JPH0675311B2 - 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. ing.

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 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) The pickup for a magneto-optical recording medium according to the present invention has a condensing diffraction grating to perform the functions of the objective lens, the beam splitter, the focusing lens, the prism, the analyzer, and the like described above. The optical waveguide element is provided, and specifically, a first optical waveguide and a light source that is attached to the first optical waveguide and makes a linearly polarized light beam enter the optical waveguide. And a first light-collecting diffractive element that is formed on the surface of the first optical waveguide and emits a light beam guided in the optical waveguide to the outside of the optical waveguide and focuses it on the reflecting surface of the magneto-optical recording medium. A grating and a second optical waveguide arranged so as to receive the reflected beam reflected by the magneto-optical recording medium on one surface are provided, and the reflected beam irradiation position on the surface of the second optical waveguide is
Second and third light converging diffraction gratings for arranging the reflected beam to enter the optical waveguide are arranged in parallel, and the second and third light converging diffraction gratings irradiate the second optical waveguide. The axes passing through the center of the reflected beam and extending on the surface of the optical waveguide at a right angle to the tracking direction are aligned with each other, and each of them excites TE or TM waveguide mode. The reflected beams that are guided are formed so as to be focused at positions separated from each other with the axis interposed therebetween, and the second and third converging diffraction gratings are formed on the surface or end face of the second optical waveguide. Error detection circuit for mounting tracking errors and focus errors based on the outputs of the first and second photodetectors. And above Those formed by providing a magneto-optical signal detection circuit for detecting the recording information based on the output of the first and / or second photodetectors.

The above focusing grating (FGC: Focusing Grating Couple)
r) is a diffraction grating having bends and chirps or bends, which directly couples the spatial light wavefront outside the optical waveguide with the wavefront of the guided light traveling inside the optical waveguide, and also outputs the light beam outside the optical waveguide. Is focused in a space outside the optical waveguide, or guided light is focused 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 optical waveguide by the second and third converging diffraction gratings, the reflected beam is bent and guided to the photodetector side. . This is the same as the function performed by the beam splitter described above. The second and third converging diffraction gratings focus the reflected beam in the second optical waveguide, which is the same as the function of the focusing lens described above. Second and third
Since the two condensing diffraction gratings are arranged at the positions as described above, the reflected beams from the magneto-optical recording medium are separated from each other in the tracking direction and converge at two positions. This is the same as the function of the prism described above.

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

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

Further, in the above configuration, since the first optical waveguide and the second optical waveguide are integrated, even if tracking control is performed, the second and third optical waveguides for the first converging diffraction grating are collected. The relative position of the optical diffraction grating is always kept constant. Therefore, as in the conventional position in which the objective lens is moved for tracking control, the amount of reflected beam detection light varies due to the inclination of the objective lens to cause noise in the recorded information read signal, or the tracking is performed due to the offset of the objective lens. Errors are prevented from occurring.

(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 holds, for example, an n-type Si substrate 23. An optical waveguide 22 is formed on the substrate 23 via a buffer layer 28. One end face 22b of the optical waveguide 22 is polished, and a semiconductor laser 16 which emits a linearly polarized light beam (laser beam) 15 is fixed thereon. The beam 15 emitted from the semiconductor laser 16 enters the optical waveguide 22 through the end face 22b, and as an example, TE
It travels in the optical waveguide 22 in the guided mode. Meanwhile optical waveguide
A surface 22a of the surface 22 is provided with a first converging 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. The substrate 23 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 later in detail, and is supported by the tracking coil 19 and the focus coil 20. Each is moved in the above direction.

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. At the position irradiated with this reflected beam 15 ', the second and third Fs are formed on the surface 22a of the optical waveguide 22.
GC31 and 32 are provided adjacent to each other. These FGC 31,3
Reference numeral 2 is also a diffraction grating having a bend and a chirp or a bend, and each is formed so that the reflected beam 15 'is made incident on the optical waveguide 22 and is focused at one point in the optical waveguide 22. 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 second and third FGCs 31 and 32 have their grating pitches set so as to receive the reflected beam 15 'and excite the TE guided mode.

