Method for manufacturing an optical disk

Details Method for manufacturing an optical disk Method for manufacturing an optical disk

1997-01-14

2002-04-30

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

C369S275100, C369S275200, C369S275300, C369S275400

Reexamination Certificate

active

06379864

ABSTRACT:

FILED OF THE INVENTION
The present invention relates to optical disks, including magneto-optical disks, on which address information is prerecorded as a series of pits.
BACKGROUND OF THE INVENTION
Among optical memories on/from which information is recorded/reproduced using light, magneto-optical disks having a recording film made of a perpendicularly magnetized film as a recording medium have been practically used. Information is recorded on the magneto-optical disks when a direction of magnetization within light spots is arranged to be upward or downward by applying a magnetic field while irradiating laser light onto the recording film.
As illustrated in
FIG. 8
, a magneto-optical disk has grooves
51
. A light spot
55
accurately follows a land
52
between the grooves
51
. The address information of a particular track that the light spot
55
follows is obtained because address information is recorded on each of the lands
52
as pits
53
.
Information is recorded on tracks as lands
52
. The track pitch is almost equal to the diameter of the light spot
55
which is determined by the wavelength of laser light and the numerical aperture of an objective lens. The objective lens converges the laser light into the light spot
55
. Usually, the wavelength of the laser light is between 780 nm and 830 nm and the numerical aperture of the objective lens is between 0.45 and 0.6. Thus, the light spot
55
has a diameter of between 1.2 and 1.4 &mgr;m and the track pitch is between 1.4 and 1.6 &mgr;m. Accordingly, the minimum diameter of an upwardly or downwardly magnetized recording domain
54
is around 0.8 &mgr;m.
A magneto-optical disk with flat mirrored sections
62
shown in
FIG. 9
is also well known. The mirrored sections
62
do not have grooves
61
but pits
63
. The light spot
55
tracks the grooves
61
, and the address information of a particular track that the light spot
55
follows is obtained by reproducing the pits
63
. Similar to the above-mentioned optical disk of
FIG. 8
, the minimum diameter of a recording domain
64
on the groove
61
of this magneto-optical disk is around 0.8 &mgr;m.
In recent years, magneto-optical disks including a recording film of a multi-layer structure have been produced so as to achieve magnetic super resolution effects. The magneto-optical disk with such a structure produces a recording domain of a size much smaller than the size of the light spot
55
, achieving improved recording density. With the magnetic super resolution technique, recording domains of size almost one half of the conventional size are stably formed. It is therefore possible to reduce the track pitch to around 0.8 &mgr;m or one half of the conventional track pitch, improving the recording density significantly. For example, there is a detailed report on magnetic super resolution in “Journal of Japanese Applied Magnetism Association”, Vol. 15, No. 5, 1991, pp. 838-845.
With the conventional structures, however, when the track pitch is reduced to a half, the size of the pit
53
is also reduced to a half, resulting in weaker signals from the pits
53
.
Further, the distance between pits
53
formed on adjacent tracks is also decreased to a half. This causes crosstalk and prevents accurate address information from being obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical disk which has a reduced track pitch and is capable of giving accurate address information.
In order to achieve the above object, an optical disk of the present invention has concentric or spiral grooves, a first series of pits formed in interrupted portions of the grooves, and a second series of pits formed in portions of lands. Both of the first and second series of pits represent address information. The portions of the lands and the interrupted portions of the grooves are located in different radial directions of the magneto-optical disk.
With this arrangement, it is possible to obtain accurate address information even when the track pitch is reduced, thereby achieving a high-density recording optical disk.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.


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