JPH0765411A - Optical recording medium and its optical reproducing method - Google Patents

Abstract

PURPOSE:To enable reproducing with high accuracy by having a reflection layer, of which the refractive index to the wavelength of a reproducing light beam exhibits a value changing at an arbitrary temp. in a temp. range between a temp. at which the recording of a recording layer is erased and room temp. CONSTITUTION:A transparent substrate 31 is made of glass, etc., and is provided thereon with a transparent dielectric layer 32 consisting of SiN, SiO, etc., and the recording layer 33 consisting of Te, TeGe, etc. Further, the substrate is further provided with the reflection layer 35, of which the refractive index to the wavelength of the reproducing light beam exhibits a value changing at a arbitrary temp. in a temp. range between the temp. at which the recording of the recording layer is erased and room temp, and an over coat layer 36. The reproduction with the high accuracy is thereby enabled. The recording signals smaller than the size of the light beam are thus reproduced by changing of the refractive index in a part of the reflection layer 35 at the time of reproduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high density optical recording medium for reproducing information using light and an optical recording / reproducing method thereof.

[0002]

2. Description of the Related Art The recording density of a memory element for reading recorded information using light is limited by the wavelength of light used for recording and reading and the numerical aperture of a condenser lens. Recently, it has been desired to increase the recording density of an optical recording medium such as a magneto-optical disk. However, in a magneto-optical disk, when a signal recorded in a recording layer is read out, it is irradiated in the reproducing layer. By blocking a part of the reproduction light beam spot, the direction of the magnetization of the reproduction layer and the recording layer correspond to each other only in a small area, and the light beam spot is substantially reduced. Methods for obtaining the effect have been proposed (Japanese Patent Laid-Open Nos. 1-143041 and 1-143042).

However, when such a method is used, it is necessary to detect a change in the magneto-optical effect in a part of the light beam spot, but the light intensity reflection of the area where the recording is to be read by the light beam is required. Since the rate is almost constant, there is the difficulty of having to detect small signals. Further, in a phase change recording medium that detects a signal based on a difference in reflectance, it is difficult to transfer information recorded in a recording layer similar to the magneto-optical recording medium to another layer.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical recording medium and an optical recording / reproducing method capable of reproducing the recording on the high density optical recording medium with high accuracy.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, an optical recording medium having a reflective layer showing a different refractive index with a certain temperature as a boundary has the above object. The inventors have found that they are suitable and completed the present invention.

That is, the present invention is an optical recording medium comprising at least a recording layer and a reflective layer for reproducing by a light beam, wherein the recording of the recording layer is erased when the refractive index of the reflective layer with respect to the wavelength of the reproducing light beam. Optical recording medium characterized by having a reflective layer exhibiting a value that changes at any temperature in the temperature range between room temperature and room temperature, and a part of the irradiation range of the reproduction light beam The recording rate was changed from a part of the irradiation range of the reproduction light beam to a recording layer in advance, and the temperature was made higher than an arbitrary temperature in a temperature range between the temperature at which recording on the recording layer was erased and the room temperature. The present invention relates to an optical recording / reproducing method for reading a signal.

The present invention will be described in detail below with reference to the drawings. FIG. 1 illustrates an optical recording / reproducing method according to the present invention.

Recording / reproduction of the optical recording medium of the present invention is performed by scanning while irradiating a recording portion with a normal light beam continuously at a constant speed. At this time, the area irradiated by the reproduction light beam is The temperature rises.

Since the reproduction light beam has an almost Gaussian intensity distribution and the light beam scans at a constant speed,
In the temperature distribution of the portion heated by the light beam, the position where the maximum temperature is reached does not always coincide with the center of the light beam spot (1 in FIG. 1), and the high temperature region is relatively high in the light beam spot. It occupies a portion in the traveling direction of the medium (portion in the direction of the arrow in FIG. 1).

Here, by adjusting the intensity of the reproduction light, a predetermined region (2 in FIG. 1) in the reproduction light beam spot exceeds the temperature (T1) at which the refractive index of the reflective layer changes, and The temperature is set to be lower than the temperature (T2) at which the recording on the recording layer is erased.

