Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-03-08
2003-04-29
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S059110
Reexamination Certificate
active
06556535
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording/reproducing apparatus and more particularly to an optical recording/reproducing apparatus for recording and reproducing data out of an overwritable optical recording/reproducing medium, e.g., a phase change optical medium.
The prerequisite for an overwritable optical recording/reproducing medium, particularly a phase change optical medium, is that in the event of overwriting, an optical head outputs both the erasing power and the recording power in a stable manner. Accordingly, when erasing power and/or recording power differ from optimal power, record marks formed on the recording film of the medium deteriorates and thereby increasing a record/reproduction error rate.
A conventional optical recording/reproducing apparatus includes a mechanism to maintain the mean output of an optical head constant. This function corresponds to maintaining recording power to be constant at the time of overwriting. As for erasing power, while the minimum value in the binary modulation condition of an optical head must be constantly maintained, it has been customary to fix a current that sets the mimimum value.
A conventional optical recording/reproducing apparatus will be described with reference to FIG.
4
. As shown, the apparatus includes a monitor sensor
110
, an amplifier
120
, a comparator
130
, current amplifiers
140
and
170
each for setting an amount of laser diode emission, a reference recording power value generator
150
, a reference erasing power value generator
160
, and a laser diode
180
playing the role of an optical head.
In operation, the monitor sensor
110
senses the amount of emission from the laser diode or optical head
180
during recording. The output signal of the monitor sensor
110
is input to the amplifier
120
and amplified to a DC level necessary for control thereby. An amplified signal output from the amplifier
120
is then fed to one input of the comparator
130
. A reference recording power value output from the reference recording power value generator
150
is applied to the other input of the comparator
130
. The comparator
130
compares the amplified signal and the reference recording power value and delivers the result of the comparison to the current amplifier
140
. Binary record data are also input to the current amplifier
140
. A current set by the current amplifier
140
is output when the record data is, e.g., (logical) ONE “1”, but it is not output when the record data is (logical) ZERO “0”. The current set by the current amplifier
140
is next fed to the laser diode
180
.
Also, the reference erasing power value generator
160
feeds a constant current to the current amplifier
170
. A current set by the current amplifier
170
is also input to the laser diode
180
. In this manner, recording power and erasing power necessary for overwriting are delivered to the laser diode or optical head
180
.
As stated above, the conventional apparatus senses the means output of the laser diode
180
, compares it with a reference value , and sets a laser diode current or recording power such that the mean output coincides with the reference value. This is adequate to maintain the recording power constant even when temperatures around the apparatus varies. On the other hand, to set erasing power, a constant current is input to the laser diode
180
. However, as shown in
FIG. 5
, the current-to-emission characteristic of the laser diode
180
is such that while a constant current is fed, the elevation of the ambient temperature causes the emission of the laser diode to decrease. Specifically,
FIG. 5
indicates that as the ambient temperature rises from 0 C. to 25 C. and further to 50 C. while a constant current is fed, the emission of the laser diode sequentially decreases. Consequently, when the ambient temperature varies, adequate erasing power cannot be set and results in the deterioration of the record/reproduction error rate.
Japanese Patent Laid-Open Publication No. 6-28676, for example, discloses circuitry for controlling not only recording power but also erasing power. The circuitry includes a pin photodiode for sensing the output of a semiconductor laser and sets erasing power and recording power on the basis of the output of the pin photodiode. A sample-and-hold circuit holds the set erasing power and recording power and continuously applies them to the semiconductor laser until the end of the recording and erasing operation. With this configuration, the circuitry may output adequate erasing power just after the start of a recording operation. However, the circuitry does not guarantee that the erasing power remains adequate despite the variation of ambient temperature that may occur after the start of recording.
Japanese Patent Laid-Open Publication Nos. 4-362525, 7-262560 and 10-134352 also teach technologies of the kind described. None of them, however, teaches a method for maintaining adequate erasing power against the varying ambient temperature.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical recording/reproducing apparatus capable of maintaining adequate recording power as well as adequate erasing power necessary for recording even when the ambient temperature varies.
An optical recording/reproducing apparatus of the present invention includes a mean value detecting device for detecting a mean value in the binary modulation condition of the output of an optical head, a minimum value detecting device for detecting a minimum value in the binary modulation condition of the output of the optical head, and an input current setting device for setting a current to be input to the optical head in accordance with the above mean value and minimum value.
REFERENCES:
patent: 4685097 (1987-08-01), van der Put
patent: 4796250 (1989-01-01), Kobayashi et al.
patent: 5040163 (1991-08-01), Sasaki et al.
patent: 5477557 (1995-12-01), Inaba et al.
patent: 5495463 (1996-02-01), Akagi et al.
patent: 5712839 (1998-01-01), Aoki
patent: 5745463 (1998-04-01), Aoki et al.
patent: 5768245 (1998-06-01), Maeda et al.
patent: 5798992 (1998-08-01), Kaneko et al.
patent: 6246659 (2001-06-01), Suzuki et al.
patent: 04157632 (1992-05-01), None
patent: 4362525 (1992-12-01), None
patent: 628676 (1994-02-01), None
patent: 7262560 (1995-10-01), None
patent: 10134352 (1998-05-01), None
Dickstein , Shapiro, Morin & Oshinsky, LLP
NEC Corporation
Tran Thang V.
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