JPH06295481A - Optical pickup - Google Patents

Abstract

PURPOSE:To suppress a decrease in C/N and stably detect a magnetooptic signal by small-sized constitution by utilizing a semiconductor substrate which has a semiconductor laser and photodetecting means, and an optical branch element, where a hologram and polarized light separating surfaces are formed, in one body. CONSTITUTION:A unit 1 is formed by integrating the substrate 7 which has the semiconductor layer 13 and photodetection parts 15 and 16 and the optical branching element 9 which has polarized light separating surfaces 12a and 12b, etc., in one body. The laser light from the laser 3 becomes a light of 0th order and lights of (+ or -)th order for tracking through a grating 10a to irradiate a magnetooptic recording medium. Their reflected lights are deflected and separated by a branching mirror to a 1st and a 2sn optical path and made incident on the hologram 10c, and they are separated by separating surfaces 12a and 12b and detected by photodetectors 17a and 17b, and 18a and 18b. This unit of small-sized constitution suppresses the decrease in C/N by the photodetection of 100% P-polarized lights and stably detects the magnetooptic signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in a recording / reproducing apparatus for recording and / or reproducing information on an optical recording medium such as an optical disk.

[0002]

2. Description of the Related Art As a conventional optical pickup, for example, the one shown in FIG. 12 is proposed in Japanese Patent Laid-Open No. 63-32743. In this optical pickup,
The divergent beam from the semiconductor laser 61 is once converged by the lens 62, then diverged again and guided to the collimator lens 64 via the hologram lens 63, converted into a parallel beam by the collimator lens 64, and converted by the objective lens 65 into a magneto-optical beam. The recording medium 66 is irradiated with spots.

Return light reflected by the magneto-optical recording medium 66 is guided to a hologram lens 63 via an objective lens 65 and a collimator lens 64, where ± 1st-order diffracted light having astigmatism is generated, and these are generated. The ± 1st-order diffracted light passes through the polarization lens 67 and is incident on the photodetectors 69 and 70 formed on the substrate 68 and each having four-divided light receiving regions. In this way, the magneto-optical signal is detected from the difference between the outputs of the photo detectors 9 and 10, and the focus error signal is obtained by the astigmatism method.

As another conventional optical pickup,
Those shown in FIGS. 13 and 14 have also been proposed. This optical pickup does not use a hologram, and the divergent beam from the semiconductor laser 61 is collimated by the collimator lens 64 and then enters the polarization beam splitter 71 as P-polarized light.
And is converged on the magneto-optical recording medium 66 by the objective lens 65.

The return light reflected by the magneto-optical recording medium 66 passes through the objective lens 65, is reflected by the polarization beam splitter 71, and is then rotated by 45 ° in the polarization direction by the ½ wavelength plate 76, and then the condenser lens 72. And enters the trapezoidal prism 73 having a polarization separating function. This trapezoidal prism 73
The S-polarized light component of the return light incident on is reflected by the polarization splitting surface 73a, and the three-divided photodetector 75b on the substrate 74
The P-polarized component is transmitted and the three-division photodetector 75 on the substrate 74
a respectively led to. In this way, the photodetector 75
Based on the outputs of a and 75b, the magneto-optical signal is detected from the difference between them, and the focus error signal is obtained by the beam size method.

In this optical pickup, since the light emitted from the semiconductor laser 61 is incident on the polarization beam splitter 71 as P-polarized light, the Kerr rotation information contained in the returned light from the magneto-optical recording medium 66 is S-polarized light. The ingredients will have. Therefore, in this case, if the S-polarized component of the return light is efficiently guided to the photodetectors 75a and 75b, the amplitude of the magneto-optical signal can be increased and the C / N can be increased. It is desirable to set the reflectance R _S of the S-polarized component of 100 to 100%. Therefore, in this optical pickup, the transmittance T and the reflectance R of the P and S polarization components of the polarization beam splitter 71 are set.
For example, T _P 80%: T _S 0%: R _P 20%: R _S 1
It is set to about 00%.

