JPH05114193A - Photomagnetic detector for optical head - Google Patents

Abstract

PURPOSE:To provide a photomagnetic detector where the structure of an enclosure and the position adjustment of parts are simplified and the number of parts is reduced. CONSTITUTION:Optical axes of respective crystal of two optical uniaxial crystal members 10a, 10b constituting a Wollaston prism 10 are made orthogonal to each other when viewed from an optical axis A of a photomagnetic detection optical system 100, and the normal direction of a joint surface 10c is inclined at 45 deg. to irradiated laser light, and a fixed face 10d of the Wollaston prism is formed into a plane. Thus, the number of parts of the photomagnetic detector is reduced, and the enclosure structure is simplified and parts are easily adjusted because the Wollaston prism is only stuck to the flat enclosure to complete attachment at the time of fixing various optical parts to the optical head enclosure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical detector used for an optical head of a magneto-optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art Conventionally, there is an apparatus for reading information recorded on a recording medium by a semiconductor laser such as a compact disc or a laser disc. Further, not only reproduction but also a recording medium capable of recording only once and a recording medium capable of recording / reproducing many times are available, and a magneto-optical recording medium is a recording medium capable of recording / reproducing many times.

In a magneto-optical recording medium, the polarization direction changes depending on the direction of magnetization on the magneto-optical recording medium when the medium is irradiated with polarized laser light. Magneto-optical effect (Kerr effect).
A magneto-optical recording / reproducing apparatus for detecting information recorded on a magneto-optical recording medium by utilizing the has been put into practical use.

An example of the optical system of the magneto-optical recording / reproducing apparatus of such an optical head is shown in FIG. The polarized light emitted from the semiconductor laser 1 is applied to the magneto-optical recording medium 5 by a laser irradiation optical system 100 including a collimator lens 2 and an objective lens 4. The reflected light from the magneto-optical recording medium 5 is influenced by the magnetization depending on the recording bit on the magneto-optical recording medium 5, and the polarization direction is modulated by the magneto-optical effect. The modulated polarized light is guided to the magneto-optical detection optical system 200 by the beam splitter 3. This magneto-optical detection optical system 200
A λ / 2 plate 6 for rotating the polarization direction by 90 degrees, a Wollaston prism 7, a condenser lens 8, and a two-part photodetector 9
Composed of and. Further, an optical head which is an improvement of this and eliminates the need for the λ / 2 plate 6 is described in Japanese Patent Application Laid-Open No. 2-113458. In this structure, as shown in FIG. 3, the Wollaston prism 7 is arranged so as to be rotated by 45 degrees about the optical axis, and the λ / 2 plate is omitted.

[0005]

However, in the above-mentioned structure, since it is necessary to rotate the prism around the optical axis, the structure of the housing for holding the optical system parts and the position adjustment of each part are complicated. There was a problem.

In view of the above-mentioned problems of the prior art,
An object of the present invention is to provide a magneto-optical detecting device in which the structure of the housing and the position of the parts are easily adjusted and the number of parts is reduced.

[0007]

The above object is to provide a laser irradiation optical system comprising a laser light source and an objective lens for irradiating a magneto-optical recording medium with a laser beam, and an electric signal for reflecting light from the magneto-optical recording medium. In a magneto-optical detection device for an optical head having a magneto-optical detection optical system for converting into a magneto-optical recording medium, the magneto-optical detection optical system guides reflected light from the magneto-optical recording medium to the magneto-optical detection optical system. Beam splitter, and a Wollaston prism having first and second optical uniaxial crystal members for splitting into a first light flux and a second light flux according to the polarization direction of the reflected light guided. A two-segment photodetector for converting the first light flux and the second light flux into an electric signal, wherein the first and second optical uniaxial crystal members have optical axes of the crystals which are the same as each other. Is it the direction of the optical axis of the magneto-optical detection optical system? The Wollaston prisms are joined so as to be orthogonal to each other when viewed, and the optical axis of the crystal of each of the optically uniaxial crystal members is inclined by about 45 degrees with respect to the polarization direction of the laser light of the laser irradiation optical system. The normal line direction of the joint surface of the both optically uniaxial crystal members is inclined by approximately 45 degrees with respect to the polarization direction of the laser light of the laser irradiation optical system when viewed from the optical axis direction of the magneto-optical detection optical system. The present invention is achieved by providing a magneto-optical detecting device for an optical head, characterized in that the fixed surface of the Wollaston prism with respect to the magneto-optical detecting device is planar.

[0008]

Operation: The optical axes of the respective crystals of the two optically uniaxial crystal members constituting the Wollaston prism as viewed from the optical axis of the magneto-optical detection optical system are made orthogonal to each other, and the normal direction of the joint surface is irradiated with laser light. Approximately 45 degrees with respect to, and forming the fixing surface of the Wollaston prism into a flat surface,
The plate can be omitted, and when fixing various optical components to the optical head casing, the attachment is completed simply by attaching the Wollaston prism to the flat casing.

[0009]

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

FIG. 1 is a perspective view showing an embodiment of the present invention. The magneto-optical detection device for the optical head shown in FIG.
The polarized light emitted from the laser irradiation optical system 100 including the collimator lens 2 and the objective lens 4 is applied to the magneto-optical recording medium 5.

The laser light applied to the magneto-optical recording medium 5 by the laser irradiation optical system 100 is p-polarized light,
Due to the magneto-optical effect, the reflected light is modulated by ± θk around the polarization direction p according to the magnetization direction of the recording bit recorded on the magneto-optical recording medium 5. The reflected light that has been modulated is guided to the magneto-optical detection optical system 200 by the beam splitter 3.

