JPH03216824A - Optical information recording medium and optical information recording method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field]

The present invention provides a wavelength multiplexing optical information recording medium that is capable of recording information associated with each wavelength as multilevel information in the same place using light of different wavelengths, and a multilayered optical information recording medium that is capable of recording information corresponding to each wavelength as multivalued information, and a multilayer optical information recording medium that uses light of different wavelengths to record information corresponding to the wavelengths as multivalued information. This invention relates to a multi-layer multi-value recording method for recording information.

[Conventional technology]

As an example of the prior art related to the present invention, JP-A-59-
152528 can be mentioned. As a cross-sectional structure of the first conventional optical information recording medium, for example, a structure as shown in FIG. 2 can be shown. In the structure of this conventional example, a first dye film 8a, a dielectric film 6, a second dye film 8b
, protective film 7 are laminated in this order. FIG. 3 shows absorption spectra of the first dye film 8a and the second dye film 8b. That is, the first dye film 8a's ? The spectrum 9b of the spectrum 9a and the second dye film 8b have different wavelengths at which the absorption is maximum. Therefore, when the wavelength multiplexing optical information recording medium of FIG. 2 is irradiated with light of wavelength λ1, which is mainly absorbed by the first pigment film 8a, most of the light is absorbed by the first pigment film 8a, and the light is absorbed by the second pigment film 8b. is almost never reached. This situation is shown by the solid line in FIG. 2(b). Conversely, when the wavelength multiplexing optical information recording medium of FIG. 2(a) is irradiated with light of wavelength λ2, which is mainly absorbed by the second pigment film 8b, the light passes through the first pigment film 8a and is absorbed into the second pigment film. Absorbed by 8b. This situation is shown by the broken line on the right side of Figure 2. Therefore, by irradiating the wavelength multiplexing optical information recording medium of FIG. 2 with strong light of wavelength λ■ or wavelength λ2, the first pigment film 8a or the second pigment film 8b is thermally or photochemically modified (photosensitized). This means that wavelength multiplexing recording can be performed. In the portion recorded in this way, the absorption rate of the first dye film 8a or the second dye film 8b changes. Therefore, by irradiating that portion with low-intensity light (wavelength λ and wavelength λ2) and checking the intensity of the reflected light or the transmitted light, the presence or absence of information can be determined. In other words, the recorded data can be reproduced. As a second conventional example, a configuration of a multi-layer multi-level recording system as shown in FIG. 4 can be shown. The structure of this conventional example is such that a first recording film 10a, a dielectric film 6, and a second recording film are disposed on a transparent substrate 1 made of glass or the like on a disc having concentric or spiral guide grooves for tracking. 10b and a protective film 7 are laminated in this order. First recording film 10a and second recording film 10
b may be made of the same material or different materials. The laser beam 5 is focused and irradiated onto the recording medium having such a configuration using the lens 11. At this time, the position (focal point) where the laser beam is focused is selectively set on the first recording film 10a or the second recording film 10b by changing the wavelength of the light or the position of the lens. To change the wavelength, we use the effect (chromatic aberration) in which the focal length of a lens changes depending on the wavelength. Therefore, since the power density of the laser beam is higher on the recording film on the side where the laser beam is focused, the first recording film 10a or the second recording film 10b is thermally or photochemically modified as in the above example. This means that multi-layer, multi-value recording can be performed. [Problem to be Solved by the Invention] However, in the first conventional example, it was necessary to make the absorption spectra of the dyes in each layer different from each other, but the spectra of dyes generally have a considerable wavelength width. Therefore, it has been difficult to increase the multiplicity by increasing the number of layers. Furthermore, in the first conventional example, the dye film is gradually denatured (sensitized) even by weak light, so there is a problem in that recorded information disappears as readout is repeated. In addition, in the second conventional example, which recording film is used for recording is selected based on the position of the focal point, each recording film must be sufficiently far away from each other than the size of the focused light spot. was there. Therefore, it is necessary to laminate the dielectric film sufficiently thickly, which is not easy to manufacture. Furthermore, in the second conventional example, when the disk recording medium is rotated for recording or reading,
It was difficult to automatically adjust the focal position to follow the shaking of the rotating surface of the recording medium. This is because a plurality of recording films exist sufficiently far apart from each other than the size of the focused light spot. An object of the present invention is to provide an optical information recording medium and an optical information recording method that can easily record a large amount of information at the same point, that is, can easily perform multi-level recording. be. It is also an object of the present invention to provide an optical information recording medium and an optical information recording method that are capable of performing multilevel recording without fear of losing recorded information even if the recorded information is repeatedly read out many times. Our goal is to provide the following. Another object of the present invention is to provide a multi-value optical information recording medium that can record multi-value information without increasing the thickness of the dielectric film that separates a plurality of recording films, and is therefore easy to manufacture. There is a particular thing. Furthermore, it is an object of the present invention to easily and easily perform automatic adjustment of the focal position following the shake of the rotating surface of the recording medium when the disk-shaped recording medium is rotated for recording or reading. An object of the present invention is to provide an optical information recording medium and an optical information recording method capable of performing multilevel recording.

