JPH08297875A - Optical pickup - Google Patents

Abstract

PURPOSE: To miniaturize a device and to reduce a cost by providing first, second polarization separating means instead of a conventional beam splitter, and a Wollaston prism. CONSTITUTION: The first polarization separating means 12 is provided on one surface of a base material 41 arranged between a light source 11 and an objective lens 13, and separates a light beam from the light source 11 and a return light beam from a recording surface of a magneto-optical recording medium MO through the objective lens 13 in the radial direction of the magneto-optical recording medium MO. The second polarization separating means 14 is provided on the other surface of the base material 41, and separates the return light beam separated by the first polarization separating means 12 to three light beams of zero-order diffracted light and ±1st-order diffracted light to send them to respective parts 15a, 15b of a photodetector 15. The photodetector 15 detects a focusing error signal based on respective output signals of the separated light receiving surfaces 15a, 15b on which the zero-order light is made incident, and further, detects a tracking error signal by a difference of the signals based on two pieces of light beams by the ±1st-order light. Thus, the first, second polarization separating means are constituted integrally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for recording and / or reproducing on a magneto-optical disk.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for recording and / or reproducing information on such a magneto-optical disk has been used.
It is configured as shown in FIG. That is, in FIG. 8, the optical pickup 1 includes a semiconductor laser element 2, a hologram element 3, a collimator lens 4, a beam splitter 5, an objective lens 6, a Wollaston prism 7, and a photodetector 8.

The semiconductor laser device 2 is a light emitting device utilizing recombination light emission of a semiconductor and is used as a light source. The semiconductor laser device 2 is actually shown in FIG. 9 and FIG.
As shown in, the light beam emitted from the semiconductor laser element 2 is guided to the hologram element 3.

Here, the Wollaston prism 7, based on the return light beam reflected by the beam splitter 5,
By performing polarization separation, a plurality of light beams, in the illustrated case, three light beams are emitted.

The photodetector 8 receives the three light beams polarized and separated by the Wollaston prism 7,
Each has a light receiving part.

Further, light receiving portions 9a and 9b are provided adjacent to the semiconductor laser element 2 as shown in FIG. The light receiving portions 9a and 9b are adapted to receive the first-order diffracted light beam that has been transmitted through the beam splitter 5 and diffracted by the hologram element 3.

[0007]

However, in the optical pickup 1 thus constructed, the diffracted light beam diffracted by the hologram element 3 is received by the light receiving portion 9
The signals required for servo can be obtained by the detection by a and 9b, but the MO signal cannot be detected. Therefore, the return signal from the magneto-optical disk MO is separated by the beam splitter 5 and divided by the Wollaston prism 7 to detect each divided beam, whereby the MO signal can be obtained. Therefore, since the beam splitter 5 and the Wollaston prism 7 are relatively expensive, the cost of the optical pickup 1 as a whole is high, and the Wollaston prism 7 is also expensive.
However, since the separation angle of the MO signal (magneto-optical signal) is limited, there is a problem that it becomes relatively large.

In view of the above points, the present invention has as its object the provision of an optical pickup which is constructed in a small size and at a reduced cost.

[0009]

According to the present invention, there is provided a light source for emitting a light beam, and a light beam emitted from the light source for focusing on a recording surface of a magneto-optical recording medium. An objective lens for irradiation and one surface of a substrate disposed between the light source and the objective lens are provided, and a light beam from the light source and a recording surface of a magneto-optical recording medium through the objective lens are provided. First polarized light separating means for separating the return light beam in the radial direction of the magneto-optical recording medium, and return light separated by the first polarized light separating means while being provided on the other surface of the substrate. This is achieved by an optical pickup that includes a second polarization splitting unit that splits the beam and a photodetector that receives each light beam split by the second polarization splitting unit.

