JPH0445134Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a magneto-optical disk device that utilizes the magneto-optic effect.

(b) Prior Art Research has been progressing on perpendicular magnetic recording and reproduction of information by applying magneto-optical effects such as the Faraday effect and the magnetic Kerr effect. Generally, an amorphous magnetic film such as GdCo, GdFe, or TbFe is used as a recording medium, and the recording medium is magnetized in one direction over its entire surface before being irradiated with light from a semiconductor laser or the like to locally magnetize the recording medium. Raise the temperature to near the Curie point, and apply bias magnetism in the opposite direction to the direction in which the recording medium is magnetized to the area including the laser beam irradiated area, to create a magnetized area in the laser beam irradiated area in the opposite direction to the surrounding area. Recording is done by this. To reproduce recorded information, light emitted from a laser light source, etc. is directly polarized through a polarizer, then irradiated onto the recording medium, and the reflected or transmitted light is passed through an analyzer to a photoelectric conversion element, etc. Information is reproduced by detecting the rotation of the plane of polarization due to the recorded information by receiving the information with a detector.

In addition, the temperature of the recording medium is locally raised by irradiating the information recording area with a laser beam, etc. in the same way as during recording, and a bias magnetic field is applied in the opposite direction to that during recording, that is, in the direction in which the entire recording medium has been previously magnetized. When this is done, the magnetization direction of the laser beam irradiated part becomes the same as that of the surrounding area, and the recorded information is erased.

FIG. 3 is a general configuration diagram of a magneto-optical recording/reproducing apparatus. In the recording optical system, the laser beam emitted from the semiconductor laser 2 is modulated by a laser modulator 1 that modulates the laser beam according to the signal to be recorded, and is turned into a parallel beam by a lens 3, and then a mirror 4 and a polarizing beam splitter. 5. The light passes through a 1/4 wavelength plate 6 and is condensed (about 1 micron) onto a disk-shaped recording medium 8 by an objective lens 7. The entire surface of the disk-shaped recording medium 8 is magnetized in one direction in advance. Recording is performed by applying a magnetic field in the opposite direction to the direction in which the recording medium 8 is already magnetized, using the bias magnetic field coil 9 or the like, to a region including the portion where the laser beam is focused and irradiated.

The reflected light passes through the objective lens 7 and the 1/4 wavelength plate 6 again, is reflected by the polarizing beam splitter 5, passes through the cylindrical lens 10, and reaches the photodetector 1.
Reach 1. Recording is performed while performing focus control and tracking control using the signal obtained from this photodetector 11.

For playback, an optical system separate from that for recording is used. The laser beam emitted from the semiconductor laser 12 becomes a parallel beam at the lens 13 and is reflected at the mirror 14, and then passes through the polarizer 1.
5, it becomes linearly polarized light. The laser beam transmitted through the half mirror 16 is focused onto the recording medium 8 by the objective lens 17. The plane of polarization of the reflected light from the recording medium 8 rotates to the right or left depending on the direction of magnetization of the recording medium 8 due to the magneto-optic effect (Kerr effect).

The reflected light whose plane of polarization has been rotated passes through the objective lens 17 again.
The reflected light enters the half mirror 16 through the half mirror 16, and is further divided into two parts by another half mirror 18, and enters the respective analyzers 19a and 19b. These two analyzers 19a and 19b have set angles that are opposite to each other and the same angle with respect to the polarization plane of the polarizer 15. The light beams that have passed through the analyzers 19a and 19b pass through lenses 20a and 20b and are received by photodetectors 21a and 21b, respectively. The outputs photoelectrically converted by the photodetectors 21a and 21b are input into the differential amplifier 22 and calculated, and the outputs are "1" and "0".
A digital signal corresponding to is obtained as output. Further, the focus signal and tracking signal output from the photodetector 21b are processed by a focus servo circuit 23 and a tracking servo circuit 24 to perform focus servo and tracking servo.

