JPH02260255A - Magneto-optical reproducing device - Google Patents

Abstract

PURPOSE:To evade mixing a noise component based on birefringence into a regenerative signal by correcting rotation of a plane of polarization generated in detecting flux of light based on birefringence of a magneto-optical recording medium by means of a correcting servo system of birefringence using a birefringence corrector. CONSTITUTION:The subject device is provided with the birefringence corrector 14 to be inserted into an optical path of the detecting flux of light LA11 and capable of rotating the polarizing direction of the detecting flux of light LA11 and a correcting servo means 31 for generating a correcting servo output IDRV to the birefringence corrector 14 based on photoelectric transducing signals S1 and S2. Then, when the detecting flux of light LA11 is rotated in the polarizing direction by varying the birefringence on the magneto-optical recording medium 2, a turning control on the birefringence corrector 14 is performed correspondingly by the correcting servo means 31, so that the rotating position is brought by the turning control so as to eliminate a birefringence signal component contained in the photoelectric transducing signals S1 and S2. By this method, the mixing of a noise component due to the birefringence is evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a magneto-optical reproducing device, and is particularly intended to reduce noise due to birefringence of a recording medium.

B. Summary of the Invention The present invention provides a magneto-optical reproducing device in which the birefringence corrector is controlled by a correction servo system, so that even if there is a change in birefringence in the magneto-optical recording medium, the effect of this change is not affected by the reproduction signal. This can effectively avoid the possibility that this may occur.

C. Conventional technology In magneto-optical recording and reproducing devices, it has been proposed to use a synthetic resin material such as polycarbonate as a recording medium. Although it has excellent functionality, it has a characteristic that when the pickup light beam passes through it, the polarization plane of the pickup light beam is rotated due to birefringence.

D Problems to be Solved by the Invention However, the magneto-optical recording and reproducing method is based on the principle of reading out the magneto-optical recorded information by rotating the plane of polarization of the pickup light beam, which is linearly polarized light, by the magneto-optical recorded information. Therefore, when using a substrate with characteristics that cause birefringence, when the birefringence of the substrate changes, the CM
This may cause deterioration of RR (common mode rejection ratio), which may cause deterioration of C/N of the reproduced signal.

Incidentally, if the birefringence of the substrate does not vary and the polarity is constant, it is sufficient to construct a pickup optical system that matches the optical conditions of the substrate, but in reality, polycarbonate
Even if the injection pressure, mold temperature, resin temperature, etc. are appropriately controlled during manufacturing, it is extremely difficult to make the three-dimensional refractive index within the substrate uniform.

In particular, the pickup light beam is actually collimated into a tiny light spot by an objective lens to increase the recording density, and therefore some light rays forming the pickup light beam are incident on the substrate from an oblique direction. Controlling this is extremely difficult.

In fact, in conventional magneto-optical recording and reproducing devices, efforts have been made to use substrates whose birefringence does not exceed a predetermined reference value. This is still insufficient.

The present invention has been made in consideration of the above points, and we would like to propose a magneto-optical reproducing device that can reliably reduce the influence of birefringence on the reproduced signal even if the substrate of the magneto-optical recording medium has birefringence. That is.

E Means for Solving the Problem In order to solve this problem, in the present invention, the detection light beam LAII obtained from the magneto-optical recording medium 2 is converted into photoelectric conversion signals S1 and S2 in the photodetection means 19.22,
The reproduced output signal S is based on the photoelectric conversion signals S1 and S2.
, 4°, the detection light flux L
A birefringence corrector 14.41 that is inserted in the optical path of AII and rotates the polarization direction of the detected light beam LAII, and a correction servo output for the birefringence corrector 14.41 based on the photoelectric conversion signals S1 and S2 ■□VI % Iotvt.

