JP2002042378A - Optical recording medium and optical information recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium on which more advantageous higher- density recording/reproducing can be performed by making the light-condensed spot minute. SOLUTION: The converged light 2 from a light source is condensed on an optical recording layer 6 through a first refractive index optical Kerr medium layer 4, having a low refractive index and the second refractive index optical Kerr medium layer 5 having high absorptivity. A thicker film can be used as the layer 4, since the absorptivity of the light 2 is small in the layer 4. The beam diameter of the light 2 can be made small due to self-converging effect, since the center part of the layer 4 has slightly higher intensity in the intensity distribution of the light 2 and consequently has higher refractive index than that of the peripheral part. The beam diameter of the light 2 can be made smaller further by the self-converging effect, since the non- linear optical constant of the layer 5 is large even thought the film thickness is small Generally, materials having high absorptivity has a high refractive index. Therefore, in this case, since the wavelength of the light 2 when passing through the layer 5 becomes still further shorter, the diffraction limit, which is fixed by the wavelength and the converging angle of the layer 5, becomes smaller so that the beam diameter of the light 2 can be made further smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical recording medium and an optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, optical recording media such as optical discs have attracted attention from the viewpoints of large-capacity / high-density storage, non-contact recording / reproducing, and easy access.

[0003] Here, in optical recording media, higher density recording has been demanded. In order to achieve this high-density recording, it is conceivable to reduce the track pitch, increase the recording linear density, perform multiplex recording, or shorten the wavelength of the laser beam. However, according to such a countermeasure, the optical system and the signal processing system become complicated, and the current optical recording / reproducing apparatus cannot cope with the problem.

In consideration of such points, Japanese Patent Laid-Open No. 6-127
According to Japanese Patent Publication No. 00, an optical recording medium as shown in FIG. 3 is proposed. That is, the recording layer 2 provided on the substrate 21
In the optical recording medium for recording, reproducing, and erasing information by irradiating a laser beam to the recording layer 2, at least a layer 23 made of a substance having a third-order nonlinear susceptibility is provided at least adjacent to the reading surface side of the recording layer 22. One layer is arranged, and recording, reproduction, and erasing are performed using the self-binding effect of the layer 23. Here, a layer 24 made of a substance having a second-order nonlinear susceptibility is added between the layer 23 and the substrate 21.

[0005]

That is, in the example shown in the publication, a medium having a third-order nonlinear susceptibility = a medium having a third-order nonlinear constant = optical Kerr medium is used. However, in the optical Kerr medium, those having a small refractive index tend to have a low absorption coefficient and a small third-order nonlinear constant. Conversely, a material having a large refractive index tends to have a high absorption rate and a large third-order nonlinear constant. For this reason, when the substrate 21 or the layer 23 of the layered optical Kerr medium is adjacent to the optical recording medium, an optical Kerr medium having a high refractive index has a large absorption, so that a too thick film cannot be used. In an optical Kerr medium having a small refractive index, a thick film can be used because of a small absorptance. However, since the third-order nonlinear constant is also small, the effects of self-convergence and self-binding near the focal point of the condensed spot are reduced. Because of its small size and low refractive index, it is not possible to shorten the wavelength of light in the medium, which is disadvantageous for miniaturization of the condensed spot and is not effective for improving the recording density. That is, self-convergence and self-constraint occur near the focal point of the converging spot, so that the depth of focus becomes longer, but does not contribute much to the focusing of the spot diameter. Therefore, it is not suitable for improving the recording density (further increasing the recording density).

Accordingly, an object of the present invention is to provide an optical recording medium which is more advantageous by miniaturization of a condensed spot and enables higher density recording and reproduction.

It is another object of the present invention to provide an optical recording medium capable of increasing the recording sensitivity by making the recording layer thinner.

Further, an optical recording / reproducing apparatus capable of coping with high-density recording / reproducing as it is without using a special light source for further shortening the wavelength or complicating an optical system is provided. With the goal.

