Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1999-10-27
2002-03-12
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C369S116000
Reexamination Certificate
active
06356515
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical storage medium for recording and reproducing information using a laser beam and an optical storage apparatus.
Recently, attention is being paid to disk and card/tape types of optical storage media, such as phase changing and magneto-optical type media. Particularly, there is an interest in optical disks with higher recording capacities than the currently available floppy disks, and in hard disks using recording pits of the sub-micron order positioned on the medium. Such magneto-optical disks utilize rare earth-transition metal based materials, and can be rewritten a hundred thousand times, or more. Therefore, there is an interest in further development of such magneto-optical disks.
A 3.5 inch optical disk with a recording capacity of either 540 MB or 640 MB on only one side has recently been developed. For comparison purposes, the recording capacity of one side of a conventional 3.5 inch floppy disk is about 1 MB. Thus, one side of an optical disk has the recording capacity equal to that of 540 or 640 floppy disks. Accordingly, it goes without saying that an optical disk is a rewritable storage medium having a very high recording density.
However, even such high recording densities must further be increased in order to satisfy the requirements of the multimedia era, both now and in future. Therefore, a larger number of marks should be recorded on the medium in order to increase the recording density. For this purpose, the marks currently used should be reduced in size, and the interval between marks should also be decreased.
When attempting to raise the recording density with the method explained above, one option is to attempt to shorten the wavelength of the laser beam from its current value of 685 nm. However, there is another option in which the pit size is reduced, while still maintaining the current wavelength of 685 nm. Under this option, it is possible during recording to form marks which are smaller than the beam diameter by controlling the power of laser beam. But, during reproducing, when a mark smaller than the beam diameter is reproduced, crosstalk to the neighboring marks increases. In the worst case, the neighboring mark is included within the reproducing beam. Practically speaking, it is very difficult to overcome this crosstalk problem under normal use conditions.
However, two methods of reproducing marks which are smaller than the beam diameter in the current wavelength of 685 nm are two different types of magnetically induced super-resolution (MSR) techniques which can be classified as a FAD (front aperture detection) system and a RAD (rear aperture detection) system.
More particularly, in the RAD system, an initialization is performed, as shown in FIG.
17
(B), using an initializing magnet
232
to set the magnetizing direction of the reproducing layer
216
to a constant direction. The reading operation is conducted with a reproducing laser (whose power is slightly increased during this operation), a mask
236
(for allowing the initial magnetizing information of the reproducing layer
216
to be retained) and an aperture
238
(for allowing the heat of the laser spot
234
to transfer the magnetizing information of the recording layer
220
to the reproducing layer
216
after erasing the initial magnetizing information). The mask
236
and the aperture
238
result from the temperature distribution of the spot
234
. The magnetizing information of the recording layer
220
transferred to the reproducing layer
216
is converted to an optical signal by means of the magneto-optical effect (e.g., the Kerr effect or the Faraday effect) for data reproduction.
In this case, although the mark
228
of the track
214
currently being read by the laser beam has been transferred to the reproducing layer
216
, the mark
230
intended to be read next is not transferred due to the formation of the mask
236
. Thus, even when the recording mark is smaller than the laser spot
234
, crosstalk is not generated, and marks smaller than the beam diameter can be reproduced. Moreover, when this magnetically induced super resolution technique is used, since the area outside of the reproducing area of the recording layer
220
is masked by the initialized reproducing layer
216
, mark interference from neighboring marks is not generated, and the mark interval can be reduced. Accordingly, since crosstalk from the neighboring tracks can also be suppressed, the track pitch can also be reduced, and high density recording/reproducing can be obtained even when using the current wavelength of 685 nm.
Japanese Published Unexamined Patent Application Nos. HEI 7-244877, HEI 9-147436 and HEI 10-134429 disclose some of the details of the principles of magnetically induced super resolution techniques, examples of rare earth-transition metal based film material of magneto-optical recording medium layers consisting of a reproducing layer, a switch layer (an intermediate layer) and a recording layer; and examples of magneto-optical storage medium manufacturing methods.
However, optical memory devices for driving optical storage mediums for high density recording have a problem in that adequate recording operations cannot be realized if the laser power for the recording operation is not strictly controlled.
Moreover, another problem that has also been found is that the sensitivity of the storage medium changes depending on the number of write and erase operations performed, which results in imperfect control of the laser power during recording, which thereby increases the rate of recording errors.
The present invention has been proposed, considering the problems of the related art explained above, and it is therefore an object of the present invention to provide an optical storage medium, a method of processing that medium, and an optical storage medium processing apparatus which enables highly reliable high density recording by strictly controlling the laser power of the recording operation in each area of an optical storage medium that is not effected by the number of write and erase operations.
The present invention is characterized in that a high power process is repeatedly performed upon an optical storage medium. In this high power process, the power of the optical beam is increased to a higher power than that used for recording or erasing, and the beam is radiated upon a power adjusting area of the optical storage medium. This power adjusting area is used, at least in part, to adjust the power of the optical beam.
Moreover, the present invention also relates to an optical storage medium processing apparatus for accessing an optical storage medium by radiating thereto an optical beam. This apparatus includes an optical head for radiating an optical beam of a predetermined power to a predetermined position of the optical storage medium; and a high power process controller for positioning the optical head to direct the optical beam to a power adjusting area. The high power process controller is also used for controlling the power of the optical beam to be a power that is higher than that used for recording or erasing, to thereby control a high power process in which the high power optical beam is radiated upon the power adjusting area.
With the present invention, the sensitivity characteristic of the power adjusting area of the medium at its initial condition (i.e., during the period immediately after the manufacture of the optical storage medium) may be changed to a sensitivity characteristic of a saturated condition after repetition of write and erase operations a plurality of times. Namely, in this saturated condition, even after the write and erase operations are repeated, sensitivity shifts (i.e., variations of the optimum recording power) do not occur, and the optimum recording power for the medium can precisely be controlled.
Naturally, it is better to conduct the high power process upon the entire medium, but processing times as long as several thousand minutes may be required for performing high power proce
Kumita Hiroshi
Nanba Yoshiyuki
Yanagi Shigenori
Dinh Tan
Fujitsu Limited
Greer Burns & Crain Ltd.
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