JPH04298836A - Magneto-optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the C/N of reproducing information and to simplify the structure of an optical pickup by electrically correcting double refractivity on the transparent base board of the magneto-optical disk. CONSTITUTION:A luminous flux from the magneto-optical disk 1 is distributed between a pair of optical detectors 19a, 19b. A pair of level control circuits 24, 25 to obtain the double refractivity information in relation with the transparent base board 1b of the magneto-optical disk based on respective low range components of detected outputs from the optical detectors, and simultaneously, to control differentially the levels of respective high range components with the detected outputs from both optical detectors is provided. By controlling the level control curcuits with the double refractivity information, the reproducing information correcting the double refractivity on the transparent base board electrically is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording and reproducing apparatus.

0002

Conventionally, in a magneto-optical recording device, a suitable magneto-optical recording material such as a transition metal is magnetized in the perpendicular direction, and the magneto-optical recording material is irradiated with laser light under an external magnetic field. Information is recorded by reversing the direction of magnetization. This recorded information is optically read out using a phenomenon in which the plane of polarization of linearly polarized light rotates in proportion to perpendicular magnetization (magnetic Kerr effect in the case of reflected light). usually,
The recording medium is formed into a disk shape, and the carrier that supports the magneto-optical recording layer is generally made of transparent synthetic resin with good heat and moisture resistance, such as polycarbonate resin, as in the case of digital audio discs. used for.

0003

However, polycarbonate resin has a relatively large optical anisotropy (birefringence), and when reproducing magneto-optical recording, the plane of polarization changes when the readout light passes through the carrier. There is a problem in that unnecessary rotation occurs, noise is generated due to this unnecessary rotation, and the C/N of reproduced information deteriorates. However, in the disc molding process, the temperature of the resin and mold, the injection pressure, etc. are carefully controlled, and although discs are shipped with the amount of birefringence kept within a predetermined standard value, It is extremely difficult to make refraction uniform.

In order to solve the above-mentioned problem of C/N deterioration of reproduced information due to the optical anisotropy of the carrier, the present applicant has published Japanese Patent Application Laid-Open No. 2-260255 (Japanese Patent Application No. −
No. 83079), a birefringence corrector for optically correcting birefringence is inserted in the reproduction optical system, and a birefringence information forming circuit is provided for forming birefringence information based on light read from the medium. A magneto-optical recording and reproducing device has already been proposed in which a birefringence corrector is controlled according to birefringence information.

First, a previously proposed magneto-optical recording/reproducing device will be described with reference to FIGS. 2 to 5.

In FIG. 2, reference numeral 1 denotes a magneto-optical disk, in which a magneto-optical recording layer 1a is formed on a carrier (substrate) 1b made of polycarbonate resin. Reference numeral 10 denotes an optical pickup, in which the light beam emitted from the laser diode 11 is transmitted through a collimator lens 12, a beam splitter 13,
After passing through the objective lens 14, the recording layer 1a of the magneto-optical disk 1 is
incident on .

The reflected light flux from the recording layer 1a passes through the objective lens 14 and enters the beam splitter 13 again, and the reflected light flux from the beam splitter 13 is polarized by a λ/2 plate (birefringence corrector) 15. The plane is rotated 45 degrees,
A p-polarized light beam Lp enters the polarizing beam splitter 16 and vibrates parallel to the plane of incidence, and s vibrates perpendicular to the plane of incidence.
It is separated into a polarized light beam Ls. Beam splitter 16
The amount of light of each of the light beams Lp and Ls separated at
They each correspond to the sum of the amount of unnecessary rotation of the plane of polarization due to birefringence of the substrate 1b, and change differentially.

One of the light beams Lp separated by the beam splitter 16 passes through the condensing lens 17a and the cylindrical lens 18.
a, the light beam Ls enters one photodetector 19a, and the other light beam Ls passes through the condenser lens 17b and the cylindrical lens 18b.
The light then enters the other photodetector 19b. Photodetector 1
As shown in FIG. 3, the photodetectors 9a and 19b are each equipped with four-split detection elements A to D, and from the photodetectors 19a and 19b, light beams Lp of p-polarized light and light beams Ls of s-polarized light are detected, respectively. , a detection signal Sp of the sum of detection outputs of all detection elements,
Ss is output.

