JPH0795372B2 - Optical head device - Google Patents

Description

The present invention relates to an optical head device for irradiating an information recording surface of an information carrier with light to detect or record information, and particularly to a small-sized optical head device.
The present invention relates to an optical head device which is lightweight and suitable for mass production.

Conventionally, an optical head device has been constructed, for example, as shown in FIG. Here, the divergent light flux emitted from the laser light source 1 enters the collimator lens 2, becomes a parallel light flux, and enters the polarization beam splitter 3. Here, the polarized beam splitter 3 has a characteristic that almost 100% of the linearly polarized light having an oscillating surface in a specific direction is transmitted and almost 100% of the linearly polarized light having an oscillating surface in the direction orthogonal thereto is reflected. Linearly polarized light transmitted through this polarized beam splitter 3 is a λ / 4 plate 4
And becomes circularly polarized light, and is condensed by the objective lens 5 on the information recording surface 7 provided on the substrate 6 of the information carrier to form spots having a spot diameter of about 1 μm. Further, the light flux reflected by the information recording surface 7 is the objective lens 5
Through the λ / 4 plate 4, and becomes a linearly polarized light whose vibrating surface is orthogonal to that at the time of incidence, and re-enters the polarization beam splitter 3. Here, the polarized beam splitter 3 functions as a light splitter due to the above-mentioned characteristics, reflects the reflected light from the information recording surface 7 and separates it from the incident light, and the light beam is converged through the sensor lens 8 as a photodetector. Lead to 9.

When information is recorded using such an optical head device, the laser light source 1 is driven in accordance with the information signal, and the incident light on the information recording surface 7 is modulated. In the case of detecting information, unmodulated light is applied to the information recording surface 7 on which information is recorded due to irregularity pits or a change in reflectance, and the reflected light modulated by the recorded information is reflected. Is detected by the photodetector 10 and information is reproduced. At this time, on the information recording surface 7, a track composed of a recording signal train or a guide track previously provided on the substrate 6 or the like is densely formed so as to extend in the direction perpendicular to the paper surface in FIG. . Therefore, in order to record or detect information correctly, it is necessary to perform control, so-called auto-tracking, so that the spot always traces the above-mentioned track.

Conventionally, as an auto-tracking method, an element having a plurality of light-receiving surfaces divided in a direction corresponding to the width direction of the track is used as a photodetector 9, and signals obtained from the respective light-receiving surfaces are differentiated. Therefore, a method of obtaining a tracking error signal is known. According to this tracking error signal, the spot is correctly guided onto the track by a method such as moving the objective lens 5 perpendicularly to the optical axis by a mechanism (not shown). However, in such a conventional method, since the photodetector 9 is provided in the vicinity of the image forming position with the information recording surface 7, the mounting error of the photodetector greatly affects the accuracy of the tracking error signal. Have a big influence,
It has a drawback that a highly accurate position adjustment between the components is required when assembling the device. Further, in order to increase the tolerance of the assembling accuracy, a method of detecting a tracking error signal in a parallel light flux of reflected light from the information recording surface using a large photodetector has been performed. However, even in this method, there is a drawback that the photodetector becomes large and the response of the photodetector to a high frequency band deteriorates or the photodetector itself becomes expensive due to the size increase of the photodetector.

