JP2001273679A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium to which a method for super- resolving/reproducing CAD is adapted by using a super-resolving/reproducing film capable of increasing the extinction coefficient by light irradiation. SOLUTION: A transparent substrate 1 usable also as a recording layer, the super-resolving/reproducing film 2 the extinction coefficient of which can be selectively increased by irradiating with the light of the amount exceeding the prescribed threshold value, a laminated interference layer 11 and a reflection film 5 are laminated successively to obtain this optical recording medium. This optical recording medium is constituted so that a region to be irradiated with the light of the amount exceeding the threshold value can be made to be an optical opening and the light reflected only from this region is detected to read the recorded information. When the film 2 is a signal layer, this region becomes an optical mask since the reflectance is lowered and the detection of the light reflected only from this region is difficult. But this region can be made to be the optical opening by providing the layer 11 to perform multiple reflection and multiple interference.

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, and more particularly to an optical recording medium using a super-resolution reproducing film capable of obtaining reflected light in an area smaller than the diameter of irradiation light.

[0002]

2. Description of the Related Art An optical disk memory for reproducing or recording / reproducing information by irradiating a light beam is a storage device having a large capacity, a high-speed access property, and a medium portability. It has been put into practical use, and its development is expected in the future.

Techniques for increasing the density of an optical disk include shortening the wavelength of a gas laser for cutting a master, shortening the wavelength of a semiconductor laser as an operating light source, increasing the numerical aperture of an objective lens, and reducing the thickness of the optical disk. Furthermore, there are various approaches to recordable optical disks, such as mark length recording and land / groove recording. In addition, a super-resolution reproduction technique using a medium film has been proposed as a technique that has a large effect of increasing the density of an optical disc. Super-resolution technology was initially
Although it has been proposed as a technology specific to magneto-optical disks,
Thereafter, an attempt has been reported to provide a super-resolution reproduction film in which the transmittance of light is changed by the irradiation of the reproduction light on the irradiation side of the reproduction light with respect to the recording layer even on the ROM disk. As described above, the super-resolution reproduction technology is a magneto-optical disk, a CD-R
It has been found that the present invention is applicable to all optical disks such as OM, CD-R, WORM, and phase-change optical recording media.

[0004] Super-resolution reproduction films proposed in the conventional super-resolution reproduction technology are roughly classified into a heat mode system and a photon mode system. In the heat mode method, a phase transition or the like is generated in a super-resolution reproduction film by heating by irradiation of reproduction light, and an optical aperture having a high transmittance is formed. The shape of the optical aperture becomes the same as the isotherm of the super-resolution reproducing film. In the photon mode method, a photochromic material is used as a super-resolution reproducing film, and in a photochromic material that uses color development or decoloration by irradiation of reproduction light, electrons are excited from a ground level to an excited state having a short life by irradiation with light, and the excitation level The transition from the phase to a metastable excitation level with a very long lifetime leads to a change in light absorption characteristics due to trapping. Therefore, to reproduce repeatedly, it is necessary to de-excit the electrons trapped by the metastable excitation level to the ground state and close the optical aperture once formed. There is also an example in which a semiconductor continuous film or a semiconductor fine particle dispersion film utilizing an absorption saturation phenomenon is used as a photon mode type super-resolution reproduction film. When the light irradiation amount of these super-resolution reproduction materials exceeds a predetermined threshold value, the transmittance of the materials themselves increases. That is, it has a characteristic that the extinction coefficient decreases.

That is, in order to increase the light transmittance in a region with a large light irradiation amount (optical aperture) and to reduce the light transmittance in a region with a small light irradiation amount (optical mask portion), light is transmitted through the optical opening. The difference between the light intensity and the light intensity transmitted through the optical mask can be increased.

On the other hand, KBr and CuB which cause two-photon absorption
In the case of using a change from a decolored state to a colored state with a material such as r, RbBr, CuCl, or a material exhibiting photochromism and thermochromism, the extinction coefficient increases when the light irradiation amount exceeds a predetermined threshold. .

For example, when this material is used as a super-resolution reproducing film and irradiated with light using a normal laser beam, the central portion of the light irradiation region where the irradiation light intensity is high becomes an optical mask portion and the irradiation light intensity is low. The vicinity of the end of the light irradiation area is an optical aperture. Therefore, it is difficult to increase the intensity difference of the transmitted light of the super-resolution reproduction film, and a region where the intensity of the irradiated light is high cannot be used for reading information.

