JPS62167637A - Optical recording medium - Google Patents

Abstract

PURPOSE:To considerably improve the sensitivity for recording and reading by successively laminating multi-layered films recording layer and reflective layer on a transparent substrate to forms a titled recording medium, providing high-refractive index transparent dielectric layers on both faces of a low-refractive index transparent dielectric layer to form the multi- layered films and specifying the thicknesses of the respective dielectric layers. CONSTITUTION:The multi-layered films, the recording layer 5 and the reflective layer are successively laminated on the transparent substrate 1. The multi-layered films are formed by providing the high-refractive index transparent dielectric layers 2, 4 on both faces of the low-refractive index transparent dielectric 3. The thicknesses of the respective dielectric layers are specified to (lambda/4n)(1+2m) (lambda is the wavelength of laser light, n is the refractive index of each dielectric layer, m is 0 or positive integer). Both the 1st high-refractive index layer and the 2nd high-refractive index layer 4 are vapor deposited ZnS films having 85nm thickness and the low-refractive index layer 3 is a vapor deposited MgF2 film having 140nm thickness. The recording with such recording medium is executed by irradiating UV light to the recording layer to convert the benzothiopyrane spiropyrane to a coloring type then irradiating semiconductor laser light thereto to return the same to a decoloring type. The extremely higher sensitivity and percentage modulation of the recording medium are thereby obtd. and the data recording at the higher speed is made possible.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to optical recording media such as optical discs.

[Summary of the Invention] The present invention provides an optical recording medium in which the recording sensitivity of the recording medium can be increased by providing a dielectric multilayer film on the recording layer.

[Prior art and problems to be solved by the invention] It is known that in an optical recording medium consisting of a transparent substrate, a recording layer, and a reflective layer, it is possible to increase the sensitivity of recording and reading by utilizing the interference effect of light. A cross-sectional view of an example of such a recording medium is shown in FIG.

In the recording medium shown in FIG. 4, the thickness of the recording layer 5 is (1+
2m+α)λ/4η1 (Here, λ is the wavelength of the laser beam, η1 is the refractive index of the recording layer 5, α is the phase constant, and m is 0 or a positive integer) to determine the upper bound of the recording layer 5. Then, the reflected lights γ and 12 from the lower interface interfere with each other, reducing the reflectance of the entire recording layer 5, and the amount of light absorption of the recording layer 5 increases by the amount of the reduction, thereby increasing the recording sensitivity and modulation. degree is improved. Furthermore, when the intensities of the reflected lights T1 and γ2 are equal to each other, the interference is strongest, and the amount of light absorbed by the recording layer is maximized, achieving high sensitivity.

However, the reflected light γ from the upper interface of the recording layer 5 is generally weaker than the reflected light T2 from the lower interface (especially if a protective layer is provided on the recording layer 5, the Fresnel reflectance of the upper interface decreases). Then, the reflected light T becomes weaker. Therefore, in such a case, in order to increase the amount of light absorption by the recording layer of the optical recording medium, the recording and
The present invention was completed by paying attention to the fact that the reading sensitivity can be significantly increased.

[Means for solving problems]

In the present invention, a multilayer film, a recording layer, and a reflective layer are sequentially laminated on a transparent substrate, and the multilayer film is formed by providing a high refractive index transparent dielectric layer on both sides of a low refractive index transparent dielectric layer, The thickness of each dielectric layer is (λ/4n)(1+2m) (where λ is the wavelength of the laser beam, n is the refractive index of each dielectric layer, and m is O or a positive integer). This relates to an optical recording medium made of.

For example, glass can be used as the transparent substrate of the present invention.

Further, as the recording layer of the present invention, a mixture of a benzothiopyran spiropyran and a vinyl chloride-vinylidene chloride copolymer can be used.

Further, as the high refractive index transparent dielectric layer of the present invention, ZnS
, TiO', , ZrO,, CdS % Ce0z, Y
A vapor deposited film such as 2O, etc. can be used, and a vapor deposited film such as MgF 2 , CaF 2 , Na, AIF, etc. can be used as the low refractive index transparent dielectric layer.

Moreover, an Ag vapor deposition film can be used as the reflective layer.

〔Example〕

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

As shown in FIG. 1, the recording medium of this embodiment includes a transparent substrate 1,
a first high refractive index layer 2, a low refractive index layer 3, a second high refractive index layer 4,
It is constructed by sequentially laminating a recording layer 5 and a reflective layer 6.

