JPH04263147A - Magneto-optical disc apparatus - Google Patents

Abstract

PURPOSE:To record information with high density by a method wherein a light emitted by an SHG device is applied to a magneto-optical disc without being subjected to optical modulation. CONSTITUTION:A light from a solid state laser 3 is applied to an SHG device 4 to make the SHG device 4 emit a light having a very short wavelength. A light emitted by the SHG device 4 is applied to a liquid crystal shutter LC and the output of the light passed through the liquid crystal shutter LC is varied by controlling the light transmissivity of the liquid crystal shutter LC. The light output is made to be maximum when information is recorded and is made to be minimum when information is reproduced. The direction of a magnetic field generated by a magnetic coil 20 is changed in accordance with the recording signal of the information. The magnetic field generated by the magnetic coil 20 is supplied to the position of an optical disc to which the light passed through the liquid crystal shutter LC to record the information.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a magneto-optical disk device that records or reproduces information on a magneto-optical disk by projecting light from a light source that generates the second harmonic of incident light onto a magneto-optical disk. It is related to.

0002

[Prior Art] A magneto-optical disk has a structure in which information is recorded by projecting a laser beam onto a position where information is to be recorded, heating it, and magnetizing the heated position in a direction according to a recording signal. ing. By the way, in a magneto-optical disk device that records information on such a magneto-optical disk,
Efforts are being made to reduce the recording bit size and improve the areal recording density by shortening the wavelength of laser light. However, it is very difficult to achieve a wavelength shorter than the 0.6 μm band of He-Ne laser in semiconductor lasers, and SHG (Second Wavelength), which can obtain the second harmonic, is extremely difficult to achieve.
Magneto-optical disk devices have been developed that record or reproduce information using the 2nd Harmonic Generation).

FIG. 5 is a block diagram showing the main part configuration of a magneto-optical disk device that has already been developed. The excitation laser diode 1 is controlled by a laser diode drive circuit 2. The light emitted from the excitation laser diode 1 is YAG.
The light is incident on a solid-state laser 3 consisting of a laser, and the emitted light is an SHG element 4 that generates a second harmonic due to a nonlinear effect.
is incident on the The light emitted from the SHG element 4 is an AO (Acoustic Optical) that utilizes the photoacoustic effect.
It passes through a modulator 5 and a beam splitter 6 and is projected onto a mirror 7. The light reflected by the mirror 7 passes through the condenser lens 8 and is projected onto the magneto-optical disk 9. The magneto-optical disk 9 is rotationally driven by a disk motor 10. On the side opposite to the surface on which light is projected onto the magneto-optical disk 9, there is a magnet 12 for initialization and recording that applies a magnetic field to the magneto-optical disk 9.
is provided. The magnet 12 is used by switching its polarity when recording and erasing information.

The reflected light from the magneto-optical disk 9 passes through a condensing lens 8 and is reflected by a mirror 7, and is then sent to a beam splitter 6.
The light is reflected there, passes through the λ/2 plate 13 , and enters the polarizing beam splitter 14 . The light that has passed straight through the polarizing beam splitter 14 is incident on the first photodetector 15, and the reflected light is incident on the second photodetector 16. The first photodetector and the second photodetector 15 and 16 convert the received light into an electrical signal, and the converted electrical signal is sent to the positive and
The playback signal SR is input separately to the negative input terminals + and -.
It is designed to output . A recording/reproducing switching signal SS for switching to an information recording operation or an information reproducing operation and a recording signal SW for recording information are given to the optical output control section 18 , and the output signal is inputted to the AO modulator drive circuit 19 . The output signal of the AO modulator drive circuit 19 is given to the AO modulator 5.

Next, the operation of this magneto-optical disk device will be explained. When the excitation laser diode 1 is driven by the laser diode drive circuit 2, the excitation laser diode 1
emits laser light and projects the emitted light onto the solid-state laser 3. The solid-state laser 3 emits light with a short wavelength of 1.06 μm and projects it onto the SHG element 4 . The SHG element 4 emits light of 0.53 μm, which is 1/2 the wavelength of the incident light. This light passes through an AO modulator 5 and a beam splitter 6, is reflected by a mirror 7, passes through a condenser lens 8, and is projected onto a magneto-optical disk 9 which is being rotated by a disk motor 10. On the other hand, in a state where the recording/reproduction switching signal SS for the recording operation is being applied, the output signal of the optical output control section 18 to which the recording signal SW is applied causes the
The AO modulator drive circuit 19 is controlled according to the recording signal SW, and the AO modulator 5 is controlled by its output signal. Thereby, the light from the SHG element 4 is transferred to the AO modulator 5.
modulates the light according to the recording signal SW.

