Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal processing for controlling recording light...
Reexamination Certificate
2000-03-23
2003-02-04
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal processing for controlling recording light...
Reexamination Certificate
active
06515953
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to processing steps of a master optical disc, and particularly to a processing method of a master optical disc, a stamper processed thereby, optical discs formed and manufactured with the stamper, and a processing method of grooves.
DESCRIPTION OF THE RELATED ART
An optical disc is generally prepared by transcribing a concave/convex pattern by the injection-molding method etc. using a stamper provided with such concave/convex pattern as tracking guides (grooves) and pits. The method conventionally adopted as a means to model a concave/convex pattern of such stamper is exposing and recording a laser beam onto a master disc coated with photosensitive material. To the photosensitive material sensitized by the above exposure, a concave/convex pattern is formed by development and a stamper is thereby prepared by plating the surface thereof such that the concave/convex pattern is transcribed onto the metal surface.
FIG. 6
shows an optical path indicating a conventional processing method of a master optical disc. A laser beam
102
emitted from a laser device
101
is subjected to intensity modulation at an acousto-optical modulator
104
while reflecting at the mirrors
103
,
105
and
107
and entering an objective lens
108
. The modulating signal to be input to the acousto-optical modulator
104
is an input signal
601
turning on/off in accordance with the existence of a pit. The laser beam
102
transmitted through the objective lens
108
is converged at a master disc
109
coated with the photosensitive material and forms a spot
111
on the surface thereof. As a moving optical stand
106
provided with the objective lens
108
and mirror
107
gradually moves at a certain speed in the radial-direction of the master disc
109
, the master disc
109
is loaded on a turntable
110
and turns simultaneously therewith. A spiral pit
112
is thus recorded on the master disc
109
.
Regarding the shape of the pit
112
, a short pit tends to be narrow and a long pit tends to be wide due to the interference of beams before and after the recording of the pit
112
. Therefront, suggested are the method of recording compensation for changing the quantity of light in proportion to the pit length or the method of recording a long pit with intermittent beams as disclosed in Japanese Patent Laid-Open Publication No. HEI10-177722.
In case of employing the conventional method above to form a pit, recording with an input signal
501
as shown in
FIG. 5
causes a problem in that the center portion
503
of a pit becomes wider than the front and rear edges
502
(hereinafter simply referred to as the ‘edges’) of a pit due to the interference of beams and the characteristics of the resist. Unevenness in the width of a pit will cause adverse effects to the jitter and the modulation degree of a reproduced signal, and it will also lower the reading accuracy. Furthermore, the angle of the edge walls
504
of the pit becomes obtuse, and causes further aggravation of the jitter.
SUMMARY OF THE INVENTION
The present invention provides a processing method of a master optical disc by converging and exposing a laser beam to the master disc coated with photosensitive material, comprising an exposure method for forming one pit by exposing a laser beam composed of a plurality of pulse arrays with said laser beam being an intermittent beam, wherein the pulse length corresponding to the front edge of the pit and/or the pulse length corresponding to the rear edge of the pit is longer than the pulse length corresponding to the center portion of the pit. This processing method corrects the differences in width between the edges and the center portion of a pit, and it also makes the angle of the edges more acute. Therefore, it is possible to process a master optical disc having a fine jitter, a fine modulating degree and consequently fine reading accuracy.
The present invention provides a processing method of a master optical disc, wherein the pulse interval behind the pulse corresponding to the front edge of the pit and/or the pulse interval in front of the pulse corresponding to the rear edge of the pit is longer than the other pulse intervals of the pit. This processing method makes the angle of the edge walls
504
of a pit more acute and makes it possible to produce pits of a uniform width and further to operate a processing method of a master optical disc having a fine jitter.
Furthermore, the present invention provides a stamper manufactured by the aforementioned processing method. The present invention also provides optical discs manufactured using such stamper.
The present invention provides a processing method for forming grooves of a certain pattern by converging and exposing a laser beam to a master disc coated with photosensitive material, comprising a step for forming one groove by exposing a laser formed of a plurality of pulse arrays with said laser beam being an intermittent beam, wherein the pulse length corresponding to the front edge of one groove and/or the pulse length corresponding to the rear edge of said groove is longer than the pulse length corresponding to the center portion of said groove. This processing method corrects the differences in width between the edges and the center portion of a groove and also makes the angle at the edges more acute, and therefore it is possible to form grooves of high accuracy.
Furthermore, the present invention provides a processing method, wherein the pulse interval behind the pulse corresponding to the front edge of the groove and/or the pulse interval in front of the pulse corresponding to the rear edge of said groove is longer than the pulse interval of the center portion of said groove. This processing method makes the angle of the edge walls of the grooves more acute, and therefore it possible to form grooves of a uniform width and high accuracy.
REFERENCES:
patent: 5109373 (1992-04-01), Ohno et al.
patent: 5327411 (1994-07-01), Iwasa et al.
patent: 5469422 (1995-11-01), Sohmuta
patent: 5490126 (1996-02-01), Furumiya et al.
patent: 5991252 (1999-11-01), Kimura et al.
patent: 06-302042 (1994-10-01), None
patent: 09-190656 (1997-07-01), None
patent: 10-177722 (1998-06-01), None
Furihata Hidemichi
Miyamae Akira
Yamada Hideaki
Harness & Dickey & Pierce P.L.C.
Hindi Nabil
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