As an optical pickup, the present applicant also
For example, Japanese Patent Application No. 4-110022 proposes the ones shown in FIGS. In this optical pickup, a semiconductor laser, a photodetector and a hologram are unitized, and the light emitted from this unit 81 is stopped by a diaphragm 82.
Also, the recording medium 84 is irradiated with the light through the objective lens 83, and the return light reflected by the recording medium 84 is made incident on the unit 1 along the reverse path.

As shown in the sectional view of FIG. 16, the unit 81 is constructed by providing a semiconductor substrate 86 on a substrate 85 and a hologram optical element 88 via a spacer 87. As shown in the plan view of FIG. 17, a semiconductor laser 89 is mounted on the semiconductor substrate 86, and three photodetectors 91, which are arranged in the y direction on both sides of the semiconductor laser 89 in the x direction, respectively. 92, 93 and 9
4, 95 and 96 are formed, and the photodetectors 92 and 95 at the center are respectively divided into three light receiving regions 92 in the y direction.
a, 92b, 92c and 95a, 95b, 95c. Further, the semiconductor laser 89 is shown in FIG.
As shown in the partial cross-sectional view in FIG. 1, the semiconductor substrate 86 is mounted in a recess 86a formed by etching, and the slope 86b formed by etching of the recess 86a is used as a mirror surface in a direction parallel to the plane of the semiconductor substrate 86 from the semiconductor laser 89. The mirror surface 86b reflects the light beam emitted to the optical disk in a direction substantially normal to the semiconductor substrate 86.

Further, in the hologram optical element 88, as shown in FIG. 16, a grating for separating the light flux from the semiconductor laser 89 into three light fluxes of 0th-order light and ± 1st-order diffracted light on the surface of the semiconductor substrate 86 side. 88a is formed, and on the opposite surface, a hologram pattern 88b is formed which diffracts the return light from the recording medium 84 and gives the ± 1st order diffracted lights a focal power in opposite directions.

In this way, the light emitted from the semiconductor laser 89 is reflected by the mirror surface 86b and then separated by the grating 88a into three beams of one main beam and two sub-beams, respectively. The recording medium 84 is irradiated through the diaphragm 82 and the objective lens 83. Also,
The return lights of the three light fluxes applied to the recording medium 84 follow the opposite paths and are diffracted by the hologram patterns 88b, respectively, and the ± first-order diffracted lights of the main beam are respectively detected by the photodetectors 92 and 95 in the center. The ± 1st-order diffracted light of one of the sub-beams received is received by, for example, photodetectors 91 and 94.
Then, the ± first-order diffracted light of the other sub-beam is detected by the photodetector 93.
And 96, respectively, receive a focus error signal by the beam size method based on the outputs of the photodetectors 92, 95, and perform tracking by the 3-beam method based on the outputs of the photodetectors 91, 93, 94, 96. I am trying to get an error signal.

[0011]

However, as shown in FIG.
In the conventional optical pickup shown in FIG. 3, the return reflected by the magneto-optical recording medium 66 is diffracted by the hologram 63 and made incident on the photodetectors 69 and 70. Since it is composed of a thin hologram that is shallower than the wavelength, the diffraction efficiency of the ± 1st order diffracted light (± 1st order diffracted light amount / incident light amount) does not depend on the polarization state,
100% of the polarized component having Kerr rotation information is detected by the photodetector 6
Can't lead to 9,70. Therefore, there is a problem that the amplitude of the magneto-optical signal becomes small and C / N decreases.

As a method for solving this problem, it is conceivable to increase the diffraction efficiency of the ± first-order diffracted light of the hologram 63. However, if this is done, the light efficiency of the 0th-order light (light amount of 0th-order light / incident light amount) Is decreased, the coupling efficiency from the semiconductor laser 61 to the magneto-optical recording medium 66 is decreased, the required emission power of the semiconductor laser 61 at the time of writing information is increased, and problems such as heat generation occur.