Then, the optically modulated light is projected onto the magneto-optical disk 9, and the magnetic field of the magneto-optical disk 9 is adjusted according to the optical output changing due to the optical modulation and the magnetic field generated by the recording magnet 12.
record information. Further, when the recording/reproducing switching signal SS for starting the reproducing operation is given to the optical output control section 18, the output signal of the AO modulator drive circuit 19 is controlled to be constant by the output signal, thereby causing the AO modulator 5 to operate. do,
The light from the SHG element 4 is controlled to a predetermined low power and projected onto the magneto-optical disk 9. The reflected light passes through the condenser lens 8 and is reflected by the mirror 7, and then is reflected by the beam splitter 6 and passes through the λ/2 plate 13, thereby rotating the polarization plane of the reflected light by 45 degrees. 14. The light beam is split into two by the polarizing beam splitter 14 and sent to the first and second photodetectors 15 and 16.
incident on . The DC component of the amount of light incident on the first and second photodetectors 15, 16 is equal for both light fluxes, and the AC component, which is a reproduced signal, appears in opposite phases to each other on the first and second photodetectors 15, 16. Therefore, by obtaining the differential signals of the first and second photodetectors 15 and 16 with the differential amplifier 17, a reproduced signal SR corresponding to the recorded magneto-optical signal pit can be obtained.

[0007]

[Problems to be Solved by the Invention] By the way, the above-mentioned magneto-optical disk device converts the light emitted from the SHG element 4 into
It is necessary to use an expensive AO modulator 5 to record information by modulating light according to the recording signal SW. Therefore, there is a problem in that the magneto-optical disk device inevitably becomes larger and more expensive. In view of such problems, the present invention
It is an object of the present invention to provide a small and inexpensive magneto-optical disk device using an inexpensive liquid crystal shutter without using an expensive AO modulator.

[0008]

[Means for Solving the Problems] A magneto-optical disk device according to the present invention includes a liquid crystal shutter for projecting light emitted from a light source that generates the second harmonic of incident light, and controls the light transmittance of the liquid crystal shutter. and a magnetic field generating section that generates a magnetic field in a direction corresponding to a recording signal on the magneto-optical disk.

[0009]

[Operation] Light from a light source that generates the second harmonic of incident light is projected onto a magneto-optical disk through a liquid crystal shutter. When the liquid crystal shutter is controlled by the output signal of the control unit that is output in response to the recording/reproduction switching signal that commands the operation of recording or reproducing information, the light transmittance of the liquid crystal shutter changes depending on whether the recording or reproducing operation is performed.
The optical output of the light projected onto the magneto-optical disk changes depending on the playback operation. When a recording signal is given to the magnetic field generating section, the direction of the magnetic field generated by the magnetic field generating section changes according to the recording signal, and the position where light is projected onto the magneto-optical disk is magnetized according to the magnetic field generated by the magnetic field generating section. . Therefore, by changing the optical output of the short-wavelength light projected onto the magneto-optical disk in accordance with the information recording or reproducing operation, information can be recorded on the magneto-optical disk at high density.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to drawings showing embodiments thereof. FIG. 1 is a block diagram showing the main structure of a magneto-optical disk device according to the present invention. The excitation laser diode 1 is controlled by a laser diode drive circuit 2. The emitted light from the excitation laser diode 1 is incident on a solid-state laser 3 made of a YAG laser, and the emitted light is sent to an SHG element 4 that generates the second harmonic of the incident light due to a nonlinear effect.
is incident on the The light emitted from the SHG element 4 passes through a liquid crystal shutter LC and a beam splitter 6 and is projected onto a mirror 7. The light reflected by the mirror 7 passes through a condenser lens 8 and is projected onto a magneto-optical disk 9. The magneto-optical disk 9 is rotationally driven by a disk motor 10. A magnetic coil 20 that applies a magnetic field to the projection position of the light projected onto the magneto-optical disk 9 is located on the side opposite to the surface on which the light is projected onto the magneto-optical disk 9. This magnetic coil 20 is supplied with an output current of a magnetic coil drive circuit 21 whose direction of output current changes depending on the recording signal SW.

