φ
Changes in proportion to. That is, when the angle φ is less than 45 °, the light amount I ₁ taken into the optical waveguide 22 by the FGCs 31 and 32 is larger than the light amount I ₂ taken into the optical waveguide 29 by the FGC 33, and the angle φ is 45 °. When exceeded, the above relationship is reversed. Therefore, for example, if the gain of the summing amplifier 38 is set appropriately, the output of the differential amplifier 41 when the direction of the linearly polarized light of the reflected beam 15 'is rotated clockwise from the direction shown by the arrow P in FIG. Is- (minus), and when it is rotating counterclockwise, the differential amplifier
The output of 41 can be + (plus). By discriminating 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.

The photodetection signals output by the first to third photodetectors 24, 25, 26 include, for example, noise due to variations in the light intensity of the semiconductor laser 16,
In many cases, fluctuations in the reflectance of the recording magnetic film of the magneto-optical disk 13 and noise due to crystal grains are included. Since these noise components are in phase with each other in the outputs of the first and second photodetectors 24 and 25 and the output of the third photodetector 26, the differential detection of the signal components as described above should be performed. As a result, these noise components are canceled out, and the read signal S1 having a high S / N can be obtained.

Also, as is clear from FIG. 11, if the change width of the angle φ is constant, the light amount is when the change center is φ = 45 °.
The amount of change in I ₁ and I ₂ is maximum, and the differential output S1 is also maximum. Therefore, even if the linear polarization plane rotation angle (Kerr rotation angle) of the reflected beam 15 'due to the difference in the magnetization direction on the magneto-optical disk 13 is extremely small (generally 0.3 to 0.5).
The rotation of the polarization plane can be detected with high accuracy.

In the above example, the first and second photodetectors 24,2
The difference between the signal obtained by adding the outputs of 5 and the output signal of the third photodetector 26 is detected.
It is also possible to read the signal by detecting the difference between the output signal of one side and the output signal of the photodetector 26. However, in that case, due to tracking error, the photodetector 24 or
Since the output of 25 fluctuates, it is preferable to do as in the above embodiment in order to prevent erroneous signal detection due to this fluctuation.

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 downward in FIG. 2, the output S3 of the differential amplifier 40 becomes-(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 15 on the reflecting surface 14 of the magneto-optical disk 13 will be described. When the light beam 15 is focused on the reflecting surface 14 of the magneto-optical disk 13, the reflected beam 1 focused by the 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 waveguides 22 and 29 by 32 and 33, the light beam 15 may be reflected by the end faces 22c and 29c of the optical waveguides 22 and 29 and received by the photodetectors 24, 25 and 26. So that the light absorbing member 45 is attached to the end faces 22c and 29c,
Alternatively, it is desirable to roughen the end surfaces 22c and 29c.

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.

Further, in the above embodiment, the first and second FGCs 31 and 32 excite the TE waveguide mode and the third FGC 33 excites the TM waveguide mode. On the contrary, the first and second FGCs 31 and 32 excite the TM waveguide mode. The FGCs 31 and 32 may excite the TM guided mode, and the third FGC 33 may excite the TE guided mode. In the above embodiment, the first and second FGC31,
The first optical waveguide 22 provided with 32 is provided on the substrate 23, and the second optical waveguide 29 is provided thereon.
2,29 may be placed opposite.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 5, the same elements as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted unless necessary (the same applies hereinafter). 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 waveguides 22 and 29 in the converged beam state. It is supposed to be. In this case also, the reflected beams 15 'of the three systems converge in the optical waveguides 22 and 29.
The first, second, and third photodetectors 24, 25, as shown in FIG.
The recording signal, the tracking error, and the focus error can be detected by detecting at 26 and processing those detection signals as described above.

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 convergence 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 central axis of the beam to 1,32 is l (see Fig. 5)
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].

On the other hand, the m-th grating pattern shape formula of the FGC33 defines the coordinates of the beam focusing position by the FGC33 in the same manner as in the first embodiment, and the distance of the beam central axis from the beam divergence point to the FGC33 is L, TM mode light. If the effective refractive index of the optical waveguide 29 with respect to N _TM is specified in the same manner as above, 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 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 transparent buffer layer 51 and travels toward the magneto-optical disk 13 side. In addition, in order to reflect the light beam 15 as described above, the buffer layer
A reflective thin film such as metal may be provided between the substrate 51 and the substrate 50. Also in this case, the reflected beam 15 ′ from the magneto-optical disk 13
Are taken into the optical waveguides 22, 29 by the three FGCs 31, 32, 33.

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. PD5 can be integrated. The photodiodes PD1 to PD5 integrated in this way are particularly preferable because they can respond at high speed.

