JPH07296420A - Optical recording medium - Google Patents

Abstract

PURPOSE:To make it possible to store the recording information quantity of about 4 times the present recording information quantity to an optical recording medium of the same size without subjecting the device side to a drastic change, such as shortening of the wavelength of reproducing light, increasing of the numerical aperture NA of a focusing lens and changing of a signal demodulation system. CONSTITUTION:At least a saturable absorbent dyestuff-contg. layer 2 formed by a vacuum thin film forming method and a reflection layer 4 are formed on a light transmissive substrate 1 formed with the recording patterns corresponding to information signals as rugged 1a, 1b shapes. Further, a short-wavelength shift layer 3 which shifts the minimal point of the light reflection spectra of the optical recording medium to a short wavelength side is disposed between the saturable absorbent dyestuff-contg. layer 2 and the reflection layer 4. As a result, the recording patterns inscribed on the substrate 1 are correctly traced on the saturable absorbent dyestuff-contg. layer 2 and the reflection layer 4 and the reflectivity is confined within an adequate rate. Then, the optical recording medium exhibits excellent ultra-definition and good reproduced signals are obtd. from the fine recording patterns formed with micropits at a period shorter than the diffraction threshold lambda/2NA of a reproducing optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reproduces recorded information recorded on a transparent substrate in a concavo-convex shape by detecting a change in reflected light amount when reproducing light is irradiated.
The present invention relates to a so-called compact disc type optical recording medium.

[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 for a magneto-optical system, and is not applicable to an ordinary optical recording system having no 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 in which the light amount increases in the center of the reproducing light spot. It is possible to change the optical characteristics of only the part where 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 reproduce a signal from a fine recording pattern in which pits are formed with a period shorter than the diffraction limit of the reproducing 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, the applicant of the present application filed Japanese Patent Application No. 5-268.
In No. 05 specification, a saturable absorbing dye was proposed as a specific photoresponsive material. The saturable absorption dye is a dye material that exhibits a phenomenon in which the absorptance becomes 0 when irradiated with a certain amount of light or more and enters an excited state, that is, a saturable absorption phenomenon.

For example, when reproducing light is irradiated onto an optical recording medium in which a saturable absorbing dye-containing layer containing the saturable absorbing dye and a reflective layer are formed on a substrate having pits and projections formed in a concavo-convex shape, As described above, since the reproduction light spot has a light amount distribution in which the light amount increases toward the center, only the portion where the light amount exceeds a certain amount becomes saturable absorption. Since the region having the saturable absorption has an absorptance of 0, the amount of light reaching the reflective layer is large and a high reflectance can be 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.

[0017]

However, the above optical recording medium has a C of about 20 dB when a signal is actually reproduced.
Only the / N ratio can be obtained, and further improvement is necessary in order to obtain a reproduction characteristic of 40 dB or more that can withstand practical use.

Therefore, the present invention has been proposed in view of such a conventional situation, has excellent super-resolution, and pits are formed in a cycle shorter than the diffraction limit λ / 2NA of the reproducing optical system. An object of the present invention is to provide an optical recording medium from which a reproduction signal having a high C / N ratio can be obtained from a fine recording pattern.

[0019]

In order to achieve the above-mentioned object, an optical recording medium of the present invention has at least a vacuum thin film on a light-transmissive substrate on which a recording pattern corresponding to an information signal is formed as an uneven shape. The saturable absorbing dye-containing layer and the reflective layer formed by the forming method are formed, and the minimum point of the light reflection spectrum of the optical recording medium is shifted to the short wavelength side between the saturable absorbing dye-containing layer and the reflective layer. It is characterized in that a short wavelength shift layer is provided.

In an optical recording medium in which a saturable absorbing dye-containing layer and a reflective layer are formed on a light transmissive substrate on which a recording pattern corresponding to an information signal is formed in an irregular shape, the reflective layer has an uneven shape of the substrate. Is reflected, and the signal reproduction is performed by detecting the reflectance change of the reflecting layer in which this uneven shape is reflected. This signal reproduction is performed by the following super-resolution mechanism.