On the other hand, in the optical head device, in addition to the above-described auto-tracking, information is recorded at a high density on the information recording surface, and in order to detect the recorded information at a high density, the light from the light source is always recorded on the information recording surface. Autofocusing is performed to focus. Conventionally, so-called astigmatism method, critical angle method, Foucault method, knife edge method,
Various methods such as the beam horizontal displacement method are known, and one example thereof will be described with reference to FIG. The apparatus whose schematic configuration is shown in FIG. 2 is proposed in Japanese Patent Laid-Open No. 57-64335. Here, the light emitted from the semiconductor laser 11 is collimated by the collimator lens 12 and is reflected by the objective lens 15 to the substrate 16
It is focused on the upper information recording surface 17. The signal read on the information recording surface 17 is reflected by the information recording surface 17, and changes in the output of the semiconductor laser 11 due to a change in the amount of return light returning to the semiconductor laser 11 through the same optical path as when incident are detected by the monitor sensor 25. The so-called scoop (SCOOP) method is used to detect this. Further, the sensor lens 21 having the focal length f occupies a part of the pupil plane of the objective lens 15, and a part 26 of the light reflected by the information recording surface becomes a focused light flux 27 by this sensor lens 21 and is divided into two. It is incident on the photodetector 22. When the information recording surface 17 moves away from or near the focal position of the objective lens 15, the focused light flux 27 moves left and right on the photodetector 22. A focus error signal is obtained by subtracting the output of each of the divided light receiving surfaces by the subtractor 23. This focusing error signal drives the focusing actuator 24, and autofocusing is performed so that the incident light is always focused on the information recording surface 17.

In the apparatus shown in FIG. 2, since the off-axis light beam of the objective lens is taken out, the detected light beam has a large effect on defocus, and highly sensitive focus error detection can be performed. However, on the other hand, from the semiconductor laser 11 to the objective lens 15
The light flux incident on is deformed by being deflected by the sensor lens 21, and as a result, the spot on the information recording surface 17 becomes large.

An object of the present invention is to provide an optical head device in which the position of the photodetector can be easily adjusted.

Another object of the present invention is to provide an optical head device capable of partially extracting the reflected light from the information recording surface to a photodetector without affecting the incident light on the information recording surface. .

The above object of the present invention is to irradiate the information recording surface with light emitted from a light source, and to reflect the light reflected from the information recording surface by an optical splitter disposed in the optical path from the light source to the information recording surface. In an optical head device that guides to a light-receiving surface of a detector to detect or record information, the division surface of the optical divider comprises a diffraction grating having a plurality of frame gratings in which at least three grating patterns different from each other are formed. Achieved by things.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic sectional view showing the construction of the first embodiment of the optical head apparatus according to the present invention. The light flux from the laser light source 31 is converted into a parallel light flux by the collimator lens 32 and is incident on the light splitter 41 in which the diffraction grating 44 is formed in the substrates 42 and 43 made of parallel flat plates. Since this light splitter 41 does not act on the incident light flux, the light flux is transmitted as it is, and the λ / 4 plate
After being incident on 34 to be circularly polarized light, it is condensed on the information recording surface 37 via the substrate 36 by the objective lens 35. Information recording surface
The light flux reflected by 37 passes through the objective lens 35 to become a parallel light flux, again passes through the λ / 4 plate 34, and enters the light splitter 41 as polarized light vibrating in a direction orthogonal to the time of incidence. The reflected light is diffracted or reflected by the diffraction grating 44 in the light splitter 41, guided through the substrate 43 while repeating total reflection, and is incident on the photodetectors 39 and 40. Here, when recording information, the laser light source 31 is driven according to the information signal,
This is done by modulating the incident light on the information recording surface 37. When detecting information, the information recording surface 37 is irradiated with unmodulated light, and the reflected light modulated according to the information recorded there is detected by the photodetectors 39 and 40 to reproduce the information. To do.

FIG. 4 is a view of the light splitter 41 shown in FIG. 3 as seen from the direction of the light source 31. Diffraction grating 44 constituting the split surface of the optical splitter 41
Is divided into two areas with a line segment AA 'as a boundary, and two frame gratings 44a and 44b each having a different grating pattern diffract the reflected light from the information recording surface 37 in different directions. It leads to different photodetectors 40 and 39. By appropriately processing the output signals of the photodetectors 39 and 40, a focus error signal, a tracking error signal and an information reproduction signal necessary for the optical head device can be obtained.