The first high refractive index layer and the second high refractive index layer 4 constituting the dielectric multilayer film are both ZnS vapor deposited films with a thickness of 85 nm, and the low refractive index layer 3 is a MgF vapor deposited film with a thickness of 140 nm. be. The recording layer 5 contains 5'-methoxy-1'-n-hexyl-3', 3'- as benzothiopyran spiropyran.
Dimethyl-6-nitro-8-methoxyspiro (2H-1
-benzothiopyran-2,2゛-indoline] and vinyl chloride-vinylidene chloride copolymer (Denkavinyl #100
0W, manufactured by Denki Kagaku Kogyo Co., Ltd.) at a weight ratio of 1:2,
Solvent (tetrahydrofuran:cyclohexanone-1:l
) and coated with a spinner to a thickness of 200 nm.
It is formed in m layers. The reflective layer 6 has a thickness of 150n.
It is a heg vapor deposited film of m or more.

Recording on the recording medium of this example is carried out by converting the benzothiopyran spiropyran in the recording layer 5 into a color-forming type by irradiation with ultraviolet light, and then returning it to a color-depleting type by irradiation with a semiconductor laser beam.

Next, the following test was conducted to compare the reflection spectrum of the recording medium of this example with the reflection spectrum of a conventional recording medium having a structure that does not use the dielectric multilayer film of the invention. The conventional recording medium used here has the same configuration as the recording medium of this embodiment except that it does not include a dielectric multilayer film. In this test, light from a 500W high-pressure mercury lamp was filtered through a glass filter (
After irradiating the recording layer 5 of each recording medium from the substrate 1 side with light obtained through a UVD36C1 (manufactured by Toshiba 0X) at an illuminance of about 20 mW/cm2 to bring the recording layer 5 into a colored state, the wavelength of about 78
It was irradiated with 0 nm semiconductor laser light to return to the decolorized state.

The reflection spectra of the recording media of this example and the conventional example obtained in this test are shown in FIG. 2 by solid lines and broken lines, respectively.

Next, the recording sensitivity of each of the recording media of the example and the conventional example was measured, and the results shown in FIG. 3 were obtained.

In addition, in the measurement of the recording sensitivity mentioned above, the wavelength was 780 nm.
, laser beam diameter 2μm (1/e2), output 10m
W and a semiconductor laser beam with a pulse width of 0.03 to 4 μs were used. The reflectance of each of the recording media of this example and the conventional example in the colored state after irradiation with ultraviolet light was about 35%. Further, in the example, the thickness of the recording layer and the ultraviolet light irradiation time were set to 200 nm and 75 seconds, respectively, and in the conventional example, they were set to 700 nm and 120 seconds, respectively. It is known that the recording sensitivity of optical recording media varies considerably depending on the degree of color development of the recording layer and the thickness of the recording layer, and each of the above settings set in Examples and Comparative Examples is the best for each recording medium. This is the value that gives the recording sensitivity of .

In Figure 3, the horizontal axis represents the pulse width of the semiconductor laser beam used to measure the recording sensitivity and the energy density at the center position of the semiconductor laser beam, and the vertical axis represents the sample of the recording medium used to measure the recording sensitivity. It represents the change in reflectance of the portion irradiated with semiconductor laser light. From Figure 3, it is clear that in this example, the energy density required to achieve a 20% change in reflectance is reduced to about 1/4 of that of the conventional example, and therefore, the recording sensitivity is approximately 4 times as high. It is.

〔Effect of the invention〕

Since the present invention provides a dielectric multilayer film on the light incident side interface of the recording layer of an optical recording medium, it is possible to realize a significantly higher sensitivity and a higher modulation degree of the recording medium, thereby making it possible to record data more easily. It becomes possible to perform the process at high speed. Furthermore, materials whose light absorption properties are inferior to other properties can also be used as recording layers of optical recording media.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the recording medium of the example, and FIG. 2 is a graph showing the reflection spectra of each recording medium of the example and the conventional example.
FIG. 3 is a graph showing the recording sensitivity of each recording medium of the example and the conventional example, and FIG. 4 is a cross-sectional view of the recording medium of the conventional example. In addition, in the symbols used in the drawings,
−・・−・・・・・−・−・・−First high refractive index layer 3
・−・・−・・−−−−1・−Low refractive index layer 4−−−−
−−・・−・−−−−−1−−Second high refractive index layer 5−−−
−−−−−−・−・・−・−Recording layer 6−−−−−−−−
−・・−・−・−Reflection layer. Figure 1 Figure 4

Claims (1)

[Claims] A multilayer film, a recording layer, and a reflective layer are sequentially laminated on a transparent substrate, and the multilayer film is formed by providing a high refractive index transparent dielectric layer on both sides of a low refractive index transparent dielectric layer, and each dielectric layer The thickness of the optical fiber is (λ/4n)(1+2m) (where λ is the wavelength of the laser beam, n is the refractive index of each dielectric layer, and m is 0 or a positive integer). formula recording medium.