That is, when the optical recording medium is irradiated with reproduction light, the reproduction light spot has a light quantity distribution in which the light quantity increases toward the center. It becomes a saturable absorption, and a saturable absorption region partially occurs. Since the region having the saturable absorption has an absorptance of 0, the amount of light reaching the reflective layer is large and a high reflectance can be 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. That is, it is possible to reproduce a signal from a fine recording pattern in which pits are formed with a cycle shorter than the diffraction limit λ / 2NA of the reproducing optical system.

However, the optical recording medium having the structure in which only the saturable absorbing dye-containing layer and the reflective layer are formed on the transparent substrate as described above can obtain only a C / N ratio of about 20 dB even if the reproducing power is increased. .

Therefore, the inventors of the present invention conducted a study to improve the C / N ratio of the optical recording medium using the saturable absorbing dye-containing layer as described above, and as a result, to improve the C / N ratio. Concluded that the selection of the film formation method for the saturable absorbing dye-containing layer is important.

That is, the saturable absorbing dye-containing layer is formed by a vacuum thin film forming method such as a spin coating method or a vacuum evaporation method.

In the spin coating method, for example, a saturable absorbing dye-containing layer is formed by applying a dye solution in which a saturable absorbing dye is dissolved onto a substrate having a recording pattern formed in an uneven shape and drying the substrate. To be done. However, the saturable absorption dye-containing layer thus formed does not completely trace the irregularities engraved on the substrate. For this reason, the reflective layer formed thereon is also affected by the influence, and the unevenness on the substrate is not accurately reflected and is formed.

In the optical recording medium having such a structure, the recording pattern on the substrate is indirectly detected by detecting the change in the reflectance of the reflecting layer formed by reflecting the unevenness engraved on the substrate as described above. In order to reproduce the signal, a good reproduction signal cannot be obtained unless the reflection layer accurately reflects the unevenness on the substrate.

On the other hand, in the vacuum thin film forming method, the saturable absorbing dye-containing layer is formed by accurately tracing the irregularities engraved on the substrate. However, when the light reflection spectrum of the optical recording medium in which the saturable absorption dye-containing layer is formed by the vacuum thin film formation method is observed, the minimum point of the spectrum is smaller than that in the case where the saturable absorption dye-containing layer is formed by the spin coating method. The maximum absorption wavelength is shifted to the longer wavelength side. This lowers the super resolution and causes the deterioration of the C / N ratio.

Therefore, in the present invention, the saturable absorbing dye containing layer is formed by the vacuum thin film forming method in order to obtain the saturable absorbing dye containing layer and the reflecting layer in which the irregularities carved on the substrate are accurately traced. Further, between the saturable absorption dye-containing layer and the reflection layer, a short wavelength shift layer for shifting the minimum point of the light reflection spectrum, that is, the maximum absorption wavelength to a short wavelength is provided, and the saturable absorption dye is contained by the vacuum thin film forming method. The long wavelength shift of the spectrum caused by depositing the layer is corrected.

A saturable absorbing dye-containing layer and a reflecting layer formed by a vacuum thin film forming method are formed on a substrate on which a recording pattern is formed in a concavo-convex shape, and between the saturable absorbing dye-containing layer and the reflecting layer. In the optical recording medium in which the short wavelength shift layer is provided in, the unevenness of the substrate is accurately reflected in the reflective layer, and the light reflection spectrum is corrected by the short wavelength shift layer. Exhibits the same super-resolution as the case of forming by the spin coating method. Then, from the fine recording pattern in which pits are formed at a cycle shorter than the diffraction limit λ / 2NA of the reproducing optical system, C /
A reproduced signal having a high N ratio can be obtained.

As the saturable absorption dye contained in the saturable absorption dye-containing layer, a silicon naphthalocyanine dye represented by Chemical formula 3 is suitable, and particularly, a trialkylsiloxy group represented by Chemical formula 4 is axially coordinated. A silicon naphthalocyanine dye as a child is suitable.

[0031]

[Chemical 3]

[0032]

[Chemical 4]

The short wavelength shift layer is preferably an inorganic material film formed by a vacuum thin film forming method. The inorganic material film formed by the vacuum thin film forming method accurately traces the unevenness of the saturable absorbing dye-containing layer located thereunder. Therefore, it is possible to contribute to the correction of the light reflection spectrum without adversely affecting the shape of the reflection layer. When this short wavelength shift layer is formed by the vacuum thin film forming method, the saturable absorption dye-containing layer, the short wavelength shift layer, and the reflection layer are all continuously formed in the vacuum device without breaking the vacuum. It is also possible to improve the productivity.

