JPH04132031A - Method and device for reproducing magneto-optical information - Google Patents

Abstract

PURPOSE:To realize the magneto-optical information reproduction of few noises, large signal reproducing margin and high reliability by controlling a differential input signal at the time of differential detection with the difference of the quantities of light of two polarized components intersecting almost orthogonally with the light reflected or transmitted from/ through a magneto-optical recording medium. CONSTITUTION:The light emitted from a laser beam source 1 is reflected by a magneto-optical disk 2, and the polarized state or reflected light 6 is changed by an information signal recorded on a magneto-optical recording film 3. This reflected light 6 is separated into two polarized components intersecting almost orthogonally with each other by using a polarizing beam splitter 7, and they are received by different photodetectors 8, 9. The output difference of signal amplifiers 10 to amplify the outputs of these photodetectors 8, 9 is detected by a DC differential amplifier 11, and one of the signal amplifiers 10 operates so as to increase an amplification factor higher than a reference amplification factor, and the other side operates so as to reduce the amplification factor lower than the reference amplification factor. Thus, the output becomes 0, and the noise of an AC differential amplifier 12 to generate a regenerative signal is canceled by the differential amplifier 12, and regenerative output 13 whose signal amplitude is uniform can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information reproducing method and a magneto-optical information reproducing apparatus using a magneto-optical storage medium such as a magneto-optical disk.

BACKGROUND OF THE INVENTION In recent years, information recording devices using magneto-optical effects, typified by magneto-optical disk devices, have come into practical use.

Like conventional optical disks, this device is capable of high-density recording of information, as well as additional writing, erasing and rewriting of information, and is seen as a promising information reproducing device to replace magnetic disk devices.

The configuration of a conventional magneto-optical information reproducing device will be explained below with reference to FIG.

In FIG. 2, 51 is a laser light source, 52 is a magneto-optical disk, 53 is a magneto-optical recording film on the magneto-optical disk 52, and 5
4 is a lens, 55 is a beam splitter, 56 is reflected light,
57 is a polarizing beam splitter, 58.59 is a photodetector,
60 is a signal amplifier, 61 is a differential amplifier, and 62 is a reproduced signal output.

In the above configuration, the light emitted from the laser light source 51 is reflected by the magneto-optical disk 52.
The polarization state of the reflected light 56 changes depending on the information signal recorded on the upper magneto-optical recording film 53. The reflected light 56 whose polarization state has been changed by this information signal is separated into two polarization components substantially perpendicular to each other using a polarization beam splitter 57, and each is received by a separate photodetector 58, 59.

The outputs of the photodetectors 58 and 59 are amplified by signal amplifiers 60 and 60, differentially detected by a differential amplifier 61, and the information signal on the magneto-optical recording film is reproduced as a reproduction signal output 62.

However, in an actual magneto-optical disk, the output of the photodetectors 58 and 59 changes depending on the birefringence of the disk substrate made of a resin material such as polycarbonate and the polarization characteristics of optical systems such as lenses and beam splitters. The polarization characteristics of the optical system depend on variations in the characteristics of the parts used and variations in the assembly precision of the optical system, but in this case, the influence on the reproduced signal is due to the state where there is a certain amplitude difference between the outputs of the photodetectors 58 and 59. As a result, noise cancellation and signal amplitude expansion by differential detection are not performed sufficiently.

On the other hand, in the case of birefringence of the disk substrate, since the birefringence characteristics change depending on the location of the disk, the output of the photodetectors 58 and 59 changes as the disk rotates, and the output of the photodetector 58 and 59 is accordingly reproduced. The amplitude of the signal is modulated and the noise cancellation effect is also reduced. In addition, the birefringence of this disk substrate changes greatly depending on the temperature of the substrate, so even if a magneto-optical disk substrate has low birefringence at a certain temperature during shipping inspection, it may not be possible to use it in a magneto-optical disk drive under actual conditions. In actual signal regeneration, the board temperature increases.
The signal will be modulated due to the effects of birefringence.

Problems to be Solved by the Invention As described above, in conventional magneto-optical disks, the output of the photodetector is modulated by the birefringence of the disk substrate and the polarization characteristics of the optical system, especially changes in the birefringence of the disk substrate due to temperature changes. Therefore, there is a problem in that it is difficult to always obtain information signals by differential detection in an optimal state.

