Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1998-05-21
2001-07-17
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
active
06262948
ABSTRACT:
TECHNICAL FIELD
The present invention relates to optical disc systems for performing recording and/or reproduction of information signals, and optical discs used in these systems.
BACKGROUND ART
An optical disc system is shown in
FIG. 1
as a system for performing recording on and/or reproduction from an optical recording medium such as an optical disc.
A conventional optical disc system, such as that shown in
FIG. 1
, is arranged such that when a one-sided dis-like optical recording medium
50
is mounted therein, an optical system including a laser unit
58
and an objective lens
59
are arranged above the one-sided optical recording medium
50
. The numerical aperture (referred to herein as NA) of the objective lens
59
has a value ranging from 0.50 to 0.53.
In order to drive the optical system in focusing and tracking directions with respect to the optical recording medium
50
, a drive system (not shown) is provided.
The one-sided optical recording medium
50
is formed as follows. A recording layer
55
and a protective cover
56
are sequentially stacked on one surface of a light-transmitting transparent substrate
51
made of polycarbonate, for example. The light-transmitting transparent substrate
51
has a predetermined thickness t
1
. The thickness of a conventional substrate is typically 1.2 mm.
An operation of the conventional optical disc system is described below.
The one-sided optical recording medium
50
is placed on and driven by a rotary table (not shown). A laser beam emitted from the laser unit
58
is focused through the objective lens
59
onto the recording layer
55
. A change in intensity of the focused laser beam in accordance with the data to be recorded produces pits in the recording layer
55
.
In order to cope with an increase in information volume, the quantity of information signals recorded in the recording layer of an optical disc must be increased. To date, however, dimensional constraints on the optical disc and other constraints on the lens and light source prevent such increases in information volume.
One option that has been proposed is to use a two-sided optical recording medium, in which recording layers are formed respectively on both surfaces of a single optical recording medium so that information signals may be recorded on each of the surfaces.
DISCLOSURE OF INVENTION
It is, therefore, an object of the present invention to provide a large-capacity optical disc system for performing high-density recording and/or reproduction, and an optical disc used in such an optical disc system.
According to an aspect of the present invention, there is provided an optical disc system for recording an information signal on an optical disc and/or reproducing the information signal from the optical disc. The optical disc is provided with a recording layer irradiated with a light beam to perform recording or reproduction and a light-transmitting cover formed to cover the recording layer and through which the light beam is transmitted. The optical disc system comprises light beam generating means for generating the light beam and an objective lens for bundling or focusing the laser beam onto the recording layer through the light-transmitting cover. The thickness of the light-transmitting cover of the optical disc ranges from about 0.05 mm to 0.6 mm, and the numerical aperture of the objective lens ranges from about 0.55 to 1.10.
In systems using the optical disc of the present invention the numerical aperture NA of the objective lens for performing high-density recording or reproduction has a value that falls within the range of 0.55 to 1.10. Therefore, when the thickness of the light-transmitting cover of the disc, formed to cover the recording layer and transmit the light beam to the recording layer, has a value that falls within the range of 0.05 mm to 0.6 mm, optical recording media for performing high-density recording or reproduction can be realized.
The optical disc may have respective recording layers on both sides of the substrate. Such an optical disc having respective recording layers on both sides of the disc can be used in an optical disc system of the present invention. In this system, a pair of optical pickup units, each having a light beam generating means and an objective lens, are arranged on opposite sides of an optical disc so as to face each other.
The optical disc having a recording layer on each of its surfaces, and the optical disc system using such a double-sided optical disc, enables higher-capacity recording and reproduction.
According to yet another aspect of the present invention, there is provided an optical disc system for recording an information signal on an optical disc and/or reproducing an information signal from the optical disc. The optical disc includes a substrate, an optical recording layer formed on the substrate and irradiated with a light beam for recording or reproduction, and a light-transmitting cover formed to cover the optical recording layer and through which the light beam is transmitted. The optical recording layer is formed to have land and groove regions which are used to facilitate tracking of the light beam on the optical recording layer. Unlike conventional optical recording discs which record information on only the land regions or only the groove regions and uses the other regions for tracking, the optical disc according to the present invention records information on both the land regions and the groove regions and uses the transition regions between the land and groove regions for tracking. Accordingly, the recording density of such an optical disc is increased. The optical recording system comprises laser beam generating means for generating the light beam and an objective lens for focusing the light beam onto the optical recording layer through the light-transmitting cover. The light-transmitting cover of the optical disc has a thickness that falls within the range of about 0.05 mm to 0.6 mm, and the numerical aperture of the objective lens has a value that falls within the range of about 0.55 to 1.10.
When the light beam is bundled or focused by the objective lens, the convergent rays have a minimum diameter given by:
2&ohgr;
0
=0.82×&lgr;/NA (1)
where &lgr; is the wavelength of the light beam.
Since the numerical aperture NA of the objective lens has a value that is larger than the conventional NA, which ranges from 0.50 to 0.53, the minimum diameter of the convergent rays is decreased and the recording density is increased accordingly. Therefore, reproduction of a high-density recording can be performed.
As the NA of the objective lens is increased, the thickness of the objective lens increases. However, the thickness of the light-transmitting cover of the disc is smaller than the conventional thickness (1.2 mm). As a result, the objective lens having a larger thickness will not be brought into contact with the optical disc.
As the NA of the objective lens and the thickness t of the light-transmitting cover of the optical disc is changed, the aberration values of the objective lens are changed according to:
(A) spherical aberration W
40
W
40
=
t
8
·
N
2
-
1
N
3
·
sin
4
α
(
2
)
where sin&agr; is the NA, and N is the refractive index of the light-transmitting cover of the disc, and
(B) coma W
31
W
31
α
t
2
·
(
N
2
-
1
)
N
2
sin
Θcos
Θ
(
N
2
-
sin
2
Θ
)
5
/
2
·
sin
3
α
(
3
)
where t is the thickness of the light-transmitting cover, N is the refractive index of the light-transmitting cover of the disc, and &thgr; is the skew.
The relationship between wavelength &lgr; of the light beam and the coma W
31
is:
W
31
=(abberation limit)·&lgr; (4)
and the relationship between t, &lgr;, and NA is:
t
1
NA
1
3
λ
1
=
t
2
NA
2
3
λ
2
(
5
)
for a constant coma W
31
. The relationship between t, &lgr;, when &lgr; is within a range from 100 nm to 780 nm, and NA is shown in the
Aoki Yoshio
Watanabe Tetsu
Dinh Tan
Maioli Jay H.
Sony Corporation
LandOfFree
Optical disk having a protective layer specified thickness... 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 disk having a protective layer specified thickness..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical disk having a protective layer specified thickness... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2521310