In the optical pickups shown in FIGS. 13 and 14, the polarization beam splitter 71 is used to guide the return light to the photodetectors 75a and 75b. Therefore, the polarization component having the Kerr rotation information. Of the polarized beam splitter 7
Since the light is reflected by approximately 90 ° at 1 and received by the photodetectors 75a and 75b, the optical path protrudes in the direction perpendicular to the optical path from the semiconductor laser 61 to the objective lens 65, which makes it difficult to downsize the device. There is a problem. In addition, since the semiconductor laser 61 and the photodetectors 75a and 75b are separated, relative positional deviation easily occurs due to changes over time and changes in temperature, which makes it difficult to obtain high reliability. .

Further, in the optical pickup previously proposed by the applicant of the present invention shown in FIGS. 15 to 18, the semiconductor laser 89, the photodetectors 91, 92, 93, 94, 95, 96,
Since the hologram optical element 88 is integrated as a unit, there is an advantage that the device can be downsized and high reliability can be obtained. However, a specific configuration for obtaining a magneto-optical signal is mentioned. Not not.

The present invention has been made by paying attention to the above-mentioned various problems, and it is possible to obtain a small size and high reliability, suppress a decrease in C / N, and stably detect a magneto-optical signal. An object of the present invention is to provide an optical pickup that is appropriately configured so as to be capable.

[0016]

In order to achieve the above object, according to the present invention, a semiconductor substrate having a semiconductor laser and a light receiving means having a plurality of photodetectors, and light emitted from the semiconductor laser are provided. A collimator lens for making a substantially parallel light beam, an objective lens for converging the light made into a substantially parallel light beam by the collimator lens on a magneto-optical recording medium, and a collimator lens arranged between the objective lens and the magneto-optical recording An optical path branching unit that polarizes and separates the optical path of the return light reflected by the medium into first and second optical paths, and is disposed as a unit integrated with the semiconductor substrate between the collimator lens and the semiconductor laser. The light emitted from the semiconductor laser is used as a main beam for reading or writing information on the magneto-optical recording medium and a tracking error. Grating that is separated into a sub beam for signal detection; First hologram that diffracts return light of the first optical path; Second hologram that diffracts return light of the second optical path; 0 of this second hologram An optical branching element that is arranged substantially parallel to the optical axis of the next light and has a polarization splitting surface that splits the + 1st-order diffracted light and / or the -1st-order diffracted light of the return light from the second hologram according to its polarization direction. And the ± first-order diffracted light from the first hologram and the light separated by the polarization splitting surface are separated by the light receiving means and received.

Further, according to the present invention, a semiconductor substrate having a semiconductor laser and a light receiving means having a plurality of photodetectors, a collimator lens for converting light emitted from the semiconductor laser into a substantially parallel light flux, and this collimator lens are used. An objective lens for converging the substantially collimated light beam on the magneto-optical recording medium, and an optical path of the return light reflected by the magneto-optical recording medium are disposed between the collimator lens and the objective lens. A first unit that is disposed as a unit integrated with the semiconductor substrate between the optical path splitting unit that splits the polarized light into a second optical path, the collimator lens, and the semiconductor laser, and that diffracts the return light of the first optical path. Hologram; a second hologram that diffracts the return light of the second optical path; a third hologram that diffracts the 0th order light of the return light of the first hologram Polarization separation that is arranged substantially parallel to the optical axis of the 0th-order light of the second hologram and that separates the + 1st-order diffracted light and / or the -1st-order diffracted light of the return light from the second hologram according to its polarization direction. A light branching element having a surface, and the ± first-order diffracted light in the first hologram,
The light separated by the polarization splitting surface and the + 1st-order diffracted light and / or the -1st-order diffracted light in the third hologram are separated and received by the light receiving means.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. This optical pickup uses one main beam and two sub-beams, and emits three beams from a unit 1 having a semiconductor laser, a photodetector, a hologram, and a polarization splitting surface, and outputs them from a collimator lens. 2. The optical path branching mirror 3 made of a non-parallel plate having a polarization splitting surface and the objective lens 4 irradiate the magneto-optical recording medium 5, and the return light of each beam reflected by the magneto-optical recording medium 5 is returned to the objective lens. 4, the optical path splitting mirror 3 and the collimator lens 2 to make the light incident on the unit 1. In this embodiment, the direction parallel to the information track of the magneto-optical recording medium 5 is Y, and the tracking direction orthogonal thereto is the X direction.

