JPS6314348A - Optical head for magneto-optical disk - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of light by transmitting all the light reflected from a magneto-optical disk to a detection means through the 1st and 2nd polarized beam splitters while the light is projected onto the magneto-optical disk from an irradiation means. CONSTITUTION:A laser light (f) reflected from a magneto-optical disk 16 is given to a Farady rotator 12, where its polarized plane is further rotated by 45 deg.+alpha, the light is made incident on a polarized beam splitter 10, where the light is split into a laser light (i) and a laser light (h), a laser light (h) is sent to a four-split photo diode 28, from which a tracking error signal and a focus error signal are detected. The polarized face of the laser light (i) is rotated by 45 deg. by the Faraday rotator 8, and a laser light (j) is obtained and made incident on a polarized beam splitter 6, made incident on an avalanche photo diode 32 without transmission and its intensity is detected. Since all the laser light projected from the semiconductor laser 2 and reflected on the magneto- optical disk 16 is transmitted to a servo signal detection system or an informa tion signal system, the utilizing efficient of light is improved.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention relates to a magneto-optical disk for reading information from or writing information on a magneto-optical disk on which information is written by thermomagnetically changing the direction of magnetization. The present invention relates to an optical head.

[Prior Art] This type of device records information on a magneto-optical disk by utilizing the Kerr effect, in which when linearly polarized light is applied to a magnetic material, the plane of polarization of the reflected light rotates by a predetermined angle depending on the direction of magnetization. It is used to read information, and usually a half mirror is installed on the optical path from a light emitting element that emits linearly polarized light, such as a semiconductor laser, to the magneto-optical disk to separate the incident light by a predetermined ratio (for example, 50%). - separates the reflected light of the light irradiated from the light emitting element onto the magneto-optical disk and transmits it to the information signal detection system and the one-no-one signal detection system. An I-nervo signal representing the state of light irradiation onto the magneto-optical disk is detected.

[Problem to be Solved by the Invention 1] However, in the above-mentioned conventional reading and mounting method, each time the irradiated light from the light emitting element passes through the half mirror, it is attenuated by a predetermined percentage, so that the light emitted from the light emitting element is attenuated by a predetermined percentage, so that the light emitted from the light emitting element is attenuated by a predetermined percentage each time it passes through the half mirror. There are problems such as the reflected light from the magneto-optical disk becomes smaller, the S/N ratio of the detection signal becomes worse, or the light utilization efficiency becomes lower, and the light source requires a high-output light emitting element. Ta. Furthermore, since the light that is not separated by the half mirror out of the reflected light from the magneto-optical disk returns to the light emitting element, there is also the problem that noise is generated in the light emitted from the light emitting element.

Therefore, the present invention provides an optical head for a magneto-optical disk that can reduce the loss of light from the light emitting element to the magneto-optical disk, and efficiently separate the reflected light, and in which the reflected light does not return to the light emitting element. It was made with the purpose of providing.

[Means for Solving the Problems] The structure of the present invention for solving the above-mentioned problems includes: an irradiation means for irradiating light onto a magneto-optical disk; Two polarizing beam splitters are arranged so that the plane of polarization of the light that passes through the road differs from each other by 45 degrees, and the polarizing beam splitter is installed between the two polarizing beam splitters to rotate the plane of polarization of the incident light by 45 degrees and transmit it. provided between a first Faraday rotator that causes the magneto-optical disk to rotate, and a deflection beam splitter on the magneto-optical disk side;
A second Faraday rotator rotates the polarization plane of the incident light by a predetermined angle from 45 degrees and transmits it, and detects the reflected light from the magneto-optical disk separated by /1') by each of the deflection beam splitters. The present invention is characterized by comprising a detection means for detecting.

[Function 1] In the optical head for a magneto-optical disk of the present invention configured as described above, the light with the polarization plane P1 that is irradiated by the irradiation means and transmitted through the first polarizing beam splitter has a polarization plane of the first polarization plane. It is rotated by 45 degrees by the Faraday rotator to become light with a polarization plane P2, and after passing through the next polarizing beam splitter, that polarization plane is rotated by 45 degrees ten α (
or -α) The light is further rotated and irradiated onto the magneto-optical disk.

