JPS6116039A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain tracking at a high response speed with simple constitution without using any mechanically mobile part, by using an acoustic/optical deflector for tracking. CONSTITUTION:An acoustic/optical deflector 24 is used in place of a normal tracking mirror. This deflector 24 is produced by attaching a transducer 34 such as a comb-shaped electrode, etc. to the side face of an acoustic/optical medium 37 containing an LiNbO3 piezoelectric crystal, etc. When a high frequency signal 35 is applied to the transducer 34, the incident light 30 is diffracted by ultrasonic traveling wave 36 and delivered in the form of a diffracted beam 32. This beam 32 is varied by the length of the wave 36 with an extremely high response speed, i.e., several musec. Thus it is possible to deflect quickly the light 30 in an optional direction within a prescribed range by changing the frequency of the signal that is supplied to the transducer 34.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical information recording and reproducing device, and in particular, it records various information on a recording medium using a light beam, and also records this recorded information using a light beam. The present invention relates to an optical information recording and reproducing device used for reproducing information.

[Background of the invention]

A recording medium capable of recording, reproducing, and erasing information using a light beam consists of a disc-shaped substrate made of glass, plastic, etc., and a perpendicular magnetization usually several microns thick provided on this substrate. A so-called magneto-optical disk memory consisting of a film is known. The perpendicularly magnetized film is made of an amorphous alloy or the like, and has the property of being magnetized in a direction perpendicular to the film surface.

To record information on such a magneto-optical disk memory, first a perpendicular magnetic field is applied to the magneto-optical disk memory to align the magnetization direction of the perpendicularly magnetized film in one direction, and then information signals are used to record information digitally. A modulated radar beam spot is irradiated onto the perpendicularly magnetized film to raise the temperature of the perpendicularly magnetized film at that location to a point or higher. Then, the magnetization direction of the part irradiated by the radar beam spot is reversed due to the influence of the surrounding magnetic field, and the logic "1" is generated.
(or "0") is recorded to form a recording bit.

When reading information recorded on a magneto-optical disk memory, a perpendicularly magnetized film is irradiated with a reading laser beam spot, and the Kerr effect is used, in which the polarization direction of the reflected beam changes depending on the magnetization direction of the perpendicularly magnetized film. and read it.

Furthermore, when erasing information recorded on a magneto-optical disk, the perpendicularly magnetized film is irradiated with an erasing radar beam spot to bring it to a temperature above the Curie point, and a bias magnetic field is applied in the same direction as the magnetization direction of the unrecorded area. All you have to do is multiply.

Now, when reading the above information, it is necessary to perform tracking control to cause the recording bit to track the light beam spot. This tracking control uses the well-known three-beam method (for example, the Japanese Patent Publication No. 53-131
(see No. 23) etc. are used. Particularly in the case of magneto-optical disk memories, since the signal components detected using the Kerr effect are minute, tracking control is difficult with the far-field method used for optical disks, and the three-beam method is effective.

FIG. 3 shows an example of an optical information recording/reproducing device using a magneto-optical disk memory. In FIG. 3, a magneto-optical disk 21 is rotated by a motor 23 via a spindle 22 at a predetermined speed. In the writing system shown in the right half of the figure, a laser beam emitted from a self-modulating semiconductor radar 1 is collimated by a collimator lens 2 and enters a polarizing beam slitter 3 . The polarization beam sinter 3 is configured to transmit P-polarized light and reflect S-polarized light. Since the polarization direction of the semiconductor laser 1 is arranged parallel to the plane of the paper, the beam passes through the polarization beam sinter 3, enters the quarter-wave plate 4, becomes circularly polarized light, and is reflected by the reflection mirror 5. It is polarized at 0°. Furthermore, the beam enters the objective lens 6 and is imaged on the surface of the disk 21, reversing the magnetization direction of the surface perpendicular magnetization film in that portion of the disk 21, as described above. The beam reflected from the disk 21 passes through a lens 6 and a mirror 5, is converted into S-polarized light by a quarter-wave plate 4, is reflected by a polarization beam splitter 3, and enters a detector 8. The light incident on the detector 8 is photoelectrically converted and the servo signal sF (autofocus)
It is used to keep the objective lens in focus at all times.

The reading system to which the three-beam method is applied is shown in the left half of FIG. It is divided into three parts. These beams pass through the half mirror 13, are reflected by the tracking mirror 14, and are imaged by the objective lens 15 on the surface of the chair 221 as three beam spots. The polarization direction of these beams hitting the disk 21 is rotated by the Kerr effect, and the polarization direction is rotated by the objective lens 15, the tracking mirror 14, and the nof mirror 13.
It is further divided into two parts by a no-f mirror 16, passes through a polarizing plate 17.18, and is transmitted to detectors 19a and 19b.
, 19c and 20 are photoelectrically detected. Polarizing plate 1
7 and 18, the polarization direction is set at a predetermined angle (for example, 9
0°).

The three beam spots imaged on the surface of the disk 21 consist of a central spot and two spots on both sides that are point symmetrical with respect to the central spot. The spot covers the recording bit string by about half the spot diameter, so at this time, the intensity of reflected light from both spots is equal, but when the center spot deviates from the recording bit string, the intensity of reflected light from both spots overlaps. Since there is a difference in the intensity of the reflected light from the two, it becomes possible to detect a tracking error. The reflected light from the center spot is detected by a detector 19b,
The light enters the light beam divided into 20 parts, and the difference between the two is extracted as an information reproduction signal SR, and a signal for focusing control (not shown) is detected by a known method. On the other hand, the reflected lights from the spots on both sides are photoelectrically detected by the detectors 19a and 19c, the difference is made, and the result is taken out as the top, bottom, and king signals S as described above.

