JPH03216828A - Substrate of optical disk - Google Patents

Abstract

PURPOSE:To improve the C/N of reproduction signals by paralleling the parts of a substrate corresponding to the regions formed with the recording tracks where the recording and reproducing of information signals are executed with an incident surface of light and forming the surfaces between the adjacent parts thereof as the surfaces non-parallel with the incident surface of light. CONSTITUTION:The parts Z1 of the optical disk substrate BP corresponding to the regions formed with the recording tracks where the recording and reproducing of the information signals are executed are paralleled with the incident surface Fpi of light of the substrate BP. The incident reproducing light Lpf on this part is, therefore, progressed in the optical path toward a signal detecting optical system by reflection. On the other hand, the parts Z2 constituted between the adjacent parts Z1 of the optical substrate BP are formed as the surfaces non-parallel with the incident light Fpi of light. The incident reproducing light Lpf on the 2nd surface of the parts Z2 do not, therefore, progress toward the optical system for signal detection any more. The C/N of the reproduction signals is improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a substrate for an optical disc. (Prior Art) As the demand for recording various information signals at high recording densities has increased, in recent years there has been an increase in the demand for recording various information signals at high recording densities. Density recording and reproduction began to be performed. That is, for example, by irradiating the recording layer of an optical disc with a recording beam whose intensity is modulated by an information signal, an information signal is recorded by causing a physical or chemical change in the recording layer of the optical disc in accordance with the information signal. An optical disc that has two or more stable structural states with different optical and/or electrical properties (light transmittance, reflectance, absorption rate, electrical resistance, and other properties), and has A film of a material (inorganic material, organic material) that undergoes a transition between the above-mentioned stable structural states upon application of optical, electrical, or thermal energy is applied to a substrate by vapor deposition or sputtering. Regarding optical discs belonging to the phase change type that are used for the recording layer, 1.
In addition to optical discs that can be added once by the user (write-once optical discs) and erasable optical discs, research and development are being actively conducted to put them into practical use in office file memories and other uses. It is well known that a variety of types have been proposed, which can be broadly categorized as magnetic type, bit forming type, bubble or uneven forming type, etc. In recent years, with the increasing demand for higher C/N of optical discs, improvements have been made in the performance of the recording material itself for optical discs, such as intensity modulation using high-frequency signals of laser beams for reproduction, and differential detection methods. The applied signal reproduction method, various improvement measures for the reproduction system such as improving the performance of optical parts, plastic substrates with compensating composition to obtain low birefringence for optical disk substrates, and problems with surface roughness and warping. Various methods have been proposed to solve this problem. (Problem to be Solved by the Invention) By the way, when performing high-density recording of information signals on an optical disc, a small diameter whose intensity is modulated by the information signal to be recorded is recorded on the recording film of the optical disc during recording. The optical spot of the optical disc is imaged to form a recording trace with a predetermined recording trace width, and when reproducing information signals from an optical disc on which information signals are recorded at high density, the optical disc's recording A spot of light with a minute diameter is focused on the trace, and the reflected light (or transmitted light) from the optical disc is detected.
is applied to the photodetector so that an electrical signal corresponding to the information signal recorded on the optical disk can be obtained from the photodetector, and a reproduced signal with a good C/N ratio can be obtained during reproduction. In order to achieve this, it is necessary to focus a light spot with a diameter corresponding to the recording trace width onto the recording trace of the optical disc. However, the intensity distribution of the light spot focused on the recording trace of the optical disk is a Gaussian distribution, and the light intensity decreases at the outer periphery. The reflected light from the optical disk due to the portion where the intensity is reduced will reduce the C/N. FIG. 3(a) is a partially enlarged plan view of the optical disc, and FIG. 3(b) is a partially enlarged longitudinal sectional side view of the optical disc. In addition, LPfl indicates the center portion of the laser beam irradiating the pit portion, and LPf2 indicates the outer peripheral portion of the laser beam protruding from the pit portion. The light intensity at the center is extremely weak compared to the light intensity at the center, and the light reflected from this area deteriorates the C/N. (Means for Solving the Problems) The present invention uses a portion of the substrate of the optical disk that corresponds to a recording trace forming area where information signals are recorded and reproduced as a first portion, and the above-described first portion of the substrate of the optical disk is When the part between adjacent parts of the optical disc is defined as a second part, the first part on the substrate of the optical disc is a plane parallel to the light incident plane, and An optical disc substrate is provided in which a second portion has a surface non-parallel to a light incident surface. (Function) The part of the substrate of the optical disc that corresponds to the recording trace formation area where information signals are recorded and reproduced on the optical disc is
This is the first part of the substrate of the optical disc that is parallel to the light incident surface, and the reproduction light incident on this part is reflected and travels to the optical path toward the signal detection optical system. The second portion formed between adjacent first portions is a surface that is non-parallel to the light incident plane, so this second portion is formed between adjacent first portions.
The reproduced light incident on the surface is prevented from traveling toward the optical system for signal detection, thereby improving the C/N of the reproduced signal. (Example) Hereinafter, the specific contents of the substrate of the optical disk of the present invention will be explained in detail with reference to the accompanying drawings. Figure 2 is a supplementary diagram for explaining the outline of the optical disc manufacturing process, and Figure 3 is a diagram for explaining problems. In (.) to (C) of FIG. 1 showing longitudinal cross-sectional side views of different embodiments of the substrate of the optical disk of the present invention. B.P.
is the substrate of the optical disk, and in (a) of Fig. 1, L
is a condensing lens. This condensing lens L is a laser beam L
Optical disc substrate BP in an optical disc by focusing p
The light enters the optical disk from the incident plane Fpi side. The focused light Lfp that has entered the optical disc from the entrance surface Fpi of the substrate BP of the optical disc is attached to the surface of the substrate BP of the optical disc shown in FIG. 1 on the opposite side to the entrance surface Fpi. The image is formed as a minute spot of light on the recording film layer (not shown). In the figure, 21 is the light incident surface F of the substrate BP of the optical disc.