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 y-axis and the x-axis (tracking direction axis), and the first FG
The focus position on the disk 13 by C17 is (fx, fy, fz), the coordinates of the beam focus position by FGC31,32 are (-Fx, Fy), (Fx, Fy), respectively, and the reflected beam 15 ' Assuming that the light wavelength is λ, the incident angle of the beam 15 ′ on the FGCs 31 and 32 is θ, and the effective refractive index of the optical waveguide 22 for TE mode light is N _TE , [Complex is given as + for FGC31 and-for FGC32].

As shown in FIG. 2, the FGCs 31 and 32 are reflected beams 15 '.
The x-axis is 45 ° with respect to the direction of the linearly polarized light
It is arranged so that it tilts. The reflected beam 15 '
Since the direction of the linearly polarized light of is rotated according to the direction of the magnetization in 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 is used as a reference, and The direction and the x axis form an angle of 45 °. The FGCs 31 and 32 are the surface 22 of the optical waveguide 22.
It may be provided on the surface opposite to a (the lower surface in FIG. 1).

The optical waveguide 22 can be formed, for example, by forming a buffer layer 28 made of SiO ₂ on the Si substrate 23 and sputtering # 7059 glass on the buffer layer 28, while the FGCs 31, 32 are formed on the optical waveguide 22. It can be formed by a method in which Si-N is formed into a film by PCVD, a resist pattern is formed by electron beam direct writing, and then transferred to a Si-N film by RIE. By the way, when the optical waveguide 22 and the FGCs 31 and 32 are formed of the above materials, the FG for which the lattice pattern is defined by the above-mentioned shape formulas
The central period of C31,32 (TE mode excitation) is 0.791μ
m.

On the other hand, on the surface 22a of the optical waveguide 22, the first reflected beam 15 ', which is focused as described above, is detected so as to be respectively detected.
The photodetector 24 and the second photodetector 25 are provided. As an example, the first photodetector 24 is composed of photodiodes PD1 and PD2 divided into two by a gap extending in parallel with the y-axis, and the second photodetector 25 is also the same photodiode PD.
It consists of 3, PD4. These photodiodes PD1 to PD4 are, for example, as shown in detail in FIG. 3, an n type Si substrate.
A buffer layer 28 for preventing the leaked light (evanescent light) of the guided reflected beam 15 ′ from entering the substrate 23 is provided on 23, and a p-type Si layer 29 and an electrode 30 are provided. It is integrated. The photodiodes PD1 to PD4 integrated in this way are particularly preferable because they can respond at high speed.

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

Next, the operation of the pickup having the above structure will be described. A light beam (laser beam) 15 emitted from 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.

The reflected beam 15 'is taken into the optical waveguide 22 by the FGCs 31 and 32. Reflected beam guided in the optical waveguide 22
15 ′ is y by the beam focusing action of each of FGC31 and 32.
It comes to focus on two points with the axis in between. Here, as described above, the second and third 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. Guide inside. 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 second and third
The FGCs 31 and 32 reduce the light amount of the reflected beam 15 'taken into the optical waveguide 22. If the direction of the linearly polarized light of the reflected beam 15 'rotates counterclockwise as compared with the direction of arrow P, the above is reversed. More specifically, assuming that the angle formed by the direction of the linearly polarized light of the reflected beam 15 'and the x axis in FIG. 2 is φ, the light quantity I ₁ taken into the optical waveguide 22 by the FGCs 31 and 32 is shown in FIG. As shown by the curve, it changes in proportion to cos ² φ. Therefore, if the reference signal Sref input to the differential amplifier 41 is set to a value corresponding to the light amount P ₀ (see FIG. 9) when the angle φ is 45 °, the linearly polarized light of the reflected beam 15 ′ is When the direction is clockwise from the direction indicated by arrow P in FIG. 2, the output of the differential amplifier 41 is-(minus), and when the direction is counterclockwise, the differential amplifier 41 is opposite. The output of can be + (plus).
By determining the output S1 of the differential amplifier 41 in this way,
The direction of magnetization on the magneto-optical disk 13, that is, recorded information can be read.