As the inorganic material film, especially cryolite (Na ₃
A thin film of AlF ₆ ) and magnesium fluoride (MgF ₂ ) formed by a vacuum forming method exhibits an excellent effect.

The reflective layer is selected to have a reflectance that meets the standard of the reproducing apparatus. For example, when it is applied to a reproducing apparatus such as a compact disc, a laser disc, and a write-once compact disc, it is used for these discs. Examples thereof include a metal thin film formed by a vacuum thin film manufacturing method represented by a known aluminum thin film, a gold thin film, or a dielectric thin film.

The substrate on which these functional films are formed may be any as long as it is transparent to the wavelength of the reproduction light and can record information as pits on its surface, such as a polycarbonate substrate or a polyolefin substrate. , A glass 2P (photopolymer method) substrate, and the like.

The above is the basic structure of the optical recording medium of the present invention. However, the optical recording medium of the present invention is not limited to this, and other structures may be added to further improve the characteristics. Is also good.

For example, in order to improve the light absorption efficiency in the saturable absorbing dye layer, the refractive index is relatively higher than that of the material of the substrate and the saturable absorbing dye containing layer between the substrate and the saturable absorbing dye containing layer. You may make it provide the high refractive index layer which consists of a high material.

Further, in order to prevent thermal deterioration of the saturable absorbing dye-containing layer due to heat generation due to reproduction light irradiation, the heat dissipation of the saturable absorbing dye-containing layer is aimed at the upper and lower sides or one side of the saturable absorbing dye-containing layer. A heat dissipation layer may be provided. This heat dissipation layer may also serve as the short wavelength shift layer depending on the material selected.

Further, in this optical recording medium, in order to enhance storage stability against light, light absorption for absorbing light having a wavelength other than reproduction light is provided between the saturable absorption dye-containing layer and the substrate-side air interface. Layers may be provided. Instead of providing the light absorbing dye layer separately, the substrate and other layers may have the function of the light absorbing layer.

Further, as widely used in optical recording media such as compact discs, the protective layer may be provided so as to cover the reflective layer for the purpose of protecting the reflective layer and other functional layers. Good.

[0042]

The optical recording medium of the present invention comprises a saturable absorbing dye-containing layer and a reflective layer formed by at least a vacuum thin film forming method on a light-transmissive substrate on which a recording pattern corresponding to an information signal is formed in an uneven shape. And a minimum wavelength shift layer for shifting the maximum absorption wavelength to the short wavelength side, which is the minimum point of the light reflection spectrum of the optical recording medium, is provided between the saturable absorption dye-containing layer and the reflection layer. Has been.

In the optical recording medium having such a structure, since the saturable absorbing dye-containing layer is formed by the vacuum thin film forming method, the saturable absorbing dye-containing layer and the reflective layer are engraved on the substrate. The uneven shape is accurately reflected. The short wavelength shift layer provided between the saturable absorbing dye-containing layer and the reflective layer corrects the long wavelength shift of the maximum absorption wavelength caused by forming the saturable absorbing dye containing layer by the vacuum thin film forming method. It For this reason, super-resolution equivalent to that when the saturable absorbing dye-containing layer is formed by spin coating is obtained.

Therefore, the diffraction limit λ / 2 of the reproducing optical system
A reproduction signal having a high C / N ratio can be obtained from a fine recording pattern in which pits are formed with a cycle shorter than NA.

[0045]

EXAMPLE A preferred example of the present invention will be described based on experimental results.

Example 1 The structure of the optical recording medium prepared in this example is shown in FIGS. This optical recording medium comprises a saturable absorption dye-containing layer 2 and a saturable absorption dye-containing layer 2 on a substrate 1 having pits formed in the shape of irregularities 1a and 1b.
The short wavelength shift layer 3 and the reflection layer 4 are sequentially laminated. In this example, an optical recording medium having such a structure was prepared as follows.

