JPH0462090A - Optical recording medium and its writing for recording and reading - Google Patents

Abstract

PURPOSE:To increase reflection factor and minimize thermal conduction and reflection losses by providing a record reflection layer consisting of surface plasmonic metal supermicroparticles and a recording substance. CONSTITUTION:Surface plasmonic microparticles 7 are capable of high electric conductivity and enhancing a surface plasma due to a light with a wavelength near an electron plasma resonance point. In more positive terms, the particles are metal particles such as gold, silver, aluminum and copper. Further, the recommended particles are such as supermicroparticles having a grain size of 3000Angstrom or less, preferably 1000Angstrom or less. A recording substance 8 is such as an organic color and polymer which become transformed or fused by a laser beam. The ratio of a recording substance 8 in a record reflection layer and the surface plasmonic microparticles 7 should preferably by 1:0.1 to 10 (weight ratio). Data is written using a laser beam of the resonance wavelength range of the surface plasmonic microparticles and is read using a laser beam of a wavelength outside the resonance wavelength area, preferably of a wavelength out of the range.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical recording medium and a recording/writing/reading method thereof, and particularly relates to recording sensitivity, recording/reproducing stability,
The present invention relates to an optical recording medium with excellent reliability, and an effective recording/writing method and recording/reading method for such an optical recording medium.

[Prior Art] Conventionally, as an optical recording medium, a laser beam is irradiated onto a recording layer containing a recording material that is metamorphosed or melted by heat to cause the recording material to melt or decompose, thereby creating permanent holes or deformed spots. There is a method that creates a signal and records the signal. The recording material is an alloy with a low melting point and high reflectivity.
Organic dyes that are thermally decomposable or have low melting points are known. on the other hand,
There is also a method of recording signals on a recording film by utilizing reversible or irreversible phase changes such as crystal-amorphous transition. In this case as well, it is necessary to irradiate the recording layer with laser light to raise the temperature. Furthermore, as another method, GdTbC.

There is a magneto-optical recording medium in which a magnetic material is irradiated with laser light in an external magnetic field to raise its temperature, reverse the magnetization direction, and read the resulting change in the rotation angle of the light as a signal. All of the above methods have in common that the temperature of the recording layer is increased to record signals, and these methods are called thermal mode recording methods.

By the way, in the thermal mode recording method, signals are written using a strong laser beam. In this case, a highly sensitive recording material is required so that high-speed writing, that is, recording can be performed with small laser energy.

On the other hand, during reproduction, a weak laser beam for reading is irradiated. At this time, the recording layer is required to be stable so that the recorded signal will not change or unrecorded areas will not be written. Normally, in order to satisfy the above conflicting conditions by varying the intensities of the recording laser beam and the reproducing laser beam, a recording material having a sufficiently large threshold value with respect to the laser intensity is required.

In addition, in optical recording media in which signals are recorded by changes in reflectance, such as deformation such as melting or decomposition of recording materials, or phase changes, and recording writing and reading methods thereof,
During recording, it is important that the irradiated laser light energy is effectively absorbed to cause a change, while during reproduction, it is necessary to effectively reflect the weak reading laser light.

[Problems to be Solved by the Invention] However, recording materials with high reflectance generally have large heat transfer losses and reflection losses, and it is not easy to find a recording material that satisfies the above two contradictory conditions.

The present invention has been made in view of the above-mentioned conventional circumstances, and is an optical recording medium that has a recording layer that satisfies the above two contradictory conditions and has excellent recording sensitivity, recording and reproduction stability, and reliability. Another object of the present invention is to provide an effective recording/writing method and reading method for such an optical recording medium.

