Optical recording/reproducing apparatus, optical system therefore and coupling lens

摘要

An optical pickup apparatus for conducting recording and/or reproducing for an optical information recording medium is provided with a light source; a coupling optical system to change a divergent angle of light flux emitted from the light source; an objective lens optical system for converging the light flux having passed through the coupling optical system on a information recording surface of the optical information recording medium; and a photo detector to detect the reflected light from the information recording surface of the optical information recording medium. The objective lens optical system comprises at least one lens made of a resin and having a positive refracting power, the coupling optical system comprises at least one lens made of a resin and having a positive refracting power and the coupling optical system further comprises an annular band-shaped diffractive surface having a negative diffracting power.