JP2645549B2 - Magneto-optical recording method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A plurality of magneto-optical recording material layers are stacked to enable high-density recording.

[Industrial applications]

The present invention relates to a magneto-optical recording method and apparatus, and more particularly to a multi-layer recording method and apparatus in which a plurality of recording layers are stacked.

[Conventional technology]

Conventionally, as a magneto-optical recording medium, an intermetallic compound such as MnBi or an amorphous metal alloy such as TbFe is mainly used, and a magneto-optical recording medium layer and a protective film sandwiching the recording medium layer on a substrate. Is formed. Recording is performed by magnetizing the entire surface in one direction and then condensing the laser beam to selectively form magnetic domains magnetized in the opposite direction. Reading of the information recorded in this manner is generally performed in a reflection mode using the Kerr effect because the above-mentioned recording medium has a large light absorption. That is, information is reproduced by utilizing the phenomenon that the polarization state of reflected light changes (the polarization angle rotates in one direction) according to the direction of magnetization of the recording medium.

[Problems to be solved by the invention]

In the record carrier and the recording method as described above, the size of one bit (magnetic domain) of optical recording is determined by the spot diameter of the laser beam. Therefore, when a recording medium having a large light absorption as described above is used. Is considered to be unable to greatly exceed the current recording density (5 × 10 ⁷ bits / cm ² ).

[Means and actions for solving the problems]

The present inventor has found that in order to solve the above problems, a plurality of magneto-optical recording material layers may be formed on a record carrier, and magneto-optical recording may be performed independently on each of the magneto-optical recording material layers. And disclosed separately (JP-A-62-214538).
However, when recording is performed on such a record carrier, it is desirable to perform recording with an appropriate power on each recording layer. Therefore,
The present invention is to further solve such a problem. That is, when recording is performed on a plurality of recording layers using a single light source, each recording layer absorbs light, so that the light attenuates every time the light passes through the recording layer, and therefore, the light source has a final power. It must have sufficient power to perform recording on the recording layer. But,
The optimal light power for recording on the final recording layer may be excessive for the first recording layer. When excessive power is applied to the recording layer, the recording bit becomes too large, the bit shape is deteriorated, and the recording layer is damaged. In order to avoid this inconvenience, the light absorption is sequentially increased from the beginning to the end of the recording layer so that the recording can be performed with the same recording power while using the same power of light. What should I do? To this end, the patent application proposes changing the composition and thickness of the magneto-optical recording material.

However, the purpose is to collect light independently on each of the magneto-optical recording material layers on a record carrier having a plurality of translucent magneto-optical recording material layers made of the same material and having the same thickness. Light is used to record information, and to record information on the plurality of magneto-optical recording layers, a plurality of light beams having different wavelengths are used. It can also be achieved by configuring and recording so that the height is gradually increased from the side toward the inside.

According to the invention of the present application, in order to achieve the above object, a light source and a plurality of translucent magneto-optical recording material layers of the same material and having the same thickness are laminated and magneto-optical recording of the plurality of layers is performed. A plurality of light beams having different wavelengths are guided from the light source to the plurality of magneto-optical recording layers on the record carrier composed of the layers, and each of the magneto-optical recording material layers is independent so that the light absorption thereof is sequentially increased. And a magneto-optical recording device comprising at least an optical component for condensing light.

〔Example〕

For example, Figure 1 shows Yttrium Iron Garnet (YIG)
FIG. 3 is a graph showing the wavelength dependence of light absorption from visible light to near-infrared light.
It can be seen that it decreases as the wavelength increases up to nm. Therefore, five YIs from the first to the fifth
The wavelength of light emitted from a single light source is adjusted on a record carrier having a G recording layer, 750 nm for the first recording layer, 725 nm for the second recording layer, 700 nm for the third recording layer, and the fourth recording layer. Has 675n
m, if light having a wavelength of 650 nm is focused on the fifth recording layer, recording can be performed with an appropriate recording power on each recording layer even if the light has the same power. Will be possible.

If a dye laser is used as the light source, it is possible to extract laser light of a plurality of wavelengths with a single laser.

FIG. 2 shows an example of a record carrier, in which a gadolinium gallium garnet (GGG) crystal or a
The second to fifth five YIG recording layers 1, 2,..., 5 have spacers 6, 7,.
And a protective layer 10 on the outside of the fifth recording layer 5.
Are formed. For example, first to fifth recording layers 1, 2,.
Is about 0.5 μm, and the thickness of the spacer layers 6, 7,.
m, the thickness of the substrate 11 is about 1 mm. These layers 1 to 10 can be formed by sputtering and subsequent heat treatment.

By changing the wavelength of the light from a single dye laser, for example, as described above, the first recording layer 1 has a light 12 having a wavelength of 750 nm and a fifth light having a wavelength of 750 nm as shown in FIG. The recording layer 5 condenses 13 having a light wavelength of 650 nm and performs each recording. At this time, high-power light is incident on the first recording layer 1, but an appropriate recording power is achieved because the light absorption coefficient of light having a wavelength of 750 nm is small.
In the figure, the power decreases due to light absorption in each recording layer before the incident light reaches the fifth recording layer. However, since the light absorption coefficient of light having a wavelength of 650 nm is large, appropriate recording power is achieved. Is done. The same applies to the second to fourth recording layers 2 to 4.

