JPS6282531A - Photomagnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the reproduction characteristics of the information signal and to secure the stable reproduction of information, by rotating a 1/2-wavelength plate having a rotary mechanism to rotate the polarized face of the transmitting luminous flux and therefore equalizing optically the outputs of the 1st and 2nd photodetectors. CONSTITUTION:A motor 8 having a gear is driven by a motor driving circuit 15 and a 1/2-wavelength plate 7 having a rotary mechanism is rotated. The rotation angle of the plate 7 is proportional to the output obtained by amplifying differentially only the DS component of the output of each photodetector via an LPF. Thus the plate 7 can be rotated with proportion to the output obtained by amplifying differentially the polarized face of the reflected light sent from a photomagnetic recording medium 6. Here the motor 8 is driven by the circuit 15 by means of the difference between the outputs of both photodetectors. Thus the plate 7 is rotated to equalize the output levels of both photodetectors.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical recording and reproducing device using a magneto-optical recording medium.

(Problems to be Solved by the Invention) A method for reproducing magnetically recorded information from a magneto-optical recording medium on which information signals are recorded utilizes magneto-optical effects called the Kerr effect and the Alladay effect.

FIG. 3 shows a magneto-optical recording and reproducing device that utilizes the Kerr effect. In this magneto-optical recording and reproducing device, a laser beam emitted from a semiconductor laser 1 is converted into parallel light by a collimator lens 2, passes through a polarizer 3 and a beam splitter 4, and is focused into a minute light spot by an objective lens 5. , is irradiated onto the surface of the magneto-optical recording medium 6 and is reflected. At this time, the polarization state of the reflected light changes depending on the magnetization state of the irradiated magneto-optical recording medium. The reflected light passes through the objective lens 5 again, has its optical path bent by the beam splitter 4, is sent to the analyzer 9, is focused by the lens 10 on the photodetector 11, and a corresponding signal is output.

FIG. 4 is a diagram for explaining the reproduction principle of magneto-optical recording using the magnetic Kerr effect. In the figure, Pi indicates the amount of polarized light incident on the magneto-optical recording medium 6, and R+ indicates magnetization below the surface of the medium film. R- represents the polarized light reflected from the magnetized region above the medium film surface, and R- represents the polarized light reflected from the magnetized region above the medium film surface. Further, θ is called the Kerr rotation angle, and represents the amount by which the vibration plane of light rotates due to the magneto-optic effect. At this time, when the reproducing light spot scans the alternately magnetized areas of the magneto-optical recording medium 6, when the analyzer 9 is mechanically rotated by a set angle θ from the extinction position, the transmitted light is transmitted from the recording medium. Assuming that the amount of reflected light is P, it becomes modulated light with an intensity difference S expressed by the following equation (1), and is optically regenerated by the photodetector 11.

5=Psin2θksin2θ
(1) In this case, the signal-to-noise ratio (S
The analyzer 9 is mechanically rotated so as to maximize the N ratio), and the set angle θ is set to the optimal set angle θ. It is necessary to set it to .

The set angle θ of the analyzer is greatly influenced by noise related to the photodetector and noise due to fluctuations in reflected light from the recording medium 6. Therefore, there is a differential detection method as shown in FIGS. 5(a) and 5(b) as a method for removing common-mode noise caused by fluctuations in reflected light. FIG. 5(a) shows that the reflected light from the recording medium 6 is split by the beam splitter 16, and each analyzer 11.1
The configuration is such that light is received at 1', a reproduced output is obtained, and differential amplification is performed. On the other hand, FIG. 5(b) shows a configuration in which the plane of polarization of the reflected light from the recording medium 6 is rotated by 45 degrees by a half-wave plate 7, and the light is split by an analyzer 9. In the case of FIG. 5(a), it is necessary to use two expensive analyzers. Furthermore, it is necessary to set the setting angle of each analyzer to an optimal angle, leading to the disadvantage that adjustment is difficult. On the other hand, Fig. 5 (b
), it is not necessary to set the analyzer at the optimal angle. However, the reflected light from the recording medium 6 is actually elliptically polarized light, and the amount of light divided by the analyzer 9 is not equal.

If the amount of light received by each photodetector is not equal, differential detection will not be effective, and common-mode noise due to fluctuations in reflected light from the recording medium cannot be removed. Also, FIG. 5(a).

When using the differential detection method as in (b), it is necessary to use photodetectors with the same characteristics, and differences in characteristics mean that it is not possible to eliminate common-mode noise due to fluctuations in reflected light from the recording medium. However, there is a drawback that the reproduced signal-to-noise ratio of the reproduced signal decreases as a result.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording and reproducing apparatus which can improve the above-mentioned drawbacks, significantly improve the reproduction characteristics of information signals, and perform stable information reproduction.