[Means for Solving the Problems] The optical recording medium according to claim (1) is characterized in that the optical recording medium according to claim (2) is provided with a recording reflective layer containing surface plasmonic metal ultrafine particles and a recording substance. The optical recording according to claim 3, wherein the recording medium comprises ultrafine metal particles having surface plasmonic properties, a nonlinear optical storage that enhances the surface plasmon of the ultrafine metal particles, and a recording reflective layer containing a recording substance. The optical recording method according to claim (4), wherein the method for recording and writing on a medium uses writing light in the resonant wavelength region of ultrafine metal particles having surface plasmonic properties when writing on the optical recording medium according to claim (1). The recording reading method of the medium is defined in claim (1).
The recording/writing method for an optical recording medium according to claim (5), characterized in that reading light in a wavelength region outside the resonant wavelength region of surface plasmonic metal ultrafine particles is used for reading the optical recording medium according to claim (5). The optical recording according to claim (6), characterized in that when writing on the optical recording medium according to claim (2), writing light in the resonant wavelength region of surface plasmonic metal ultrafine particles and/or nonlinear optical materials is used. A recording/reading method for a medium is characterized in that when reading an optical recording medium according to claim (2), reading light in a wavelength range outside the resonant wavelength range of surface plasmonic metal ultrafine particles and/or a nonlinear optical storage is used. shall be.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an optical recording medium according to an embodiment of the present invention, and FIG. FIG. 2 is an enlarged cross-sectional view showing an example of a composite particle of a recording material and a recording material. FIG. 4 is a schematic cross-sectional view showing another embodiment of the optical recording medium of the present invention.

The optical recording medium 1 shown in FIG. 1 has a structure in which a transparent substrate 2, a recording reflective layer 3, and a protective layer 4 are sequentially laminated. Composite particles 6 with a recording material are contained in a uniformly dispersed state.

There is no particular restriction on the form of this composite particle 6, and even if it has a surface plasmonic fine particle 7 as a nucleus and its surface is coated with a layer of recording material 8 as shown in FIG. 3, as shown in FIG. As shown, the particles of the recording material 8 may be used as cores, which may be coated with surface plasmon characteristic particles.
Note that, as shown in FIG. 2, composite particles can be produced by depositing a recording material or a nonlinear optical material using, for example, metal fine particles as a core, and composite particles shown in FIG. Manufactured by electrostatic adsorption.

In the optical recording medium IA shown in FIG. 4, a recording reflective layer 3A is formed on a transparent substrate 2, and the recording reflective layer 3A is made of a finely structured thin film layer formed by co-evaporation of surface plasmonic fine particles 7 and recording substance 8 fine particles, and the surface thereof is protected. It is coated with layer 4.

Note that the optical recording medium shown in FIGS. 1 to 4 is an example of the optical recording medium of the present invention, and the structure of the optical recording medium of the present invention is not limited to that shown in the figures. .

In the present invention, the surface plasmonic fine particles have high conductivity and whose surface plasma is enhanced by light having a wavelength near the electron plasma resonance point, and specifically, gold, silver, Examples include fine particles of metals such as aluminum and copper. Although these metals are known to have high reflectance, the reflectance significantly decreases and light absorption increases for laser light having a wavelength near the resonance point.

Furthermore, as the surface plasmonic particles become ultra-fine, the surface plasma effect within the system increases, and the interaction between the recording material and the surface plasma increases, making it possible to effectively record the absorbed laser energy. It can be used to transform or melt materials. Therefore, it is desirable that the surface plasmonic fine particles be ultrafine particles with a particle diameter of 3000A or less, more preferably 1oooA or less. Such ultrafine particles can be produced by, for example, methods such as laser ablation, adiabatic expansion of a gas containing metal vapor, co-evaporation of metal and matrix, or co-evaporation.

On the other hand, in the present invention, examples of the recording material include organic dyes and polymers that are denatured or melted by laser heating. Specifically, quinocyanine dyes, merocyanine dyes, phthalocyanine dyes, naphthalocyanine dyes and their metal complexes, squarylium dyes, metal complexes such as dithiol, diazole, and mercaptonaphthol, condensed aromatic quinone dyes, triphenylmethane dyes, aminium,
Diimmonium dyes, azo disperse dyes, indoaniline metal complex dyes, pigments, and the like can be used.

