JPH07320301A - Optical recording medium and reproduction method therefor - Google Patents

Abstract

PURPOSE:To facilitate application to a medium other than a magneto-optical recording medium and to a mark edge recording without requiring a high optical intensity while realizing density recording/reproduction of information through super resolution effect by providing a mask layer containing photochromic color molecules. CONSTITUTION:A mask layer 12, a recording layer 13, a reflection layer 14, and a protective layer 15 are laminated sequentially on a transparent substrate 11 made of polycarbonate to form an optical recording medium. The mask layer 12 contains photochromic color molecules which absorb a reproduced light of corresponding wavelength to cause photochemical reaction thus developing a color. Transmission of the reproduced light is retarded in the colored region 3 and the reproduced light reaches the recording layer 13 only at the faded part in the first half part of a reproduced light spot 1. Consequently, a recorded mark 2 is read out at an effective reproduction spot 4 having smaller region than the reproduced light spot 1. Since super resolution effect is achieved, the line recording density is enhanced resulting in the high density recording/ reproduction of information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of high density recording and reproduction.

[0002]

2. Description of the Related Art In recent years, in optical disc devices and media, so-called MSR has been used as a super-resolution means for recording / reproducing an area smaller than a recording spot determined by the diffraction limit of light.
(Magnetically induced Sup
er Resolution) method is drawing attention.
Such an MSR method is used, for example, in Technical Digest of Data Storage Topical Meeting 1991 Volume 5 (Technical).
Digest of Optical DataStr
age 1991 Volume 5) pp. 112
~ 115 (lecture number TuB-3) and the same pp. 116-
119 (lecture number TuB-4). This system is characterized by using a plurality of optical recording magnetic recording films and providing a mask layer for masking surrounding information other than the information recording layer. Since the information (recording marks) recorded on the mask layer whose temperature has risen due to the irradiation of the relatively strong reproducing light is transferred, the influence of the adjacent tracks and the recording marks in the linear density direction is suppressed even if the recording density becomes high. The optical resolution will be improved.

Further, as an optical recording medium for obtaining a similar super-resolution effect, for example, in Japanese Patent Laid-Open No. 5-225611, an optical absorption center which causes a nonlinear optical absorption phenomenon such as saturable absorption characteristics is used as a mask layer. A medium provided with a layer containing is disclosed. The saturable absorption characteristic is that when the light irradiation intensity is weak, the electronic state of the absorption center is often in the ground state, so it is efficiently excited, and when the light irradiation intensity is strong, most of the electrons are excited. Therefore, on the contrary, the ratio of electrons excited from the ground state decreases.
Therefore, it has the property of absorbing light when the light intensity is low and decreasing the absorptance when the light intensity is high. Therefore, when reproducing is performed by irradiating a medium provided with a layer having such a saturable absorption property with a strong reproducing light, the light around the spot has a low light intensity, and the reproducing light does not reach the recording layer. At the center of the spot where the light intensity is high, the absorption is small and the reproduction light can reach the recording layer. Therefore, the above MSR
The super-resolution effect can be obtained in the same manner as the method.

Japanese Patent Laid-Open No. 242524/1993 also discloses a recording / reproducing method utilizing a non-linear optical phenomenon. In this publication, an example using spiroselenazolinobenzopyran exhibiting inverse photochromic is disclosed. Has been done. Further, in Japanese Patent Laid-Open No. 5-266478, as a similar technique, the central portion is normally opaque to the reproducing light but is irradiated with the reproducing light controlled so that the central portion has a predetermined intensity or more. It has been proposed to use a mask layer that has the property that only the light is transparent and becomes non-transparent again after passing through the reproducing light. As a concrete example of the material for the mask layer, an indoline-based spiropyran exhibiting reverse photochromism is proposed. Is disclosed.

[0005]

However, the conventional method using the above-mentioned MSR method has a problem that the recording medium is limited to the magneto-optical recording medium. There is also a problem that it is difficult to obtain a high CN ratio because the temperature of the magnetic layer in the medium is raised by using light of relatively high intensity for reproduction. Furthermore, as has been studied in the past, when using a green or blue laser by shortening the wavelength of the recording / reproducing laser for higher density, it is necessary to use a new magneto-optical recording material different from the current near infrared laser. Occurs. In such a case, it is necessary to design new magnetic characteristics of the magnetic layer in order to realize the MSR effect. Further, since the effect of heat is used to transfer the recording information to the mask layer, the influence of thermal diffusion occurs, and it is difficult to apply it to mark edge recording, which is a powerful means of increasing the density. there were.

The method of using a layer containing absorption centers having nonlinear light absorption characteristics as a mask layer does not cause the problem of being limited to a magneto-optical recording medium like the MSR method, but generally causes a saturable absorption phenomenon. Therefore, a very high light intensity is required, which causes a new problem that the information recorded in the recording layer may be destroyed by heat. In addition, although a higher light intensity is required during recording than during reproduction, the light intensity is extremely high, so that the recording mark may be expanded due to the influence of thermal diffusion, and conversely the recording density may be reduced.