The present invention solves the above-mentioned conventional problems, and even when the photodetector is modulated due to the various causes mentioned above, there is no fluctuation in the amplitude of the reproduced signal, the noise removal effect is large, and the signal It is an object of the present invention to provide a highly reliable magneto-optical information reproducing method and a magneto-optical information reproducing device with a large reproduction margin.

Means for Solving the Problems In order to achieve the above object, in the present invention, when a signal is reproduced from a magneto-optical storage medium, two polarized lights of light reflected or transmitted from the magneto-optical storage medium, which are substantially orthogonal to each other, are used. The light amount difference between the components is detected, and the differential input signal at the time of differential detection of the two polarization components is controlled based on the light amount difference.

Furthermore, in the present invention, as a means for embodying the above method, a light source such as a laser, a first optical system that guides a light beam emitted from the light source, a magneto-optical storage medium, and a light beam reflected or reflected from the magneto-optical storage medium are provided. a second optical system that separates the transmitted light beam into two polarized components substantially perpendicular to each other; and two photodetectors that respectively detect the light intensities of the two polarized components separated by the second optical system. vessel and the above 2
It consists of a DC differential amplifier for calculating the difference between the photocurrent signals obtained by the two photodetectors, and an AC differential amplifier for calculating the difference between the photocurrent signals obtained by the two photodetectors. The output signals of the two photodetectors input to the AC differential amplifier are controlled by the output of the dynamic amplifier.

Furthermore, in the above means, the high cut-off frequency of the DC differential amplifier is substantially matched with the low cut-off frequency of the AC differential amplifier, and output signals of the two photodetectors input to the AC differential amplifier are controlled. A variable gain amplifier is used as a means for changing the amplitude of the output signals of the two photodetectors according to the output of the DC differential amplifier, and the outputs of the two photodetectors are input to the AC differential amplifier. As a method of controlling the signal, the output amplitude of the signal of one of the two photodetectors is increased by the output of the DC differential amplifier, and at the same time, the output amplitude of the signal of the other photodetector is increased. By reducing the output amplitude, the output of the DC differential amplifier is controlled to become O.

Effects According to the present invention having the above configuration, even if the output of the photodetector is modulated by the polarization characteristics of the optical system or changes in the birefringence of the disk substrate due to temperature changes, the differential signal is always maintained in an optimal state. By obtaining information signals through detection, there is no need to adjust the polarization characteristics of the optical system, and at the same time, a large signal reproduction margin can be obtained, making it possible to realize a highly reliable magneto-optical information reproducing device.

Example Examples thereof will be described below with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the magneto-optical reproducing apparatus of the present invention. In the figure, 1 is a laser light source, 2 is a magneto-optical disk, 3 is a magneto-optical recording film on the magneto-optical disk 2, 4 is a lens, 5 is a beam splitter, 6 is reflected light, 7 is a polarizing beam splitter, 8.9 is a photodetector, 10 is a signal amplifier,
11 is a DC differential amplifier, 12 is an AC differential amplifier, and 13 is a reproduction signal output.

In FIG. 1, light emitted from a laser light source 1 is reflected by a magneto-optical disk 2, and the polarization state of the reflected light 6 is changed by an information signal recorded on a magneto-optical recording film 3 on the magneto-optical disk 2. The reflected light 6 whose polarization state has been changed by this information signal is separated into two polarization components that are substantially orthogonal to each other using a polarization beam splitter 7, and each is separated by a separate photodetector 8,
The light is received at 9. However, at this time, the signals detected by the photodetectors 8 and 9 include not only information signals recorded on the magneto-optical recording film 3, but also information signals from magneto-optical disks made of resin materials such as polycarbonate. Birefringence of the substrate and lens 4
This includes fluctuations in polarization components due to phase differences in optical systems such as the beam splitters 5 and 7, and the like. In particular, the birefringence of the substrate of a magneto-optical disk changes greatly depending on the temperature of the disk substrate. These fluctuations affect the information signals originally recorded on the magneto-optical disk by causing signal amplitude fluctuations and peak shifts. In the present invention, the output difference of the signal amplifier 10.10 that amplifies the output of the photodetector 8.9 is detected by the DC differential amplifier 11 that detects the DC component, and the control signal amplifier 10.10 is The amplification factor of the DC differential amplifier 11 is controlled such that the output of the DC differential amplifier 11 becomes O. At this time, the reference amplification factor of the signal amplifier 10.10 and the offset voltage of the DC differential amplifier 11 are calibrated in advance using a disk with little birefringence, and the reference position is set. In this way, when a disc with birefringence is reproduced, one of the two signal amplifiers 10.10 adjusts the amplification factor with respect to the reference amplification factor according to the output of the DC differential amplifier 11. The other serves to lower the amplification factor relative to the reference amplification factor. As a result, the output of the DC differential amplifier 11 becomes 0, and the noise of the output of the AC differential amplifier 12 that produces the reproduced signal is canceled by the differential amplifier 12.
A reproduced signal output 13 with uniform signal amplitude can be obtained.

