JPH02308423A - Reproducing method for optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the deterioration by giving energy to only the surface of a recording layer, and also, to efficiently detect its variation and to reproduce the information with high sensitivity by reproducing the information of an optical recording medium by using an evanescent wave or a surface plasma wave. CONSTITUTION:An optical recoding medium is manufactured by forming a thin film of silver of 10nm thick as a recording layer 12 on a quartz substrate 11. To this medium, recording is executed by irradiating the layer 12 with a YAG pulse laser from the substrate side. Subsequently, an optical system consisting of a reproducing laser 13 and a detector 14 is constituted so that an incident angle theta of a reproducing light becomes an angle of plasma vibration of silver before recording, and reproduction is executed by irradiating the layer 12 with a light beam through the substrate 11 by using a continuous oscillation type semiconductor laser. In a write area and a non-write area, a clear variation is observed in the reflection factor and information can be read out.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a method for reproducing an optical recording medium.

(Prior Art) In recent years, with the rapid development of information processing technology, the need for large-capacity memory has been advocated, and optical disk memory is attracting attention as the core of this.

Optical memory is a general term for systems that record and reproduce information using the interaction between light and matter.

The principles of optical recording include a photon mode, which utilizes direct changes in materials caused by photons, and a heat mode, which utilizes changes in the shape of materials caused by thermal energy converted from light energy.

Optical disk memories currently in practical use are based on the principle of heat mode, and use the energy of irradiated laser light as a heat source.

Previous disk memories based on this heat mode principle include those that change the shape of the recording layer by forming small holes or bubble-like bulges in the recording layer, and those that change the shape of the recording layer by making use of thermal phase transition of the recording layer material. There are some that change optical properties such as optical index, refractive index, and reflectance.

However, in heat mode recording, it is difficult to obtain high spatial resolution because thermal energy is diffused within the recording medium, and in order to obtain high resolution, strong light must be irradiated in a short period of time. be.

On the other hand, photon mode recording uses irradiated light energy for direct recording, so there is less energy diffusion and generally exhibits high spatial resolution. However, since photon mode recording uses a photochemical reaction in the recording process, the efficiency of the reaction is generally low and the change in optical properties of the recording layer before and after recording is small, making it difficult to detect information during reproduction. Furthermore, since reproduction is performed using the difference in reflectance before and after recording in the recording layer, it is essential to irradiate the recording layer with strong light during reproduction, and deterioration of the recording layer during reproduction becomes a major problem.

For the above reasons, optical memory using photon mode has not been put into practical use, and this principle has only been applied to silver salt materials such as photographs, polymer photoresists, photochromic materials, etc.

Another problem with optical recording is that the recording density is limited by the wavelength of the light. This is a fundamental problem that cannot be avoided as long as recording is performed using a normal optical system using lenses, reflecting mirrors, etc.

Methods to increase recording density include shortening the wavelength used and applying photochemical burning, but these are essentially solutions that take advantage of the spatial resolution that is limited by the wavelength of the light being used. Not yet.

(Problems to be Solved by the Invention) The present invention has been made in view of the above problems, and provides an optical recording medium that can prevent deterioration of the recording layer during reproduction and reproduce information with high sensitivity. The purpose is to provide a reproduction method.

[Configuration of the Invention (Means and Effects for Solving the Problems) The method for reproducing an optical recording medium of the present invention uses evanescent light as the reproducing light when reproducing information by irradiating light onto an optically recorded optical recording medium. It is characterized by the use of waves or surface plasma waves.

The evanescent wave used as reproduction light in the present invention is generally generated by making light enter a material with a large refractive index into a material with a small refractive index at an angle equal to or greater than the total reflection angle.
Alternatively, it is an electromagnetic wave that is generated by passing light through a small hole having a diameter equal to or less than the wavelength of the light, and is attenuated exponentially in the direction of propagation.

In the former case, reproduction is performed as shown in FIG.

That is, a recording layer 12 is formed on a transparent substrate 11, and reproduction light is incident on the recording layer 12 from a reproduction laser 13 through the transparent substrate 11 onto an optical recording medium on which writing has already been performed. At this time, the incident angle θ of the reproduction light on the recording layer 12
is greater than the angle of total reflection. An evanescent wave is generated at the position where the reproduction light is incident on the recording layer 12, and this wave penetrates into the recording layer 12 side by a distance on the order of the wavelength. Recording layer 1
The reflected light from 2 is detected by a detector 14. Information can then be read out based on the difference in the amount of evanescent waves absorbed in the write area and the non-write area.

In the latter case, reproduction is performed as shown in FIG. That is, the recording layer 12 is formed on the transparent substrate 11, and the recording layer 12 of the optical recording medium has already been written.
on the side, below the wavelength of the reproduction light (1/1O of the wavelength of the light used)
A thin plate 21 in which a small hole 22 having a diameter of about 1/3 of the diameter of the recording layer 12 is formed is installed, and a reproduction light from a reproduction laser is incident on the recording layer 12 through the small hole 22. When the reproducing light passes through the small hole 22, it oozes out to the recording layer 12 side as an evanescent wave. The reflected light from the recording layer 12 is detected by a detector. Information can then be read out based on the difference in the amount of evanescent waves absorbed in the write area and the non-write area.

