JPH0834011B2 - Pickup for optical recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical pickup for reading a signal recorded on an optical recording medium such as an optical disc, and more particularly for an optical recording medium using an optical waveguide. It's about pickups.

(Prior Art) Recently, an optical recording medium such as an optical disk has been widely put into practical use as a recording medium for image signals, audio signals and the like. A signal recorded in the form of pits, a difference in reflectance, and the like (the following description will be made by taking pits as an example) on the optical recording medium is read by an optical pickup, that is, an optical pickup. This optical pickup is such that the surface of the optical recording medium is irradiated with light such as laser light, and the level of the light reflected on the recording medium is detected to detect the presence or absence of the pits.

In such an optical recording medium pickup, the recording information is read as described above, and the light beam for tracking error detection, that is, pit detection shifts from the center of a predetermined pit example (track) to the left or right side. 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 optical recording medium. Is required. 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 onto a predetermined track, and the light beam is reflected from the optical recording medium. It is used to focus correctly on the surface. Conventionally, push-pull method, heterodyne method, time difference detection method, etc. are known as tracking error detection methods, while astigmatism method, critical angle detection method, Foucault method, etc. are known as focus error detection methods. Has been.

In order to have the above-mentioned functions, the conventional optical recording medium pickup has an objective lens for focusing the light beam emitted from the light source on the reflection surface of the optical recording medium and a beam reflected by the optical recording medium. A beam splitter for separating the light beam emitted toward the medium, a focusing lens for focusing the reflected beam in the vicinity of a photodetector such as a photodiode, and the above tracking error detection method and It is composed of a micro optical element such as a prism for executing the focus error detecting method.

(Problems to be Solved by the Invention) However, the above-mentioned micro optical element requires precise processing, and it is troublesome to adjust the mutual positions when assembling the pickup. It was inevitably expensive. Further, since the pickup having such a configuration is large and heavy, it is disadvantageous in terms of reducing the size and weight of the reading device and shortening the 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, an optical pickup using such an element is similar in structure to the optical pickup as described above in terms of cost even though the configuration is simplified. .

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 an optical recording medium, which is compact and lightweight and can be formed at an extremely low cost.

(Means for Solving the Problems) In the optical recording medium pickup of the present invention, the optical waveguide element provided with the condensing diffraction grating has the functions of the objective lens, the beam splitter, the focusing lens and the prism described above. Specifically, the first optical waveguide, a light source that is attached to the first optical waveguide and causes a linearly polarized light beam to enter the optical waveguide, and the first optical waveguide. A first converging diffraction grating formed on the surface of the optical waveguide, which 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 optical recording medium; A second optical waveguide arranged so that one surface receives the reflected beam reflected by the optical waveguide, and the optical waveguide is provided with the reflected beam at the reflected beam irradiation position on the surface of the second optical waveguide. Incident inside Second and third converging diffraction gratings are provided, and these second and third converging diffraction gratings pass through substantially the center of the reflected beam that irradiates the second optical waveguide and on the surface. A plurality of axes extending in a direction substantially perpendicular to the tracking direction are arranged so as to be sandwiched, and the reflected beams respectively guided in the second optical waveguide are formed so as to be focused at positions separated from each other by sandwiching the axis, and The reflected beams focused by the second and third converging diffraction gratings are detected on the surface or the end face of the second optical waveguide so as to read recorded information, detect tracking errors, and detect focus errors. , A first set and a second set of photodetectors each including a plurality of photodetector elements are attached.

The above focusing grating (FGC: Focusing Grating Couple)
r) is a diffraction grating having bends and chirps or bends, which directly couples the wavefront outside the optical waveguide with the spatial light wavefront of the guided light traveling inside the optical waveguide, and also emits the light beam outside the optical waveguide. Is focused in the space outside the optical waveguide, or the reflected beam is focused in the optical waveguide.

