JPH0675310B2 - 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.

The conventional magneto-optical recording medium pickup in order to have the above-mentioned function in addition to the signal reading function is an objective lens for focusing the light beam emitted from the light source on the reflecting surface of the magneto-optical recording medium, A beam splitter for separating a beam reflected from the magneto-optical recording medium from a light beam irradiated toward the medium, and a focusing lens for focusing the reflected beam in the vicinity of a photodetector such as a photodiode. In addition, it is composed of the above-mentioned analyzer and a micro optical element such as a prism for executing the tracking error detecting method and the focus error detecting method.

(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 Problems) A pickup for a magneto-optical recording medium according to the present invention includes an objective lens, a beam splitter, a focusing lens, a prism, an analyzer, and a half for performing differential detection described above. The action of a mirror or the like is obtained by an optical waveguide element having a converging diffraction grating, and the first pickup thereof is attached to the first optical waveguide and the first optical waveguide. A light source for making a linearly polarized light beam enter the optical waveguide, and a light beam formed on the surface of the first optical waveguide and guided inside the optical waveguide to be emitted to the outside of the optical waveguide for magneto-optical recording. The first converging diffraction grating for focusing on the reflecting surface of the medium, and the second optical waveguide arranged so as to receive the reflected beam reflected by the magneto-optical recording medium on one surface are provided. 2 light The reflected beam irradiation position on the surface of the road is,
Second, third, and fourth converging diffraction gratings for making the reflected beams incident on the optical waveguide are arranged in parallel, and the second and third converging diffraction gratings are the second optical waveguide. Of the reflected beam for irradiating the laser beam and the surface of the optical waveguide are aligned with an axis extending substantially at right angles to the tracking direction, each of which excites either TE or TM of the guided mode, Reflected beams guided in the two optical waveguides in the same waveguide mode are formed so as to be respectively focused at positions separated from each other with the axis interposed therebetween, while the fourth converging diffraction grating is formed by the second converging diffraction grating. And a guided mode different from the guided mode by the third converging diffraction grating (that is, TM guided mode when the second and third converging diffraction gratings excite the TE guided mode) Then, the reflected beam is made incident on the inside of the second optical waveguide. The waveguide is reflected beams formed so as to converge in the optical waveguide, and the surface or end face of the second optical waveguide, said first
Attached are first, second and third photodetectors for detecting the respective reflected beams focused by the second, third and fourth converging diffraction gratings, and further the first and second photodetectors described above. An error detection circuit that detects a tracking error and a focus error based on the output of the first photodetector, the output of the first and / or second photodetector, and the third photodetector.
And a differential detection circuit for detecting recorded information based on the difference between the outputs of the photodetectors.

Further, the second magneto-optical recording medium pickup according to the present invention is the same as the above-mentioned first pickup, except that the second optical waveguide has a fourth light condensing diffraction grating arranged in parallel with the second optical waveguide. Characteristic diffraction grating is provided in another optical waveguide, that is, in addition to the above-mentioned first and second optical waveguides, a third optical waveguide is overlapped with the second optical waveguide. And the fourth converging diffraction grating is formed on the surface of the third optical waveguide so as to overlap with the second and third converging diffraction gratings on the second optical waveguide. The first, second and third photodetectors are attached to the surface or end face of the second or third optical waveguide.

In this configuration, the reflected beam that has passed through the fourth (or second, third) converging diffraction grating is converted into the third optical waveguide by the second, third (or fourth) converging diffraction grating. It is taken in and focused.

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 guides the light beam emitted outside the optical waveguide. The reflected beam is focused in the space outside the waveguide or in the optical waveguide.

(Operation) As described above, the light beam applied to the magneto-optical recording medium is
It is focused on the reflection surface of the recording medium by the first converging diffraction grating provided in the first optical waveguide. As a result, the function of the above-mentioned objective lens is obtained. On the other hand, when the reflected beam from the magneto-optical recording medium is taken into the second or third optical waveguide by the second, third, and fourth converging diffraction gratings, the reflected beam bends the optical path and Guided to the detector side. This is the same as the function performed by the beam splitter described above. The second, third, and fourth converging diffraction gratings focus the reflected beam in the second or third optical waveguide, which is the same as the function of the focusing lens described above. Further, the second and third converging diffraction gratings are 2
Since the individual beams 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 second and third condensing diffraction gratings are formed so as to excite the TE (TM) guided mode, while the fourth 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 fourth converging diffraction grating in addition to the second and third converging diffraction gratings, the beam splitting function performed by the above-mentioned half mirror or the like can be obtained, and each condensing 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.

