JP3356814B2 - Light beam separation optical system in magneto-optical recording and reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam separating optical system in a magneto-optical recording / reproducing apparatus for reproducing information recorded on a magneto-optical recording medium using an optical head.

[0002]

2. Description of the Related Art Various devices for optically reproducing information have heretofore been proposed. These devices irradiate a recording medium with a light beam from a light source and receive reflected light with a detector to reproduce the information. It is. In this case, a light beam is radiated by an optical head, which is a component of the optical information reproducing apparatus, and reflected light is received. Beam shaping and beam separation are performed by one optical member in an optical system constituting the optical head. May be provided.

For example, Japanese Patent Publication No. 3-21973 (Conventional Example 1) discloses that a single prism performs beam shaping and beam separation in an optical head of an optical disk apparatus using a semiconductor laser as a light source. The contents are disclosed. FIG. 3 is a schematic diagram of the optical head disclosed in the above conventional example. According to this, the prism 32 is provided between the semiconductor laser 30 and the recording medium portion 31a of the optical disk 31, the condenser lens 33 is provided between the semiconductor laser 30 and the prism 32, and the prism 32 and the recording medium portion 31a are connected to each other. An objective lens 34 is provided therebetween.

The prism 32 has an incident end face 32a functioning as a beam splitter, shaping the beam shape of the incident light from the semiconductor laser 30 from an ellipse to a circle, and refracting the incident light in a direction perpendicular to the recording medium section 31a. It is configured to be. The laser light emitted from the emission end faces 32b and 32c travels straight without being refracted. Further, a lens 35 and a light receiver 36 are provided on the exit end face 32c side of the prism 32 so as to detect return light from the recording medium section 31a.

The laser beam from the semiconductor laser 30 is obliquely incident on the incident end face 32a of the prism 32 via the condenser lens 33, is beam-shaped, is emitted from the emission end face 32b, and is emitted to the recording medium section 31a by the objective lens 34. Irradiated. The reflected light reflected by the recording medium unit 31a follows the same optical path, enters the output end face 32b of the prism 32, and is reflected by the incident end face 32a to reach a detection system that receives return light. Thus, beam shaping and beam separation are performed by the single prism 32.

Japanese Patent Publication No. 4-72202 (Conventional Example 2) discloses a double image in which a dielectric multilayer film is formed on a bonding surface of two crystals and a beam splitter function (three beam splitter) is provided. A recording / reproducing optical system of a magneto-optical disk device provided with a prism and a light receiving element arranged on an emission surface of a light beam reflected by a dielectric multilayer film of the prism is disclosed. Incidentally, in this conventional example, a Wollaston prism, which is the most common as a double image prism, is used.

Further, Japanese Patent Publication No. 59-4771 (Conventional Example 3) discloses a method for separating a modulated beam reflected by an information medium and a non-modulated read beam from a radiation source and an objective lens system. In addition, an information record carrier reading device in which a polarization sensing beam splitter in which three crystals are bonded and a λ / 4 plate are disposed in a radiation path between the objective lens system and the detector is disclosed.

[0008]

However, in the above-mentioned conventional example, beam shaping and beam separation are performed by a single prism, and there is an advantage that the apparatus can be downsized. There is a problem that playback is not possible. Further, Conventional Example 2 has a three-beam splitter configuration, but is a joined body of two crystals.
Although there is a large beam separating function, it is a bonded body of three crystal bodies, and there is a problem that the optical member becomes expensive.

The present invention has been proposed in order to solve the above-mentioned problems, and has a simple and inexpensive configuration to shape an incident beam to be applied to a magneto-optical recording medium and to form a return beam from the magneto-optical recording medium. It is an object of the present invention to provide a light beam separation optical system in a magneto-optical recording / reproducing apparatus which can perform beam separation for separating a light beam of the incident beam so that a magneto-optical signal can be detected, thereby improving light efficiency. .

