JPS61188752A - System for optical information recording - Google Patents

Abstract

PURPOSE:To improve a tracking and focusing performance as well as obtain large reproduction signals by using optical recording discs having a layer and a light absorbing layer which can cause dispersion or phase transposition between the layers to raise a reflectance before writing. CONSTITUTION:A recording medium consists of the substrate 1 made of a transparent material coated on one side with the first vapor deposition layer 2 of Sb2Se3 which is further coated with the second vapor deposition layer 3 of Bi. Optical characteristics such as reflectance of the first layer are variable due to heating or other treatment, and the second layer has absorbency of light for writing. These characteristics are selected to have a sort of like spectral characteristic 4 so that a minimum reflectance occurs due to interface between two films at wavelength lambda0. This enables writing to cause a large change in reflectance, and therefore, a large reflectance before writing, assuring increase in the quantity of incident light on a photo detector for controlling focusing and tracking and resulting in a stable control operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an apparatus for optically recording and reproducing information such as video, audio, combiator information, etc.
This invention relates to an information recording method that allows high-density recording and easy search and playback.

[Background of the invention]

The conventional recording method, as described in Japanese Patent Laid-Open No. 57-186243, consists of a first layer whose optical properties change when heated and a second layer that absorbs writing light on a substrate. 1
- By using a recording medium constructed by forming
The price is set so that it will be higher after the harvest. However, the magnitude of the reflection potential is necessary not only for reproducing information but also for detecting all focus and tracking signals, and it is necessary to make the reflection base high before writing. Conventionally, there has been no method that satisfies the contradictory requirements of increasing the reflection quality by writing and increasing the reflection output before writing.

In other words, if you set the reflection height before writing to be small and increase the change in reflectance due to writing, the focus during writing or reading may not be on the substrate surface, or the reflectance may be too low. However, there is a problem that neither of them is in focus, and the objective lens for writing and reading light comes into contact with the substrate. Furthermore, if the reflectance before writing is increased, the change in reflectance due to writing becomes smaller and the reproduced signal becomes smaller, which is a problem.

[Purpose of the invention]

An object of the present invention is to provide a recording medium that has a large reflective wheel before writing, improves tracking and focusing performance, and allows large changes in reflectance due to writing.

[Summary of the invention]

In order to achieve the above object, the present invention uses an optical disc consisting of at least two layers, a recording layer and a light absorption layer,
The entire feature is that information tbiF is recorded by causing diffusion or phase transition between the two layers depending on the intensity of the irradiated light, and the information is reproduced by utilizing the difference in optical properties between the two states of diffusion or phase transition. .

The present inventor discovered that in a recording medium with a two-layer structure of a recording layer and a light absorption layer, for example, a two-layer structure recording medium of S625g 3 and B1, 5 At Sa 3 and Ei are irradiated with laser light, and the reflection in the process of generating heat. Xt-Seki Tomo Tokoro, S b, S
Tomo discovered a phenomenon in which the reflectance decreases compared to before heating, before reaching the temperature at which the reflectance increases due to the phase transition of g3.

This is because a diffusion phenomenon occurred between the 5 b t Sg 3 and Bi films, the interference state of the two-layer film changed, and the reflectance decreased compared to before heating.

Therefore, due to this diffusion phenomenon, the reflectance decreases and the next state
The two states in which the reflectance has increased due to phase transition are made to correspond to the Low and Highk write signals to increase the change in reflectance due to writing, and the reflection before writing at that time! ?
By increasing the size, the intensity of reflected light for focus and tracking control is increased, and control stability is achieved.

[Embodiments of the invention]

The present invention will be explained in detail below. First, the basic operation of the recording medium according to the present invention will be explained.

! ! Figure 1 is a cross-sectional view of the main part of a recording medium, Figure 2 is a diagram showing the spectral characteristics of the reflection layer of the recording medium according to the present invention, and Figure 3 is a diagram showing the following:
FIG. 7 is a characteristic diagram showing the relationship between the recording light intensity and the reflectance of the recording medium when a signal is recorded on the recording medium using a writing light having a wavelength λ.