[0010]

According to the above construction, the return light beam separated by the first polarized light separating means is separated by the second polarized light separating means into three light beams, that is, 0th order diffracted light and plus or minus 1st order diffracted light. . Therefore, the MO signal is detected by the detection signal of the photodetector based on the 0th-order light beam, and the differential signal 3 is generated based on each output signal of the split light-receiving surface on which the 0th-order light of the photodetector is incident. The focusing error signal is detected by the division method, and the tracking error signal is detected based on the difference between the detection signals based on the two light beams of plus and minus primary light beams.

When the first and second polarization splitting means are polarization holograms, especially birefringent diffraction grating type elements, they are split into 0th order ordinary light and plus or minus 1st order extraordinary light. The first polarized light separating means is a hologram or birefringent diffraction grating type element formed on one surface of the substrate, and the second polarized light separating means is a hologram or birefringent diffraction grating formed on the other surface of the substrate. In the case of a lattice type element, the first polarized light separating means and the second polarized light separating means are integrally formed, and the number of parts is reduced.

When the first polarized light separating means is a birefringent diffraction grating type element formed on one surface of the substrate and the second polarized light separating means is a birefringent crystal forming the substrate, Since the structure is simple, it can be easily formed and the cost is reduced.

When the first and second polarized light separating means, the light source and the photodetector are integrally formed as one package, the polarized light separating means, the light source and the photodetector are mutually assembled at the time of assembly. Since the positioning of the optical pickup is unnecessary, the optical pickup can be easily assembled, and the assembly cost can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to FIGS. In addition, since the Examples described below are preferred specific examples of the present invention, various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 1 shows an embodiment of an optical pickup according to the present invention. The optical pickup 10 includes a semiconductor laser device 11, a first polarization separation means 12, an objective lens 13, and a second polarization separation means 14. And a photodetector 15. Here, the semiconductor laser device 1
1, first polarized light separating means 12, second polarized light separating means 14
In the illustrated case, the photodetector 15 and the photodetector 15 are integrally formed by being incorporated in one resin package 10a, for example. The first polarized light separating means 12 is formed, for example, on the surface of the glass substrate 14 on the side of the objective lens 13 which transmits light as a base material. The second polarized light separating means 14 is formed on the surface of the base material 41 on the semiconductor laser element 11 side.

The semiconductor laser device 11 is a light emitting device utilizing recombination light emission of a semiconductor and is used as a light source. The light beam emitted from the semiconductor laser device 11 is
It is guided to the objective lens 13.

The first polarization separation means 12 is, for example, a polarization hologram and is configured to transmit ordinary light and diffract extraordinary light. As a result, the polarization splitting means 12 splits the return light from the recording surface of the magneto-optical disk MO into plus / minus first-order diffracted light, as will be described later.

Here, the first polarized light separating means 12 is shown in FIG.
As shown in FIG. 4, it is configured as a birefringence diffraction grating type element, and includes a substrate 12a made of lithium niobate and a grating 12b formed on the incident side of the substrate 12a by, for example, a proton exchange method using benzoic acid. Has been done. As a result, in the region of the grating 12b, the refractive index for ordinary light is increased by about 0.13, and the refractive index for extraordinary light is decreased by about 0.04.

Here, the first polarized light separating means 12 has a thickness selected on the grating 12b formed by the above-mentioned proton exchange so as to cancel the phase difference received by the transmitting ordinary ray as shown in FIG. The first phase compensation film 12c made of the dielectric material is provided. Thereby, it is apparent that the extraordinary ray is observed so that the refractive index change due to the proton exchange occurs.

In practice, the phase compensation films 12c and 12d are
The phase adjustment by is performed as follows. That is, when the duty ratio of the grating 12b is 50%,
The diffraction efficiency η0 of the 0th-order light and the diffraction efficiency η1 of the plus / minus 1st-order light are respectively determined by the phase difference φ.

[Equation 1]

[Equation 2] Is represented by Therefore, the optical axis of the substrate 12a is set to be perpendicular to the polarization direction of the light beam from the semiconductor laser element 11, that is, the emitted light is the ordinary light, and the phase difference φ with respect to the ordinary light is about 70 degrees. When the phase difference φ for extraordinary light is set to about 130 degrees or 230 degrees,
The birefringence diffraction grating type element 12 described above is
67% of the 0th-order light and 27% of the plus / minus primary light, and 18% of the 0th-order light and 76% of the plus / minus 1st-order light with respect to the extraordinary light, the enhancement function is realized.

