US Patent 7764582 Focus servo apparatus

A focus servo apparatus which comprises an optical pickup having a power lens that changes an incidence angle of laser light incident on an objective lens and a power lens actuator that drives the power lens along an optical axis direction. In a focus search operation, the focus servo apparatus controls the power lens actuator to drive the power lens along the optical axis direction and detects having been brought into the focus servo area on the basis of a focus error signal obtained from photo-reception outputs from a photo-detector of the optical pickup, and then allows a focus servo to be in lock and returns the power lens to its initial position with driving the objective lens so as to maintain the lock state.