Further, in the above configuration, since the first optical waveguide and the second optical waveguide (and the third optical waveguide in the second pickup) are integrated, even if tracking control is performed, 2nd and 1st for 1 converging diffraction grating
The relative positions of the third and fourth converging diffraction gratings are always kept constant. Therefore, as in the conventional apparatus that moves the objective lens for tracking control, the amount of reflected beam detection light varies due to the tilt of the objective lens, and noise is generated in the recorded information read signal, or tracking occurs due to the offset of the objective lens. Errors are prevented from occurring.

As in the first pickup, the second, third, fourth
Forming all of the condensing diffraction gratings in (1) into one optical waveguide (second optical waveguide) simplifies the configuration and facilitates manufacturing. However, in such a case, the S (P) polarization component of the reflected beam, which is coupled with the TE (TM) mode guided light by the second and third converging diffraction gratings, may enter the optical waveguide depending on the fourth converging diffraction grating. In such a case, S ( P ) of such a reflected beam cannot be incident.
The portion of the polarized light component irradiated on the portion of the fourth converging diffraction grating cannot be used at all. And, of course, the opposite can happen.

Therefore, as in the second pickup of the present invention,
A third converging diffraction grating and a fourth converging diffraction grating,
If they are provided so as to overlap with each other, the polarization components of the reflected beams that have not entered the second (third) optical waveguide by the second and third (fourth) converging diffraction gratings will also be reflected by this diffraction grating. Through the fourth (second, third) converging diffraction grating, so that the light can be made incident on the third (second) optical waveguide,
The detection efficiency of the reflected beam and thus the light utilization efficiency are improved as compared with the first pickup.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a first embodiment of the first pickup for a magneto-optical recording medium 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 is driven by, for example, a precision feed screw and an optical system feed motor, in a direction perpendicular to the direction of the track (direction of arrow U at the beam irradiation position). Or, it is designed to be moved in a direction close to it.

The block 12 holds an n-type si substrate 23, for example. A first optical waveguide 22 is formed on the substrate 23 via a buffer layer 28. 1 of this optical waveguide 22
One end face 22b is polished, and a semiconductor laser 16 for emitting a linearly polarized light beam (laser beam) 15 is fixed thereon. The light beam 15 emitted from the semiconductor laser 16 enters the optical waveguide 22 through the end face 22b and travels in the optical waveguide 22 in the TE waveguide mode as an example. On the other hand, a surface 22a of the optical waveguide 22 is provided with a first condensing diffraction grating (hereinafter referred to as FGC) 17. The FGC 17 is a diffraction grating having a bend and a chirp, and emits the light beam 15 guided in the optical waveguide 22 to the outside of the optical waveguide and focuses it on the reflecting surface 14 of the magneto-optical disk 13. Board 23
Is movably supported in the tracking direction (direction perpendicular to the arrow U direction) and the focus direction (direction of the arrow V) for tracking control and focus control, which will be described in detail later. It is designed to be moved in the direction of.

The optical waveguide 22 is arranged so that the light beam 15 does not specularly reflect on the reflecting surface 14, and therefore, the magneto-optical disk.
The reflected beam 15 'reflected at 13 is reflected at a position away from the first FGC 17. Second, third, and fourth FGCs 31, 32, and 33 are provided adjacent to each other on the surface 22a of the optical waveguide 22 at the position where the reflected beam 15 'is irradiated. These FGCs 31, 32, and 33 are also diffraction gratings having bends and chirps, or bends, and are formed so that the reflected beams 15 ′ are made incident on the optical waveguide 22 and are focused at one point in the optical waveguide 22. ing. The second and third FGCs 31, 32 are arranged side by side with an axis (y-axis in FIG. 2) on the optical waveguide 22 which is perpendicular 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. The fourth FGC 33 is provided between the second and third FGCs 31 and 32 side by side with the FGCs 31 and 32. The second and third FGCs 31, 32 excite the TE waveguide mode, while the fourth FGC 33 excites the TM waveguide mode, with the grating pitches set respectively.

