JPS59168955A - Reproducing structure of optical magnetic information recording device - Google Patents

Abstract

PURPOSE:To enhance the use efficiency of the light of a light source laser to improve the S/N ratio of the signal of an optical magnetic recording medium by providing a Faraday rotating element, which rotates the polarization direction at a prescribed angle, between a beam splitter and the recording medium. CONSTITUTION:The laser parallel light from a laser light source 28 is reflected by a polarizing beam splitter 31 and passes through a Faraday rotating element 32 and is flare diaphragmed by an object lens 33 and is irradiated to an optical magnetic recording medium 34. This light is reflected by the medium 34 and passes through the lens 33, the element 32, the splitter 31, and lenses 35 and 36 again and is made incident to a detector 37.The beam which passes through the element 32 on the returning path becomes a beam having two kinds of oscillation direction of 45 deg.+Qk and 45 deg.-Qk in accordance with the recording direction of the medium 34. The splitter 31 is used as an analyzer also, and therefore, a signal which has a variable intensity in accordance with the recording direction of the medium 34 is obtained with a high S/N ratio in an element (b).

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a method for recording and reproducing information on a magnetic recording medium having magnetic anisotropy in the direction perpendicular to the film surface using a laser beam or the like. The present invention relates to an information reproducing structure in a magnetic information recording device.

(b) Conventional technology Research is underway on recording and reproducing information by applying magneto-optical effects such as the Faraday effect and the magnetic Kerr effect. Generally, an amorphous magnetic film such as GdCo, GdFe, or TbFe is used as a recording medium.The recording medium is magnetized in one direction over its entire surface in advance, and is irradiated with light from a semiconductor laser to locally increase the temperature of the recording medium. To create a magnetized region in the laser beam irradiated area in the opposite direction to the surroundings by raising the magnetic field to near the Curie point and applying a bias magnetic field in the opposite direction to the direction in which the recording medium is magnetized to the area including the laser beam irradiated area. Recording is performed by

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

In addition, the temperature of the recording medium is locally increased by irradiating the information recording area with a laser beam, etc. in the same way as during recording, and a 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 magnetized in advance. The magnetization direction of the laser beam irradiated part becomes the same as that of the surrounding area, and the recorded information is completely erased. In other words, this method of recording and reproducing information on a recording medium allows information to be rewritten.

FIG. 1 is a general configuration diagram of an existing magneto-optical recording and reproducing device, with the left side showing the recording optical system and the right side showing the reproducing optical system. In the recording optical system, a laser modulator (2) modulates laser light according to the signal to be recorded, and the modulated laser light emitted from the semiconductor laser (1) is passed through a condenser lens (3).
), it becomes a parallel beam, passes through a mirror (4), a polarizing beam splitter (5), and a wavelength plate (6), and is focused and irradiated onto a disk-shaped recording medium (8) by an objective lens (7).

The entire surface of the disk-shaped recording medium (8) is magnetized in one direction in advance.The recording medium (8) is already magnetized by the bias magnetic field coil (9) in the area including the part where the laser beam is focused and irradiated. Recording is performed by applying a magnetic field in the opposite direction to the direction of magnetization.The reflected light passes through the objective lens (7) and the wavelength plate (6) again, and then is sent to the polarizing beam splitter (5). It is reflected, passes through a cylindrical lens (10), and passes through a photodetector (11).
The signal obtained from this photodetector (11) is used to perform focus control during recording.

For reproduction, as shown on the right side of FIG. 1, a reproduction optical system separate from that for recording is used. Laser light emitted from the semiconductor laser (12) is collected by a condensing lens (13) and then passed through a mirror (14).
After being reflected by the polarizer (15), it becomes linearly polarized light. The laser beam transmitted through the half mirror (16) is focused onto the recording medium (8) by the objective lens (17). The plane of polarization of the reflected light from the recording medium (8) rotates to the right or left depending on the direction of magnetization of the recording medium (8) due to the magneto-optic effect. After the reflected light whose polarization plane has been rotated in this way is again focused by the objective lens (17), it enters the half mirror (16) again, and the reflected light is further divided into two by another half mirror (17).
The light is divided and enters each analyzer (19a) and (19b). These two analyzers (19a) and (19b) have set angles that are opposite to each other but at the same angle with respect to the polarization plane of the polarizer (15). Analyzer (19a), (llb)
The beam light that has passed through passes through lenses (20a) and (20b), and is received by photodetectors (21a) and (21, b), respectively. Differential amplification of the photoelectrically converted output by the photodetectors (21a) and (21b)! i! (22), and digital signals corresponding to "1" and '0' are obtained as output.Furthermore, the focus signal and tracking signal output from the photodetector (21b) are sent to the focus servo circuit (23), It is processed by a tracking servo circuit (24) to perform focus servo and tracking servo during playback.

In devices that reproduce recorded information by detecting the rotation of the plane of polarization of reflected light from these recording media (8), as shown in Figure 1, as one of the amounts of light, it is necessary to A half mirror is used. In particular, since the laser beam passes through the half mirror (16) of the reproduction optical system twice in a round trip, the amount of light decreases to %. This is a very large loss. As described above, the optical system of the conventional reproducing apparatus has the drawback that the efficiency of using laser light is very low.

Furthermore, since the Kerr rotation angle in the magneto-optical recording medium is very small, around 1°, the degree of signal modulation is extremely small. Therefore, the S/N ratio of the entire recording medium is expressed as follows.

