Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-08-31
2001-05-01
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
Reexamination Certificate
active
06226251
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 97-43069, filed Aug. 29, 1998, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a signal detection method of a phase-change optical disk, and more particularly, to a signal detection method of a phase-change optical disk which can greatly improve a degree of modulation of a reproduction signal and enhance reliability of the reproduction signal.
Generally, a laser beam is irradiated on an optical disk in order to reproduce an information signal recorded on a phase-change optical disk. An angle of reflection with respect to the beam irradiated on the optical disk is varied due to a difference of the complex refractive index of each phase by a phase-change between a crystal state and an amorphous material formed on a recording layer of the optical disk. An optical pickup which is used in conjunction with a phase-change optical disk is designed to convert light which reaches a light receiving element (of the optical pickup) into an electric signal and to reproduce a recorded information signal, using an optical characteristic of a recording layer of the phase-change optical disk.
An operation of optical pickup with respect to a general phase-change optical disk is described with reference to
FIG. 1. A
semiconductor laser
1
emits a laser beam. A collimation lens
2
collimates the laser beam emitted from the semiconductor laser
1
in the form of a parallel light beam. The laser beam emitted in the form of the parallel light beam by the collimation lens
2
is incident to a quarter-wave plate
4
via a beam splitter
3
. The beam incident to the quarter-wave plate
4
is in a plane-polarized state, and is converted into a circularly polarized beam by the quarter-wave plate
4
. The circularly polarized beam is incident to an objective lens
5
, and the objective lens
5
focuses the incident beam on an information recording surface of an optical disk
7
. A beam reflected from the information recording surface of the optical disk
7
is incident to the quarter-wave plate
4
via the objective lens
5
. The quarter-wave plate
4
converts the reflected beam into a plane-polarized beam to emit the plane-polarized beam, and a polarized plane of the emitted beam is rotated by 90° with respect to the incident beam. The beam emitted from the quarter-wave plate
4
is reflected from the beam splitter
3
and is incident to a photodetector
6
. The photodetector
6
receives the light reflected from the beam splitter
3
and converts the received light into an electric signal.
A construction of the photodetector
6
is shown in detail with reference to
FIG. 2. A
general photodetector
6
is composed of four-divided light receiving regions
6
a
,
6
b
,
6
c
and
6
d.
That is, the reflected light from the optical disk is incident to the four light receiving regions
6
a
,
6
b
,
6
c
and
6
d
of the photodetector
6
. When light quantities of the reflected light which reach the respective four light receiving regions
6
a
,
6
b
,
6
c
and
6
d
are called I
1
, I
2
, I
3
and I
4
, respectively, the total of the light quantities of the reflected light which reaches the respective light receiving regions
6
a
,
6
b
,
6
c
and
6
d,
which is I
1
+I
2
+I
3
+I
4
, is detected as a reproduction signal.
FIG. 3
is an enlarged view showing an arrangement of a track
8
and marks
9
of a phase-change optical disk, and particularly shows the arrangement of the marks
9
on the track
8
when a signal is recorded on the phase-change optical disk by mark length recording.
However, in the case of detecting information recorded by the mark length recording using the above signal detection method, a difference in amplitude between a signal having a longer mark and a signal having a shorter mark in the reproduced signal becomes large, and thus there is high probability that an error occurs in reproducing a signal. Practically, when detecting a signal by the above method, it has been known that a degree of modulation in the reproduced signal is about 30%.
FIG. 4
shows a waveform diagram of a reproduction signal detected by a general method, which shows a low modulation degree.
FIGS. 5A
,
5
B and
5
C are views schematically showing states that laser beams are located at a front portion, an intermediate portion and a rear portion of the mark
9
, respectively, and
FIGS. 6A
,
6
B and
6
C are views showing distribution of light quantities corresponding to the states when the laser beam is respectively positioned as shown in FIGS.
5
A,
5
B and
5
C.
FIGS. 6A and 6C
show that the laser beam is out of the center of the mark, and it can be seen that the distribution of light quantities is asymmetrical from the right and left. This phenomenon causes a problem to lessen reliability of a reproduction signal. Particularly, such a problem is remarkably severe when a signal is detected from an optical disk recorded with a high density, i.e., an optical disk having a narrow interval between marks.
SUMMARY OF THE INVENTION
In order to solve the above problems, an object of the present invention is to provide a signal detection method of a phase-change optical disk which can greatly improve a degree of modulation of a reproduction signal and enhance reliability of the reproduction signal.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To accomplish the above and other objects and advantages of the present invention, there is provided a method for detecting a reproduction signal from an optical disk using an optical pickup having a photodetector which includes a plurality of light receiving regions, the method comprising the steps of (a) allowing light reflected from the optical disk to be incident to the plurality of light receiving regions of the photodetector; and (b) detecting, as a reproduction signal, a difference between light quantities of light incident to the light receiving regions which are located forward from an optical axis of the optical pickup along a tracking direction of the optical pickup and those of light incident to the light receiving regions which are located backward from the optical axis of the optical pickup along the tracking direction of the optical pickup, among the plurality of light receiving regions of the photodetector in step (a). The light quantities of each of the light receiving regions forward from the optical axis of the optical pickup along the tracking direction of the optical pickup are summed to determine a first sum and the light quantities of each of the light receiving regions backward from the optical axis of the optical pickup along the tracking direction of the optical pickup are summed to determine the second sum. The reproduction signal is determined to be the difference of the first and second sums.
REFERENCES:
patent: 5682372 (1997-10-01), Yamakawa et al.
patent: 7-14170 (1995-01-01), None
patent: 8-96368 (1996-04-01), None
patent: 8-147708 (1996-06-01), None
Huber Paul W.
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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