That is, a material whose extinction coefficient is increased by light irradiation exceeding a threshold value has a problem that the central portion of a light spot having a high irradiation light intensity does not become an optical aperture, and the light use efficiency is reduced.

[0009]

As described above, when a material whose extinction coefficient increases when irradiated with light exceeding a predetermined threshold value is used as the super-resolution reproduction film, the intensity of the irradiated light is high. There is a problem that light utilization efficiency is reduced because the region is used as an optical mask portion.

The present invention has been made in view of such a problem, and uses a material whose extinction coefficient is increased by light irradiation exceeding a predetermined threshold value as a super-resolution reproduction film, and a light irradiation region. It is an object of the present invention to provide an optical recording medium capable of reading information in a region having a high irradiation light intensity therein.

[0011]

The optical recording medium of the present invention comprises:
The recording layer, the reflective layer irradiated with irradiation light through the recording layer, formed at least on the irradiation light side of the reflective layer, the extinction coefficient selectively by light irradiation of an amount exceeding a predetermined threshold An optical recording medium comprising a super-resolution reproduction film that increases in size, in the light spot irradiated on the optical recording medium, in a region exceeding the threshold, and in a region equal to or less than the threshold, the reflectance of the optical recording medium is increased. A high-refractive-index layer and a low-refractive-index layer, which are formed at least on the irradiation light side with respect to the reflective layer and cause multiple reflection and multiple interference of incident light of the irradiation light and light reflected by the reflective layer, in different optical recording media. It is characterized by comprising a laminated interference layer having a layer.

That is, a super-resolution reproduction film whose extinction coefficient increases (irradiation coefficient generally increases due to increase in absorptance and light reflectivity and light transmittance decrease) by light irradiation exceeding a predetermined threshold value is a single layer. When used, the absorptance increases in a region with a large amount of light irradiation, so that the light transmittance and the light reflectance are reduced. However, the light having a recording layer, a laminated interference layer, and a super-resolution reproduction film laminated on a reflective layer It has been found that in a recording medium, the reflectance of the optical recording medium is increased only in a region irradiated with light exceeding a predetermined threshold.

According to such an optical recording medium of the present invention,
A region to be irradiated with light exceeding a predetermined threshold can be a region having a high reflectance, and the light use efficiency can be improved.

Further, according to the optical recording medium of the present invention, a region having a high reflectivity (hereinafter referred to as an optical aperture) and a region having a low light reflectivity (hereinafter referred to as an optical mask) of the optical recording medium. Can be increased, and problems such as reading errors can be reduced.

It is preferable that the laminated interference layer is a laminate of three or more layers in which a high refractive index layer and a low refractive index layer are sequentially laminated.

That is, the order of lamination of high refractive index layer / low refractive index layer / high refractive index layer / low refractive index layer... Or low refractive index layer / high refractive index layer / low refractive index layer / high refractive index By laminating the layers in the order of lamination and increasing the chances of multiple reflection and interference, the above-described effects become remarkable.

The high refractive index layer is a layer having a relatively high refractive index with respect to the adjacent interference layer, and the low refractive index layer is a layer having a relatively low refractive index with respect to the adjacent interference layer. .

The super-resolution reproducing film may be used as at least one of the high refractive index layer and the low refractive index layer.

A super-resolution reproducing film having a smaller refractive index than the high refractive index layer is formed adjacent to the high refractive index layer of the laminated interference layer composed of the low refractive index layer / high refractive index layer, or a low refractive index layer. By forming a super-resolution reproduction film having a higher refractive index than that of the low-refractive-index layer adjacent to the refractive index layer, the super-resolution reproduction film can be used as a part of the laminated interference layer.

Further, between the reflection layer and the laminated interference layer, the reflectance of the optical recording medium with respect to the irradiation light exceeding the threshold value is substantially maximized, or the optical recording medium with respect to the irradiation light having the threshold value or less is provided. Can be provided with an optical matching layer whose film thickness is controlled so as to substantially minimize the reflectance.