Reference numeral 20 denotes a recorded information reproducing circuit, and 30 denotes a birefringence detection circuit, each of which is equipped with differential amplifiers 21 and 31. 23, to the differential amplifier 21, and through low-pass filters 32, 33.
The signal is supplied to the differential amplifier 31. A reproduction signal of recorded information is derived from the differential amplifier 21, and the output of the differential amplifier 31 is supplied to the drive coil 15c of the birefringence corrector 15 via the servo circuit 34.

As shown in FIG. 4A, when the light beam from the pickup 10 scans the recording track TK on the magneto-optical disk 1, the angular positions (...θ1, θ2, θ3,
When the pickup light beam illuminates θ4...), the birefringence of the substrate 1b at each angular position (...θ1, θ2, θ3, θ4...) is a three-dimensional refractive index ellipse, as shown in Figure B. field vector (...n1 , n2 , n3
, n4...), and varies in various directions as a characteristic specific to the polycarbonate used.

This variation in birefringence can be observed when the birefringence corrector 15 is fixed without being rotated, and each photodetector 19a, 19
When detected at point b, a curve K shown in FIG. 5 is obtained for one round of the recording track.

Such a fluctuation component of the detection signal due to the birefringence of the substrate 1a exists in a relatively low frequency band up to about 300 kHz. On the other hand, the recorded information component of the magneto-optical recording layer 1a of the disk 1 ranges from about 300 kHz to several MHz.
It exists in a relatively high frequency band up to.

In the conventional example shown in FIG. 2, the birefringence corrector 15 disposed in the optical pickup 10 is rotated about the optical axis of the condensing lens 17a by the output of the birefringence detection circuit 30, and the birefringence corrector 15 is rotated about the optical axis of the condensing lens 17a. Unnecessary rotation of the plane of polarization due to birefringence of the substrate 1a of the magnetic disk 1 is optically corrected to achieve a predetermined C//
N playback information is obtained. Therefore, in the conventional example shown in FIG. 2, there were problems in that the configuration of the optical pickup became complicated and the price increased.

In view of the above, an object of the present invention is to improve the C/N of reproduced information without the need to optically correct birefringence in the transparent substrate of a magneto-optical disk, and to simplify the structure of an optical pickup. An object of the present invention is to provide a magneto-optical recording and reproducing device whose cost is reduced.

[0015]

[Means for Solving the Problems] The present invention provides an optical pickup that irradiates a pickup light beam onto a magneto-optical recording medium 1 and distributes the light beam from the magneto-optical recording medium to a pair of photodetectors 19a and 19b; A reproduction circuit that reproduces information recorded on the magneto-optical recording medium based on each high-frequency component of the detection output of the pair of photodetectors, and a reproduction circuit that reproduces information recorded on the magneto-optical recording medium based on each low-frequency component of the detection output of the pair of photodetectors. In a magneto-optical recording and reproducing apparatus including a birefringence information forming circuit 30 that forms birefringence information regarding a carrier of a magneto-optical recording medium, the level of each high-frequency component of the detection output of a pair of photodetectors is differentiated. This is a magneto-optical recording and reproducing apparatus which is provided with level control circuits 24 and 25 for controlling the birefringence information, and which is controlled by the output of a birefringence information forming circuit.

[0016]

[Operation] According to the present invention, there is no need to optically correct birefringence in the transparent substrate of the magneto-optical disk, the C/N of reproduced information can be improved, and the structure of the optical pickup can be simplified. , the price is reduced.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the magneto-optical recording and reproducing apparatus according to the present invention will be described below with reference to FIG.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, parts corresponding to those in FIG. 2 are given the same reference numerals and redundant explanation will be omitted.

In FIG. 1, 10F is an optical pickup, and in this embodiment, a fixed λ/2 plate 1 is used instead of the movable birefringence corrector 15 used in the conventional example shown in FIG.
5f is arranged between both beam splitters 13 and 16. 20C is a recorded information reproducing circuit, and in this embodiment,
A pair of voltage control coefficient multipliers 24 and 25 are inserted between the input terminal of the differential amplifier 21 and the high-pass filters 22 and 23. The voltage control coefficient multipliers 24 and 25 are supplied with the output of the birefringence detection circuit 30. The rest of the configuration is the same as that shown in FIG. 2 above.

The operation of one embodiment of the present invention is as follows. As shown in FIG. 1, the coefficients of the voltage control coefficient multipliers 24 and 25 are set to k (0<k<1), 1-k, and both coefficients k, 1-k are determined by the output of the birefringence detection circuit 30. are controlled differentially with respect to each other, and the sum of the outputs of each coefficient multiplier 24 and 25 is made a constant value.

