JPH03254445A - Magneto-optical disk and its reproducing method - Google Patents

Abstract

PURPOSE:To obtain this magneto-optical disk capable of reproduction even for a reproduction-only type or a DRAW type optical disk reproducing device by providing a reflecting luminous quantity reduction means whose distribution state is changed with the direction of magnetization onto the surface of a perpen dicular magnetization film. CONSTITUTION:The magneto-optical disk 6 consists of a 1st transparent base 1, a perpendicular magnetization film 2, an oil layer 3, a spacer 4 and a 2nd transparent base 5. In this case, the perpendicular magnetization film 2 is made of a rare-earth transition metallic alloy such as TbFeCo, GdTbFe or DyFeCo, garnet or an oxide magnetic substance and magnetic powder being a reflecting luminous quantity reduction means in the thickness of several hundred Angstrom , prefer ably 100 - 200Angstrom is applied to the surface of the perpendicular magnetization film 2. Since the magnetic powder is concentrated onto a magnetic domain wall in response to the direction of magnetization of the perpendicular magneti zation film 2, the magneto-optical disk 6 is reproduced even for the conventional reproduction-only type or the DRAW type optical disk reproducing device by detecting the change in the reflecting luminous quantity reduction means due to the scattering of the magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical disk that can be played back by a read-only or write-once optical disk playback device, and a method for playing the same.

[Conventional technology]

Optical discs that reproduce information using optical beams are widely used as high-density, large-capacity recording memories along with their reproducing devices. An optical disk is a disc-shaped thin transparent substrate (for example, plastic) on which a chrono-order signal is recorded in the form of a physically uneven bit string. The above-mentioned optical disc is played back by a playback-only type or a write-once type optical disc playback device. That is, the pit rows are formed, for example, in a spiral shape, and the pitch thereof is about 1.6 μm. A laser spot narrowed down to 1 μm or less by an objective lens is irradiated onto a desired area through the transparent substrate via a focusing servo mechanism and a tracking servo mechanism to record or reproduce information.

Thereby, since the laser beam on the surface of the transparent substrate is thick, the influence of scratches and scratches attached to the surface can be reduced. Recorded information is obtained by guiding reflected light from the signal surface of the optical disc to a photodetector through an objective lens, where it is converted into an electrical signal that changes depending on the amount of reflected light, and a reproduced signal is obtained.

On the other hand, a magneto-optical disk records information by reversing the direction of magnetization of a desired portion of its perpendicularly magnetized film. Information is reproduced by a magneto-optical disk recording and reproducing device using the magneto-optical Kerr effect or the Faraday effect. That is, when light linearly polarized by a polarizer is incident on a perpendicularly magnetized film, the plane of polarization of the reflected light and transmitted light is rotated by a predetermined angle with respect to the direction of magnetization in the initial state. These reflected or transmitted lights pass through an analyzer and change the intensity of the light (change in the amount of light).
The light is converted into an electric signal and guided to a photodetector, where it is converted into an electric signal that changes depending on the amount of reflected light, and a reproduced signal is obtained.

Also, when circularly polarized light is incident, depending on the direction of magnetization,
A signal detection method that uses the so-called circular dichroism effect of magnetic materials, where the intensity and phase of light differ, is also theoretically possible, and there are also examples of detecting differential signals at bit boundaries using garnet films. (Journal of the Japanese Society of Applied Magnetics, 12.198B).

[Problem to be solved by the invention]

However, the above-mentioned conventional magneto-optical disks cannot be played by read-only or write-once optical disk playback devices. That is, conventional magneto-optical disks can only be played back with a dedicated magneto-optical disk playback device. Therefore, it is necessary to prepare a dedicated magneto-optical disk playback device to play magneto-optical disks, and considering that read-only or write-once optical disk playback devices are widely available, it is difficult to efficiently use them. cannot be used on a regular basis, and there is no compatibility between playback devices. In addition, in the signal detection method using the circular dichroism effect, when a rare earth transition metal alloy thin film is used as the recording medium, the circular dichroism effect is very small, and it cannot be used practically as it is. There is a problem with this.

[Means for Solving the Problem] In order to solve the above problem, a magneto-optical disk according to claim 1 is a magneto-optical disk having a transparent substrate and a perpendicularly magnetized film formed on the transparent substrate. The present invention is characterized in that reflected light amount reducing means, such as magnetic powder, whose distribution state changes depending on the direction of magnetization is provided on the surface of the perpendicularly magnetized film.

Further, in order to solve the above problem, a method for reproducing a magneto-optical disk according to claim 2 includes a transparent substrate and a perpendicularly magnetized film formed on the transparent substrate, and a surface of the perpendicularly magnetized film is provided. When using a magneto-optical disk equipped with a means for reducing the amount of reflected light whose distribution state changes depending on the direction of magnetization, and when reproducing the magneto-optical disk with a magneto-optical disk reproducing device, a light beam is incident from the side of the transparent substrate. The rotation of the plane of polarization of the light that occurs when
The method is characterized in that this is carried out by detecting a change in the amount of reflected light caused by the reflected light amount reducing means.