Based on the tracking signal sT thus obtained, the tracking mirror 14 or the objective lens 15 is moved to the disk 210.
By moving the beam in the radial direction, tracking control or tracking is performed so that the central beam spot for recording and reproduction is always kept on the recording bit string.

By the way, in the above three-beam type optical information reproducing device, which performs tracking by moving the tracking mirror, the beam does not enter parallel to the optical axis of the objective lens, so the beam on the detector moves due to the angle of the mirror. The autofocus servo operation is unstable, and in those that perform tracking by moving the objective lens, the support means and drive means for the objective lens are complicated, the number of parts is large, and assembly is difficult. Ta.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a simple and compact optical information recording and reproducing device that is capable of highly accurate tracking control.3 [Summary of the Invention] The present invention has the following features: In an optical information recording and reproducing apparatus that records or reproduces information or both by irradiating a light beam onto a recording medium and also controls tracking of a light beam spot on the recording medium, 1. A light beam is irradiated onto a recording medium through an acousto-optic deflector that utilizes the phenomenon that the diffraction angle of light incident on the medium due to ultrasonic waves in an acoustic medium changes depending on the frequency of the ultrasonic waves, and this acousto-optic deflector The tracking control is performed by controlling the frequency of the ultrasonic waves.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, and corresponds to the left half of FIG. Portions designated by the same reference numerals as in FIG. 3 are portions that perform the same functions, and therefore, description thereof will not be repeated here.

In this embodiment, the system shown on the left side of FIG. 3 is arranged vertically, the tracking mirror 14 is omitted, and an acousto-optic deflector 24 is provided in its place. Alternatively, the acousto-optic deflector 24 may be placed between the tracking mirror 14 and the objective lens 15 in FIG. 3, in which case the systems on the left side of FIG. 3 will be shown in the same orientation. .

The acousto-optic deflector 24 is made of, for example, LiNb as shown in FIG.
0. It is constructed by providing a transducer 34 such as a comb-shaped electrode on the side surface of an acousto-optic medium 37 made of a piezoelectric crystal or the like. When a high frequency signal is applied to this transducer 34, an ultrasonic traveling wave 3 is generated in the acousto-optic medium 37.
6 occurs. Normally, the incident light 30 passes through the acousto-optic medium 37 as it is and is emitted as undiffracted light 33, but when a high frequency signal is input from the voltage source 35 to the transducer 34, the incident light 30 becomes an ultrasonic traveling wave. It is diffracted by 36 and output as diffracted light 32.

Further, this diffraction angle changes depending on the wavelength (therefore, the frequency) of the ultrasonic traveling wave 36, and its response speed is extremely fast at several microseconds. Therefore, by changing the frequency of the signal input to the transducer 34, the incident light 30 can be quickly deflected in any direction within a predetermined range. Note that 31 in FIG. 2 is a sound absorbing material, which is used to prevent the reflected wave of the ultrasonic traveling wave 360 from affecting the diffraction of light, but it is not necessarily necessary.

Since the acousto-optic deflector 24 is as described above, the input high-frequency signal is input to the acousto-optic deflector 24 via the tracking circuit 25 as shown in FIG. By adjusting the frequency, it is possible to control the position of the light beam irradiated onto the disc 21 to perform correct tracking and kinging.

〔Effect of the invention〕

According to the present invention, by using an acousto-optic deflector for tracking, it is possible to track and king with a fast response speed without mechanically moving parts, and the structure is relatively simple and can be miniaturized and manufactured. The above can be simplified, and the tracking operation can be prevented from having an adverse effect on the operation of the autofocus serve system.

The present invention is applicable not only to magneto-optical disks but also to optical information recording and reproducing devices of the type that use other recording media to read and/or write information and track information by irradiation with a light beam. The present invention is also applicable to an optical information recording/reproducing device of the type that uses transmitted light in place of the reflected light of the light beam irradiated onto the recording medium.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a schematic diagram of an acousto-optic deflector used in the embodiment, and Fig. 3 is a conventional optical information recording and reproducing method using a magneto-optical disk memory. FIG. 2 is a schematic diagram showing the device. 1... Semiconductor laser 3... Polarizing beam sinter 4... 174 wavelength plate 6... Objective lens 8... Detector 9... Semiconductor laser 1
1... Polarizing plate 12... Grating 1
3...Half mirror 14...Tracking mirror 15...Objective lens 16...No1-7
Mirrors 17.18...Polarizing plates 19a+19b, 19c+20...Detector 21.
・・Magneto-optical disk 23 ・・Spindle motor 2
4... Acousto-optic deflector 25... Tracking circuit 30... Laser incident light 31... Sound absorbing material 32...
・Diffracted light 33...Transmitted light 34...Piezoelectric vibrator (transducer) 35...High frequency electrical signal
36... Ultrasonic traveling wave 37... Acousto-optic medium Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an optical information recording and reproducing device that records or reproduces information, or both, by irradiating a light beam onto a recording medium and also controls tracking of a light beam spot on the recording medium, ultrasonic waves in the acoustic medium are used to stimulate the medium. irradiating the recording medium with a light beam through an acousto-optic deflector that utilizes the phenomenon that the diffraction angle of incident light changes depending on the frequency of the ultrasonic wave;
An optical information recording/reproducing apparatus characterized in that tracking control is performed by controlling the frequency of the ultrasonic waves of the acousto-optic deflector.