[Means to solve the problem]

In order to achieve the above object, the present invention uses the following means. 1. In an optical information recording medium that has at least a recording film and a reflective film on a substrate, and in which recording is performed by irradiating a laser beam from the side of the recording film toward the reflective film, a laser beam in which the reflected light of the laser beam is incident. The wavelength division multiplexing multilevel recording is performed by utilizing the fact that the laser beam interferes with the laser beam to produce an intensity distribution of light, and the fact that the intensity distribution differs depending on the wavelength of the irradiated laser beam. As a result, there is no need to prepare multiple types of recording film materials corresponding to each wavelength to perform multi-value recording, so an optical information recording medium and optical information recording device that can easily perform multi-value recording How can you get it? Furthermore, since there is no need to use a material sensitive to weak light such as a dye as the recording film, there is no risk that the recorded information will be lost even if the recorded information is read out many times. Furthermore, since there is no need to selectively focus the light spot on the layer to be recorded, there is no need to make the dielectric film separating the plurality of recording films extremely thick. Therefore, manufacturing becomes easy. Furthermore, since the entire thickness of the recording film can be made to fall within the depth of focus of the lens, when the recording medium on the disc is rotated for recording or reading, the surface of rotation of the recording medium is This makes it easy to automatically adjust the focus position to follow camera shake. 2. In an optical information recording medium that has at least two layers of a recording film and a reflective film on a substrate, and in which recording is performed by irradiating a laser beam from the side of the recording film toward the reflective film, the reflected light of the laser beam is By using the fact that the light interferes with the incident laser light to produce an intensity distribution of the light and the fact that the intensity distribution differs depending on the wavelength of the irradiated laser light, it is possible to select which of the above-mentioned multilayer recording films should be recorded. We decided to perform multi-layer, multi-level recording. As a result, it is no longer necessary to use multiple recording film materials corresponding to each wavelength as the material for each layer, so that an optical information recording medium and an optical information recording method capable of easily performing multi-layer multi-level recording can be obtained. I can do it. Furthermore, since there is no need to use a material sensitive to weak light such as a dye as the recording film, there is no risk that the recorded information will be lost even if the recorded information is read out many times. Furthermore, there is no need to selectively focus the light spot on the layer to be recorded. Therefore, there is no need to make the dielectric film that separates the plurality of recording films extremely thick, and manufacturing becomes easier. Furthermore, since the entire thickness of the recording film can be made to fall within the depth of focus of the lens, when the recording medium on the disc is rotated for recording or reading, the surface of rotation of the recording medium is This makes it easy to automatically adjust the focus position to follow camera shake. 3. A dielectric layer was provided between the recording film and the reflective film. This eliminates the need to change the wavelength significantly when performing multilevel recording by changing the wavelength. That is, since wavelength selectivity is improved, it becomes possible to increase the multiplicity. 4. A dielectric layer was provided between the at least two recording films described above. This makes it possible to widen the spacing between each layer while keeping the recording film thickness of each layer thin, and even if a material with extremely high absorption rate is used for each layer, the irradiated laser light will be sufficiently reflected by the film. It is possible to cause interference with the reflected light. That is, it becomes possible to use a material with high absorption rate. 5. When recording is performed by condensing the above laser beam onto the optical information recording medium with a lens, the above recording film is arranged so that the entire thickness thereof falls within the range of the focal depth of the above lens. The wavefront of the laser beam is approximately flat within the focal depth of the lens. Therefore, the intensity distribution due to interference between the reflected light and the incident light also becomes planar. Therefore, this plane can be aligned with each recording film, and the selectivity of each layer can be increased. 6. In the present invention, at least one of the recording films is located at a position where the incident light of the recording laser light of a specific wavelength and the reflected light from the reflective film interfere to increase the intensity of the light, and at least one of the other recording films is located at a position where the intensity of the light increases due to interference between the incident light of the recording laser light of a specific wavelength and the reflected light from the reflective film. They are formed at predetermined intervals from the reflective film at positions where the intensity of light is weakened. With this, it is possible to select a specific recording film among a plurality of recording films on one substrate in accordance with the wavelength.