First, pits were formed in a spiral shape on the disk-shaped glass substrate 1 by the glass 2P (photopolymer) method. The pits have a cycle of 0.6 μm in the traveling direction of the reproducing light (direction of arrow A in FIG. 2), and 0.3 μm of the one cycle is the concave portion 1a and the remaining 0.3 μm is the convex portion 1b. It was formed with such a recording pattern. This recording pattern is below the diffraction limit in a reproducing apparatus using a commonly used red to infrared semiconductor laser, and cannot be reproduced unless it is an optical recording medium having super-resolution. .

Then, a saturable absorption dye-containing layer 2, a short wavelength shift layer 3, and a reflective layer 4 are sequentially formed on the surface of the substrate on which the pits are formed (signal recording surface) by a vacuum vapor deposition method. ,
An optical recording medium was created. Details are shown below.

First, the saturable absorbing dye-containing layer 2 was formed as follows by using a vacuum vapor deposition apparatus manufactured by Showa Vacuum Co., Ltd. under the trade name SIP-514. The saturable absorption dye formed here is bis (trihexylsiloxy) silicon naphthalocyanine (SiNC, manufactured by Aldrich Chemical Co., unpurified).
Is.

Using 100 mg of this SiNC as a vapor deposition source, a resistance heating boat [trade name S-16 (O) W manufactured by Niraco Co., Ltd.]
0.3] and placed on the resistance heating electrode provided in the vacuum chamber of the vacuum vapor deposition apparatus. On the other hand, the substrate was attached to a substrate attachment jig which was rotatably supported in the vacuum chamber.

After setting the vapor deposition source and the substrate in this way, the pressure in the vacuum chamber was reduced to 3.0 × 10 ^-6 Torr, and vapor deposition was started while the substrate was revolved.

Here, the reason why the substrate is revolved is to deposit SiNC on the substrate with a uniform film thickness. The revolution speed of the substrate is 65% on the scale of this vacuum evaporation system.
Therefore, temperature control such as heating and cooling was not particularly performed on the substrate.

The current applied to the resistance heating board is 7
6 to 77A. The vapor-deposited film was formed at a rate of 1.5 to 3.1 Å / sec while manually adjusting the current in this range. The vapor deposition rate and the film thickness were measured using a crystal oscillator film thickness monitor. In this measurement, the sample density was assumed to be 1 g / cm ³ and the Z-ratio was assumed to be 1.0.
The vapor deposition was completed when the film thickness measured by the crystal oscillator film thickness monitor was 1116Å. Under the same conditions, the ratio of the actual film thickness of the deposited film to the film thickness measured by the crystal oscillator monitor is 0.085, so here the film thickness of the finally formed deposited film is 95Å.
I estimated.

After the saturable absorbing dye-containing layer 2 was formed in this way, it was left for about 15 minutes until the resistance heating boat cooled. Then, the vacuum chamber was filled with nitrogen, and the substrate was taken out from the vacuum chamber.

Next, the short-wavelength shift layer 3 was formed as follows by using a vacuum vapor deposition device of EVD-500 manufactured by Nichiden Anelva Co., Ltd. The short wavelength shift layer material formed here is cryolite.

A powdery cryolite was used as a vapor deposition source for a resistance heating boat (manufactured by Nilaco, trade name S-13W0.3) in an amount corresponding to the capacity, and the resistance heating was provided in a vacuum chamber of a vacuum vapor deposition apparatus. It was installed on the electrode. On the other hand, the substrate was mounted on a substrate mounting jig rotatably supported in the vacuum chamber.

After setting the vapor deposition source and the substrate in this way, the vacuum chamber was depressurized to 3.0 × 10 ⁻⁴ Pa, and vapor deposition was started while the substrate revolved around its axis. The revolution speed of the substrate was 40% on the scale of this vacuum device, and the temperature control such as heating and cooling was not particularly performed on the substrate.

The current applied to the resistance heating boat is 6
It is 0 A and the vapor deposition rate is 25 Å / sec. The vapor deposition rate and the film thickness were measured using a crystal oscillator film thickness monitor. At the time of this measurement, the density of cryolite is 4.09g
/ Cm ^3, Z-ratio was assumed to 0.775. The vapor deposition was completed when the film thickness thus measured by the crystal unit film thickness monitor reached 390Å. Under the same conditions, the ratio of the actual film thickness of the deposited film to the film thickness measured by the crystal oscillator monitor is 2.70, so here the film thickness of the finally formed deposited film is 1056Å. I estimated.