If the detector is a PIN photodiode, the S/N ratio is 2θsl 100].

If the detector is an avalanche photodiode, the S/N
oe 2θK fi17. - Here, θ is the Kerr rotation angle of the magneto-optical recording medium, ro is the amount of light incident on the recording medium, and 'R is the ratio of the amount of light received by the detector to the amount of light incident on the recording medium.

Therefore, in order to increase this S/N ratio, it is important to reduce the amount of light loss in the reproduction optical system.

(c) Purpose of the invention The present invention has been made in view of the above points, and
The purpose of this invention is to improve the light utilization efficiency of a light source laser and to obtain a structure that can obtain a signal from a magneto-optical recording medium with a good S/N ratio.

(d) Structure of the Invention The present invention provides a Faraday rotation element that rotates the polarization direction by a predetermined angle between the beam splitter and the recording medium.

(E) Embodiments Prior to describing embodiments of the present invention, the principle of the present invention will be explained using FIG. 2. In this Figure 2, (25) is a polarizer, (26) is a Faraday rotator, and (27) is a reflector, and the laser beam that has passed through the polarizer (25) vibrates in the y-axis direction. It becomes linearly polarized light. When the angle of rotation of the polarization plane of the Faraday rotator (26) is set as the final angle, it is reflected by the reflector (27) and then the Faraday rotator (26)
The polarization plane of the linearly polarized laser beam that has passed through is rotated by 2 degrees with respect to the y-axis and vibrates, as shown in FIG. 2(b). Therefore, if the reflecting plate (27) is a magneto-optical recording medium having a Kerr rotation angle of θ, the laser beam reflected by the medium and passing through the Faraday rotation element (26) will be as shown in Fig. 2(c). Depending on the direction of magnetic recording, beams having two types of rotation angles with respect to the y-axis, 2 meters θ〆 and 2〆〆〆 θ, are generated. Therefore, there are two types of strong and weak signals in the laser beam that has passed through the polarizer (25) again, and it is possible to read the signal completely recorded on the magneto-optical recording medium.

When a polarizer in the X-axis direction is inserted, the magnitude of the signal at that time is as follows from Fig. 2 (c): Co5 (2 (+07.) - Co5 (2d - θ) =
It is proportional to 5in4 i ・5in2θ, that is, 5in4〆・5in2θba, so 1, -2
Maximum signal output can be obtained at 2.5°.

The structure of the present invention based on this principle is shown in FIG. In the figure, (28) is a semiconductor laser light source, (29) is a collimator lens, (30) is a diffraction grating, (31) is a pin 7-1 oscillator, and (32) is a Faraday rotation element, as described above. It has a rotation angle of 22.5°. (33)
is an objective lens, (34) is a magneto-optical recording medium, (35) is an intermediate lens, (36) is a cylindrical lens, and (37) is an intermediate lens.
) is a detector.

Therefore, the laser beam A emitted from the laser light source (28)
becomes parallel light due to the collimator lens (29),
The polarized beam splitter (3) passes through the diffraction grating (30).
1), passes through the Faraday rotator (32), is focused by the objective lens (33), and is irradiated onto the magneto-optical recording medium (34).The laser beam reflected by the recording medium (34) is reflected by the objective lens again. (33), Faraday rotation element (3
2), Polarized beam brick (31L intermediate lens (35
) and the cylindrical lens (36) to the detector (
37). The laser beam passing through the Faraday rotation element (32) on the return path in this optical system is rotated at 45°+Q and 45° depending on the recording direction of the magneto-optical recording medium (34).
The resulting laser beam has two types of vibration directions: °-QK. At this time, the polarizing beam splitter (31) also serves as an analyzer, so the 8-center element (b) in the detector (37) has a light intensity that corresponds to the recording direction of the magneto-optical recording medium (34). signal can be obtained. In addition, the diffraction grating (30) is installed for tracking control, and its ±1st-order light enters the upper and lower elements (a) and (c) of the detector (37), respectively, and the pixels Child (a
) (C) A tracking error signal is obtained, and tracking adjustment is performed from this error signal. In addition, the cylindrical lens (36) was installed to perform focus control using its astigmatism effect, and the central element (b) of the detector (37) was divided into four parts, and each of the four elements was Focus control is performed by obtaining a focus error signal by calculating between the outputs.

(f) Effects of the Invention As is clear from the above description, the present invention has a simple configuration of just arranging a Faraday rotation element between the beam splitter and the recording medium, so the optical system is simplified and the amount of light can be reduced. Loss is reduced, and a read signal from the recording medium can be obtained with a high S/N ratio.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the configuration of a magneto-optical information storage device;
The figure is an optical system diagram for explaining the principle of the structure of the present invention, and FIG. 3 is an optical system diagram showing the structure of the present invention, in which (31) is a beam splitter, (32) is a Faraday rotation element, (34)
indicate the recording medium, respectively. 11- ■ Sect 304-

Claims (1)

[Claims] 1) A device that irradiates a magneto-optical recording medium with a laser beam and optically reads information magnetically recorded on the recording medium from the reflected light, comprising: a laser light source; a beam splitter that guides the laser beam from the magneto-optical recording medium toward the magneto-optical recording medium and guides the reflected light from the recording medium to the detector; A reproducing structure in a magneto-optical information recording device comprising a Faraday rotation element rotated by a magneto-optical information recording device. 2) A reproducing apparatus in a magneto-optical information recording apparatus according to claim 1, wherein the Faraday rotation element has a polarization direction rotated by 22.5 degrees.