The unit 1 has a substrate 6 as shown in FIG. 2 which is a plan view seen from the entrance / exit surface side and FIG. 3 which is a view taken in the direction of arrow A in FIG.
In addition to providing the semiconductor substrate 7 in the above, the optical branching element 9 is provided via the spacer 8.

The optical branching element 9 comprises an optical block 10 in the form of a parallel plate and parallel plates 11a, 11 attached to both side surfaces thereof.
and b. On the surface of the optical block 10 facing the semiconductor substrate 7, a grating for separating light from a semiconductor laser described later into one main beam (0th order light) and two subbeams (± 1st order diffracted light). 10a
Are formed by an etching method, a 2P method, or the like. On the opposite surface, the return lights of the three beams from the magneto-optical recording medium 5 are diffracted respectively, and the ± 1st order diffracted lights have focal powers in opposite directions. The given hologram 10b having a lens action and the hologram 10c having no lens action are separately formed by an etching method, a 2P method or the like. The diffraction direction of the hologram 10b is the X direction, and the diffraction direction of the hologram 10c is a direction inclined by 45 ° with respect to the X and Y directions.

The joint surfaces 12a and 12b between the parallel plates 11a and 11b and the optical block 10 are polarization splitting surfaces formed by coating a dielectric multilayer film. In this optical branching element 9, the normal line to the polarization splitting surfaces 12a and 12b is X.
• Arrange so as to be approximately 45 ° with respect to the X and Y axes on the Y plane.

On the other hand, as shown in the plan view of FIG. 4, a concave portion is formed on the semiconductor substrate 7 by etching or the like, and the semiconductor laser 13 is mounted in this concave portion. A light flux emitted in a direction parallel to the direction is reflected by the mirror 14 in a direction substantially normal to the semiconductor substrate 7 by raising a slope formed by etching the concave portion or the like. Further, the light receiving unit 15 and the light receiving unit 16 for respectively receiving the ± first-order diffracted lights from the hologram 10b are provided, and the ± of the main beam which is diffracted by the hologram 10c and separated by the polarization splitting surfaces 12a and 12b according to the polarization directions. Photodetectors 17a, 17b; 18a, 18b for receiving the first-order diffracted light are provided.

The light receiving section 15 is composed of three photodetectors 15a, 15b and 15c corresponding to the + 1st order diffracted light of each beam, and the central photodetector 15b which receives the + 1st order diffracted light of the main beam is Three light receiving regions 15d, 15e, which have dividing lines in the diffraction direction of the hologram 10b,
It is configured with 15f. Similarly, the light receiving unit 16 also has three photodetectors 16a, corresponding to the minus first-order diffracted light of each beam.
The central photodetector 16b which receives the -1st-order diffracted light of the main beam is constituted by three light receiving regions 16d, 16e, 16f having a dividing line in the diffraction direction of the hologram 10b.