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

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

In the above example, the first and second photodetectors 24,2
Although the signal reading is performed based on the signal obtained by adding the outputs of 5, it is also possible to perform the signal reading based on the output signal of one of the photodetectors 24 and 25. In such a case, the second and third FGCs 31 and 32 may excite different waveguide modes. However, in that case, the output of the photodetector 24 or 25 fluctuates due to a tracking error. Therefore, in order to prevent signal erroneous detection due to this fluctuation, it is preferable to adopt the above-mentioned embodiment.

As described above, the block 12 is fed in the direction perpendicular to the arrow U direction or a direction close to it by the driving of the optical system feed mode, whereby the irradiation position of the light beam 15 on the magneto-optical disc 13 (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 second and third FGCs 31, 32 are formed such that their respective lattices are continuous and in close contact with each other, but these FGCs 31, 32 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.

Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, in these FIGS.
Elements that are the same as the elements in FIG. 3 are assigned the same numbers, and explanations thereof are omitted unless necessary (the same applies below). 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. 4, a buffer layer is formed on the substrate 23.
The second optical waveguide 52 is formed via 28, and the first optical waveguide 51 is formed thereon via the transparent buffer layer 50. The first FGC 17 is formed on the surface 51a of the first optical waveguide 51.
And the second and third FGCs 31 and 32 are formed on the surface 52a of the second optical waveguide 52. This first FGC17
The second and third FGCs 31 and 32 are provided at positions overlapping with each other, but as shown in FIGS. 5 and 6, the lattice arrangement directions are formed so as to form an angle of 45 ° with each other. There is. The optical waveguides 51 and 52 are arranged so that 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 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 is incident on the second and third FGCs 31,32. Then, these FGCs 31 and 32 take the light into the second optical waveguide 52. In this case as well, the two systems of reflected beams 15 'which are focused in the optical waveguide 52 are converted into the first and second photodetectors 24,2.
If the signals are detected by 5, and the detected signals are processed as described above, the recording signal, the tracking error, and the focus error can be detected.

Next, a third embodiment 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, 52 are formed separately, and they are formed on separate substrates 53, 23. The substrate 53 is a transparent substrate, and the second optical waveguide
It is fixed on top of 52.

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 and third FGCs 31 and 32 are the second embodiment. They are installed in the same positional relationship as in the example, 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 and second photodetectors 24, 25 are the optical waveguide 22 or the surface 22a, 5 of the optical waveguide 52.
Although integrated in 2a, these photodetectors 24, 25 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 and 25 can be arranged close to the surface 22a of the optical waveguide 22, as shown in FIG. 10, for example. Further, in this way, the photodetector 24, on the surface 22a of the optical waveguide 22,
When arranging 25 close to each other, as shown in FIG. 11, a diffraction grating 80 for emitting a reflected beam 15 ′ (guided light) to the outside of the optical waveguide 22 is provided on the surface 22a of the optical waveguide 22, and a photodetector is provided. 2
It is also possible to increase the light receiving efficiency of 4,25. Further 12th
As shown in the figure, after the end face 22c of the optical waveguide 22 is polished, the photodetectors 24 and 25 can be closely fixed to the end face 22c. Further, as shown in FIG. 13, a lower transparent electrode 27a, a thin film photoconductive material 27b, and an upper electrode 27 are provided on the optical waveguide 22.
The photodiodes PD1 to PD4 can be formed by loading c 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 PD4 of 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. The thin film photoconductive material 27b is
For example, Group IV Si, Ge, Group IV Se, Group III-V GaAs, II-VI
It can be formed from an epitaxial film such as ZnO, CdS of the group III, PbS of the group IV-VI, a polycrystalline film, an amorphous film, etc., and an amorphous chalcogen film (a-Se, a-Se-As- Te, etc.), a film mainly composed of amorphous Si and containing hydrogen and / or fluorine (a-Si: H, a-
SiGe: H, a-SiC: H, etc.) to which a group III or V group atom (B, P, etc.) is added to obtain a pn junction or a pin junction to form a photodiode. It is also possible to form the film from a film or the like for forming a photodiode by using an electrode that mainly forms a film containing hydrogen and / or fluorine to form a Schottky junction.