Thus, the birefringent diffraction grating type element 12 is
As shown in FIG. 2, with respect to the direction of the optical axis X, the incident light is split into normal light in a direction perpendicular to the normal light and extraordinary light in a direction parallel to the normal light. That is, in the incident return light beam, the ordinary light is transmitted as the 0th-order light and the extraordinary light is diffracted as the plus / minus 1st-order light, as shown in the figure.

The objective lens 13 is a convex lens, and forms an image of the light beam that has passed through the first polarization separation means 12 on a desired track on the recording surface of the magneto-optical disk MO that is rotationally driven.

The light beam applied to the recording surface of the magneto-optical disc MO is returned to the objective lens 13 as a return light beam.
Is guided to the first polarized light separating means 12 via. And
The plus / minus first-order diffracted light of the return light beam diffracted by the first height separation means 12 is incident on the second polarization separation means 14, respectively.

The second polarized light separating means 14 is provided on the surface of the base material 41 facing the laser light source 11 so as to avoid the light beam from the semiconductor laser light source 11, and is divided into left and right in FIG. Are arranged. The left and right portions 14a and 14b are polarization holograms, respectively, and are configured to diffract extraordinary light. As a result, the polarized light separating means 14 has the left and right parts 14a, 1
4b separates the plus / minus first-order diffracted light from the first polarized light separating means 12 into 0th-order light and plus / minus 1st-order light.

Here, the second polarized light separating means 14 is constructed as a birefringent diffraction grating type element like the first polarized light separating means, and as shown in FIG. A first phase compensation film 11d made of a dielectric material having a thickness selected so as to cancel the phase difference received by the extraordinary ray that passes therethrough is provided on the top. Specifically, in the second polarization splitting means 14, the optical axis of the substrate is
It is arranged so as to form an angle of 45 degrees with respect to the polarization direction of the light beam from the semiconductor laser element 11, and the phase difference φ for ordinary light is 0 degree and the phase difference φ for abnormal light is 180 degrees.
It is set so that it becomes a degree.

The photodetector 15 has a second polarization separation means 14
Each of the 0th-order light and the plus / minus 1st-order diffracted light beams separated by is provided with a light receiving portion.

The grating 16 is for diffracting the incident light, and at least the main beam composed of the 0th order diffracted light and the side beam composed of the plus and minus 1st order diffracted light of the light beam emitted from the semiconductor laser element 11 in the tangential direction. It is used to split into three light beams.

Here, the first polarization separating means 12 and the second polarization means 14 are constructed as birefringence diffraction grating type elements as shown in FIG. As shown in FIG. 5, it may be configured as a structural birefringent diffraction grating. In FIG. 5, the structural birefringence diffraction grating 17 sets the direction of the structural birefringence body in the same direction as the optical axis of the birefringence diffraction grating type element. The phase difference is, as shown in FIG. 6, the pitch P1 between the individual fine structures 17a of the structural birefringent body or the pitch P of the fine structures 17a themselves.
It is adjusted by setting 2 and the length L as appropriate. In this case, since there is no birefringence inside the base material 41, two structural birefringence diffraction gratings are integrally formed by disposing the structural birefringence bodies on both surfaces of the same base material 41. Therefore, it is not necessary to adjust the mutual positions of the two polarized light separating means 12 and 14, and the positioning accuracy is improved.

Thus, the P-polarized light beam emitted from the semiconductor laser device 11 is separated by the grating 16 into 0th order diffracted light and plus or minus 1st order diffracted light and transmitted through the first polarized light separating means 12. After that, it is converged on the signal recording surface of the magneto-optical disk MO via the objective lens 13. To be precise, the 0th-order diffracted light is applied to a predetermined track on the recording surface, and the plus / minus 1st-order diffracted light is applied to the positions separated by the front and rear sides of the predetermined track.