In the m-th grating pattern shape formula of the FGCs 31 and 32 that performs the above-described action, the position on the optical waveguide 22 is defined by the x-axis (tracking direction axis) and the y-axis shown in FIG.
The focus position of the disk 13 by the FGC 17 of is set to (fx, fy, fz), the coordinates of the beam focusing position by the FGC 31 and 32 are set to (−Fx, Fy) and (Fx, Fy), respectively, and the reflected beam 15 ′ The light wavelength is λ, the incident angle of the beam 15 'to the FGCs 31, 32 is θ,
Let N _TE be the effective refractive index of the optical waveguide 22 for TE mode light, [Compounds are given as + for FGC31 and-for FGC32].

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

Then, as shown in FIG. 2, the FGC 31, 32, and 33 are reflected beams 1
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 FGCs 31, 32, 33 may be provided on the surface of the optical waveguide 22 opposite to the surface 22a (lower surface in FIG. 1).

The optical waveguide 22 can be formed, for example, by forming a transparent buffer layer 28 made of SiO ₂ on a Si substrate 23 and sputtering # 7059 glass on it, while FGC 31, 32, 33.
Is a film of Si-N formed on the optical waveguide 22 by PCVD, a resist pattern is formed by direct electron beam writing, and then S
It can be formed by a method such as transferring to an iN film. By the way, the optical waveguide 22 (thickness 0.76μ
m) and FGC31, 32, 33 are formed, the center period of FGC31, 32 (TE mode excitation) whose lattice pattern is defined by each of the above-mentioned shape formulas is 0.782 μm, FGC33 (TM mode excitation) The center period of is 0.786 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.
Photodetector 24, second photodetector 25 and third photodetector 2
Six are provided. As an example, the first photodetector 24 is composed of photodiodes PD1 and PD2 which are divided into two by a gap extending parallel to the y-axis, and the second photodetector 25 is also composed of similar photodiodes PD3 and PD4. On the other hand, the third photodetector 26 consists of one photodiode PD5. These photodiodes PD1 to PD5 are, for example, as shown in detail in FIG. 3, on the n-type Si substrate 23, the leaching light (evanescent light) of the guided reflected beam 15 'is formed on the substrate 23. A buffer layer 28 is provided to prevent light from entering the inside.
It is integrated by providing a p-type Si layer 29 and an electrode 30. The photodiodes PD1 to PD5 thus integrated
Is particularly preferable because it enables high-speed response.

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 guided in the optical waveguide 22 in a divergent beam state is
The light is emitted from the optical waveguide 22 by the first FGC 17 and focused so as to be focused on the reflecting surface 14 of the magneto-optical disk 13. The magneto-optical disk 13 is rotated by a rotation driving means (not shown) so that the track moves in the arrow U direction at the irradiation position of the light beam 15. As is well known, the track is a train of image signals and audio signals recorded in the direction of magnetization (indicated by an arrow above the reflecting surface 14 in FIG. 1). The direction of the 15 'linearly polarized light is the reflected beam 1 from the unmagnetized part.
Compared to the 5'direction of linearly polarized light, 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.

This reflected beam 15 'is reflected by the FGC 31, 32, 33 by the optical waveguide 2
Captured within 2. The reflected beam 15 'guided in the optical waveguide 22 is focused at two points on the y axis and one point on the y axis by the beam focusing action of each of the FGCs 31, 32, 33. Here, as described above, the second and third FG
C31 and C32 are formed to excite the TE guided mode,
The light having the electric field vector in the direction indicated by the arrow E in the figure is guided in the optical waveguide 22, while the fourth FGC 33 is formed so as to excite the TM waveguide mode, and the direction perpendicular to the plane of the paper in FIG. The light having the electric field vector of 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 light quantity of the reflected beam 15' taken into the optical waveguide 22 by the fourth FGC 33 increases, while 2, the third FGC31,
The light quantity of the reflected beam 15 'taken into the optical waveguide 22 is reduced by 32. 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, if the angle between the direction of the linearly polarized light of the reflected beam 15 'and the x-axis in FIG. 2 is φ, and the aperture area of FGC31 or 32 is equal to the aperture area of FGC33, then F
Amount of light taken into the optical waveguide 22 by GC31 or 32
I ₁ and the amount of light I taken into the optical waveguide 22 by FGC 33 I
₂ is cos as shown by the curve in Fig. 9, respectively.
^{2 φ,} changes in proportion to the sin ^{2 φ.} That is, the angle φ is 4
When the angle is less than 5 °, the light amount I ₁ taken into the optical waveguide 22 by the FGC 31 or 32 becomes larger than the light amount I ₂ taken into the optical waveguide 22 by the FGC 33, and when the angle φ exceeds 45 °, the above The relationship is reversed. Therefore, if the gain of the summing amplifier 38 is set appropriately, for example, the reflected beam 1
When the direction of the linearly polarized light 5'is rotated clockwise from the direction shown by the arrow P in FIG. 2, the output of the differential amplifier 41 is-
(Minus), on the contrary, when rotating counterclockwise, the output of the differential amplifier 41 can be made positive (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.

