JPH07105068B2 - Optical memory device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical memory device capable of optically recording and reproducing or erasing information.

[Conventional technology]

2. Description of the Related Art In recent years, an optical memory device capable of optically recording and reproducing or erasing information has been attracting attention as a demand for a storage device capable of high capacity, high density and high speed access has been increased. In particular, an optical disk capable of additional recording, a rewritable optical disk, and an optical card having excellent portability have been actively researched and developed as a means for expanding the application range of the optical memory device.

In the above-mentioned optical memory device, it has been general practice to adopt an antireflection structure having a multilayer film structure. For example, as shown in FIG. 4 (a), a recording medium 20 including a recording layer 11, a transparent dielectric layer 12 and a reflective film layer 13 is formed on a transparent substrate 14, and FIG. ), A recording medium 21 composed of two transparent dielectric layers 15 and 16 and a recording layer 11 is formed on a transparent substrate 14, and further, as shown in FIG. Two transparent dielectric layers 17
A recording medium 22 including a recording layer 11, a recording layer 11, and a reflective film layer 13 formed on a transparent substrate 14 is known. All of them realize an antireflection structure by the interference effect of the transparent dielectric layers 12, 15, 16, 17, and 18. As described above, the antireflection by the multilayer film structure is a technique necessary for improving the reproduction contrast and obtaining a high recording sensitivity in the additionally recordable optical memory device represented by the hole punching type. In a magneto-optical recording element known as a representative of possible optical memory elements, it is a technique necessary for increasing the enhancing effect of the magneto-optical effect and improving the reproducing performance.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional structure, although the recording performance and the reproducing performance in the optical memory device are improved, it is necessary to effectively interfere the light with the transparent dielectric layers 12, 15, 16, 17, 18. The amount of reflected light from the recording layer 11 is inevitably small. Therefore, the optical memory device having this type of structure has a dark tone in appearance, and has a highly reflective metallic luster such as a compact disc or a video disc which is a read-only disc, a cash card, a credit card, and It has a drawback in that it is inferior in terms of appearance in color as compared with the colorful designs applied to magnetic cards such as various prepaid cards.

[Means for Solving the Problems]

In order to solve the above problems, the optical memory device according to the present invention has one side of a transparent substrate that transmits light used for recording / reproduction, while having a wavelength other than that, which is in the visible light range. Is characterized in that at least one optical film is formed so as to be reflected.

[Action]

According to the above configuration, since a part of light in the visible light region is reflected, the optical memory element looks colored in a color according to the wavelength, and the disadvantage that the appearance becomes a blackish color tone is solved. be able to. On the other hand, since the light used for recording / reproducing is transmitted, the recording / reproducing characteristics of the optical memory element are not impaired.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 1, an optical memory device according to the present invention includes a transparent substrate 1 which transmits a light beam used for recording and reproducing information, and a recording medium 2 formed on one surface of the transparent substrate 1. The transparent dielectric thin film laminated body 3 formed on the other surface of the transparent substrate 1 is provided. The recording medium 2 has an antireflection structure in which a recording layer is combined with a transparent dielectric layer or a reflective film layer, as in the conventional case.

The transparent dielectric thin film laminate 3 has a high refractive index dielectric thin film 3a, which is an optical film having a refractive index larger than that of the transparent substrate 1, and a refractive index smaller than that of the transparent substrate 1. And a low-refractive-index dielectric thin film 3b, which is an optical film having a layer, are alternately laminated, and the high-refractive-index dielectric thin film is the first layer as seen from the incident side of the light beam used for recording and reproduction. 3a is arranged. Therefore, the high-refractive-index dielectric thin films 3a ... Are located in the odd-numbered layers, and the low-refractive-index dielectric thin films 3b are located in the even-numbered layers.

The high-refractive-index dielectric thin film 3a and the low-refractive-index dielectric thin film 3b have film thicknesses of n _k and d _k , respectively, for the refractive index of the k-th transparent dielectric thin film when viewed from the light beam incident side. The wavelengths of the recording / reproducing light beam are set to λ, and are set so as to satisfy the following first expression.

According to the above configuration, due to the interference effect of the multilayer thin film,
The reflectance for the light beam of wavelength λ is high refractive index dielectric thin film
It is equal to the reflectance when the thin film 3a and the low refractive index dielectric thin film 3b are not formed, and can take a minimum value. In other words, the reflected light is emphasized with respect to light having a wavelength other than the wavelength λ, and as a result, the optical memory element appears colored in a color corresponding to the wavelength of the reflected light.