The disk 8 has a structure as shown in FIG. 8a is a plastic transparent substrate, 8b is a magnetic film (indicated by hatching), and 8c is a protective layer made of SiO ₂ . Laser light 30 for recording and reproduction is irradiated from the transparent substrate 8a side. Tracking control is performed so that the laser beam spot traces the groove 31. Therefore, recording is performed in the groove 31 (31 is a recording track).

On the other hand, the erasing operation is performed by applying a magnetic field in the opposite direction to that during recording to the disk 8 and raising the temperature of the portion to be erased using a laser beam, as described above. At this time, the strength of the applied magnetic field needs to be greater than the magnetic field during recording due to the influence of the surrounding magnetized parts. However, it is known that when the applied magnetic field during erasing becomes larger than a predetermined value, the CN ratio of adjacent tracks decreases, and it is difficult to set the applied magnetic field during erasing.

Furthermore, differences in the composition ratio of the magnetic film, manufacturing conditions, or
The Curie point, thermal conductivity, etc. caused by differences in substrates, etc.
Variations in heat capacity, variations in the intensity distribution of the laser beam spot in each player, eccentricity of the disk,
Erasing characteristics are greatly affected by surface runout and the like.

By the way, in the past, the same laser beam spot as that for recording was used as the laser beam for erasing. As described in Japanese Patent Application Laid-open No. 58-83347,
If the tracking during erasing is off (the focus servo and tracking servo are applied even during erasing), there is a risk that erasing will not be completed completely. Further, due to the above-mentioned variations in disk characteristics, etc., there is a similar risk when a beam spot having the same diameter as that used for recording is used.

Therefore, the above-mentioned Japanese Patent Laid-Open No. 58-83347 discloses a configuration in which the width of the laser spot light in the scanning direction during erasing is larger than that during recording. The methods for realizing this configuration are 1) increasing the power of the irradiated laser beam during erasing to increase the effective spot diameter of the beam, and 2) forming the laser beam spot into an elliptical shape during recording. By aligning the long axis direction with the scanning direction and rotating the beam spot 90 degrees during erasing to make the long axis direction the width of the scanning direction, the width of the spot in the scanning direction during erasing is made larger than during recording. .

However, in the first method, the laser beam intensity at the center of the spot becomes too strong, which may damage the magnetic film 8b of the disk 8 and deteriorate its characteristics. Furthermore, in the second method, the spot diameter in the scanning direction increases during recording, so
This hinders the improvement of recording density. Furthermore, since it is necessary to rotate the trapezoidal prism in order to rotate the optical axis, the configuration becomes complicated.

(c) Problems to be Solved by the Invention As described above, the configuration of the prior art has the problem that there is a risk of damaging the disk magnetic film and hinders improvement in recording density. The present invention has been devised in view of this point, and it is an object of the present invention to provide a magneto-optical disk device which has a simple structure and is capable of reliably erasing data.

(d) Means for solving the problem In the present invention, an acousto-optic element is provided in the optical system during erasing, and the diameter of the laser beam spot focused on the magneto-optical disk is substantially smaller than that during recording. It is meant to make it bigger.

(E) Effect Since the acousto-optic element is provided in the optical system, the diameter of the laser beam spot focused on the magneto-optical disk can be made substantially larger than that during recording, so that erasing operation is possible. You can definitely do it.

(F) Embodiment An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 shows the optical system of the embodiment, Fig. 2 shows the laser beam spot on the disk, Fig. 5 shows the operation of the acousto-optic element, and Fig. 6 shows the laser beam focused on the disk. FIG.

In FIG. 1, 2 is a semiconductor laser, 3 is a collimator lens, 5 is a polarizing beam splitter, 32
7 is an acousto-optic element, 7 is an objective lens, and 8 is a magneto-optical disk. The acousto-optic element utilizes the acousto-optic effect, and as shown in Fig. 5, the incident light 33
On the other hand, when Ramannus diffraction occurs (when the applied ultrasonic frequency is low or the width of the ultrasonic wave (L in the interaction length diagram) is narrow), multiple-order diffraction occurs.

