JP3435805B2 - Optical recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a reproducing light from the transparent substrate side with an information signal recorded as a recording pattern due to the uneven shape or a change in optical characteristics, and changes the amount of reflected light. The present invention relates to an optical recording medium that reproduces a signal by detecting it.

[0002]

2. Description of the Related Art In recent years, in the field of information recording, researches on optical information recording methods have been advanced in various places. This optical information recording system can perform non-contact recording / reproducing, can achieve a recording density higher than the magnetic recording system by an order of magnitude, and supports read-only, write-once, and rewritable memory types. A wide range of applications from industrial to consumer use are considered as those that have a number of advantages such as being able to do and can realize an inexpensive large-capacity file.

Among the above-mentioned memory types, a read-only type optical recording medium is a digital audio disc (so-called compact disc, CD), an optical video disc (so-called laser disc, LD), or a CD.
-ROM etc. are already widely used.

In these read-only type optical recording media, pits are usually recorded on a transparent substrate in a pattern corresponding to an information signal as, for example, a concave-convex shape or a layer for changing an optical constant, and this recording pattern is formed. , A reflective layer made of a metal material such as Al is adhered and formed. In such an optical recording medium, reproducing light such as laser light is irradiated from the transparent substrate side to check the presence / absence of pits in the reproducing spot.
The information is reproduced by identifying by detecting the intensity of the reflected light.

By the way, in the read-only optical recording medium, digitization of VTR and high-definition TV (H
Further improvement in recording density is required in order to secure a capacity capable of supporting DTV) and the like. On the other hand, the size of the optical recording medium is required to be small for the convenience of operation, and the improvement of the recording density is also demanded from such requirements.

Here, as a means for improving the recording density of the optical recording medium, it is first considered to make the recording pattern finer, for example, to shorten the pit period. However, since the reproduction optical system has a diffraction limit λ / 2NA (λ: reproduction light wavelength NA: objective lens numerical aperture of the optical system) that cannot reduce the spot diameter further, if the pit cycle becomes too short, reproduction will occur. A situation occurs in which a plurality of pits are duplicated in the spot, which causes a problem that the information signal cannot be reproduced. That is, the reproducing apparatus has an MTF (Modu) that is an index of the resolution determined by the reproducing optical system.
There is a cut-off spatial period of the transfer transfer function.

For this reason, the signal code is compressed with the pit period unchanged, or the numerical aperture NA of the objective lens of the optical system is increased so as to cope with a recording pattern with a short pit period. Attempts have been made to improve the diffraction limit of reproduction light by shortening the reproduction light wavelength. In addition, recently, super resolution (super
A method called "resolution" is drawing attention as a method that can be applied to a recording pattern with a short pit period.

[0008] Super-resolution means setting an aperture (aperture) smaller than the diffraction limit of the irradiation light at the object point position so that the apparent spot diameter of the irradiation light becomes smaller than the diffraction limit, thereby increasing the resolution. The principle is to improve. Regarding this super-resolution, for example, “Charles W.
McCutchen, “Super-resolution in Microscopy and the
Abbe Resolution Limit. ”Journal of Optical Societ
y of America, 57 (10), 1190 (1967) ”, Tony Wilson
and Colin Sheppard, “Theory and Practiceof Scannn
ing Optical Microscopy. ”, Academic Press (London),
1984 ”and the like.

In order to actually apply such super-resolution to the signal reproduction of the optical recording medium, it is necessary that the aperture also moves following the movement of the reproducing light on the optical recording medium.

As an example in which super-resolution is applied to a magneto-optical recording medium, the applicant of the present application discloses the magnetic Kerr effect of the magneto-optical recording / reproducing system in Japanese Patent Application Laid-Open Nos. 1-143041 and 1-143042. We propose a method to achieve high-density recording by making the area narrower than the spot diameter of the reproducing light to develop the super-resolution effect. However, this method is used only in a magneto-optical system, and cannot be applied to an ordinary optical recording system that does not use a magnetic head.

As a super-resolution method applicable to a general optical recording system, Japanese Patent Laid-Open No. 2-96926 proposes to use a photoresponsive material for the reflective layer. The principle of this super-resolution reproduction is as follows.

That is, in an optical recording medium using a photoresponsive material for the reflective layer, when reproducing light is irradiated, there is a light amount distribution having a peak at the focal position in the reproducing light spot, and therefore, a local minimum in the vicinity of the focal position. It is possible to change the optical characteristics of only the part. The portion where the optical characteristics have changed functions as an aperture.