As described above, in this embodiment, all the photodiodes PD1 to PD5 are formed on the surface of the first optical waveguide 22. Therefore, as shown in FIG. 6, the second optical waveguide
On the surface of the buffer layer 28 side of 29, a linear diffraction grating (Linear Grating Coupler: for emitting the reflected beam 15 ′ which is guided while focusing inside the optical waveguide 29 to the outside of the optical waveguide 29.
(Hereinafter referred to as LGC) 55 is provided, while the first optical waveguide 2 is provided.
The LGC56 is also provided on the surface of the second buffer layer 28 side at a position facing the LGC55. Second by LGC55
The reflected beam 15 ′ emitted from the optical waveguide 29 of the
It is taken into the first optical waveguide 22 by 6 and detected by the photodiode PD5. Photodiode PD1
The planar positional relationships of 5 to 5 are the same as in the first embodiment shown in FIG.

In contrast to the above example, the first optical waveguide
Two systems of guided light focusing from 22 (reflected beam 1
5 ') is emitted and made incident into the second optical waveguide 29, and all the photodiodes PD1 to PD5 are provided in the second optical waveguide 29 so that the guided light of three systems can be detected. May be.

FIG. 8 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.
This is different from the third embodiment in that the light is reflected at the interface between the buffer layer 51 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 waveguides 22 and 29 and the objective lens 18 are fixed to and integrated with one head 60, and the head 60 is movably supported with respect to the block 12 in the tracking direction and the focus direction. There is. The head 60 is moved by the tracking coil 19 and the focus coil 20. That is, in this example, the optical waveguides 22 and 29 are 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 optical waveguides 22 and 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.

In the example of FIG. 9, the substrate 50 and the buffer layer 51 are
The light beam 15 reflected at the interface of the optical waveguides is irradiated onto the magneto-optical disk 13.
Even when integrally moving the objective lens 18 and
The optical beam 15 transmitted through the optical waveguides 22 and 29 is converted into a magneto-optical disk 1.
It is also possible to irradiate the light beam on the light source 3, and it goes without saying that the light beam may be transmitted through the optical waveguides 22 and 29 or reflected on the interface in the state of a divergent beam. In addition, the semiconductor laser 16 and the collimator lens 17 are also heads.
It is also possible to fix it to 60 and move it integrally with the optical waveguides 22 and 29 and the objective lens 18.

Next, a sixth embodiment of the present invention will be described with reference to FIG. In this embodiment, the first optical waveguide 22 is formed on the transparent substrate 23 as in the first embodiment,
The photodiodes PD1, 2 and PD3, 4 forming the first and second photodetectors 24, 25 are the end faces 22b of the optical waveguide 22.
Is ground and then adhered and fixed on it. While the second
The optical waveguide 29 is formed on a transparent substrate 70 different from the substrate 23, and the photodiode PD5 also has an end face 2 of the optical waveguide 29.
Bound to 9b. And the first and second optical waveguides 22, 29
Are integrated so that the first and second PGCs 31 and 32 and the third PGC 33 overlap each other. Except for the points described above, the device of this embodiment is formed similarly to the device of the first embodiment.

As described above, even if the first and second optical waveguides 22 and 29 are formed on different substrates and then stacked, the same effect as when both optical waveguides 22 and 29 are laminated on the common substrate can be obtained. To be Even when the pickup is constructed as in the second to fifth embodiments described above, it goes without saying that the first and second optical waveguides 22 and 29 can be formed on different substrates as described above. Is.

In the six embodiments described above, the first, second, and third photodetectors 24, 25, and 26 are loaded or integrated on the surfaces 22a and 29a of the optical waveguides 22 and 29, and the end face 22b, Although coupled to 29b, these photodetectors 24, 25, 26 can be attached to the optical waveguides 22, 29 in other forms. That is, for example, as shown in FIG. 12, the photodetectors 24, 25, 26 can be arranged close to the surface 29a of the optical waveguide 29.
In this case, the guided light guided in the optical waveguide 22 may be emitted therefrom and taken into the second optical waveguide 29 as described in the third embodiment. When the photodetectors 24, 25, and 26 are arranged close to the surface 29a of the optical waveguide 29 in this way, as shown in FIG. 13, the reflected beam 15 '(guided light) is reflected on the surface 29a of the optical waveguide 29. It is also possible to increase the light receiving efficiency of the photodetectors 24, 25 and 26 by providing a diffraction grating 80 for emitting the light to the outside of the optical waveguide 29.

The PGCs 31, 32, and 33 are not limited to the above-described manufacturing method, but can be formed by the planar technique by a known photolithography method, holographic transfer method, or the like, and can be easily mass-replicated.

(Effects of the Invention) As described in detail above, in the magneto-optical recording medium pickup of the present invention, the optical elements such as the beam splitter, the lens, the prism, the half mirror, and the analyzer in the conventional pickup perform the optical waveguide. It can be obtained by a converging diffraction grating formed on the road. 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 optical waveguide, Also in this respect, cost reduction can be achieved.

Further, in the pickup of the present invention, the first and second light-collecting diffraction gratings and the third light-collecting diffraction grating are arranged so as to overlap each other, so that the light utilization efficiency is improved and thus the power consumption is reduced. The effect of keeping it low is also obtained.

