Optical disk drive system for use with disks having different protection layer depths

摘要

The objective lens of an optical disk drive has a suitable positioning and numerical aperture so that the light beam will be focused into a spot on the optical media of a first optical disk having a cover plate with a first thickness. When a second optical disk is utilized having a cover plate with a second thickness different from the first thickness, a liquid crystal compensator lens is actuated in the optical path between the light source and the objective lens for focusing the light beam into a spot on the optical media of the second optical disk. A correction signal may be applied to the liquid crystal in the compensator lens for altering a refractive index thereof. This substantially eliminates a wavefront aberration in the reflected light beam which would otherwise occur if the beam were focused onto the optical media of the second optical disk solely by use of the objective lens. The lower alignment film of the liquid crystal compensator lens has a cross-section which is approximately sinusoidal in order to complement three waves of aberration (measured from peak-to-valley) in the reflected wavefront.