Further, as is clear from FIG. 9, 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 according to the direction of the tracking error indicated by the signal S3 to the tracking coil 19, and moves the substrate 23 in the direction in which the tracking error is eliminated. Let 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, the current If corresponding to the direction of the focus error indicated by the signal S2 is supplied to the focus coil 20, and the substrate 23 is moved in the direction in which the focus error is eliminated. As a result, the light beam 15 is always reflected on the reflecting surface 14 of the magneto-optical disk 13.
It will focus correctly on top.

In this embodiment, the light beam 15 is designed not to be specularly reflected by the reflecting surface 14, so that the reflected beam 15 'enters the optical waveguide 22 from the first FGC 17 and the semiconductor laser 16
Never return to. Therefore, it is possible to prevent the semiconductor laser 16 from causing a mode hopping due to the returning light and causing a defect such as an output fluctuation.

In this embodiment, the three FGCs 31, 32, 33 are formed such that their respective lattices are continuous and in close contact with each other, but these FGCs 31, 32, 33 are formed independently of each other with a small distance. May be done. 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.

Furthermore, in the above-mentioned embodiment, the second and third FGCs 31 and 32 excite the TE guided mode and the fourth FGC 33 excites the TM guided mode. The FGCs 31 and 32 may excite the TM guided mode and the fourth FGC 33 may excite the TE guided mode. Alternatively, the FGCs 31 and 32 may be arranged so as to be close to or close to each other, and the fourth FGC 33 may be arranged outside one or both of these FGCs 31 and 32.

Next, a second embodiment of the first magneto-optical recording medium pickup of the present invention will be described with reference to FIG. In FIG. 4, 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 first embodiment, the first optical waveguide and the second optical waveguide are common, but in the pickup of the second embodiment, they are formed separately. That is, as shown in FIG.
A second optical waveguide 52 is formed on 23 via a buffer layer 28, and a first optical waveguide 51 is formed thereon via a transparent buffer layer 50. And the surface of the first optical waveguide 51
The first FGC 17 is formed on 51a, and the second, third and fourth FGCs 31, 32, 33 are formed on the surface 52a of the second optical waveguide 52. This first FGC 17 and the second, third and fourth FGCs
Although 31,32,33 are provided at the position where they overlap each other,
As shown in FIGS. 5 and 6, the lattice arranging directions are formed so as to form an angle of 45 ° with each other. And the optical waveguide 51,5
2 is arranged in a direction in which the light beam 15 emitted from the first FGC 17 is specularly reflected by the reflecting surface 14 of the magneto-optical disk 13.

In this case, the light beam guided in the first optical waveguide 51
Part of 15 is diffracted by the first FGC 17 toward the substrate 23 side, and the light beam 15 is reflected at the interface between the buffer layer 50 and the second optical waveguide 52, and further at the interface between the buffer layer 28 and the substrate 23. And advances upward (to the side of the magneto-optical disk 13). The light beam 15 that is diffracted in this direction and then reflected is also effectively used.
In order to prevent the light beam 15 diffracted from 7 toward the magneto-optical disk 13 side from being weakened, the reflected light and the light diffracted toward the magneto-optical disk 13 side by the FGC 17 interfere with each other by a buffer layer 28. It is preferable to choose a thickness of 50.

In the apparatus of this embodiment, the reflected beam 15 'from the magneto-optical disk 13 passes through the first FGC 17, the first optical waveguide 51 and the buffer layer 50, and then the second, third and fourth FGCs 31, 32 are formed. , 33, and are taken into the second optical waveguide 52 by these FGCs 31, 32, 33. In this case as well, the three systems of reflected beams 15 'which are focused in the optical waveguide 52 are detected by the first, second and third photodetectors 24, 25, 26 as shown in FIG. By processing the detection signal as described above, the recording signal, tracking error, and focus error can be detected.