[0009]

According to a first aspect of the present invention, there is provided an optical recording medium formed on a substrate and receiving convergent light from a light source; An optical Kerr medium layer formed close to a light incident side, wherein the optical Kerr medium layer has a first refractive index Kerr medium layer and the converging than the first refractive index Kerr medium layer. A second refractive index Kerr medium layer disposed on the light incident side, wherein the first refractive index Kerr medium layer has an absorptivity for the wavelength of the convergent light of the second refractive index Kerr medium layer. The absorptance of the medium layer for the wavelength of the convergent light is set relatively higher.

Therefore, when recording, reproducing, or erasing information on the optical recording layer through the optical Kerr medium layer with the convergent light from the light source, the second refractive index Kerr medium layer having a low refractive index absorbs the convergent light. Since the refractive index is small, a thick film can be used. The intensity distribution of the convergent light is slightly higher in the central part, so that the refractive index in the central part is higher than that in the periphery, and the beam diameter of the convergent light can be reduced by the self-converging effect. On the other hand, in the first refractive index optical Kerr medium layer having the next higher absorptance, the layer thickness is small but the nonlinear optical constant is large, so that the self-focusing effect is further emphasized, and the beam diameter of the convergent light can be reduced. In addition, a material having a high absorptivity generally has a high refractive index, and in this case, the wavelength in the first refractive index optical Kerr medium layer is further shortened. The diffraction limit determined by the wavelength and the converging angle becomes smaller, and the beam diameter of the convergent light can be further reduced. Therefore, it is possible to provide an optical recording medium capable of recording, reproducing, or erasing at a higher density than the conventional example.

According to a second aspect of the present invention, in the optical recording medium of the first aspect, the optical recording medium further comprises a reflection layer formed on a side of the optical recording layer opposite to the first refractive index optical medium layer. .

Therefore, this is basically the same as the case of the first aspect of the present invention. In particular, when the reflection layer is provided on the side opposite to the optical Kerr medium layer with the recording layer interposed, the case where the optical recording layer is thin However, since the reflectance of the reflected return light can be increased, the optical recording layer can be thinned without any trouble, and the recording sensitivity can be improved.

An optical recording / reproducing apparatus according to a third aspect of the present invention comprises:
A light source that emits light to be incident on the optical recording medium, an objective lens that causes light emitted from the light source to enter the optical recording medium as convergent light, light emitted from the light source, and the optical recording medium A beam splitter for separating the reflected light reflected by the beam splitter; and a photodetector for receiving the reflected light separated by the beam splitter, wherein the recording density of the optical recording medium according to claim 1 or 2 is increased. Recording, reproduction, or erasure can be performed accordingly.

Therefore, information can be recorded, reproduced, or erased using the optical recording medium according to the first or second aspect of the present invention, which is adapted to high density recording. It is possible to cope with high-density recording and reproduction without changing the wavelength and using a special light source or complicating the optical system.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a layer configuration example of an optical recording medium 1 according to the present embodiment. Optical recording medium 1 of the present embodiment
Then, on the substrate 3 located on the incident side of the convergent light 2 emitted from the light source and converged by the objective lens, a low refractive index optical Kerr medium layer (second refractive index optical The medium layer 4, a high refractive index optical Kerr medium layer (first refractive index optical Kerr medium layer) 5, an optical recording layer 6, a reflective layer 7, and a protective layer 8 are sequentially laminated. The optical Kerr medium layers 4 and 5 are basically the same layer, but are different layers in that the absorptance for the wavelength of the convergent light 2 is relatively different and the former is lower and the latter is higher.

FIG. 2 is a schematic diagram showing an example of an optical system configuration of an optical recording / reproducing apparatus for performing recording, reproducing or erasing operations on such an optical recording medium 1. A semiconductor laser 11 as a light source that emits light so as to be incident on the optical recording medium 1 from the substrate 3 side, a collimator lens 12 that converts light emitted from the semiconductor laser 11 into a parallel light flux,
An objective lens 13 for condensing the light actually illuminating the optical recording medium 1 as convergent light 2, and a beam for separating the light emitted from the semiconductor laser 11 side and the reflected light reflected by the optical recording medium 1 A splitter 14 for receiving the reflected light separated by the beam splitter 14 to receive an information signal;
A photodetector 15 detects a tracking / focusing signal and the like.

