Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-02-27
2004-05-04
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053220, C369S094000
Reexamination Certificate
active
06731578
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical disc recording and/or playback apparatus and method, for playback of information signal recorded in an optical disc having a plurality of recording layers or data layers, and also to a focus servo controller and focus servo pull-in method, for controlling the focusing of a light beam to any one of a plurality of recording layers.
BACKGROUND ART
Conventionally, as a recording medium for a variety of information such as audio information, video information, etc., optical discs are widely used from which information recorded therein is read out optically, namely, using a light beam. There have recently been proposed such optical discs having formed therein many recording layers for the purpose of recording a further increased amount of information.
An optical disc having a plurality of recording layers formed therein is known from the disclosure in the Japanese Unexamined Patent Publication No. 8-235641.
Referring now to
FIG. 1
, there is illustrated in the form of a sectional view a conventional optical disc, that is, the optical disc having a plurality of recording layers as in the above Japanese Unexamined Patent Publication No. 8-235641. As shown in
FIG. 1
, the optical disc, generally indicated with a reference
1
, includes a first record carrier
4
a
having a first recording layer
3
a
formed on one side of a first substrate
2
a
which is light-transmissive and a second record carrier
4
b
having a second recording layer
3
b
formed on one side of a second substrate
2
b
which is also light-transmissive. The first and second record carriers
4
a
and
4
b
are joined to each other with the sides of the first and second recording layers
3
a
and
3
b
having formed thereon the first and second recording layers
3
a
and
3
b,
respectively, being opposite to each other as well as with a light-transmissive adhesive layer
5
being disposed between the first and second record carries
4
a
and
4
b.
Information such as video information or the like is recorded as pit patterns
6
a
and
6
b
each defined by tiny pits and lands on the sides of the first and second substrates
2
a
and
2
b
forming the first and second record carriers
4
a
and
4
b,
respectively, on which the first and second recording layers
3
a
and
3
b
are formed, respectively. The first recording layer
3
a
is formed on the pit pattern
6
a
formed on the first record carrier
4
a
by forming a translucent or semi-reflective layer of SiN, SiO
2
or the like along the pit pattern
6
a
by evaporation, sputtering or the like. The first recording layer
3
a
reflects 20 to 50%, and transmits 30 to 80%, of a light beam incident upon it. The second recording layer
3
b
is formed on the pit pattern
6
b
formed on the second record carrier
4
b
by forming an aluminum evaporated layer or the like along the pit pattern
6
b.
The second recording layer
3
b
reflects 60% or more of an incident light, but it will reflect 20 to 50% of a light beam having passed through the first recording layer
3
a
and reflected from the second recording layer
3
b.
From the optical disc
1
having the first recording layer
3
a
which is a translucent or semi-reflective as in the above, information recorded in the second recording layer
3
b
can be read by directing a light beam L
2
in the same direction as that in which a light beam L
1
is directed towards the first recording layer
3
a
as shown in FIG.
1
. In this case, either information recorded in the first recording layer
3
a
or information recorded in the second recording layer
3
b
is selected for reading by changing the focused position of the light beams L
1
and L
2
directed towards the optical disc
1
.
Also, as the optical disc having a plurality of recording layers, there has been proposed a one shown in FIG.
2
. This example of optical disc is generally indicated with a reference
11
. As shown in
FIG. 2
, the optical disc
11
includes a first record carrier
14
a
having a first recording layer
13
a
formed on one side of a first substrate
12
a
which is light-transmissive and a second record carrier
14
b
having a second recording layer
13
b
formed on one side of a second substrate
12
b
which is also light-transmissive. The first and second record carriers
14
a
and
14
b
are joined to each other with an adhesive layer
15
of a light-transmissive, ultraviolet-settable resin or the like. They are joined in parallel with each other so that the second substrate
12
b
is disposed above the first recording layer
13
a.
On the second recording layer
13
b,
there is provided a protective layer
17
for the second recording layer
13
b.
Information such as audio information or the like is recorded as pit patterns
16
a
and
16
b
each defined by tiny pits and lands on the sides of the first and second substrates
12
a
and
12
b
forming the first and second record carriers
14
a
and
14
b,
respectively, on which the first and second recording layers
13
a
and
13
b
are formed, respectively. The first recording layer
13
a
transmits only a light beam having a predetermined wavelength while reflecting a light beam having any other wavelength. It is formed on and along the pit pattern
16
a
formed on the first record carrier
14
a.
The first recording layer
13
a
is formed to have a multilayered structure consisting of five layers of Si
3
N
4
, SiO
2
, Si
3
N
4
, SiO
2
and Si
3
N
4
, respectively, for example. The first recording layer
13
a
reflects approximately 34% of a light beam of 635 nm in wavelength while reflecting little of a light beam of 780 nm in wavelength.
On the pit pattern
16
b
formed on the second record carrier
14
b,
there is formed the second recording layer
13
b
by forming a highly reflective aluminum evaporated layer or the like along the pit pattern
16
b.
The second recording layer
13
b
reflects 80% or more of a light beam having passed through the first recording layer
13
a.
It reflects 84% or more of a light beam of 780 nm in wavelength, most of which is transmitted through the first recording layer
13
a,
while reflecting about 38% of a light beam of 635 nm in wavelength, of which about 34% is reflected by the first recording layer
13
a.
In case of the optical disc
11
constructed as in the above, a light beam is directed from the side of the first substrate
12
a
of the first record carrier
14
a
to read information recorded in the first and second recording layers
13
a
and
13
b.
At this time, a light beam L
3
of 780 nm in wavelength, used to read the information, will be transmitted through the first recording layer
13
a
and incident upon the second recording layer
13
b,
and a portion of the light beam will be reflected as a return light from the second recording layer
13
b.
By detecting the return light, information such as the audio information or the like recorded in the second recording layer
13
b
is read. Since the light beam L
3
of 780 nm in wavelength is used to play back a so-called compact disc which is a read-only optical disc of 12 cm in diameter, information recorded in the second recording layer
13
b
can be read by a general-purpose or versatile optical disc player.
Also, a light beam L
4
of 635 nm in wavelength, directed from the side of the first substrate
12
a
of the first record carrier
14
a,
will be reflected from both the first and second recording layers
13
a
and
13
b
to provide a return light each. More specifically, since the first reflecting layer
13
a
reflects about 34% of a light beam of 635 nm in wavelength, the light beam will pass through the first recording layer
13
a
and incident upon the second recording layer
13
b
to provide a return light from the second recording layer
13
b.
The second recording layer
13
b
reflects approximately 34% of the light beam incident upon it.
By focusing the light beam L
4
of 635 nm in wavelength on either the first or second recording layer
13
a
or
13
b
of the optical disc
11
, information recorded in either the
Inokuchi Tatsuya
Ogawa Hiroshi
Sako Yoichiro
Maioli Jay H.
Tran Thang V.
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