First, the principle of detecting a focus error signal will be described. In the photodetector 39 described above, the light receiving surface is divided into three as shown in FIG. Now, when the minimum light spot is generated on the information recording surface 37 (that is, in the focused state), the photodetector is arranged so that the light amount distribution is as shown by the shaded portion in FIG. 5 (b). It has been done. At this time, if the distance between the information recording surface 37 and the objective lens 35 is too large (that is, the object is out of focus), the spread of the light beam in the light receiving surface arrangement direction decreases as shown in FIG. If the information recording surface 37 and the objective lens 35 become too close to each other and become out of focus, the fifth
The light amount distribution spreads as shown in FIG. Therefore, the photodetector
The respective outputs I _A , I _B , and I _C of the light receiving surfaces 39A, 39B, and 39C of 39 are calculated by the calculator 4
The focus error signal I _F can be obtained by performing the following calculation processing by 5.

I _F = (I _A + I _B ) −I _C Next, detection of a tracking error signal will be described. The dividing surface of the optical splitter is divided into two areas by the line segment AA 'as described above. The direction of this AA' is the track composed of the signal train recorded on the information recording surface 37 or the area in advance. It is arranged so as to coincide with the extending direction of the guide track provided on the substrate 36 and the like. Therefore, the light received by the photodetectors 39, 40 contains information from the right side and the left side of the track, respectively, and by subtracting the outputs of these photodetectors 39, 40 by the calculator 46, A so-called push-pull type tracking error signal I _T can be detected. Here, when the output of the photodetector 40 is represented as I _{D by} an arithmetic expression, I _T = (I _A + I _B + I _C ) −I _D.

Further, when the arithmetic unit 47 calculates the sum of the signal outputs of the photodetectors 39 and 40, I _RF = (I _A + I _B + I _C ) + I _D , this becomes the information reproduction signal I _RF . The photodetector 40 used here may be an element of the same type as the photodetector 39, or may be one whose light-receiving surface is not divided. Further, when the photodetector 40 uses an element whose light-receiving surface is divided into three, if the outputs from the respective light-receiving surfaces are I _D1 , I _D2 , and I _D3 , then I ′ _T = (I _D1 + I _C ) − Yotsute to carrying out the calculation of (I _D3 + I _a), it is also possible to obtain a tracking error signal I _'T by the heterodyne method.

In the present embodiment, since the light splitter is formed in a parallel plate type, there is a feature that the entire optical head device can be made thin. Also, this light splitter itself can be easily manufactured by collectively processing a plurality of substrates on a large substrate and cutting them out, which is excellent in mass productivity. Further, in the present embodiment, the reflected light from the information recording surface is divided by the division surface of the optical divider, and each of them is detected by different photodetectors. Therefore, the attachment of the photodetector for detecting the tracking error signal is performed. The accuracy is eased and the assembly and adjustment are easy. Further, when the photodetector is integrally formed on the end surface of the substrate of the light splitter, such assembly adjustment is unnecessary. It is well known that it is generally desirable to detect the intensity distribution on the pupil plane of the objective lens in order to obtain a good tracking error signal.
In this embodiment, since the intensity distribution on the split surface of the light splitter placed near the objective lens is detected, the detection is effectively performed by splitting the pupil plane, and highly reliable tracking is achieved. It can be controlled.

FIG. 6 schematically shows the structure of the diffraction grating used in the embodiment shown in FIG. FIG. 6 (a) is a partial sectional view of an optical splitter 41 using a volume diffraction grating. The diffraction grating 44 is sandwiched between the substrates 42 and 43 formed of parallel flat plates, and includes a layer 50 having a low refractive index and a layer 51 having a high refractive index. Incident light 52 from the information recording surface is generated by this diffraction grating.
The light is diffracted by 44 and becomes diffracted light 53. When the diffraction grating 44 substantially satisfies the Bragg condition for the incident light 52, most of the energy of the diffracted light 53 is concentrated in a specific diffraction direction. Further, when the angle formed by the incident light 52 and the diffracted light 53 is close to a right angle, the diffraction efficiency is greatly affected by the polarization state of the light beam, and the P polarized light has a transmittance of 100% and the S polarized light has a transmittance of 1%.
It has a diffraction efficiency close to 00%. Therefore, by making the light traveling from the laser light source 31 toward the information recording surface 37 into the linearly polarized light of P polarization by the configuration as shown in FIG. 3, this light is transmitted by the light splitter 41 with almost no influence. The light reflected from the information recording surface 37 is efficiently diffracted into S-polarized light by the function of the .lamda. / 4 plate 34 and guided to the photodetectors 39 and 40.