Next, a third embodiment of the first magneto-optical recording medium pickup of the present invention will be described with reference to FIGS. 7 and 8. In this embodiment, as in the second embodiment, the first and second optical waveguides 51 and 52 are formed separately, and they are formed on separate substrates 52 and 23. The substrate 53 is a transparent substrate, and is fixed on the second optical waveguide 52 in an overlapping manner.

Also in this case, the optical waveguides 51 and 52 are arranged so that the light beam 15 emitted from the FGC 17 is specularly reflected by the magneto-optical disk 13, and the first FGC 17 and the second, third, and fourth FGCs 31, 32, and 33 is installed in the same positional relationship as in the second embodiment, and their actions and effects are the same as in the second embodiment.

In the second and third embodiments described above, the first optical waveguide 51 is located closer to the magneto-optical disk 13,
Although the second optical waveguide 52 is arranged on the side farther from the magneto-optical disk 13, both optical waveguides 51, 52 may be arranged in a positional relationship opposite to this.

In the three embodiments described above, the first, second, and third photodetectors 24, 25, 26 are integrated on the surface 22a, 52a of the optical waveguide 22 or the optical waveguide 52. Photo detector 24,
25 and 26 can be attached to the optical waveguide 22 or 52 in other forms. That is, if one optical waveguide is used as an example, the photodetectors 24, 25, and 26 can be arranged close to the surface 22a of the optical waveguide 22, as shown in FIG. Also, in this way, the surface 22 of the optical waveguide 22 is
If the photodetectors 24, 25 and 26 are placed close to a,
As shown in the figure, the reflected beam 1 is reflected on the surface 22a of the optical waveguide 22.
Diffraction grating 80 for emitting 5 '(guided light) to the outside of the optical waveguide 22.
It is also possible to increase the light receiving efficiency of the photodetectors 24, 25, and 26 by providing. Further, as shown in FIG. 12, after the end face 22c of the optical waveguide 22 is polished, the photodetectors 24, 25, and 26 can be closely fixed to the end face 22c. Further, as shown in FIG. 13, the photodiodes PD1 to 5 can be formed by loading the lower transparent electrode 27a, the thin film photoconductive material 27b, and the upper electrode 27c on the optical waveguide 22 in this order. In this case, a predetermined electric field is applied from the power source 27d between the lower transparent electrode 27a and the upper electrode 27c. In the photodiodes PD1 to 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. Note that the thin film photoconductive material 27b is, for example, IV group Si, Ge, or IV group S
e, III-V group GaAs, II-IV group ZnO, CdS, IV-VI group PbS
It can be formed from an epitaxial film such as a polycrystal film, an amorphous film, etc., and an amorphous chalcogen film (a-Se, a-Se-A
s-Te), amorphous Si as a main component and hydrogen and / or fluorine-containing films (a-Si: H, a-SiGe: H, a-SiC: H, etc.) III
Pn by adding a group V or V atom (B, P, etc.)
Formed from a film that forms a photodiode by obtaining a junction or a pin junction, a film that forms a photodiode by using an electrode that forms a Schottky junction with the film that mainly contains amorphous Si and contains hydrogen and / or fluorine You can also do it.

Further, the FGCs 31, 32, and 33 are not limited to the above-described manufacturing method, and all can be formed by a planar technique by a known photolithography method, holographic transfer method, or the like, and mass replication can be easily performed.

Next, an embodiment of the second magneto-optical recording medium pickup of the present invention will be described. In the first magneto-optical recording medium pickup described above, the second, third and fourth converging diffraction gratings are all formed on a common optical waveguide. In the recording medium pickup, the second and third converging diffraction gratings and the fourth converging diffraction grating are formed on different optical waveguides, respectively, and they are arranged so as to overlap each other.

In the first embodiment apparatus of the second magneto-optical recording medium pickup of the present invention shown in FIG. 14, the first optical waveguide 22
Are stacked on the second optical waveguide 52 via the transparent buffer layer 50. A first FGC 17 for emitting a light beam and a fourth FGC 33 for injecting a reflected beam are formed on the surface 22a of the first optical waveguide 22. That is, in this embodiment, as the third optical waveguide provided with the fourth FGC 33,
The first optical waveguide 22 is shared. On the other hand, the surface 52a of the second optical waveguide 52 is provided with the second and third FGCs for injecting the reflected beam.
31,32 are formed. FIGS. 15 and 16 show the planar shapes of the first optical waveguide 22 and the second optical waveguide 52, respectively. As shown in these figures, the fourth FG
The C33 has an opening area that is substantially equal to that of the second and third FGCs 31, 32, and is provided at a position overlapping these FGCs 31, 32. In addition, the first optical fiber mounted on the second optical waveguide 52
The first and second photodetectors 24 and 25, and the third photodetector 26 attached to the first optical waveguide 22 are, for example, the thirteenth photodetector.
It is of the type shown.