The optical path branching mirror 3 is composed of a first surface 3a coated with a dielectric multilayer film and a second surface 3b which acts as a total reflection surface. Is reflected by the first surface 3a and guided to the magneto-optical recording medium 5 via the objective lens 4. In the return path, the return light from the magneto-optical recording medium 5 is changed to the first optical path reflected by the first surface 3a. , Through the first surface 3a, the second
The second optical path is reflected by the surface 3b and is again separated from the second optical path through the first surface 3a. In this embodiment, the first surface 3a is covered with the transmittance T _p and the reflectance R _p of the P-polarized component,
The transmittance T _s and reflectance R _{s of the} S-polarized component are T _p = 100%, R _p = 0%, T _s = 30%, and R _s = 7, respectively.
It is configured to be 0%.

In such a structure, the emitted light from the semiconductor laser 13 mounted on the semiconductor substrate 7 is reflected by the rising mirror 14 in the direction perpendicular to the semiconductor substrate 2 and enters the grating 10a of the optical block 10. One main beam (0
(Second light) and two sub-beams for track error detection (± first-order diffracted light) are separated into three beams. The three beams separated by the grating 10a pass through the hologram 10b, pass through the collimator lens 2 and are reflected by the first surface 3a of the optical path splitting mirror 3, and further pass through the objective lens 4 and the magneto-optical recording medium 5. Is converged to. In this embodiment, the light from the semiconductor laser 13 is incident on the first surface 3a of the optical path splitting mirror 3 as S-polarized light.

The return light of each beam reflected by the magneto-optical recording medium 5 passes through the objective lens 4 and the optical path branching mirror 3 is provided.
A first optical path which is incident on the first surface 3a and is reflected by the first surface 3a, and a first optical path which is transmitted through the first surface 3a and is reflected by the second surface 3b and is transmitted again through the first surface 3a. It is separated into two optical paths.

The return light of the first optical path branched by the optical path branching mirror 3 passes through the collimator lens 2 and the hologram 10.
b, and each beam is diffracted as shown in the sectional view taken along line BB of FIG. 2 in FIG. 5, and the ± first-order diffracted light of the main beam is received by the photodetector 15b;
d, 15e, 15f; 16d, 16e, 16f, and the + 1st order diffracted light of the two sub-beams is detected by the photodetector 15.
The -1st-order diffracted light is detected by the photodetectors 16a and 16c on a and 15c.
Incident on each.

Here, since the hologram 10b has a pattern in which the ± 1st-order diffracted lights are provided with focal powers in opposite directions, the size of the spot on the photodetector 15b and the size of the spot on the photodetector 16b are large. The values are equal when the recording surface of the magneto-optical recording medium 5 is in focus, and change in opposite directions when the focus is shifted back and forth. Therefore, the light receiving regions 15d, 1 of the photodetector 15b are
The outputs of 5e and 15f are A1, A2 and A3,
Assuming that the outputs of the light receiving regions 16d, 16e, 16f of the photodetector 16B are A4, A5, A6, the focus error signal FES is

FES = (A1 + A5 + A6)-(A2 + A3 + A4)
Can be obtained from

Further, the photodetectors 15a, 15c, 16a,
If the output of 16c is A7, A8, A9, A10, the tracking error signal TES is

2 can be obtained from TES = (A7 + A9)-(A8 + A10).

On the other hand, the second beam split by the optical path splitting mirror 3
The return light of the optical path of is passed through the collimator lens 2 and the return light of the main beam is incident on the hologram 10c, where it is separated into ± first-order diffracted lights as shown in the sectional view taken along the line CC in FIG. Then, the S-polarized components are incident on the polarization splitting surfaces 12a and 12b, respectively, and the S-polarized components are reflected to the photodetector 17
a and 18a, the P-polarized component is transmitted to the photodetector 17b,
18b respectively.

[0031] Here, the polarization direction of the main beam of the return light incident on the hologram 10c, depending on the information recorded on the magneto-optical recording medium 5, as shown in FIG. 7, ± theta _k
Is subjected to Kerr rotation of, but the polarization separation surfaces 12a and 12b are
Since they are arranged at an angle of about 45 ° with respect to the polarization direction of the return light, the polarization splitting surfaces 12a and 12b have a structure shown in FIG.
The return light is incident with the polarization direction as shown in.
Therefore, the direction (recording information) of the Kerr rotation (θ _k ) generated in the magneto-optical recording medium 5 is the polarization separation planes 12a, 1
Since it can be obtained by the difference (S ₁ -P ₁ , S ₂ -P ₂ ) between the S-polarized component and the P-polarized component separated by 2b, the magneto-optical signal MOS can be detected by the photodetectors 18a, 17a,
The outputs of 17b and 18b are B1, B2, B3 and B, respectively.
Assuming 4

## EQU3 ## It can be obtained from MOS = (B1 + B2)-(B3 + B4).

The operation of the optical path splitting mirror 3 will be described below.
It will be described in more detail. In this embodiment, as described above, the emitted light of the semiconductor laser 13 is incident on the first surface 3a of the optical path branching mirror 3 as S-polarized light. Therefore, 70% of the light from the semiconductor laser 13 is reflected by the first surface 3 a, and the light is irradiated onto the magneto-optical recording medium 5 via the objective lens 4. The return light that has undergone the Kerr rotation in the magneto-optical recording medium 5 enters the optical path branching mirror 3 through the objective lens 4, but the linearly polarized light of this return light has a small Kerr rotation angle, so the optical path branching mirror 3 receives it. The light enters with almost S-polarized light and is split into the first and second optical paths as described above.

About 70% of the S-polarized component of the return light incident on the optical path branching mirror 3 is reflected by the first surface 3a thereof, and P
Since almost 100% of the polarized component is transmitted, the light of the S-polarized component, which is approximately 70% of the incident light, is guided to the first optical path, and this light enters the hologram 10b through the collimator lens 2 and is described above. Thus, the focus error signal and the tracking error signal are detected. In addition, the light that passes through the first surface 3a, is reflected by the second surface 3b, and then passes through the first surface 3a again is guided to the second optical path, and thus is guided to the second optical path. The light is an S-polarized component of about 9% of the return light incident on the optical path branching mirror 3 and a P-polarized light of about 100%.
It becomes a polarized component, and this light enters the hologram 10c through the collimator lens 2, and the magneto-optical signal is detected as described above.

Here, the return light from the magneto-optical recording medium 5 is directed to the optical path branching mirror 3 as shown in FIG.
Since the _K- rotation of ± θ _k is received and the S-polarized light enters, the magneto-optical signal component is included in the P-polarized light. In this embodiment, one P-polarized component is added to the second optical path for obtaining the magneto-optical signal.
Since it is designed to lead to 00%, a high C / N can be obtained.

FIG. 9 shows a second embodiment of the present invention. This embodiment is different from the first embodiment in that the polarization direction of the emitted light of the semiconductor laser is different from the configuration of the first surface 3a as the polarization splitting surface of the optical path splitting mirror 3, and other configurations are the same. This is the same as the first embodiment. That is, in this embodiment, the emitted light of the semiconductor laser is incident on the optical path branching mirror 3 as P-polarized light. In the first surface 3a, the transmittance T _p and reflectance R _p of the P-polarized component and the transmittance T _s and reflectance R _s of the S-polarized component are T _p = 80.
%, R _p = 20%, T _s = 0%, and R _s = 100% so that the dielectric multilayer film is coated.

In this way, in the forward path, the light incident on the optical path branching mirror 3 is transmitted through the first surface 3a, reflected by the second surface 3b, and transmitted through the first surface 3a again. Then, it irradiates the magneto-optical recording medium 5 through the objective lens 5. On the return path, the return light from the magneto-optical recording medium 5 is made incident on the optical path branching mirror 3, where it is transmitted through the first surface 3a, reflected by the second surface 3b, and again the first surface 3a. The first optical path that passes through the surface 3a and the second optical path that is reflected by the first surface 3a are separated, and the light in the first optical path is directed to the hologram 3b and the light in the second optical path is directed to the hologram 3c. When they are respectively made incident, the focus error signal and the tracking error signal are obtained by the light of the first optical path and the magneto-optical signal is obtained by the light of the second optical path in the same manner as in the first embodiment.