[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 partial plan view showing a first optical waveguide of the device, FIG. 4 is a side view showing the photodetector of the first embodiment device in detail, and FIGS. 5 and 6 are respectively second embodiment device of the present invention.
FIG. 7 is a side view showing a device of the third embodiment, FIG. 7 is a side view showing the photodetector of the device of the third embodiment in detail, and FIGS. 8, 9 and 10 are respectively the fourth, sixth and sixth embodiments of the present invention. FIG. 11 is a side view showing an example device, FIG. 11 is a graph showing the relationship between the reflected beam linear polarization plane angle according to the present invention and the amount of light taken into the optical waveguide by the converging diffraction grating, and FIGS. 12 and 13 are respectively FIG. 6 is a side view showing another example of the photodetector used in the device of the present invention. 13 ... Magneto-optical disc, 14 ... Reflective surface of disc 15 ... Light beam, 15 '... Reflected beam 16 ... Semiconductor laser, 17 ... Collimator lens 18 ... Objective lens, 19 ... Tracking coil 20 ... Focus coil, 22 ... First Optical waveguide 22a ... Surface of first optical waveguide 22b ... End surface of first optical waveguide 23, 50, 70 ... Substrate, 24 ... First photodetector 25 ... Second photodetector, 26 ... Third Photodetectors 28, 51 ... Buffer layer, 29 ... Second optical waveguide 29a ... Second optical waveguide surface 29b ... Second optical waveguide end face 31 ... First FGC, 32 ... Second FGC 33 ... Third 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 60 ... Head, PD1 ... 5 ... Photodiode

Claims (10)

[Claims] 1. A light source for irradiating a surface of a magneto-optical recording medium with a linearly polarized light beam, and an objective lens for converging the light beam on a reflecting surface of the magneto-optical recording medium, which are integrated in a state of overlapping with each other. A first and second optical waveguides arranged in a direction to receive a reflected beam reflected by the magneto-optical recording medium on one surface, and the reflected beam irradiation position on the surface of the first optical waveguide, The first and second optical waveguides are arranged in parallel with each other with an axis passing through the center and extending on the surface substantially at right angles to the tracking direction, each of which excites either TE or TM waveguide mode. And let it enter inside,
First and second converging diffraction gratings for converging the reflected beams guided in the optical waveguide in the same waveguide mode at positions separated from each other with the axis in between, and the second optical waveguide Is provided in a position where the reflected beam is irradiated on the surface of the first and second converging diffraction gratings, and the reflected beam is excited by exciting a guided mode different from the guided mode by these diffraction gratings. A third converging diffraction grating that is incident on the second optical waveguide and focuses the light; and the first or second and third converging gratings attached to the surface or the end face of the first or second optical waveguide. Tracking error and focus error detection based on the outputs of the first, second and third photodetectors, which detect each reflected beam focused by the optical diffraction grating, and the outputs of the first and second photodetectors. Error detection circuit And a differential detection circuit that detects information recorded on the recording medium based on the difference between the output of the first and / or second photodetector and the output of the third photodetector. Pickup for magneto-optical recording medium. 2. A magneto-optical recording device according to claim 1, wherein the first and second optical waveguides are formed on a common substrate via a transparent buffer layer. Media pickup. 3. The first and second optical waveguides are formed on separate substrates, respectively, and the substrate located between the optical waveguides is a transparent substrate. The pickup for a magneto-optical recording medium according to item 1. 4. The first and second optical waveguides are arranged such that 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 45 °. A pickup for a magneto-optical recording medium according to any one of claims 1 to 3. 5. 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 4, characterized in that it comprises a two-part photodetector. 6. A substrate for the first and second optical waveguides is made of a transparent member, and the optical waveguides are arranged between the light source and the objective lens. The pickup for a magneto-optical recording medium according to any one of items 1 to 5. 7. A buffer layer is provided between the first or second optical waveguide and the substrate, and the optical waveguide reflects a light beam emitted from the light source at an interface between the buffer layer and the substrate. The magneto-optical recording medium pickup according to any one of claims 1 to 5, wherein the pickup is arranged so as to move toward the magneto-optical recording medium. 8. The first and second optical waveguides and an objective lens are arranged independently of each other, and only the objective lens is moved for tracking control and focus control. The pickup for a magneto-optical recording medium according to any one of claims 1 to 7, which is characterized. 9. The first and second optical waveguides are integrated with the objective lens, and are moved together with the objective lens for tracking control and focus control. The magneto-optical recording medium pickup according to any one of claims 1 to 7. 10. The reflected beam, which is guided in one of the first and second optical waveguides, is emitted from the optical waveguide to the surfaces of the first and second optical waveguides, and is introduced into the other optical waveguide. Diffraction gratings for incidence are provided respectively,
10. The magneto-optical recording device according to claim 1, wherein the photodetectors 1, 2, and 3 are all mounted on the surface or the end face of the other optical waveguide. Media pickup.