In such a configuration, the objective lens 13
Convergent light 2 from the substrate 3 passes through the low-refractive-index optical Kerr medium layer 4 and the high-refractive-index optical Kerr medium layer 5 and enters the optical recording layer 6 from the substrate 3 side. At this time, the refractive index of the portion 9 of the low-refractive-index optical Kerr medium layer 4 and the high-refractive-index optical Kerr medium layer 5 irradiated with the condensed spot becomes higher due to the optical Kerr effect, and the central portion becomes higher and becomes lower toward the periphery. A refractive index distribution occurs. Due to this effect, the diameter of the focused spot becomes smaller. More specifically, in the low-refractive-index Kerr medium layer 4 having a low refractive index, since the absorptance of the convergent light 2 is low, a thick film as shown in the illustrated example can be used. Since the refractive index is slightly higher, the refractive index at the center becomes higher than that at the periphery, and the beam diameter of the convergent light can be reduced by the self-focusing effect. On the other hand, in the next high-refractive-index optical medium layer 5 having a high absorptance, the layer thickness is small but the nonlinear optical constant is large, so that the self-focusing effect is further emphasized, and the beam diameter of the convergent light can be reduced. In addition, in general, a material having a high absorptivity often has a high refractive index, and the wavelength in the high-refractive-index optical Kerr medium layer 5 is further shortened. The diffraction limit determined by the light angle is reduced, and the beam diameter of the convergent light can be further reduced. Therefore, the optical recording medium 1 can be recorded, reproduced, or erased at a higher density than the conventional example. As described above, the optical recording medium 1 itself has been devised to increase the density, and the optical recording / reproducing apparatus side does not need to use a special light source for further shortening the wavelength or to complicate the optical system. Thus, high-density recording and reproduction can be dealt with as it is.

Here, among the various materials that can be used for the low-refractive-index optical Kerr medium layer 4 and the high-refractive-index optical Kerr medium layer 5, organic materials include polydiacetylene, polydiacetylenetoluenesulfonic acid, polyarylenevinylene, and polyacetylene. ,
Phthalocyanine and the like. The inorganic material _{C-SnO 2, h-BN} , CdS 1-x Se x containing glasses, semiconductors Ge, GaAs, AlGaAs, InP,
_{InSb, As 2 S 3, As} 2 Se 3 , and the like.

For example, as the low refractive index optical Kerr medium layer 4, C
dS _1-x Se with _x-containing glass is formed on the substrate 3 by sputtering or the like, the As ₂ S ₃ layer can similarly be formed thereon and then as a high refractive index optical Kerr medium layer 5. Also, CdS _1-x
The Se _x containing glass absorption edge wavelength and increasing the value of x is shifted to the long wavelength side. Therefore, it is possible to select a low refractive index optical Kerr medium layer 4 having a large value of x and a high refractive index optical Kerr medium layer 5 having a small value of x. In the infrared light region, polydiacetylenetoluenesulfonic acid is added to the low-refractive-index optical medium layer 4 by GaAs.
s, AlGaAs, InP, etc., with a high refractive index optical Kerr medium layer 4
Can be used as

In this embodiment, since the optical recording medium 1 includes the reflection layer 7, even if the optical recording layer 6 is thin, the reflection layer 7 can increase the reflectance of the reflected return light. Therefore, the optical recording layer 6 can be thinned without any trouble, and as a result, the recording sensitivity can be improved.