[0010]

According to a first aspect of the present invention, there is provided a recording medium which is formed of an anisotropic member, refracts and transmits an incident beam from a light source and shapes its cross-sectional shape. And the return beam reflected and incident on the recording medium is emitted separately from the optical path of the incident beam, and the polarization state of the incident beam and the polarization state of the return beam are determined by the anisotropy. In a light beam separating optical system in a magneto-optical recording / reproducing apparatus having a prism adapted to respectively match two independent polarization states unique to a member,
A light-rotating element for rotating the polarization state of the incident beam by approximately 45 ° is provided between the light source and the prism, and the crystal axis direction of the prism is parallel to the direction of a light beam traveling in the prism toward the recording medium. The prism is configured as described above. Further, the invention according to claim 2 is formed of an anisotropic member, refracts and transmits an incident beam from a light source, shapes its cross-sectional shape, emits it to the recording medium side, and reflects the incident beam from the recording medium. The incident return beam is emitted separately from the optical path of the incident beam, and the polarization state of the incident beam and the polarization state of the return beam are respectively changed to two independent polarization states unique to the anisotropic member. In the light beam separating optical system in the magneto-optical recording / reproducing apparatus having the prism set to be coincident, the prism is configured such that the crystal axis direction of the prism is inclined by 45 ° with respect to the light beam traveling in the prism toward the recording medium. It is characterized by having done.

[0011]

As described above, according to the present invention, the beam shaping of the incident beam irradiating the magneto-optical recording medium is performed by using a prism which is formed of one anisotropic crystal and whose crystal axis is set in a required direction. And the beam separation that separates the return beam from the magneto-optical recording medium from the optical path of the incident beam so that the magneto-optical signal can be detected, so that the configuration can be made simple and inexpensive, and the light efficiency can be improved. Becomes

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows an optical system of an optical head according to a first embodiment of the present invention. The semiconductor laser (LD) 1 emits a light beam polarized in the plane of the paper. A collimating lens 2 that converts the light beam into a parallel light beam is provided in the direction in which the light beam is emitted.
A half-wave plate 3 for rotating by an angle is provided.
FIG. 1B is an explanatory diagram showing a state in which the polarization direction is rotated by 45 °.

A prism 4 for shaping a beam is provided in a direction in which the light beam passes through the half-wave plate 3. The prism 4 is made of a uniaxial crystal (for example, clockwise quartz), and the crystal axis W is parallel to the light beam traveling in the prism 4 toward the disk 5. Prism 4
The incidence end face 4a is provided with a special coat for performing beam shaping, and shapes the beam shape of the light beam from the LD 1 from an ellipse to a substantially perfect circle. Further, the angle of the incident end face 4a of the prism 4 is set such that the light beam entering the prism 4 is refracted in a direction perpendicular to the surface of the disk 5. The exit end faces 4b and 4c other than the entrance end face 4a are set so that the light beam is emitted straight without being refracted.

An objective lens 6 for imaging a light spot on a disk 5 on which a magneto-optical signal is recorded is provided in a direction in which the light beam passes through the prism 4. The return light reflected by the disk 5 passes through the objective lens 6 again, enters the prism 4, and is reflected by the incident surface 4a (reflection surface for the return light) on which the special coating is applied as described above. ,
A condenser lens 7 is provided in the direction of emission from the prism 4, and two photodetectors 8 a and 8 b are provided in a direction in which the light beam passes through the condenser lens 7.

The first embodiment is configured as described above. Next, an operation for obtaining a magneto-optical reproduction signal will be described. The light beam reflected by the disk 5 undergoes a Kerr rotation of ± θk with respect to the incident linearly polarized light. The light beam generated by the Kerr rotation passes through the objective lens 6 along the same optical path as the outward path, enters the prism 4, and is reflected by the reflection surface (incident surface 4a). At this time, since the crystal axis W of the prism 4 is substantially orthogonal to the reflected light beam, the reflected light beam is separated into two independent and unique polarization directions in the crystal. One of the polarization directions is an in-plane direction, and the other polarization direction is a direction perpendicular to the paper plane. Then, since the refractive index of the polarized light in the in-plane direction changes after reflection, the polarized light travels inside the prism 4 at an angle of ε with respect to the other polarized light.

After being separated and further changed in refractive index in this manner, the two polarized light beams taken out of the prism 4 are condensed by a condenser lens 7, and then are separated into two small photodetectors 8a, 8b. Then, the photodetector 8a,
If a differential output from 8b is obtained, a magneto-optical signal with a good C / N can be obtained.