Finally, the reflection layer 4 was formed into a film by forming a short wavelength shift layer.
Using the vacuum vapor deposition apparatus of D-500, the film formation of the short wavelength shift layer was continuously performed without breaking the vacuum state. The reflective layer material formed here is aluminum.

Aluminum serving as a vapor deposition source was placed in a vacuum chamber, and vapor deposition was performed on the substrate with an attached 5-unit electron gun (power: 6 kW).

The vapor deposition is performed by a thin film vapor deposition controller (infoco).
The film thickness was controlled at a vapor deposition rate of 10Å / sec and a film thickness of 4000Å while controlling by a product name IC600 manufactured by N. The vapor deposition rate and the film thickness were measured using a crystal oscillator film thickness monitor. In this measurement, the density of aluminum is 2.7 g / cm ³ , and Z-ratio is 1.0.
8 is assumed. Here, since the ratio of the actual film thickness of the deposited film to the film thickness measured by the crystal oscillator monitor under the same conditions is 0.50, here the film thickness of the finally formed deposited film is Was estimated as 2000Å.

After the aluminum reflective film 4 was formed as described above, the vacuum state in the vacuum chamber was maintained for 30 minutes, nitrogen was then introduced, and the optical recording medium produced was taken out of the vacuum chamber.

Example 2 An optical recording medium was prepared in the same manner as in Example 1 except that the short wavelength shift layer was formed by using magnesium fluoride as a vapor deposition source as follows. The vacuum vapor deposition apparatus used for forming the short wavelength shift layer was a vacuum vapor deposition apparatus of EVD-500 manufactured by Nichiden Anerva Co., Ltd., as in the case of Example 1.

Using a powdery magnesium fluoride as a vapor deposition source, a resistance heating boat (trade name: S-13W0.
Then, 3) was charged by that amount and placed on the resistance heating electrode provided in the vacuum chamber of the vacuum vapor deposition apparatus. On the other hand, the substrate was mounted on a substrate mounting jig rotatably supported in the vacuum chamber.

After setting the vapor deposition source and the substrate in this way, the vacuum chamber was depressurized to 3.0 × 10 ⁻⁴ Pa, and vapor deposition was started while the substrate revolved around its axis. The revolution speed of the substrate was 40% on the scale of this vacuum device, and the temperature control such as heating and cooling was not particularly performed on the substrate.

The current applied to the resistance heating board is 7
It is 5 A and the vapor deposition rate is 2.0 to 3.0 Å / sec.
The vapor deposition rate and the film thickness were measured using a crystal oscillator film thickness monitor. In this measurement, it was assumed that the density of magnesium fluoride was 4.09 g / cm ³ and the Z-ratio was 0.775. The vapor deposition was completed when the film thickness thus measured by the crystal unit film thickness monitor reached 950Å. Under the same conditions, the ratio of the actual film thickness of the deposited film to the film thickness measured by the crystal oscillator monitor is 2.20. Therefore, the film thickness of the finally formed deposited film is 2095Å. I estimated.

Comparative Example 1 An optical recording medium was prepared in the same manner as in Example 1 except that the layer containing the saturable absorbing dye was formed by spin coating as follows.

0.262 g of SiNC was added to cyclohexanone and sufficiently dissolved by heating and stirring and application of ultrasonic waves to prepare a dye solution. Cyclohexanone was used as the solvent because it has excellent coating properties and can form a uniform spin coat film on the substrate.

The dye solution thus prepared was subjected to a maximum rotation speed of 200 using a spin coater (manufactured by Mikasa).
The substrate was spin-coated at a rotation speed of 0 to 2400 rpm. As a result, a uniform dye coating film having a film thickness of about 100Å was formed. Then, the substrate on which this coating film was formed was held in a vacuum environment at a temperature of 80 ° C. for 2 hours to dry the solvent and form a saturable absorption dye-containing layer.

Comparative Example 2 An optical recording medium was prepared in the same manner as in Example 1 except that the short wavelength shift layer was not formed.

Regarding the optical recording media prepared in Examples 1 and 2 and Comparative Examples 1 and 2 as described above,
A light reflection spectrum was observed with a spectrophotometer (trade name: U-3210, manufactured by Hitachi, Ltd.), and a light wavelength giving a minimum reflectance, that is, a maximum absorption wavelength was obtained. The maximum absorption wavelength of each optical recording medium is summarized in Table 1.