The surface plasma wave used as reproduction light in the present invention is one of elementary excitations generated on the surface of a metal, and is a combination of plasma vibration of electrons and electromagnetic waves. When surface plasma waves are used, regeneration is performed as shown in FIG. 1 in the same manner as described above. However, the recording layer 1 of the reproduction light
The incident angle θ to 2 is the angle of plasma oscillation, and the recording layer is made of metal. In this case, information can be read out based on the difference in the amount of absorption of surface plasma waves between the written region and the non-written region.

(Function) If information on an optical recording medium is reproduced using evanescent waves or surface plasma waves as in the present invention, energy is applied only to the surface of the recording layer, so deterioration of the recording layer can be prevented. I can do it.

Further, by using evanescent waves or surface plasma waves, changes in the recording layer can be detected efficiently, so information can be reproduced with high sensitivity.

(Example) The present invention will be explained in detail below.

Example 1 An optical recording medium was manufactured by forming a thin silver film with a thickness of 10 nn+ as a recording layer on a quartz substrate. Recording was performed on this optical recording medium by irradiating the recording layer with pulsed light through the quartz substrate using a YAG pulsed laser. Next, the optical system is arranged so that the incident angle of the reproduction light is the angle of plasma vibration of the silver before recording, and the reproduction system shown in Fig. 1 is constructed. Reproduction was performed by irradiating the recording layer with light through the substrate.

As a result, a reproduced signal as shown in FIG. 3 was obtained. As is clear from FIG. 3, there is a clear change in the reflectance between the written area and the non-written area, which indicates that information can be read.

For comparison, when the incident angle of the reproduction light was set to 0'' under the same conditions as above, no clear change in reflectance as shown in FIG. 3 was observed.

Example 2 An optical recording medium was manufactured by forming a cast film of azobenzene as a recording layer on a quartz substrate. For this optical recording medium, a KrF excimer laser was used to inject the recording layer through the quartz substrate at a wavelength of 248 rv and an output of 10a+J/pulse.
Recording was performed by irradiating with pulsed light. next,
The reproduction system shown in Figure 1 is constructed by arranging the optical system so that the incident angle of the reproduction light is the total reflection angle, and a continuous wave semiconductor laser is used to irradiate the recording layer with light through the quartz substrate. It was regenerated by this. As a result, a reproduced signal as shown in FIG. 3 was obtained.

Example 3 An optical recording medium was manufactured by forming a cast film of azobenzene as a recording layer on a quartz substrate. For this optical recording medium, a KrF excimer laser is used to coat the recording layer with a wavelength of 248.
Recording was performed by irradiating pulsed light with a power of r+m and an output of 10a+J/pulse. Next, as shown in FIG. 2, a 3p thick aluminum foil with small holes was placed above the recording layer of this optical recording medium. The diameter of this small hole is estimated to be several tens to hundreds of r.v.

ing. Then, reproduction was performed by irradiating pulsed light with a wavelength of 248 nm and an output of 10 mJ/pulse perpendicularly to the recording layer through a small hole in the aluminum foil using a KrF excimer laser. As a result, a reproduced signal as shown in FIG. 3 was obtained. A 1% change in reflected light intensity was observed before and after laser irradiation.

[Effects of the Invention] As detailed above, according to the method of the present invention, information on an optical recording medium is reproduced using evanescent waves or surface plasma waves, and energy is applied only to the surface of the recording layer. Therefore, deterioration of the recording layer can be prevented. Further, since changes in the recording layer can be detected efficiently by using evanescent waves or surface plasma waves, information can be reproduced with high sensitivity.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a method for reproducing an optical recording medium according to the present invention, FIG. 2 is an explanatory diagram showing a method for reproducing another optical recording medium according to the present invention, and FIG. FIG. 2 is an explanatory diagram of a reproduction signal of an optical recording medium. DESCRIPTION OF SYMBOLS 11... Transparent substrate, 12... Recording layer, 13... Reproduction laser, 14... Detector, 21... Thin plate, 2
2...Small hole. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Scope of Claims] (1) Reproduction of an optical recording medium characterized in that evanescent waves or surface plasma waves are used as reproduction light when reproducing information by irradiating light onto an optically recorded optical recording medium. Method. (2) Utilizes evanescent waves generated by making the reproduction light incident on the recording layer at an angle greater than the total reflection angle or by passing the reproduction light through a small hole having a diameter less than the wavelength of the reproduction light. The method for reproducing an optical recording medium according to claim (1). (3) The method for reproducing an optical recording medium according to claim (1), characterized in that surface plasma waves generated by making reproducing light incident on the recording layer made of metal at an angle of plasma vibration are utilized.