Patent ID: 7903531

Claim:
An optical disk apparatus for recording or reproducing information on or from an optical disk which has a transparent planar disk base member, a recording layer formed on the disk base member, and a reflecting layer for reflecting a laser beam by way of the disk base member, the reflecting layer being disposed on an opposite side of the disk base member than the recording layer, and the optical disk being configured such that an interval between the recording layer and the reflecting layer is longer than a wavelength of the laser beam, said optical disk apparatus comprising: a light source which irradiates the laser beam for recording or reproducing the information on or from the optical disk, wherein said light source irradiates the laser beam onto the recording layer of the optical disk by way of the disk base member to form a focusing spot on the recording layer; a photo detector which receives from the reflecting layer a reflected beam of the laser beam irradiated from said light source; a tilt detecting unit which detects tilt of the optical disk by using an output from said photo detector; a beam splitter which splits the reflected beam and the laser beam incident onto the optical disk such that the reflected beam and the laser beam incident onto the optical disk propagate along different optical paths from each other; an objective lens which focuses the laser beam split by the beam splitter onto the recording layer of the optical disk; an objective lens actuator which moves the objective lens to focus the laser beam onto the recording layer of the optical disk; an aberration canceling unit which is disposed on an optical path for guiding the reflected beam to the photo detector to cancel a defocus aberration and a spherical aberration of the reflected beam split by the beam splitter, and wherein the aberration canceling unit includes a condenser lens which focuses the reflected beam on the photo detector and a condenser lens actuator which moves the condenser lens to cancel the aberration of the reflected beam.