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OPTICAL RECORDING MEDIUM, RECORDING SYSTEM AND REPRODUCING SYSTEM
FIELD OF THE INVENTION AND RELATED 3
ART
The present invention relates to an optical recording medium (inclusive of a record blank and the resultant record) for optical information recording and reproduction, 10 and a system (method and apparatus) for optical information recording and/or reproduction using the optical recording medium.
Optical recording media have received attention in recent years because of, e.g., capability of non-contact recording 15 and reproduction and quick accessibility.
Optical recording media proposed heretofore may principally include the following types:
(a) One including a recording layer comprising a film of 2Q a low-melting point metal;
(b) One including a recording layer comprising a layer of an organic coloring matter showing a high reflectance; and
(c) One including a recording layer having a two-layer 25 structure including a metal reflection layer and an organic light-absorbing layer.
More specifically, an optical recording medium of the above type (a) includes a recording layer of a film comprising principally a low-melting point metal, such as Te, in 30 which recording layer a pit is formed by producing a hole by light illumination or by causing a change in reflectance through a crystal-amorphous phase transition. The optical recording medium of this type is accompanied with problems, such as a poor storage stability and a high production 35 cost, because vapor deposition, for example, is required for forming the recording layer.
An optical recording medium of the above type (b) has a structure, e.g., as shown in FIG. 4, including on a substrate 1 a recording layer of an organic coloring matter film 4 40 which is further laminated with a protective substrate 6 by the medium of an adhesive layer 5. This type of recording medium is expected to provide a high sensitivity and a high C/N ratio because the organic coloring matter film 4 shows a higher melting point and decomposition temperature and a 45 lower thermal conductivity than a polymer. Further, the film formation can be effected by coating which is advantageous with respect to low production cost.
In the conventional optical recording medium of this type (b), the recording layer plays both roles of light reflection for 50 information reproduction and light absorption for recording. The recording is effected by forming pits by converting absorbed light into heat energy and causing decoloration, melting, decomposition or/and sublimation of the coloring matter due to the heat, so that an increase in amount of 55 absorbed light is required in order to provide a higher sensitivity. On the other hand, as for the reflectance, a wavelength giving a maximum reflectance is generally longer than a wavelength giving a maximum absorptance as shown in FIG. 5, so that there arises a contradictory problem 60 that a maximum reflectance for providing an excellent S/N ratio can result in a shortage of absorption which leads to a lowering in sensitivity. For this reason, it has been difficult to effect both recording at a high sensitivity and reproduction at a high S/N ratio by using a single laser light source. 65 Further, there is also a problem of degradation due to reproducing light that the recording layer can cause degra
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dation (e.g., a lowering in reflectance) by irradiation with even weak laser light for reproduction which still causes some degree of heat generation.
Then, in the optical recording medium of the type (c), an organic light-absorption layer is irradiated with laser light to form pits therein due to heat generation in the absorption layer, and a metal reflection layer is provided to compensate for the low reflectance of the organic light-absorption layer (as disclosed in U.S. Pat. Nos. 4,189,735 and 4,305,081). In this type of optical recording medium, the problem of degradation due to reproducing light hardly occurs but, on the other hand, there is an accompanying difficulty that the recording sensitivity is remarkably impaired. Further, the production cost becomes higher because vapor deposition, etc., is required for forming the metal reflection film.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems of the conventional optical recording media using an organic material, an object of the present invention is to provide an optical recording medium which can show a high reflectance for reproducing recorded information at a high contrast while retaining a high recording sensitivity and can be produced at a low production cost.
Another object of the present invention is to provide such an optical recording medium which does not readily cause degradation due to reproducing light.
A further object of the present invention is to provide an optical recording method and an optical reproducing method capable of producing high contrast signals.
A still further object of the present invention is to provide an information recording apparatus capable of information recording providing high contrast signals, and an information reproducing apparatus capable of reproducing the recorded information at a high contrast.
According to the present invention, there is provided an optical recording medium, comprising in sequence a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer, wherein the light-reflecting layer, the transparent intermediate layer and the light-absorbing layer in combination constitute a multilayer optical element showing a high reflectance with respect to a light beam having a prescribed wavelength.
According to the present invention, there is also provided an optical recording medium, comprising in sequence a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer, wherein the light-reflecting layer, the transparent intermediate layer and the light-absorbing layer in combination constitute a multilayer optical element showing a high reflectance with respect to a reproducing light beam having a wavelength Ax.