The recording medium has one surface of a base material 1 made of an optically transparent material, for example glass such as soda glass or quartz, or synthetic resin such as polymethyl methacrylate (PMMA) lfl resin or polycarbonate resin. To,
Depositing a first layer 2 consisting of Sb, Ss3 vapor deposited film,
A second layer 3 made of a Bi vapor deposited film is deposited thereon. The first layer is a layer whose optical properties such as reflectance change when heated, and the second layer is a layer that has light absorption properties for writing light, and the thickness of these layers depends on the spectral properties. Wavelength λ as in 4. The reflectance was selected so that the two-layer film would interfere with each other, resulting in the lowest reflectance.

When the base material 1 is heated, at a temperature t6 between the temperature t at which the first layer 2 undergoes a phase transition and the room temperature t4, the reflectance reaches its lowest level due to interference, as shown in spectral characteristic 6. The wavelength becomes λ1. Thereafter, due to heating, the wavelength at which the reflectance is lowest gradually shifts, and at the same time, the lowest reflectance increases, and when the first layer 2 undergoes a phase transition, it becomes the characteristic shown in spectral characteristic 5. The change in reflectance due to phase transition occurred at the 99th time when the transmittance of the first layer 2 suddenly decreased due to the phase transition, but the change in reflectance before this occurred between the first layer 2 and the second layer 3. In between, heating causes diffusion of Bi, 56, and the permeation blockage of the first layer 2 changes little by little.

Next, the light intensity when this recording medium was irradiated with writing light of wavelength λ1 and the reflective portion of the recording medium were investigated. The light intensity is P
At the time of o, the second layer 3 that has absorbed the light radiates a lot of heat, so it does not heat the first layer 2 and takes a reflection value of 87 (L. This corresponds to 4a of the spectral characteristics. Next, when the light intensity is set to 1 (pL) and the second layer 3 generates all the heat, and the first layer is heated, the light intensity decreases to reflection g7b, which corresponds to the spectral characteristic 6α.

When the light intensity is further increased to reach PH, the first layer undergoes a phase transition and becomes reflected light 7c. This corresponds to 5α of the spectral characteristics.

Here, a method for recording signals on this recording medium will be explained. Light intensity f PII corresponding to High and Low signals
, PL. In this state, when the light intensity is switched to Pg and pL according to the signal, the portions irradiated to P and PL' have reflection heights of 7c and 7b, respectively, and are recorded on the recording medium. High-Low of this resultant signal
is recorded as a reflection height of 7c and 7b.90 When reproducing this trust, light is irradiated onto the recording medium at an intensity of P0, the reflected light is observed, and its strength is determined by the Ei of the signal.
It is sufficient to detect it as gh-Low.

As described above, the recording medium according to the present invention is as follows.

Even if the reflection height before writing is high, the change in the recorded signal can be large.Finally, by increasing the reflection height before writing, the amount of light incident on the photodetector can be increased. As a result, tracking and focus control can be stabilized.

Hereinafter, it will be explained in detail using examples.

Example 1: In Fig. 4, a guide groove 9't'' for tracking and two base materials 1α have s
A first layer 2 made of B, S and a second layer 3 made of Bt.
An example according to the invention is shown, which was obtained by depositing by vapor deposition. Here, the base material 1a was obtained by injection molding a PHMA resin gold using a mold having guide grooves 9 in advance. In addition, the first layer 2
is 20TLm thick and the second layer is 3Qnm thick.

The reflection height of the recording medium obtained in this way before writing (8eL) is
It was about 25 excellent at the wavelength of a semiconductor laser (83 Atsushi Kan).

In addition, the reflectance (8b and 80) when recording signals by switching the output power of the semiconductor laser to 'i3mF and 8i is 15
The figure was 40% for foreigners. This reflection height difference is comparable to that of conventional recording media and is a value that can be used for practical purposes.

Therefore, the reflected light with a reflectance of more than 25 before writing enters the photodetector for focus and tracking control, so the control signal becomes large 4, the control is excellently stabilized, and tracking due to vibration is However, it has been possible to prevent this and improve the performance of recording media.

Example 2 Next, an example in which there is no guide groove will be described.

