Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2001-12-27
2004-01-06
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S059100, C369S116000
Reexamination Certificate
active
06674701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording medium readout apparatus in which read beam power is controlled based on the amplitude ratio of a readout signal from a magnetic super resolution optical recording medium.
2. Description of the Related Art
Magnetic super resolution magneto-optical readout art has been developed that in magneto-optical disks representing optical recording media provided with a readout layer possessing in-plane magnetization and a recording layer, readout of recorded marks smaller in diameter than the spot size of a beam of light is permitted by as a result of irradiation with a beam of light directed from a readout layer of an magneto-optical disk, causing transfer of magnetic state at the recording layer in correspondence to magnetic state at the readout layer, with transition from in-plane magnetization to perpendicular magnetization, in a portion (hereinafter “aperture”) of the irradiated region at which the temperature rises above a predetermined temperature.
In such art, due to changes in ambient temperature during readout it is possible for the optimum readout power of the beam to fluctuate despite the fact that the drive current causing generation of the beam is held constant. Furthermore, when readout power is too high, this causes aperture size to become too large, increasing the presence of crosstalk from adjacent tracks in the output readout signal, decreasing the signal-to-noise ratio of the data being read, and increasing the frequency of occurrence of read errors. Moreover, when readout power is too low, this can cause aperture size to become smaller than the size of recorded marks, and can cause the output of the readout signal from the track being read to become too weak, increasing the frequency of occurrence of read errors.
As a remedy to the foregoing problem, in the conventional art as disclosed at Japanese Unexamined Patent Publication JP-A 8-63817 (1996), two species of readout power control marks having different lengths are provided on a magneto-optical disk, readout power being constantly maintained at an optimum value and frequency of occurrence of read errors being held to an acceptable level as a result of reading these marks and controlling readout power so as to cause the ratio between amplitudes of the signals read from those marks to approach a predetermined value.
Furthermore, in the conventional art as disclosed at Japanese Unexamined Patent Publication JP-A 2000-99945 (2000), in the event that normal detection of amplitude ratio from the signals read from the foregoing readout power control marks is for some reason interrupted, by holding readout power at the value it had immediately preceding occurrence of the inability to carry out normal detection it is possible to prevent abnormality in the controlled readout power.
FIG. 11
is a block diagram showing the constitution of an optical recording medium readout apparatus
1
in the conventional art.
FIG. 12
is a drawing showing the structure of a magneto-optical disk
10
representing an optical recording medium. A first sector
15
at a track on an information recording surface of the magneto-optical disk
10
comprises an address region
15
a
indicating the location of the sector, a readout power control region
15
b
in which a repeating pattern of short and long marks representing readout power control marks is recorded, and a data recording region
15
c
in which digital data is recorded. At a track on an information recording surface of the magneto-optical disk
10
other than the track containing the first sector
15
, there is a second sector
16
, and the second sector
16
comprises regions similar to those of the first sector
15
.
The optical recording medium readout apparatus
1
comprises an optical head
2
, an amplitude ratio detection circuit
3
, a differential amplifier
4
, a readout power control circuit
5
, a switch
6
, a readout power value storage circuit
7
, a seek status detection circuit
8
, and a data readout circuit
9
. The optical head
2
comprises a semiconductor laser source
2
a
and a photodiode
2
b
. Laser light from a light beam emitted by the semiconductor laser source
2
a
is incident at the address region
15
a
of sector
15
of the optical disk
10
and is reflected therefrom. The laser light reflected at the address region
15
a
is incident on the photodiode
2
b
, where it undergoes photoelectric conversion, allowing the optical recording medium readout apparatus
1
to identify the sector address corresponding to the location of sector
15
.
Furthermore, laser light emitted from the semiconductor laser source
2
a
is incident at the readout power control region
15
b
of sector
15
and is reflected therefrom. The laser light reflected at the readout power control region
15
b
, now containing information about a repeating pattern of short and long marks thereat, is incident on the photodiode
2
b
, where it undergoes photoelectric conversion to become a control readout signal. The control readout signal is input at the amplitude ratio detection circuit
3
, where an average amplitude ratio is calculated. The average amplitude ratio and a target value for amplitude ratio are input at the differential amplifier
4
, where a value is calculated by subtracting the target value from the average amplitude ratio. The readout power control circuit
5
outputs a signal indicating a value corresponding to an optimum readout power based on which the semiconductor laser source
2
a
can be controlled so as to cause the value calculated by the differential amplifier
4
to go to zero. The signal indicating a value corresponding to an optimum readout power which is output from the readout power control circuit
5
is input at the switch
6
, and is also input at the readout power value storage circuit
7
, where it is stored.
In accordance with a signal from the seek status detection circuit
8
which is connected to the optical head
2
, the switch
6
causes either the readout power control circuit
5
or the readout power value storage circuit
7
to be electrically connected to the semiconductor laser source
2
a
, causing a drive current corresponding to the readout power value to be delivered to the semiconductor laser source
2
a
. The seek status detection circuit
8
detects the status of movement(hereinafter “seek”) of the optical head
2
between tracks. When the seek status detection circuit
8
sends a detection signal to the switch
6
indicating that the optical head
2
is not in mid-seek, in accordance with such detection signal the switch
6
causes the readout power control circuit
5
to be electrically connected to the semiconductor laser source
2
a
. The semiconductor laser source
2
a
is thereafter driven with a drive current such as will produce an optimum readout power value as indicated by the signal output from the readout power control circuit
5
, emitting laser light, and the laser light is incident at the data recording region
15
c
of sector
15
, is reflected therefrom, and is incident on the photodiode
2
b
, where it undergoes photoelectric conversion to become a readout signal, and this is input at the data readout circuit
9
. The foregoing sequence of events is repeated for sectors following sector
15
within the same track as sector
15
, with the optimum readout power being reset to a new value for each sector. This allows readout information data to be output with a low error rate.
When the seek status detection circuit
8
delivers a detection signal to the switch
6
indicating that the optical head
2
has initiated a seek operation which will move it from the track containing sector
15
to the track containing sector
16
, in accordance with such detection signal the switch
6
causes the readout power value storage circuit
7
to be electrically connected to the semiconductor laser source
2
a
. At this time, the semiconductor laser source
2
a
is supplied with a drive current such as will produce a readout po
Maeda Shigemi
Okumura Tetsuya
Conlin David G.
Edwards & Angell
Sharp Kabushiki Kaisha
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