Patent ID: 7920449
Filing Date: 2011-04-05
Classification: G11B

Abstract:
1. A method of controlling a focusing operation by moving an objective lens in a direction towards or away from an optical information storage medium comprising a plurality of data layers, the method comprising: receiving a focusing lead-in command signal to focus an optical beam on a target data layer; compensating for spherical aberration with respect to the target data layer; detecting a focus error signal based on an intensity of the optical beam reflected from the optical information storage medium and condensed by an optical detector; identifying the target data layer using an amplitude or a frequency of the focus error signal; focusing the optical beam on the target data layer by moving the objective lens in an opposite direction from a direction in which the objective lens is initially moved; identifying the n-th data layer as the target data layer, in response to the amplitude between the highest level and the lowest level of the focus error signal with respect to the n-th data layer being greater than the amplitude between the highest level and the lowest level of the focus error signal with respect to the (n+1)-th data layer; moving the objective lens away from the optical information storage medium; and moving the objective lens towards the optical information storage medium until an (n+2)-th data layer is detected, in response to the amplitude between the highest level and the lowest level of the focus error signal with respect to the (n+1)- th data layer being greater than the amplitude between the highest level and the lowest level of the focus error signal with respect to the n-th data layer, wherein the focusing of the optical beam on the target data layer comprises turning a focus servo signal on, wherein the identifying of the target data layer comprises identifying a data layer comprising a greatest amplitude of the focus error signal among a plurality of amplitudes corresponding to the plurality of data layers as the target data layer, and wherein the identifying of the target data layer further comprises: