JPS59203259A - Optical magnetic disc device - Google Patents

Abstract

PURPOSE:To make an analyzer unnecessary by dividing a reflected laser light from a disc into two with a polarizing element which uses the double refraction property of crystal to separate light into two polarized light components and making these divided light incident to respective light detecting means. CONSTITUTION:A condenser lens 25, an optical rotator 26, a Wollaston prism 27, and a detector 28 where two detecting means are made into one body are provided. The reflected light from a disc 8 reaches the condenser lens 25 through an objective 17 and a half mirror 16, and the light from the condenser lens 25 has the plane of polarization rotated at a prescribed angle by the optical rotator 26 and is made incident to the Wollaston prism 27. Thereafter, the light is separated into polarization components P and S by the prism 27, and they are given to light detecting means 28a and 28b respectively, and their outputs are given to a differential amplifier 29, and an output 30 is outputted as a reproduced signal output.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Industrial Field of Application The present invention relates to a magneto-optical disk device that utilizes the magneto-optic effect.
Two matters.

(B) Prior art Conventional technology (I) Research on perpendicular magnetic recording and reproduction of information by applying magneto-optical effects such as the Faraday effect and the magnetic Kerr effect is underway. Generally speaking, G (100%) is used as a recording medium.
) dFe, T11F6, or other amorphous magnetic film is used, and the recording medium is magnetized in one direction over the entire surface (two directions) and is irradiated with light from a semiconductor laser or the like to locally reduce the temperature of the recording medium to around the Curie point. area including the laser beam irradiated area (: applying a bias magnetic field in the opposite direction to the direction in which the recording medium is magnetized, to create a magnetized area in the opposite direction to the laser beam irradiated area C 2 0). Recording is performed by

To reproduce recorded information, the light emitted from a laser light source, etc. is converted into linearly polarized light through a polarizer, and then the recording medium is irradiated with light.
Information is reproduced by detecting the rotation of the plane of polarization due to the recorded information by receiving the reflected light or transmitted light from the light through an analyzer and a photodetector such as a photoelectric conversion element.

In addition, the temperature of the recording medium is locally raised by irradiating the information recording part (-1) with a laser beam, etc. in the same way as when recording, and the bias magnetic field is applied in the opposite direction to that during recording, that is, in the direction in which the entire recording medium has been previously magnetized. When it is turned on, the direction of magnetization of the laser source irradiation part becomes the same as that of turning I), and the recorded information is erased.

FIG. 1 is a general configuration diagram of a magneto-optical recording/reproducing apparatus.

In the e+ system, the laser modulator (1) (2) modulates the radar light according to the signal to be recorded. The polarized beam passes through the mirror (4), the polarized beam (5), the wavelength plate (6), and the objective lens (
7) (Therefore, a condensed light (approximately 1 micron) is irradiated onto the disc-shaped recording medium (8).
is already magnetized in one direction over its entire surface.

I) Recording by applying a magnetic field in the opposite direction to the direction in which the recording medium (8) is already magnetized using a bias magnetic field coil (9) or the like to the area including the part where the laser beam is focused and irradiated. will be carried out. The reflected light passes through the objective lens (
7), after passing through the X wavelength plate (6), it is reflected by the polarizing beam splitter (5), and is reflected by the cylindrical lens (10
) to reach the photodetector σD.

Recording is performed while performing focus control using a signal obtained from this photodetector (111).

For playback, an optical system separate from that for recording is used. The laser light emitted from the semiconductor laser mackerel is turned into a parallel beam by making it into a lens! ] After being reflected by the mirror [141], it becomes linearly polarized light C2 by the polarizer (151).The laser beam transmitted through the half-mirror head is focused on the recording medium (8) by the objective lens (17). Due to the magneto-optical effect (Kerr effect), the reflected light from the recording medium (8) rotates the plane of polarization to the right or left (twice) depending on the direction of magnetization of the recording medium (8).The reflected light with the rotated plane of polarization rotates again. The reflected light passes through the objective lens r17) and enters the eight-half mirror 0011, and the reflected light is further divided into two parts by another half mirror α1, each of which is sent to an analyzer (19a).
, (19b) (Two people shoot. (7) Two analyzers (19a), (19111) set the setting angle to polarizer + 151
The polarization planes (two pairs, opposite to each other and at the same angle. The beam origin that passed through the analyzers (11L) and (19b) passes through the lenses (20a) and (20)) and is detected by the respective photodetectors (21a). ), (21b). Photodetector (2
1B), (21b) (2), the photoelectrically converted output is put into the differential amplifier (24) and calculated, and digital signals corresponding to "1" and "0' are obtained as output. Also, the photodetector (21b) ) The output focus signal and tracking signal are processed by a focus servo circuit (c) and a tracking servo circuit <241 to perform focus servo and tracking servo.

The optical system shown in Figure 1 (the problem with 2 is the reproduction optical system is that the reflection beam from the disk (8) is divided into two half mirrors (11all 2 and 1), and each source is divided into two by an analyzer (2). Even if the light is detected after passing through 19a) and 19b, the amount of light that enters each photodetector (21 &) (211) is the reflected light from the disk (8), which reduces the efficiency of use of the light source laser. bad.