When the aperture is formed in this manner, even if a plurality of pits are present in the spot of the reproduction light, only the pits present in the aperture are detected, and the other pits are masked. It will not be detected as a state. Therefore, it is possible to perform signal reproduction from a fine recording pattern in which pits are formed with a cycle shorter than the diffraction limit of the reproduction optical system.

However, in this publication, as a photoresponsive material, a nonlinear optical material whose optical characteristics are directly changed by reproduction light, or a phase in which the optical characteristics are indirectly changed by heat generation due to absorption of reproduction light. Only the change material is described, and no specific material is mentioned.
Therefore, it can be said that its realization is difficult.

Therefore, as specific photoresponsive materials, chalcogenite materials and saturable absorption dyes have been proposed. A chalcogenite-based material undergoes a phase change from a solid state to a melt state by laser heating, and at that time, the complex refractive index changes greatly. On the other hand, the saturable absorbing dye is a photoresponsive material proposed by the applicant in Japanese Patent Application No. 5-26805, and is irradiated with a certain amount of light or more.
It is a pigment material that exhibits a phenomenon such that the absorptance becomes 0 when it is in an excited state, that is, a saturable absorption phenomenon.

For example, when an optical recording medium having a saturable absorbing dye-containing layer containing the saturable absorbing dye and a reflective layer formed on a substrate having pits and projections formed in an uneven shape is irradiated with reproducing light, As described above, since the reproduction light spot has a light amount distribution having a peak at the focal position, only a minimal portion near the focal position is strongly saturable. Since the absorptivity is lowered in this saturable absorption region, the amount of light reaching the reflective layer is large and a high reflectance is obtained as compared with other regions. Therefore, this saturable absorption region functions as an aperture, and even if a plurality of pits are duplicated in the reproduction light spot, only the pits present in this saturable absorption region are detected. The above saturable absorbing dye-containing layer is reported in the publication as a structure composed of a saturable absorbing dye and a polymer material such as PMMA.

[0017]

As described above, various photoresponsive materials for exhibiting super-resolution have been proposed so far, and their application in various medium configurations has been attempted. But,
In either case, there is still a lot of room for improvement. For example, in the case of using a saturable absorbing dye-containing layer, the sensitivity for developing super-resolution is low and the C / N of 40 dB or more is obtained.
There is a problem that a reproducing power of 4 mW or more is required to obtain the ratio.

Therefore, the present invention has been proposed in view of such a conventional situation and has a high super-resolution expression sensitivity and a high C / N even when the reproduction power is set low.
An object of the present invention is to provide an optical recording medium in which super-resolution reproduction is performed at a ratio.

[0019]

Means for Solving the Problems As a result of intensive studies made by the present inventors in order to achieve the above-mentioned object, as a polymer material used in the saturable absorbing dye-containing layer, polymethyl methacrylate (PMMA) was used in place of polymethyl methacrylate (PMMA). It has been found that the use of polyvinylcarbazole (PVK) as the material improves the super-resolution expression sensitivity.

The present invention has been proposed on the basis of such knowledge, and it is possible to form a saturable absorbing dye and a polymer material on a transparent substrate having pits formed in a recording pattern corresponding to an information signal. The saturated absorption dye-containing layer is formed, and the saturable absorption dye has a molecular extinction coefficient ε at the wavelength of the reproduction light of 10 ⁴ ≦ ε and a relaxation time τ of 1 ns ≦ τ ≦ 1.
00 ns, and the polymer material is polyvinyl carba
Sol and compatibility with the polyvinylcarbazole
Glass transition temperature of 150 ° C or higher
It is a mixture of transfer temperature polymers.

An optical recording medium to which the present invention is applied has a saturable absorption dye-containing layer made of a saturable absorption dye and a polymer material on a transparent substrate having pits formed in a recording pattern corresponding to an information signal, A reflective layer is formed. The pit is, for example, an uneven shape or a layer for changing the optical constant, and is used as a diffraction limit λ / 2NA of the reproducing optical system.
It is formed in a shorter cycle. Signal reproduction from such a pit recording pattern is performed by the following super-resolution reproduction mechanism.

That is, when the optical recording medium is irradiated with reproducing light, the reproducing light spot has a light amount distribution having a peak at the focal position. Therefore, only the minimum portion near the focal position is strongly saturable. And a saturable absorption region partially occurs. Since the absorptivity is lowered in this saturable absorption region, the amount of light reaching the reflective layer is large and a high reflectance is obtained as compared with other regions. Therefore, it functions as an aperture, and even if a plurality of pits are duplicated in the reproduction light spot, only the pits present in this saturable absorption region are detected. Therefore, it is possible to reproduce a signal from a fine recording pattern of pits formed in a cycle shorter than the diffraction limit λ / 2NA of the reproducing optical system.