When the rotation of the polarization direction occurs in the detected light beam LAII due to variations in birefringence in the F-action magneto-optical recording medium 2, the correction servo means 31 and 42 adjust the birefringence corrector 14 accordingly.
．． By controlling the rotation of 41, the photoelectric conversion signals S1, S
The rotation is controlled to a rotational position that removes the birefringence signal component contained in 2.

In this way, it is possible to effectively avoid the noise component based on birefringence from being mixed into the photoelectric conversion signal, and thereby it is possible to obtain a reproduced output signal S, 4° with a good C/N ratio.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

(G1) First Embodiment In FIG. 1, l indicates a magneto-optical reproducing device as a whole, and has a structure in which a magneto-optical recording layer 2B is formed on two substrates made of polycarbonate as a magneto-optical disk 2. A pickup light beam LAO is emitted from the pickup optical system 3.

The optical pickup optical system 3 converts the emitted light LA1 of the laser diode 11 as a light source into a parallel light beam LA2 using a collimator lens 12, and inputs the parallel light beam LA2 into a polarizing beam splitter 13. The birefringence corrector 14 performs rotational correction, and the emitted light beam LA4 is focused on the magneto-optical recording layer 2B through the objective lens 15 as a pickup light beam LAO.

As a result, the optical information beam LA whose polarization plane is rotated by the magneto-optical recording information when reflected at the magneto-optical recording layer 2B.
II, the detection light flux is converted into a parallel light flux LA12 by the objective lens 15, the polarization plane is again corrected by rotation in the posterior ventral refraction corrector 14, and the emitted light flux LA13 is reflected at the polarizing beam splitter 13 to become a reflected light flux LA.
Pull out 14.

The reflected light beam LA14 has its polarization plane rotated by 45 degrees by the λ/2 plate 15 as a detection light beam, and the emitted light beam LA15 is separated into a p-wave beam LA16 and an S-wave beam LA17 at the polarizing beam splitter 16, and the p-wave beam LA16 is The S-wave light flux LA1 passes through the condensing lens 17 and the cylindrical lens 18 and enters the first photodetector 19.
7 passes through the condensing lens 20 and the cylindrical lens 21 and enters the second photodetector 22.

In this way, the first and second photodetectors 19 and 22 detect that the pickup light beam LAO has the rotation amount of the plane of polarization given by the magneto-optical recording information of the magneto-optical recording layer 2B and the polarization given by the birefringence of the substrate 2A. The p-wave light beam LA16 and the S-wave light beam LA17, which have a light amount corresponding to the sum of the amount of rotation of the surface and whose light amounts change differentially, are converted into photoelectric conversion signals S1 and S2 and sent out.

In this embodiment, the first and second photodetectors 19 and 2
2 has four divided detection elements A-D as shown in FIGS. 2(A) and (B), and each detects a sum signal (A+B+C+D).
are obtained as photoelectric conversion signals S1 and S2 and inputted to the information detection circuit 25 and the birefringence detection circuit 26, respectively.

The information detection circuit 25 receives the photoelectric conversion signals S1 and S2 through the bypass filters 25A and 25B, respectively, into the differential amplifier circuit 25C, and sends out the differential output as the reproduced signal SMO.

On the other hand, the birefringence detection circuit 26 outputs the photoelectric conversion signal S1
and S2 are low pass filters 26A and 26B, respectively.
is received by the differential amplifier circuit 26C, and the differential output thereof is sent out as a birefringence detection signal SCP.

Here, among the signal components of the photoelectric conversion signals S1 and S2, the optical information beam LA having the magneto-optical recording information of the magneto-optical recording layer 2B
The signal component corresponding to II is 300 [kHz] to several [
MHz], while the substrate 2A
The fluctuation component due to birefringence is from DC to 300 [kHz]
It has a low frequency of about. Thus, the birefringence detection signal SC
P is a reproduction signal S. . The signal is frequency-separated and sent out from the birefringence detection circuit 26.

