Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-09-25
2004-12-28
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S064800, C430S270140
Reexamination Certificate
active
06835432
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium such as an optical disc, and a method for manufacturing the optical recording medium. More particularly, the present invention relates to a write-once type optical disc on which data can be recorded using an organic dye, or the like.
Compact Discs (CD) have achieved widespread use, and optical discs have already won a position as important recording media. In addition to a CD of read-only type, the widespread use of a CD-R as a disc of write-once type on which information can be recorded is remarkable. In recent years, research and development on high-density optical discs are intensively performed, and a DVD of higher density than that of a CD is proposed and practically used. Among the standards of the DVD, a DVD-R which is a write-once type optical disc is expected as a medium which is relatively inexpensive and on which information can be recorded. In addition, development on higher-density optical discs for recording signals with further higher density for high-definition TV in the future or the like which require a large capacity is pursued.
Conventionally, the write-once type optical disc, typified by CD-R, mainly uses a recording material including an organic dye as a primary component. In the case of DVD-R, substantially the same recording material is used.
Hereinafter a conventional configuration of a write-once type optical disc will be described by using an example of DVD-R.
FIG. 2
illustrates a sectional configuration of a conventional DVD-R disc. The shown DVD-R disc has a configuration in which a first base plate
201
and a second base plate
204
are bonded together by means of an adhesion layer
205
. In the first base plate
201
, a guide tracking groove
201
a
is formed in a first surface
201
c,
and a second surface
201
d
is a mirror face.
FIG. 2
illustrates a plurality of cross sections of a single spiral form of the groove
201
a.
The first base plate
201
is formed by injection molding. The shape of the first surface
201
c
is transferred from a stamper.
On the first surface
201
c
of the first base plate
201
, a recording layer
202
containing an organic dye, and a reflection layer
203
are stacked. The recording layer
202
is applied by spin coating, and the reflection layer
203
is deposited on the recording layer
202
by a method such as sputtering. The inside of the groove
201
a
of the first base plate
201
is filled with the applied recording layer
202
, so that a surface of the recording layer
202
is substantially flat, regardless of the unevenness of the first surface
201
c
of the underlying recording layer
202
. Accordingly, a surface of the reflection layer
203
deposited on the recording layer
202
is substantially flat.
The second base plate
204
is formed by injection molding, similarly to the first base plate
201
. The second base plate
204
is bonded, via an adhesion layer
205
, to the first base plate
201
in which the recording layer
202
and the reflection layer
203
are stacked.
Writing/reading radiation or light is converged by an objective
206
on an optical head, and is applied onto an optical disc from the side of the second surface
201
d
of the first base plate
201
. More specifically, the groove
201
a
is irradiated with the writing/reading radiation that is transmitted through the first base plate
201
.
Next, with reference to
FIG. 3
, another example of an optical disc will be described.
The optical disc of
FIG. 3
includes an organic dye type recording layer
302
formed by deposition instead of spin coating. In the optical disc, since the recording layer
302
is deposited, a surface of the recording layer
302
has a shape reflecting a shape of a groove or a pit formed on a first surface
301
c
of a first base plate
301
. The shape is reflected in a surface of a reflection layer
303
. To the optical disc, writing/reading radiation is applied from the side of a second surface
301
d
of the first base plate
301
.
In both of the above-described optical discs, tracking control is performed so that the writing/reading radiation tracks the groove. Usually, the detection of the tracking deviation is performed by a push-pull method. In the push-pull method, reflected radiation from a disc is converged on two detectors divided along a line which is parallel to a groove direction, and a difference in intensities of radiation detected by the right and left detectors is detected as a tracking signal. Due to a phase difference between reflected radiation from a groove and reflected radiation from a land between grooves, the signal is zero when a converged radiation beam spot of the writing/reading radiation is in a center position of the groove or the land. When the converged radiation beam spot is positioned between the center of the groove and the center of the land, the signal is a positive value or a negative value. When a wavelength of the writing/reading radiation is &lgr;, and k is 0 or a natural number, an amplitude of the tracking signal is the maximum in a condition where an absolute value (unit: radian) of a phase difference between reflected radiation from a groove and a land is &pgr;(2k+1)/2.
In the conventional optical disc shown in
FIG. 2
, the recording layer
202
is formed by spin coating, so that there is an advantage that the period of time required for the step of forming the recording layer
202
can be shortened. However, since the surface of the reflection layer
203
is formed so as to be substantially flat, the following drawback arises. That is, a phase difference &dgr; of reflected radiation through a groove portion and reflected radiation through a land portion is represented by an equation of &dgr;=4&pgr;×((n
1
−n
2
)×d
1
+n
2
×d
2
)/&lgr;, when a diffraction index of the first base plate
201
is n
1
, a diffraction index of the recording layer
202
is n
2
, a depth of a groove is d
1
, and a surface step of the recording layer
202
between a groove portion and a non-groove portion is d
2
.
When d
2
is small and a difference between the diffraction index n
1
of the first base plate
201
and the diffraction index n
2
of the recording layer
202
is small, in order to obtain a sufficient amplitude of the tracking signal, it is necessary to increase the groove depth d
1
for generating a phase difference. As a result, for the purpose of transferring a deep groove or pit, the period of time is elongated because a temperature of resin and mold is set high when the base plate is formed by injection molding. In addition, it is difficult for the molded base plate to be released from the stamper, and a mold release non-uniformity and a cloud may easily occur. Thus, it is difficult to improve the productivity.
In the case of the optical disc of
FIG. 3
, the recording layer
302
is formed by deposition, so that the reflection layer
303
is formed in accordance with the shape of the groove of the base plate
301
. As a result, the phase difference &dgr; is represented by an equation of &dgr;=4&pgr;×n
1
×d
1
/&lgr;. Thus, a sufficient phase difference can be attained, and a good tracking signal amplitude can be obtained without increasing the groove depth d
1
.
However, the formation of a film by depositing a recording material containing an organic dye is slow, and it is difficult to improve the productivity.
Moreover, in both of the optical discs, since the writing/reading radiation is applied through the base plate in which grooves or pits are formed, it is important to fabricate the base plates
201
and
301
in which grooves or pits are formed with high precision and good reproducibility. The thickness of the respective base plates
201
and
301
affects the recording density. Generally, in order to improve the recording density of an optical disc, it is necessary to reduce a beam spot diameter of laser radiation used for writing/reading. For this purpose, it is necessary to shorten the wavelength of the las
Abe Shinya
Hayashi Kazuhiro
Akin Gump Strauss Hauer & Feld L.L.P.
Mulvaney Elizabeth
LandOfFree
Optical disc and method for manufacturing the optical disc does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical disc and method for manufacturing the optical disc, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical disc and method for manufacturing the optical disc will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3330625