As described above, in the optical recording medium using the saturable absorbing dye-containing layer, the saturable absorbing dye-containing layer partially saturates in the reproduction light spot to become the saturable absorption, thereby increasing the reflectivity. Sex is expressed. In the present invention, a polymer having a carbazole group is used as the polymer material forming the saturable absorbing dye-containing layer in order to improve the sensitivity of developing the super-resolution.

In an optical recording medium using a polymer having a carbazole group as the polymer material of the saturable absorbing dye-containing layer, the reflectance greatly increases at the minimum portion in the reproduction light spot as the reproduction light power increases. This tendency of increasing the reflectance is far superior to that of an optical recording medium using PMMA, for example.

In this case, the increase of the reflectance means the formation of the aperture, and the fact that the reflectance greatly increases with the increase of the reproducing light power means that the super-resolution is expressed with high sensitivity. means. Therefore, in the above optical recording medium, even if the irradiation power of the reproduction light is reduced, super-resolution reproduction is performed with a high C / N ratio.

As the polymer material, it is desirable to use a mixture of a polymer having a carbazole group and another polymer, and in order to sufficiently improve the superresolution sensitivity, the polymer material should be used. The content of the polymer having a carbazole group in it needs to be 50% by weight or more.

Examples of the polymer having a carbazole group include polyvinyl carbazole (P
VK) is typical.

[0028]

[Chemical 1]

Incidentally, in the optical recording medium using PVK in the saturable absorbing dye-containing layer, when the same portion is repeatedly irradiated with reproducing light, birefringence and linear dichroism are exhibited and the laser noise level is increased. Rises. This is considered to be due to the following reasons.

That is, PVK is likely to have a linear conformation due to the influence of side chains. Therefore, when the saturable absorption dye-containing layer composed of PVK and the saturable absorption dye is irradiated with reproduction light, PVK undergoes a glass transition, and at this time, the saturable absorption dye molecule has a linear conformation. Oriented by an array. This is considered to be the cause of causing birefringence and linear dichroism in the saturable absorbing dye-containing layer.

Therefore, when such PVK is used, it is desirable to mix a polymer having a high glass transition temperature of 150 ° C. or higher in order to prevent the orientation of the dye without impairing the heat resistance.

When two kinds of polymers having different glass transition temperatures are mixed, the glass transition temperature of the mixture becomes an intermediate value between the glass transition temperatures of the respective polymers. The same is true when PVK is mixed with a polymer having a high glass transition temperature, and the mixture shows a higher glass transition temperature than PVK alone.

Therefore, when the saturable absorbing dye-containing layer is formed by using a polymer material which is a mixture of PVK and a polymer having a high glass transition temperature, it is difficult for the polymer material to undergo glass transition when irradiated with laser light. The orientation of the saturable saturated absorption dye molecule is suppressed. As a result, it is possible to realize an optical recording medium for super-resolution reproduction which has high super-resolution reproduction sensitivity and which does not increase the laser noise level even when the reproduction light is repeatedly irradiated, and which has excellent heat resistance. Also in this case, it is necessary to set the content ratio so that the content of PVK in the polymer material does not fall below 50% by weight.

Any polymer having a high glass transition temperature may be used as long as it has a glass transition temperature of 150 ° C. or higher and is compatible with PVK. Examples of such a polymer include polyacenaphthylene represented by Chemical formula 2. For example, Scientific Polymer
Product # 266, polyacenaphthylene, has a glass transition temperature of 214 ° C.

[0035]

[Chemical 2]

The saturable absorption dye-containing layer is composed of the above polymeric material and the saturable absorption dye. In the present invention,
This saturable absorption dye has a molecular extinction coefficient ε at the reproduction light wavelength of 10 ⁴ or more and a relaxation time τ of 1 ns ≦ τ.
Use one with ≦ 100 ns.

In the saturable absorbing dye-containing layer having such characteristics, the molecular extinction coefficient ε at the reproducing light wavelength is 10 ⁴
From the above, the irradiation of the reproduction light causes saturable absorption in a portion of the reproduction light spot where the light amount exceeds a certain amount, so that a saturable absorption region partially occurs. Further, the relaxation time τ of the saturable absorbing dye is 1 ns ≦ τ ≦
Since it is regulated within the range of 100 ns, the saturable absorption region quickly returns to the initial state within a certain time range due to the decrease in the light amount accompanying the movement of the reproduction light. Therefore, saturable absorption is maintained in a region where the amount of light is reduced, and for example, the saturable absorption region does not have a trailing tail, and only a certain region within the reproduction light spot is saturable absorption at all times. An aperture with an ideal shape can be formed.

