Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-02-09
2004-03-02
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S094000, C369S283000
Reexamination Certificate
active
06700845
ABSTRACT:
TECHNICAL FIELD
This invention relates to an optical disc and an optical disc reproducing device which uses this optical disc, and particularly to an optical disc which has a plurality of recording layers and an optical disc reproducing device which uses this optical disc.
BACKGROUND ART
Conventionally, as a recording medium for various types of information such as audio information and video information, there has been broadly used an optical disc such that information recorded thereon is reproduced using a laser beam. For this type of optical disc, an optical disc having multiple recording layers has been proposed in order to realize further increase in the quantity of information that can be recorded.
As an optical disc having multiple recording layers, there has been proposed an optical disc as described in the Japanese Publication of Unexamined Patent Application No. Hei 8-235641.
In the optical disc
1
described in this publication, a first recording carrier
4
a
constituted by forming a first recording layer
3
a
on one side of an optically transparent first substrate
2
a
and a second recording carrier
4
b
constituted by forming a second recording layer
3
b
on one side of an optically transparent second substrate
2
b
are arranged in such a manner that the sides where the first and second recording layers
3
a
and
3
b
are formned face each other, and these first and second recording carriers
4
a
and
4
b
are joined with each other via an optically transparent adhesive layer
5
, as shown in FIG.
1
.
On the side where the first and second recording layers
3
a
and
3
b
are formed, of the first and second substrates
2
a
and
2
b
constituting the first and second recording carriers
4
a
and
4
b
, information such as video information is recorded in the form of pit patterns
6
a
and
6
b
made of minute recesses and protrusions. On the pit pattern
6
a
provided on the first recording carrier
4
a
, the first recording layer
3
a
is formed by depositing a semitransparent film of SiO, SiO
2
or the like along the pit pattern
6
a
by evaporation or sputtering. The first recording layer
3
a
has a reflectance of 20 to 50% and an optical transmittance of 30 to 80%. On the pit pattern
6
b
provided on the second recording carrier
4
b
, the second recording layer
3
b
is formed by depositing an aluminum evaporation film along the pit pattern
6
b
. The second recording layer
3
b
has a reflectance of 60% or higher, but the reflectance of a laser beam transmitted through the first recording layer
3
a
and reflected by the second recording layer
3
b
is 20 to 50%.
With such an optical disc
1
having the first recording layer
3
a
which is optically semitransparent, information recorded on the second recording layer
3
b
can be reproduced by casting a laser beam L
2
from the same direction as the direction of casting a laser beam L
1
to the first recording layer
3
a
, as shown in FIG.
1
. In this case, selection of either the information recorded on the first recording layer
3
a
or the information recorded on the second recording layer
3
b
is carried out by changing the focal positions of the laser beams L
1
and L
2
cast onto the optical disc
1
.
As another optical disc having multiple recording layers, an optical disc as shown in
FIG. 2
has been proposed. In this optical disc
11
, a first recording carrier
14
a
constituted by forming a first recording layer
13
a
on one side of an optically transparent first substrate
12
a
and a second recording carrier
14
b
constituted by forming a second recording layer
13
b
on one side of an optically transparent second substrate
12
b
are joined with an adhesive layer
15
made of an optically transparent ultraviolet-cured resin or the like, as shown in FIG.
2
. The first and second recording layers
14
a
and
14
b
are joined in parallel in such a manner that the second substrate
12
b
is located on the first recording layer
13
a
. On the second recording layer
13
b
, a protection layer
17
for protecting the second recording layer
13
b
is provided.
On the sides where the first and second recording layers
13
a
and
13
b
are formed, of the first and second substrates
12
a
and
12
b
constituting the first and second recording carriers
14
a
and
14
b
, information such as audio information is recorded in the form of pit patterns
16
a
and
16
b
made of minute recesses and protrusions. On the pit pattern
16
a
provided on the first recording carrier
14
a
, the first recording layer
13
a
having wavelength selectivity is formed along the pit pattern
16
a
. The first recording layer
13
a
is formed, for example, as a five-layer film made up of Si
3
N
4
, SiO
2
, Si
3
N
4
, SiO
2
, and Si
3
N
4
. The first recording layer
13
a
has a reflectance of approximately 34% for a laser bean with a wavelength of 635 nm, and has a reflectance of approximately zero for a laser beam with a wavelength of 780 nm and thus substantially transmits this laser beam.
On the pit pattern
16
b
provided on the second recording carrier
14
b
, the second recording layer
13
b
is formed by depositing an aluminum evaporation film with a high reflectance along the pit pattern
16
b
. The second recording layer
13
b
has a reflectance of 80% or higher for the laser beam transmitted through the first recording layer
13
a
. The second recording layer
13
b
has a reflectance of 84% or higher for the laser beam with a wavelength 780 nm, which is substantially transmitted through the first recording layer
13
a
, and has a reflectance of approximately 38% for the laser beam with a wavelength of 635 nm, which is reflected approximately 34% through the first recording layer
13
a.
In the optical disc
11
thus constituted, information recorded on the first and second recording layers
13
a
and
13
b
is reproduced by casting a laser beam from the side of the substrate
12
a
of the first recording carrier
14
a
. In this case, if a laser beam L
3
with a wavelength of 780 nm is used as a laser beam for reading the information, this laser beam is transmitted through the first recording layer
13
a
and cast onto the second recording layer
13
b
, and a return laser beam reflected from the second recording layer
13
b
is obtained. By detecting this return laser beam, the information such as audio information recorded on the second recording layer
13
b
is read and reproduced. The laser beam L
3
with a wavelength of 780 nm is what is used for reproduction of an optical disc using a reproduction-type optical disc with a diameter of 12 cm, that is, a so-called compact disc, as a recording medium. Therefore, the information recorded on the second recording layer
13
b
can also be reproduced by a general-purpose optical disc reproducing device.
If a laser beam L
4
with a wavelength of 635 nm is cast from the side of the substrate
12
a
of the first recording carrier
14
a
, a return laser beam reflected from the first recording layer
13
a
and the second recording layer
13
b
can be obtained. Specifically, since the first recording layer
13
a
has a reflectance of approximately 34% for the laser beam with a wavelength of 635 nm, this laser beam is transmitted through the first recording layer
13
a
and becomes incident on the second recording layer
13
b
, and a return laser beam reflected from the second recording layer
13
b
is obtained. The reflectance for the laser from the second recording layer
13
b
in this case is approximately 34%.
In this optical disc
11
, by using the laser beam L
4
with a wavelength of 635 nm and setting the focal position of the laser beam L
4
on the first or second recording layer
13
a
or
13
b
, the information recorded on the first or second recording layer
13
a
or
13
b
can be reproduced.
In the optical disc
1
shown in
FIG. 1
in which the first and second recording carriers
4
a
and
4
b
are joined in such a manner that the sides having the first and second recording layers
3
a
and
3
b
formed thereon face each other, reproduction of the
Ihashi Takao
Inokuchi Tatsuya
Ogawa Hiroshi
Sako Yoichiro
Yamamoto Masanobu
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