JPH0241288A - Optical recording medium and optical recording method - Google Patents

Abstract

PURPOSE:To recording a large capacity of information in high density, and to reproduce it by a single wavelength light source by employing an optical recording medium of multilayer structure which exhibits spectral absorption maximum value in different wavelengths in a recording layer, and detecting variation in the reflectivity of the recording layer by a reproduced light which exhibits intrinsic reflectivity. CONSTITUTION:Three recording layer A, B, C are formed on a base 4, and respectively have maximum absorptions. The layer A is varied only by a light having a wavelength lambda1. Similarly, only the layer B is varied by the light having lambda2, and only the layer C is varied by the light having lambda3. The reflectivities of the reproduced light in an unrecorded state of the layers A, B, C are respectively R1, R2, R3, and when the layer A is varied by recording by DELTAR1, the total reflectivity after recording becomes {(R1+R2+R3)-R1}. Similarly, the layers B, C are varied by DELTAR2, DELTAR3 after recording. The total reflectivity after recording is eight different values according to the recording states of the layers A, B, C, and the recording states of the layers can be detected by type of light.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical recording medium and an optical recording method.

2. Description of the Related Art Optical recording media are expected to develop as external storage media because of their large capacity and low cost per bit. However, since all optical recording media put into practical use today are two-dimensional recording, the recording density is limited by the wavelength of the laser used for recording, and the upper limit is 108 bits per ld. Although this recording density provides sufficient storage capacity for applications such as filing document information, it is by no means sufficient for storing images, especially moving images, and for this reason even higher-density recording is required. A medium is required for these purposes. One method for increasing density is multilayering, and multilayer recording using laminated films has been proposed. (Japanese Unexamined Patent Publication No. 58-209594) Photochemical hole burning has also been proposed.

Problems to be Solved by the Invention In all of the above-mentioned multiplex recording methods, light of the same wavelength as that used for recording is required during playback, so the playback device must also prepare multiple light sources. A playback device using such a light source requires a very complicated optical system, resulting in a very expensive device.The present invention provides a high-density optical disc for consumer use that can be played with an inexpensive playback device. That is.

Means for Solving the Problems The present invention is capable of recording a large amount of information at high density, such as recording an image, and also enables reproduction using a light source of a single wavelength. The optical recording method uses a multilayer structure in which each layer of the recording layer exhibits a maximum spectral absorption value at a different wavelength, and at the wavelength at which each layer exhibits maximum absorption, the absorption rate of other recording layers is sufficiently low. Using a medium, only the reflectance of one recording layer is changed by recording light of a specific wavelength near the wavelength showing the absorption maximum, and the reflectance of the recording layer has a wavelength other than the wavelength showing the absorption maximum, and at that wavelength. The present invention is characterized in that light in which each recording layer exhibits a different open reflectance is used as reproduction light, and changes in reflectance for each recording layer are identified and detected.

As described above, in the optical recording method using the optical recording medium of the present invention, the recording density per unit area can be significantly higher than conventional methods, so even long videos that require a large capacity can be recorded in a relatively small area. can be stored in

Further, since an organic dye having a single absorption maximum wavelength between 300 nm and 900 nm can be selected and used as a recording material, a wet coating method with low manufacturing cost can be used. In addition, since a single light source can be used for reproduction, it is advantageous for reducing the cost of the reproduction machine.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic diagram of a three-layer optical recording medium as an example. That is, three recording layers A, B, and C are formed on the substrate, and each recording layer has a wavelength of λ1.
λ2. As is clear from FIG. 2, the absorption coefficients of the recording layers B and C are sufficiently small at the wavelength λ, which has an absorption maximum value at λ3, which indicates the absorption maximum value of the recording NA, and the absorption coefficients of the recording layers B and C are sufficiently small for light of the wavelength λ1. Only A changes. Similarly, a ninth-order reproduction method will be described in which only the recording layer B changes with the light of λ2, and only the recording layer 1c changes with the light of λ8.

As shown in FIG. 3, each recording layer A in a laminated state,
The reflectances of B and C at the wavelength of the reproduction light in an unrecorded state are R, , R2, and R3, respectively, and the total reflectance is (R1+R2+
R,), and if the recording layer A changes by ΔR8 due to recording, the total reflectance after recording is ((R, +R2+R
, )-R,l. Similarly, assuming that recording layers B and C change by ΔR2°ΔR8 after recording, ΔR8≠ΔR2≠
If ΔR3 is assumed, the total reflectance after recording is recording layer A, B,
Since C takes different values depending on the recording state of C, the recording state of each recording layer can be detected with one type of light. Here, properties required for each component of the optical recording medium of the present invention will be described. The material forming the recording layer need only have the property of absorbing light and causing a certain amount of change in reflectance, and the form of change may be either heat mode or font mode.

However, materials that change due to recording and impede the transmission of light are not suitable; in other words, they may absorb light and oxidize and decompose and decolorize, or they may decompose and form bubbles due to the heat generated due to light absorption. It may also be one that develops color or changes its crystalline phase when heated, or may undergo photoisomerization.In many cases, heat is generated during recording, so as shown in FIG. 4, the adjacent recording layer 11 It is preferable to provide a transparent heat insulating layer 13 between the recording layer 1i14 and the recording layer 12. Also, the protective layer 15 may be formed directly on the recording layer 1i14, or a well-known so-called air gap method may be used. It may also be used as a form of protection. The optical recording material may be any material as long as it has a single absorption maximum value in its spectral absorption curve in the wavelength range from 300 nm to 900 nm, and has a certain amount of reflectance at the absorption maximum wavelength. Preferably, a dye having a molar extinction coefficient of 1 x 104 or more at the absorption maximum wavelength is desirable from the viewpoint of recording sensitivity and reflectance characteristics.The recording layer itself may be composed of such a dye alone or may be composed of a transparent material. From these viewpoints, specific dyes that may be used in the form of a composition include cyanine dyes and squalirium dyes.