Explaining with a specific example, for example, a high refractive index dielectric thin film
ZnS (refractive index n = 2.39) as 3a, low refractive index dielectric thin film 3
If MgF ₂ (refractive index n = 1.39) is used as b, polycarbonate (refractive index n = 1.585) is used as the transparent substrate 1, and the wavelength λ of the recording / reproducing light beam is 780 nm, then from the first equation above, The ZnS film thickness t _ZnS is 163 nm, and the MgF ₂ film thickness t _{MgF 2} is 281 nm. Under such setting conditions,
As shown in FIG. 2, the wavelength dependence of the reflectance on the surface of the optical memory element when the transparent dielectric thin film laminate 3 is composed of two layers and when it is composed of four layers is as shown in FIG.
The reflectance shows a minimum value R _o (when there is no transparent dielectric thin film, that is, the reflectance when the transparent substrate 1 is alone), while the wavelength is 520n.
High reflectivity is shown near m. This allows
The recording / reproducing light beam can pass through the transparent substrate 1 and reach the recording film without being reflected, while light of other wavelengths,
In particular, since light near 520 nm is reflected, the recording and reproducing characteristics of the optical memory element are not impaired, and an optical memory element colored yellowish in appearance can be obtained. Further, when the transparent substrate 1 is made of a resin-based material, insufficiency remains in terms of surface hardness, but as in the present embodiment, the surface of the transparent substrate 1 is coated with an inorganic transparent dielectric thin film. If this is the case, it becomes possible to improve the insufficient surface hardness.

Further, when only the film thickness of the MgF ₂ layer, which is the low-refractive-index dielectric thin film 3b, is slightly shifted from the film thickness obtained from the above-mentioned first equation (for example, t _MgF2 = 100 nm), it is transparent. As shown in FIG. 3, the wavelength dependence of the reflectance on the surface of the optical memory device in the case where the dielectric thin film laminated body 3 is composed of four layers is as shown in FIG. However, the reflectance at a wavelength of 780 nm is lower than the minimum value R _o , and the influence of reflected light on the surface of the optical memory element, which is a problem in recording and reproduction in the optical memory element, can be further reduced.

In the above specific examples, the transparent dielectric thin film as the optical film is laminated to allow the recording / reproducing light beam to be transmitted by the interference effect of the multi-layered thin film structure, while at the other wavelengths and in the visible light region. Although a part of the light is reflected, it goes without saying that a single layer thin film structure using only one predetermined optical film may be used instead of the multilayer thin film structure of the transparent dielectric thin film. The transparent dielectric thin film laminate 3 is not limited to the combination of ZnS and MgF _2, and may be, for example, Sb ₂ S ₃ , TiO ₂ , CdS, CeO ₂ , PbC.
_{l 2, WO 3, SiO,} Al 2 O 3, SiO 2, CaF 2, LiF, NaF, AlN, among SiN or the like, may be combined with those satisfying the magnitude relationship of the predetermined refractive index. Further, in the above embodiment, the transparent substrate 1
Although the transparent dielectric thin film laminate 3 was formed on the surface of the recording medium 2 facing the recording medium 2, the location of the transparent dielectric thin film laminate 3 is not limited to the above-mentioned location, and for example, the transparent substrate 1 It may be between the recording medium 2.

〔The invention's effect〕

As described above, the optical memory element according to the present invention allows one side of the transparent substrate to transmit the light used for recording / reproduction, while the other wavelengths of the light are part of the visible light. This is a configuration in which at least one optical film is formed so as to be reflected.

As a result, a part of the light in the visible light region is reflected, so that the optical memory element appears to be colored in a color corresponding to the wavelength thereof, and it is possible to eliminate the disadvantage that the appearance has a blackish color tone. In addition, the effect of being able to improve the insufficient surface hardness, which is a drawback of the transparent substrate made of a resin material, is also exhibited.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a sectional view showing an essential part of an optical memory device, and FIG.
The figure shows the case where the transparent dielectric thin film laminate is composed of two layers and 4
FIG. 3 is a graph showing the wavelength dependence of the reflectance on the surface of the optical memory element for each of the cases of layers, and FIG. 3 shows that only the thickness of the low refractive index dielectric thin film is slightly shifted from the thickness obtained from the first formula. FIG. 4A to FIG. 4C are graphs showing the wavelength dependence of the reflectance on the surface of the optical memory device when the transparent dielectric thin film laminated body is composed of four layers, respectively, and FIGS. FIG. 1 is a transparent substrate, 2 is a recording medium, 3 is a transparent dielectric thin film laminated body, 3a is a high refractive index dielectric thin film (optical film), and 3b is a low refractive index dielectric thin film (optical film).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Ota, 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture Sharp Corporation (72) Hideka Yamaoka, 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (72) Inventor Toshio Ishikawa 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture

Claims (1)

[Claims] 1. A transparent substrate having at least one optical layer so that light used for recording / reproducing is transmitted to one side of the transparent substrate while light having a wavelength other than the transparent substrate is partially reflected. An optical memory device having a film formed thereon.