Then, the plane of polarization of the light was rotated by a predetermined angle (10) according to the magnetization direction of the magneto-optical disk and reflected, and then further rotated by 45 degrees by 10 α (or -α) by the second Faraday rotator. After that, it enters a polarizing beam splitter. The polarizing beam splitter splits the incident light into light with a polarization plane P2 and light with a polarization plane S2 perpendicular thereto, and the light with the polarization plane S2 is separated from this optical path. Also, the polarization plane P2
After the light passes through the polarizing beam splitter, the plane of polarization is rotated by 45 degrees by the first Faraday rotator, and the plane of polarization is P1.
The light beam has a polarization plane S1 orthogonal to the polarization plane S1, and is separated from the optical path by the next polarization beam splitter.

As a polarizing beam splitter, conventionally, for example, BK
A rectangular prism made of grade 7 optical glass whose slopes are coated with various dielectric thin films in multiple layers and then laminated with other uncoated rectangular prisms, or a crystal exhibiting birefringence such as calcite. There are known devices constructed by the following, and these devices may be used. In addition, as a Faraday rotator, paramagnetic material FR-5 (product name Nido 1
A permanent magnet coil is installed to apply a predetermined magnetic field to Farade glass (manufactured by 0YA), Shigeru-11 J-net crystal such as YIG (yttrium iron carnet), or a thin film thereof ( There are some well-known scripts available, and you can use them.

[Example] Fig. 2 is an explanatory diagram showing the polarization plane of the laser beam that changes as it passes through the optical system. When the laser beam a with the polarization plane p1 is cut from the body laser 2, the laser beam a is made into parallel light by the collimating lens 4 and then enters the polarizing beam splitter 6 q.J. The polarizing beam splitter 6 is installed so as to transmit the light of the polarization plane p1 and reflect the light of the polarization plane S which is perpendicular to the polarization plane p1, and transmits the incident rake light a as it is. ,−
The light is incident on the Faraday rotator 8, which rotates the polarization plane of the incident light by 45 degrees and transmits it, so that the polarization plane changes from pl to 45 degrees.
The laser beam C becomes the laser beam C with the polarization plane p2 rotated by a degree and enters the polarization beam splitter 10. This polarizing beam splitter 10 is installed so as to transmit light with a polarization plane p2 and reflect light with a polarization plane S2 perpendicular thereto, and transmits the incident laser beam C as it is.

Next, the laser beam d transmitted through the polarizing beam splitter 10 is incident on the Faraday rotator 12, which rotates the polarization plane of the incident light by 45 degrees and ten α, and transmits the laser beam. It is transmitted as light e. Then, the transmitted laser light e is irradiated onto the magneto-optical disk 16 through the objective lens 14, and the plane of polarization is rotated ±θ according to the magnetization direction at the focal point and reflected. The laser beam f thus generated is again incident on the Faraday rotator 12 via the objective lens 14.

In a Faraday rotator, the direction in which the plane of polarization rotates differs depending on the direction of magnetization of the Faraday rotator with respect to the direction of light incidence.If the magnetization is in a constant direction, the direction of rotation of the plane of polarization will be reversed depending on the direction of incidence, resulting in a Faraday rotator. The rotation angle of the polarization plane of the light that has passed back and forth through the rotator is twice the rotation angle of the polarization plane of the light that has passed in one direction.

Therefore, in the Faraday rotator 12, the magneto-optical disk 16
The laser beam f reflected from
The light is rotated by 10 degrees, transmitted, and sent to the polarizing beam splitter 10. By passing through the Faraday rotator 12 and reflecting from the magneto-optical disk 16, the polarization plane of the laser beam Ω incident on the polarization beam splitter 10 is changed to 90 degrees from the polarization plane p2 of the light passing through the dark beam splitter 10.
The plane of polarization is rotated by +2α±θ degrees. Therefore, in the polarizing beam splitter 10, the laser beam q having the intensity I is polarized at the polarization plane p2. A laser beam i with an intensity of 1 sin (2α±θ) and a polarization plane S2. Laser “light” with intensity IC08 (2α±θ),
The laser beam is separated from the optical path. This separated laser light is then split by a half mirror 20 that transmits 50% of the incident light and reflects 50% of the incident light.The reflected light is directly sent to a two-split photodiode 22, and the transmitted light is sent via a lens 24 and a cylindrical lens 26. The tracking error signal and focus error signal are respectively transmitted to the four-divided foot diode 28 and detected by the well-known push-pull method and astigmatism method.

