Optical pickup device and objective lens used in the same

摘要

An optical system (1,2) has an optical functional surface including a common region (A) used for conducting information recording and/or reproducing for both of a first optical information recording medium and a second optical information recording medium. The common region (A) comprises a refractive surface (A,1) of an imaginary basic aspherical surface and an optical path difference providing structure (A,2) in which plural ring-shapes zones are separated around the center of an optical axis and neighboring ring-shaped zones are displaced to each other in a direction of an optical axis so as to cause an optical path difference obtained by multiplying a predetermined wavelength lambda s ( lambda 1 < lambda s < lambda 2) with almost an integer. The refractive surface (1) of the imaginary basic aspherical surface is structured such that a spherical aberration becomes under connected on the first information recording medium and a spherical aberration becomes over connected on the second information recording medium. <IMAGE>