In order to reduce or increase the reflected light intensity of the light beam from the region where the refractive index of the reflecting layer is changed,
The layer thickness of the reflective layer, the recording layer, or the interference layer arranged for the purpose of making the signal intensity appropriate can be appropriately set.

The reflectance of the region (3 in FIG. 1) of the reproduction light beam spot where the temperature does not exceed T1 does not decrease or increase, and the intensity of the reflected light reflected from the region 3 is relative. Since it is larger than area 2, the recorded signal in area 3 can be selectively read.
Therefore, it is possible to obtain the same effect as when the light beam spot is substantially reduced.

In the optical recording / reproducing method of the present invention,
The reproduction signal is obtained from the reflected light from the medium. At this time, the signal is detected from the rotation of the polarization plane of the light, the signal is detected from the change in the intensity of the reflected light, and the signal is detected from the change in the phase of the reflected light. A detection method or the like can be used. Therefore, a magneto-optical recording layer or a phase change type optical recording layer can be used as the recording layer of the optical recording medium of the present invention. At this time, the magneto-optical recording layer and the phase change type optical recording layer may be composed of one layer or a plurality of layers.

An embodiment of the optical recording medium of the present invention is shown in FIG.
Shown in 3. In the figure, 21 and 31 are transparent substrates, and a polymer substrate such as a glass substrate or polycarbonate is usually used. In the figure, 22 and 32 are transparent dielectric layers, such as SiN, SiO,
AlN, ZnS, SiAlON or the like can be used, and the thickness is set for the purpose of making the signal strength appropriate. In the figure, reference numerals 23 and 33 denote recording layers, which are composed of a film, which can be read out by light, formed of an alloy such as Te or TeGe or TbFeCo. 24 in the figure,
34 is a transparent dielectric layer, and can have the same composition and thickness as the dielectric layer 22.

In the figure, reference numerals 25 and 35 are reflection layers which characterize the optical recording medium of the present invention, and have a refractive index with respect to the wavelength of the reproduction light beam,
It is essential to have a reflective layer that exhibits a value that varies at any temperature in the temperature range between the temperature at which the recording on the recording layer is erased and room temperature. The change referred to here means that the value of the refractive index differs at least at an arbitrary temperature within the above-mentioned temperature range.

Such a reflective layer is formed of a material such as In or In alloy having a melting point higher than room temperature and a relatively low temperature, and recrystallized when cooled from a molten state.

Further, in order to make the reflectance and the signal strength appropriate, Al, Cu, Pt, Ni, C are formed on or under the reflection layer.
A second reflective layer containing r, Ti, etc. can also be provided.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 An optical recording disk having the structure shown in FIG. 3 was produced. Transparent dielectric layer (32 in the figure) on a polycarbonate substrate (31 in the figure)
As the recording layer (33 in the figure), a rare earth transition metal alloy (TbFeCo), SiN as the transparent dielectric layer (34 in the figure), an In alloy as the reflective layer (35 in the figure), and Al as the second reflective layer. Films were formed in this order by sputtering, and an overcoat film was further applied as a protective film (36 in the figure). The rare earth transition metal alloy used as the recording layer was a perpendicular magnetization film, and the Curie temperature was 310 ° C. The melting point of the In alloy used as the reflective layer was 180 ° C.

A signal previously recorded in the recording layer by the direction of magnetization perpendicular to the film surface of the medium was read by the following method. 780 nm laser light is used as reproduction light,
A condenser lens with an NA of 0.5 was used. While irradiating a 4 mW laser beam at a linear velocity of 10 m / sec on the recorded disk, the Kerr rotation angle of the reflected light from the recording medium was detected and the recorded signal was reproduced. When the recorded magnetic domain length was 0.3 μm, the C / N ratio of the reproduced signal was 40 dB.

Example 2 ZnS as a transparent dielectric layer on a polycarbonate substrate,
Ge-Te alloy as recording layer, Z as transparent dielectric layer
nS, In alloy as the reflective layer, Al as the second reflective layer
Were sequentially formed in this order by a sputtering method, and an overcoat film was further applied as a protective film to manufacture an optical recording disk.
The melting point of the Ge—Te based alloy used as the recording layer was 520 ° C. The melting point of the In alloy used as the reflective layer was 180 ° C.