The diffraction grating 44 as shown in FIG. 6 (a) is manufactured using a volume hologram sensitive material such as dichromated gelatin. For example, the above-mentioned sensitive material is formed on a substrate to have a uniform thickness, the light flux from the same laser is split, and the interference fringes generated by overlapping at a predetermined angle are exposed and further developed. By processing, a diffraction grating is formed. In order to manufacture a diffraction grating that diffracts a light beam in different directions as in the present invention, first, in the first step, a part of the photosensitive material is covered with a mask and one interference fringe is exposed. Next, in a second step, the exposed portion is masked, and the interference fringes of different patterns are exposed by the light incident on the portion covered with the mask from an angle different from that in the first step. Finally, the mask is removed, and the interference fringes exposed in the first and second steps are processed by development. Further, even if the two sets of light fluxes are simultaneously irradiated to different portions of the photosensitive material without performing the baking twice in this way, an optical system that exposes interference fringes of different patterns to a desired area is used at a time. It can also be baked.

FIG. 6 (b) is a partial cross-sectional view showing another configuration example of the optical splitter 41 used in the present invention. The diffraction grating 44 is a layer 54,5 having a reflection film 60 having an appropriate reflection characteristic, for example, a polarized beam splitting characteristic, and having an unevenness and having substantially the same refractive index.
It has a shape that is sandwiched by 5. Therefore, with respect to the linearly polarized light 56 which is incident as P-polarized light, the diffraction grating 44 behaves as a simple parallel plate without any action, and acts as a reflecting mirror with respect to the linearly polarized light 57 which is incident as S-polarized light. ,
Diffracted light 58 is produced.

The diffraction grating 44 as shown in FIG. 6 (b) can be produced by exposing a relief type photosensitive material such as a photoresist to a grating pattern through an appropriate optical system and developing it. In addition, it is also possible to fabricate by a method of mechanically processing a die and transferring it to a layer to be a substrate by a method such as infusion, complexion, thin layer copy, or a method of directly cutting the substrate. .

Further, in the embodiment shown in FIG. 4, the diffracted light from the diffraction grating 44 is diffracted as focused light, but the diffraction grating which produces the lens action in this way is, for example, FIG. 6 (a).
In the configuration as shown in (b), it can be realized by making the lattice into a conical shape. When an optical means is used for producing the diffraction grating 44, an optical system as shown in FIG.
It can have a focusing effect. In FIG. 7, parallel light beams 61 and 62 emitted from the same laser light source and split by an optical system (not shown) are incident on conical mirrors 63 and 64 sharing a rotation axis 65, respectively, in parallel to the rotation axis 65. . The two light beams reflected by the respective conical mirrors form a conical wavefront having a focal line on the rotation axis 65 and enter the hologram photosensitive material 67 on the substrate 66. At this time, the interference fringes generated in the region 68 on the surface of the photosensitive material are three-dimensionally conical with the rotation axis 65 as the center of rotation. Therefore, by developing the interference fringes thus exposed, a diffraction grating having a focusing effect as shown in FIG. 4 is formed.

Although the first embodiment has been described above, the present invention is not limited to this, and various modifications can be made depending on the configuration of the split surface of the optical splitter. An example is shown below. The following embodiments are all described with reference to the figure of the light splitter as seen from the light source side, and the optical elements other than the light splitter are not shown, but they are constructed in the same way as the embodiment shown in FIG.

FIG. 8 is a diagram showing an optical splitter used in the second embodiment of the present invention. In the present embodiment, two diffracted lights guided to different end faces of the light splitter in the first embodiment are detected by the end faces on the same side, and the same members as those in FIG. 4 are the same. Will be assigned and the detailed description will be omitted. Here, the diffraction grating 74 constituting the dividing surface of the optical splitter 71 is divided into two areas having different grating patterns with a line segment AA 'corresponding to the track extending direction of the information recording surface as a boundary. Each of the frame gratings 74a and 74b focuses the reflected light from the information recording surface and diffracts it to different positions on one end face of the light splitter 71, and guides it to the photodetectors 40 and 39, respectively. By processing the output signal of this photodetector in exactly the same manner as described in FIGS. 4 and 5, the focus error signal I _F , tracking error signal I _T , and information reproduction signal I _RF are obtained. can get. In this embodiment, since the photodetectors can be concentrated on one side of the light splitter,
Compared with the first embodiment, there is an advantage that the optical head device can be further downsized.

