Patent ID: 6728042
Filing Date: 2004-04-27
Classification: G02B,G11B

Abstract:
An optical pickup apparatus, comprising:a first light source to emit a first light flux having a wavelength &lgr;1; a second light source to emit a second light flux having a wavelength &lgr;2 (&lgr;12); a converging optical system to converge the first or second light flux on a information recording plane in such a way that recording or reproducing information for a first optical information recording medium with a transparent base board having a thickness t1 is conducted by using the first light source and the converging optical system and recording or reproducing information for a second optical information recording medium with a transparent base board having a thickness t2 (t12) is conducted by using the second light source and the converging optical system; the converging optical system including an objective lens, wherein a first necessary numerical aperture of the objective lens to conduct recording or reproducing information for a first optical information recording medium is NA1 and a second necessary numerical aperture of the objective lens to conduct recording or reproducing information for a second optical information recording medium is NA2 (NA1>NA2); the objective lens comprising: a central region provided from an optical axis to a position corresponding to the second necessary numerical aperture and a peripheral region provided at an outside of the central region on at least one optical surface of the objective lens; a diffractive structure including a diffractive ring-shaped zones which is blazed on a basis of a wavelength &lgr;0 (&lgr;102) 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.