JPH076439A - Optical recording and reading method - Google Patents

Abstract

PURPOSE:To enable recording and reading with high density by increasing the limit of the high density of optical recording and reading without remarkably revising a light source and a convergence optical system. CONSTITUTION:An optical disk provided with a substrate 2 and a recording layer 3 consisting of a material where an optical characteristic is changed according to a temperature is rotated, and is converged and irradiated by a laser beam, and recorded information is read by detecting the refelcted beam. In the optical recording and reading method, the optical disk is constituted so that a first minute area and a second minute area whose absorption amounts of the laser beam are different from each other are formed on the recording layer 3, and recording information is shown by the presences or the lengths of the first and the second minute areas. The optical disk is provided with a refelection film 5 reflecting the incident laser beam on the disk to the recording layer 3, and is provided with a light transmission film 4 changing a reflection light quantity to the recording layer 3 selectively between the reflection film 5 and the recording layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reading method.

[0002]

2. Description of the Related Art As information devices such as computers, communications, and video devices have become more sophisticated and personalized, the amount of information to be processed is unavoidable. Against this background, high performance of recording devices and media has become a big development target in recent years, and in particular, high density and large capacity of recording are very large in view of the coming digital age of image information. It can be said that it is a request. There is no doubt that the optical method for reading the recording from the medium will continue to be a promising method for high density and large capacity memories.

Products using the optical recording / reading method are now widely provided as music CDs, CD-ROMs, LDs, magneto-optical disks, and the like. In these systems, incident light from a light source (a semiconductor laser is often used for downsizing of a reading device) is focused on a rotating disk that is a recording medium, and recorded information on the disk is reflected by the light. It is detected by light.

The recorded information is unevenness provided on the disk in a CD or the like, and the magnitude of the reflected light from the unevenness becomes the reproduced information. Further, in the magneto-optical disk, the magnetization direction of the recording medium serves as information, and the information is read by changing the polarization plane of the reflected light (or transmitted light) depending on the magnetization direction.

As described above, in the optical recording / reading method,
By condensing the incident light on the recording disk small, the information unit can be reduced to that size, and thus a large recording density is realized. At present, it is about 10 ⁸ marks / cm ² in a magneto-optical disk.

[0006]

However, as described above, in the optical recording / reading method, the degree of collection of incident light (spot diameter) determines the size of the information unit, that is, the recording density. The minimum value of the spot diameter is limited by the wavelength of the light source and the numerical aperture of the condenser lens system, and cannot be made smaller than the diffraction limit.

Currently, the recording density of the light source and the optical system is almost at its limit, and if the recording density is further increased, a large numerical aperture can be obtained by modifying the optical system or a short wavelength can be obtained. It may be possible to obtain a light source, but both are not easy due to the enormous size and cost of the device.

The present invention has been made by paying attention to such a conventional problem, and raises the limit of high density of optical recording and reading without making a large change in the light source and the focusing optical system. An object of the present invention is to provide an optical recording / reading method that enables recording / reading with a density.

[0009]

[Means for Solving the Problems] To achieve the above object,
In the optical recording / reading method according to the invention of claim 1 of the present application, an optical disk provided with a substrate and a recording layer made of a material whose optical characteristics change with temperature is rotated, and laser light is focused and irradiated, In an optical recording / reading method for reading recorded information by detecting reflected light,
In the optical disc, a first minute area and a second minute area having different absorption amounts of the laser light are formed on the recording layer, and the recorded information is determined by the presence or absence or the length of the first and second minute areas. It is characterized in that it represents.

An optical recording / reading method according to a second aspect of the present invention is the optical recording / reading method according to the first aspect of the invention, wherein the optical disc is a reflection for reflecting the laser light incident on the disc toward a recording layer. A film is provided, and a light transmission film that changes the amount of light reflected to the recording layer is selectively provided between the reflection film and the recording layer, and the light transmission film is provided in the first minute region. It is a region provided, and the second minute region is a region where the light transmitting film is not provided.

An optical recording / reading method according to a third aspect of the present invention is the optical recording / reading method according to the first aspect of the invention, wherein the optical disc is a reflection for reflecting a laser beam incident on the disc toward a recording layer. A film is provided, and a light-transmitting film having a selectively changed film thickness is provided between the reflective film and the recording layer, and the first minute region has a large film thickness of the light-transmitting film. The second minute region is a region where the film thickness of the light transmitting film is small.

An optical recording / reading method according to a fourth aspect of the present invention is the optical recording / reading method according to the first aspect of the present invention, wherein the optical disc has an optical recording layer in the first or second minute area. It is characterized in that a substance that changes the absorption rate of is added.

