Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-12-18
2003-02-11
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S053200
Reexamination Certificate
active
06519210
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical storage apparatus for recording and reproducing information by using a laser beam and to a recording and reproducing method of an optical storage medium. More particularly, the invention relates to an optical storage apparatus for recording and reproducing data at a density that is smaller than a beam diameter as is known as an MSR (Magnetically induced Super Resolution) technique and to a recording and reproducing method of an optical storage medium.
In recent years, an optical disk is being highlighted as an external storage medium of a computer. In the optical disk, by forming magnetic recording pits of a submicrometer order onto a medium by using a laser beam, a recording capacity can be remarkably increased as compared with a floppy disk or a hard disk as a conventional external storage medium. Further, information can be rewritten in a magnetooptic disk as a perpendicular magnetic storage medium using a rare earth—transition metal system material, so that its future development is more and more expected.
The optical disk of, for example, 3.5 inches has a storage capacity of 540 MB or 640 MB on one side. This means that a storage capacity of one floppy disk of 3.5 inches is equal to about 1 MB and one optical disk has a storage capacity as much as that of 540 or 640 floppy disks. As mentioned above, the optical disk is a rewritable storage medium having an extremely high recording density. However, in order to get ready for the multimedia age in the future, it is necessary to increase the recording density of the optical disk even higher than that of the present optical disks. To increase the recording density, a greater number of pits have to be recorded on the medium. For this purpose, it is necessary to further decrease the pit size from the present size and to narrow the interval between the pits. In case of raising the recording density by such a method, it is further necessary to shorten a wavelength of the laser beam below the present wavelength of 670 nm. However, in case of considering the practical use, the pit size has to be reduced in the present wavelength of 670 nm. In this case, as for the recording, a pit which is smaller than the beam diameter can be formed by controlling a power of the laser beam. As for the reproduction, however, when the pit that is smaller than the beam diameter is reproduced, a crosstalk with the adjacent pit increases. In the worst case, the adjacent pit also enters the reproducing beam. When a practical use is considered, it is very difficult to use such a method.
As a method of reproducing a pit smaller than the beam diameter by the existing wavelength of 670 nm, there is a magnetooptical recording and reproducing method represented by JP-A-3-93058 and this method is known as a recording and reproducing method by the MSR (Magnetically induced Super Resolution). Presently there are two general methods of MRS an FAD (Front Aperture Detection) system and an RAD (Rear Aperture Detection) system. In the FAD system, as shown in
FIGS. 1A and 1B
, a recording medium is divided into a recording layer
220
and a reproducing layer
216
. Data is reproduced using a reproducing magnetic field Hr applied to the medium in a state in which a laser spot
222
of a reading beam is irradiated, in this instance. In this instance, as depending on a temperature distribution within heating by the laser spot
222
, a magnetic coupling of a switching layer
218
formed in a boundary with the recording layer
220
is released, such and such a portion of the beam spot is influenced by the reproducing magnetic field Hr and becomes a mask. On the other hand, as for a portion of the next recording pit, the magnetic coupling in the switching layer
218
is held and this portion becomes an opening
224
. Consequently, within the laser spot
222
, only a pit
230
of the opening
224
can be read without being influenced by the adjacent pit
226
. On the other hand, according to the RAD system, as shown in
FIGS. 2A and 2B
, an initialization to align a magnetizing direction of the reproducing layer
216
to a predetermined direction is performed by using an initializing magnet
232
. The reading operation is performed by slightly raising a reproducing laser power upon reproduction. Depending on the temperature distribution within laser spot
234
of the reading beam, a mask
236
in which initial magnetization information remains and an opening
238
in which the initial magnetization information is erased and magnetization information of the recording layer
220
is transferred are formed in the reproducing layer
216
. The magnetization information of the recording layer
220
transferred to the reproducing layer
216
is converted into an optical signal by a magnetooptic effect (Kerr effect or Faraday effect), so that data is reproduced. In this instance, as compared with a pit
228
of the recording layer
220
which is being read out at present, the pit
230
of the recording layer
220
to be subsequently read out is not transferred due to the formation of the mask
236
by the initial magnetization information in the reproducing layer
216
. Therefore, even when the recording pit is smaller than the laser spot
234
, no crosstalk occurs and the pit which is smaller than the beam diameter can be reproduced. Further, by using such a magnetically induced super resolution, since an area of the recording layer
220
except for the reproduced portion is masked by the initialized reproducing layer
216
, a pit interference from the adjacent pit doesn't occur. Further, since a pit interval can be reduced and a crosstalk from the adjacent track can be also suppressed, a track pitch can be reduced and a high density can be realized even by using the existing wavelength of 780 nm.
However, in the conventional optical disk apparatus using such a magnetically induced super resolution, there is a problem that a proper reproducing operation cannot be performed unless an intensity of the reproducing magnetic field which is used upon reproduction is strictly controlled. The reason is that, for example, when the reproducing magnetic field Hr is too low in the FAD system in
FIG. 1A
, a forming range of the mask
226
in
FIG. 1B
by the magnetization of the reproducing layer
216
is reduced and the pit
228
is not masked, so that a crosstalk occurs. When the reproducing magnetic field is too strong, the forming range of the mask
226
is widened and the pit
230
is also partially masked, so that a reproducing level decreases and an error occurs. At the same time, the reproducing magnetic field Hr also acts on the recording layer
220
and there is a possibility of erasure of the recording data. When the initializing magnetic field is too low in the RAD system in
FIG. 2A
, an erasing range by a beam heating of the initializing magnetization of the reproducing layer
216
is widened and the forming range of the mask portion decreases, so that the pit
230
in
FIG. 2B
is not masked and a crosstalk occurs. When the initializing magnetic field is too strong, the erasing range by the beam heating of the initializing magnetization of the reproducing layer
216
is narrowed and the forming range of the mask
236
is widened, so that the pit
228
is partially masked, the reproducing level decreases, and an error occurs. At the same time, when the initializing magnetic field is too strong, the magnetic field also acts on the recording layer
220
and there is a possibility of erasure of the recording data. Moreover, the reproducing magnetic field and the initializing magnetic field are dependent upon the an environmental temperature of the apparatus. That is, when the environmental temperature in the apparatus changes to the lower side, hysteresis characteristics of the reproducing layer become thick. In order to obtain the same magnetizing characteristics (magnetic flux density), the reproducing magnetic field has to be intensified. On the contrary, when the environmental temperature changes to the highe
Ikeda Toru
Yanagi Shigenori
Fujitsu Limited
Greer Burns & Crain Ltd.
Neyzari Ali
LandOfFree
Optical storage apparatus having reproducing magnetic field... 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 storage apparatus having reproducing magnetic field..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical storage apparatus having reproducing magnetic field... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3170181