The return light beam including the MO signal (magneto-optical signal) of the S-polarized component, which is reflected by the signal recording surface of the magneto-optical disk MO and whose polarization plane is rotated by the Kerr effect,
Again via the objective lens 13, the first polarized light separating means 12
Incident on. Here, in the return light beam, the 0th-order light of ordinary light is transmitted by the first polarization separation means 12, and the plus / minus 1st-order diffracted light of extraordinary light is diffracted, respectively, so that the second polarization separation means is obtained. Each part 14a of 14,
It is incident on 14b.

Here, the part 1 of the second polarization separation means 14
At 4a, the plus first-order diffracted light diffracted by the first polarized light separating means 12 is incident, the zero-order light thereof is transmitted, and the first-order diffracted light is refracted as shown. Also,
In the portion 14b of the second polarization splitting means 14, the minus first-order diffracted light diffracted by the first polarization splitting means 12 is incident, the zero-order light is transmitted, and at the same time minus one.
Next-order diffracted light is refracted as shown.

Thus, the 0th-order light and the plus / minus 1st-order diffracted light by the portions 14a and 14b of the second polarization separation means 14 are respectively the portions 15a and 15b of the photodetector 15.
Will be incident on. That is, the second polarized light separating means 14
The 0th-order light and the minus 1st-order diffracted light by the portion 14a of
The 0th-order light and the positive 1st-order diffracted light from the portion 14b of the second polarization splitting means 14 are incident on the portion 15b of the photodetector 15, and are incident on the portion 15b of the photodetector 15.

Here, the photodetector 15 is constructed as shown in FIG. That is, in the photodetector 15, the respective portions 15a and 15b which are separated into the right and left with respect to the center are divided into three in the tangential direction of the magneto-optical disk MO by the grating 16 respectively, and the first polarized light separating means 12 separates the magneto-optical information. The light receiving portions 18, 19, 20 and the light receiving portions 21, 22 arranged side by side in the tangential direction of the magneto-optical disk MO so as to receive the respective beams separated in the radial direction of the disk MO.
2 and 23 are provided.

Further, each of the light receiving portions 19 and 22 is set to 1 in the radial direction so as to receive the two beams separated in the radial direction by the second polarization splitting means 14, respectively.
It is divided into two parts 9a, 19b, 22a, 22b, and is divided into three parts in the tangential direction, a relatively thin central part and side parts on both sides thereof.

As a result, the 1st-order diffracted light of the 0th-order light from the grating 16 by the first polarization splitting means 12 enters the light-receiving portion 19, and the plus-minus 1st-order light from the grating 16 enters the light-receiving portions 18 and 20. The first-order diffracted light from the first polarized light separating means 12 enters. The minus first-order diffracted light of the 0th-order light from the grating 16 by the first polarization splitting means 12 is incident on the light-receiving part 22, and the first plus-minus first-order light from the grating 16 is incident on the light-receiving parts 21 and 23. The minus first-order diffracted light by the polarized light separating means 12 is incident.

Thus, the side portion of the light receiving portion 19a outputs the detection signal a and the central portion outputs the detection signal b. The side portion of the light receiving portion 19b outputs the detection signal c, and the central portion outputs the detection signal d.

On the other hand, the side portion of the light receiving portion 22a outputs the detection signal e, and the central portion outputs the detection signal f.
Further, the side portion of the light receiving portion 22b outputs the detection signal g, and the central portion outputs the detection signal h.

Further, the light receiving portions 18 and 21 output the detection signal i, and the light receiving portions 20 and 23 output the detection signal j.

Therefore, the detection signals a, b, c, d, e, f, g, h, from the respective light receiving portions 19 to 23 of the photodetector 15 are detected.
i and j are respectively amplifiers 24 and 2 as shown in FIG.
5,26,27,28,29,30,31,32,33
After being amplified by, the signals such as the read signal of the magneto-optical disk MO, the focus error signal, and the tracking error signal are generated by performing an appropriate calculation. For example, the MO reproduction signal MO is output by the matrix amplifier 34 by

(Equation 3) Given in. Also, the focusing error signal FE
Is a matrix amplifier 35, by a so-called differential three-division method,

[Equation 4] And the tracking error signal TE is given by the matrix amplifier 26 by the push-pull method.