The present invention can be easily applied to media other than magneto-optical recording media, does not require extremely high light intensity such as saturable absorption, and is not affected by thermal diffusion of the mask layer. It is an object of the present invention to provide an optical recording medium which can be easily applied to edge recording and enables recording and reproduction of high density information by a super-resolution effect.

[0008]

The optical recording medium of the present invention comprises:
A recording layer on which information is recorded, and a mask layer containing a photochromic dye molecule that has absorption at the wavelength of the reproduction light and causes a photochemical reaction by the absorption of the reproduction light to increase the absorption of the reproduction light. I am trying.

In the optical recording medium of the present invention, the recording layer may contain photochromic dye molecules, and the recording layer and the mask layer may be formed as the same layer. The mask layer may be provided on the reproducing light incident side of the recording layer, or may be provided on the opposite side. The position of such a mask layer can be set in consideration of the type of recording material used for the recording layer of the optical recording medium and whether the optical recording medium is a transmissive type or a reflective type. . Further, as the photochromic dye molecule used in the present invention,
It is desirable that after the photochemical reaction is caused by irradiation of the reproducing light to increase the absorption, the material is returned to a small absorption state by a thermal reaction when left standing. Here, the thermal reaction may be brought about by heating or may proceed gradually at room temperature.

The reproducing method of the present invention is a method for reproducing information recorded by irradiating the recording layer of the above-mentioned optical recording medium of the present invention with the reproducing light, and irradiating the mask layer with the reproducing light for the photon mode. A step of causing a reaction to form a low transmittance portion in the latter half of the reproduction light spot of the mask layer,
And reproducing the information recorded in the recording layer in the reproduction light spot portion excluding the portion of the mask layer having a low transmittance.

[0011]

1 is a plan view for explaining the reproducing method according to the present invention. Referring to FIG. 1, reproduction light spot 1 is scanned in the direction indicated by the arrow, and reproduction light spot 1 is moving relative to the optical recording medium. In the present invention, the mask layer contains a photochromic material that causes a photon mode reaction by absorption of reproduction light and increases absorption of reproduction light. In the first half of the reproduction light spot 1, the amount of irradiation light is not sufficient, so that the photon mode reaction does not sufficiently occur and the absorption state of reproduction light does not change.
In the latter half of the reproduction light spot 1, the absorption amount of the reproduction light becomes sufficient, the photon mode reaction occurs, and the absorption of the reproduction light increases. The colored region 3 is formed by such an increase in the absorption of the reproduction light. In the colored region 3 as described above, it is difficult for the reproduction light to pass therethrough, so that the reproduction light reaches the recording layer only in the decolored state of the first half of the reproduction light spot 1. As a result, the recording mark 2 is formed in the effective reproduction spot 4 in an area smaller than the reproduction light spot 1.
Is read. Therefore, according to the present invention, a super-resolution effect can be obtained and the linear recording density can be improved.

In the desirable mask layer material, the colored portion after regeneration returns to a state of small absorption by a thermal reaction at room temperature. Therefore, the mask layer returns to the state of small absorption before the reproduction light spot is scanned again, and there is no need to perform a process of returning the mask layer to the state of low absorption by heating or irradiation with light of another wavelength in advance.

[0013]

EXAMPLE An optical recording medium having a structure as shown in FIG. 2 was produced. Referring to FIG. 2, mask layer 12 was formed on transparent substrate 11 made of polycarbonate or the like. As the mask layer 12, a polystyrene film containing a photochromic material having the following structure was formed.

[0014]

[Chemical 1]

The diarylethene-based photochromic material having the above structural formula has an absorption spectrum as shown in FIG. This material has a large quantum yield of the reaction from the decolored state (broken line state) to the colored state (solid line state) as compared with the quantum yield of the reaction from the colored state to the decolorized state. Therefore, for example, when light having a wavelength of 477 nm is irradiated in the decolored state, the state changes to a colored state in which absorption is large at that wavelength. That is, this material is a photochromic material that has absorption at the wavelength of the reproduction light and causes a photon mode reaction by the absorption of the reproduction light to increase the absorptance at the reproduction light wavelength. In this embodiment, the mask layer is made to function by utilizing this wavelength range. Mask layer 12
Is 1 part by weight of polystyrene resin and 40 parts by weight of cyclohexanone as a solvent for 1 part by weight of photochromic material.
By mixing parts by weight to form a solution, the solution was applied by a spin coating method to form a film having a thickness of 0.5 μm. The concentration of the photochromic material in the mask layer 12 is preferably 30% by weight or more, and is 80% by weight in this embodiment.

A recording layer 13 was formed on the mask layer 12. As the recording material of the recording layer 13, various known magneto-optical materials and phase change materials can be used. In this embodiment, a TbFeCo-based magneto-optical material was used. Recording layer 1
The thickness of 3 was 0.1 μm.

A reflective layer 14 was formed on the recording layer 13. The reflective layer 14 has a thickness of about 2 by depositing Ag.
It was formed with a thickness of 00 nm. A protective layer 15 is formed on the reflective layer 14.
Was formed. The protective layer 15 was formed by spin-coating an ultraviolet curable resin and irradiating the resin with ultraviolet rays to cure the resin so as to have a film thickness of 10 μm.

