Patent ID: 7920450

Claim:
An optical disc apparatus for reading and writing information on optical discs having different thicknesses of transparent layers by projecting a same wavelength of laser light onto the same, the apparatus comprising: an aberration correction unit for passing the laser beam so as to correct its spherical aberration; an objective lens for condensing the laser beam that passed through the aberration correction unit onto a recording surface of an optical disc; an actuator for moving the objective lens with respect to the optical disc; a signal detection unit for detecting reflection light from the optical disc so as to deliver a focus error signal or a sum light signal; and a control unit for controlling the aberration correction unit, the actuator and the signal detection unit, wherein the control unit drives and sets the aberration correction unit so that the laser beam has a predetermined spherical aberration, performs a focus search operation of moving the objective lens to approach the optical disc in a state where the laser beam is projected onto the optical disc, and uses at least one of the focus error signal and the sum light signal delivered from the signal detection unit at a just focus position as an optical disc type discrimination signal, and the control unit sets spherical aberration of the laser beam so that a waveform and an amplitude of the optical disc type discrimination signal are the same between the case where the focus search operation is performed for the optical disc having a thick transparent layer and the case where the focus search operation is performed for the optical disc having a thin transparent layer, performs the focus search operation, and discriminates a type of the optical disc by comparing the focus drive voltage signal value supplied to the actuator when the optical disc type discrimination signal is detected with a predetermined threshold value of the focus drive voltage signal.