An optical recording / reading method according to a fifth aspect of the present invention is the optical recording / reading method according to the first aspect of the invention, wherein the optical disk is in contact with the recording layer and selectively a heat insulating layer or a heat reflecting layer. And the first or second minute region is a region where the heat insulating layer or the heat reflecting layer is formed.

An optical recording / reading method according to a sixth aspect of the present invention is the optical recording / reading method according to the first aspect of the invention, wherein the optical disc is provided with a thermal diffusion layer selectively in contact with the recording layer. The first or second minute region is a region in which the thermal diffusion layer is formed.

[0015]

According to the present invention constructed as described above, the optical recording / reading is performed by irradiating the laser beam with the temperature rise of the recording layer irradiation portion. At that time, the temperature gradient of the recording layer is set within the probe light spot. The information unit can be made smaller by increasing the size and detecting the change in the reflected light due to the temperature difference. This method is preferably applied to a magneto-optical recording method.

In the present invention, the optical characteristics of the recording layer of the disk are changed by heating by irradiation with probe light, and information is read out by the change of reflected light (light amount, polarization plane) due to this change, and the recording layer is Unlike an ordinary recording medium, the optical characteristics of the medium return to the original state by cooling after the probe light is heated, and only the heated portion becomes an information unit. Examples of the material forming the recording layer include a magneto-optical material, a phase change material, and a thermo-optical material.

The principle of the optical recording / reading method of the present invention will be described below with reference to FIGS. In addition, (a) of the figure
Is a diagram schematically showing a part of the cross section of the disc,
(B) is a figure which shows a part of disk from the direction orthogonal to a disk.

When a large number of binarized information units are contained in the incident light spot condensed to the diffraction limit, it cannot be identified by the conventional optical recording / reading method. That is, when three information units "1" and "0" are included in a spot, for example, "100", "001", and "010" show almost the same detection signal intensities, and these are distinguished. I couldn't.

However, according to the reading method of the present invention, even when a plurality of information units are recorded in the laser spot, the information can be read as follows.
That is, when the disc is irradiated with the laser beam light focused by the condenser lens 1, the beam heats the disc (recording layer 3), but the temperature depends on the amount of light absorbed. In the disk used in the present invention, read-only optical recording is formed by setting the material and film thickness so as to change the light absorption amount of "0" and "1" of the information unit.

If the amount of light reflected and transmitted from the disc is large and the light absorption in the recording layer is small, the temperature does not rise so much. It is possible to control the amount of light absorbed in the recording layer portion by changing the laminated thin film structure. By selectively providing a film for each information unit or partially changing the film thickness, the temperature Different information units "0" and "1"
Is formed.

As the recording medium constituting the recording layer 3, a material having different optical characteristics depending on temperature is used, and thus the reflected light intensity or the polarization direction differs depending on the presence or absence of this information unit. Here, if the intensity of the reflected light is largely modulated by the layer provided for controlling the light absorption, it may be noise to the signal. To reduce the impact of this,
A magneto-optical recording method that uses a difference in polarization direction as a signal is more suitable than a method that detects the intensity of reflected light itself.

Now, as a preferred example, in the optical disk shown in FIGS. 1 and 2, a recording layer 3 made of a magneto-optical medium is provided on a substrate 2, and a reflective film 5 is provided in contact with the recording layer 3 and selectively. The area where the light-transmissive film 4 is provided to form the area where the reflected light is strong and the area where the reflected light is weak due to the interference of the light, the information "1" is given by the area where the temperature of the recording layer 3 is increased, Information "0" by the area that was set not to go up
Is displayed.

The recording layer 3 is first aligned in the downward magnetization direction by the initializing magnetic field 10 (downward). An external magnetic field 9 (upward) is applied at the time of reading information, and only the portion where the temperature rises is magnetized to be inverted, and becomes a signal as a change in polarization direction. After being read, the magnetization of the recording layer 3 is aligned downward again by the initialization magnetic field 10 and is returned to the initial state.

In the case of FIG. 1, three minimum information units 6, 7 and 8 (information is "101") are included in the area of the beam spot 1a. The light intensity distribution of the beam spot is stronger near the center of the beam, and exhibits a Gaussian distribution approximately, but the spot moves on the disk by the rotation of the disk (arrow 12 in the figure indicates the moving direction of the disk). The temperature distribution due to the heating has a shape slightly deviated rearward from the position of the beam spot as shown in the diagram 11 of the figure.