Methine dyes, naphthoquinone dyes, quinoneimine dyes, diphenylmethane dyes, triphenylmethane dyes, phthalocyanine dyes, naphthalocyanine dyes,
Spiropyran compounds, fulgide compounds, azo compounds, choline dyes, etc. can be used. When dispersing these materials, the transparent material may be selected depending on its compatibility with the dye used and its solubility.Also, when providing a heat insulating layer between each recording layer, Basically, it does not matter whether it is an organic material or an inorganic transparent material as long as it does not have any adverse effects, but in consideration of the influence on the recording material when forming the heat insulating layer, a transparent organic polymer material is preferable. In addition to spin coating, dip coating, web coating, etc., a plasma polymerized film can also be used as a forming method. The recording layer can also be formed by vapor deposition in addition to the above-mentioned wet coating method.

A more detailed explanation will be given below using specific examples.

Specific Example As shown in FIG. 4, a chloroform solution of compound (1) was formed on a 5C11×5C11 glass substrate 11 by spin coating to form a first recording layer 12 with a thickness of 60 nm. A transparent layer 13 having a thickness of 200 nm was formed by spin coating an aqueous solution of polyvinyl alcohol thereon. Furthermore, a 50 nm second recording layer 14 was formed thereon using a Victoria Blue alcohol solution. Finally, polyvinyl alcohol was formed once again to a thickness of 300 nm to form a protective layer 15. As shown in Figure 5, the spectral absorption curve for each recording layer shows that at the absorption maximum wavelength of one recording layer, the absorption of the other layer is extremely small, and that the spectral reflectance of each layer in the unrecorded state is As shown in FIG. 6, recording jW12.14 has sufficient reflectance even at 830 nm, where absorption is low. When a laser beam of 830 nm was used as the reproduction light in the completed optical recording medium as shown in FIG. 4, the overall reflectance was 22% in the unrecorded state. Wavelength 78 with output 30mW
When a 0 nm laser was focused onto a spot with a diameter of 3 μm on the first recording layer 12 made of compound (1) through the glass substrate 11, the reflectance was 10%. That is, the amount of change in reflectance was 12%. Next, when a He-Ne laser with a wavelength of 633 nm and a power of 30 mW was focused on a spot with a diameter of 3 μm on the second recording layer 14 made of Victoria Blue through the glass substrate 11 at another position, the reflectance was 15. %. That is,
The amount of change in reflectance is 7% at the 0th order, and 63% in advance.
When the same position recorded at 3 nm was irradiated with 780 nm light, the reflectance decreased to 8%. On the other hand, in advance, 7
When additional writing was performed at 633 nm after recording at 80 nm, the reflectance was still 8%. As shown above, in this specific example with a two-layer recording film, the reflectance varies depending on the recording state. Because it showed three different amounts of change, it was possible to easily identify and detect which layer it was recorded in.

Effects of the Invention As explained in the above embodiments, the optical recording medium and optical recording method of the present invention have the excellent feature that multiple recording can be performed at the same position and detection can be performed with a single reproduction beam. have.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically explaining the structure of the optical recording medium of the present invention, FIG. 2 is a graph showing a spectral absorbance curve for explaining the optical recording method of the present invention, and FIG. 3 is a graph showing the spectral absorbance curve of the present invention. A graph showing a spectral reflectance curve to explain the optical recording method, FIG. 4 is a cross-sectional structural diagram of a two-layer multilayer optical recording medium that is a specific example of the present invention, and FIG. 5 is a graph showing a spectral absorbance curve of a specific example. 6th
The figure shows the following: 1...Recording layer A, 2...Recording layer B, 3...Recording layer C1 4...Substrate.

Claims (3)

[Claims] (1) An optical recording medium with a multilayer structure in which recording layers having spectral absorption maximum values at different wavelengths are laminated, and at the wavelength where one recording layer shows the absorption maximum value, the spectral absorption of other layers is sufficiently low. In addition, each recording layer maintains the property of transmitting light of a specific wavelength belonging to a wavelength range showing a sufficiently low absorption rate even after changes due to recording, and An optical recording medium characterized in that it exhibits unique amounts of change in reflectance that are different from each other. (2) The optical recording medium according to claim (1), wherein each recording layer is separated by a transparent layer. (3) An optical recording medium with a multilayer structure in which each layer of the recording layer exhibits a spectral absorption maximum value at a different wavelength, and the absorbance of other recording layers is sufficiently low at the wavelength at which each layer exhibits the absorption maximum value, Only one recording layer is changed by recording light of a specific wavelength near the wavelength showing the maximum absorption value, and the recording layer has a wavelength other than the wavelength showing the maximum absorption value, and at that wavelength, each recording layer is changed before and after recording. 1. An optical recording method characterized in that the reflectance changes of each recording layer are identified and detected by using, as reproduction light, light that exhibits unique reflectance change amounts that are different from each other.