Here, the birefringence corrector 14 is rotatably supported around the optical axis of the objective lens 15, and a drive current I DIVI is supplied from the correction servo drive circuit 31 to the drive electromagnetic coil 32.
The rotation of the birefringence corrector 14 can be controlled by supplying the birefringence corrector 14.

The birefringence detection signal SCP is supplied as a correction servo signal to the correction servo drive circuit 31, and a drive current I□ is obtained by superimposing the wobbling signal SWV sent from the wobbling signal generation circuit 33 on the birefringence detection signal Sc. Send □.

Thus, the correction servo drive circuit 31 receives the wobbling signal S.
The electromagnetic coil 32 is driven by a drive current component based on WV.
When the birefringence corrector 14 is caused to wobble in the rotational direction through the oscilloscope, and as a result the birefringence detection signal SCF changes in the same direction as the wobbling signal SHw, the birefringence detection signal SCF is suppressed. By generating a drive current I□v1 such that the birefringence corrector 14 becomes O, the birefringence corrector 14 is operated by correction servo to a position where the birefringence detection signal SCP becomes O.

In the above configuration, as shown in FIG. 3(A), when the pickup light beam LAO scans the recording track TR on the magneto-optical disk 2, the angular position (... θ3
, θ2. θ1. When the pickup light beam LAO irradiates the angular position (......θ4...), the angular position (......θ
, θt, θ3, θ4...)
The birefringence of is expressed as a three-dimensional index ellipsoid vector (... nl, nt, n3, n4
The birefringence expressed by ...), and as a characteristic unique to the polycarbonate used,
Fluctuations in various directions.

When this variation in birefringence is detected by the first and second photodetectors 19 and 22 with the birefringence corrector 14 fixed without rotation, it follows a curve as shown in FIG. It can be detected as a change.

In the configuration shown in FIG. 1, the birefringence detection circuit 26 is connected to the photodetector 1.
A correction servo loop consisting of three correction servo drive circuits, a drive electromagnetic coil 23, and a birefringence corrector 14 is created by sending out a birefringence detection signal SCP representing the birefringence variation occurring in the photoelectric conversion signals S1 and S2 of 9 and 22. The rotational positions of the planes of polarization of the exit light beam LA4, which becomes the pickup light beam LAO, and the exit light beam LA13, which becomes the product light beam, are corrected through the change in the photoelectric conversion signals S1 and S2 based on birefringence as described above with respect to FIG. The birefringence corrector 14 is rotationally controlled to a rotational position that does not cause the birefringence.

By performing the correction operation of the birefringence corrector 14 in this way, when there is no birefringence correction servo loop, the change occurring in the photoelectric conversion signals S1 and S2 is caused by the change in the magneto-optical recording layer 2.
Among the magneto-optical recording information component read from B, a fluctuation component caused by the influence of birefringence of the substrate 2A, and a wobbling component generated based on the wobbling signal SWV,
By correcting the fluctuation components generated based on the change in birefringence of the substrate 2A and the change in the wobbling signal S@V, the p-wave light fluxes LA16 and S that ultimately irradiate the first and second photodetectors 19 and 22 are The fluctuation components of the wave light flux LA17 are substantially only those corresponding to the recorded information read from the magneto-optical recording layer 2B.

Incidentally, since the birefringence corrector 14 is composed of a λ/2 plate, the light emitted from the polarizing beam splitter 13 through the birefringence corrector 14 as the pickup light beam LAO undergoes birefringence again as the optical information light beam LA11. The relationship between the planes of polarization when passing through the corrector 14 and returning to the polarizing beam splitter 13 is designed so that it does not change even if the birefringence corrector 14 rotates (rotation of the plane of polarization by the birefringence corrector 14). is one wavelength (=λ)).