z2 is the first portion formed on the substrate BP of the optical disk as a surface parallel to pi, and z2 is the first portion formed on the substrate BP of the optical disk as a surface non-parallel to the light incident plane Fpi of the substrate BP of the optical disk. This is the second part configured adjacent to part z1 of 1. The first portion Z1 in the substrate BP of the optical disc described above
is a portion corresponding to a recording trace formation area in the recording film layer where information signals are recorded and reproduced in the optical disk, and z2 is a portion between adjacent first portions Zl on the substrate of the optical disk. This is the part. First, in the substrate BP of the optical disc of the present invention shown in FIG. 1(a), the second portion Z2,
By configuring Z2... to have a finely uneven surface shape, the second portions Z2, Z2... are made to be surfaces that are non-parallel to the light incidence plane Fpi, and , in the optical disc substrate BP of the present invention shown in FIG. 1(b), the second portions Z2, Z
2... is configured as a curved surface, the second portions Z2, Z2... are made into surfaces that are non-parallel to the light incident plane Fpi, and furthermore, as shown in FIG. The substrate BP of the optical disc of the present invention shown in (c) of
In the above, the second portions Z2, Z2... are assumed to have an inclined surface shape, and the second portions Z2, Z2...
・ is a surface that is non-parallel to the light incidence plane Fpi. As described above, in the substrate BP of the optical disk of the present invention, the first portion Z1 of the substrate BP of the optical disk that corresponds to the formation area of the recording trace in the recording film layer where information signals are recorded and reproduced in the optical disk. Since the portion between the objects, that is, the second portion Z2 described above, is a surface that is non-parallel to the light incidence plane Fpi, the convergent light Lpf condensed by the condenser lens L is small. When the recording film layer is irradiated with a light spot of diameter,
In a state where the part Lpfl with high light intensity at the center is correctly positioned on the recording trace and illuminates the first part z1, the part Lpf2 with low light intensity on the outer circumferential side of the light spot The second portion Z2 is irradiated, and the reflected light from the second portion Z2 is prevented from returning to the condenser lens L. Therefore, in the optical disc equipped with the optical disc substrate according to the present invention, the C/N can be greatly increased since the light reflected by the outer peripheral portion of the reproducing light beam irradiated onto the optical disc during the reproducing operation can be prevented from contributing to the reproduced signal. It is possible to improve this. Next, with reference to FIG. 2, a description will be given of how the optical disc substrate BP shown in FIGS. 1(a) to 1(c) can be manufactured. FIG. 2(a) shows the glass master disk 1, and FIG. 2(b) shows the glass master disk 1 with a photoresist layer 2 formed on the mirror-polished surface. (.) to (f) in Fig. 2 show that the photoresist layer 2 formed on the glass master 1 as shown in Fig. 2 (b) described above is exposed in a predetermined pattern. Later, photoresist patterns 2a to 2 obtained by development
d is the photoresist layer 2 formed on the glass master 1
This example shows how the exposure conditions for the photoresist layer and the development conditions for the exposed photoresist layer can be varied. Note that (a) to (f) in FIG. 2 all show longitudinal side views. (Q) in Fig. 2 shows that, for example, when manufacturing an optical disc substrate with a tracking guide groove, a predetermined pattern corresponding to the tracking guide groove can be obtained by using appropriate exposure conditions and appropriate development conditions. The state in which the photoresist pattern 2a of the pattern is formed is illustrated for reference, and (d) to (f) in FIG. 2 are similar to those in (c) in FIG. 2 described above. Photoresist pattern 2
By performing exposure and development under different exposure and development conditions (over-exposure, under-exposure, under-development) from those applied to obtain (a) to (a) in Figure 1.
The second on the substrate BP of the disk shown in (C)
Photoresist pattern 2 corresponding to part z2 of
b to 2d are obtained. In addition, by using a plurality of laser beams (for example, two beams) during the exposure described above and adjusting the intensity distribution of the plurality of laser beams, the results shown in (a) to (C) of FIG. 1 can be obtained. The first part Zl and the second part Z on the substrate BP of the disk
It is also possible to obtain a photoresist pattern corresponding to 2. A conductive treatment was applied to the surface on which the photoresist patterns of the glass master disc on which the photoresist patterns 2b to 2f as illustrated in (d) to (f) of FIG. 2 are formed were formed. Afterwards, for example, nickel plating and electroforming are performed in sequence, and then peeled off to create a mother plate.
After plating and electroforming the base plate, it is peeled off from the base plate to obtain a stanbar, and the stanbar is used to form a polymer material as shown in (a) to (Q) in Figure 1. It is possible to manufacture a substrate BP for a disk like this. Note that a recording film layer, a reflective film, and a protective film are laminated on the surface of the substrate BP of the optical disc shown in FIGS. 1(a) to (c) on the side opposite to the light incident surface Fpi. It is well known that optical discs can be obtained by The explanations of the embodiments so far have been about optical discs in which laser light that has passed through a transparent substrate is applied to the recording film layer, but the present invention relates to recording light that does not pass through a transparent substrate or Of course, the present invention may also be applied to an optical disc in which the reproduction light is applied to the recording film layer. (Effects of the Invention) As is clear from the above detailed explanation, the present invention includes a first portion of the substrate of the optical disk that corresponds to a recording trace formation area where information signals are recorded and reproduced; When the portion between the adjacent first portions of the substrate of the optical disk is defined as the second portion, the first portion of the substrate of the optical disk is defined as a plane parallel to the plane of incidence of light. and an optical disc substrate in which the second portion of the optical disc substrate is a surface non-parallel to the light incident plane, and the optical disc has a recording trace forming area where information signals are recorded and reproduced. The corresponding part of the substrate of the optical disk is the first part parallel to the light incident surface of the substrate of the optical disk, and the reproduced light incident on this part is reflected onto the optical path toward the signal detection optical system. However, since the second portion formed between the adjacent first portions on the substrate of the optical disk is a surface that is non-parallel to the plane of incidence of the light, this The reproduced light incident on the second surface is prevented from traveling toward the optical system for signal detection, thereby improving the C/N of the reproduced signal. According to the present invention, the C/N of the reproduced signal is improved. The problem is solved well.