(Means for solving the problem) A semiconductor laser and a light beam emitted from the semiconductor laser are irradiated onto the surface of a magneto-optical recording medium, and the reflected light or transmitted light has a rotation that can be rotated around the optical axis in the optical path. first and second photodetectors which are provided with a mechanical half-wave plate and a light splitting means, and which detect information signals of both light beams split by the light splitting means; a first differential amplifier for detecting a difference signal between the information signals from the photodetector;
a 20th differential amplifier that detects a difference signal by passing the information signal from the photodetector through a low-pass filter; and rotationally driving the half-wave plate with a rotating mechanism using the output of the second differential amplifier. the first and second lights by rotationally driving the half-wave plate with a rotating mechanism to rotationally change the plane of polarization of the light beam that passes through the half-wave plate; A magneto-optical recording and reproducing device is obtained which is characterized in that the detector output is optically equalized.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the magneto-optical recording and reproducing apparatus of the present invention. This magneto-optical recording and reproducing apparatus has a structure in which the half-wave plate 7 shown in FIG. The configuration is such that the geared electric motor 8 is driven using the output obtained by differentially amplifying the output through a low-pass filter. At this time, a reproduced signal can be obtained by performing differential amplification of each output of each photodetector 611.11'.

In such a magneto-optical recording/reproducing apparatus, a motor drive circuit 15 drives a geared motor 8 to rotate a half-wave plate 7 with a rotating mechanism. This rotation angle changes in proportion to the output obtained by differentially amplifying only the DS component of the output of each photodetector through a low-pass filter. Therefore, the polarization plane of the reflected light from the magneto-optical recording medium 6 can be rotated in proportion to the differentially amplified output. FIG. 2 is a diagram showing DC components B1 and B2 of each output after the output of each photodetector is passed through a low-pass filter. At this time, the geared electric motor 8 is driven from the electric motor drive circuit 15 using the difference (B1-B2) between the outputs, and the half-wave plate 7 with a rotation mechanism is driven.
By rotating , the output level of each photodetector can be equalized. Therefore, by performing differential amplification of the outputs Bl and B2 of each photodetector at this time, it is possible to remove in-phase noise due to fluctuations in the reflected light from the magneto-optical recording medium 6 and improve the reproduction S/N ratio of the reproduction signal. It becomes possible.

In the above embodiment, the rotation of the plane of polarization of the reflected light from the magneto-optical recording medium is achieved by mechanically rotating the half-wave plate. A similar effect can be obtained by rotating the reproduction optical system including only the analyzer around the optical axis without using the analyzer.

(Effects of the Invention) As explained above, the magneto-optical recording and reproducing apparatus of the present invention eliminates the problem of bias in the amount of light to each photodetector and imbalance of the characteristics of the photodetector itself when information is reproduced using the differential detection method. Since the balance is solved optically, it is possible to efficiently remove in-phase noise caused by fluctuations in the amount of light reflected from the magneto-optical recording medium. This makes it possible to improve the reproduction signal-to-noise ratio of the reproduced signal and to perform more stable information reproduction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the magneto-optical recording and reproducing apparatus of the present invention, FIG. 2 is a diagram showing the output after passing the output of each photodetector through a low-pass filter, and FIG. A block diagram showing a magnetic recording/reproducing device, FIG. 4 is a diagram for explaining the principle of reproducing magneto-optical recording using the magnetic Kerr effect, and FIGS. 5(a) and (b) show a conventional magneto-optical recording/reproducing device. FIG. 2 is a block diagram showing another example. In the figure, 1... Semiconductor laser, 2... Collimator lens, 3... Polarizer, 4... Beam splitter, 5... Objective lens, 6... Magneto-optical recording medium, 7...・Half-wave plate with rotation mechanism 7'...Half-wave plate 8...Electric motor with gear, 9...Analyzer, 10, 1
0'...Lens, 11.11'...Photodetector,
12.14... Differential amplifier, 13.13'... Low pass filter, 15... Motor drive circuit.

Claims (1)

[Claims] A semiconductor laser and a half-wave plate with a rotation mechanism capable of rotating around the optical axis, which irradiates the light flux emitted from the semiconductor laser onto the surface of a magneto-optical recording medium, and includes a half-wave plate with a rotation mechanism capable of rotating around the optical axis in the optical path of the reflected light or transmitted light. a first and a second light beam which are arranged with a splitting means and detect information signals of both light beams split by the light splitting means;
a first differential amplifier that detects a difference signal between information signals from the first and second photodetectors; and a first differential amplifier that detects a difference signal between information signals from the first and second photodetectors; a second differential amplifier that detects a difference signal via a filter;
Using the output signal of the differential amplifier of
a driving means for rotationally driving a wavelength plate, the first wavelength plate being rotationally driven to rotate a polarization plane of a light beam passing through the half wavelength plate; and a magneto-optical recording/reproducing apparatus characterized in that the output of the second photodetector is optically equalized.