Objective lens comprising a diffraction structure for distributing light in to light of different diffraction orders, optical pickup device, and optical information recording or reproduction apparatus having same

摘要

An objective lens includes a diffraction structure for distributing much of a quantity of an incident light beam into two diffracted lights having different diffraction orders from each other, wherein recording or reproduction of information on an optical disk is performed by converging the diffracted light having a longer focal length of the two diffracted lights onto an information recording surface through a protective layer of the optical disk, and a distance from the objective lens to a surface of the protective layer along an optical axis is longer than a distance between focuses of the two diffracted lights along the optical axis when the diffracted light having the longer focal length is converged onto the information recording surface of the optical disk.