Patent ID: 8369191

Claim:
A hard disk drive, comprising: a recording medium; a magnetic head including a laser diode that emits laser light, a photodiode that measures light strength of the laser light emitted from the laser diode, a near field generator that generates near field light from the laser light emitted from the laser diode at an air bearing surface facing the recording medium, a main pole for recording that is disposed adjacent to the near field generator and having a tip part positioned at the air bearing surface, and a reproducing element; a housing incorporating the recording medium and the magnetic head; a temperature sensor that measures temperature inside the housing; and a controller, wherein the controller includes: means for recording information to the recording medium by the main pole as the near field generator generates near field light, while varying driving current of the laser diode and observing output current of the photodiode; means for reproducing the recorded information with the reproducing element and for obtaining reproducing signal current; means for determining one output current of the photodiode as a first saturated output current, the one output current being defined where temperature measured by the temperature sensor is a first temperature and where signal-to-noise-ratio (SNR) of the reproducing signal current of the reproducing element is saturated with respect to an increase in the output current of the photodiode; means for determining another output current of the photodiode as a second saturated output current, the another output current being defined where temperature measured by the temperature sensor is a second temperature, which is different from the first temperature, and where SNR of the reproducing signal current of the reproducing element is saturated with respect to an increase in the output current of the photodiode; means for estimating a target saturated output current at operation temperature from the operation temperature measured by the temperature sensor during the hard disk device operation, the first and second temperatures, and the first and second saturated output currents; and means for controlling the laser diode that controls the driving current of the laser diode in order to obtain the estimated target saturated output current.