Optical pick-up device and objective lens used therein

摘要

An optical pickup apparatus comprises two light sources having two wavelengths (lambd1<lambd2) and a converging optical system having an objective lens. The objective lens comprises a central region; a peripheral region provided at an outside of the central region on at least one optical surface of the objective lens; a diffractive ring-shaped zones which is blazed on a basis of a wavelength lambd0 (lambd1<lambd0<lambd2) and is formed on each of the central region and the peripheral region; and a phase difference suppressing structure to suppress a phase difference between a wavefront of a light flux passing the central region and a wavefront of a light flux passing the peripheral region when recording or reproducing information is conducted for the first optical information recording medium.