JPH06139611A - Optical head - Google Patents

Abstract

PURPOSE:To perfectly separate a transmitted light beam from a reflected light beam, to prevent the generation of a stray light, to improve the availability of light and to reduce a number of parts by providing a polarization prism between a light source and an image forming optical system. CONSTITUTION:A circular polarized beam 7 reflected from the surface 4 of an information medium is made incident again a double refraction prism 33 constituting a palarization prism 31 but the beam 7 goes straight on. Then, when the beam 7 passes through a double refraction plate 34, the beam 7 changes to a reflected beam 6 of linear polarization. However, the polarization direction 22 of the beam 6 is perpendicular to the polarization direction 21 of a beam 5. When the beam 6 passes through a double refraction prism 32, since the polarization direction 22 of the beam 6 is parallel with the direction 35 of an optical axis of the prism 32, the beam 6 propagates through the prism 32 as an extraordinary light. At this time, since the cemented surface of the prism 32 is inclined, the beam 6 propagates in the different direction from that of the beam 5 and the beam 6 is introduced to a photodetector 2 adjacent to a semiconductor laser 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used in optical information processing devices such as optical disk devices, optical card devices, optical tape devices and the like.

[0002]

2. Description of the Related Art Conventionally, when a semiconductor laser and a photodetector are arranged on the same plane or in the vicinity thereof in order to miniaturize an optical head, the emitted beam of the semiconductor laser and the reflected beam from the information medium surface are separated. Therefore, a diffraction grating or a hologram element is used as the separation element.

For example, in the optical head described in Japanese Patent Laid-Open No. 62-137736, an incident beam on an information medium surface is formed by using a diffraction grating having different grating directions with a boundary line crossing the optical axis as a boundary. The 0th order light of the diffraction grating is used, and the + 1st and -1st order of the reflected beam from the information medium surface is used for signal detection.
The next diffracted light is utilized and guided to two or four sets of two-division photodetectors adjacent to the semiconductor laser.

Further, in the optical head described in Japanese Patent Application Laid-Open No. 2-172033, the hologram element is tilted with respect to the optical axis, and the incident beam into the information medium also uses 0th order light. For signal detection, the hologram element is tilted from the optical axis to prevent the generation of conjugate diffracted light, and only the + 1st order diffracted light of the reflected beam from the information medium surface is used for guiding to the photodetector.

[0005]

In order to reduce the size of the optical head, when a diffraction grating or a hologram element is used as in the prior art in order to place a semiconductor laser and a photodetector in a close position, the following problems occur. There is.

First, since the diffraction grating or the hologram element has a diffractive action not only on the reflected beam but also on the beam emitted from the semiconductor laser to the information medium surface, the light utilization efficiency is lowered.

Second, the 0th order light of the reflected beam returns to the semiconductor laser, which causes laser noise.

Thirdly, since the diffraction grating or hologram element produces conjugate diffracted light, a plurality of sets of photodetectors are required, and the number of parts is increased. Depending on the diffraction grating, JP-A-62
In some cases, four sets of photodetectors are required as in the embodiment disclosed in Japanese Patent Publication No. 137736. If these detectors are simply reduced in order to reduce the number of parts, new stray light is generated. Further, according to the example disclosed in Japanese Patent Laid-Open No. 2-172033, the above-mentioned problems are solved by inclining the normal line of the hologram surface from the optical axis to eliminate the generation of conjugate diffracted light. However, in this case, since no conjugate diffracted light is generated, the amount of 0th-order light returning to the semiconductor laser increases, which causes an increase in laser noise.

Fourth, since the diffraction angle of the diffraction grating or the hologram element, that is, the separation angle has a large wavelength dependency of light, when the wavelength of the light source such as a semiconductor laser fluctuates, the emitted beam and the reflected beam are correspondingly changed. The separation angle also varies.

The object of the present invention is to completely separate the beam emitted from the light source and the reflected beam from the surface of the information medium, without the generation of stray light, high light utilization efficiency, and reduction in the number of parts. An object is to provide a small-sized optical head that is resistant to fluctuations in the wavelength of light.

[0011]

To achieve the above object, in the first invention, a light source, an imaging optical system for narrowing an outgoing beam from the light source onto the information medium surface, and the light source are substantially the same. A beam separating optical system including a photodetector arranged on a plane or in the vicinity thereof and a polarizing prism for guiding a reflected beam from the information medium surface onto the photodetector is configured.

According to a second aspect of the present invention, in the first aspect of the invention, the polarizing prism included in the beam splitting optical system converts the circularly polarized light into linearly changed light when the circularly polarized light is incident on the polarizing prism. Depending on the polarization direction of the polarized light, it has a function of advancing or refracting / separating the light emitted from the polarizing prism.