In the above example, the change in the wavelength and the change in the light absorption coefficient linearly change, but this need not be the case. It suffices that the light absorption coefficient of the recording material has wavelength dependence, and the light absorption coefficient can be adjusted by selecting a specific wavelength. Further, it is desirable that the light absorption be different for each recording layer, but condensing light of the same wavelength on a plurality of recording layers is not excluded if acceptable recording is obtained. Further, the composition and thickness of the recording layer may be changed in combination with the change of the wavelength of the light focused on the recording layer. Further, changing the power of the light source or adjusting the power of the light from the light source on the way is not excluded. In short, the present invention is based on the fact that the light absorption coefficient may be different due to the different wavelength of the light condensed on each of the magneto-optical recording layers composed of multiple layers, based on the selection of the wavelength of the recording light alone or In combination with other methods, recording is performed on each recording layer with an appropriate recording power.

Although YIG is used in the above example, bismuth-substituted garnet, cobalt ferrite, barium ferrite, and the like can also be used as the magneto-optical recording medium.

FIG. 3 schematically shows an example of an apparatus for performing multi-layer magneto-optical recording according to the present invention, in which 21 is a record carrier, 22 is a light source, and 23, 24, 25 and 26 are lenses. , 27 is a half mirror, 28 is a mirror, 29, 30, 31 are polarizing filters, 32, 3
3 is a photodetector.

The laser light 34 generated from the light source 22 is converted into parallel light by the lens 23, reflected by the mirror 28, and focused on a desired recording layer in the record carrier 21 by the lens 24. At this time, the reflected light 35 from the record carrier 21 is the lens 24, the mirror 28, the half mirror 27,
The light reaches the photodetector 32 via the lens 25, and focuses and tracks the laser beam using the reflected light. For this purpose, the record carrier 21 is provided with a reflective layer for focusing and tracking. Thus, recording is performed by scanning the recording layer with the laser beam. In general, recording is performed by magnetizing the entire body in one direction, irradiating a laser beam to selectively heat the recording layer, and reversing the magnetization direction of that part (at this time, generally, an external magnetic field is applied. Although not necessary, an external magnetic field may be applied.), And information is recorded by the arrangement of the magnetization directions.

To focus on a desired recording layer in the record carrier 21,
For example, the lens 24 is adjusted up and down.

Reproduction is performed by focusing and scanning on a desired recording layer by basically the same operation as the writing, but the power of the reproduction laser light is smaller than the power of the writing laser light. This power adjustment may be performed by the light source 22 or may be performed by the filter 29 or the like. As described above, the laser beam focused on the desired recording layer does not disturb the information in the other recording layers due to the presence of the spacer layer, but only the information on the specific focused recording layer. , That is, the Faraday rotation is performed right or left based on the information of the recording layer, and the recording layer 21 is transmitted. Lens for transmitted light 36
26. When the light is detected by the photodetector 33 through the polarizing filter 31, the information in the recording layer can be reproduced.

〔The invention's effect〕

According to the present invention, magneto-optical recording using a multilayer recording layer is provided, and the recording density is dramatically increased. In addition, in order to increase the number of recording layers, it is necessary to perform recording with an appropriate power on each recording layer. However, the present invention makes this possible, and the range of means for that purpose is expanded.

[Brief description of the drawings]

FIG. 1 is a graph showing the wavelength dependence of the light absorption coefficient of YIG, FIG. 2 is a schematic sectional view of a multilayer magnetic recording carrier used in an embodiment of the present invention, and FIG. 3 is a magnetic recording of the embodiment of the present invention. It is a schematic diagram of an apparatus. 1 ... first recording layer, 2 ... second recording layer, 5 ... fifth recording layer, 6,7,9 ... spacer layer, 10 ... protection layer, 11 ... substrate, 12,13 ... Laser beam, 21 ... Record carrier, 22 ... Light source, 23,24,25,26 ... Lens, 27 ... Half mirror, 28 ... Mirror, 29,30,31 ... Polarizing filter, 32,33 ... ... Photodetector, 34 ... Laser light, 35 ... Reflected light, 36 ... Transmitted light.

Claims (2)

(57) [Claims] A record carrier having a plurality of translucent magneto-optical recording material layers of the same material and having the same thickness laminated on each other,
By independently collecting light and recording information on each of the magneto-optical recording material layers, and using a plurality of lights having different wavelengths to record information on the plurality of magneto-optical recording layers, A magneto-optical recording method characterized in that the plurality of magneto-optical recording layers are arranged so that the light absorption increases in order from the light incident side toward the inside, and recording is performed. 2. A recording medium comprising a light source and a plurality of translucent magneto-optical recording material layers of the same material and having the same thickness and having a plurality of layers, and comprising a plurality of these magneto-optical recording layers. An optical component for guiding a plurality of lights having different wavelengths from the light source to a plurality of the magneto-optical recording layers, and condensing the light independently of each of the magneto-optical recording material layers so that the light absorption thereof is sequentially increased; And at least the following.