[Effect]

FIG. 5(a) shows one of the laminated structures of the optical information recording medium of the present invention.
This is an example. A first recording [[
3a, a first dielectric film 2a, a second recording film 3b, a second dielectric film 2b, and a reflective film 4 are laminated in this order. An incident laser beam 5a is irradiated onto such an optical information recording medium from the transparent substrate 1 side. Since the first dielectric film 2a and the second dielectric film 2b are transparent, and the first recording film 3a and the second recording film 3b are thin, a considerable portion of the incident laser beam 5a reaches the reflective film 4 and is reflected there. do. The reflected laser beam 5b reflected by the reflective film 4 interferes with the incident laser beam 5a to create a light intensity distribution (standing wave 3). At this time, the position of the strong-intensity portion of the 5 light beams (the antinode portion of the standing wave) changes depending on the wavelength of the incident laser beam 5a. Therefore, as shown in FIG. 5(a), the first recording film 3a is arranged at a portion that becomes the antinode of the standing wave when irradiated with light of wavelength λ1, and
By arranging the second recording film 3b at the part that becomes the antinode of the standing wave when the light of 2 is irradiated, the wavelength can be changed.
It is possible to select which recording film to record on. In other words, wavelength multiplexing recording can be achieved. At this time, in order to prevent the light of wavelength λ2 from affecting the first recording film 3a, when the light of wavelength λ1 is irradiated, the nodes of the standing wave are It is desirable to arrange the second recording film 3b in a portion where Similarly, it is desirable to arrange the first recording film 3a at a portion that becomes a node of a standing wave when irradiated with light of wavelength λ2. When reading out such a record as described above, it is possible to read out information on the recording film in the antinode of the standing wave, that is, in the part where the light intensity is strong, as in the case of recording. In FIG. 1, a first dielectric film 2a, a first recording film 3a, a second dielectric film 2b, a second recording film 3b, a third dielectric film 2c, and a reflective film 4 are laminated in order on a transparent substrate 1. It is a recording medium. The first dielectric film 2a formed between the transparent substrate 1 and the first recording film 3a has the function of strengthening the effect of light interference and increasing the amplitude (degree of interference) of standing waves. That is, the reflected laser beam 5b reflected by the reflective film 4 is reflected again at the interface between the transparent substrate 1 and the first dielectric film 2a and returned to the reflective film 4 side, thereby enhancing the interference effect. Based on the above principle, the material of the recording film used in the optical information recording medium of the present invention has optical properties (absorption rate, refractive index, etc.) that change due to light or heat generated by absorbing light. It turns out that something that changes is good. That is, there is no need to use a material whose light absorption rate differs depending on the wavelength, as was used in conventional wavelength multiplexing recording. Furthermore, when there are multiple recording films, all the recording films can be made of the same material. Therefore, as the recording film material, magneto-optical recording materials such as rare earth transition metal non-quality alloys and phase change recording materials that have been conventionally used in optical disks can be used as they are, making it possible to fabricate optical information recording media. becomes very easy. Furthermore, the laminated structure of the optical information recording medium is not limited to the structure shown in FIG. For example, it is possible to increase the wavelength multiplicity by using three or more layers of recording films. In this case, each recording film may be placed at a position where the intensity of the light is maximum corresponding to the wavelength of the laser light to be irradiated. Also, the recording film can be a single thick layer. In this case, the shape of the light intensity distribution (interference fringes) is recorded as is within the recording film. This is because the interval between interference fringes is half the wavelength of the light. This is the same as recording the wavelength. This can be regarded as holographic recording using interference in the direction perpendicular to the film surface. Therefore, a type of three-dimensional recording is performed, and the recording density increases dramatically. In other words, a high degree of wavelength multiplexing can be achieved. (Example) Examples of the present invention are shown below and will be described in more detail. <<Example 1>> Fig. 6 shows the structure of an optical information recording medium according to an example of the present invention.For tracking A first dielectric film 2a of SiO is deposited to a thickness of 100 nm on a transparent substrate 1 made of glass or the like provided with guide grooves.Furthermore, a first recording film 2a (GeSbTe
