Patent attributes
An optical disc drive according to the present invention reads and/or writes data from/on an optical disc having at least one information layer with a light beam and includes: a spherical aberration detecting section for generating a spherical aberration signal representing a spherical aberration produced at a focal point of the light beam on the information layer of the disc; a spherical aberration changing section for changing the spherical aberration; a spherical aberration regulating section for generating an aberration correction signal to correct the spherical aberration by driving the changing section; and means for detecting a value of the aberration correction signal that minimizes the spherical aberration when the focal point of the light beam is located on the information layer of the disc and for detecting the depth of the information layer, which corresponds to a distance from the information layer on which the focal point of the light beam is located to the surface of the disc, based on the value.
