Objective lens and optical system for optical pick-up

Abstract

An optical system of an optical pick-up is provided. The optical system includes an optical element including at least a phase shift surface among the surfaces thereof, and located closer to a light source than the objective lens. In this configuration, ttis satisfied, where trepresents a thickness of a cover layer of a first optical disc for which a first laser beam is employed, and ta thickness of a cover layer of a second optical disc for which a second laser beam, having a longer wavelength than the first laser beam, is employed. NANAis satisfied, where NArepresents a numerical aperture for the first optical disc, and NAthe numerical aperture for the second optical disc. The phase shift surface includes a first region that converges the first laser beam on a recording surface of the first optical disc, and the second laser beam on a recording surface of the second optical disc. The first region includes at least an annular zone structure having an annular zone group including a step that gives an additional optical path length to the first laser beam generally by two wavelengths, with respect to an inner refracting surface at a boundary between adjacent refracting surfaces, and a return step portion located at an outer position of the annular zone group.