Therefore, even if the next information unit "1" (8 in the figure) newly enters the beam spot, it is not identified as a change in the polarization direction. That is, the information of only the information unit “1” (6 in the figure) that has become high in temperature behind the traveling direction in the beam spot is reflected, and as a result, a large number of minimum information pieces in the beam spot are reflected. It is possible to take out only one unit. Thus, according to the recording / reading method of the present invention, high density of recording (reading) information is realized.

In order to control the light absorption of the recording layer, a light-transmitting film 4 having an optical film thickness which satisfies an appropriate interference condition is selected in contact with the recording layer 3 in accordance with the wavelength of the light source as described above. It is conceivable that the light reflection layer 5 is laminated and the light reflection layer 5 is laminated (FIG. 2). As the light transmitting film 4, SiO ₂ or ZnS-
SiO ₂ , SiN and the like are preferable, and the light reflecting layer 5 is preferably a metal film of Al, Au, Ag or the like.

As for the thickness of the light transmitting film 4, for example, when a transparent film having a refractive index n and a thickness d is provided as a single layer on a transparent substrate having a refractive index n ₀ , the reflectance is R is represented by the following formula, and the film thickness of the light transmitting film for changing the reflectance can be determined from the formula, for example.

R = [(1-n ₀ ) ² · cos ² δ +
{(N ₀ / n) -n} ² · sin ² δ] / [(1 + n
₀ ) ² · cos ² δ + {(n ₀ / n) + n} ² · sin
² δ]

In the above equation, δ = (2πn / λ) · d.

It is also possible to selectively provide the light reflecting film 5 to form a region having a large reflectance and a region having a small reflectance.

Further, as shown in FIG. 3, by adding a light absorbing additive that selectively changes the light absorption rate to the recording layer 3, the recording layer 3 itself has a large amount of light absorption. It is also possible to form 3a and a small region 3b. As the light absorbing additive, fine metal particles such as Al and Ag, fine carbon particles, and pigment are used.
The addition of the additive can be realized by a method such as ion implantation. Further, it is desirable to take care not to significantly change the signal intensity due to the magnetization of the recording layer when adding the light absorbing additive.

Further, the temperature of the recording layer also largely depends on the escape of heat from the layer. In general, when layers having a large coefficient of thermal conductivity are adjacent to each other, the temperature of the portion becomes low, and when a layer having a heat insulating effect or a layer having a heat reflecting effect is provided, the temperature is kept high.

That is, in the inventions of the fifth to sixth aspects, in the area of the recording layer where the heat insulating layer or the heat reflecting layer is provided, the absorption amount of the laser light is large, while the heat diffusing layer is provided. The amount of absorption of the laser light in the high region becomes small.

The SiO shown as the light transmitting film is used.
₂ , ZnS-SiO ₂ , and SiN all function as a heat insulating layer, and Al and A shown as the light reflecting film are used.
The metal films of u and Ag all function as a heat diffusion layer.

On the contrary, there are diamond-like carbon which is transparent but has a large thermal diffusion, and In-Sb alloy which functions as a light reflecting layer but has a small thermal conductivity. By appropriately laminating these films, It is possible to realize a configuration for increasing the temperature difference.

[0036]

Embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a schematic view showing a part of the cross section of a disc used in the optical recording / reading method according to one embodiment of the present invention. The disc used in this embodiment was prepared as follows.

First, a glass substrate having a diameter of 5 inches and a thickness of 1 mm is prepared, and ZnS—SiO ₂ (weight ratio 4: 1) is deposited on the substrate 42 by sputtering to a thickness of about 100 nm to form a heat insulating layer 46. . Next, D, which is a magneto-optical material
The recording layer 43 is formed by stacking yFeCo (composition ratio 22:55:23) by 30 nm by sputtering. This film causes magnetization reversal by an external magnetic field at about 150 ° C.

Further, an Al ₂ O ₃ layer having a thickness of 200 nm is laminated on the recording layer 43, and then a KrF excimer laser (wavelength 2 is used).
(49 nm) This film was patterned by an exposure machine as a signal original plate (created by an Ar laser cutting machine), and the Al ₂ O ₃ layer was selectively left on the recording layer (4
4). The Al ₂ O ₃ layer 44 is a film that is transparent but relatively easily releases heat. The patterning was performed by dry etching.

Finally, an In--Sb alloy, which functions as a light reflecting layer but has a low thermal conductivity, is formed by sputtering to 100%.
nm lamination to form the reflection layer 45, and then ZnS-SiO
₂ (weight ratio 4: 1) was deposited to a thickness of 100 nm to form a heat insulating layer 47, and a polycarbonate 49 was sealed with an epoxy resin 48 to complete an optical disc.

In the optical disc thus prepared,
The reflectance of a portion of the Al ₂ O ₃ layer 44 is about 22%,
The non-existing portion is about 7%, and the portion having the Al ₂ O ₃ layer in the recording layer has a large light absorption amount, and the heating effect is high.