Various wavelengths were recorded in advance on the recording layer by the magnetic field modulation method, and reproduction was performed. Reproducing light has a wavelength of 47
A 7 nm Ar laser beam was focused at a spot of 1.1 μm and scanned on the medium. The reproducing power was 1 mW and the relative speed was 1.4 m / sec. For comparison, an optical recording medium was produced in the same manner as in this example except that the mask layer was not provided.

The frequency of the reproduction signal was measured for the optical recording media of Examples and Comparative Examples thus obtained. The frequency when the output drops by 6 dB is 1 MHz in the comparative example.
While the mark length was 0.7 μm (corresponding to a mark length of 0.7 μm), it was 1.5 MHz (mark length 0.47 μm) in the example, and it was found that the linear recording density can be improved by about 1.5 times.

Another example of the desirable mask layer material of the present invention will be described. The photochromic material whose structure is shown in Chemical formula 2 below and whose absorption spectrum is shown in FIG. 4 changes from a solid line state to a broken line state by a photochemical reaction by irradiation with light having a wavelength near 550 to 570 nm as reproduction light. Absorption is increased.

[0021]

[Chemical 2]

Therefore, the linear recording density can be improved by the super-resolution effect by the above-mentioned operation. Further, this material is in a broken line state after irradiation with the reproducing light, but has a property that after the reproduction, the broken line state gradually returns to the solid line state by a thermal reaction at room temperature. Therefore, by including such a material in the mask layer, the absorption is increased by the photon mode reaction by the irradiation of the reproducing light, and after the reproduction, the mask layer is returned to the small absorption state by the thermal reaction at room temperature. You can

In the above-mentioned embodiment, an example in which a magneto-optical recording material is used as the recording layer has been shown, but the present invention is not limited to such a material, and other rewritable media such as a phase change type medium can be used. The present invention can also be applied to write-once media, write-once media, read-only media, and the like.

In the above embodiment, an example in which the mask layer is provided on the reproducing light incident side of the recording layer has been shown, but the present invention is not limited to such a structure, and is provided on the side opposite to the reproducing light incident side. A mask layer may be provided. Further, the recording layer and the mask layer may be formed as the same layer by containing a photochromic dye molecule of the mask layer in the recording layer.

[0025]

According to the present invention, there is provided the mask layer containing a photochromic material which has absorption at the wavelength of the reproduction light and which causes a photochemical reaction by the absorption of the reproduction light to increase the absorption of the reproduction light. By providing such a mask layer, the effective spot at the time of reproduction can be made smaller than the reproduction beam spot, and recording / reproduction of information with higher density becomes possible.

[Brief description of drawings]

FIG. 1 is a plan view for explaining a reproducing method according to the present invention.

FIG. 2 is a sectional view showing the structure of an optical recording medium according to an embodiment of the present invention.

FIG. 3 is a diagram showing an absorption spectrum of a photochromic material used for a mask layer in one example according to the present invention.

FIG. 4 is a diagram showing an absorption spectrum of another example of the photochromic material that can be used for the mask layer in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reproduced light spot 2 ... Recording mark 3 ... Colored area 4 ... Effective reproduction spot 11 ... Transparent substrate 12 ... Mask layer 13 ... Recording layer 14 ... Reflective layer 15 ... Protective layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Torasazawa, 2-5-5 Keihan Hon-dori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Satoshi Washimi 2-chome, Keihan-hondori, Moriguchi-shi, Osaka No. 5-5 Sanyo Electric Co., Ltd.

Claims (7)

[Claims] 1. A mask layer containing a recording layer on which information is recorded and a photochromic dye molecule which has absorption at a wavelength of reproduction light and causes a photon mode reaction due to the absorption of the reproduction light to increase absorption of the reproduction light. An optical recording medium comprising: 2. The photochromic dye molecule causes a photon mode reaction by irradiation of reproduction light to increase absorption, and then returns to a state in which absorption of reproduction light is small again by thermal reaction. Optical recording medium. 3. The photovoltaic recording medium according to claim 1, wherein the photochromic dye molecule is a photochromic dye molecule that reduces absorption of the reproduction light by absorbing light having a wavelength other than the reproduction light. . 4. The optical recording medium according to claim 1, 2 or 3, wherein the recording layer contains the photochromic dye molecule, and thereby the recording layer and the mask layer are formed as the same layer. 5. The mask layer is provided on the reproducing light incident side of the recording layer or on the opposite side thereof,
The optical recording medium as described in 3 or 4. 6. A method for reproducing information recorded by irradiating a recording layer of the optical recording medium according to claim 1, with the reproducing light, wherein the reproducing light is applied to a mask layer. A step of forming a low-transmittance portion in the latter half of the reproduction light spot of the mask layer by causing a photon mode reaction by irradiating with, and a portion of the reproduction light spot excluding the low-transmittance portion of the mask layer. And a step of reproducing information recorded on the recording layer. 7. The optical recording medium according to claim 6, further comprising the step of irradiating light having a wavelength other than the reproduction light to reduce absorption of the reproduction light before irradiating the reproduction light. How to play.