It should be noted that the reproduction light is 750 to 830 nm at present.
In the case of the light having the above wavelength, cyanine dyes, phthalocyanine dyes, naphthalocyanine dyes and the like are suitable as the saturable absorption dyes. Among them, naphthalocyanine dyes
It is preferable because it has a large molecular extinction coefficient and high optical stability.

The saturable absorption dye-containing layer composed of these saturable absorption dyes and PVK is, for example, a saturable absorption dye and PVK.
Is formed by a spin-coat method using a dye solution in which is dissolved in a solvent.

It is desirable that the thickness of the saturable absorbing dye-containing layer is such that the reflected light intensity due to interference is substantially minimal with respect to the light intensity of the reproduction light. This film thickness differs depending on the refractive index of a reflective layer or a dielectric layer, which will be described later, which constitutes a multilayer structure together with the saturable absorbing dye-containing layer. Reflective layer is Al, A
When the reflective layer or the dielectric layer is made of a material having a higher refractive index than that of the dye-containing layer, it is approximately m · λ / 2n ( However,
λ is the wavelength of the reproduction light, n is the real part refractive index, and m is an arbitrary positive integer. On the contrary, when the dielectric layer is made of a material having a refractive index lower than that of the dye-containing layer, the thickness is approximately (2m−1) λ / 4n. With this film thickness, the contrast of the reflectance increase depending on the light intensity of the reproduction light becomes large, and the super resolution is improved.

A reflective layer is formed on such a saturable absorbing dye-containing layer. The reflective layer is selected to have a reflectivity that meets the standard of the reproducing device, and is used for these discs when it is applied to a reproducing device such as a compact disc, a laser disc, and a write-once compact disc. Examples thereof include a metal thin film or a dielectric thin film which has a reflectance of 70% or more with respect to an air interface and is formed by a vacuum thin film manufacturing method typified by an aluminum thin film and a gold thin film.

The above is the basic constitution of the optical recording medium of the present invention. In the optical recording medium of the present invention, in addition to such a saturable absorbing dye-containing layer and a reflecting layer, a substrate and a saturable absorbing dye are provided. A high refractive index layer having a higher real part refractive index than the substrate and the saturable absorption dye-containing layer may be provided between the containing layers.

When the high refractive index layer is provided between the substrate and the saturable absorbing dye-containing layer, Fresnel reflection becomes strong, and a resonator structure for confining light in the saturable absorbing dye containing layer is formed. As a result, the reproduction signal strength is significantly improved.

Here, the real-part refractive index of the light-transmitting substrate or the saturable absorbing dye-containing layer that is usually obtained is 1.5 to 1.7.
It is a degree. Therefore, as the high refractive index layer, a material film having a real part refractive index of 1.8 or more, for example, an inorganic material, a semiconductor material or the like formed by a vacuum thin film forming method is used. The effect of strengthening Fresnel reflection is that the real part refractive index greatly differs from the value of the substrate or the saturable absorbing dye-containing layer,
It is remarkable.

Examples of the vacuum thin film forming method for forming the high refractive index layer include a vacuum vapor deposition method, a sputtering method, a CVD (chemical vapor deposition method) and the like. When the substrate is made of a polymer or has a resist film formed by the glass 2P method, a good quality film can be formed at a relatively low temperature and the film forming speed is relatively high. The sputtering method is advantageous.

The material of the high refractive index layer is not particularly limited as long as the real part refractive index satisfies the above conditions as described above, but inorganic ceramics are suitable because they are excellent in heat resistance and film forming property. Above all, when a mixed film of ZnS and SiO ₂ is formed as a high refractive index layer on an optical disc of a type having pits formed in a concavo-convex shape, a relatively large reproduction output of 40 dB or more can be surely obtained.

Further, as the high refractive index layer, it is desirable to select one having a relatively small extinction coefficient among those having a real part refractive index of 1.8 or more. This is for the purpose of efficiently absorbing the irradiated light in the saturable absorbing dye-containing layer.

Instead of such a high refractive index layer,
On the contrary, even when the substrate and the low refractive index layer whose real part refractive index is lower than that of the saturable absorption dye-containing layer are provided, a resonator structure for confining light in the saturable absorption dye-containing layer is similarly formed. be able to.

However, in the material which can be used as the low refractive index layer, about 1.3 of the fluorine-based polymer has the lowest real part refractive index, and for example, a generally used low refractive index material such as magnesium fluoride. Most of them have a real part refractive index of about 1.4. For this reason, it is practically difficult to obtain a low refractive index layer having a real part refractive index greatly different from those of the substrate and the saturable absorbing dye-containing layer, that is, a low refractive index layer having a high effect of increasing Fresnel reflection. Materials that can be used for the high refractive index layer include various materials having a maximum refractive index of 4 including inorganic materials and semiconductor materials. Therefore, it can be said that providing the high refractive index layer is more convenient than providing the low refractive index layer.

