Laser mode hopping detection for heat-assisted magnetic recording device
First Claim
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1. A method for detecting mode hopping in a laser diode of a storage device, the method comprising steps of:
- receiving a time-variant signal from a photodetector optically connected to the laser diode while the laser diode is engaged for writing data to a recording media of the storage device, the time-variant signal indicating a light energy output of the laser diode;
differentiating the signal over time to produce a differentiated signal representing a rate of change in the light energy output of the laser diode;
determining whether the differentiated signal exceeds a threshold value indicating a rapid change in an oscillation wavelength of the laser diode; and
upon determining that the differentiated signal exceeds the threshold value, asserting a fault signal to a controller of the storage device indicating a potential write-fault due to a mode hopping event in the laser diode.
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Abstract
Methods and apparatuses for detecting mode hopping in a laser diode or other optical energy source in heat-assisted magnetic recording. An output power of the laser diode or other optical energy source is measured and the output power is differentiated over time to determine a rate of change. If it is determined that the rate of change exceeds a threshold value, a fault signal is asserted indicating a potential mode hopping event.
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Citations
18 Claims
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1. A method for detecting mode hopping in a laser diode of a storage device, the method comprising steps of:
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receiving a time-variant signal from a photodetector optically connected to the laser diode while the laser diode is engaged for writing data to a recording media of the storage device, the time-variant signal indicating a light energy output of the laser diode; differentiating the signal over time to produce a differentiated signal representing a rate of change in the light energy output of the laser diode; determining whether the differentiated signal exceeds a threshold value indicating a rapid change in an oscillation wavelength of the laser diode; and upon determining that the differentiated signal exceeds the threshold value, asserting a fault signal to a controller of the storage device indicating a potential write-fault due to a mode hopping event in the laser diode. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A storage device configured to:
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measure a voltage output of a photodetector optically connected to a laser diode in an optical heating element of a read/write head configured for heat-assisted magnetic recording (“
HAMR”
) during a write operation of data to a recording media of the storage device, the voltage output representing a light energy output of the laser diode;determine a rate of change in the voltage output of the photodetector over time; determine whether the rate of change in the voltage output of the photodetector exceeds a threshold value indicating a rapid change in an oscillation wavelength of the laser diode; and if the rate of change of the voltage output of the photodetector exceeds the threshold value, assert a fault signal to a controller of the storage device indicating a potential write fault. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A preamplifier for a hard disk drive (“
- HDD”
) implementing heat-assisted magnetic recording (“
HAMR”
), the preamplifier comprising;a differentiator circuit configured to receive a signal from a photodetector and produce a differentiated signal representing a rate of change in light energy output of a laser diode at any given time, the photodetector optically coupled to the laser diode in an optical heating element of a read/write head in the HDD; and a threshold detector configured to determine if the differentiated signal exceeds a threshold voltage level indicating a rapid change in an oscillation wavelength of the laser diode, and upon determining that the differentiated signal exceeds the threshold voltage level, assert a fault signal to a controller of the HDD. - View Dependent Claims (15, 16, 17, 18)
- HDD”
Specification