In the optical recording medium of the present invention, the layer structure is adjusted so that the light reflectance of the optical opening becomes the maximum or the light reflectance of the optical mask is the minimum, and the optical mask and the optical mask are combined. It is desired to increase the difference in the intensity of the reflected light from the optical aperture. Depending on the thickness and refractive index of the super-resolution reproduction film, or the refractive index and reflectance of the transparent substrate provided as needed, the light reflectance of the optical opening may not be maximum. A layer made of a material with a predetermined refractive index is placed between the reflective film and the laminated interference layer, and by controlling the film thickness, it is possible to adjust the optical reflectance of the optical aperture to be the maximum. Becomes

The extinction coefficient of the super-resolution reproducing film used in the present invention refers to the imaginary part of the complex refractive index, and the refractive index refers to the real part of the complex refractive index.

[0023]

FIG. 1 shows an example of a sectional view of an optical recording medium according to the present invention.

In the optical recording medium of FIG. 1, a laminated interference layer in which a plurality of low-refractive index layers 2 and high-refractive index layers 3 are sequentially laminated on an optical disc substrate 1 which is a recording layer in which recorded information is formed as pits. 11, a super-resolution reproduction film 4 and a reflection film 5 are sequentially formed. In the example of FIG. 1, three sets of the low refractive index layer 2 and the high refractive index layer 3 are laminated.

Next, the reflectance characteristics of the optical recording medium when the extinction coefficient of the super-resolution reproducing film according to the present invention changes will be described.

FIG. 2 is a diagram showing the relationship between the irradiation light wavelength and the reflectance of the optical recording medium of the present invention.

First, in FIG. 2, the super-resolution reproducing film is
Refractive index 2.3 (no change by irradiation light), extinction coefficient when irradiation light is below threshold (hereinafter referred to as initial extinction coefficient)
Is used. As shown in FIG. 1, a six-layered interference layer using SiO ₂ as the low refractive index layer and ZnS as the high refractive index layer is used.
The thickness of the super-resolution reproduction film is set to 73.5 nm so that the initial reflectance of the optical recording medium is minimized when laser light having a wavelength of 410 nm is used as irradiation light.

FIG. 2 shows the reflectivity of the optical recording medium when such an optical recording medium is irradiated with irradiation light of a predetermined threshold value or less (the refractive index of the super-resolution reproducing film is 2.3 and the extinction coefficient is 0). Irradiating light exceeds a predetermined threshold, the extinction coefficient of the super-resolution reproduction film is 0.1,
The calculation result of the reflectance when changing to 0.2 or 0.5 is shown.

FIG. 3 shows the reflectance difference between the case where the extinction coefficient of the super-resolution reproducing film is the initial refractive index and the case where the extinction coefficient exceeds a predetermined threshold value and changes.

As is apparent from FIG. 2, the irradiation light 410n
It can be seen that near m, the reflectance increases as the extinction coefficient increases. In other words, the extinction coefficient of the super-resolution reproduction film increases in a light irradiation region exceeding a predetermined threshold, and the light reflectance of the optical recording medium increases only in that region to become an optical aperture, and the super-resolution reproduction film is initially It can be seen that, in a light irradiation area below a predetermined threshold, which remains at the extinction coefficient, the reflectance of the optical recording medium is small and the optical recording medium becomes an optical mask portion.

The reason why the reflectance increases with the increase of the extinction coefficient of the super-resolution reproducing film is that the irradiation light is reflected multiple times in the optical recording medium due to the provision of the laminated interference layer. This is because they interfered.

FIG. 3 shows that as the rate of change of the extinction coefficient increases, the reflectance difference between the optical aperture and the optical mask increases.

Next, a super-resolution reproduction technique using such an optical recording medium will be described.

FIG. 4 is a schematic view of an optical recording medium viewed from a light irradiation direction for explaining a super-resolution reproduction technique.

In the optical recording medium 41, tracks T1, T
2, recording areas 42 are formed at a predetermined pitch along T3, and the recording information of each track is read by sequentially scanning the track T1, the track T2, and the track T3 with the reproduction light.

FIG. 4 is a drawing when the track T2 is irradiated with reproduction light using a laser beam or the like, and the light spot of the reproduction light is indicated by S. In an optical recording medium having no super-resolution reproduction film, since the reflected light is received from the same area as the light spot S, if the recording area is formed at a pitch smaller than the light spot diameter, a plurality of light spots are formed in the light spot. The recording area 42 cannot accurately read the recording information.

In the optical recording medium of the present invention, for example,
When using a laser beam having a light irradiation amount exceeding a predetermined threshold only near the center of the light spot S, the reflectance of the optical recording medium is increased only in a light irradiation region exceeding the predetermined threshold,
An optical aperture A narrower than the light spot S is formed, and an area of the light spot irradiated with light having a predetermined threshold or less is an optical mask M having a low reflectance. As a result, it is possible to read a recording area only in the optical aperture A that is narrower than the light spot S, and it is possible to accurately read recorded information in which a recording area is formed at a smaller pitch than the light spot S. .