A signal previously recorded on the recording layer due to the difference in the refractive index of the recording layer was read by the following method.
780 nm laser light is used as reproduction light, and NA is 0.5
The condenser lens of was used. Linear velocity on recorded disc 1
The recorded signal was reproduced by detecting the phase difference of the reflected light from the recording medium while irradiating the laser beam of 4 mW at 0 m / sec. When the recorded signal length is 0.3 micron,
The C / N ratio of the reproduced signal was 42 dB.

Example 3 ZnS as a transparent dielectric layer on a polycarbonate substrate,
Ge-Te alloy as recording layer, Z as transparent dielectric layer
nS, In alloy as the reflective layer, Al as the second reflective layer
Were sequentially formed in this order by a sputtering method, and an overcoat film was further applied as a protective film to manufacture an optical recording disk.
The melting point of the Ge—Te based alloy used as the recording layer was 520 ° C. The melting point of the In alloy used as the reflective layer was 180 ° C.

A signal previously recorded on the recording layer 53 as a difference in the refractive index of the recording layer 53 was read by the following method. 780 nm laser light is used as reproduction light, and NA
A condensing lens of 0.5 was used. While irradiating a 4 mW laser beam at a linear velocity of 10 m / sec on the recorded disc, the difference in the intensity of the reflected light from the recording medium was detected and the recorded signal was reproduced. When the length of the recorded signal was 0.3 micron, the C / N ratio of the reproduced signal was 42 dB.

As is clear from the above embodiments, according to the present invention, as the recording reproduced by a light beam such as magneto-optical recording or phase change optical recording, the wavelength limit of 2/2 NA, which is the diffraction limit, is exceeded. Even small recordings can be reproduced with high accuracy.

Further, the recording layer, the reflection layer and the transparent dielectric layer are not limited to the substances used in this embodiment, and it is sufficient that the recording layer has a record readable by light, Further, it suffices to have a reflective layer that reduces the reflectance of a predetermined part of the irradiated reproduction light spot by the reproduction light beam having an intensity that does not erase the recording.

[0027]

The optical recording medium of the present invention enables highly accurate reproduction, and the recording signal smaller than the size of the light beam due to a change in the refractive index of a part of the reflective layer during reproduction. Can be played.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical recording / reproducing method of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing an optical recording medium of Example 1.

[Explanation of symbols]

 1: Light beam spot 2: Area where reflectance is decreased due to temperature rise 3: Area where reflectance is not decreased due to irradiation of light beam 4: Recorded signal 21: Transparent substrate 22: Transparent dielectric layer 23: recording layer 24: transparent dielectric layer 25: reflective layer 31: transparent substrate 32: transparent dielectric layer 33: recording layer 34: transparent dielectric layer 35: reflective layer 36: overcoat layer

Claims (2)

[Claims] 1. An optical recording medium comprising at least a recording layer and a reflective layer for reproducing by a light beam, wherein the refractive index of the reflective layer with respect to the wavelength of the reproducing light beam is the temperature at which recording on the recording layer is erased. An optical recording medium having a reflective layer that exhibits a value that changes at an arbitrary temperature within a temperature range between room temperature and room temperature. 2. An optical recording medium comprising at least a recording layer and a reflecting layer for reproducing by a light beam, wherein the refractive index of the reflecting layer with respect to the wavelength of the reproducing light beam is the temperature at which recording on the recording layer is erased. In an optical recording / reproducing method for an optical recording medium having a reflective layer that exhibits a value that changes at an arbitrary temperature between room temperature and a temperature of a part of the irradiation range of the reproducing light beam, the temperature at which recording on the recording layer is erased. Optical recording / reproducing, characterized in that the signal recorded in advance in the recording layer is read from the irradiation range of the reproduction light beam or the remaining region thereof by increasing the temperature between the room temperature and the room temperature above the temperature at which the refractive index changes. Method.