The apparatus of this embodiment has the same configuration as the apparatus shown in FIGS. 1 and 2 except the points described above. In this pickup, the reflected beam 15 'is transmitted by the FGC 33 to the optical waveguide 22'.
Taken in. Further, the reflected beam 15 'that has passed through the optical waveguide 22 is reflected by the FGCs 31 and 32 in the second optical waveguide 52.
Taken in. The two systems of reflected beams 15 'focused in the second optical waveguide 52 by the FGCs 31 and 32 are respectively
The reflected beam 15 'detected by the second photodetectors 24, 25, while being focused by the FGC 33 in the first optical waveguide 22,
It is detected by the third photodetector 26. Thereby, the recording signal, the tracking error, and the focus error can be detected in the same manner as described above.

In the above embodiment, the first optical waveguide 22 is configured so as to also serve as the third optical waveguide. However, the first optical waveguide 22 (that is, the first FGC 17 is provided)
Also serves as the second optical waveguide (those provided with the second and third FGCs 31 and 32), and another third optical waveguide (those provided with the fourth FGC33) is provided to this optical waveguide. It may be arranged so as to overlap with 22.

Next, with reference to FIG. 17, a second embodiment of the second magneto-optical recording medium pickup of the present invention will be described. In this embodiment, a transparent buffer layer is formed on the second optical waveguide 52.
The third optical waveguide 56 is provided via 55, and the first optical waveguide 51 is provided thereon via the transparent buffer layer 50. FGC 31, 32 formed on the surface 52a of the second optical waveguide 52
And the FGC 33 formed on the surface 56a of the third optical waveguide 56 are similar to those in the second embodiment shown in FIGS. Also, in this way, the FGC 31, 32 overlapping each other
And FGC33 are arranged so as to overlap with the first FGC17.

In the present embodiment, in particular, the reflected beam 15 ′, which is guided while focusing inside the optical waveguide 56, is emitted to the outside of the optical waveguide 56 on the surface of the third optical waveguide 56 on the buffer layer 55 side. A linear diffraction grating (hereinafter referred to as LGC) 57 is provided, and on the other hand, an LGC 58 is provided on the surface of the second optical waveguide 52 on the buffer layer 28 side at a position facing the LGC 57. The reflected beam 15 ′ emitted from the third optical waveguide 56 by the LGC 57 is taken into the second optical waveguide 52 by the LGC 58. Third photodetector
26 is attached to the surface 52a of the second optical waveguide 52 together with the first and second photodetectors 24 and 25, and is connected to the second optical waveguide 56 from the third optical waveguide 56 as described above. The reflected beam 15 'that has entered the 52 is detected. The photodetectors 24, 25 and 26 are of the type shown in FIG. 13 as an example. The apparatus of this embodiment has the same configuration as the apparatus shown in FIG. 4 except for the points described above.

Incidentally, of course, the third photodetector 26 is connected to the third optical waveguide 56.
It may be attached to the surface or the end face of, and LGC57 and 58 may not be provided.

Further, even when the first, second, and third optical waveguides 51, 52, and 56 are separately provided in this way, the FGC 31,
The 32 and the FGC 33 may be arranged so as not to overlap with the first FGC 17. Furthermore, the first, second, and third optical waveguides 51, 52, 56
May be formed on separate substrates and then stacked. This is the same when the third optical waveguide or the second optical waveguide is shared with the first optical waveguide as shown in FIG. Also,
The first, second and third optical waveguides 51, 52 and 56 may be stacked in any order with respect to each other.

Further, in the second magneto-optical recording medium pickup of the present invention, various photodetectors as shown in FIG. 3 or FIGS. 11 to 12 can be used.

As described above, the second and third PGCs 31 and 32 are the fourth PGC33.
If it is placed so that it overlaps with the reflected beam, it will not enter the optical waveguide 56 (52) by the FGC 33 (31, 32).
The 15 'polarized component is also reflected by the optical waveguide 52 by FGC31, 32 (33).
Since the light enters the inside of (56), the light utilization efficiency is improved.

(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 objective lens, the beam splitter, the focusing lens, the prism, the half mirror, and the analyzer are used in the conventional pickup. The action is obtained by the converging diffraction grating formed on the optical waveguide. 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.