According to the present invention, there is further provided an optical recording medium for use in combination with a reproducing light beam having a prescribed wavelength and a prescribed intensity and a recording light beam having a wavelength different from the prescribed wavelength, comprising: in sequence, a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer; the light-reflecting layer, transparent intermediate layer and light-absorbing layer having respectively prescribed thicknesses so as to constitute a multi-layer optical element showing a high reflectance with respect to a light beam having the prescribed wavelength; the lightreflecting layer, transparent intermediate layer and lightabsorbing layer being comprised of such materials that an
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optically detectable change could be formed in the optical recording medium when irradiated with the reproducing light beam if the light-reflecting layer, transparent intermediate layer and light-absorbing layer were disposed in different thicknesses failing to provide such a high reflectance; 5
whereby the optical recording medium is capable of information recording so as to cause an optically detectable change in the light-reflecting layer by irradiation with the recording light beam and is capable of information reproduction without causing an optically detectable change by irradiation with the reproducing light beam.
According to the present invention, there is further provided an optical recording medium for use in combination with a reproducing light beam having a prescribed wave- 15 length and a first intensity and a recording light beam having the same wavelength as the prescribed wavelength and a second intensity larger than the first intensity, comprising: in sequence, a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer; 2Q the light-reflecting layer, transparent intermediate layer and light-absorbing layer having respectively prescribed thicknesses so as to constitute a multi-layer optical element showing a high reflectance with respect to a light beam having the prescribed wavelength; the light-reflecting layer, 25 transparent intermediate layer and light-absorbing layer being comprised of such materials that an optically detectable change could be formed in the optical recording medium when irradiated with the reproducing light beam having the first intensity if the light-reflecting layer, trans- 3Q parent intermediate layer and light-absorbing layer were disposed in different thicknesses failing to provide such a high reflectance;
whereby the optical recording medium is capable of information recording so as to cause an optically detectable 35 change in the light-reflecting layer by irradiation with the recording light beam and is capable of information reproduction without causing an optically detectable change by irradiation with the reproducing light beam.
According to the present invention, there is also provided 40 an optical recording method, comprising:
providing an optical recording medium comprising in sequence a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer; and 45
focusing a light beam at the light-absorbing layer through the transparent substrate to provide an optically detectable change in both the light-absorbing layer and the lightreflecting layer for recording information.
The present invention further provides an optical recording method, comprising:
providing an optical recording medium comprising in sequence a transparent substrate, a first organic coloring matter layer, a transparent intermediate layer and a second 55 organic coloring matter layer, the first and second organic coloring matter layers having mutually different maximum absorption wavelengths, each of the first organic coloring matter layer, transparent intermediate layer and second organic coloring matter layer having a prescribed thickness; go and
focusing a light beam at the second organic coloring matter layer through the transparent substrate to provide an optically detectable change at least at a focused part in the second organic coloring matter layer and a corresponding 65 part in the first organic coloring matter layer for recording information; the light beam having a frequency and an
intensity sufficient to be absorbed by the second organic coloring matter layer.
The present invention further provides an optical reproducing method, comprising:
providing an optical recording medium comprising in sequence a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer; the light-reflecting layer and light-absorbing layer having mutually different maximum absorption wavelengths, each of the light-reflecting layer, transparent intermediate layer and light-absorbing layer having a prescribed thickness; and
irradiating the optical recording medium with a reproducing light beam through the substrate to reproduce information; the reproducing light beam having a frequency and an intensity such that the optical recording medium shows a high reflectance state with respect to the reproducing light beam and is free from causing an optically detectable change when irradiated with the reproducing light beam.
The present invention further provides an information recording apparatus for writing in an optical recording medium which comprises in sequence a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer, each of the light-reflecting layer and light-absorbing layer comprising an organic coloring matter layer; the apparatus including:
a light source for issuing a recording light beam,
means for focusing the light beam at the light-absorbing layer of the optical recording medium,
means for continuously moving the light-absorbing layer relative to the focused light beam, and
means for modulating the light beam to have an intensity varying between a high level and a low level, so that the light beam at its high intensity level is focused at the lightabsorbing layer to have a frequency and an intensity sufficient to be absorbed by the light-absorbing layer to provide an optically detectable change at a focused part in the light-absorbing layer and a corresponding part in the lightreflecting layer.
The present invention further provides an information reproducing apparatus for reproducing information recorded in an information record which comprises in sequence a transparent substrate, a light-reflecting layer, a transparent intermediate layer and a light-absorbing layer, a pit being formed as an optically detectable change at mutually corresponding parts in the light-absorbing layer and the lightreflecting layer, a series of such pits constituting an information track; the apparatus including:
a light source for issuing a reproducing light beam having a substantially constant intensity,
means for focusing the reproducing light beam at the information track,
means for continuously moving the information track relative to the focused reproducing light beam, and
optical detection means for detecting the reproducing light beam reflected from the information track;
the reproducing light beam having a frequency and an intensity after the focusing such that the information record, at parts free from the pits, shows a high reflectance state with respect to the reproducing light beam and is free from causing an optically detectable change when irradiated with the reproducing light beam.
Thus, in the present invention, an optical recording medium is constituted to have a multi-layer optical element including an organic coloring matter layer as a light-reflecting layer, thereby forming an optical recording medium capable of reproducing a high contrast signal while retaining a good recording sensitivity by forming a high reflection
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