Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-04-24
2004-05-25
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013540
Reexamination Certificate
active
06741527
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magneto-optical recording medium and a magneto-optical recording and reproducing device which use a magnetic super-resolution method.
BACKGROUND OF THE INVENTION
In magneto-optical disk devices which use the magnetic super-resolution method, a magneto-optical disk is used which is provided with a recording layer and with a reproducing layer having in-plane magnetization. In this type of magneto-optical disk device, during reproducing, a light beam is projected onto the reproducing layer side of the magneto-optical disk. Then, part of the area of the reproducing layer within the light beam spot is heated to above a predetermined temperature, and the magnetization of this portion (referred to as an aperture) shifts from in-plane magnetization to a perpendicular magnetization conforming to that of the recording layer beneath the aperture, i.e., the magnetization of the recording layer is copied to the reproducing layer. In this way, with this type of magneto-optical disk device, by reproducing the magnetization of the aperture, recorded marks smaller in diameter than the light beam spot can be reproduced.
In magneto-optical disk devices using this magnetic super-resolution method, it is preferable if the power of the light beam during reproduction (the reproducing power) is continuously at an optimum level. However, there are cases in which the optimum level of the reproducing power fluctuates with changes in the ambient temperature at the time of reproducing. For this reason, even if the current for driving the structure which produces the light beam (the driving current) is held constant, there are cases in which the reproducing power deviates from the optimum level.
If reproducing power is much stronger than the optimum level, the aperture formed on the magneto-optical disk becomes too large. Consequently, output of reproducing signals from tracks adjacent to the track being reproduced (crosstalk) is increased, the proportion of noise signals included in the reproduced data increases, and reading errors are more likely to occur.
Again, if reproducing power is much weaker than the optimum level, the aperture becomes smaller than the recorded mark, and the reproducing signal output from the target track is reduced. Accordingly, reading errors are more likely to occur in this case as well.
In a recording and reproducing device disclosed in Japanese Unexamined Patent Publication No. 63817/1996 (Tokukaihei 8-63817, published on Mar. 8, 1996) (U.S. Pat. No. 5,617,400), in order to control reproducing power, long marks and short marks formed on a magneto-optical disk are reproduced. These long and short marks are two types of recorded marks for reproducing power control of different mark lengths. In this device, reproducing power is controlled so as to bring close to a predetermined value a ratio of the quantities of the reproducing signals from these recorded marks. By this means, in this device, reproducing power is maintained at an optimum value, and the likelihood of reading errors is reduced.
FIG. 12
schematically shows a construction of a reproducing power control section in the recording and reproducing device of the above publication. Further,
FIG. 13
is a schematic diagram showing a construction of a magneto-optical disk
30
used for the recording and reproducing device.
Prior to the explanation on the construction of the recording and reproducing device described in the publication, the construction of the magneto-optical disk
30
is firstly discussed. A track
320
is concentrically formed in the magneto-optical disk
30
. A plurality of sectors
300
are successively formed in the track
320
. As shown in
FIG. 13
, an address area
301
, a reproducing power control area
302
, and a data recording area
303
are formed in each of the sectors
300
. The address area
301
is provided for recording information about a position of the sector. The reproducing power control area
302
is provided for recording a pattern of repeated short marks and a pattern of repeated long marks as recording marks for controlling reproducing power. The data recording area
303
is provided for recording digital data.
Here, the long mark is a mark having a larger diameter than the aperture, and the short mark is a mark having a shorter diameter than the aperture.
Next, referring to
FIG. 12
, the following explanation describes a reproducing operation in the recording and reproducing device. Firstly, when a light beam emitted from a semiconductor laser
32
reaches the address area
301
of the sector
300
on the magneto-optical disk
30
, a sector address is recognized. And then, the emitted light is projected onto the reproducing power control area
302
. Next, the light is reflected from a pattern of repeated long marks and short marks that is recorded in the area
302
, and the light is converted to a reproducing signal by a photo-diode
33
. The reproducing signal is inputted to an amplitude ratio detecting circuit
34
. And an amplitude ratio detected in the amplitude ratio detecting circuit
34
is compared with a standard amplitude ratio by a differential amplifier
35
, feedback is performed in a direction reducing a difference of the ratios, and a laser power control circuit
36
controls a driving current of the semiconductor laser
32
.
After a driving current of a laser beam is controlled in such a manner so as to provide optimum reproducing power, the emitted light is projected to the area
303
, the reproducing signal which has been read is inputted to a reproducing data processing circuit
37
, and the likelihood of reading errors is reduced.
And then, when the emitted light reaches the next sector, the same operation is repeated so as to reset the optimum reproducing power.
In this way, the recording area of recording marks for controlling reproducing power is provided for each sector, and the quantity of reproducing signals for controlling reproducing power is detected for each sector, so that the reproducing power control can provide a response with a short time interval and correspond to short-time fluctuation of the optimum reproducing power.
However, the above magneto-optical reproducing method using the magnetic super-resolution method is more likely to be affected by a magnetic field from the outside because a signal is read based on a magnetic field stored in the recording medium and a temperature increase caused by radiation of a light beam. Namely, even when a length of the recording mark and the reproducing power remain the same, an amplitude of a signal may be changed according to the intensity of the external magnetic field.
The intensity of the external magnetic field varies due to leak of a magnetic field and others from an actuator of an optical head, and the intensity is also affected by a magnetic field from a recording mark recorded around a recording mark to be reproduced.
The intensity of the magnetic field from the surrounding recording mark depends upon a relationship between the recording mark to be reproduced and the surrounding recording mark with respect to size and polarity. Therefore, in the magneto-optical reproduction using the magnetic super-resolution method, an amplitude value of a reproducing signal may be varied depending upon a kind of recording mark recorded in adjacent tracks.
FIG. 14
is a graph showing measurement results of amplitude values regarding long and short marks (2T pattern and 8T pattern) relative to a change in reproducing power with respect to the following cases: when no recording mark is recorded in adjacent tracks of a track to be reproduced, and when a recording mark is recorded in the adjacent tracks with the same length as a recording mark belonging to a track to be reproduced. Here, a horizontal axis represents a reproduction power and a vertical axis represents an amplitude value (PEAK TO PEAK value).
According to the results, it is understood that when short marks are adjacent to each other, an amplitude value is hardly affected by the presence or ab
Maeda Shigemi
Okumura Tetsuya
Conlin David G.
Daley, Jr. William J.
Dinh Tan
Edwards & Angell LLP
Sharp Kabushiki Kaisha
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