[0072]

[Table 1]

In Table 1, comparing Example 1, Example 2 and Comparative Example 2, which are the same in that the saturable absorbing dye-containing layer was formed by the vacuum thin film forming method, comparing the short wavelength shift layer with the saturable absorbing layer. The optical recording media of Examples 1 and 2 provided between the dye-containing layer and the reflective layer had a maximum absorption wavelength of 1 compared to the optical recording medium of Comparative Example 2 in which the short wavelength shift layer was not provided.
It is on the short wavelength side of about 3 nm.

From this, the cryolite layer and the magnesium fluoride layer function as a short wavelength shift layer, and the saturable absorption dye-containing layer is formed by vacuum thin film formation to correct the maximum absorption wavelength shifted to the long wavelength. I know that I can do it.

The optical recording medium of Comparative Example 1 in which the saturable absorbing dye-containing layer was formed by the spin coating method had a maximum absorption wavelength shorter than that of the optical recording mediums of Examples 1 and 2. is there. This is because there was no long-wavelength shift of the maximum absorption wavelength because the saturable absorption dye-containing layer was formed by the spin coating method.

Next, signals were actually reproduced from these optical recording media and the reproduction characteristics were examined.

FIG. 3 shows an optical system of the reproducing apparatus used for measuring the reproducing characteristic. That is, in the optical system of this reproducing apparatus, the objective lens 11 is disposed so as to face the substrate side of the optical recording medium 10, and the ¼ wavelength plate 12, the polarization beam splitter 13, and the light source 14 are arranged from the objective lens 11 side. It is provided in this order. In this optical system, the laser light L emitted from the light source 14 passes through the beam splitter 13, the quarter-wave plate 12 and the objective lens 11, and the optical recording medium 1
The recording pit of 0 is irradiated. Then, the optical recording medium 10
The reflected light R from the objective lens 11 and the quarter-wave plate 12
It reaches the beam splitter 13 via, is reflected there, and is detected by a light receiving element (not shown) such as a photodiode.

The apparatus conditions used in this example are shown below. Light source: semiconductor laser with wavelength of 792 nm Irradiation power: 1 to 10 mW Numerical aperture (NA) of objective lens: 0.53

The cutoff spatial period λ / 2NA of the optical system under this condition is 0.75 μm, which is larger than the pit length of 0.3 μm and the pit period of 0.6 μm of the recording pattern formed on the optical recording medium. large. Therefore, the recording pattern of the optical recording medium cannot be read unless the super-resolution phenomenon appears in the optical recording medium.

Using the reproducing optical system as described above, signal reproduction was performed at a linear velocity of 3.6 m / s and a frequency of 6 MHz, and the relationship between the reproducing power and the C / N ratio was investigated. The results are shown in FIGS. 4 to 7, respectively. 4 shows the measurement results of the optical recording medium of Example 1, FIG. 5 shows the optical recording medium of Example 2, FIG. 6 shows the optical recording medium of Comparative Example 1, and FIG. 7 shows the measurement results of the optical recording medium of Comparative Example 2. .

First, as shown in FIGS. 4 and 5, the saturable absorbing dye-containing layer was formed by a vacuum thin film forming method, and the short wavelength shift layer was provided. Looking at the reproduction characteristics, it can be seen that a C / N ratio of 40 dB or more is obtained by setting the reproduction light power to 4 mW or more, and the reproduction characteristics are practically sufficient.

On the other hand, looking at the reproducing characteristics of the optical recording medium of Comparative Example 1 in which the saturable absorbing dye-containing layer was formed by the spin coating method shown in FIG. 6, 20 dB at a reproducing power of 2 mW was observed.
However, even if the reproducing power is further increased, the C / N ratio does not rise above 20 dB. This is because the saturable absorbing dye-containing layer was formed by the spin coating method, so that the uneven shape of the substrate was accurately reflected in the saturable absorbing dye-containing layer and the reflective layer.

Further, when the reproducing characteristics of the optical recording medium shown in FIG. 7 in which the saturable absorbing dye-containing layer is formed by the vacuum thin film forming method but the short wavelength shift layer is not provided, the reproducing power is 2 The C / N ratio rises to 23 dB at 0.1 mW, but after that, the C / N ratio unstablely decreases as the reproducing power increases. This is due to the long wavelength shift of the maximum wavelength caused by forming the saturable absorbing dye-containing layer by the vacuum thin film forming method.