Here, the film thickness of the high refractive index layer and the low refractive index layer is (2m-1) λ / 4n (where λ is the wavelength of the reproduction light,
(n is the real part refractive index of the high refractive index layer or the low refractive index layer, and m is an arbitrary positive integer), and it is preferable that the film thickness is generally represented by λ / 4n. When the high refractive index layer or the low refractive index layer is formed with this thickness, the high refractive index layer or the low refractive index layer, the reflected light at the interface with the substrate, the high refractive index layer or the low refractive index layer, The phase difference with the reflected light at the interface with the saturable absorbing dye-containing layer becomes 180 °, which satisfies the so-called non-reflection condition. As a result, the Fresnel reflection at the saturable absorbing dye-containing layer is maximized and the intensity of the reproduced signal can be increased. However, even if the film thickness deviates from this value by about 10%, there is no particular problem and a sufficient effect can be obtained.

The high-refractive index layer and the low-refractive index layer are not used individually, but a multilayer film in which these layers are alternately laminated is provided between the substrate and the saturable absorbing dye-containing layer. The reproduction signal strength can be improved.

[0052]

[Function] A saturating absorption dye-containing layer composed of a saturable absorption dye and a polymer material is formed on a transparent substrate in which pits are formed in a recording pattern corresponding to an information signal. In an optical recording medium in which a signal is reproduced by a resolution reproducing mechanism, when a polymer having a carbazole group is used as the above-mentioned polymer material, the super-resolution expression sensitivity is improved and the irradiation power of the reproducing light is set low. Even in this case, super-resolution reproduction can be performed with a high C / N ratio.

When polyvinylcarbazole is used as the polymer material, the glass transition temperature is 150 ° C.
When the above-mentioned high glass transition temperature polymer is used in combination, the occurrence of birefringence and linear dichroism, which are observed when the reproducing light is repeatedly irradiated, is suppressed, and the rise of the laser noise level caused by this is avoided.

[0054]

EXAMPLES Preferred examples of the present invention will be described below based on experimental results.

Example 1 The structure of the optical recording medium prepared in this example is shown in FIG. In this optical recording medium, a high refractive index layer 2, a saturable absorption dye-containing layer 3, and a substrate 1 on which pits 5 are formed in a concavo-convex shape.
The reflective layer 4 is sequentially laminated. In this example, an optical recording medium having such a structure was prepared as follows.

First, a disk-shaped glass substrate 1 having a diameter of 120 mm and a thickness of 1.2 mm was prepared, and pits 5 were formed on this glass substrate by the glass 2P (photopolymer) method. The recording pattern of the pits 5 has a pit length of 0.3 μm and a pit period of 0.6 μm.

Next, the ZnS high refractive index layer 2 was formed on the surface of the substrate 1 on the side where the pits 5 were formed by using a vacuum vapor deposition apparatus (Nikden Anelva, trade name EVD500A). The film forming conditions are shown below.

Degree of ultimate vacuum: 3 × 10 ^-4 P Vacuum degree during vapor deposition: Approximately 1 × 10 ^-3 P Heating of vapor deposition source: Resistance heating vapor deposition source: ZnS having a purity of 99.99% Vapor deposition rate: 0.4 to 0.5 nm / s

During the vapor deposition, the substrate 1 was not heated, but was rotated around the vapor deposition source in order to make the film thickness uniform.
Further, the film thickness of the vapor deposition film was controlled while monitoring the transmission spectrum with an optical film thickness monitor to which a fiber spectroscope was applied, and finally the film thickness was adjusted to 85 nm. This film thickness is λ / 4 at which the high refractive index layer exhibits its effect most.
n (λ: reproduction light wavelength, n: real part refractive index of the high refractive index layer).

Next, the saturable absorption dye-containing layer 3 is spin-coated on the high refractive index layer 2 (manufactured by Mikasa Co., Ltd., product name 700L).
Was used at a maximum rotation speed of 1000 to 1500 rpm.

The dye solution for spin coating was bis (tri-n-hexylsiloxy) silicon naphthalocyanine (S
INC) and polyvinylcarbazole (PVK, manufactured by Anan Co.) in cyclohexanone (ANON), SINC:
PVK: ANON was dissolved at a composition ratio of 1: 10: 300 (weight ratio). This dye solution is
PVK was added to NON and dissolved by stirring and heating for several hours, after which SINC was added and completely dissolved with an ultrasonic cleaner to prepare. In addition, SINC, PV
Structural formulas of K and ANON are shown in Chemical formulas 3 to 5, respectively.