[0021]

According to the optical recording medium of the first aspect of the present invention, an optical recording layer formed on a substrate and receiving convergent light from a light source, An optical Kerr medium layer formed in close proximity to the incident side, wherein the optical Kerr medium layer has a first refractive index optical Kerr medium layer and the first Kerr medium layer.
And a second refractive index Kerr medium layer disposed closer to the incident side of the convergent light than the refractive index Kerr medium layer, and the first refractive index Kerr medium layer absorbs the convergent light with respect to the wavelength. Since the refractive index is set relatively higher than the absorptance of the second refractive index optical Kerr medium layer with respect to the wavelength of the convergent light, the convergent light from the light source passes through the optical Kerr medium layer side onto the optical recording layer. When recording, reproducing or erasing information, the second refractive index optical Kerr medium layer having a low refractive index can use a thick film because the absorptance of the convergent light is small, and the intensity distribution of the convergent light is slightly centered. Since the refractive index at the center is higher than that at the periphery, the beam diameter of the convergent light can be reduced due to the self-focusing effect. On the other hand, the layer thickness is thin in the first refractive index optical Kerr medium layer having the next higher absorption. Has a large nonlinear optical constant, so the self-focusing effect is more emphasized In addition, the beam diameter of the convergent light can be reduced, and in addition, in general, a material having a high absorption rate often has a high refractive index, and in this case, the wavelength in the first refractive index optical medium layer is further shortened. Therefore, the diffraction limit determined by the wavelength and the converging angle in the first refractive index optical Kerr medium is reduced, and the beam diameter of the convergent light can be further reduced. For this reason,
It is possible to provide an optical recording medium capable of recording, reproducing, or erasing at a higher density than the conventional example.

According to the second aspect of the present invention, in the optical recording medium according to the first aspect, a reflection layer formed on the opposite side of the optical recording layer from the first refractive index optical Kerr medium layer. Therefore, it is basically the same as the case of the invention described in claim 1, but particularly, by providing a reflective layer on the opposite side to the optical Kerr medium layer with the recording layer interposed, even when the optical recording layer is thin. Since the reflectance of the reflected return light can be increased, the optical recording layer can be thinned without any trouble, and the recording sensitivity can be improved.

According to the optical recording / reproducing apparatus of the present invention, a light source for emitting light to be incident on the optical recording medium, and the light emitted from the light source is converged to the optical recording medium. An objective lens to be incident, a beam splitter that separates light emitted from the light source and reflected light reflected by the optical recording medium, and a photodetector that receives the reflected light separated by the beam splitter, Since recording, reproduction or erasing according to the recording density of the optical recording medium according to claim 1 or 2 is enabled,
In particular, high-density recording and reproduction can be dealt with as it is without using a special light source for further shortening the wavelength or complicating the optical system.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an example of an optical system configuration of an optical recording / reproducing apparatus.

FIG. 3 is a sectional structural view of an optical recording medium showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical recording medium 2 Convergent light 3 Substrate 4 Second refractive index optical Kerr medium layer 5 First refractive index optical Kerr medium layer 6 Optical recording layer 7 Reflective layer 11 Light source 13 Objective lens 14 Beam splitter 15 Photodetector

Claims (3)

[Claims] 1. An optical recording layer formed on a substrate and receiving convergent light from a light source, and an optical Kerr medium layer formed close to the optical recording layer on the incident side of the convergent light. Wherein the optical Kerr medium layer is provided with a first refractive index Kerr medium layer and a second refractive index Kerr medium disposed on the incident side of the convergent light with respect to the first refractive index Kerr medium layer. The first refractive index optical Kerr medium layer has an absorptance for the wavelength of the convergent light, which is relatively higher than the second refractive index optical Kerr medium layer has an absorbance for the convergent light wavelength. Optical recording medium set high. 2. The optical recording medium according to claim 1, further comprising a reflection layer formed on a side of the optical recording layer opposite to the first refractive index optical Kerr medium layer. 3. A light source for emitting light incident on an optical recording medium, an objective lens for causing light emitted from the light source to enter the optical recording medium as convergent light, and light emitted from the light source 3. The optical recording according to claim 1, further comprising: a beam splitter configured to separate the light reflected by the optical recording medium from the light, and a photodetector configured to receive the reflected light separated by the beam splitter. 4. An optical recording / reproducing device capable of recording, reproducing, or erasing according to the recording density of a medium.