) is 10 nm, and the second dielectric film 3b (Sin) is 150 nm.
m, the second recording film 2b (GeSbTe) is 10 nm thick, the third
The dielectric film 2c (SiO) is 250 nm thick, the reflective film 4 (A1
) were laminated in order of 50 nm by high frequency magnetron sputtering. A recording medium having such a configuration has a wavelength of 8 from the side of the transparent substrate 1.
Laser light of 30 nm and laser light of wavelength 530 nm are irradiated. When calculated from the optical constants of each layer, the wavelength was 83
For a laser beam of 0 nm, the first recording film 3a
It was found that the second recording film 3b absorbed 55% of the light. It was also found that when irradiated with laser light having a wavelength of 530 nm, the first recording film 3a absorbed 53% of the light, and the second recording film 3b absorbed 5% of the light. The amount of light absorbed by the reflective film 4 is small. Therefore, recording can be performed by heating the first recording film 3a with 530 nm light and deteriorating its quality. At this time, the rise in temperature of the second recording film 3b is extremely small. Similarly, the second recording film 3 is exposed to light of 830 nm.
Recording can be performed by heating b to dequality it. In the case of the recording film material GeSbTe in this example, when high-intensity light is irradiated, the quality is degraded and recorded. Conversely, when irradiated with light of relatively low intensity, crystallization can occur, so recorded information can be erased. Therefore, by alternately modulating and irradiating high-intensity light and low-intensity light in accordance with the information to be recorded, it is possible to directly overwrite the previous information. Actually, by rotating the recording medium at 240 Orpm, the wavelength is 83
When overwrite recording was performed using 0 nm light, the reflectance was 17% at recorded points, and the reflectance at unrecorded points was 17%.
The reflectance was 28% and the modulation degree was 40%. The intensity of the laser light required for this recording was 12 mW for strong light and 6 mW for weak light. Further, when overwrite recording was performed using light with a wavelength of 530 nm, the reflectance at recorded points was 17%, the reflectance at unrecorded points was 40%, and the degree of modulation was 57%. The intensity of the laser light required for this recording was 8 mW for strong light and 4 mW for weak light. When the recording using light with a wavelength of 830 nm was read out with light having a wavelength of 530 nm, the degree of modulation was 0.4% or less. Therefore, the crosstalk is -40 dB or less. Further, when a record made by light having a wavelength of 530 nm was read out by light having a wavelength of 830 nm, the modulation degree was 0.5% or less, and the crosstalk was -35 dB or less. The recording density at this time is approximately twice as high as that recorded by the conventional method, assuming that recording is performed at the same linear recording density. Furthermore, since the recording film is made as thin as 10 nm, the recording sensitivity is improved by about 50% compared to the conventional method. A GaAs semiconductor laser was used as a laser with a wavelength of 830 nm, and a second harmonic (SHG) of an Nd:YAG laser excited by a semiconductor laser was used as a laser with a wavelength of -530 nm. <<Embodiment 2>> FIG. 7 shows the structure of an optical information recording medium according to an embodiment of the present invention. SiN is deposited as a first dielectric film 2a to a thickness of 100 nm by high-frequency magnetron sputtering on a transparent substrate 1 made of glass or the like provided with a guide groove for tracking. Further, the first recording film 2a (TbFeCo
) is 10 nm, and the second dielectric film 3b (SiN) is 360 nm.
m, second recording film 2 b (T b Fe Co
) is 10 nm thick, and the third dielectric film 2c (SiN) is 460 nm thick.
m, and a reflective film 4 (Ag) was laminated in order of 50 nm by high frequency magnetron sputtering. Furthermore, a 5 μm thick ultraviolet curable resin was applied thereon as a protective coat. A recording medium having such a configuration has a wavelength of 6 from the side of the transparent substrate 1.
Semiconductor laser light of 30 nm and semiconductor laser light of wavelength 830 nm are irradiated. Calculation from the optical constants of each layer shows that for laser light with a wavelength of 630 nm, the first recording film 3a absorbs 75% of it, and the second recording film 3b absorbs 5% of it.
It was found that it absorbs light. In addition, the wavelength is 830 nm