The reflected light from the magneto-optical disk 9 passes through the condenser lens 8, is reflected by the mirror 7, and is transmitted to the beam splitter 6.
The light is reflected there, passes through the λ/2 plate 13, and enters the polarizing beam splitter 14. The light that has passed straight through the polarizing beam splitter 14 is incident on the first photodetector 15, and the reflected light is incident on the second photodetector 16. The first photodetector 15 and the second photodetector 16 convert the received light into electrical signals, and the converted electrical signals are sent to the positive and
They are input to the negative input terminals + and - separately, and the differential amplifier 1
7 differentially amplifies the input signal and outputs a reproduced signal SR. A recording/reproducing switching signal SS that commands the operation of recording or reproducing information, and a detection signal of the monitoring photodetector 23 that monitors the optical output of the light that is incident on the beam splitter 6 and passes through the liquid crystal shutter LC. Both are given to the light output control section 18. The output signal of the light output control section 18 is given to the liquid crystal shutter drive circuit 22, and the output signal is given to the liquid crystal shutter LC to control the light transmittance of the liquid crystal shutter LC.

Next, the operation of the magneto-optical disk device configured as described above will be explained with reference to FIG. 2 showing a timing chart of signals and operations of each part. When a constant driving current is applied from the laser diode drive circuit 2 to the excitation laser diode 1 as shown in FIG. Project to 3. As a result, the solid-state laser 3 has a wavelength of 1
．． Light with a short wavelength of 0.6 μm is emitted, and the optical output of the light is constant as shown in FIG. 2(c). This emitted light is projected onto the SHG element 4, which has a wavelength of 0.53μ, which is 1/2 of the wavelength of the light from the solid-state laser 3.
emits light of m. This light passes through the liquid crystal shutter LC and the beam splitter 6, is projected onto the mirror 7, is reflected by the mirror 7, passes through the condenser lens 8, is projected onto the rotating magneto-optical disk 9, and its projection position is determined. Heat.

On the other hand, when the recording and reproducing switching signal SS shown in FIG.
Change the light transmittance of the liquid crystal shutter LC. That is, Figure 2 (a
) As shown in FIG. 2(d), during the period of the H-level recording/reproducing switching signal SS which commands the recording operation, the light transmittance of the liquid crystal shutter LC is increased as shown in FIG. The optical output of the light projected onto the
e) Enhanced as shown in . On the other hand, the period of the L-level recording/playback switching signal SS that commands the playback operation is as follows:
The light transmittance is lowered as shown in FIG. 2(d), and the optical output of the light projected onto the magneto-optical disk 9 through the beam splitter 6 is lowered as shown in FIG. 2(e). Further, a monitoring photodetector 23 detects the optical output of the light after passing through the liquid crystal shutter LC, and controls the liquid crystal shutter drive circuit 22 according to the optical output to control the light transmittance of the liquid crystal shutter LC. Thus, the optical output of the light passing through the liquid crystal shutter LC is held constant.

While projecting light onto the magneto-optical disk 9, the recording signal SW is transmitted to the magnetic coil drive circuit 21.
is applied to the magnetic coil 20 according to the recording signal SW.
The direction of the magnetic field generated changes, and the position of the magneto-optical disk 9 heated by the projection of light is magnetized in the direction of the magnetic field generated by the magnetic coil 20, and information is transferred to the magneto-optical disk 9 in accordance with the recording signal SW. recorded. Furthermore, if there is already recorded information, new information is overwritten to replace that information. On the other hand, when a recording/reproducing switching signal SS instructing a reproducing operation is given to the optical output controller 18, the optical output controller 18 controls the liquid crystal shutter drive circuit 22 in response to the recording/reproducing switching signal SS, which greatly increases the light transmittance of the liquid crystal shutter LC. make low. In this case, the optical output of the light projected onto the magneto-optical disk 9 through the beam splitter 6 is significantly reduced, and the temperature at the light projection position does not increase, so that the magnetization direction of the magneto-optical disk 9 does not change.