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

(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, and the analyzer in the conventional pickup have the optical function. It can be obtained by a converging diffraction grating formed on the 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.

[Brief description of drawings]

FIG. 1 is a side view showing the first embodiment device of the present invention, FIG. 2 is a schematic view showing the planar shape of an optical waveguide and an electric circuit of the first embodiment device, and FIG. 3 is the first embodiment. FIG. 4 is a side view showing the photodetector of the apparatus in detail, FIG. 4 is a side view showing the apparatus of the second embodiment of the present invention, and FIGS. 5 and 6 are the first of the apparatus of the second embodiment.
And FIG. 7 are a side view and a plan view showing a third embodiment of the present invention, and FIG. 9 is a reflected beam linear polarization according to the present invention. Graph showing the relationship between the surface angle and the amount of light taken into the optical waveguide by the converging diffraction grating, FIGS. 10, 11, 12 and 13 are respectively other examples of the photodetector used in the device of the present invention. It is a side view shown. 13 ... Magneto-optical disc, 14 ... Reflecting surface of disc 15 ... Light beam, 15 '... Reflected beam 16 ... Semiconductor laser, 17 ... First FGC 19 ... Tracking coil, 20 ... Focus coil 22 ... Optical waveguide, 22a ... Optical Surface of waveguide 22b, 22c ... End face of optical waveguide 23, 50, 53 ... Substrate, 24 ... First photodetector 25 ... Second photodetector, 28, 50 ... Buffer layer 31 ... Second FGC, 32 … Third FGC 34,35,36,37,38… Adding 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 PD1 to 4 ... Photodiode

Claims (9)

[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. Moreover, they are juxtaposed on the surface with an axis extending substantially at right angles to the tracking direction, each of which excites a TE or TM waveguide mode to cause the reflected beam to enter the optical waveguide, and the second Reflection guided in the optical waveguide Second and third condensing diffractive gratings for focusing a beam respectively at positions separated from each other with respect to the axis, and attached to a surface or an end surface of the second optical waveguide, and the second and third First and second photodetectors for detecting the respective reflected beams focused by the condensing diffraction grating, and tracking error and focus error detection based on the outputs of the first and second photodetectors. A magneto-optical recording medium pickup comprising: an error detection circuit; and a magneto-optical signal detection circuit that detects information recorded on the recording medium based on the output of the first and / or second photo-detector. 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 and third condensing diffraction gratings are provided at positions that do not overlap each other. A pickup for the magneto-optical recording medium described. 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 and third condensing diffraction gratings are arranged so as to be specularly reflected on a reflecting surface, and the first converging diffraction grating and the second converging diffraction grating 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 and third converging diffraction gratings are formed so as to excite a common waveguide mode, and the magneto-optical signal detection circuit includes a first photodetector and a second photodetector. Claims 1 to 6 characterized in that the information is detected based on the sum of outputs.
Item 7. A pickup for a magneto-optical recording medium according to any one of items. 8. A plane including the axis and the central axis of the reflected beam, and a polarization direction of the reflected beam are inclined by approximately 0 ° to 45 °,
8. The pickup for a magneto-optical recording medium according to claim 1, wherein the second optical waveguide is arranged. 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.