(Operation) The light beam with which the optical recording medium is irradiated as described above is focused on the reflecting 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 optical recording medium is taken into the 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. Again
The second and third converging diffraction gratings focus the reflected beam in the second optical waveguide, which has the same function as the focusing lens described above. Further, since two such second and third converging diffraction gratings are arranged at the above-mentioned positions, the reflected beams from the optical recording medium are separated from each other in the tracking direction and are focused at two positions. . This is the same as the function of the prism described above.

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 provided.
The relative position of the condensing diffraction grating is 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.

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

FIG. 1 shows a pickup for an optical recording medium according to a 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. Since this block 12 follows the pit train (track), for example, by means of a precision feed screw and an optical system feed motor or the like, a direction perpendicular to the direction in which the pits 21 of the optical disc 13 are arranged (the arrow U direction at the beam irradiation position), or It is designed to be moved in a direction close to it.

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. Light beam emitted from this semiconductor laser 16
15 enters the optical waveguide 22 from the end face 22b and travels in the optical waveguide 22 in the TE waveguide mode as an example. On the other hand, on the surface 22a of the optical waveguide 22, the first converging diffraction grating (hereinafter, F
(Referred to as GC) 17 is provided. The FGC 17 is a diffraction grating having a bend and a chirp, and causes the light beam 15 guided in the optical waveguide 22 to be emitted to the outside of the optical waveguide and then focused on the reflecting surface 14 of the optical disc 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 optical disc 13
The reflected beam 15 'reflected by is reflected at a position away from the first FGC 17. On the surface 22a of the optical waveguide 22 at the position where the reflected beam 15 'is irradiated, the second and third FGCs are formed.
31,32 are provided adjacent to each other. These FGC 31,32
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 incident on the optical waveguide 22 and is focused at one point in the optical waveguide 22. These FGCs 31 and 32 are arranged side by side with the axis (y-axis in FIG. 2) on the optical waveguide 22 passing through the center of the reflected beam 15 'at a right angle to the above-mentioned tracking direction, respectively. Are formed so as to focus the reflected beam 15 'at positions apart from each other across the y axis. The FGCs 31 and 32 may be provided on the surface of the optical waveguide 22 opposite to the surface 22a (lower surface in FIG. 1).

The m-th lattice pattern shape formula of the FGCs 31 and 32 that performs such an action defines the position on the optical waveguide 22 by the x-axis (tracking direction axis) shown in FIG. Set the focus position on the optical disk 13 by the FGC 17 of (f
x, fy, fz), the coordinates of the beam focusing position by the FGCs 31 and 32 are (−Fx, Fy) and (Fx, Fy), respectively, and the light wavelength of the reflected beam 15 ′ is λ, and the FGC31 of the beam 15 ′ is FGC31. Let θ be the angle of incidence on the light beams 32 and 32 and N be the effective refractive index of the optical waveguide 22. Given in.

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.

On the other hand, the surface 22a of the optical waveguide 22 is provided with a first set of photodetectors 24 and a second set of photodetectors 25 so as to detect the reflected beams 15 'focused as described above. There is. The first set of photodetectors 24 is, for example, a photodiode divided into two parts by a gap extending parallel to the y-axis.
It is composed of PD1 and PD2, and the second set of photodetectors 25 is also composed of similar photodiodes PD3 and PD4. These photodiodes PD1 to PD4 are, for example, as shown in detail in FIG. 3, a reflected beam guided on an n type Si substrate 23.
A buffer layer 28 for preventing the seeping light (evanescent light) of 15 ′ from entering the substrate 23 is provided, and a p-type Si layer is provided.
29 and electrodes 30 are provided and 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 a summing amplifier 33.
Similarly, the outputs of PD4 are added by the adding amplifier 36, and the outputs of the photodiodes PD1, PD4 outside the first and second photodetectors 24, 25 are added by the adding amplifier 34, respectively.
The output of the inner photodiodes PD2 and PD3 is the summing amplifier 35.
Is added. The outputs of the addition amplifiers 33 and 36 are input to the addition amplifier 37 and the differential amplifier 39, and the outputs of the addition amplifiers 34 and 35 are input to the differential amplifier 38. The output S1 of the adding amplifier 37, the output S2 of the differential amplifier 38, and the output S3 of the differential amplifier 39 are input to the reading circuit 40, the focus coil drive control circuit 41, and the tracking coil drive control circuit 42, 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 reflection surface 14 of the optical disc 13. The optical disc 13 is rotated by a rotation driving means (not shown) so that the light beam
At the irradiation position of 15, the row (track) of pits 21 is rotated so as to move in the direction of arrow U. As is well known, the pit 21 carries an image signal, an audio signal, etc., and the reflected beam 15 'from the optical disk 13 is the pit.
The level is high in the area without 21 and low in the area where the pit 21 exists. This reflected beam 15 'is FG
It is taken into the optical waveguide 22 by C31 and C32. The reflected beam 15 'guided in the optical waveguide 22 is focused at two points across the y axis by the beam focusing action of each of the FGCs 31 and 32. The light quantity of the reflected beam 15 ′ focused by the FGC31 is detected by the photodiodes PD1 and PD2, while the light quantity of the reflected beam 15 ′ focused by the FGC32 is detected by the photodiode PD.
3 and PD4, the output S1 of the summing amplifier 37 that adds the respective outputs of the summing amplifiers 33 and 36 indicates the overall light quantity of the reflected beam 15 'reflected on the optical disk 13, that is, the pit 21 It indicates the presence or absence. The output S1 is read by the reading circuit 40, and the information recorded on the optical disc 13 is read.