When Ramannus diffraction occurs, the diffraction angle θm of the m-th order diffracted light is given by θm=sm ^-1 (mλ/Λ) (1). Note that λ is the wavelength of the laser beam, and Λ is the wavelength of the ultrasonic wave in the medium. Ultrasonic wave is vibrator 3
4 by applying a high frequency signal from a high frequency power source 35.

Next, based on FIG. 6, the passing light, the first-order diffracted light, -
The position of the first-order diffracted light on the disk 8 will be explained. When the focal length of the objective lens 7 is f and the angle of diffraction by the acousto-optic element 32 is θ, the distance d between the transmitted light 40 and the diffracted lights 41 and 42 is given by d=ftanθ (2). That is, since the distance d depends on the diffraction angle θ, a desired state can be obtained by controlling the frequency of the ultrasound applied to the acousto-optic element 32.

For example, as shown in Fig. 2, in the case of a magneto-optical disk with a recording track width T of 0.8 μm and a recording track pick P of 1.6 μm, if the distance d is 0.4 μm, the effective spot of the laser beam during erasing is The diameter can be made approximately 1.8 μm. (The spot diameters of transmitted light and diffracted light are each assumed to be 1.0 μm.) f = 3.9 mm,
When d=0.4μm, θ=1×10 ^-4 radian. When a lithium tantalate crystal is used as an acousto-optic element, assuming that the wavelength of the laser beam is 8300 angstroms, it is sufficient to apply an ultrasonic wave of about 750 KHz from equation (1).

If the intensity of the laser beam irradiated onto the disk 8 decreases due to the occurrence of multiple-order diffraction, the power of the semiconductor laser 2 may be increased during erasing (the supplied current may be increased). As described above, during erasing, the diameter of the laser beam spot becomes substantially large, so that the erasing operation becomes reliable.

The same optical system as in FIG. 1 is used during recording as well. However, no ultrasonic signal is applied to the acousto-optic element 32. Therefore, no Ramannus diffraction occurs, and only the transmitted light is applied to the objective lens 7, and the same operation as in the conventional example is performed.

Further, in the above embodiment, only the first-order diffracted light 41, 42 and the transmitted light 40 were used, but the second-order diffracted light 43,
The -second-order diffracted light 44 may also be used (by reducing the diffraction angle θm) to substantially increase the spot diameter during erasing.

(g) Effects of the invention As described above, according to the invention, the temperature of a part of the magnetic film does not rise abnormally and damage the magnetic film unlike the conventional technology, and the magnetic film is not damaged during recording. The spot can be kept the same as before, and the spot diameter during erasing can be made substantially larger than during recording without reducing the recording density, which eliminates uneven disk characteristics, uneven player characteristics, and tracking servo. Even if an error occurs, the erasing operation can be performed reliably, which is effective.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the optical system of the embodiment of the present invention;
The figure shows a laser beam spot on a disk.
Figure 3 is a block diagram of the magneto-optical disk device, Figure 4 is a diagram showing the structure of the magneto-optical disk, Figure 5 is a diagram showing the operation of the acousto-optic element, and Figure 6 is a diagram showing the focusing of light onto the disk. It is a figure showing a laser beam. 8... Magneto-optical disk, 9... Coil for bias magnetic field, 32... Acousto-optic element.

Claims (1)

[Claims for Utility Model Registration] In a magneto-optical disk device that records information by applying a recording bias magnetic field to a magneto-optical disk and irradiating it with laser light, a method for erasing in a direction opposite to the recording bias magnetic field during erasing. means for applying a bias magnetic field; a vibrator that vibrates at a high frequency when a high frequency signal is applied during erasing; and a vibrator that forms an optical grating when vibrated at a high frequency by the vibrator during erasing, and A magneto-optical disk device comprising: an acousto-optic element that forms diffracted light of the laser beam in the width direction of a recording track.