The reflected light guided to the magneto-optical detection optical system 200 enters the Wollaston prism 10. This Wollaston prism 10 includes a first optical uniaxial crystal member 10a and a second optical uniaxial crystal member 1 as shown in FIG.
0b and 0b are bonded together at the joint surface 10c.

The Wollaston prism 10 has a magneto-optical detecting optical system 2 as shown in FIG. 4 and as shown in FIG.
The optical axes of the optically uniaxial crystal members are orthogonal to each other when viewed from the optical axis A direction of 00. Further, when viewed from the direction of the optical axis A of the magneto-optical detection optical system 200, the normal direction N of the joint surface 10c is inclined by 45 degrees about the optical axis A with respect to the polarization direction p of the laser light of the laser irradiation optical system 100. The first optical uniaxial crystal member 10a and the second optical uniaxial crystal member 10b are molded so as to be located at different positions. Further, the fixing surface 10d of the Wollaston prism 10 with respect to the casing of the magneto-optical detection optical system 200 (not shown) is formed to have a planar shape.

The incident light on the Wollaston prism 10 through the beam splitter 3 is ± θk centered on the polarization direction p.
The reflected light that is modulated only is split into a first light flux and a second light flux according to the polarization direction. The respective divided light beams are condensed by the convex lens 8 on the two light receiving elements 9a and 9b of the two-divided photodetector 9 and converted into electric signals. Then, the two light receiving elements 9a, 9b of the two-divided photodetector 9 are
Is detected as a magneto-optical signal.

As shown in FIG. 5, if the ratio of the ridges that form the Wollaston prism 10, that is, the width, the height, and the depth is approximately 1: 1: 1.414, the depth can be minimized. However, it is not limited to this.

The assembled Wollaston prism 10 need only be fixed to a housing (not shown) so that the central axes of the convex lenses 8 are aligned, and high positional accuracy is not required. In addition, the structure of the housing becomes simple and the adjustment work of the optical axis alignment becomes easy.

[0017]

As described above, according to the magneto-optical detecting apparatus of the present invention, the crystals of the two optical uniaxial crystal members constituting the Wollaston prism as viewed from the optical axis of the magneto-optical detecting optical system are formed. By making the optical axes orthogonal to each other and inclining the normal direction of the joining surface to the irradiation laser beam by about 45 degrees and forming the fixing surface of the Wollaston prism on a flat surface, the number of parts of the magneto-optical detection device is reduced, and When fixing various optical parts to the optical head housing, simply attach the Wollaston prism to the flat housing to complete the installation.
The case structure becomes simple and the parts adjustment becomes easy.

[Brief description of drawings]

FIG. 1 is a perspective view showing a magneto-optical detector according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a magneto-optical detector of a conventional example.

FIG. 3 is a perspective view showing a conventional magneto-optical detector.

FIG. 4 is a perspective view showing the structure of a Wollaston prism used in the magneto-optical detecting device according to the embodiment of the invention.

5 is a view showing the structure of the optical axis of the Wollaston prism of FIG. 4 and is an arrow view seen in the A direction.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimating Lens 3 Beam Splitter 4 Objective Lens 6 λ / 2 Plate 7 Wollaston Prism 8 Convex Lens 9 Two-Division Photo Detector 10 Wollaston Prism 10a First Optical Uniaxial Crystal Member 10b Second Optical Uniaxial Crystal member 10c Bonding surface 10d Fixed surface

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Shohei Hashiguchi 5-10-1, Fuchinobe, Sagamihara-shi Nippon Steel Corporation Electronics Research Laboratory (72) Inventor Tadashi Takeda 5329 Shimosuwa-cho, Suwa-gun, Nagano Prefecture San Co., Ltd. Kyoseiki Seisakusho Shimosuwa factory

Claims (2)

[Claims] 1. A laser irradiation optical system comprising a laser light source and an objective lens for irradiating a magneto-optical recording medium with a laser beam, and a magneto-optical detection for converting reflected light from the magneto-optical recording medium into an electric signal. In a magneto-optical detection device for an optical head having an optical system, the magneto-optical detection optical system includes a beam splitter for guiding reflected light from the magneto-optical recording medium to the magneto-optical detection optical system. And a Wollaston prism having first and second optical uniaxial crystal members for splitting into a first light flux and a second light flux according to the polarization direction of the reflected light,
2 for converting the first light flux and the second light flux into electric signals
A split photodetector, and the first and second optical uniaxial crystal members are bonded so that the optical axes of the crystals are orthogonal to each other when viewed from the optical axis direction of the magneto-optical detection optical system. In the Wollaston prism, the optical axis of the crystal of each of the optically uniaxial crystal members is tilted by about 45 degrees with respect to the polarization direction of the laser light of the laser irradiation optical system, and the both optical uniaxial crystal members are provided. Is arranged so that the normal line direction of the joining surface of the optical disc is tilted by approximately 45 degrees with respect to the polarization direction of the laser light of the laser irradiation optical system when viewed from the optical axis direction of the magneto-optical detection optical system, and the Wollaston prism 2. A magneto-optical detecting device for an optical head, wherein a fixing surface of the magneto-optical detecting device is planar. 2. The Wollaston prism has ridges, that is, width, height,
The magneto-optical detection device for an optical head according to claim 1, wherein the depth ratio is approximately 1: 1: 1.414.