[For production]

In the structure of the invention as claimed in claim 1, by simply providing a means for reducing the amount of reflected light on the surface of the perpendicularly magnetized film, it is possible to perform playback with a dedicated magneto-optical disk reproducing device, and also with a read-only or write-once optical disk reproducing device. Can be played.

In addition, in the configuration of the invention as claimed in claim 2, the optical disc reproducing apparatus can be used simply by changing the direction of incidence of the light beam for reproduction on the magneto-optical disc without complicating the configuration of the optical disc reproducing apparatus. But it can be played.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 7.

The magneto-optical disk 6 according to the present invention is composed of a first transparent substrate 1, a perpendicularly magnetized film 2, an oil layer 3, a spacer 4, and a second transparent substrate 5, as shown in FIG.

The first transparent substrate 1 is made of glass having a thickness of 1.2 wn, for example. Other materials for the first transparent substrate 1 include PC (polycarbonate),
P MM A (polymethyl methac
rylate), etc. The perpendicular magnetization film 2 formed on the first transparent substrate 1 is made of, for example, TbFeCo, Gd
It is made of a rare earth transition metal alloy such as TbFe or DyFeCo, garnet, or an oxide magnetic material.

On the surface of the perpendicularly magnetized film 2, about several hundred, more preferably about 100 to 200, magnetic powder is applied as a means for reducing the amount of reflected light. The first transparent substrate 1 and the second transparent substrate 5 are coupled by a spacer 4,
A space surrounded by the first transparent substrate 1 , the perpendicularly magnetized film 2 , the spacer 4 , and the second transparent substrate 5 is formed as an oil layer 3 . The oil layer 3 is a means for reducing the amount of reflected light. Note that the facing distance between the perpendicularly magnetized film 2 and the second transparent substrate 5 is, for example, 10 μm to 0.3 m. Moreover, the oil layer 3 is filled with transparent oil.

Next, the case where the magneto-optical disk 6 having the above configuration is reproduced by a read-only type or write-once type optical disk reproducing apparatus will be described below with reference to FIGS. 2 to 6.

FIG. 2 is a diagram illustrating a main part of an optical system of a read-only type or write-once type optical disc reproducing apparatus. Light for reproduction (reproduction light) irradiated from a light source (not shown) such as a semiconductor laser passes through a polarizing beam splitter 21, a quarter-wave plate 22, and an objective lens 23 to the second optical disc of the magneto-optical disk 6. The light is irradiated from the transparent substrate 5 side. Note that the 1/4 wavelength plate 22 converts linearly polarized light into circularly polarized light. The reflected light from the perpendicularly magnetized film 2 is again incident on the polarizing beam splitter 21 via the objective lens 23 and the 1/4 wavelength plate 22.

Since the reflected light passes through the 1/4 wavelength plate 22, it becomes linearly polarized light whose polarization plane is rotated by 90' from the initial linearly polarized light, is reflected by the polarizing beam splitter 21, and then passes through the condensing lens 24 and the cylindrical lens 25. The light is incident on the photodetector 26. Here, it is converted into an electrical signal that changes depending on the amount of reflected light, and a reproduced signal is obtained.

Here, the behavior of the magnetic powder applied to the surface of the perpendicularly magnetized film 20 when the reproduction light is incident on the oil layer 3 will be described below.

In the perpendicular magnetization film 2, as shown in FIG. 3, recording marks 2a and 2b correspond to 1 in binary logic, for example, and non-recording marks (including guide grooves) other than recording marks 2a and 2b correspond to binary logic. Suppose that it corresponds to O in logic. In the perpendicularly magnetized film 2 in which the direction of magnetization is set as described above, as shown in FIG. (for convenience, indicated by diagonal lines). In this state, when reproduction light is incident on the perpendicularly magnetized film 2 through the oil layer 3, the amount of reflected light is reduced due to scattering of the concentrated magnetic powder.

Next, as an example of reproduction of recording marks, a case where the shapes thereof are different will be described below with reference to FIGS. 5 and 6.

FIG. 5 shows the case where an oval recording mark is reproduced. When digital data is recorded as shown in Fig. 5(a), the magnetic powder becomes a recording mark A (see Fig. 5(b)), which is shown by a solid line for convenience, and cannot be reproduced. The reproduced signal obtained is as shown in Figure 5(C).
This corresponds to the above digital data.

FIG. 6 shows the case where a semi-circular recording mark is reproduced. When digital data is recorded as shown in FIG. 6(a), the magnetic powder becomes a recording mark B (see FIG. 6(b)), which is shown by a solid line for convenience, and cannot be reproduced. The reproduced signal obtained by this process corresponds to the digital data as shown in FIG. 6(c).

As described above, when magnetic powder is applied to the surface of the perpendicular magnetization film 2, the magnetic powder concentrates on the domain wall depending on the direction of magnetization of the perpendicular magnetization 11!2. By detecting this, the magneto-optical disk 6 can be played back by a general read-only or write-once optical disk playback device.

Here, the case where the magneto-optical disk 6 is reproduced by the magneto-optical disk reproducing apparatus will be explained below based on FIG. 7.