FIG. 2A shows a second embodiment of the present invention, and portions corresponding to those of the first embodiment are denoted by the same reference numerals. In the second embodiment, unlike the first embodiment, no half-wave plate is provided between the collimator lens 2 and the prism 4. Further, the direction of the crystal axis W of the prism 4 is different. Other configurations are substantially the same as those of the first embodiment.
In the second embodiment, the crystal axis W of the prism 4 is oriented in a direction in which the z axis is rotated by 45 ° around the y axis in the coordinate axes shown in FIG. 2B.

The second embodiment is configured as described above. Next, the operation for obtaining a magneto-optical reproduction signal will be described. The light beam reflected by the disk 5 undergoes a Kerr rotation of ± θk with respect to the incident linearly polarized light. The luminous flux of the return light reflected by the disk 5 follows the same optical path as the outward path and passes through the objective lens 6
Pass through the prism 4 and split into two independent and unique polarization directions in the crystal. One of the polarization directions is an in-plane direction, and the other polarization direction is a direction perpendicular to the paper plane. These two beams have different velocities, but do not separate at an angle until they are reflected by the reflecting surface (incident surface 4a).

The luminous flux of the return light reflected by the reflection surface is such that the y axis is ±± around the z axis with respect to the coordinate axes shown in the prism 4.
It becomes two polarized lights rotated by 45 °. Of these, the light flux in one polarization direction changes its refractive index, so that it travels separated by an angle ε from the light flux in the other polarization direction. In this way, the two polarized light beams taken out of the prism 4 are condensed by the condensing lens 7 and then are turned into two small photodetectors 8.
a and 8b are received. Therefore, if differential outputs from the photodetectors 8a and 8b are obtained, a magneto-optical signal having a good C / N can be obtained. FIG. 2C is an explanatory diagram illustrating a polarization direction of a light beam received by the photodetector 8a, and FIG. 2D is an explanatory diagram illustrating a polarization direction of a light beam received by the photodetector 8b. In the case of the second embodiment, since the half-wave plate is not used, the configuration can be further simplified.

[0020]

As described above, according to the light beam separating optical system in the magneto-optical recording / reproducing apparatus of the present invention, a prism formed of one anisotropic crystal and having its crystal axis set in a required direction is provided. Since the beam shaping of the incident beam irradiating the magneto-optical recording medium and the beam separation for separating the return beam from the magneto-optical recording medium from the optical path of the incident beam so that the magneto-optical signal can be detected are performed. In addition, the size, the number of parts, and the cost can be reduced, the configuration can be simplified and inexpensive, and the light efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical system of an optical head according to a first embodiment of the present invention, and a diagram for explaining an optical rotation effect by a half-wave plate constituting the optical system.

FIG. 2 is a schematic diagram of an optical system of an optical head according to a second embodiment of the present invention, an explanatory diagram showing a crystal axis direction of a prism constituting the optical system, and a polarization direction of a light beam received by a photodetector. FIG.

FIG. 3 is a schematic diagram of an optical system of an optical head according to a conventional example.

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Claims (2)

(57) [Claims] 1. A refracting beam formed by an anisotropic member, refracting and transmitting an incident beam from a light source, shaping its cross-sectional shape, and radiating the beam toward a recording medium. Separated from the optical path of the incident beam and emitted,
Beam splitting optics in a magneto-optical recording / reproducing apparatus having a prism in which the polarization state of the incident beam and the polarization state of the return beam coincide with two independent polarization states unique to the anisotropic member. In the system, between the light source and the prism, there is provided an optical rotation element for rotating the polarization state of the incident beam by approximately 45 °, and the crystal axis direction of the prism and the light beam direction traveling in the prism toward the recording medium. A light beam separating optical system in a magneto-optical recording / reproducing apparatus, wherein the prism is configured to be parallel. 2. A return beam, which is formed of an anisotropic member, refracts and transmits an incident beam from a light source, shapes its cross-sectional shape and emits it to a recording medium side, and reflects a return beam that is reflected and incident on the recording medium. Separated from the optical path of the incident beam and emitted,
Beam splitting optics in a magneto-optical recording / reproducing apparatus having a prism in which the polarization state of the incident beam and the polarization state of the return beam coincide with two independent polarization states unique to the anisotropic member. A beam splitting optical system in a magneto-optical recording / reproducing apparatus, wherein the prism is configured such that a crystal axis direction of the prism is inclined by 45 degrees with respect to a light beam traveling in the prism toward the recording medium.