Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2002-04-18
2004-07-20
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013070, C369S275400, C428S064200
Reexamination Certificate
active
06765847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk that is used for information recording or reproduction and further to a method of magnetically separating tracks of the optical disk.
2. Related Background Art
It has been desired in the area of optical disks to achieve higher-density information recording. A method for realizing such high-density recording has been proposed in the form of a DWDD (domain wall displacement detection) type optical disk.
In the DWDD type optical disk, it is necessary to weaken magnetic coupling between adjacent recording/reproducing tracks. Therefore, when manufacturing the DWDD type optical disk, prior to recording of information signals, a magnetically separating process for magnetically separating adjacent recording/reproducing tracks is performed. The magnetically separating process is performed by methods such as those disclosed in JP 6(1994)-290496 A and JP10(1998)-340493 A.
A structure of the DWDD type optical disk and a method of magnetically separating process according to a conventional technique are described as examples with reference to FIG.
7
. In an optical disk shown in
FIG. 7
, a first dielectric layer
702
, a magnetic layer
703
, a second dielectric layer
704
, and a protective coating layer
705
are laminated in this order on a substrate
701
. On a surface of the substrate
701
on a side of the thin film layers, grooves
706
are formed. A portion between two of the grooves
706
adjacent to each other in a radial direction is referred to as a land
707
that is used as a recording/reproducing track. The grooves
706
have a width of, for example, 0.2 &mgr;m, and the lands
707
have a width of 1.4 &mgr;m. The magnetic layer
703
includes at least three magnetic thin films that are used for reproduction employing a DWDD system. In order for the DWDD system to be performed, it is necessary to magnetically separate the lands
707
as the tracks used for recording/reproduction.
The following description is directed to a method of performing the magnetically separating process with respect to this optical disk. In the magnetically separating process, a laser beam
708
to be used for annealing is focused on the groove
706
by an objective lens
709
and allowed to scan along the grooves
706
, so that magnetic coupling between the magnetic layers
703
on the grooves
706
is lost. As a result, in each of the lands
707
, which is a region interposed between the grooves
706
that have been subjected to annealing, both sides of the land
707
is magnetically separated, thereby allowing a DWDD operation to be performed. The laser beam
708
used in this process has, for example, a laser power of 2 mW and a wavelength &lgr; of 780 nm. The objective lens
709
has a NA of 0.5, and a beam spot of about 800 nm in diameter is formed. The beam spot of the laser beam
708
travels at a speed of, for example, 2 m/second.
When the lands
707
interposed between the grooves
706
are used as the recording/reproducing tracks as in the foregoing description, at an innermost or outermost end of a recording/reproducing track region, the groove
706
is provided. That is, even the land
707
positioned at the innermost or outermost end is interposed between the grooves
706
. Accordingly, both sides of each of all land tracks can be magnetically separated by allowing the laser beam
708
for annealing to scan over all the grooves
706
.
When manufacturing a disk provided with grooves, generally, portions exposed to a laser beam during master disk cutting correspond to the grooves of the disk. In the master disk cutting, due to a limit in the degree to which a laser beam is converged, it is difficult to manufacture grooves of a width as narrow as 0.1 to 0.2 &mgr;m. When a laser having a wavelength of 351 nm and an objective lens having a NA of 0.9 are used as in conventional cutting, an obtained groove width is inevitably not less than 0.3 &mgr;m. However, as a region for magnetically separating tracks so as to enable the DWDD operation, it is sufficient to have a width of about not less than 0.02 &mgr;m, which corresponds to a width of a domain wall.
In order for an excellent DWDD operation to be performed, a domain wall driving force is required to be greater than a domain wall displacement inhibiting force, and thus a recording/reproducing track is required to have a width of 0.3 to 0.6 &mgr;m. Accordingly, when lands are used as the recording/reproducing tracks, a track pitch is inevitably not less than 0.6 &mgr;m.
Alternatively, the grooves may be used as the recording/reproducing tracks, with the lands being subjected to the magnetically separating process. In this case, the lands can be reduced in width to 0.1 to 0.2 &mgr;m while maintaining the width of the grooves of 0.3 to 0.5 &mgr;m, which is advantageous from a processing standpoint.
When the grooves are used as the recording/reproducing tracks, annealing is performed by allowing a light beam to scan over the lands, so that groove tracks are magnetically separated. In this case, it is possible to allow the light beam to scan over the lands of a narrower width by operating tracking servo using 1st-order diffracted light diffracted from the lands. However, on an innermost track and an outermost track in a recording/reproducing track region, the following problem arises.
In a conventional technique in which the lands are used for recording, since the groove always is formed on an inner side of an innermost recording/reproducing track, annealing is performed by tracking on the groove, so that the magnetically separating process can be performed with respect to both sides of an innermost land track.
On the other hand, when the grooves are used for recording, there is difficulty in performing the magnetically separating process as follows. As for an innermost groove track, for example, on an outer side of the groove track, the land is formed; however, on an inner side of the groove track, a flat surface spreads, on which no land region of a narrower width is formed. Therefore, while the magnetically separating process can be performed with respect to the land on the outer side of the innermost groove track, the magnetically separating process hardly can be performed on the inner side of the groove track, because tracking servo cannot be operated on the same side. The same applies to an outermost groove track. While the magnetically separating process can be performed with respect to an inner side of the outermost groove track, it hardly can be performed with respect to an outer side of the groove track.
SUMMARY OF THE INVENTION
In order to solve the aforementioned problem, it is an object of the present invention to provide an optical disk that achieves high-density recording and allows an excellent DWDD (domain wall displacement detection) operation to be realized by performing a magnetically separating process with respect to both sides of each of all recording/reproducing tracks provided in a region extending from an innermost track to an outermost track, and a method of performing the magnetically separating process with respect to the optical disk.
An optical disk of the present invention has a basic configuration including a disk-shaped substrate with pits and grooves formed by emboss processing, and at least a first dielectric layer, a magnetic layer, and a second dielectric layer that are formed on the substrate. In the substrate, a predetermined region ranging in a radial direction is used as a data region for recording/reproducing data. The data region includes a plurality of recording/reproducing tracks ranging from an innermost track to an outermost track, and is divided into a plurality of segments in a tangential direction. Each segment includes a pit region and a groove region. The pit region is provided with at least a pair of wobble pits to be used for sample servo. The groove region is provided with the recording/reproducing track. The recording/reproducing tracks are composed of the grooves. The magnetic anisotr
Birukawa Masahiro
Hino Yasumori
Hiroki Tomoyuki
Hozumi Yasushi
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Neyzari Ali
LandOfFree
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