In this embodiment, the optical path branching mirror 3
The magneto-optical signal component of the return light from the magneto-optical recording medium 5 that is incident on the S-polarized light is included in the S-polarized light. Here, the efficiency of the outgoing light with respect to the incident light on the optical path branching mirror 3 for the returning light is 64% for P-polarized light in the first optical path, 20% for P-polarized light and 100% for S-polarized light in the second optical path. Therefore, 100% of S-polarized light containing the magneto-optical signal component is guided to the second optical path for detecting the magneto-optical signal. Therefore, as in the first embodiment, a high C / N magneto-optical signal can be obtained. Further, in this embodiment, since the second optical path contains 20% of P-polarized light which is orthogonal to the magneto-optical signal component, the amplitude of the magneto-optical signal is increased as compared with the case of 9% in the first embodiment. Can be made.

FIG. 10 and FIG. 11 show the structure of the main part of the third embodiment of the present invention. In this embodiment, a push-pull method is used to detect a tracking error signal. Therefore, in this embodiment, in place of the grating 10d on the side of the optical block 10 which faces the semiconductor substrate 7 in the first and second embodiments, FIG.
As shown in, a hologram 10d for generating a push-pull signal detection beam is formed. Further, as shown in FIG. 11, the semiconductor substrate 7 is provided with the photodetector 21 having the two-divided light receiving regions 21a and 21b for receiving the + 1st order diffracted light or the −1st order diffracted light of the return light diffracted by the hologram 10d. . Since the sub-beam is not used in this embodiment, the photodetectors 15a, 15c, 1 are provided on the semiconductor substrate 7.
It is not necessary to form 6a and 16c.

Thus, in the forward path, the beam from the semiconductor laser 13 is irradiated onto the magneto-optical recording medium without diffracting in the same manner as in the first or second embodiment described above, and in the return path, the hologram 10b. The light that has passed through is diffracted by the hologram 10d, and the + 1st order diffracted light or the −1st order diffracted light is made incident on the photodetector 21. Therefore, the outputs of the light receiving regions 21a and 21b of the photodetector 21 are C
1 and C2, the tracking error signal TES is
By the push-pull method,

It can be obtained from TES = C1-C2. The focus error signal and the magneto-optical signal can be obtained in the same manner as in the above-mentioned first and second embodiments.

In each of the above embodiments, the hologram 1
The ± 1st-order diffracted light at 0c is divided into the polarization splitting surfaces 12a,
12b separates the light according to the polarization direction and receives it. However, only one of the ± 1st order diffracted lights is separated according to the polarization direction on the polarization splitting surface, and the separated lights are received respectively to receive the magneto-optical signal. Can also be configured to detect. In this case, only one polarization separation surface is required.

[0041]

As described above, according to the present invention, since the semiconductor substrate having the semiconductor laser and the light receiving means and the optical branching element having the hologram and the polarization splitting surface and the like are integrated into a unit, a small size is achieved. Since high reliability can be realized and the efficiency of use of the return light from the magneto-optical recording medium can be increased, it is possible to suppress a decrease in C / N and stably detect a magneto-optical signal.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a plan view of the unit 1 of FIG. 1 viewed from its entrance / exit surface side.

3 is a view on arrow A in FIG. 2. FIG.

FIG. 4 is a plan view of the semiconductor substrate shown in FIG.

5 is a sectional view taken along line BB of FIG.

6 is a cross-sectional view taken along the line CC of FIG.

FIG. 7 is a diagram for explaining the operation of the embodiment shown in FIG.

FIG. 8 is a diagram for explaining the operation of the embodiment shown in FIG.

FIG. 9 is a diagram showing a second embodiment of the present invention.

FIG. 10 is a sectional view showing the structure of a unit according to the third embodiment of the present invention.