In the optical recording medium of the present invention, the absorption coefficient can be further increased by coexisting in the recording layer a nonlinear optical substance that enhances the surface plasmon of the surface plasmonic fine particles. In this case, the nonlinear optical substances include conjugated polymers such as polydiacetylene, polyphenylene vinylene, and polythenylene vinylene, and derivatives thereof, cyanine dyes, benzylideneaniline, porphyrin, phthalocyanine, naphthalocyanine, 4-
Low-molecular nonlinear optical compounds such as diethylamino-4°-nitrostilbene and nitroaniline or their complexes, and derivatives of these low-molecular nonlinear optical compounds with side chains such as polymethacrylic acid ester, polyvinyl alcohol, and polyacrylic acid ester It is possible to use a nonlinear optical polymer added to the molecule. Among these, in particular, polydiacetylene, cyanine dye, aminonitrostilbene,
Nitroaniline, derivatives thereof, and polymers containing these in the main chain or side chain are suitable.

In the present invention, the ratio of the recording material to the surface plasmonic fine particles in the recording reflective layer is preferably such that recording material: two surface plasmonic fine particles = t:o, i~1° (weight ratio). That is, if the surface plasmonic fine particles are too small, the sufficient improvement effect of the laser energy efficiency according to the present invention cannot be obtained, and if the surface plasmonic particles are too large, the signal strength and S/N ratio will decrease, so it is recommended to set the surface plasmonic particles within the above range. preferable. In addition, when a nonlinear optical material is used together, the ratio of its use is 1! It is preferable that t: nonlinear optical material=1:0.05 to 20 (weight ratio).

Incidentally, as described above, surface plasmonic fine particles have a high reflectance, but the reflectance greatly decreases and light absorption increases for laser light having a wavelength near the resonance point.

Therefore, in the present invention, in an optical recording medium having a recording reflective layer containing a recording material and surface plasmonic fine particles, writing is performed with a laser beam in the resonant wavelength region of the surface plasmonic fine particles, and preferably a laser beam outside the resonant wavelength region. Reading is performed using a laser beam that is distant from the area.

In addition, in an optical recording medium having a recording reflective layer containing a recording material, surface plasmonic particles, and a nonlinear optical material, writing is performed with a laser beam in the resonant wavelength region of the surface plasmonic particles and/or the nonlinear optical material, and the resonant wavelength is Reading is performed using a laser beam in a wavelength range outside the area, preferably a wavelength range away from the area.

According to such a writing and reading method, good recording and reproduction can be performed.

The method for manufacturing the optical recording medium of the present invention will be explained below.

The method for creating the recording reflective layer of the optical recording medium of the present invention is as follows:
The following methods such as ■ to ■ can be adopted.

(2) The recording substance, surface plasmonic fine particles, and if necessary, the nonlinear optical substance are made into ink, and the dope is applied to the substrate and cured (for example, the optical recording medium shown in FIG. 1 is prepared by this method).

■ A finely structured thin film of a recording material, surface plasmonic particles, and if necessary a nonlinear optical material is formed on a substrate by a PVD method such as co-evaporation or cosbatter (for example, the optical recording medium shown in Fig. 4 is created by this method). ).

■ Paste the recording reflective film formed by the method of (1) or (3) above on a recording reflective film containing a separately prepared recording material, surface plasmonic particles, and nonlinear optical material if necessary, or a base film separate from the substrate, to the substrate. Ru.

Note that when forming the recording reflective layer, positioning signals such as guide groups and wobbles can be created on the substrate in advance. Further, ROM signals, read control signals, sector numbers, etc. can be created in advance.