FIG. 7 is a diagram showing the main part of the optical system of the magneto-optical disk reproducing apparatus. Linearly polarized reproduction light for reproduction emitted from a light source (not shown) such as a semiconductor laser is transmitted to the side of the first transparent substrate 1 of the magneto-optical disk 6 via a half-dimension lens 11 and an objective lens 12. irradiated from. The reflected light from the perpendicularly magnetized film 2 is incident on the polarizing beam splinter 14 via the objective lens 12, the half mirror 11, and the condensing lens 13. In the polarizing beam splitter 14,
The light is divided into a P-polarized light component and an S-polarized light component, and is incident on photodetectors 15 and 16, respectively, and is converted into an electrical signal that changes depending on the amount of reflected light. Then, the outputs of the photodetectors 15 and 16 are differentially amplified to reproduce information.

In this way, the magneto-optical disk 6 according to the present invention can be reproduced even by a conventional magneto-optical disk reproducing device.

〔Effect of the invention〕

As described above, the magneto-optical disk according to the first aspect of the invention has a configuration in which a means for reducing the amount of reflected light whose distribution state changes depending on the direction of magnetization is provided on the surface of the perpendicularly magnetized film.

Further, as described above, the method for reproducing a magneto-optical disk according to the invention of claim 2 provides a method for reproducing a magneto-optical disk, in which a means for reducing the amount of reflected light is provided on the surface of the perpendicularly magnetized film, the distribution state of which changes depending on the direction of magnetization. When a magnetic disk is used and a magneto-optical disk is played back by a magneto-optical disk playback device, the rotation of the plane of polarization of the light that occurs when a light beam is incident from the side of the transparent substrate is detected. When reproducing the magneto-optical disc with a type of optical disc reproducing apparatus, a light beam is incident on the side of the reflected light amount reducing means, and the change in the amount of reflected light caused by the reflected light amount reducing means is detected.

According to the configuration of the magneto-optical disk according to claim 1, by simply providing a means for reducing the amount of reflected light, it is possible to reproduce the disk with a dedicated magneto-optical disk reproducing device, and also with a read-only or write-once optical disk reproducing device. becomes.

Further, according to the structure of the method for reproducing a magneto-optical disk according to claim 2, it is possible to perform playback with a general optical disk reproducing apparatus without complicating the structure of the optical disk reproducing apparatus.

[Brief explanation of drawings]

1 to 7 show one embodiment of the present invention. FIG. 1 is a sectional view showing the structure of a magneto-optical disk according to the present invention. FIG. 2 shows a read-only type magneto-optical disk according to the present invention.
Alternatively, it is a main part configuration diagram of an optical system when playing back with a write-once type optical disc playback device. FIG. 3 is an explanatory diagram showing the state of magnetization of the perpendicular magnetization film of the magneto-optical disk. FIG. 4 is a schematic illustration of magnetic powder distributed in accordance with the direction of magnetization shown in FIG. 3. FIG. 5 shows a case where a magneto-optical disk having oval recording marks is reproduced by an optical disk reproducing device, in which (a) is an explanatory diagram of digital data, and (a) and (b) are illustrations of digital data. is an explanatory diagram of the distribution state of magnetic powder;
C) is an explanatory diagram of a reproduced signal. FIG. 6 shows a case where a magneto-optical disk having circular recording marks is reproduced by an optical disk reproducing device, in which (a) is an explanatory diagram of digital data, and (b) is an explanatory diagram of the magnetic data. It is an explanatory diagram of the distribution state of powder, and the same figure (c) is an explanatory diagram of a reproduction signal. FIG. 7 is a diagram showing the main parts of an optical system when a magneto-optical disc according to the present invention is reproduced by a magneto-optical disc reproducing apparatus. 1 is a first transparent substrate, 2 is a perpendicular magnetization film, 3 is an oil layer (means for reducing the amount of reflected light), 4 is a spacer, and 5 is a second transparent substrate. Fig. 2 Reproduction light Fig. wo☆ji9ruko-tahiki mark (a) (b) 01111100141100114100Cgo4Cde4σ4
0100100100 History Ba limb mark (b)
Cf"Cf8σ8C5-8 (zu-8C5-8Fig.

Claims (1)

[Claims] 1. In a magneto-optical disk having a transparent substrate and a perpendicular magnetization film formed on the transparent substrate, a reflection whose distribution state changes depending on the direction of magnetization is formed on the surface of the perpendicular magnetization film. A magneto-optical disk characterized by being provided with a light amount reducing means. 2. A magneto-optical disk comprising a transparent substrate and a perpendicularly magnetized film formed on the transparent substrate, and provided with means for reducing the amount of reflected light whose distribution state changes depending on the direction of magnetization on the surface of the perpendicularly magnetized film. When playing the magneto-optical disk using a magneto-optical disk reproducing device, the rotation of the plane of polarization of the light that occurs when a light beam is incident from the side of the transparent substrate is detected.
Alternatively, when the magneto-optical disk is played back by a write-once type optical disk playback device, a light beam is incident on the side of the reflected light amount reducing means, and a change in the amount of reflected light caused by the reflected light amount reducing means is detected. How to play magneto-optical discs.