[0062]

[Chemical 3]

[0063]

[Chemical 4]

[0064]

[Chemical 5]

After coating the spin coat film, the solvent was dried by leaving it for 2 hours in a vacuum environment at a temperature of 80 degrees.

Finally, the Al reflective layer 4 was formed on the saturable absorbing dye-containing layer 3 by using a vacuum vapor deposition apparatus (product name EVD500A, manufactured by Nichiden Anelva Co., Ltd.) to prepare an optical recording medium. The vapor deposition conditions for the Al reflective layer are as follows.

Degree of ultimate vacuum 3 × 10 ⁻⁴ P Degree of vacuum during vapor deposition: 1 × 10 ⁻³ P Heating of vapor deposition source: electron gun vapor deposition source: Al having a purity of 99.99% Al vapor deposition rate: 1 to 2 nm / s

During the vapor deposition, the substrate was not heated and was rotated around the vapor deposition source in order to make the film thickness uniform. Further, the vapor deposition rate of the vapor deposited film was controlled by a quartz type film thickness monitor so that the final film thickness was 400 nm.

Comparative Example 1 In the same manner as in Example 1 except that polymethyl methacrylate (PMMA, manufactured by Scientific Polymer Products Co., Ltd.) was used in place of PVK when forming the saturable absorbing dye-containing layer 3. An optical recording medium was created. The structural formula of polymethylmethacrylate is shown in Chemical formula 6.

[0070]

[Chemical 6]

By irradiating the two kinds of optical recording media thus prepared with reproducing light and increasing the irradiation power, the amount of reflected light increases at the minimum portion corresponding to the focal position of the reproducing light spot. Can be seen. At this time, the amount of reflected light changes, but the amount of irradiated light does not change. Therefore, the increase in the amount of reflected light seen at this minimal part is due to the increase in reflectance, and the saturable absorption, that is, the super-resolution It can be said that the expression is suggested.

Therefore, here, the sensitivity of developing the super-resolution is examined by variously changing the irradiation power of the reproducing light and examining the reflectance change in the minimum portion. The structure of the optical system used for the investigation of the reflectance characteristics is shown in FIG.

In this optical system, a focus lens 11 is disposed so as to face the substrate side of the optical recording medium 10, and a quarter wavelength plate 12, a polarization beam splitter 13, and a reproducing light source unit 14 are arranged from the focus lens 11 side. It is provided in this order. The optical recording medium 10 is placed on a turntable (not shown) and is rotatable by operating the turntable.

In this optical system, the laser beam L emitted from the reproducing light source unit 14 is polarized beam splitter 13, 1 /
It is transmitted through the four-wave plate 12 and the focus lens 11 and focused on the optical recording medium 10. Then, the reflected light R from the optical recording medium 10 reaches the polarization beam splitter 13 via the focus lens 11 and the quarter-wave plate 12, where it is split from the reproduction light and received by a photodiode or the like ahead of it. It is detected by an element (not shown). The apparatus conditions used in this example are shown below.

Reproducing light wavelength: 780 nm Irradiation power of reproduction light: 1-5mW Focus lens numerical aperture: 0.53 Rotation speed of optical recording medium: 4 m / s

FIG. 3 shows the relationship between the irradiation power and the reflectance of the reproduction light measured using the above optical system. Note that FIG. 3 also shows the reflectance characteristics of the optical recording medium of Example 1 and the optical recording medium of Comparative Example 1.

As can be seen from FIG. 3, in both the optical recording medium of Example 1 and the optical recording medium of Comparative Example 1, the reflectance increases as the irradiation power of the reproducing light increases. However, the rate of the change is higher in the PMM in the optical recording medium of Example 1 using PVK as the polymer material of the saturable absorbing dye-containing layer.
It is much larger than the comparative recording medium of Comparative Example 1 using A.

For example, in the optical recording medium of Example 1, when the irradiation power of the reproducing light is increased from 0 mW to 3.8 mW,
The reflectivity rises from 2% to 13%. On the other hand, Comparative Example 1
In the above optical recording medium, even if the irradiation power of the reproducing light is increased from 0 mW to 4.8 mW, the reflectance is increased only from 1.5% to 9%. When the irradiation power required to increase the reflectance to 8% is compared, 2 mW is sufficient for the optical recording medium of Example 1, while Comparative Example 1
The optical recording medium of No. 2 requires 4 mW.

The above results suggest that the optical recording medium of Example 1 has a higher superresolution expression sensitivity than the optical recording medium of Comparative Example 1.