The Kerr rotation angle of a magneto-optical disk is around 1 degree, which is very small (
Since it is two-handed, the degree of m variation is extremely small. Therefore, the signal SN
The ratio is considered to be proportional to the amount of light incident on the photodetectors (21) (21b). In fact, if the Kerr rotation angle of the magneto-optical disk is θ and the incident V angle to the photodetector is the factor, the S/N ratio is:
It is known that when the detector is configured with a PIN photodiode (= is proportional to 2θk・It−), and when it is configured with an avalanche photodiode, it is proportional to 2θkJT (2θkJT). Therefore, the S/N ratio of the reproduced signal is In order to improve this, it is necessary to increase the efficiency of laser use and increase the amount of light incident on the photodetector.

(c) Purpose of the Invention The present invention has been made in view of the above points, and an object of the present invention is to provide a magneto-optical disk device with improved utilization efficiency of a light source laser and an improved signal-to-noise ratio.

B) Structure of the Invention The present invention utilizes birefringence to introduce a laser beam reflected from a recording medium into a polarized single-element element that separates the reflected laser beam into two 8 components. = This is a magneto-optical disk device characterized in that two people can emit light from each other.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 2 is an enlarged view of a part of the optical system during reproduction.

The same thing as in Figure 1 (- indicates the same number). In the figure, (C) is a condenser lens, (26) is a writing photon, (2
7) is a Wollaston prism, and the fin is at least two detection means or a detector integrated.

The reflected light from the disk (8) reaches the condenser lens (c) via the objective lens 17) and the half mirror. The light from this condensing lens (c) is i-photon! ] The plane of polarization is rotated by a predetermined angle, and the light enters the Wollaston prism (2?).

As is well known, the Wollaston prism is a type of polarizing element that utilizes the birefringence of crystals, and has the function of separating the P-polarized light component and the S-polarized light component of incident light. (Secondly, there are Nicol prisms, Glan-Thomson prisms, Rochon prisms, Senarmont prisms, etc.) In Wollaston prisms, Rochon prisms, Senarmont prisms, etc., P polarized light components and S polarized light components are taken in approximately the same direction as the incident direction. ] However, in the Wollaston prism, both the S-polarized light component and the P@Original acid component are refracted (2), whereas in the Rochon prism, only the S-polarized light component is refracted, and the P-polarized light component travels straight.

The reason why the photon (A) is provided is to cause the light incident on the Wollaston prism Qη to become a Wollaston prism. That is, by Motoko Saka+2E9)) the plane of polarization is rotated by a predetermined angle C''-as shown in FIG.

Wollaston Prism CI! The light incident on D is divided into two by the prism (27) (=therefore, a P polarized light component and an S polarized light component C, and are provided to the respective light detection means (28a) and (281)). The output of each photodetection means (2B&) (281) is supplied to a differential amplifier (2B&), and the output of the differential amplifier C
3Q or playback signal output. As mentioned above, the photodetector■
At least two light detection means are integrated (or one detection means is divided so that outputs can be obtained separately from each other). When performing tracking and focus control, it is sufficient to divide the image into two parts.

Now, the reflected light from the disk is shifted by ±θk (Kerr rotation angle) as shown by Bl in FIG. 3, depending on the signal (direction of magnetization) recorded on the disk. The reflected light with such a polarized component is the Wollaston Prism Q.
When it is incident on By differentially amplifying the outputs of the light detection means (28a) and (281)), a binary signal that is unaffected by fluctuations in light intensity occurring at the light source or medium surface can be obtained.

The angle ψ at which the differential output is maximum is determined by the Wollaston prism when the light whose polarization plane is rotated by ψ + θk and ψ - θ is determined by the Wollaston prism.
), so 0os2(ψ1θ1c)−Cos2
(ψ−θk) is calculated to be %45 degrees. Since the photon element (2e) is provided to set this 45 degree angle, the position of the photon capturer is between the condenser lens (c) and the Wollaston prism Qη (not limited to two. In this connection, it is sufficient to enter the Wollaston prism, so if the laser light source is a semiconductor laser (
The output beam of the semiconductor laser is substantially linearly polarized light) (the semiconductor laser is rotated around the optical axis of the output beam), or the σ configuration in which the Wollaston prism is rotated is also conceivable.

In the Wollaston prism used in the examples, the separation angle of the P-polarized light component and the S-polarized light component can be set by 1) the size, length, and width of the Wollaston prism, and the interval between the laser beams directly on the photodetector is It can be controlled by this separation angle and the position of the condensing lens. Polarizing elements (including Rochon prisms, Senarmont prisms, etc.) that emit light separated in approximately the same direction as the incident light (2), such as the Wollaston prism (1),
As shown in Figure 2, one photodetector can be used (because both the P and S components are taken out in the same direction), the reproduction optical system can be made smaller, and the adjustment is easier (-). accompany.

(f) Effects of the Invention As described above, the present invention (according to which the reflected laser beam from the disk is divided into two by a polarizing element that divides the light into two polarized components (two) by utilizing the birefringence of the crystal). However, since the light is made incident on each photodetection means, an analyzer is not required, and the amount of light incident on the photodetection means is increased.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional magneto-optical disk device, FIG. 2 is a block diagram of a part of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the plane of polarization of incident light on a Wollaston prism. Explanation of the main figure number 12η...Wollaston prism (polarizing element), (2
8a) (281))...Photodetection means, G...Differential amplifier. Figure 2 Figure 18, □min.

Claims (1)

[Claims] (1) A magneto-optical disk device (2) that irradiates light from a laser light source onto a magneto-optical recording medium and uses reflected light from the recording medium (1) to optically read information recorded on the recording medium. Then, the reflected light is introduced into a polarizing element that separates the incident light into two polarized light components using birefringence, and the two polarized light components extracted from the polarized confectionery are respectively supplied to a light detection means. A magneto-optical disk device characterized by: