Patent ID: 7307933

Claim:
An optical disc drive for reading and/or writing data from/on an optical disc, having at least one information layer, by using a light beam, the optical disc drive comprising: a spherical aberration detecting section for generating a spherical aberration signal representing a spherical aberration that has been produced at a focal point of the light beam on the information layer of the optical 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 spherical aberration changing section; a memory for storing information on relationship between predetermined values of the aberration correction signal and distances from information layers of different types of optical discs to the surface of the optical discs; and means for detecting a value of the aberration correction signal that minimizes the spherical aberration in a situation where the focal point of the light beam is located on the information layer of the optical 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 optical disc, by comparing the value detected with the predetermined values of the aberration correction signal stored on the memory.