Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-09-20
2003-11-11
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C428S064400
Reexamination Certificate
active
06646978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a storage medium for storing informations, and more particularly to an optical storage medium for storing and reproducing informations upon irradiation of a laser beam.
2. Description of the Related Art
An optical disk comprises a substrate, an optical recording layer overlying the substrate, and an light transmitting layer overlying the optical recording layer.
It is desirable to improve a recording density of the optical disk which includes lands and grooves. Japanese laid-pen patent publication No. 4-079483 discloses that both the lands and grooves are used for recording informations to increase the recording density by approximately two times of when only either the lands or the grooves used for recording informations.
It is also know as another conventional measure for improving the recording density to increase a numerical aperture of an objective lens performing as a condensing lens. The increase in the numerical aperture of the objective lens decreases a beam spot area on the optical disk, thereby improving the recording density.
For reproducing the information from the compact disk (CD), the numerical aperture is 0.45. For reproducing the information from the digital versatile disk (DVD), the numerical aperture is 0.6. In recent years, an optical disk with a high numerical aperture of 0.85 has been proposed.
The high numerical aperture for realizing the highly dense recording may decrease an acceptable range of an aberration which is caused by the fact that the normal of a surface of the disk is tilted from an optical axis of the condensed laser beam. For this reasons, it is preferable for the high numerical aperture that the substrate of the optical disk is thin. A substrate thickness for CD is 1.2 millimeters, whilst a substrate thickness for DVD is only 0.6 millimeters.
If the numerical aperture is increased up to at least 0.85, then after the recording layer has formed over the substrate, an light transmitting layer with a thickness of about 0.1 millimeter is then formed over the recording layer, so that a laser beam is irradiated through the light transmitting layer onto the recording layer for recording and reproducing the informations.
The combined use of the lands and the grooves for recording and reproducing the informations and the increase in the numerical aperture of the optical disk allow that the recording density is increased by about 4 to 5 times. This structure, however, causes the following disadvantages.
FIG. 1
is a fragmentary cross sectional elevation view illustrative of a conventional structure of an optical storage medium allowing lands/grooves recordings. An medium
100
comprises a substrate
101
, a reflective layer
102
over the substrate
101
, a first dielectric layer
103
over the reflective layer
102
, a recording layer
104
over the first dielectric layer
103
, a second dielectric layer
105
over the recording layer
104
, and an light transmitting layer
106
over the second dielectric layer
105
.
The substrate
101
has substrate grooves
101
a
with a substrate groove width
110
a
and substrate lands
101
b
with a substrate land width
110
b
. The substrate groove width
110
a
is defined to be a distance between two intermediate points of adjacent substrate sloped surfaces defining the substrate groove
101
a
. The substrate land width
110
b
is defined to be another distance between two intermediate points of another adjacent substrate sloped surfaces defining the substrate land
101
b
. The substrate groove width
110
a
is equal to the substrate land width
110
b.
The medium
100
has an effective groove width
111
a
and an effective land width
111
b
. The effective groove width
111
a
is defined to be a distance between two intermediate points of adjacent sloped surfaces of the recording layer
104
. The effective land width
111
b
is defined to be another distance between two intermediate points of adjacent another sloped surfaces of the recording layer
104
. Therefore, the effective groove width
111
a
is different from the substrate groove width
110
a
. The effective land width
111
b
is different from the substrate land width
110
b
. The effective groove width
111
a
is narrower than the substrate groove width
110
a
. The effective land width
111
b
is wider than the substrate land width
110
b
. Since the substrate groove width
110
a
is identical with the substrate land width
110
b
, the effective groove width
111
a
is narrower than the effective land width
111
b.
A difference in width between the effective groove width
111
a
and the effective land width
111
b
is increased as a distance in vertical direction between the substrate
101
and the recording layer
104
is increased. The recording layer
104
is separated by double layers, for example, the reflective layer
102
and the first dielectric layer
103
from the substrate
101
. Further, the reflective layer
102
is thick as being larger in step coverage than the first dielectric layer
103
. Those results in that the distance in vertical direction between the substrate
101
and the recording layer
104
is relatively large.
Since the effective groove width
111
a
is narrower than the effective land width
111
b
, the following disadvantages are raised. Recording marks are formed on both grooves and lands of the recording layer
104
. A signal amplification from the recording mark on the narrow groove of the recording layer
104
is smaller than another signal amplification from the other recording mark on the wide land of the recording layer
104
. A difference in signal amplification between the recording marks on the narrow groove and the wide land of the recording layer
104
means it difficult for the conventional medium to obtain a desirable uniform quality of both signals from the groove recording mark and the land recording mark.
In the above circumstances, the development of a novel optical storage medium free from the above problems is desirable.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel optical storage medium free from the above problems.
It is a further object of the present invention to provide a novel optical storage medium for recording and reproducing informations onto and from both grooves and lands at a uniform signal quality.
It is a still further object of the present invention to provide a novel optical storage medium for recording and reproducing informations onto and from both grooves and lands, wherein the medium is suitable for a highly dense recording.
The present invention provides an optical storage medium including: a substrate having grooves and lands; a first dielectric layer overlying the substrate; a recording layer overlying the first dielectric layer; a second dielectric layer overlying the recording layer; and a light transmitting layer overlying the second dielectric layer, wherein each of the grooves is larger in width than adjacent two of the lands.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.
REFERENCES:
patent: 6287660 (2001-09-01), Hosaka et al.
patent: 6400677 (2002-06-01), Kagawa et al.
patent: 6452899 (2002-09-01), Fujii et al.
patent: 5/282705 (1993-10-01), None
Ide Tatsunori
Okubo Shuichi
Neyzari Ali
Young & Thompson
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