From the above results, in order to obtain good reproduction characteristics in the optical recording medium having the saturable absorbing dye-containing layer, the saturable absorbing dye containing layer was formed by the vacuum thin film forming method and the wavelength was changed. It was found that it is necessary to provide a short wavelength shift layer for correction on the short wavelength side.

[0085]

As is apparent from the above description, the optical recording medium of the present invention can be formed by at least a vacuum thin film forming method on a light-transmissive substrate on which a recording pattern corresponding to an information signal is formed as an uneven shape. The saturable absorption dye-containing layer and the reflection layer thus formed are formed to shift the minimum point of the light reflection spectrum of the optical recording medium between the saturable absorption dye-containing layer and the reflection layer to the short wavelength side. Since the short wavelength shift layer is provided, the saturable absorption dye-containing layer and the reflection layer are
The recording pattern engraved on the substrate is accurately traced, and the reflectance is within the proper range. Therefore, an excellent reproduction signal can be obtained from a fine recording pattern which exhibits excellent super-resolution and in which minute pits are formed with a period shorter than the diffraction limit λ / 2NA of the reproducing optical system.

Therefore, according to the present invention, the wavelength of the reproduction light can be shortened, the numerical aperture NA of the focus lens can be increased, and the signal demodulation method can be changed without making any significant changes 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.

If these high density recording techniques are applied to the device side, the recording density on the optical recording medium will be 10
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 perspective view showing an optical recording medium to which the present invention is applied with a part thereof cut away.

FIG. 2 is a schematic sectional view of a main part of the optical recording medium.

FIG. 3 is a schematic diagram showing a configuration of an optical system of a reproducing apparatus for reproducing a signal from an optical recording medium.

FIG. 4 is a reproduction characteristic of an optical recording medium in which a saturable absorption dye-containing layer is formed by a vacuum thin film forming method, and a short wavelength shift layer made of cryolite is provided between the saturable absorption dye-containing layer and the reflection layer. FIG.

FIG. 5: Reproduction characteristics of an optical recording medium in which a saturable absorption dye-containing layer is formed by a vacuum thin film forming method, and a short wavelength shift layer made of magnesium fluoride is provided between the saturable absorption dye-containing layer and the reflective layer. FIG.

FIG. 6 shows reproduction characteristics of an optical recording medium in which a saturable absorption dye-containing layer is formed by spin coating and a short wavelength shift layer made of cryolite is provided between the saturable absorption dye-containing layer and the reflection layer. It is a characteristic view to show.

FIG. 7 is a characteristic diagram showing reproduction characteristics of an optical recording medium in which a saturable absorbing dye-containing layer is formed by a vacuum thin film forming method but a short wavelength shift layer is not provided.

[Explanation of symbols]

 1 Substrate 1a Recess 1b Convex 2 Saturable absorption dye containing layer 3 Short wavelength shift layer 4 Reflective layer

Claims (6)

[Claims] 1. A saturable absorbing dye-containing layer and a reflective layer formed by at least a vacuum thin film forming method are formed on a light transmissive substrate on which a recording pattern corresponding to an information signal is formed as an uneven shape. An optical recording medium, characterized in that a short wavelength shift layer for shifting the minimum point of the light reflection spectrum of the optical recording medium to the short wavelength side is provided between the saturated absorption dye containing layer and the reflective layer. 2. The optical recording medium according to claim 1, wherein the saturable absorbing dye contained in the saturable absorbing dye-containing layer is a silicon naphthalocyanine dye represented by Chemical formula 1. [Chemical 1] 3. The saturable absorbing dye contained in the saturable absorbing dye-containing layer is bis (tri-n-hexylsiloxy) -silicon naphthalocyanine represented by Chemical formula 2. Optical recording medium. [Chemical 2] 4. The optical recording medium according to claim 1, wherein the short wavelength shift layer is an inorganic film formed by a vacuum thin film forming method. 5. The optical recording medium according to claim 4, wherein the short wavelength shift layer is made of cryolite. 6. The optical recording medium according to claim 4, wherein the short wavelength shift layer is made of magnesium fluoride.