On the other hand, for comparison, the extinction coefficient of the super-resolution reproduction film is 0 to 0 in the optical recording medium having the super-resolution reproduction film and the reflection film in the configuration of FIG. .1,
FIG. 9 shows the reflectance at each wavelength when changed to 0.2 and 0.5, and FIG. 10 shows the amount of change in reflectance. However, the thickness of the super-resolution reproducing film was set to 73.5 nm so that the light reflectance became minimum when the super-resolution reproducing film had an initial extinction coefficient.

As can be seen from FIGS. 9 and 10, when there is no laminated structure of the low refractive index layer and the high refractive index layer, the reflectance decreases as the extinction coefficient increases.

The super-resolution reproduction using this recording medium is shown in FIG.
This will be described with reference to FIG.

In the vicinity of the center of the light beam where the light beam is strong, the extinction coefficient of the super-resolution reproducing film increases, the absorption rate increases, the reflectance of the optical recording medium decreases, and the optical spot near the center of the light spot S A mask M is formed. In the vicinity of the boundary area of the light spot S, since the extinction coefficient is small, the reflectance increases and the optical aperture A is formed.

That is, since the reflectance in the area with a large amount of irradiation light is low and the reflectance in the area with a small amount of irradiation light is high, the difference in the intensity of the reflected light between the optical mask M and the optical aperture A is small. There is a high possibility that a plurality of recording areas 102 are included in the part A, and there is a possibility that a reading error of recorded information may occur.

The super-resolution reproducing film according to the present invention is a material whose extinction coefficient is selectively increased by light irradiation exceeding a predetermined threshold value as described above, and is generally a heat mode type or a photon mode type. It has been known.

The heat-mode super-resolution reproducing film selectively generates a phase transition or the like only in a portion exceeding a threshold value by heating by light beam irradiation to change an extinction coefficient. Examples thereof include phase change materials such as chalcogen-based GeSbTe and AgInSbTe, and thermochromic materials such as Bianthrone-based and spiropyran.

As the photon mode type super-resolution reproducing film, for example, a film utilizing color development or decoloration by light irradiation, such as a photochromic material, may be mentioned. In a photochromic material, electrons are excited by light irradiation from a specified order to an excited state with a short lifetime, and further, transition from the excited level to a metastable excited state with a very long lifetime is captured, thereby selectively changing the refractive index. Change. Specific examples include pyrobenzopyran-based molecules, fulgide-based molecules, diarylethene-based molecules, cyclophane-based molecules, and azobenzene. Further, a semiconductor whose optical constant changes due to absorption saturation, a semiconductor fine particle dispersed film, and the like can be given. Further, a semiconductor whose extinction coefficient changes due to absorption saturation, a semiconductor fine particle dispersed film, and the like can be given.

It is desirable that the laminated interference layer according to the present invention has an optical thickness λ / 4 substantially with respect to irradiation light such as reproduction light in order to produce an interference effect. In addition, it is desirable to increase the difference in refractive index between the adjacent high refractive index layer and low refractive index layer. Specifically, SiO ₂ , Al ₂ O ₃ , ZrO ₂ ,
TiO _2, ZrO _2, etc. oxides, MgF _2, CaF _2, etc. fluorides, AlN, Si ₃ N nitrides such _4, sulfides such as ZnS, or may be used such as mixtures thereof.

The high refractive index layer or the low refractive index layer constituting the laminated interference layer according to the present invention is a laminated interference layer in which layers having different refractive indices are laminated, and is relatively to an adjacent layer. Refers to a layer made of a material having a high or low refractive index. For example, as a combination thereof, as a high refractive index layer, Z
rO ₂ , TiO ₂ , ZnS, ZnS · SiO _2, etc., as a low refractive index layer, MgF ₂ , CaF ₂ , SiO ₂ , Al ₂ O ₃ ;
Na ₃ Al ₂ F ₆ or the like can be used.