As described above, the amount of light beams Lp and Ls separated by the beam splitter 16 is
They correspond to the sum of the normal rotation amount of the polarization plane by the magneto-optical recording layer 1a and the unnecessary rotation amount of the polarization plane due to the birefringence of the substrate 1b, and change differentially. When the amount of positive rotation of the plane of polarization increases due to a change in the birefringence of the substrate 1b, for example, the amount of light of one light beam Lp increases and the amount of light of the other light beam Ls decreases. Corresponding to this increase/decrease in the amount of light, the level of the output Sp of one photodetector 19a increases, the level of the output Ss of the other photodetector 19b decreases, and the level of the output of the birefringence detection circuit 30 increases. descend.

The level drop of the output of the detection circuit 30 is as follows:
The coefficient k of one voltage control coefficient multiplier 24 is decreased, and the coefficient 1-k of the other voltage control coefficient multiplier 25 is increased. As a result, in one coefficient unit 24, the output Sp of the photodetector 19a is supplied via the high-pass filter 22.
At the same time, in the other coefficient multiplier 25, a decrease in the level of the output Ss of the photodetector 19b, which is supplied via the high-pass filter 23, is canceled out.

Contrary to the above, when the amount of positive rotation of the plane of polarization decreases due to the birefringence of the substrate 1b, one of the light beams Lp
The amount of light of the other light beam Ls decreases, the amount of light of the other light beam Ls increases, the level of the output Sp of one photodetector 19a decreases, and the level of the output Ss of the other photodetector 19b increases. Then, the level of the output of the birefringence detection circuit 30 rises, and the coefficient k of one voltage control coefficient multiplier 24 increases, and the coefficient 1-k of the other voltage control coefficient multiplier 25 decreases. 24, 25, corresponding photodetectors 19a, 1
The level fluctuations of the outputs Sp and Ss of 9b are canceled out.

As described above, the differential amplifier 21 obtains a reproduced signal with a predetermined high C/N in which variations in the birefringence of the substrate 1b of the disk 1 are electrically compensated. In addition, since variations in birefringence are electrically compensated, shipping standards for the amount of birefringence of the substrate in the disk molding process can be relaxed, making various management easier and reducing disk costs. .

[0025]

[Effects of the Invention] As detailed above, according to the present invention,
A pair of photodetectors 19a,
19b, and based on each low frequency component of the detection output of this photodetector, birefringence information regarding the transparent substrate 1b of the magneto-optical disk is obtained, and the level of each high frequency component of the detection output of both photodetectors is obtained. A pair of level control circuits 24 and 25 are provided to differentially control the level control circuits 24 and 25, and this level control circuit is controlled by birefringence information to obtain reproduction information in which birefringence in the transparent substrate is electrically corrected. Therefore, the C/N of playback information
A magneto-optical recording/reproducing device is obtained in which the optical pickup can be improved and the structure of the optical pickup can be simplified.

[Brief explanation of drawings]

[Fig. 1] A block diagram showing the configuration of an embodiment of a magneto-optical recording/reproducing device according to the present invention.

[Figure 2] Block diagram showing a configuration example of a conventional magneto-optical recording/reproducing device

[Figure 3] Schematic plan view showing the configuration of the main parts of the conventional example

[Fig. 4] Perspective view for explaining this invention

[Figure 5]
Diagram for explaining this invention

[Explanation of symbols]

10F Optical pickup 11 Laser diode 16 Polarizing beam splitter 19a, 19b Photodetector 20C Information detection circuit 24, 25 Voltage control coefficient unit (level control circuit) 30
Birefringence detection circuit

Claims (1)

[Claims] 1. An optical pickup that irradiates a magneto-optical recording medium with a pickup light beam and distributes the light beam from the magneto-optical recording medium to a pair of photodetectors, and each detection output of the pair of photodetectors. a reproducing circuit that reproduces information recorded on the magneto-optical recording medium based on the high-frequency components; and a reproducing circuit that reproduces information recorded on the magneto-optical recording medium based on the high-frequency components; A magneto-optical recording/reproducing device comprising a birefringence information forming circuit for forming birefringence information regarding the above, and a level control circuit for differentially controlling the level of each high frequency component of the detection output of the pair of photodetectors. 1. A magneto-optical recording and reproducing apparatus, characterized in that the level control circuit is controlled by the output of the birefringence information forming circuit.