As described above, the block 12 is driven 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 light beam on the optical disk 13 is transmitted.
The irradiation position of 15 (the position in the disk radial direction) is changed, and the pits 21 are continuously read. Where the above light beam 15
Must be correctly irradiated to the center of a given pit 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
The first set of photodetectors when located between FGC31 and FGC32.
The amount of light detected by 24 (photodiodes PD1 and PD2) and the second set of photodetectors 25 (photodiodes PD2 and PD2
It agrees with the amount of light detected by 4). Therefore, in this case, the output S3 of the differential amplifier 39 is 0 (zero).
On the other hand, the irradiation position of the light beam 15 becomes incorrect and the reflected beam
When the light intensity distribution of 15 'is displaced to the upper side in FIG.
The amount of light detected by the photodetectors 24 in the set exceeds the amount of light detected by the photodetectors 25 in the second set. Therefore, the output S3 of the differential amplifier 39 is +
It 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 39 is output.
Is- (minus). That is, the output S3 of the differential amplifier 39
Is the direction of the tracking error (arrow x direction in FIG. 2)
Is shown. This output S3 is sent to the tracking coil drive control circuit 42 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 42 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 the substrate 23 in the direction in which this tracking error is eliminated.
To move. As a result, the light beam 15 is always correctly irradiated to the center of the pit row.

Next, focus control, that is, control for correctly focusing the light beam 15 on the reflecting surface 14 of the optical disk 13 will be described. When the light beam 15 is focused on the reflecting surface 14 of the optical disc 13, the reflected beam 15 'focused by the FGC 31 is focused at an intermediate position between the photodiodes PD1 and PD2. At this time, the reflected beam 15 'which is similarly focused by the FGC 32
Is focused at an intermediate position between the photodiodes PD3 and PD4. Therefore, the output of the adding amplifier 34 and the output of the adding amplifier 35 become equal, and the output S2 of the differential amplifier 38 becomes 0 (zero). On the other hand, when the light beam 15 is focused at a position closer than the reflecting surface 14, the reflected beam 1 incident on the FGCs 31 and 32 is
5'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 34 becomes lower than the output of the addition amplifier 35, and the output S2 of the differential amplifier 38 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 and 32 becomes a divergent beam, and the reflected beam 15 ′ at each of the photodetectors 24 and 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 34 exceeds the output of the adding amplifier 35, and the output S2 of the differential amplifier 38 becomes + (plus). Thus, the output S2 of the differential amplifier 38
Indicates the direction of the focus error. This output S2 is sent to the focus coil drive control circuit 41 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 41 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 correctly focused on the reflecting surface 14 of the optical disk 13.