The laminated interference layer is formed by sequentially laminating a high-refractive index layer and a low-refractive index layer, and the number of layers is desirably about 5 to 8 layers. However, depending on the order of lamination of the high refractive index layer and the low refractive index layer and the refractive index, the reflectance of the recording medium increases with an increase in the extinction coefficient even in other cases. In the optical recording medium shown in FIG. 1, the difference in the reflectance when the super-resolution reproduction film whose extinction coefficient changes from 0 to 0.5 by light irradiation is used for the stacked interference layers having different numbers of layers is shown in FIG. Show. Here, a low refractive index layer, a high refractive index layer,
Four layers are stacked in the order of a high refractive index layer and a low refractive index layer. Even if the extinction coefficient increases to 0.5, the reflectivity is lower than when the extinction coefficient is 0, but 6 layers. , 8 layers have a higher reflectance than when the extinction coefficient is 0, and can form an optical aperture. When the number of layers is 10, the reflectance is lower than when the extinction coefficient is 0. On the other hand, in the configuration in which the laminated interference layers are laminated in the order of high refractive index layer / low refractive index layer from the substrate side in the layer configuration of FIG. FIG. 5B shows the difference in reflectance when a super-resolution reproducing film that changes to 0.5 is used. In this case, from 4 layers to 1
Even if the number of layers is changed up to 0 layers, the reflectivity is higher than when the extinction coefficient is 0, but the reflectivity difference is greatest when there are 6 layers. Thus, the optimum number of layers is determined by the order of lamination of the high refractive index layer and the low refractive index layer and the refractive index of each layer. In any case, the reflectance at the set wavelength when the extinction coefficient is 0 is preferably 20% or less, and the smaller the reflectance, the better.

In order to increase the number of laminated interference layers, the super-resolution reproducing film can be made to function as a part of the laminated interference layer. For example, when the laminated interference layer and the super-resolution reproduction film are formed adjacent to each other, and the layer adjacent to the super-resolution reproduction film is a high refractive index layer, the super resolution When the layer adjacent to the super-resolution reproduction film is a low-refractive-index layer, a super-resolution reproduction film made of a material having a higher refractive index may be formed.

As shown in FIG. 1, the recording layer according to the present invention may be formed by forming an appropriate layer such as an optical disk substrate made of polycarbonate, polymethyl methacrylate, glass or the like and forming pits. For example,
A recording layer is made of a phase-change material such as a Ge-Sb-Te system or an Ag-In-Sb-Te system, and the recording layer is irradiated with a light beam to change a part of its optical characteristics, thereby recording information. May be created.

The reflection layer according to the present invention comprises the above-described recording layer,
It is preferable to totally reflect the light irradiated through the laminated interference layer and the super-resolution reproducing film, for example, Al and Al-C
r, Al alloy such as Al-Ti, Al-Mo, Au, A
It is desirable that g, Cu, and the like be a layer having an average thickness of 50 nm or more.

In the optical recording medium shown in FIG.
By adjusting the thickness of the super-resolution reproduction film, the reflectance of the optical mask portion of the optical recording medium was adjusted to be the minimum, but an optical matching layer was formed between the interference layer and the reflection film, By adjusting the refractive index and the film thickness of the optical matching layer, the reflectance of the optical mask portion of the optical recording medium can be minimized even if the super-resolution reproduction film has an arbitrary value. Further, the refractive index and the thickness of the optical matching layer may be adjusted so that the reflectance of the optical opening of the optical recording medium is maximized.

FIG. 6 shows a modification of the optical recording medium as described above.
Shown in

FIG. 6 shows a laminated interference layer 11 having a six-layer structure in which a low refractive index layer 2 and a high refractive index layer 3 are sequentially laminated on an optical disk substrate 1 made of a transparent substrate.
A super-resolution reproduction film 4 is formed on 1, and this super-resolution reproduction film is formed of a material having a lower refractive index than the adjacent high-refractive-index layer. On the super-resolution reproduction film, a recording layer 9 made of a phase change material, an optical matching layer 10, and a reflection film 5 are sequentially laminated.

As described above, according to the optical recording medium of the present invention, a super-resolution reproduction film whose extinction coefficient is increased by light irradiation exceeding a predetermined threshold is used, and a region having a high light intensity is used as an optical aperture. As a result, an optical recording medium with high light use efficiency can be obtained.

Although the reproduction technique of the optical recording medium using the super-resolution film has been described, the optical recording medium of the present invention can form a recording area smaller than the light spot by the same technique. is there.

