JPS6371949A - Direct-read after-write type optical disk - Google Patents

Abstract

PURPOSE:To obtain high-quality reproduced information by constituting a heat absorptive layer to the film thickness at which said layer is increasingly thicker from the outer to the inner periphery of a disk. CONSTITUTION:The heat absorptive layer 3 of the direct-read after-write type optical disk formed by providing a phase change layer 2 of which the optical characteristic is changed by heating and the heat absorptive layer 3 which has heat by absorbing light to writing light on a substrate 1 is constituted to the film thickness at which said layer is gradually thicker from the outer to the inner periphery of the disk. The heat capacity of the recording film increases and further, the heat radiation in the thickness direction of the film is improved to decrease the temp. elevation by the projection of reproduction light if the heat absorptive layer 3 is formed thick. The temp. of the substrate and recording film at the time of disk reproduction is, therefore, lower than in the case in which the heat absorptive layer is formed thin. The optical characteristics of the substrate and recording film are then no longer changed and the noise of the reproduction signal when the disk is reproduced is not increased. The high-quality reproduction is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a write-once optical disc that has a recording film consisting of a phase change layer and a heat absorption layer and is capable of recording and reproducing information, and is particularly suitable for obtaining high-quality reproduced information. The present invention relates to a film structure of a write-once optical disc.

[Conventional technology]

The conventional write-once optical disc is disclosed in Japanese Patent Application Laid-Open No. 57-159692.
As described in the publication, a phase change layer whose optical properties change when heated and a heat absorption layer which generates heat by absorbing writing light are provided on a substrate, and the thickness of each layer is , were the same on the entire inner and outer circumferences of the disc. However, when reproducing information written by rotating the disc at a constant angular velocity, the same location on the inner circumference must be held for a long time, e.g.
No consideration was given to the fact that after continuous playback for about 00 hours, noise occurs in the playback signal and the quality deteriorates.

[Problem that the invention seeks to solve]

An optical disc that is irradiated with playback light during playback has a heat absorption layer that absorbs the light, even though the amount of light is smaller than the write light, and when the same area is played back, if the playback time is long, humidity also increases. In particular, since the energy per unit area of the reproduction light is large at the inner circumference, the temperature becomes higher. As a result, the optical characteristics of the substrate and recording medium gradually change, and this effect also appears on the reflected playback light, causing noise in the playback signal and, for example, deteriorating the image quality of image information. There was a problem that occurred.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a write-once optical disc that can obtain high-quality reproduction information.

[Means for solving problems]

The above object is achieved by configuring the heat absorbing layer to be thicker from the outer circumference to the inner circumference of the disk.

[Effect]

When the thickness of the heat absorption layer is thick, the heat capacity of the recording film becomes large, and furthermore, heat dissipation in the direction of the thickness of the film is improved, so that the temperature rise due to irradiation with reproduction light is reduced. therefore,
The temperature of the substrate and recording film during disk playback is lower than when the heat absorption layer is thin, and the optical properties of the substrate and recording film do not change, and the noise of the playback signal increases when the disk is played. A high-quality playback signal can be obtained without any interference.

〔Example〕 The present invention will be explained in detail below.

(Embodiment) FIG. 1 shows an enlarged sectional view of a main part of a write-once optical disc according to the present invention. 5b40 atomic %, 5e60 atomic %, 5e60 A phase change layer 2 of atomic % is provided, and a heat absorption layer 3 of Bi is deposited thereon by vacuum evaporation.
In addition, a protective film, an adhesive film, etc. are provided (not shown). Here, the vacuum evaporation is performed at a vacuum degree of 1O-3Pa.
The evaporation source was a resistance heating method. Further, the thickness of the heat absorption layer 3 is set according to the condition of the straight line 4 shown in FIG. 2, and the thickness of the phase change layer 2 is also set to 32 nm on the inner circumference in advance so that the reflectance toward the substrate side is constant at 15%.

The outer circumference was gradually changed to 30 nm. This was easily achieved by providing a control plate for limiting the amount of evaporation between the evaporation source and the substrate and making it into an arbitrary shape.

In order to write a signal on the write-once optical disc according to the present invention obtained in this way, the disc is rotated at 180 rpm and a laser beam (wavelength 830 nm) is emitted for 8 m according to the signal.
This is done by blinking between w and Omw. Here, the heat absorption layer 3 generates heat due to laser irradiation of 8 mW, and this heat heats the phase change layer 2 to cause a phase change and change the optical characteristics. During reproduction, the disk is irradiated with a laser beam of 1 mW, which is weaker than the writing laser output, and the signal is reproduced based on the magnitude of the change in reflected light.

When the portion written in the above manner was continued to be reproduced, there was no change corresponding to noise in one reflected light even after 700 hours had elapsed. Moreover, the present invention.

Compared to conventional products, the film gets thicker towards the inner periphery, so
The writing laser power became more necessary toward the inner circumference, and writing was performed at 8 mW over the entire inner and outer circumferences. Therefore, in the present invention, there is no bending, such as holes in the film due to the laser energy ray density being too large, which occurs when writing at 8 mW on the inner periphery when the film thickness on the inner and outer peripheries is constant, as in the conventional case. The present invention also has the side effect that the circuit that changes the writing laser power according to the radius, which has been used as a countermeasure in the past, is completely unnecessary.

(Example 2) Next, the phase change layer of the above-mentioned example was
e45 atomic % and BiLO atomic %.

At this time, the thickness of the phase change layer is 30 nm on the inner circumference and 28 nm on the outer circumference.
m, and the heat absorption layer was formed of Bi in the same manner as in Example 1,
A constant reflectance of 15% was obtained over the entire surface.

As a result of the same long-time playback experiment as in Example 1, no noise was observed even after 700 hours or more, and a high-quality disc was obtained.

Here, in Examples 1 and 2, the thickness of the heat absorption layer had the same tendency, but as a result of the experiment, if the thickness exceeds the relationship of straight line 5 in FIG. No noise occurs over time, and performance without any practical problems can be obtained. Note that similar effects can be obtained if the phase change layer is made of a Se compound or Te compound, and the heat absorption layer is made of -Bi or a Bi compound. The substrate is not limited to acrylic resin, but may also be made of polycarbonate resin, vinyl chloride, or the like.

〔Effect of the invention〕

According to the present invention, even if the same part of a write-once optical disc is continuously reproduced for a long time (700 hours or more), no noise is generated in the reproduced signal, and it is effective in obtaining a high-quality reproduced signal.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a main part of a write-once optical disk according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the thickness of a heat absorbing layer and the radius of the disk according to the present invention. ■...Substrate, 2...Phase change layer, 3...Heat absorption layer.

Claims (1)

[Claims] 1. In write-once optical discs that have a phase change layer whose optical properties change when heated and a heat absorption layer that generates heat by absorbing writing light on the substrate, the film thickness of the heat absorption layer is 1. A write-once optical disc characterized by having a structure in which the thickness gradually increases from the outer circumference to the inner circumference.