The laser beam transmitted to the servo signal detection system after the beam splitter 20 is such that the polarization plane of the laser beam q incident on the polarization beam splitter 10 is relative to the polarization plane S2 of the light reflected by the polarization beam splitter 10. Since the deviation is only 2α±θ degrees, attenuation is small and a large amount of light can be transmitted to the servo signal detection system, making it possible to obtain a good detection signal that is not affected by noise. Furthermore, the intensity of this laser beam changes depending on the Kerr rotation angle θ, which is rotated according to the magnetization direction of the magneto-optical disk 16. Since the intensity of the laser beam is small, fluctuations are small, and a more stable detection signal can be obtained.

On the other hand, the plane of polarization of the laser beam i transmitted through the polarizing beam splitter 10 is rotated by 45 degrees by the Love rotator 8.
The laser beam j with the polarization plane S1 is incident on the polarization beam splitter 6. And this person fj48 laser beam j
is separated from the optical path without passing through the polarizing beam splitter 6, enters the avalanche photodiode 32 via the lens 30, and its intensity is detected. In other words, the intensity of the laser beam i transmitted through the polarizing beam splitter 10 is proportional to sin2α±θ, and varies greatly depending on the rotation direction (100, -0) of the reflected light on the magneto-optical disk 16. By detecting the intensity using the first avalanche diode 32, the magnetization direction of the magneto-optical disk 16, that is, the recorded information can be detected.

As explained above, according to the photoelectric system of this embodiment, all the laser light projected from the semiconductor laser 2 and reflected by the magneto-optical disk 16 is transmitted to the servo signal detection system or the information signal detection system. Since the light is transmitted, the light is used efficiently and a good detection signal can be obtained. Also, since the reflected light does not return to the semiconductor laser 2, this
It is also possible to prevent the occurrence of ti'Fi.

In the above embodiment, a semiconductor laser was used as the irradiation means, but a JS ray, solid-state laser, etc. may also be used. Further, tracking error Shintan is configured to be detected by a push-pull method, or can also be detected by other detection methods such as a three-beam method. Similarly, the focus error signal is configured to be detected by the astigmatism method, or can also be detected by other detection methods such as the Knifezi method. Furthermore, since the reflected light separated by the dark beam splitter 10 is the same as the reflected light from the habo disk, it is possible to use a perforated type or compatible type in which the light reflectance changes depending on the information recorded using the reading device. Information can also be read from the disc of change.

[Effects of the Invention 1] As detailed above, according to the optical head for a magneto-optical disk of the present invention, the irradiation means irradiates the magneto-optical disk,
All of the light reflected from the magneto-optical disk can be transmitted to the detection means by the first and second polarizing beam splitters, and the efficiency of light utilization can be improved. Furthermore, since the reflected light from the magneto-optical disk does not return to the irradiation means, it is also possible to prevent the generation of noise due to this.

[Brief explanation of drawings]

FIG. 1 is a groove diagram showing the overall configuration of the optical system of the reading device of the embodiment, and FIG. 2 is an explanatory diagram showing changes in the polarization plane of Rayleigh light passing through the optical system. 2...Semiconductor laser 6.10...Polarizing beam splitter 8.12...Faraday rotator 16...Magneto-optical disk

Claims (1)

[Scope of Claims] An irradiation means for irradiating light onto a magneto-optical disk, and two devices disposed on an optical path between the irradiation means and the magneto-optical disk so that the polarization planes of the light transmitted therethrough differ by 45 degrees from each other. a first Faraday rotator which is provided between the two polarizing beam splitters and rotates the plane of polarization of the incident light by 45 degrees and transmits the incident light; a second Faraday rotator provided between the polarizing beam splitter and transmitting the polarized light by rotating the polarization plane of the incident light by a predetermined angle from 45 degrees; and the magneto-optical disk separated by each of the polarizing beam splitters. 1. An optical head for a magneto-optical disk, comprising: a detection means for detecting reflected light from a magneto-optical disk.