[0057]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 The layer structure of this example is a PC (polycarbonate) substrate /
The laminated interference layer / super-resolution reproduction film / reflection film are sequentially laminated. The laminated interference layer has a structure in which six layers are sequentially laminated in order of a low refractive index layer and a high refractive index layer from the PC substrate side.

On a PC board, 0.2 μm to 0.2 μm for each track.
A pit row having the same length of 6 μm, width of 0.3 μm, and interval is formed. The reproduction wavelength is 413 nm. The refractive indices of the low refractive index layer and the high refractive index layer are 1.5 and 2.4, respectively, and the film thickness is such that the optical film thickness corresponds to λ / 4, the low refractive index layer is 68.8 nm, and the high refractive index is high. Rate layer 43.
0 nm. The super-resolution reproducing film has a refractive index of 2.3 and an initial extinction coefficient of 0.05.

The film thickness of the super-resolution reproducing film is adjusted so that the reflectance becomes minimum in the initial state where the reproducing light is not irradiated.
It is 3.5 nm. The extinction coefficient of this super-resolution reproduction film changes to 0.3 when irradiated with reproduction light. The reflective film is made of AlTi and has a thickness of 50 nm.

As a comparative example, a disk having the same configuration as in Example 1 except that no laminated interference layer was provided was produced.

The disks of Example 1 and Comparative Example were replaced with Kr ⁺
The pit length dependence of the CNR was measured with a reproduction evaluator using a gas laser as a light source. However, the reproduction wavelength 41 of the reproduction evaluation machine
3 nm, reproduction power 1 mW. The result is shown in FIG.

As can be seen from FIG. 7, the pit length is 0.4
When the length is as long as μm or more, the CNR is larger in the comparative example having no super-resolution reproduction film, but the CNR sharply decreases when the pit length is shorter than 0.4 μm. This is because a sufficient super-resolution effect has not been obtained.

On the other hand, the disk of this embodiment maintains a high CNR even when the pit length is reduced to 0.2 μm. From the above, it was confirmed that the multilayer dielectric was effective in improving the characteristics of the super-resolution reproduction film.

Example 2 The layer structure of this example is a PC substrate / laminated interference layer / low refractive index layer / super-resolution reproduction film / matching layer / reflection film. The laminated interference layer has a structure in which four layers are sequentially laminated in the order of a low refractive index layer and a high refractive index layer from the PC substrate side. 0.
Pit rows having the same length of 2 μm to 0.6 μm, the width of 0.3 μm, and the same interval are formed. The reproduction wavelength is 413 nm. The refractive indices of the low refractive index layer and the high refractive index layer are 1.5 and 2.4, respectively.
/ 4, a low refractive index layer of 68.6 nm, and a high refractive index layer of 43.0 nm. The refractive index of the super-resolution reproducing film is 2.
3. The initial extinction coefficient is 0.05, and the film thickness is 44.9 nm, the film thickness corresponding to the optical film thickness of λ / 4. The extinction coefficient of this super-resolution reproduction film is set to 0.
Change to 3.

AlN was used for the matching layer. AlN
Has a refractive index of 1.8. The thickness of the matching layer is set to 100 nm so that the reflectance becomes minimum in the initial state where the reproduction light is not irradiated. AlTi for reflective film
And the film thickness is 50 nm.

The same measurement as in Example 1 was performed, and substantially the same effect as in Example 1 was confirmed.

Embodiment 3 The layer configuration of this embodiment is the same as that of Embodiment 1. However, the refractive index of the super-resolution reproduction film is 2.25, and the initial extinction coefficient is 0.05.

This super-resolution reproduction film is irradiated with reproduction light to
The refractive index changes to 2.3 and the extinction coefficient changes to 0.25. The same measurement as in Example 1 was performed, and substantially the same effect was confirmed.

Embodiment 4 The layer configuration of this embodiment is a PC substrate / laminated interference layer / super-resolution reproduction film / matching layer / recording layer / interference layer / reflection film. The laminated interference layer has a laminated structure in which six layers are sequentially laminated in the order of a low refractive index layer and a high refractive index layer from the PC substrate side.

That is, when the recording layer is Ge ₂ Sb ₂ Te ₅ ,
The configuration is the same as that of the first embodiment, except that the thickness is 0 nm and the interference layer is ZnS-SiO ₂ , 40 nm.

As a comparative example, a disk having no laminated interference layer was manufactured.