As in the case of FIG. 1, a light source with λ = 830 nm and a condenser lens numerical aperture of 0.5 is used as the incident light, and the beam moves on this disk at a constant linear velocity of 7 m / sec. Then, the recording was read out. An initializing magnetic field (downward) of 10 kOe (disk surface) is provided, and an external magnetic field (upward) of 300 Oe during reading.
Is being applied. Read-out tracking was realized by a push-pull signal which is the diffracted light from the patterning film array.

By detecting the polarization difference signal by this reading method, a signal train (A with a laser power of 5 mW, a minimum mark size length of 0.4 μm and a mark interval of 0.4 μm) is obtained.
The pattern size of the l ₂ O ₃ film is C / N of 30 dB or more.
I was able to read at the level.

As described above, according to the present invention, a mark having a size smaller than the diffraction limit spot size can be identified, and high-density optical recording can be read out without changing the light source wavelength and the numerical aperture. Furthermore, since the method retains the recording by the method of patterning the laminated film, it is possible to record the data on a conventional writable disc (such as a magneto-optical disc, a phase change type disc, a volume change type disc, a color change type disc). compared,
It excels in stability against magnetic fields, temperatures, and light.

Further, according to the present invention, since the pattern rows having different light reflectances can be formed, the pattern rows can be used for tracking, and it is not necessary to provide a tracking groove or the like on the substrate. .

[0045]

As described above, according to the present invention,
It is possible to raise the limit of increasing the recording density of optical recording and reading without making a large change in the light source and the condensing optical system, and enable recording and reading of high density.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating the principle of an optical recording / reading method of the present invention.

FIG. 2 is a schematic view showing a part of a cross section of an optical disc used in the optical recording / reading method of the present invention.

FIG. 3 is a schematic view showing a part of a cross section of another optical disk which is also used in the optical recording / reading method of the present invention.

FIG. 4 is a schematic view showing a part of a cross section of a disc used in an optical recording / reading method according to an embodiment of the present invention.

[Explanation of symbols]

1 Condensing Lens 1a Laser Light Spot 2,42 Substrate 3,43 Recording Layer (Arrow Shows Magnetization Direction) 3a Part Added with Light Absorption Additive 3b Part Not Added Light Absorption Additive 4,44 Light transmission film (transparent film for light interference) 5,45 Reflection film 6 Information unit "1" that is read by magnetization reversal due to temperature increase 7 Information unit "0" 8 that light absorption is small and temperature does not increase 8 1 ”9 External magnetic field 10 Initializing magnetic field 11 Temperature distribution curve of recording layer 12 Rotation direction of disk 46,47 Heat insulating layer 48 Epoxy resin 49 Sealing layer (polycarbonate layer) Show.

Claims (6)

[Claims] 1. An optical disk comprising a substrate and a recording layer made of a material whose optical characteristics change depending on temperature is rotated, laser light is focused and irradiated, and the reflected light is recorded to record. In the optical recording / reading method for reading information, in the optical disc, a first minute area and a second minute area having different absorption amounts of the laser light are formed in the recording layer, and the first and second minute areas are formed. The optical recording / reading method, wherein the recording information is represented by the presence or absence of the minute area or the length thereof. 2. The optical disc comprises a reflective film for reflecting laser light incident on the disc toward a recording layer, and light for changing the amount of reflected light to the recording layer between the reflective film and the recording layer. A permeable membrane is selectively provided,
The optical recording / reading method according to claim 1, wherein the first minute area is an area provided with the light transmitting film, and the second minute area is an area not provided with the light transmitting film. 3. The optical disk comprises a reflective film for reflecting a laser beam incident on the disk toward a recording layer, and a light transmission having a film thickness selectively changed between the reflective film and the recording layer. A film is provided, the first minute region is a region where the film thickness of the light transmitting film is large, and the second minute region is a region where the film thickness of the light transmitting film is small. The optical recording and reading method described in. 4. The optical recording / reading method according to claim 1, wherein the optical disc has a recording layer of the first or second minute region to which a substance that changes a light absorption rate is added. 5. The optical disc is one in which a heat insulating layer or a heat reflecting layer is selectively provided in contact with the recording layer, and the first or second minute area is formed of the heat insulating layer or the heat reflecting layer. The optical recording and reading method according to claim 1, which is a formed area. 6. The optical disc is one in which a thermal diffusion layer is selectively provided in contact with the recording layer, and the first or second minute region is a region in which the thermal diffusion layer is formed. Item 2. The optical recording / reading method according to Item 1.