It was found that when irradiated with laser light, the first recording film 3a absorbed 15% of the light, and the second recording film 3b absorbed 65% of the light. ``The amount of light absorbed by the reflective film 4 is small. Therefore, magneto-optical recording can be performed by heating the first recording film 3a with 630 nm light to a temperature equal to or higher than the Curie temperature. At this time, the rise in temperature of the second recording film 3b is extremely small. Also, similarly 8
Magneto-optical recording can be performed by heating the second recording film 3b with 30 nm light to a temperature equal to or higher than the Curie temperature. Using the recording medium 15 described above, magnetic field modulation recording was performed using the floating magnetic head 14 as shown in FIG. Two sets of lenses 16 and floating magnetic heads 14 were prepared corresponding to the above two wavelengths. Magnetic field modulation recording uses strong laser light5
is continuously irradiated onto the recording medium 14 to raise the recording film (magnetic film) above the Curie temperature, a magnetic field modulated according to the information is applied, and the magnetization of the recording film is caused in the direction of the applied magnetic field. This is a method to record the data in parallel. Therefore, it is possible to directly overwrite the previous information. Actually, by rotating the recording medium at 360 Orpm, the wavelength is 83.
When overwrite recording (frequency 5 MHz) was performed using 0 nm (10 mW) light, the C/N ratio was 55 dB.
I got it. Also, when overwrite recording (5MHz) was performed using light with a wavelength of 630nm (8mW), the C/N ratio was 5.
Obtained 6dB. Recording using light with a wavelength of 830 nm at wavelength 6
The crosstalk is -35 dB or less when reading with 30 nm light and when reading out a record with 630 nm wavelength light with 830 nm wavelength light. The recording density at this time is approximately twice as high as that recorded by the conventional method, assuming that recording is performed at the same linear recording density. Furthermore, since the recording film is made as thin as 10 nm, the recording sensitivity is improved by about 50% compared to the conventional method. FIG. 9 shows the relationship between the wavelength of light irradiated onto the recording medium 15 of the present invention and the absorption amount of each layer. For light with a wavelength of 630 nm, the absorption amount 17a of the first recording film is the maximum, and the absorption amount 17b of the second recording film is the minimum. Conversely, for light with a wavelength of 830 nm, the absorption amount 17b of the second recording film is the maximum and the absorption amount 17a of the first recording film is the minimum. Embodiment 3 FIG. 10 shows the structure of an optical information recording medium according to an embodiment of the present invention. A dielectric film 12a is placed on a transparent substrate 1 made of glass or the like provided with a guide groove for tracking.
(AIN: 9nm). Recording film 12b (InTe:
A multilayer recording film 12 having a total thickness of 0.5 μm was formed by alternately stacking 50 sets of 1 nm). On top of that, a reflective film 4 (Au) of 50% is applied.
nm layered. When such a recording medium is irradiated with light of various wavelengths to crystallize and record, the reflectance for the light of the recording wavelength increases, as shown in FIG. The reason for this will be explained below. When irradiated with light, interference fringes corresponding to the wavelength of the light are formed in the multilayer recording film 12, and each recording layer 12b is crystallized according to the intensity of the interfered light. Therefore, interference fringes are recorded in the multilayer recording film 12. When recording is performed in this way and then irradiated with the same light that was used for recording, the wavelength of the interference fringes matches the wavelength of the light, so the interaction is maximized and the reflectance of the light is changes compared to before recording, but since the wavelength of the interference fringes and the wavelength of the light are different for other lights, the phase of each part is shifted, so the reflectance is the same as when no recording was made. In this example, recording is performed at wavelength intervals of about 50 nm to obtain 10 multiplexes. Although a multilayer recording film is used as the recording film in this example, it is also possible to use a single layer film by using a material with a lower absorption rate (a material with high transparency). Such materials include, for example, transparent substances such as PMMA to which absorbers such as dyes are added. In any case, it is important to use a material that has a sufficient absorption rate to allow light to reach the reflective film and has a thickness of approximately 0.5 μm. This is because if the thickness is thinner than this, the number of interference fringes will be reduced and the multiplicity will be reduced.