Moreover, in the pickup of the present invention, the integrated first and second optical waveguides are moved when executing the tracking control and the focus control, so that even if these controls are performed, the light beam is emitted. The relative positional relationship between the first converging diffraction grating and the second and third converging diffraction gratings for receiving the reflected beam does not change. Therefore, as in the conventional device that moves the objective lens for these controls, the amount of reflected beam detection light varies due to the inclination of the objective lens, which causes noise in the recorded information read signal, or the offset of the objective lens. No tracking error will occur. Even if the light source side and the reflected beam receiving side are integrally moved in this way, since they are both composed of lightweight optical waveguide elements as described above, good control responsiveness is maintained.

More particularly, in the second pickup of the present invention,
Since the second and third light-collecting diffraction gratings and the fourth light-collecting diffraction grating are arranged so as to overlap with each other, the light utilization efficiency is improved, and the effect of suppressing the power consumption is also obtained.

[Brief description of drawings]

FIG. 1 is a side view showing a first embodiment of a first pickup of the present invention, FIG. 2 is a schematic view showing a planar shape of an optical waveguide and an electric circuit of the device of the first embodiment, and FIG. FIG. 4 is a side view showing a photodetector of the first embodiment device in detail, FIG. 4 is a side view showing a second embodiment of the first pickup of the present invention, and FIGS. 5 and 6 are the second embodiment device. First of
Plan views showing the optical waveguide and the second optical waveguide of FIG. 7, FIGS. 7 and 8 are a side view and a plan view showing a third embodiment of the first pickup of the present invention, and FIG. 9 is the present invention. A graph showing the relationship between the linear polarization plane angle of the reflected beam and the amount of light taken into the optical waveguide by the condensing diffraction grating, and FIGS. 10, 11, 12 and 13 are photodetectors used in the device of the present invention, respectively. FIG. 14 is a side view showing another example of the container, FIG. 14 is a side view showing the first embodiment of the second pickup of the present invention, and FIGS. 15 and 16 are the first part of the first embodiment device, respectively.
And FIG. 17 is a side view showing a second embodiment of the second pickup of the present invention. 13 ... Magneto-optical disk, 14 ... Disk reflecting surface 15 ... Light beam, 15 '... Reflected beam 16 ... Semiconductor laser, 17 ... First FGC 19 ... Tracking coil, 20 ... Focus coil 22 ... First optical waveguide 22a ... Surface of first optical waveguide 22b ... End surface of first optical waveguide 23, 53 ... Substrate, 24 ... First photodetector 25 ... Second photodetector, 26 ... Third photodetector 28, 50, 55 ... Buffer layer, 31 ... Second FGC 32 ... Third FGC, 33 ... Fourth FGC 34, 35, 36, 37, 38 ... Summing amplifier 39, 40, 41 ... Differential amplifier, 42 ... Reading circuit 43 ... Focus coil drive control circuit 44 ... Tracking coil drive control circuit 51 ... First optical waveguide 51a ... First optical waveguide surface 52 ... Second optical waveguide 52a ... Second optical waveguide surface 56 ... Third optical waveguide 56a ... Surface of third optical waveguide, 57, 58 ... LGC PD1 to 5 ... Photodiode

Claims (12)