In this embodiment, since the light beam 15 is not specularly reflected by the reflecting surface 14, the reflected beam 15 'is incident on the optical waveguide 22 from the first FGC 17 and the semiconductor laser 1
Never return to 6. 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 and 32 are formed such that their respective lattices are continuous and in close contact with each other, but these two FGCs 31 and 32 are independent of each other with a small distance. It may be formed. This also applies to the embodiments described below.

Also, the reflected beams focused by the FGCs 31 and 32 respectively
15 'intersect each other, that is, FG if explained in FIG.
FGC31,32 so that the beam focusing position by C31 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. 4, 5 and 6, the same elements as those in FIGS.
Descriptions thereof are 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 and third FGCs 31, 32 are formed on the surface 52a of the second optical waveguide 52. This first FGC17 and the second and third FGC31, 32
Are provided at positions overlapping with each other (see FIGS. 5 and 6). The optical waveguides 51 and 52 are arranged so that the light beam 15 emitted from the first FGC 17 is regularly reflected by the reflection surface 14 of the optical disc 13.

In this case, part of the light beam 15 guided in the first optical waveguide 51 is diffracted by the first FGC 17 toward the substrate 23 side,
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 travels upward (to the optical disk 13 side). The light beam 15 that is diffracted in this direction and then reflected is also effectively used.
The thickness of the buffer layers 28 and 50 so that the reflected light and the light diffracted to the optical disk 13 side by the FGC 17 strengthen each other by interference so that the light beam 15 diffracted from the optical disk 13 side is not weakened. Is preferably selected.

In the apparatus of this embodiment, the reflected beam 15 'from the 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,
It is taken into the second optical waveguide 52 by these FGCs 31 and 32. In this case as well, 2 which is focused in the optical waveguide 52
The reflected beam 15 'of the system is supplied to the first and second beams as shown in FIG.
Tracking error and focus error can be detected by detecting with a pair of photodetectors 24 and 25.

Next, a third embodiment of the present invention will be described with reference to FIG. 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 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 on the optical disk 13, and the first FGC 17 and the second and third FGCs 31 and 32 are the same as those in the second embodiment. They are installed in the same positional relationship as that of No. 1 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 arranged on the side closer to the optical disc 13, and the second optical waveguide 52 is arranged on the side farther from the optical disc 13. Both optical waveguides 51, 5 are placed in the opposite positional relationship.
Two may be arranged.

In the three embodiments described above, the first set, the second set
A pair of photodetectors 24 and 25 are integrated on the surfaces 22a and 52a of the optical waveguide 22 or the optical waveguide 52.
4,25 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. When the photodetectors 24 and 25 are arranged close to the surface 22a of the optical waveguide 22 as described above, the reflected beam 15 '(guided light) is guided to the surface 22a of the optical waveguide 22 as shown in FIG. Providing a diffraction grating 80 that emits to the outside of the waveguide 22,
It is also possible to increase the light receiving efficiency of the photodetectors 24 and 25.
Further, as shown in FIG. 10, 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. 11, the lower transparent electrode 26a, the thin film photoconductive material 26b, and the upper electrode 26c are loaded in this order on the optical waveguide 22 to form the photodiodes PD1 to PD4.
Can also be formed. In this case, the lower transparent electrode
A predetermined electric field is applied from the power supply 26d between the 26a and the upper electrode 26c. In the photodiodes PD1 to PD4 having this configuration, when the photoconductive material 26b is irradiated with light, a photocurrent corresponding to the amount of light flows. Therefore, the amount of light received by the photoconductive material 26b can be detected by detecting the potential change at the terminal 26e. The thin film photoconductive material 26
b is, for example, group IV Si, Ge, group IV Se, group III-V GaAs,
II-VI group ZnO, CdS, IV-VI group PbS, etc. epitaxial film, polycrystalline film, amorphous film, etc. can be formed, and amorphous chalcogen film (a-Se, a-Se -As-Te), amorphous
A film mainly composed of Si and containing hydrogen and / or fluorine (aS
i: H, a-SiGe: H, a-SiC: H, etc.) by adding a group III or V group atom (B, P, etc.) to a pn junction, p-i-
A film for forming a photodiode by obtaining an n-junction, a film for forming a photodiode by using an electrode forming a Schottky junction with the film containing hydrogen and / or fluorine mainly containing amorphous Si. You can also

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 pickup of the present invention, the action that optical elements such as the objective lens, the beam splitter, the focusing lens, and the prism in the conventional pickup play is obtained by the FGC formed on the optical waveguide. It is designed to be used. 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.