【Effect of the invention】

By using the present invention, it is possible to obtain an optical information recording medium and an optical information recording method on which wavelength multiplexing recording can be easily performed without preparing films corresponding to each wavelength. Therefore, it becomes possible to dramatically improve the recording density of optical information recording. Further, as the recording material, those used in conventional optical recording can be used. Therefore, unlike PHB recording materials, there is no need to keep the medium at a low temperature. Furthermore, overwrite recording can be performed in the same way as conventional optical recording. Therefore, as the recording density increases, the transfer speed can also be improved.

[Brief explanation of drawings]

1, 5, 6, 7, and 10 are cross-sectional views showing the laminated structure of the optical information recording medium of the present invention, and FIG. 2 shows the laminated structure of the conventional optical information recording medium. 3 is a diagram showing the absorbance of a conventional optical information recording medium, FIG. 4 is a diagram showing the laminated structure of a conventional optical information recording medium and the configuration of an optical information recording system, and FIG. 8 is a diagram showing magnetic field modulation recording. A diagram showing the configuration of the method,
FIG. 9 is a diagram showing the absorption amount of the optical information recording medium of the present invention, and FIG. 11 is a diagram showing the reflectance of the optical information recording medium of the present invention. Explanation of symbols 1...Transparent substrate, 2...Dielectric film, 3...Recording film, 4゛゜Reflection film, 5...Laser light, 6...Dielectric film, 7...Protection Film, 8... Pigment film, 9... Absorbance of dye film, 10... Recording film, 11... Lens, 12.
...Multilayer recording film, 13. Protective coat, 14.. Flying type magnetic head, 15.. Lecture diagram Sb Anti-eaves crepe" first λ front system 3 Figure 4 (ku) <b) Troubled pole 圀柀? Figure name q Box branch length [・8m heko) Ku^ One kudzu absorbs 4 grudges ψ ノ?b g2N1t Hako 11 (H shaku 1E No. 10 Uzusada / 1 diagram) N, lL length rη1heko

Claims (1)

[Scope of Claims] 1. In an optical information recording method that has at least a recording film and a reflective film on a substrate, and performs recording by irradiating a laser beam from the side of the recording film toward the reflective film, the laser beam The reflected light interferes with the incident laser light to produce a light intensity distribution, and the fact that the intensity distribution differs depending on the wavelength of the irradiated laser light is used to perform wavelength division multiplexing and multilevel recording. Characteristic optical information recording method. 2. In an optical information recording method that has at least two layers of a recording film and a reflective film on a substrate and performs recording by irradiating a laser beam from the side of the recording film toward the reflective film, reflection of the laser beam is performed. By utilizing the fact that light interferes with the incident laser beam to produce a light intensity distribution, and by utilizing the fact that the intensity distribution differs depending on the wavelength of the irradiated laser beam, it is possible to determine which of the above-mentioned multilayer recording films should be recorded. An optical information recording method characterized by selectively performing multi-layer multi-value recording. 3. The optical information recording method according to claims 1 and 2, characterized in that an optical information recording medium is used in which a dielectric layer is provided between the recording film and the reflective film. 4. The optical information recording method according to claims 2 and 3, characterized in that an optical information recording medium is used in which a dielectric layer is provided between the at least two recording films. 5. When recording is performed by condensing the laser beam onto the optical information recording medium with a lens, the recording film is made to fall within the depth of focus of the lens at all positions irradiated with the laser beam. An optical information recording method according to claims 2 and 3. 6. At least one of the reflective films is located at a position where the incident light of a recording laser beam of a specific wavelength and the reflected light from the reflective film interfere and the intensity of the light is increased, and at least one other is located at a position where the intensity of the light increases due to the interference. An optical information recording medium having a plurality of recording films formed at predetermined intervals from a reflective film at positions where the intensity of the recording film is weakened.