[Claims] 1. A first optical waveguide, a light source which is attached to the first optical waveguide and causes a linearly polarized light beam to enter the optical waveguide, and which is formed on the surface of the first optical waveguide. A first converging diffraction grating for emitting the light beam guided in the optical waveguide to the outside of the optical waveguide and converging the light beam on the reflecting surface of the magneto-optical recording medium; A second optical waveguide arranged so as to receive the reflected beam reflected by the magneto-optical recording medium on one surface thereof, and at a reflected beam irradiation position on the surface of the second optical waveguide, the second optical waveguide passes through substantially the center of the beam. And on the surface are arranged side by side with an axis extending substantially at right angles to the tracking direction, and each of TE, TM excites one of the guided modes to cause the reflected beam to enter the optical waveguide, Inside this second optical waveguide Second and third converging diffraction gratings for converging a reflected beam guided in a new guided mode at positions separated from each other with the axis in between, and irradiation of the reflected beam on the surface of the second optical waveguide Is provided side by side with the second and third converging diffraction gratings, and a guided mode different from the guided mode by these diffraction gratings is excited to cause the reflected beam to enter the second optical waveguide. A fourth converging diffraction grating for focusing in this optical waveguide, and a surface or an end face of the second optical waveguide, which is focused by the second, third and fourth converging diffraction gratings. A first, a second and a third photodetector for detecting each reflected beam; an error detection circuit for detecting a tracking error and a focus error based on the outputs of the first and second photodetectors; First and / Or a magneto-optical recording medium including a differential detection circuit that detects information recorded on the recording medium based on a difference between the output of the second photodetector and the output of the third photodetector. For pickup. 2. The first and second optical waveguides are common to each other, and the optical waveguides are oriented so that the light beam emitted from the first converging diffraction grating is not specularly reflected on the reflecting surface. The first condensing diffraction grating and the second, third, and fourth condensing diffraction gratings are provided in positions that do not overlap each other. A pickup for a magneto-optical recording medium according to item 1. 3. The first and second optical waveguides are formed separately, and are superposed on each other and integrated, and the optical waveguides emit light beams emitted from the first converging diffraction grating. The first condensing diffraction grating and the second, third, and fourth condensing diffraction gratings are arranged so as to be specularly reflected on a reflecting surface, and are provided at positions overlapping with each other. The pickup for a magneto-optical recording medium according to claim 1. 4. The magneto-optical recording medium according to claim 3, wherein the first and second optical waveguides are formed on a common substrate with a transparent buffer layer interposed therebetween. For pickup. 5. The first and second optical waveguides are formed on separate substrates, respectively, and the substrate located between the optical waveguides is a transparent substrate. 3. A pickup for a magneto-optical recording medium according to item 3. 6. The light source is directly fixed to an end face of the first optical waveguide, and is formed so that a light beam is incident from the end face into the first optical waveguide. The pickup for a magneto-optical recording medium according to any one of claims 1 to 5. 7. The second optical waveguide is arranged such that the 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 °. The pickup for a magneto-optical recording medium according to any one of claims 1 to 6. 8. The fourth condensing diffraction grating is disposed between the second condensing diffraction grating and the third condensing diffraction grating. The pickup for a magneto-optical recording medium according to any one of items 1 to 7. 9. 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 a push-pull method and a Foucault method, respectively. A magneto-optical recording medium pickup according to any one of claims 1 to 8, characterized in that it comprises a two-divided photodetector. 10. A first optical waveguide, a light source which is attached to the first optical waveguide and causes a linearly polarized light beam to enter the optical waveguide, and which is formed on the surface of the first optical waveguide. A first converging diffraction grating for emitting the light beam guided in the optical waveguide to the outside of the optical waveguide and converging the light beam on the reflecting surface of the magneto-optical recording medium; A second optical waveguide arranged so as to receive the reflected beam reflected by the magneto-optical recording medium on one surface thereof, and at a reflected beam irradiation position on the surface of the second optical waveguide, the second optical waveguide passes through substantially the center of the beam. And on the surface are arranged side by side with an axis extending substantially at right angles to the tracking direction, and each of TE, TM excites one of the guided modes to cause the reflected beam to enter the optical waveguide, In this second optical waveguide Second and third converging diffraction gratings for respectively focusing the reflected beams guided in the same guided mode at positions separated from each other with the axis interposed therebetween, and the second and the third optical waveguides are integrated with each other. A third optical waveguide, and a third optical waveguide and a waveguide mode provided by the diffraction grating on the surface of the third optical waveguide so as to overlap with the second and third converging diffraction gratings at the reflected beam irradiation position. A fourth converging diffraction grating that excites different waveguide modes to cause the reflected beam to enter the third optical waveguide and focus the reflected beam in the third optical waveguide; and the second or third optical waveguide. First, second and third photodetectors attached to the surface or the end face of each of the first, second and third condensing diffraction gratings for detecting the respective reflected beams, and the first And a track based on the output of the second photodetector. Recorded on the recording medium based on an error detection circuit for detecting a focusing error and a focus error, and a difference between an output of the first and / or second photodetector and an output of the third photodetector. A pickup for a magneto-optical recording medium, which comprises a differential detection circuit for detecting information. 11. The magneto-optical recording medium according to claim 10, wherein the second and third optical waveguides are formed on a common substrate with a transparent buffer layer interposed therebetween. For pickup. 12. The second and third optical waveguides are formed on separate substrates, respectively, and the substrate located between the optical waveguides is a transparent substrate. Item 10. A pickup for a magneto-optical recording medium according to item 10.