Originally, the control band of the DC differential amplifier 1 used in the present invention should be set to cover the entire frequency range in which birefringence fluctuations occur. However, depending on the signal modulation method, the signals actually recorded on magneto-optical storage media have a certain degree of low frequency components, and the frequency band of the AC differential amplifier that reproduces the signal is usually a certain degree of low frequency. It is set wide on the side. Therefore, when the low cutoff frequency of this AC differential amplifier 12 is fL, the high cutoff frequency of the DC differential amplifier 11 that detects the influence of birefringence of the substrate in the magneto-optical reproducing apparatus of the present invention is It is most effective to set the control frequency band from DC to fL.

In the above embodiments, the magneto-optical disk (magneto-optical storage medium) is of a reflective type, but the present invention is also applicable to a transmissive type.

Effects of the Invention As is clear from the above explanation, by using the method and apparatus of the present invention, the photodetector can be Even when the output of a and a large signal regeneration margin.
It is possible to realize a highly reliable magneto-optical information reproducing method and apparatus, and at the same time, it is possible to achieve the effect that the polarization characteristics of the optical system can be made unadjusted.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the magneto-optical information reproducing apparatus of the present invention, and FIG. 2 is a block diagram showing a conventional example of the same apparatus. 1... Laser light source (light source), 2...
Magneto-optical disk (magneto-optical storage medium), 4...lens, 5...beam splitter, 6...
・Reflected light, 7...Polarizing beam splitter, 8,
9...Photodetector, 10...Signal amplification equipment, 11...DC differential amplifier, 12...
- AC differential amplifier, 13... Reproduction signal output.

Claims (4)

[Claims] (1) When reproducing a signal from a magneto-optical storage medium, the difference in the amount of light between two polarized components that are substantially perpendicular to each other in the light reflected or transmitted from the magneto-optical storage medium is detected, and the difference in the amount of polarized light is determined based on the difference in the amount of light. A magneto-optical information reproducing method characterized by controlling a differential input signal during differential detection of components. (2) a light source, a first optical system that guides a light beam emitted from the light source, a magneto-optical storage medium, and two mutually orthogonal polarization components of the light beam reflected or transmitted from the magneto-optical storage medium; a second optical system that separates the second optical system;
two photodetectors that respectively detect the light intensities of the two polarized components separated by the optical system; and a DC differential amplifier that calculates the difference between the photocurrent signals obtained by the two photodetectors. and an AC differential amplifier for determining the difference between the photocurrent signals obtained by the two photodetectors, and the output signals of the two photodetectors are input to the AC differential amplifier by the output of the DC differential amplifier. 1. A magneto-optical information reproducing device configured to control. (3) Set the high cutoff frequency of the DC differential amplifier to
3. The magneto-optical information reproducing apparatus according to claim 2, wherein the low cutoff frequency of the differential amplifier is substantially the same as that of the differential amplifier. (4) As a means of controlling the output signals of the two photodetectors that are input to the AC differential amplifier, the amplification factor of the output signals of the two photodetectors is changed by the output of the DC differential amplifier. 3. The magneto-optical information reproducing apparatus according to claim 2, further comprising means for supplying the signal to said AC differential amplifier via a variable gain amplifier.