FIG. 9 is a diagram showing an optical splitter used in the third embodiment of the present invention. The diffraction grating formed in the light splitter 81 is manufactured by the same method as that of the above-described embodiment, and is divided into the piece gratings 82 and 83. Each piece grating 82, 83 is formed with a lens action so that the diffracted light forms a focal line in a predetermined direction,
Each diffracted light is guided to a four-division photodetector 80 formed on one end face of the light splitter. Here, the direction of the focal line of the frame grating 82 coincides with the direction AA 'of the track image on the information recording surface. Output from each of the divided light receiving surfaces of the four-division photodetector 80
I _A , I _B , I _C , and I _D can be appropriately processed by a calculator (not shown) to obtain various signals necessary for the optical head device.
For example, the information reproduction signal I _RF is the sum of the output obtained from the _{I RF = I A + I B} + I C + I D. Also, the focus error signal I _F is the frame grid.
This is obtained by detecting the shake and spread in the plane of the paper of FIG. 9 of the light beam split by 83 at approximately the pupil plane position of the objective lens. The position of the frame grating 83 and the diffraction direction of the light diffracted by it can be arbitrarily made as described above, and the photodetector 80 may be arranged anywhere, but as shown in FIG.
The focusing error signal I _F can be detected with high sensitivity by arranging so that the change of the diffracted light is large in the division direction of the light receiving surface of 80. Specifically, the difference between the outputs I _A and I _{B on} the light receiving surface is obtained as I _F = I _A −I _B. Since the tracking error signal I _T is obtained from the light amount distribution in the reflected light beam from the information recording surface,
It is obtained from the light amount difference of the light flux divided by the focal line of the frame grating 82 which coincides with the direction AA 'of the track image. Actually, the output from each light receiving surface of the four-division photodetector 80 is calculated to obtain I _T = I _A + I _B + I _C −I _D.

With the light flux control signals (focus error signal, tracking error signal) obtained as described above, the optical head device is controlled so that the desired light flux is incident on the information recording surface, and the detection or recording of information is surely performed. It can be done to. In the embodiment shown in FIG. 9, since the structure of the diffraction grating can be arbitrarily set as described above, it is not shown in the drawing, but the 4-split photodetector is a combination of the 2-split photodetectors or the 2-split photodetector. It is also possible to replace it with a combination of a detector and a photodetector whose light receiving surface is not divided. Further, it goes without saying that the position of the piece lattice 83 can be set to an arbitrary position within the lattice plane.

FIG. 10 shows an optical splitter used in the fourth embodiment of the present invention. In this embodiment, the optical splitter 91 is provided with a frame grating 93 for detecting a focus error signal as in the third embodiment, and the other portion is divided in the direction AA 'of the track image. It is further divided by lines to form piece lattices 92a and 92b, respectively. The light diffracted or reflected by the frame grating 93 is guided to the two-division photodetector 95. Also, piece lattices 92a and 9
The two light beams diffracted or reflected by 2b are guided in the focal line direction by the respective gratings in the light splitter, and are guided to the corresponding photodetectors 97 and 96. The outputs of the light receiving surfaces of the two-division photodetector 95 are I _A and I _B , the output of the photodetector 96 is I _C , and the photodetector 97
When the output of I is I _D , the focus error signal, the tracking error signal, and the information reproduction signal are obtained by processing them by an unillustrated arithmetic unit in exactly the same manner as in the third embodiment. In this embodiment, since the light from the information recording surface is divided by the division gratings that match the direction of the track image by the frame gratings 92a and 92b, and is guided to different photodetectors, the track position information is included. Since the light amount distribution of the sub-beam is divided and detected almost at the pupil plane position of the objective lens, a more reliable tracking error signal can be detected.