The recording / reproducing wavelength was 413 nm, and the self-recording / reproducing characteristics were evaluated using the optical disks of the present example and the comparative example. At 6 m / s, the recording power level was set to 9 mW, the erasing power level was set to 4 mW, and a recording mark having a mark length of 0.3 μm was recorded at a single frequency in the overwrite mode while changing the mark interval.

At this time, recording compensation for dividing a recording pulse was applied in order to prevent the influence of thermal interference.

The optical disk recorded as described above was reproduced. When the reproducing power was set to 1 mW, the high-density recording characteristics of reproducing tracks having different mark intervals were evaluated. The result is shown in FIG.

In the optical disk of the comparative example, the mark interval is set to 0.
At less than 3 μm, the influence of intersymbol interference is strong, and the CNR is reduced. Also, since the crosstalk from the adjacent track is large, even when the mark interval on the track is long, the CNR is high.
Level is not so high. On the other hand, in the disk of the present embodiment, reproduction can be performed with a high CNR even when the mark interval is 0.15 μm. Further, since there is no influence of crosstalk, the CNR when the mark interval is longer than 0.15 μm is higher than that of the comparative example.

[0077]

According to the present invention, a CAD super-resolution reproducing method can be performed even if a super-resolution reproducing film whose extinction coefficient increases by light irradiation is used by laminating a low refractive index layer and a high refractive index layer. Thus, a recording mark having a narrow mark pitch and a narrow track pitch can be reproduced with high resolution. Materials applicable to super-resolution films can be expanded.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical recording medium of the present invention.

FIG. 2 is a diagram showing the relationship between the irradiation light wavelength and the reflectance of the optical recording medium of the present invention.

FIG. 3 is a diagram showing a reflectance difference between a case where the extinction coefficient of the super-resolution reproduction film is an initial refractive index and a case where the extinction coefficient changes beyond a predetermined threshold value.

FIG. 4 is a diagram for explaining a super-resolution reproduction technique.

FIG. 5 is a diagram showing a difference in reflectance of an optical recording medium due to a difference in the number of stacked interference layers.

FIG. 6 is a diagram showing a modification of the optical recording medium of the present invention.

FIG. 7 shows a CNR that is hot in an optical recording medium according to an embodiment of the present invention.
FIG. 3 is a diagram showing the pit length dependence of the pit.

FIG. 8 shows a CNR in an optical recording medium according to an embodiment of the present invention.
FIG. 3 is a diagram showing mark interval dependency.

FIG. 9 is a graph showing the reflectance when the extinction coefficient of the super-resolution reproduction film of the optical recording medium having only the super-resolution reproduction film and the reflection film is changed.

FIG. 10 is a diagram showing a reflectance change amount in FIG. 9;

FIG. 11 is a diagram for explaining a super-resolution reproduction technique in an optical recording medium without a laminated interference layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Super-resolution reproduction film 3 ... Refractive index layer 4 ... High refractive index layer 5 ... Reflective film 11 ... Laminated structure

Claims (5)

[Claims] 1. A recording layer, a reflective layer to which irradiation light is irradiated through the recording layer, and at least a reflection layer formed on the irradiation light side of the reflection layer. An optical recording medium comprising a super-resolution reproduction film having a large extinction coefficient, and optical recording is performed in an area exceeding the threshold value and an area equal to or less than the threshold value in an irradiation light spot on the optical recording medium. In an optical recording medium having a different reflectivity of a medium, a high refractive index formed at least on the irradiation light side with respect to the reflective layer, causing multiple reflection and multiple interference of incident light of the irradiation light and light reflected by the reflective layer. An optical recording medium comprising a laminated interference layer having a layer and a low refractive index layer. 2. The optical recording medium according to claim 1, wherein the laminated interference layer is a laminate of three or more layers in which a high refractive index layer and a low refractive index layer are sequentially laminated. 3. The optical recording medium according to claim 2, wherein the super-resolution reproducing film is used as at least one of the high refractive index layer and the low refractive index layer. 4. The optical recording apparatus according to claim 2, wherein when the wavelength of the irradiation light is λ, the thickness of the high refractive index layer and the low refractive index layer is substantially λ / 4. Medium. 5. An optical recording medium between the reflective layer and the laminated interference layer, which substantially maximizes the reflectance of the optical recording medium with respect to irradiation light exceeding the threshold, or with respect to irradiation light below the threshold. The optical recording medium according to claim 1, further comprising an optical matching layer whose film thickness is controlled so as to substantially minimize the reflectance of the optical recording medium.