According to a third invention, in the first or second invention, when a semiconductor laser is used as the light source and the polarizing prism converts the circularly polarized light into S-polarized light, the S-polarized light beam goes straight, Further, when the circularly polarized light is converted into P-polarized light, the P-polarized light has a function of refracting / separating.

In a fourth invention, in the first or second invention, when a semiconductor laser is used as the light source, and the polarization prism converts the circularly polarized light into P-polarized light, the P-polarized light beam goes straight, When the circularly polarized light is converted into S-polarized light, the S-polarized light beam has a function of refracting and separating, and a half-wave plate is arranged between the semiconductor laser and the polarizing prism.

[0015]

According to the first aspect of the invention, the light source, the imaging optical system for forming an image of the beam emitted from the light source on the information medium surface, and the photodetector for receiving the reflected beam returned from the information medium surface, In an optical head arranged on the same plane as the light source or in the vicinity thereof, by providing a polarizing prism between the light source and the imaging optical system, the optical path of the outgoing beam and the optical path of the reflected beam are separated from each other. It can be displaced only in one direction and at an angle, and the reflected beam can be guided to the photodetector. As a result, the number of components can be reduced without generating stray light, as compared with the case where a diffraction grating or a hologram element is used. If the polarizing prism made of a material having a small wavelength dispersion is used, the separation angle of the polarizing prism is hardly affected by the fluctuation of the wavelength of the light source.

According to a second invention, in the first invention, the polarizing prism has a function of converting linearly polarized light into circularly polarized light and converting circularly polarized light into linearly polarized light, depending on a polarization direction of the linearly polarized light. By having the function of advancing or refracting / separating the light emitted from the polarization prism, the arrangement of the semiconductor laser, the polarization prism, and the imaging optical system can be uniaxial, and the design and assembly of the optical head are easy. Is.

In a third aspect based on the first or second aspect, a semiconductor laser is used as the light source, and when the linearly polarized light is S-polarized light, the linearly polarized light is made to go straight to the polarizing prism, and when the linearly polarized light is P-polarized light. When a polarizing prism having a refracting / separating action is used, the polarization direction 604 of the emitted beam 603 from the semiconductor laser 601 is parallel to the active layer 602 as shown in FIG. In addition, since the semiconductor laser 101 and the photodetector 201 can be arranged close to each other, the separation angle of the S-polarized light 401 and the P-polarized light 402 can be small, and the S-polarized light 401 and the P-polarized light 402 of the polarization prism 301 can be small. A material having a small difference in refractive index with respect to can be used. Further, usually, the semiconductor laser and the photodetector are used by being bonded on the submount and the substrate. For example, in FIG.
1 is fixed on the submount 102 and the substrate 103,
The photodetector 201 is fixed on the submount 202 and the substrate 203. In the case of FIG. 4, since the photodetector 201 is arranged above the semiconductor laser 101, the S-polarized light 401
The separation angle between the P polarized light 402 and the P polarized light 402 is the submount 102 or the substrate 1.
It is not affected by the size of 03 and has a high degree of freedom in design.

On the other hand, in FIG. 5, the light beam of P-polarized light 403 is made to go straight to the polarizing prism, and the light beam of S-polarized light 404 is refracted.
The arrangement of the semiconductor laser 101 and the photodetector 201 is shown when the polarization prism 302 having a function of separating is used. To reduce the separation angle of the P-polarized light 403 and the S-polarized light 404 as much as possible, the submount 102 and the substrate are shown. It is necessary to reduce the size of 103 or to bring the semiconductor laser 101 and the submount 102 closer to the edge of the substrate 103, which increases design restrictions.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, a semiconductor laser is used as a light source, and a P-polarized light beam is made to go straight on and a S-polarized light beam is refracted / separated by a polarizing prism. Even in the case of using a prism, as shown in FIG. 6, a half-wave plate 501 is arranged between the semiconductor laser 101 and the polarization prism 302, and the S-polarized light 405 is converted into the P-polarized light 407. The photodetector 201 can be arranged in the vicinity above 101,
The separation angle between the P-polarized light 407 and the S-polarized light 408, or the separation angle between the S-polarized light 405 and the P-polarized light 406 can be reduced, and the degree of freedom in design is increased.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram of an optical head according to the present invention. The polarizing prism 31 in FIG. 1 is composed of two birefringent prisms 32 made of a positive or negative uniaxial birefringent crystal,
33 and a birefringent plate 34 which also consists of positive or negative uniaxial birefringent crystal and has a function of shifting the phase of ordinary light and extraordinary light by a quarter wavelength. , 33 so that the optical axes 35 and 36 thereof are perpendicular to each other, and the optical axis direction 35 of the birefringent prism and the optical axis direction 37 of the birefringent plate 34 are inclined by 45 ° when viewed from the incident surface. Are joined to have. However, the birefringent prism 3 that constitutes the polarization prism 31
The joint surfaces of the birefringent plates 2 and 33 and the birefringent plate 34 are different when the positive uniaxial birefringent crystal and the negative uniaxial birefringent crystal are used.

