Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1997-12-10
2001-08-21
Huber, Paul W. (Department: 2753)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S047360, C369S116000
Reexamination Certificate
active
06278674
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an initializing apparatus for initializing a state of a recording layer of a phase change optical disk (hereinafter referred to as an “optical disk”).
2. Description of the Related Art
A first prior art device will be described below with reference to FIGS.
5
(
a
) and
5
(
b
).
In the first prior art device, laser light L is emitted from a gain waveguide type high output semiconductor laser
50
. The laser light L is focused on an optical disk D through a collimator lens
52
and an objective lens
54
. In cases where the objective lens
54
has a NA (numerical aperture) of 0.5, the size of the spot S
10
on the optical disk D is 1×50 &mgr;m
2
at the half-width of the beam intensity distribution. The initialization of a recording layer of the optical disk is accomplished by crystallization of the whole region in the spot S
10
of the recording layer, irradiated by the erasing laser light from the laser
50
driven by a DC (direct current) signal (referred to as a “DC drive” below) to emit at a constant output.
A second prior art device will be described below with reference to FIGS.
6
(
a
)-
6
(
d
).
The second prior art device is disclosed in Japanese Patent Application Laid-open No. Hei 4-278224. Unlike the first prior art device, a pulsed output of the laser light is used for initialization in this case, and a broad area is initialized with the same spot size of the laser light.
FIG.
6
(
a
) shows a condition of the recording layer irradiated with laser light driven by a one-shot drive pulse. A melting amorphous portion S
11
is the region where the recording layer melts during the one-shot pulse laser drive and is rendered amorphous after cooling, and a melting re-crystallization ring S
12
is the region where the recording layer melts during the one-shot pulse laser drive and crystallizes after cooling.
By making the output of the laser stronger than in the case of the first prior art device, a spot periphery S
12
in a crystalline state has a large outer diameter. But the light quantity of the center portion S
11
of the spot exceeds a threshold level for forming an amorphous state and a center portion S
11
of the spot is rendered amorphous. The laser is repeatedly driven by switching by pulse signals having a low duty ratio (referred to as a “pulse drive” below) with the cycle time corresponding to the width of crystallined portions as shown in FIG.
6
(
c
) so that a crystalline portion of the spot periphery S
12
for each pulse is linked with that produced by the next pulse as shown in FIG.
6
(
b
). By repeating this pulse drive, the whole recording layer is crystallized as shown in FIG.
6
(
d
)
However, the above-described prior art has the following disadvantages:
1. When an initialization is performed by driving a laser light source in a DC drive as in the first prior art device, a noise (media noise) is considerably caused due to the recording medium. Thus, a sufficient S/N ratio cannot be obtained, thereby resulting in the deterioration of a bit error rate.
2. When the initialization is performed by a pulse drive as in the second prior art device, the sizes of the melting re-crystallization ring portions vary. This also causes media noise.
3. A track address, which is partially recorded on an optical disk, is also undesirably initialized.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical disk initializing apparatus which can reduce the media noise in an initialization and can obtain excellent recording/reproducing characteristics without the initialization of a track address.
An initializing apparatus of the present invention comprises a laser light source for emitting an erasing laser light for initializing an optical disk, a laser drive circuit for driving the laser light source so as to vary the output of the light source according to an AC signal, and an optical system for irradiating the optical disk with the erasing laser light emitted from the laser light source.
The laser light source for initializing an optical disk is driven so as to vary the output according to an AC signal (referred to as an “AC drive” below), not by a DC drive and not by a pulse drive. Since the laser light source is driven by an AC drive, media noise is more reduced than in the prior art. This has been experimentally confirmed by the inventor.
Also in the initializing apparatus of the present invention, the laser light source, the laser drive circuit and the optical system are adjusted so that an amorphous portion having a size of ½ or less of a wavelength of the erasing laser light may be formed at the inside of a re-crystallization portion.
Thus, the media noise is more considerably reduced. This has also been experimentally confirmed by the inventor.
Further, the initializing apparatus of the present invention comprises track address detecting means for detecting a track address. The laser drive circuit drives the laser light source so as to stop the irradiation of portions where the track address is detected by the track address detecting means.
Since the irradiation of the optical disk is stopped when a track address is detected by the track address detecting means, the track address is not erased.
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patent: 5130971 (1992-07-01), Ohno et al.
patent: 5272667 (1993-12-01), Yamada et al.
patent: 5383172 (1995-01-01), Holtslag et al.
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patent: 5745463 (1998-04-01), Maegawa et al.
patent: 5761179 (1998-06-01), Iwasaki et al.
patent: 5784355 (1998-07-01), Abe
patent: 5848043 (1998-12-01), Takada et al.
patent: 61-13453 (1986-01-01), None
patent: 61-206938 (1986-09-01), None
patent: 3-272022 (1991-12-01), None
patent: 4-125829 (1992-04-01), None
patent: 4-103029 (1992-04-01), None
patent: 4-102227 (1992-04-01), None
patent: 4-278224 (1992-10-01), None
patent: 6-168446 (1994-06-01), None
patent: 7-161038 (1995-06-01), None
patent: 7-192266 (1995-07-01), None
Araki Shigeru
Fujimura Yuki
Matsui Tsutomu
Huber Paul W.
NEC Corporation
Young & Thompson
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