It is shown in FIG. The first layer and the second layer provided on the base material 1 were the same as those in the example shown in FIG. When recording signals on a recording medium configured in this way, there is a method, for example, of recording signals by providing a flat track instead of a guide groove (Japanese Patent Publication No. 58734/1983). In this case, the flat track 10A is prepared in advance with the writing light intensity at the point where the reflection height is lowered due to diffusion (7h in FIG. 3), and information is recorded at the point where the phase transition occurs (7h in FIG. Figure 7
C), and the point due to the spreading is assumed to be Bsh-Low of the signal.

With this configuration, the flat track 10b can be distinguished from the left and right reflections $1[1α before writing, and tracking control can be performed, and a large reflection output change can be obtained for both high and low signals. Conventionally, as the intensity of the writing light increases, the reflection increases monotonically, so if a flat track is provided and a signal is written on it, the Hi yA of the signal
-The change in reflectance due to Law becomes smaller and becomes a problem, but
According to the present invention, there was a sufficient change in reflectance and good performance was obtained. In addition, the base material of the above-mentioned example is Glass 1
Can produce sheets or films made of synthetic resin, etc.

As described in detail above, the thickness of the first and second layers of the recording medium according to the present invention is such that the wavelength of the light used for writing is longer than the wavelength at which the reflection height is the lowest due to interference between the two layers. so that 2
The size is not particularly limited as long as it is large enough to cause interference between layers, since the same effect as in the example will be produced.

Further, Sh, Sm, in the first layer are not limited to the stoichiometric composition, and the amount of sb mixed with respect to S- is in the range of 10 to 80 atomic %, and the Bi in the second layer is is not limited to Bi alone, but any alloy or compound containing 70 or more elements can be written with a semiconductor laser to produce the phenomenon shown in the example and obtain the same effect.

In the above example, the Bi layer is formed on the 5h and 5g three layers, but on the contrary, the sb and s layers are formed on the Bi layer, and information is written from the 5hSes layer side. You can also do this.

In the above embodiment, a two-layer structure was explained, consisting of a first layer that changes phase and a second layer that absorbs light. A similar effect occurs in a three-layer structure formed by depositing layers of, for example, 5 z Ox or TtOtf. In this case, the light intensity at the low level during writing is set to 1. Diffusion between the second layers is set to a size that gives energy to pass through the anti-diffusion layer, and heating by light irradiation causes diffusion, and at the same time changes the optical properties and changes the interference state, reducing the reflection output. Hereinafter, as in the above-mentioned embodiment, if the first layer phase transition is made to reach the Eilh level, even if the reflectance before writing is high, the change in reflectance due to Hsh-Low of the signal to be recorded will be suppressed. Can be made larger.

The first layer is a material that undergoes a phase transition upon heating and simultaneously changes its optical properties, such as a single substance such as Ax, Sg, 5b, or Tg, or an alloy thereof.

′! ), the @20 layer absorbs light and converts it into heat.
It is a simple substance such as Bi or Ta, or an alloy thereof.

〔Effect of the invention〕

According to the present invention, the amount of reflection caused by writing is large enough to increase the reflectance before writing, which increases the amount of light incident on the photodetector for focus and tracking control, which is effective in stabilizing control. There is.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a recording medium according to the present invention, FIG. 2 is a spectral characteristic measurement diagram of reflectance of the recording medium of FIG.
1 is a characteristic diagram showing the relationship between recording light intensity and reflectance of the recording medium of FIG. 1, FIG. 4 is a perspective view of a recording medium having a guide groove according to the present invention, and FIG. FIG. 2 is a perspective view of a recording medium without grooves. 1... Base material - 2... First layer 3 made of S b2S g 3...
20th layer consisting of B1 Figure 1 σ°−“°°7 Figure 2 t5 Cg>t+

Claims (1)

[Claims] 1. In an optical information recording system using an optical disc,
As the optical disc, an optical disc consisting of at least two layers, a recording layer and a light absorption layer, is used, and depending on the intensity of the irradiated light,
An optical information recording system characterized in that information is recorded by causing diffusion between the two layers or phase transition of the recording layer. 2. The optical information recording system according to claim 1, wherein the minimum wavelength of reflectance due to interference between the two-layer film in an initial state is smaller than the wavelength of light used for recording. 3. The recording layer is a layer containing Sb and Se as main components,
3. The optical information recording system according to claim 2, wherein the light absorption layer is a layer containing Bi as a main component.