In the optical recording medium of the present invention, when a reflective layer is formed on the side opposite to the transparent substrate of the recording reflective layer provided with the reflective layer, a reflective layer or an antireflection layer may be formed as necessary. For example, a highly reflective metal such as gold, silver, copper, aluminum or alloys thereof is evaporated or sputtered behind the recording layer. Alternatively, a separately prepared reflective layer film may be laminated together. When forming an antireflection layer, a polymer sheet mixed with carbon black particles may be laminated, or an antireflection paint may be sprayed.

Furthermore, a layer having a lower refractive index than the recording layer can be formed between the substrate and the recording layer by vapor deposition or sputtering as a reflective layer for confining laser light energy.

Such an optical recording medium of the present invention can be used in any form such as an optical disk, an optical card, or an optical tape.

[Function] Surface plasmonic fine particles generally react with the wavelength or laser intensity of irradiated laser light as shown in Figures 5 and ! It has the reflectance shown in Figure 6.

That is, as shown in FIG. 5, the reflectance is low in the resonant wavelength region A.
That is, the absorption rate is high, and in the other region B, the reflectance is high, that is, the absorption rate is low.

The resonant wavelength can be adjusted by a combination of the type of surface plasmonic metal, the dielectric constant and dimensions of the material in contact with the surface plasmonic metal, and the nonlinear constant of a nonlinear compound when it coexists.

Therefore, by performing writing using laser light in the resonant wavelength region A, it is possible to obtain a good effect of improving the laser light absorption efficiency by the surface plasma of surface plasmonic particles, which will be described later, and to perform good recording. . on the other hand,
By performing reading using laser light with a wavelength in region B outside of resonance wavelength region A, the laser light is reflected by surface plasmonic particles and no change occurs in the recording material, so stable reproduction is performed. be able to.

In addition, with respect to laser light intensity, the reflectance is high in the area C where the laser intensity is low, and the reflectance is low in the area C where the laser intensity is high.Therefore, the writing light with high laser intensity is effectively absorbed and recorded. In contrast, the reading light with low laser intensity is effectively reflected to provide a reading signal, and no change occurs in the recording material during reproduction.

Regarding the effects of the surface plasmonic fine particles in the present invention, referring to FIGS. An example case will be explained.

The writing laser beam 10A incident on the recording layer is absorbed within the layer and causes a local temperature rise, and as shown in FIG. 347(a), the surface plasmonic fine particles of the composite particles 6 are On the surface of 7, a strong surface electric field (plasmon) 9 is formed along the surface.

When the intensity of the laser beam is high, this surface plasmon 9
Increases non-linearly. In particular, by matching the wavelength of the writing laser beam to the resonant wavelength region A of plasma electrons shown in FIG. 5, the absorption efficiency increases rapidly and a high surface plasmon intensity can be obtained.

This surface plasmon increases the surface temperature of the surface plasmon characteristic particle, and as a result, denaturation or melting of the recording material 8 covering it is promoted. In particular, when a nonlinear optical material coexists, the absorbed energy increases rapidly by optimizing the interaction between the surface plasmonic metal particles and the nonlinear optical material, further inhibiting the metamorphosis or melting of the recording material 8. promote

In the case of reproduction, as shown in FIG. 7(b), the intensity of the reading laser beam 10B is usually about ten tenths less than the intensity of the recording laser beam 10A, and the surface plasmon effect (
Furthermore, since the self-focusing effect caused by the nonlinear optical material does not occur, the recording material 8 is stably stored without changing. Furthermore, by setting the wavelength of the reading laser beam to a wavelength far from the resonance region, the reflection intensity is increased and the threshold value is further improved.

[Example] The present invention will be described in more detail with reference to Examples below.

Example 1 Aluminum and N,N-diethylnitroaniline (2:1 (weight ratio)
) was codeposited to create a recording reflective layer. Signals were written on the obtained optical recording medium at a constant linear velocity of 1.3 m/s and 500 kHz using a recording laser beam (7800 m) with an output of 4 mW. After that, a 0.5 mW reproduction laser beam (78
As a result of repeated reproduction using 0nm), it was confirmed that recording was stably maintained.

