Optical pickup optical system, optical pickup apparatus, coupling optical system, coupling optical system lens and recording/reproduction apparatus

Abstract

An optical pickup apparatus for recording and/or reproducing information on an optical information recording medium includes a light source emitting a light flux, a light-converging optical system to converge a light flux emitted from the light source, having a coupling optical system which changes a divergent angle of a light flux emitted from the light source and an objective lens optical system which converges a light flux emerging from the coupling optical system on an information recording surface of the optical information recording medium, and an optical detector for detecting reflected light or transmitted light coming from the information recording surface of the optical information recording medium. In the optical pickup apparatus, at least one surface of the coupling optical system is provided with a diffraction surface by which the longitudinal spherical aberration on the occasion wherein light having a wavelength differing from that of light with a prescribed wavelength by a prescribed difference of wavelength is made to enter the objective lens optical system through the coupling optical system is made to be smaller, compared with the longitudinal spherical aberration on the occasion wherein light having a wavelength different by a prescribed difference of wavelength is made to enter the objective lens optical system.