Since the polarization direction 21 of the outgoing beam 5 from the semiconductor laser 1 is perpendicular to the optical axis direction 35 of the birefringent prism 32, the outgoing beam 5 is directed to the birefringent prism 3.
Go into 5 as the usual light. When the outgoing beam 5 passes through the birefringent plate 34, the optical axis direction 37 of the birefringent plate 34 with respect to the polarization direction 21 of the outgoing beam is 45 when viewed from the incident surface.
The output beam 5 becomes a circularly polarized beam 7 when it passes through the birefringent plate 34 because it is inclined and has a function of shifting the phases of ordinary light and extraordinary light by a quarter wavelength. Since the traveling direction of the circularly polarized beam 7 and the optical axis direction 36 of the birefringent prism 33 are parallel, the birefringent prism 33 travels straight in the circularly polarized light state. After all, when the outgoing beam 5 passes through the polarizing prism 31, it changes to a circularly polarized beam 7 and is condensed on the information medium surface 4 by the objective lens 3.

Circularly polarized beam 7 reflected from the information medium surface 4
Is the birefringent prism 3 which again constitutes the polarizing prism 31.
Although it is incident on the circularly polarized light beam 3, the optical axis direction 36 and the traveling direction of the circularly polarized light beam 7 are parallel, so that the circularly polarized light beam 7 goes straight through the birefringent prism 33. Next, when the circularly polarized beam 7 passes through the birefringent plate 34, the phase difference between the ordinary ray and the extraordinary ray is further shifted by a quarter wavelength, so that the circularly polarized beam 7 is changed to the reflected beam 6 which is linearly polarized light. However, the reflected beam 6
The polarization direction 22 of is perpendicular to the polarization direction 21 of the outgoing beam 5. When the reflected beam 6 passes through the birefringent prism 32, the polarization direction 22 of the reflected beam 6 and the optical axis direction 35 of the birefringent prism 32 are parallel to each other, so that the reflected beam 6 passes through the birefringent prism 32. Propagate as extraordinary light. At this time, since the cemented surface of the birefringent prism 32 is inclined, the reflected beam 6 propagates in a direction different from that of the outgoing beam 5, and the reflected beam 6 reaches the photodetector 2 adjacent to the semiconductor laser 1. Be guided.

FIG. 2 is an explanatory view of the second embodiment of the present invention. The polarization prism 71 in FIG. 2 is composed of two birefringent prisms 72, 73 made of a positive or negative uniaxial birefringent crystal.
And a birefringent plate 74, which is also made of positive or negative uniaxial birefringent crystal and has a function of shifting the phase of ordinary light and extraordinary light by a quarter wavelength, the birefringent prism 72, 73 so that the optical axes 75 and 76 are perpendicular to each other, and the optical axis direction 75 of the birefringent prism is
And the optical axis direction 77 of the birefringent plate 74 are joined so as to have an inclination of 45 ° when viewed from the incident surface. However,
Birefringent prisms 72 and 7 that constitute the polarization prism 71
3 and the birefringent plate 74 are joined together by using a positive uniaxial birefringent crystal and a negative uniaxial crystal, the orientations of which differ.

The polarization direction 61 of the emitted beam 5 from the semiconductor laser 1 changes to the polarization direction 91 as the emitted beam 5 passes through the half-wave plate 81. Since the polarization direction 91 is perpendicular to the optical axis direction 75 of the birefringent prism 72, the outgoing beam 5 travels through the birefringent prism 75 as ordinary light. When the outgoing beam 5 passes through the birefringent plate 74, the optical axis direction 77 of the birefringent plate 74 is inclined by 45 ° from the incident surface with respect to the polarization direction 91 of the outgoing beam, and the ordinary light Since it has a function of shifting the phase of the extraordinary light by a quarter wavelength, the outgoing beam 5 becomes a circularly polarized beam 7 when passing through the birefringent plate 74. Since the traveling direction of the circularly polarized beam 7 and the optical axis direction 76 of the birefringent prism 73 are parallel, the birefringent prism 73 goes straight on as circularly polarized light. After all, when the outgoing beam 5 passes through the polarizing prism 71, it changes to a circularly polarized beam 7 and is condensed on the information medium surface 4 by the objective lens 3.

