JPH06162588A - Substrate for optical disk and optical disk - Google Patents

Abstract

PURPOSE:To attain the higher sensitivity of the optical disk without impairing its durability by an increase in the laser energy density of only the surface of the recording layer without strongly heating a substrate and to enable recording, reproducing and erasing with incident light of the energy density lower than heretofore. CONSTITUTION:The section in the land parts of the substrate 1 of the optical disk is made into a structure having arc-shaped projecting parts, thereby, the refractive index of the layer between the substrate 1 and the recording layer 3 is made smaller than the refractive index of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc for recording / reproducing / erasing information by using optical means such as laser light.

[0002]

2. Description of the Related Art As optical disks, there are magneto-optical disks capable of erasing and writing data, in addition to read-only CDs. Due to their large capacity, high density and random access, their importance It is increasing year by year.

As a substrate for these optical discs, a plastic substrate such as polycarbonate having a guide groove is usually used. The structure has a flat surface,
The extent to which the shape of the guide groove is changed. Since such a substrate is made of plastic, it is unavoidable that it has heat resistance.

Therefore, it is preferable that the energy density of the laser used for the optical disk is small, but for recording, reproduction, erasing, etc., if the energy density of the laser is small, the irradiation time increases and the spread of heat increases. There is a problem that there is no.

In order to solve such a problem of thermal stability, it is necessary to reduce the thickness of the recording layer so that the medium has a four-layer structure, as in JP-A-2-40148. Has been done.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disc suitable for improving its sensitivity without affecting the substrate of the optical disc.

[0007]

In order to solve the above-mentioned problems, the present invention uses a substrate in which a land portion has an arcuate convex portion, and the refractive index of the layer between the substrate and the recording layer is smaller than that of the substrate. By doing so, an optical disk characterized by increasing the energy density of incident light on the recording film is provided.

That is, according to the present invention, since the land portion of the substrate has a convex lens shape, light passing through the inside of the substrate is refracted at the interface between the substrate and the dielectric layer and the like, and The light beam is condensed while passing through it, and has a smaller beam diameter on the recording layer than when it is incident, so that the density of the laser energy on the recording layer is substantially increased.

Therefore, even if the same recording system is used, the sensitivity of the optical disk is improved as compared with the conventional one. Further, even if a laser having a lower power than the conventional one is used, the same effect as the conventional one can be obtained, so that the power consumption can be reduced and the life of the laser can be extended.

[0010]

EXAMPLES Examples of the present invention will be specifically described below.

(Embodiment 1) FIG. 1 shows an example of a conventional magneto-optical disk. On the other hand, FIG. 2 shows a disk-shaped polycarbonate substrate 1 having a diameter of 3.5 inches and having a guide groove of 1.6 μm pitch, which is produced by an injection molding method so that the land portion is raised to a spherical shape according to the present invention. Refractive index 1.5
8) on top of which SiO is used as the dielectric layer 2 by sputtering.
₂ (refractive index 1.45), TbFeCo as the recording layer 3,
This is a magneto-optical disk in which thin films are laminated in the order of SiN _x as the dielectric layer 4 and Al as the reflective layer 5.

A CNR (Carrier to Noise Ratio) was measured by writing / reproducing / erasing a recording signal on a land portion of the disk using a laser having a wavelength of 830 nm.
The conventional sensitivity was 6mW, but improved to 3mW. FIG. 4 shows this.

(Embodiment 2) FIG. 3 shows 1.6 μm produced by an injection molding method so that the bottom of the groove is raised to a spherical shape.
A disk-shaped polycarbonate substrate 1 having m-pitch guide grooves is formed on the dielectric layer 2 by sputtering to form SiO ₂
This is a magneto-optical disk in which thin films are laminated in this order (refractive index 1.45), TbFeCo as the recording layer 3, SiN _x as the dielectric layer 4, and Al as the reflective layer 5.

When a recording signal was written / reproduced / erased in the groove portion of this disk using a laser having a wavelength of 830 nm, the conventional sensitivity was 6 mW.
Improved to 5mW.

[0015]

According to the optical disk of the present invention, by increasing the laser energy density only on the surface of the recording layer without strongly heating the substrate, the sensitivity of the medium is enhanced without impairing the durability. It is possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a conventional magneto-optical disk.

FIG. 2 is a schematic view showing an example of a sectional structure of a magneto-optical disk according to the present invention.

FIG. 3 is a schematic view showing an example of a sectional structure of a magneto-optical disk according to the present invention.

FIG. 4 is a comparison of CNR characteristics of the present invention shown in Examples and a conventional product.

[Explanation of symbols]

 1 substrate 2 dielectric layer 3 recording layer 4 dielectric layer 5 reflective layer

Claims (4)

[Claims] 1. A substrate for an optical disc having a convex portion having a circular arc cross section. 2. A substrate for an optical disk, wherein a bottom surface of the land portion or the groove portion has an arcuate cross section. 3. The optical disk substrate according to claim 1 or 2, wherein a layer made of at least a material having a refractive index lower than that of a material forming the substrate and a magnetic layer are laminated. optical disk. 4. The optical disk substrate according to claim 1 or 2, wherein a layer made of at least a material having a refractive index lower than that of a material forming the substrate and a reflective layer are laminated. optical disk.