Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1999-08-13
2004-02-03
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S053200
Reexamination Certificate
active
06687194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical storing apparatus for recording and reproducing information by using a laser beam and a recording and reproducing method of an optical storage medium. More particularly, the invention relates to an optical storing apparatus for optimizing a retry in the case where a read error occurs in the recording and reproducing operation of an optical storage medium including an MSR medium to record and reproduce data at a density smaller than a beam diameter and a recording and reproducing method of an optical storage medium.
2. Description of the Related Arts
In recent years, an optical disk is highlighted as an external storage medium of a computer. In the optical disk, by forming magnetic recording pits on the submicron order onto the medium by using a laser beam, a recording capacity can be remarkably increased as compared with that of a floppy disk or a hard disk so far as an external storage medium. Further, in a magnetooptic disk as a perpendicular magnetic storage medium using a rare earth—transition metal system material, information can be rewritten and the future development is more and more expected.
The optical disk has a memory capacity of, for example, 128 MB, 230 MB, 540 MB, or 640 MB for one side of the disk of 3.5 inches. The 128 MB medium and 230 MB medium are based on a pit position modulation (PPM) recording. The 540 MB medium and 640 MB medium are based on a pulse width modulation (PWM) recording. This means that one optical disk has a memory capacity of 128 to 640 floppy disks when considering a fact that a memory capacity of one floppy disk of 3.5 inches is equal to about 1 MB. As mentioned above, the optical disk is a rewritable storage medium of a very high recording density. However, for preparations for a future multimedia era, it is necessary to further raise the recording density of the optical disk to a value larger than the present one. To raise the recording density, further more pits have to be recorded on the medium. For this purpose, it is necessary to further reduce the size of pit and to narrow an interval between the pits. In case of raising the recording density by such a method, although it is necessary to further reduce a wavelength of a laser beam to a value shorter than the present wavelength of 670 nm, when considering the case of putting into practical use, the pit size has to be reduced at the existing wavelength of 670 nm. In this case, as for the recording, by controlling a power of the laser beam, the pit smaller than the beam diameter can be formed. As for the reproduction, however, if the pit smaller than the beam diameter is reproduced, a crosstalk with the adjacent pit increases. In the worst case, since information of the adjacent pit is also included in a reproducing beam, such a method is very difficult when considering practicality.
As a method of reproducing a pit smaller than the beam diameter by using the beam of the existing wavelength of 670 nm, there is a magnetooptic recording and reproducing method represented by JP-A-3-93058 and is known as a recording and reproducing method by an MSR (Magnetically induced Super Resolution). The above method has two methods of an FAD (Front Aperture Detection) system and an RAD (Rear Aperture Detection) system. According to the FAD system, as shown in
FIGS. 1A and 1B
, an MSR medium is divided into a recording layer
320
and a reproducing layer
316
on a substrate
311
and a reproducing magnetic field Hr is applied in a state where a laser spot
322
of a read beam is irradiated, thereby reproducing. In this instance, in the portion where the reproducing layer
316
is the recording pit, a magnetic coupling of a switching layer
318
which is formed at a boundary with the recording layer
320
is released in dependence on a temperature distribution of the medium heating by the laser spot
322
and such a portion is influenced by the reproducing magnetic field Hr and becomes a mask. On the other hand, with regard to the portion of the next recording pit, the magnetic coupling of the switching layer
318
is held and such a portion becomes an aperture
324
. Therefore, like a laser spot
322
, only a pit
330
of the aperture
324
can be read without being influenced by an adjacent pit
328
.
According to the double mask RAD system, as shown in
FIGS. 2A and 2B
, the MSR medium is constructed by three layers of the reproducing layer
316
, an intermediate layer
317
, and the recording layer
320
on the substrate
311
. A reproducing laser power upon reproduction is slightly raised and information is read. Upon reading, depending on a temperature distribution of the medium heating by a laser spot
334
of the read beam, a front mask
336
, an aperture
338
in which magnetization information of the recording layer
320
is transferred to the reproducing layer
316
, and a rear mask
337
are formed in the reproducing layer
316
. That is, in the front mask
336
at a low temperature by the read beam laser spot
334
, no signal is derived because the reproducing layer
316
has been initialized by a reproducing magnetic field
332
. In the aperture
338
at an intermediate temperature, since the intermediate layer
317
is perpendicularly magnetized, its coupling force is enhanced, the magnetization information of the recording layer
320
is transferred to the reproducing layer
316
, and a signal is derived. In the rear mask
337
at a high temperature, since it is close to the Curie temperature of the intermediate layer
317
, the coupling force between the recording layer
320
and reproducing layer
316
decreases and the magnetization of the reproducing layer
316
is aligned in the direction of the reproducing magnetic field
332
. The magnetization information of the recording layer
320
transferred to the reproducing layer
316
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
328
of the recording layer
320
which is being read out at present, in the pit
330
of the recording layer
320
to be subsequently read out, since the information is not transferred because of the formation of the front mask
336
by initial magnetization information of the reproducing layer
316
, even if the recording pit is smaller than the laser spot
334
, no crosstalk is generated and the pit smaller than the beam diameter can be reproduced. Further, if the double mask RAD is used, since the area of the recording layer
320
other than the reproducing portion is in a state where it has been masked by the initialized reproducing layer
316
, a pit interference from the adjacent pit does not occur and the pit interval can be further narrowed. The crosstalk from the adjacent track can be also suppressed. Thus, a track pitch can be narrowed more than that of the FAD and the reproduction can be performed at a high density even by using the beam of the existing wavelength of 680 nm.
However, in the conventional optical disk apparatus using the MSR medium as mentioned above, there is a problem such that unless the reproducing magnetic field which is used upon reproduction and the reading power are strictly controlled, the proper reproducing operation cannot be performed. This is because, for example, when a reproducing power Pr of the laser beam in the FAD system of
FIGS. 1A and 1B
is too small, a forming range of the mask
326
in
FIG. 1B
by the magnetization of the reproducing layer
316
decreases, the pit
328
is not masked, and a crosstalk occurs. When the reproducing power Pr is too strong, the forming range of the mask
326
is widened, the pit
330
is also partially masked, a reproducing level decreases, and an error occurs. At the same time, the reproducing magnetic field Hr also acts on the recording layer
320
and there is a possibility that the recording data is erased. When the reproducing power and the reproducing magnetic field are too small in the double mask RAD system of
F
Imamura Kiyomi
Kobayashi Shin'ya
Yamakawa Teruji
Yanagi Shigenori
Fujitsu Limited
Greer Burns & Crain Ltd.
Neyzari Ali
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