Circularly polarized beam 7 reflected from the information medium surface 4
Is a birefringent prism 7 that constitutes the polarizing prism 71 again.
Although it is incident on the circularly polarized light beam 3, the optical axis direction 76 and the traveling direction of the circularly polarized light beam 7 are parallel, so that the circularly polarized light beam 7 goes straight through the birefringent prism 73. Next, when the circularly polarized beam 7 passes through the birefringent plate 74, the phase difference between the ordinary ray and the extraordinary ray is further shifted by a quarter wavelength, so that the circularly polarized beam 7 is changed to the reflected beam 6 which is linearly polarized light. However, the reflected beam 6
The polarization direction 92 is perpendicular to the polarization direction 91 of the outgoing beam 5. When the reflected beam 6 passes through the birefringent prism 72, since the polarization direction 92 of the reflected beam 6 and the optical axis direction 75 of the birefringent prism 72 are parallel to each other, the reflected beam 6 passes through the birefringent prism 72. Propagate as extraordinary light. At this time, since the cemented surface of the birefringent prism 72 is inclined, the reflected beam 6 propagates in a direction different from that of the outgoing beam 5, and the reflected beam 6 reaches the photodetector 2 adjacent to the semiconductor laser 1. Be guided. The polarization direction 92 of the reflected beam 6 is 2 before the reflected beam 6 is guided to the photodetector 2.
The polarization direction 62 is changed by the half-wave plate 81.

FIG. 3 is an explanatory view of the third embodiment of the present invention. This is a case where the optical system is made infinite by using the collimator lens 8.

In the embodiment, the reflected beam 6 does not return to the semiconductor laser 1 and no stray light is generated, as compared with the case where a conventional diffraction grating or hologram element is used.
Since the reflected beam 6 is refracted / separated in only one direction, the number of photodetectors is reduced, which is an improvement. In addition, if a crystal having a small wavelength dispersion of light such as rutile is used for the birefringent prisms 32, 33, 72, 73 and the birefringent plates 34, 74 constituting the polarizing prisms 31, 71, semiconductors can be obtained. The separation angle of the outgoing beam 5 and the reflected beam 6 of the polarization prisms 31 and 71 is hardly affected by the wavelength variation of the laser 1, which is superior to the conventional technique.

[0028]

According to the present invention, the optical path of the imaging optical system and the optical path of the detection optical system can be shared, and the emitted beam of the semiconductor laser and the reflected beam from the information medium surface can be completely separated.
Moreover, stray light is not generated, light utilization efficiency is high, the number of parts can be reduced, and a small optical head that is resistant to fluctuations in the wavelength of the light source can be realized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a third embodiment of the present invention.

FIG. 4 is a perspective view showing the arrangement of a semiconductor laser and a photodetector.

FIG. 5 is a perspective view showing the arrangement of a semiconductor laser and a photodetector.

FIG. 6 is a perspective view showing the arrangement of a semiconductor laser and a photodetector.

FIG. 7 is an explanatory view showing the polarization direction of the emitted beam of the semiconductor laser.

[Explanation of symbols]

1 ... Semiconductor laser, 2 ... Photodetector, 3 ... Objective lens, 4
... information medium surface, 5 ... outgoing beam, 6 ... reflected beam, 7 ...
Circularly polarized beam, 21 ... Polarization direction of outgoing beam, 22 ... Polarization direction of reflected beam, 31 ... Polarizing prism, 32, 33
... Birefringent prism, 34 ... Birefringent plate, 35, 36
... optical axis direction of birefringent prism, 37 ... optical axis direction of birefringent plate.

Claims (4)

[Claims] 1. A light source, an image forming optical system for forming an image of an outgoing beam from the light source on an information medium surface, and a beam separating means for separating the reflected beam returning from the information medium surface and the outgoing beam. In an optical head including a photodetector that receives the reflected beam separated by the beam separation means, the beam separation means is a polarization separation means by a polarization prism, and the light source and the photodetector are on substantially the same plane, Alternatively, the optical head is arranged in the vicinity thereof. 2. The polarizing prism according to claim 1, wherein the polarizing prism has a function of converting linearly polarized light into circularly polarized light and converting circularly polarized light into the linearly polarized light. An optical head that is a prism that has a function of straightening or refracting / separating the light emitted from. 3. The light source according to claim 1 or 2, wherein the light source is a semiconductor laser, and the polarization prism advances straight when the linearly polarized light is S-polarized light and refracts / separates when the linearly polarized light is P-polarized light. An optical head that is a polarizing prism that acts. 4. The light source according to claim 1, wherein the light source is a semiconductor laser, and the polarization prism advances straight when the linearly polarized light is P-polarized light, and refracts / separates when the linearly polarized light is S-polarized light. It is a polarizing prism with action,
An optical head having a half-wave plate between the semiconductor laser and the polarizing prism.