FIG. 11 is a diagram showing an optical splitter used in the fifth embodiment of the present invention. In the present embodiment, the diffraction grating on the optical splitter 101 is divided into piece gratings 102, 103 and 104, and has a shape just like that in which the piece grating 104 is added to the configuration of the third embodiment. The light beam diffracted or reflected by the frame gratings 102 and 103 is detected by the four-division photodetector 100, and the light beam diffracted or reflected by the frame grating 104 is detected by the photodetector 105. . In this embodiment, by compensating for the symmetry with the direction AA ′ of the track image of the light flux in the frame grating 82 as the axis of symmetry in this way, it is possible to simplify the arithmetic processing of the signals after the photodetector. . Specifically, the outputs from the divided light receiving surfaces of the four-division photodetector 100 are respectively I _A , I _B , I _C , and I _D, and the photodetector 105
When the output of the I _E, information reproducing signal I _RF are obtained as _{I RF = I A + I B} + I C + I D + I E. Further, the focus error signal I _F is obtained as the difference between I _A and I _B as I _F = I _A −I _B. The tracking error signal I _T is simply detected by the addition of the frame grating 104.
It is obtained as the difference between the output signals I _C and I _D of 00.

I _T = I _C −I _{D In} the embodiment, the photodetector 105 can be removed and the information reproduction signal I _RF can be obtained as I _RF = I _A + I _B + I _C + I _D. In this case, the light beam diffracted or reflected by the frame grating 104 may be reflected and scattered at the end surface of the light splitter 101 to generate stray light, so a light absorber is installed at a position where the photodetector 105 is removed. You may.
In this embodiment as well, modifications such as replacement of the photodetector as described in the third embodiment are possible.

FIG. 12 is a diagram showing an optical splitter used in the sixth embodiment of the present invention. In this embodiment, the diffraction grating on the optical splitter 111 is divided into piece gratings 112a, 112b, 113, and each piece grating diffracts or reflects a light beam while converging a light beam so as to form a focal line in a different direction. The light flux from the frame grating 113 is guided inside the light splitter and detected by the two-split photodetector 114. See also piece lattice 1
The dividing line between 12a and 112b coincides with the track image direction AA ', and the respective diffracted lights are detected by the photodetectors 115 and 116.
If the outputs of the respective light receiving surfaces of the two-division photodetector 114 are I _A and I _B , the output of the photodetector 115 is I _C , and the output of the photodetector 116 is I _D ,
The information reproduction signal I _RF is obtained from the sum of these outputs, I _RF = I _A + I _B + I _C + I _D. Further, Fuo Kas error signal I _F is obtained Te cowpea almost shake and detection spread on the light receiving surface of the photodetector 114 of the divided light beams at the pupil plane position of the objective lens by piece grid 113. The position and diffraction direction of the bridge grating is the third
As described in the examples, it can be arbitrarily produced, and an optimum design capable of highly sensitive detection is made. Specifically, by taking the difference between the two output signals of the two-split photodetector, I _F = I _A −I _B is obtained. The tracking error signal I _T is detected by detecting the amount of light from the frame gratings 112a, 112b divided at the track image direction AA ′ by the corresponding photo detectors 116, 115, and taking the difference between the output signals. can get.

I _T = I _C −I _{D In} the present embodiment, the photodetectors 115 and 116 can be replaced with a single two-division photodetector, and the photodetectors 114 and 11 can be replaced.
It is also free to combine 5,116 into a four-division photodetector.