Example 2 Fine particles of 20% indium-20% tin-silver alloy (average particle size 10100 nm and diethylaminonitrostilbene (2
:1 (weight ratio)) in a polyurethane binder was coated with a blade on a polycarbonate substrate to form a recording reflective layer, and recording and playback tests were conducted under the same conditions as in Example 1. . As a result, it was confirmed that the records were maintained stably.

Example 3 Ultrafine silver particles (average particle size 30 nm), a silicon complex of naphthalocyanine having an alkyl side chain, and an indolenine cyanine dye (3:, 1:1 (weight ratio)) were melt-kneaded with polycarbonate. , the sheet was made by extrusion. An optical disc was created by pasting this sheet onto a polycarbonate pregroove substrate. When recording and reproducing tests were performed on this optical disc in the same manner as in Example 1, it was confirmed that recording was stably maintained.

Example 4 Gold fine particles (
(average particle size 10 nm) and cyanine dye in a 3:1 ratio.
1 (weight ratio)), and a sheet was laminated onto a polycarbonate pregroove substrate to create an optical disc. For this optical disc, the constant linear velocity was 5.5 m/s.

Same as Example 1 except that the frequency was set to 6.3 MHz,
Recording and playback tests were conducted. As a result, it was confirmed that the records were maintained stably.

[Effect of the invention] As detailed above, according to claim (1), with high sensitivity,
An optical recording medium with high stability and reliability in recording and reproduction is provided.

Moreover, according to claims (3) and (4), it is possible to perform recording and reproduction of such an optical recording medium extremely stably and effectively.

According to claims (2), (5) and (6), even better effects are achieved.

[Brief explanation of the drawing]

Figure 't%1 is a schematic cross-sectional view of an optical recording medium according to an embodiment of the present invention, Figure 's2 and '! Figure J3 is an enlarged sectional view showing an example of a composite particle of a surface plasmonic metal ultrafine particle and a recording substance in the recording layer of the optical recording medium shown in Figure 1. FIG. 4 is a schematic cross-sectional view showing another embodiment of the optical recording medium of the present invention. FIG. 5 is a graph showing the relationship between the laser beam wavelength and the reflectance of the surface plasmonic fine particles, and FIG. 6 is a graph showing the relationship between the laser beam intensity and the reflectance of the surface plasmonic fine particles. FIG. 7 is a schematic diagram illustrating the effects of surface plasmonic fine particles. 1. IA... Optical recording medium, 2... Transparent substrate, 3.3A-... Recording reflective layer,
4...Protective layer, 5...Transparent polymer 6...
- Composite particle, 7... Surface plasmonic fine particle, 8... Recording substance. Figure 1 Patent Applicant Ube Industries Co., Ltd. Representative Patent Attorney Tsuyoshi Shigeno Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Wavelength (nm) Leb'i! LII Figure 7(b)

Claims (6)

[Claims] (1) An optical recording medium characterized by comprising a recording reflective layer containing surface plasmonic ultrafine metal particles and a recording substance. (2) An optical recording medium comprising a recording reflective layer containing ultrafine metal particles having surface plasmonic properties, a nonlinear optical substance that enhances the surface plasmon of the ultrafine metal particles, and a recording substance. (3) Claim (1) characterized in that writing light in a resonant wavelength region of surface plasmonic metal ultrafine particles is used.
A recording/writing method for optical recording media. (4) The recording/reading method for an optical recording medium according to claim (1), characterized in that reading light in a wavelength region outside the resonant wavelength region of ultrafine metal particles having surface plasmonic properties is used. (5) The method for recording and writing on an optical recording medium according to claim (2), characterized in that writing light in a resonant wavelength region of surface plasmonic metal ultrafine particles and/or nonlinear optical material is used. (6) The method for reading and recording information on an optical recording medium according to claim (2), characterized in that reading light in a wavelength region outside the resonant wavelength region of surface plasmon metal ultrafine particles and/or nonlinear optical material is used.