According to the above configuration, by providing the birefringence corrector 14 and its correction servo loop, even if a change in birefringence occurs in the substrate 2A, it is practically possible for the light to enter the photodetectors 19 and 22. By avoiding the possibility of causing fluctuations in the light intensity of the p-wave beam LA16 and the S-wave beam LA17, it is possible to output a reproduction signal S, 4° that corresponds with high precision to the recorded information read from the magneto-optical recording layer 2B. I can do it.

(G2) Second Embodiment FIG. 5 shows a second embodiment. As shown by assigning the same reference numerals to corresponding parts as in FIG. A birefringence corrector 41 is provided, and the drive current I Dl of the correction servo drive circuit 42 is
llll! Rotation control is performed around the optical axis of the emitted light beam LA14 by a drive electromagnetic coil 43 supplied with the light beam LA14.

In the configuration shown in FIG. 5, when the birefringence detection signal SCP is obtained in the birefringence detection circuit 26, by supplying the drive current I DIIVR to the drive electromagnetic coil 43 such that the birefringence detection signal SCP becomes O. , the rotational position of the birefringence corrector 41 is servo operated.

This birefringence correction servo operation is executed each time the amount of birefringence of the substrate 2A of the magneto-optical disk 2 changes and the polarization direction of the detection light beam LA14 rotates. The S-wave beam LA17 can be configured so as not to include a change due to the change in birefringence.

In this way, the information detection circuit 25 can output the reproduced signal S14° based on the photoelectric conversion signals S1 and S2 that are not affected by the birefringence of the substrate 2A.

According to the configuration shown in FIG. 5, even if there is a variation in the birefringence inherent to the two substrates of the magneto-optical disk 20, this is absorbed by the detection light beam that is extracted from the optical system between the laser diode 11 and the magneto-optical disk 2. The LA 14 can be corrected by a birefringence correction servo system, and thereby can be effectively removed so as not to be mixed into the reproduced signals S and o.

(G3) Other Embodiments (1) In the embodiments shown in FIGS. 1 and 5, in order to obtain the photoelectric conversion signals S1 and S2, the emitted light beam LA15 as the detection light beam is sent to the polarization beam splitter 16 into the p-wave light beam LA16. and an S-wave beam LA17, and a condenser lens 17, a cylindrical lens 18, and a photodetector 1 for the p-wave beam LA16 and the S-wave beam LA17, respectively.
9, and a condenser lens 20. Although the configuration is configured to use the cylindrical lens 21 and the photodetector tS22, instead of this, as shown in FIG. Other configurations may be applied, such as a configuration in which the light is incident on the photodetectors 42 and 43.

Effects of the Invention As described above, according to the present invention, the rotation of the plane of polarization that occurs in the detected light beam based on the birefringence of the magneto-optical recording medium is corrected by a birefringence correction servo system using a birefringence corrector. By doing so, it is possible to effectively avoid the possibility of noise components being mixed into the reproduced signal based on birefringence.

A system diagram showing an example, FIG. 2 is a route diagram for explaining the photodetectors 19 and 22, and FIGS. 3 and 4 are for explaining variations in birefringence occurring in the substrate of a magneto-optical disk and its effects. The route map, signal waveform diagram, and FIGS. 5 and 6 are system diagrams showing other embodiments.

1... magneto-optical reproducing device, 2... magneto-optical disk, 13.16... polarizing beam splitter, 14.41... birefringence corrector, 25...
... Information detection circuit, 26 ... Birefringence detection circuit, 31.42 ... Correction servo drive circuit, 33.
...Wobbling signal generation circuit, 32.43...
...Drive electromagnetic coil.

Claims (1)

[Scope of Claims] A magneto-optical reproducing device that converts a detection light flux obtained from a magneto-optical recording medium into a photoelectric conversion signal in a photodetection means and sends out a reproduction output signal based on the photoelectric conversion signal, comprising: A birefringence corrector inserted in an optical path and rotating the polarization direction of the detection light beam; and a correction servo means generating a correction servo output for the birefringence corrector based on the photoelectric conversion signal. A magneto-optical reproducing device.