The reflected light from the magneto-optical disk 9 passes through the condenser lens 8, is reflected by the mirror 7, is reflected by the beam splitter 6, and passes through the λ/2 plate 13, thereby changing the polarization plane of the emitted light. is rotated by 45 degrees and enters the polarizing beam splitter 14. and polarizing beam splitter 14
The light beam is separated into two parts by the first and second photodetectors 15.
, 16. The DC component of the amount of light incident on the first and second photodetectors 15 and 16 is equal for both light beams, and the AC component that is the reproduced signal appears in opposite phases to each other on the first and second photodetectors 15 and 16. Therefore, by obtaining the differential signals of the first and second photodetectors 15 and 16 with the differential amplifier 17, a reproduced signal SR corresponding to the recorded magneto-optical signal pit can be obtained. In this way, the magneto-optical disk 9 is
Since information is recorded on the magneto-optical disk 9 by changing the optical output of the light projected onto the magneto-optical disk 9 and changing the direction of the magnetic field applied to the magneto-optical disk 9 according to the recording signal, the information is projected onto the magneto-optical disk 9. There is no need to modulate the optical output of the light to be recorded according to the recording signal. Therefore, there is no need to use an expensive AO modulator, and the size and cost of the magneto-optical disk device can be reduced.

FIG. 3 is a block diagram showing the main structure of a magneto-optical disk device according to another embodiment of the present invention. The output signal of the optical output control section 18 is given to the laser diode drive circuit 2, and the laser diode drive circuit 2 controls the optical output of the excitation laser diode 1.The other components are shown in FIG. It has the same configuration as the magneto-optical disk device shown in FIG. Next, the operation of this magneto-optical disk device will be explained with reference to FIG. 4, which shows a timing chart of signals and operations of each part.

Recording/reproduction switching signal SS shown in FIG. 4(a)
When is given to the optical output control section 18, the laser diode drive circuit 2 is driven by the output signal of the optical output control section 18,
When a recording operation is commanded, the optical output of the excitation laser diode 1 is increased as shown in FIG. 2(b). but,
Even if the optical output of the excitation laser diode 1 is increased, the optical output of the emitted light of the solid-state laser 3 driven by the emitted light does not increase rapidly and its responsiveness is poor. Therefore, from a predetermined period of time before switching to the recording operation, the laser diode drive circuit 2 switches the excitation laser diode 1 as shown in FIG. 2(b).
Apply the drive current as shown in . Then, the optical output of the light emitted by the solid-state laser 3 is as shown in Fig. 4(c).
It rises along a gentle curve, and the optical output of the solid-state laser 3 reaches its maximum when switching to recording operation.

When the optical output of the solid-state laser 3 changes in this way, the optical output of the light emitted by the SHG element 4 changes in accordance with the optical output change of the solid-state laser 3, and the optical output is detected by the monitoring photodetector 23. detects the light and provides the detection output to the light output control section 18. Thereby, the light output control unit 18 controls the drive signal given to the liquid crystal shutter drive circuit 22 for changing the light transmittance of the liquid crystal shutter LC so that the detection output of the monitoring photodetector 23 is constant. That is, Figure 4 (
d) As shown in d), the light transmittance of the liquid crystal shutter LC is gradually reduced, minimized at the time of switching to the recording operation, and controlled so as to instantly maximize the light transmittance at the time of switching to the recording operation. Then, as shown in FIG. 4(c), during the period when the optical output of the solid-state laser 3 increases, that is, the period immediately before the regeneration operation ends, even if the optical output of the excitation laser diode 1 increases, the optical transmittance decreases. LCD shutter L
The optical output of the light passing through S does not change as shown in FIG. 4(e), and light with an optical output suitable for reproducing information can be projected onto the magneto-optical disk 9.

By the way, the light transmittance of the liquid crystal shutter LC reaches its maximum when the optical output of the solid-state laser 3 reaches its maximum and switches to recording operation, so the optical output of the light passing through the liquid crystal shutter LC is As shown in FIG. 4(e), the maximum optical output is achieved, and light having an optical output suitable for recording information can be projected onto the magneto-optical disk 9. Furthermore, at the time of switching to the playback operation thereafter, the optical output control unit 1
8 is the excitation laser diode 1 as shown in Fig. 4(b).
control to reduce the light output of the Then, the optical output of the solid-state laser 3 gradually decreases as shown in FIG. 4(c). The light output control section 18 controls a drive signal given to a liquid crystal shutter drive circuit 22 that changes the light transmittance of the liquid crystal shutter LC so that the detection output of the monitoring photodetector 23 is constant. Therefore, the light transmittance of the liquid crystal shutter LC is minimized at the time of switching to the reproduction operation, and is gradually increased from the time of switching to the reproduction operation. That is, the light transmittance is increased in inverse proportion to the change in the optical output of the solid-state laser 3. Then, the light from the solid-state laser 3 with its optical output reduced,
The light passes through the liquid crystal shutter LC with a constant light output, so that light with an optical output suitable for reproducing information can be projected onto the magneto-optical disk 9. Furthermore, during the recording operation and the reproduction operation, the light transmittance of the liquid crystal shutter LC is controlled by the light output control section 18 according to the detection output of the monitoring photodetector 23, and the light passing through the liquid crystal shutter LC is controlled. Adjust to keep output constant.

