Patent ID: 7885155
Filing Date: 2011-02-08
Classification: G11B

Abstract:
1. A data readout method for reading data recorded in an optical disk by irradiating a laser beam onto the optical disk, said method comprising the steps of: varying a light emission power level of the laser beam while the laser beam is irradiated on the optical disk, and acquiring a reflectivity of the optical disk corresponding to each of the light emission power levels; calculating a second derivative of a curve representing correlation between the reflectivity and the light emission power with respect to the light emission power; calculating an extreme value of the second derivative; and calculating an optimum readout power level for super resolution readout based on the extreme value, wherein said super resolution readout, data recorded at a recording density beyond a diffraction limit are read out; and wherein in the step of calculating the extreme value, two extreme values are calculated, and in the step of calculating the optimum readout power for super resolution readout, two light emission power levels are obtained corresponding to the two extreme values, respectively, and a larger one of the two light emission power levels is selected as the optimum readout power for super resolution readout; and wherein data having a recording density not exceeding the diffraction limit is recorded in the optical disk, said method further comprising a step of: calculating an optimum readout power for usual readout based on a smaller one of the two light emission power levels respectively corresponding to the two extreme values, wherein said usual readout, data recorded at a recording density not exceeding the diffraction limit are read out.