From this, it is understood that it is more advantageous to form the saturable absorbing dye-containing layer with PVK than with PMMA, in order to improve the super-resolution expression sensitivity.

Further, in order to evaluate the reproducibility of the super resolution exhibited by these optical recording media, reproduction was performed 10,000 times with various reproduction light powers, and the change in reflectance between the first reproduction and the first reproduction 10,000 times. I checked the quantity. FIG. 4 shows the relationship between the irradiation power of reproduction light and the amount of change in reflectance.

As can be seen from FIG. 4, in the optical recording medium of Comparative Example 1 in which PMMA was used as the polymer material for the saturable absorbing dye-containing layer, when the reproducing power was raised to 1.2 mW or more, the first reproducing and the reproducing 10000 were performed. The reflectance will be significantly different from the first time. When the reproducing power is further increased, the amount of change in the reflectance sharply increases. On the other hand, in the optical recording medium of Example 1 in which PVK was used as the polymer material of the saturable absorbing dye-containing layer, the reproduction power was 1.5.
When the power is raised to mW or more, the reflectance is changed between the first reproduction and the 10,000th reproduction, but the change amount is small, and even if the reproduction power is further increased, Comparative Example 1
The amount of change in reflectance does not increase as much as the optical recording medium.

From the above, the super-resolution exhibited by the optical recording medium using PVK as the polymer material of the saturable absorbing dye-containing layer is extremely stable against repeated reproduction operations and has high reproducibility. I understand.

Next, signal reproduction was actually performed on the above optical recording media, and the C / N ratios were compared. The signal reproduction was performed by using the same optical system as that used for the reflectance measurement and changing the irradiation power of the reproduction light variously.

The cutoff period λ / 2NA of the above optical system is 0.736 μm, which is larger than the pit length of 0.3 μm and the pit period of 0.6 μm formed in this embodiment. Therefore, in this case, the pit recording pattern is
A carrier signal cannot be obtained unless super-resolution is exhibited in the optical recording medium.

As a result of signal reproduction, in the optical recording medium of Example 1 in which PVK was used as the polymer material of the saturable absorption dye-containing layer, the C / N of 40 dB or more was obtained at the reproducing power of 2.5 mW.
On the other hand, in the optical recording medium of Comparative Example 1 using PMMA, the C / N ratio of 40 dB could not be obtained unless the reproducing power was raised to 4 mW. Incidentally, FIG. 5 shows a reproduction signal output spectrum when the optical recording medium of Example 1 is reproduced with a signal having a reproduction power of 2.5 mW.

From the above, when the saturable absorbing dye-containing layer is composed of PVK, the super-resolution expression sensitivity is improved, and even when the reproduction power is set low, the super-resolution reproduction is performed at a high C / N ratio. You can see that

By the way, when PVK is used as the polymer material of the saturable absorbing dye-containing layer, the super-resolution expression sensitivity is improved.

However, when the reproducing power is continued to be radiated to the optical recording medium using PVK with the irradiation power of 3 to 4 mW, the laser noise level rises. To elucidate this phenomenon, when the signal surface that had risen to the noise level was reproduced and scanned under the crossed Nicols polarization condition, there were bright areas, and birefringence or linear dichroism was induced in these areas. It was determined that the main axis direction was the disk circumference, the radial direction, or the laser scanning direction.

This birefringence and linear dichroism are caused by the fact that the PVK of the saturable absorbing dye-containing layer undergoes a glass transition when irradiated with reproduction light, and the saturable absorbing dye molecule is in a linear state at this time. It is considered that the orientation is caused by the arrangement of polyvinyl carbazole having the conformation of.

Therefore, from the idea that the orientation of such saturable absorbing dye molecules can be suppressed if the glass transition of the polymer material is difficult to occur, PVK, a polymer having a high glass transition temperature, polyacenaphthylene (Sien) is used. Manufactured by Tiffic Polymer Products, # 266; Tg = 214 ° C)
Was mixed, and the mixture was used as a polymeric material for the saturable absorbing dye-containing layer to prepare an optical recording medium. The saturable absorption dye-containing layer using this mixture as a polymer material is PVK50.
Parts by weight, polyacenaphthylene 50 parts by weight, SINC15
It was formed by spin-coating a dye solution having a part by weight dissolved in cyclohexanone. Except for this, Example 1
The manufacturing process is the same as.

Then, regarding the prepared optical recording medium,
Irradiation of reproducing light was continuously performed with various irradiation powers using the above optical system, and the occurrence of laser noise, the birefringence of the signal surface, and the linear dichroism were examined. As a result, the laser noise did not increase even when the irradiation power was raised to 9 mW, and birefringence and linear dichroism were not recognized in the reproduction scanning portion.
On the other hand, in signal reproduction, a C / N ratio of 45 dB or more was obtained.