Further, in the pickup of the present invention, the reflected beam, which is focused on the optical recording medium by the first converging diffraction grating formed on the surface of the first optical waveguide and then reflected from the optical recording medium, is reflected by the first optical waveguide. Since the second and third light converging diffraction gratings formed on the surface of the second optical waveguide integrated with the waveguide divide the light into two, these second and third light converging diffraction gratings are It means that it is located at the pupil position.
Generally, the tracking error has the highest sensitivity when the reflected beam is divided and detected at the pupil position, and in the present invention, the reflected beam is divided into two at the position close to the pupil position. The detection sensitivity, and thus the detection accuracy, will be sufficiently high. Further, in the pickup of the present invention, since each of the reflected beams after being divided into two as described above is detected at the focusing position, there is no need to use a large photodetector, and therefore the response speed is high and the high speed. It becomes possible to follow the tracking adjustment.

[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.
FIG. 7 is a side view showing the optical waveguide and the second optical waveguide of FIG. 7, FIG. 7 is a plan view showing the device of the third embodiment of the present invention, and FIGS. 8, 9, 10 and 11 are the light used in the device of the present invention. It is a side view which shows the other example of a detector. 13 …… Optical disc, 14 …… Reflecting surface of optical disc 15 …… Light beam, 15 ′ …… Reflected beam 16 …… Semiconductor laser, 17 …… First FGC 19 …… Tracking coil, 20 …… Focus coil 21… … Pits, 22 …… Optical waveguide 22a …… Surface of optical waveguide, 22c …… End face of optical waveguide 23,53 …… Substrate, 24 …… First set of photodetectors 25 …… Second set of photodetectors , 28, 50 …… Buffer layer 31 …… Second FGC, 32 …… Third FGC 33, 34, 35, 36, 37 …… Summing amplifier 38, 39 …… Differential amplifier, 40 …… Reading circuit 41 ... Focus coil drive control circuit 42 ... Tracking coil drive control circuit 51 ... First optical waveguide 51a ... Surface of first optical waveguide 52 ... Second optical waveguide 52a ... Second optical waveguide Surface PD1-4 ... Photodiode

Claims (7)

[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 a 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 reflection surface of the optical recording medium, and being integrated with the first optical waveguide, A second optical waveguide arranged so that one surface thereof receives the reflected beam reflected by the optical recording medium, 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 The reflection beams are arranged in parallel on the surface with axes extending substantially at right angles to the tracking direction, and the reflection beams are made incident on the optical waveguide, respectively, and the reflection beams guided in the second optical waveguide are arranged on the axes. Each is located at a distance from each other Second and third converging diffraction gratings for respectively focusing, and each of the reflected beams that are attached to the surface or end face of the second optical waveguide and focused by the second and third converging diffraction gratings. An optical recording medium pickup comprising a first set of photodetectors and a second set of photodetectors, each of which comprises a plurality of photodetector elements for detecting recorded information, tracking error detection, and focus error detection. 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 an optical recording medium as described above. 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. Patented that the first converging diffraction grating and the second and third converging diffraction gratings are arranged in a direction of regular reflection on a reflecting surface, and are provided at positions overlapping each other. An optical recording medium pickup according to claim 1. 4. The 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. pick up. 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. An optical recording medium pickup 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. An optical recording medium pickup according to any one of claims 1 to 5. 7. A gap extending substantially parallel to the axis so that the first and second photodetectors can perform tracking error detection and focus error detection by a push-pull method and a Foucault method, respectively. The optical recording medium pickup according to any one of claims 1 to 6, wherein the optical pickup comprises a split photodetector.