JPS61145739A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain an optical disk that causes no level reduction of the signal output even in case the record is reproduced with the large DC power, by providing a transparent layer having a higher heat dispersion factor than a substrate only at a position under a recording layer at the inner circumferential side. CONSTITUTION:A transparent layer 4 which has a refractive index almost equal to that of a substrate 2 and a larger heat dispersion factor then the substrate 2 is provided only at a position under a recording layer 3 of an inner circumferential part. Therefore, the optical characteristics have no change according to the presence/absence of the layer 4. Thus the effect of the layer 4 is not given to the reproduction signal and the servo characteristics. While the rise of temperature of the recording layer 3 owing to irradiation of the laser light beam for reproduction can be reduced less than a case where no layer 4 exists, since the heat dispersion factor of the layer 4 is lager than that of the substrate. Thus the reproduction is possible with a laser light beam of the larger power than conventional. Thus the stable condensing servo is secured. It is desirable to set the layer 4 at the inner circumferential side centering on about half of the width of the layer 3. The material of the layer 4 can use various types of metallic oxides, metallic fluorides, metallic nitrides and metallic carbides.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the structure of an optical disk used in an optical disk storage device.

(Prior art and its problems) Optical disk storage devices record and reproduce information by irradiating a rotating disk with a laser beam. As shown in FIG. 2, a recording layer 3 is provided on one side of an acrylic resin substrate 2 with a guide groove having a center hole 1. Generally, a disk rotates at a constant angular velocity, so the linear velocity of the medium relative to the laser beam is smaller at the inner circumference of the disk than at the outer circumference of the disk. Therefore, the temperature rise due to laser beam absorption in the recording layer at the inner circumference is To reproduce a 7-optical disc that is larger than the outer periphery, the recording layer is focused and irradiated with a laser beam with a DC power so low that it cannot be recorded.

It detects the reflected light from there, but in order to perform stable focusing servo, it is desirable to irradiate a laser beam with as much power as possible.At that time, the 2-digit recording on the outer periphery is repeatedly reproduced. Although the signal output does not decrease at all, the signal output decreases when recording in the inner circumferential area is repeatedly reproduced, which is a problem.

That is, one object of the present invention is to provide an original disk in which the signal output does not decrease even when recording is reproduced with high DC power.

(Means for Solving the Problems) The present invention provides an optical disc in which a recording layer is provided on a substrate, and information is recorded and read using a laser beam. It is characterized by the provision of a layer with a high thermal diffusivity.

(Operation) The present invention solves the conventional problems by adopting the above-described configuration.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a sectional view for explaining the optical disc of the present invention. A transparent layer 4 having a refractive index almost equal to that of the substrate 2 and a thermal diffusivity higher than that of the substrate is provided only under the recording layer in the inner peripheral portion. Since it is transparent and has the same refractive index as the substrate, the optical characteristics do not change depending on the presence or absence of one layer 4, so there is no effect of layer 4 on the reproduced signal and servo characteristics.
on the other hand.

Since the thermal diffusivity of the layer 4 is greater than that of the substrate, the temperature increase in the recording layer due to the irradiation with the reproduction laser beam can be suppressed more than when the layer 4 is not provided.

Therefore, it becomes possible to perform reproduction with a laser beam of higher power than in the past, and it becomes possible to carry out stable focusing servo. Note that by inserting layer 4, the recording sensitivity at the inner circumference is lower than when there is no layer 4, but since the recording sensitivity at the outer circumference is lower than the recording sensitivity at the inner circumference when layer 4 is not included, layer 4 is inserted.
The six layers 4, which are advantageous because the recording sensitivities of the inner and outer peripheries become the same by insertion, are preferably placed on the inner periphery side from about half the width of the recording layer 3.

+14 materials include various metal oxides, metal fluorides,
Metal nitrides and metal carbides can be used.

(Example) An embodiment of the present invention will be described below.

Approximately 1000^ of SiO□ was deposited on an acrylic resin disk substrate with a guide groove having an inner diameter of 15 & 11I, an outer diameter of 1201m, and a thickness of 1.2u, in an area from llI52ml to d85m. At that time, the evaporation mask was separated from the disk substrate by approximately 5 μ, and the 0th-order evaporation mask was changed so that the film thickness gradually changed at the boundary of the Sin region.

5-amino-8-CP-ethoxyanilino)-2゜3-
An 825A thick organic thin film containing dicyano-1,4-naphthoquinone dye of 90eI11 or more was prepared from 554-m to 9111
4n area was coated.

The thus produced optical disc was irradiated with semiconductor laser light having a wavelength of 810 nm, condensed through the substrate by an optical system. Disk rotation speed of 1800 rpm, recording frequency 2.
9156111;11 at 4MHz, recording power 5mW
Good recording was possible over the entire area from k to 0112 m1. The reproducing power was Q, 33 mW, which was a large power, and the reproduced signal did not deteriorate even if it was repeatedly reproduced in the entire range from Ji1561m to 3211120. In addition, Si
1.O, since the maximum reproducing power was 0.63 mW when no film was applied. +The invention has resulted in an improvement of 32 inches.

(Effects of the Invention) As is clear from the above embodiments, according to the present invention, it is possible to obtain a source disk which can be reproduced with a large power and has good recording characteristics over the entire area.

[Brief explanation of drawings]

FIG. 1 shows the cross-sectional opening of an optical disk according to an embodiment of the present invention, and
The figure is a cross-sectional view of a conventional optical disc. In the figure, 1 is a central hole, 2 is a substrate, 3 is a recording layer, and 4 is a layer of a material that is transparent and has a higher thermal diffusivity than the substrate. Showa year month day 1. Indication of the case: Patent Application No. 268888, filed in 1982 2, Title of the invention: Optical disk 3, Person making the amendment Relationship to the case: Applicant: 5-33-1 Shiba, Minato-ku, Tokyo (423) Representative of NEC Corporation Tadahiro Sekimoto 4, Agent Sumitomo Sanda Building 5, 37-8 Shiba 5-chome, Minato-ku, Tokyo Contents of the amendment 1) In the 3rd line of page 5 of the specification Correct l'-mmJ to r, mJ.

Claims (1)

[Claims] An optical disc in which a recording layer is provided on the substrate, and information is recorded and read using a laser beam, characterized by the provision of a layer that is transparent and has a higher thermal diffusivity than the substrate only under the recording layer on the inner peripheral side. optical disc.