From the above, it was found that when PVK is used and a polymer having a high glass transition temperature is mixed, an increase in the level of laser noise due to repeated reproduction is suppressed and the number of reproducible cycles is significantly improved. .

[0094]

As is apparent from the above description, the optical recording medium of the present invention comprises a saturable absorbing dye and a polymer material on a transparent substrate having pits formed in a recording pattern corresponding to an information signal. The saturable absorbing dye-containing layer is formed, and the saturable absorbing dye has a molecular extinction coefficient ε at the reproducing light wavelength of 10 ⁴ ≦ ε and a relaxation time τ of 1 ns ≦ τ ≦ 10.
It is 0 ns, and since the above-mentioned polymer material contains a polymer having a carbazole group, the super-resolution expression sensitivity is high, and even when the reproduction power is set low, super-resolution reproduction is performed with a high C / N ratio. It

Therefore, according to the present invention, the wavelength of the reproduction light is shortened, the numerical aperture NA of the focus lens is increased, and the signal demodulation method is not significantly changed on the apparatus side. It is possible to store about twice the amount of recorded information in an optical recording medium of the same size.

Further, if these high-density recording techniques are applied to the device side, the recording density on the optical recording medium will be several tens of the current level.
Can be doubled. As a result, for example, a digital video disc, a high definition video disc, a CD
It can be configured in a size, which can be said to be extremely useful industrially.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing a configuration example of an optical recording medium to which the present invention is applied.

FIG. 2 is a schematic diagram showing a configuration of an optical system used for investigating reflectance characteristics and reproduction characteristics of the optical recording medium of the present invention.

FIG. 3 shows an irradiation power of reproduction light for an optical recording medium,
It is a characteristic view which shows the relationship of reflectance.

FIG. 4 shows the irradiation power of reproduction light for an optical recording medium,
It is a characteristic view which shows the relationship of the change amount of the reflectance in the 1st reproduction and the 10000th reproduction.

FIG. 5 is a characteristic diagram showing a reproduction signal output spectrum of an optical recording medium.

[Explanation of symbols]

1 substrate 2 High refractive index layer 3 Saturable absorption dye-containing layer 4 Reflective layer 5 pits

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Tamura 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo, Sony Corporation (56) Reference JP-A-4-339865 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B 7/24

Claims (10)

(57) [Claims] 1. A saturable absorption dye-containing layer comprising a saturable absorption dye and a polymer material is formed on a transparent substrate having pits formed in a recording pattern corresponding to an information signal. Is a molecular extinction coefficient ε at the wavelength of the reproduction light of 10 ⁴ ≦ ε and a relaxation time τ of 1 ns ≦ τ ≦ 100.
The polymer material is polyvinyl carbazole
Glass compatible with rivinylcarbazole
Of high glass transition temperature polymers with a transition temperature of 150 ° C or higher
An optical recording medium characterized by being a mixture . 2. The optical recording medium according to claim 1, wherein the content of the polymer having a carbazole group in the polymer material is 50% by weight or more. 3. The optical recording medium according to claim 1, wherein the saturable absorbing dye is a naphthalocyanine dye. 4. The polymer having a carbazole group is polyvinylcarbazole.
The optical recording medium described. 5. The optical recording medium according to claim 1 , wherein the high glass transition temperature polymer is polyacenaphthylene. The thickness of 6. saturable absorption dye containing layer, claims 1, characterized in that a thickness of approximately minimum reflected light intensity due to interference with the light intensity of the reproduction beam 5 Either
The optical recording medium according to 1 . 7. The optical recording according to claim 1, wherein a reflective layer having a reflectance at the air interface of 70% or more is provided on the saturable absorbing dye-containing layer. Medium. 8. A low refractive index layer having a real refractive index lower than that of the saturable absorption dye-containing layer and the transparent substrate is provided between the saturable absorption dye-containing layer and the transparent substrate. An optical recording medium according to any one of claims 1 to 7 . 9. A high refractive index layer having a real refractive index higher than that of the saturable absorption dye-containing layer and the transparent substrate is provided between the saturable absorption dye-containing layer and the transparent substrate. An optical recording medium according to any one of claims 1 to 7 . 10. A low refractive index layer having a refractive index lower than those of the saturable absorbing dye-containing layer and the transparent substrate, and a saturable absorbing dye containing layer having a refractive index of between the saturable absorbing dye-containing layer and the transparent substrate. claim 1 請, characterized in that the multilayer film a high refractive index layer are alternately laminated is formed higher than the transparent substrate and
The optical recording medium according to any one of claim 7 .