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) are longitudinal sectional side views of different embodiments of the optical disk substrate of the present invention, and FIGS. 2(a) to (c) are
f) is a diagram for explaining the outline of the manufacturing process of an optical disc, and FIGS. 3(a) and 3(b) are diagrams for explaining problems. BP... Optical disk substrate, L... Condensing lens, L
p...Laser luminous flux, Lpf...Focused light, Fpi...
・Incidence surface of the optical disc substrate BP in the optical disc,
Z1: A first portion configured on the optical disc substrate BP as a plane parallel to the light incidence plane Fpi of the optical disc substrate BP, Z2: Non-parallel to the light incidence plane Fpi of the optical disc substrate BP As a surface, the second portion 1, which is configured adjacent to the first portion 21 described above on the substrate BP of the optical disc, includes a glass master disk, 2 a photoresist, and 28 to 2d a photoresist. pattern, D
... optical disc, P... bit}-Lpfl... center portion of the laser beam irradiated on the bit portion, L
pf2...the outer peripheral part of the laser beam that protrudes from the bit part,

Claims (1)

[Claims] The part of the substrate of the optical disc corresponding to the recording trace formation area where information signals are recorded and reproduced on the optical disc is defined as a first part, and the first part of the substrate of the optical disc is
When the part between adjacent parts of the optical disc is defined as a second part, the first part in the substrate of the optical disc is a plane parallel to the light incident plane, and the part in the substrate of the optical disc is An optical disk substrate in which the second portion of the substrate is a surface non-parallel to the light incident surface.