In this way, the excitation laser diode 1
When a recording operation is commanded by controlling the optical output of the liquid crystal shutter LC and the optical transmittance of the liquid crystal shutter LC, when a recording signal SW is given to the magnetic coil drive circuit 21, the magnetic coil 20 receives the recording signal SW.
A magnetic field is generated in a direction corresponding to the magnetic field, and the magnetic field is applied to the magneto-optical disk 9 to magnetize the magneto-optical disk 9 at the light projection position. Then, as described above, the magneto-optical disk 9
record information. Further, light with reduced optical output is projected onto the magneto-optical disk 9, and the reflected light is received by the first photodetector 15 and the second photodetector 16 to reproduce information using detection signals obtained. As mentioned above, when switching the recording/reproducing operation so that the optical output of the excitation laser diode 1 is made high during recording operation and lowered during reproduction operation, the responsiveness of the optical output change of solid-state laser 3 must be considered. In the process of changing its light output, the liquid crystal shutter L changes in inverse proportion to the change in light output.
By changing the light transmittance of C and maximizing the light transmittance during both recording and reproducing operations, the magneto-optical disk 9 Information can be recorded or played back. In this case, since the optical output of the excitation laser diode 1 is reduced during the reproducing operation, power consumption can be significantly reduced.

According to the present invention, the liquid crystal shutter L can be used without using an expensive AO modulator for modulating the light from the SHG element 4.
Information can be recorded on and reproduced from the magneto-optical disk 9 using C. Further, information can be overwritten on the magneto-optical disk 9. Furthermore, since the SHG element 4 generates light with an extremely short wavelength, the spot diameter of the light projected onto the magneto-optical disk 9 can be reduced, and the recording density of information can be greatly increased.

[0022]

[Effects of the Invention] As detailed above, the present invention provides SHG
The light emitted by the element is projected onto a liquid crystal shutter, the light transmittance of the liquid crystal shutter is controlled according to the information recording/reproducing operation, the optical output of the light passing through the liquid crystal shutter is changed, and the light is projected onto a magneto-optical disk. Since information is recorded and reproduced using this method, there is no need to use an expensive AO modulator that optically modulates the light emitted by the SHG element as in conventional magneto-optical disk devices. Therefore, it is possible to reduce the size of the magneto-optical disk device, reduce costs, and provide an inexpensive magneto-optical disk device that can record information at high density.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of main parts of a magneto-optical disk device according to the present invention.

FIG. 2 is a timing chart of signals and operations of each part in FIG. 1;

FIG. 3 is a block diagram showing the configuration of main parts of a magneto-optical disk device showing another embodiment of the present invention.

FIG. 4 is a timing chart of signals and operations of each part in FIG. 3;

FIG. 5 is a block diagram showing the configuration of main parts of a conventional magneto-optical disk device.

[Explanation of symbols]

1 Laser diode for excitation 3 Solid-state laser 4 SHG element 6 Beam splitter 9 Magneto-optical disk 14 Polarizing beam splitter 15 First photodetector 16 Second photodetector 18 Optical output control section 20 Magnetic coil 22 Liquid crystal shutter drive circuit LC LCD shutter

Claims (1)

[Claims] 1. A magneto-optical disk device that records or reproduces information on a magneto-optical disk by projecting light from a light source that generates a second harmonic of incident light onto a magneto-optical disk, wherein the light emitted from the light source is a liquid crystal shutter for projecting images, a control section for controlling the light transmittance of the liquid crystal shutter, a monitoring photodetector for detecting the optical output projected onto the magneto-optical disk, and a control section for controlling the light transmittance of the liquid crystal shutter; 1. A magneto-optical disk device, comprising: a magnetic field generating section that generates a corresponding magnetic field, and is configured to change the light transmittance of a liquid crystal shutter in relation to information recording and reproducing operations.