(Equation 5) Given in.

In the case of reproducing an optical disk such as a compact disk in which a pit signal is recorded instead of the magneto-optical disk MO, the pit reproduction signal is output by the matrix amplifier 37.

(Equation 6) Given in.

In the above-mentioned embodiment, the first and second polarized light separating means are configured as a birefringence diffraction grating type element or a structural birefringence diffraction grating, but the invention is not limited to this.
Obviously, it may be configured as a polarization hologram having another configuration. Further, when it is not necessary to obtain the tracking error signal TE and the focusing error signal FE and only the MO signal needs to be obtained, the grating 16 and the light receiving unit 1 of the photodetector 15 in the above-described embodiment.
8, 20, 21, 23 are unnecessary.

[0042]

As described above, according to the present invention, the return light beam is polarized and separated by the polarization separating means without using a beam splitter or a Wollaston prism as in the conventional case. The whole structure will be small in size and low in cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of an optical pickup according to the present invention.

FIG. 2 is a plan view showing a configuration example of a birefringence diffraction grating type element as polarization separation means in the optical pickup of FIG. 1 and a polarization direction of an incident light ray.

FIG. 3 is a partially enlarged sectional view of the birefringence diffraction grating type element of FIG.

FIG. 4 is a partially enlarged cross-sectional view of another configuration example of the birefringence diffraction grating type element of FIG.

5 is a plan view showing a structural example of a structural birefringence diffraction grating as a polarization separation means in the optical pickup of FIG. 1 and a polarization direction of an incident light beam.

6 is a partially enlarged sectional view of the structural birefringence diffraction grating of FIG.

7 is a circuit diagram showing a configuration of a photodetector and a signal processing circuit in the optical pickup of FIG.

FIG. 8 is a schematic diagram showing a configuration of an example of a conventional optical pickup.

9 is an enlarged perspective view showing a polarization hologram and a photodetector in the optical pickup of FIG.

10 is an enlarged perspective view of a photodetector in the optical pickup of FIG.

[Explanation of symbols]

10 Optical Pickup 11 Semiconductor Laser Element 12 First Polarization Separation Means 12a Substrate 12b Grating 12c Phase Compensation Film 13 Objective Lens 14 Second Polarization Separation Means 14a Grating 14b Phase Compensation Film 15 Photodetector 16 Grating 17 Structure Birefringence Diffraction Grating 18, 19, 20, 21, 22, 23 Light receiving part 24, 25, 26, 27, 28, 29, 30, 31, 3,
2,33 Amplifier 34,35,36,37 Matrix amplifier

Claims (5)

[Claims] 1. A light source for emitting a light beam, an objective lens for irradiating the light beam emitted from the light source so as to focus on a recording surface of a magneto-optical recording medium, and a space between the light source and the objective lens. A light beam from the light source and a return light beam from the recording surface of the magneto-optical recording medium via the objective lens are separated in the radial direction of the magneto-optical recording medium. A first polarized light separating means for separating the second light, and a second polarized light separating means which is provided on the other surface of the substrate and separates the return light beam separated by the first polarized light separating means; An optical pickup comprising: a photodetector for receiving each light beam separated by the second polarization separation means. 2. The optical pickup according to claim 1, wherein each of the first and second polarized light separating means is a birefringence diffraction grating type element. 3. The optical pickup according to claim 1, wherein each of the first and second polarized light separating means is a polarization hologram. 4. The birefringence diffraction grating type element formed on one surface of the base material, wherein the first polarized light separating means is formed on the other surface of the base material. The optical pickup according to claim 2, wherein the optical pickup is a birefringent crystal. 5. The first and second polarized light separating means, and all members of the light source and the photodetector are integrally configured as one package. Optical pickup.