Optical system for optical disk, optical head unit for optical disk, and optical drive device

摘要

An optical system for an optical disk, comprising a light source (61), a collimating optical system (63) for converting a luminous flux from the light source into parallel rays of light, and an object lens (66) for condensing the parallel rays onto the information recording surface (71) of an optical disk. The object lens consisting of two or three lenses and having a numerical aperture (NA) of at least 0.82 enables a high-density recording. Since a third-order astigmatism produced when the object lens is tilted 0.7 degree with respect to an optical axis is as small as up to 10 m lambda, a residual aberration, after a third-order comatic aberration produced when the optical disk is tilted due to warping or the like is corrected by tilting the optical lens, can be reduced. Therefore, a tilted optical disk still can ensure a satisfactory recording and/or reproducing quality.