FIG. 11 is a plan view of the same semiconductor substrate.

FIG. 12 is a diagram showing an example of a conventional optical pickup.

FIG. 13 is a diagram showing another example of the same.

FIG. 14 is a plan view of the substrate shown in FIG.

FIG. 15 is a diagram showing an optical pickup previously proposed by the applicant.

16 is a cross-sectional view of the unit shown in FIG.

FIG. 17 is a plan view of the semiconductor substrate shown in FIG.

FIG. 18 is a partial sectional view of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 unit 2 Collimator lens 3 Optical path branching mirror 3a 1st surface 3b 2nd surface 4 Objective lens 5 Magneto-optical recording medium 6 Substrate 7 Semiconductor substrate 8 Spacer 9 Optical branching element 10 Optical block 10a Grating 10b, 10c, 10d Hologram 11a , 11b Parallel plates 12a, 12b Polarization separation surface 13 Semiconductor laser 14 Raising mirror 15, 16 Light receiving parts 15a, 15b, 15c Photodetector 16a, 16b, 16c Photodetector 17a, 17b Photodetector 18a, 18b Photodetector 15d, 15e, 15f light receiving area 16d, 16e, 16f light receiving area 21 photodetector 21a, 21b light receiving area

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[Procedure amendment]

[Submission date] August 11, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] Fig. 16

[Correction method] Change

[Correction content]

FIG. 16

Claims (2)

[Claims] 1. A semiconductor substrate comprising a semiconductor laser and a light receiving means having a plurality of photodetectors, a collimator lens for converting light emitted from the semiconductor laser into a substantially parallel light beam, and a collimator lens for converting the light beam into a substantially parallel light beam. An objective lens for converging the reflected light on a magneto-optical recording medium, and an optical path of return light reflected by the magneto-optical recording medium, the optical path being arranged between the collimator lens and the objective lens. Optical path branching means for polarization splitting into, and between the collimator lens and the semiconductor laser, arranged as a unit integrated with the semiconductor substrate, the emitted light from the semiconductor laser, the information of the information for the magneto-optical recording medium. A grating for separating a main beam for reading or writing and a sub-beam for detecting a tracking error signal; the first beam A first hologram that diffracts the return light of the optical path; a second hologram that diffracts the return light of the second optical path; and a second hologram that is arranged substantially parallel to the optical axis of the 0th order light of the second hologram. And a light splitting element having a polarization splitting surface for splitting the + 1st-order diffracted light and / or the -1st-order diffracted light of the return light in the hologram of 1) according to the polarization direction thereof, and the ± 1st-order diffracted light in the first hologram and An optical pickup characterized in that the light separated by the polarization splitting surface is received by the light receiving means. 2. A semiconductor substrate comprising a semiconductor laser and a light receiving means having a plurality of photodetectors, a collimator lens for converting the light emitted from the semiconductor laser into a substantially parallel light beam, and a collimator lens for forming a substantially parallel light beam. An objective lens for converging the reflected light on a magneto-optical recording medium, and an optical path of return light reflected by the magneto-optical recording medium, the optical path being arranged between the collimator lens and the objective lens. A first hologram that is disposed between the collimator lens and the semiconductor laser as a unit integrated with the semiconductor substrate, and that diffracts the return light of the first optical path; A second hologram that diffracts the return light of the second optical path; a third hologram that diffracts the 0th order light of the return light of the first hologram.
Hologram, which is arranged substantially parallel to the optical axis of the 0th-order light of the second hologram, and separates the + 1st-order diffracted light and / or the -1st-order diffracted light of the return light from the second hologram according to its polarization direction. And a light splitting element having a polarization splitting surface, the ± 1st-order diffracted light in the first hologram, the light split in the polarization splitting surface, and the +1 in the third hologram.
An optical pickup characterized in that the second-order diffracted light and / or the -1st-order diffracted light are separated and received by the light receiving means.