FIG. 13 is a diagram showing an optical splitter used in the seventh embodiment of the present invention. In this embodiment, the direction AA ′ of the track image makes an arbitrary angle θ with the optical splitter 121.
Here, the diffraction grating of the optical splitter 121 is a piece grating 122a, 122b, 12
It is divided into 3,124 and diffracts or reflects while converging the light flux so as to form focal lines in different directions. Piece lattice 12
The line dividing the lines 2a and 122b coincides with the direction AA 'of the track image, and the frame gratings 123 and 124 are formed at line symmetric positions with the dividing line as the axis of symmetry. The light beams diffracted or reflected by the frame gratings 122a and 122b are guided to the respective light receiving surfaces of the two-divided photodetector 126. The luminous flux from the frame grating 123 is a two-split photodetector 125.
Detected in. Further, the light flux from the piece grating 124 is the light absorber 1.
Absorbed by 27. If the outputs of the light receiving surfaces of the two-divided photodetector 125 are I _A and I _B , and the outputs of the light receiving surfaces of the two-divided photodetector 126 are I _C and I _D , the information reproduction signal I _RF and focus The error signal I _F and the tracking error signal I _T are obtained by arithmetically processing the above output by an unillustrated arithmetic unit in the same manner as in the sixth embodiment.

In this embodiment, the frame grating 124 is provided to compensate the symmetry of the two light beams split by the frame gratings 122a and 122b when the tracking error signal is detected. It plays the same role. Therefore, the light absorber 127 may be replaced with a photodetector, and the information reproduction signal and the light flux control signal may be obtained in the same process as in the fifth embodiment shown in FIG. Further, in this embodiment, it is also conceivable that the frame grating 124 is removed and the above-mentioned compensation is performed by the arithmetic processing after the photodetector as in the fourth embodiment shown in FIG.

Although various structural examples of the optical splitter have been described above, the present invention can be modified such as one using another optical splitter or one having a different configuration other than the optical splitter. For example, when reading magneto-optical recording, in the configuration shown in FIG. 3, the λ / 4 plate 34 is removed and a polarizing plate is placed immediately in front of the photodetectors 39 and 40, or the λ / 4 plate 34 is replaced with a Faraday element. It becomes possible to detect by doing. In the embodiment, the light beam from the light splitter is directly guided to the photodetector.However, the light beam is sent to the photodetector via an appropriate optical system by processing a cylindrical lens on the end face of the light splitter. You may guide it.

As described above, according to the present invention, in the conventional optical head device, by providing a plurality of areas for guiding the reflected light to different light receiving surfaces on the split surface of the optical splitter that splits the reflected light from the information recording surface. In addition, the position adjustment of the photodetector is facilitated, and the reflected light can be partially extracted to the photodetector without affecting the light incident on the information recording surface.

[Brief description of drawings]

1 and 2 are schematic diagrams showing the configuration of a conventional optical head device, FIG. 3 is a schematic configuration diagram showing an embodiment of the optical head device according to the present invention, and FIG. The figure which looked at the optical splitter of an apparatus from the light source side, FIGS. 5 (a), (b), and (c) are the figures explaining the principle of detection of the focus error signal in the apparatus of FIG. 3, respectively, FIG. (A) and (b) are schematic cross-sectional views each showing an example of the structure of the diffraction grating used in the present invention, FIG. 7 is a view for explaining an example of a method for manufacturing the diffraction grating, and FIGS. 8 to 13 are respectively It is a figure which shows the structure of the optical splitter used for the other Example of this invention. 31 …… Laser light source, 32 …… Collimator lens, 34 …… λ
/ 4 plate, 35 ... Objective lens, 36 ... Substrate, 37 ... Information recording surface, 39, 40 ... Photodetector, 41 ... Optical splitter, 42, 43 ... Substrate composed of parallel plates, 44 ……Diffraction grating.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyonobu Endo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tetsuro Kuwayama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Osawa Dai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasuo Nakamura 1248 Shimokagemori, Chichibu-shi, Saitama Canon Electronics Inc. (56 ) References JP-A-60-129938 (JP, A)

Claims (1)

[Claims] 1. A light detector which irradiates light emitted from a light source onto an information recording surface, and which reflects light reflected from the information recording surface by an optical splitter disposed in an optical path from the light source to the information recording surface. In the optical head device which guides to the light receiving surface of and detects or records information, the division surface of the optical divider comprises a diffraction grating having a plurality of frame gratings in which at least three different grating patterns are formed. Characteristic optical head device.