Objective lens for optical pick-up

Abstract

An objective lens for an optical pick-up which is used to record data to and/or to reproduce data from at least three types of optical discs by selectively using one of at least three light beams having different wavelengths is provided. When thicknesses of a first, second and optical discs are represented by t, tand t, respectively, a relationship t≦t<tis satisfied. When numerical apertures required for the first, second and third optical discs are represented by NA, NAand NA, respectively, a relationship NA≧NA>NAis satisfied. The first, second and third light beams are incident on the objective lens as substantially collimated light beams, respectively. In this configuration, at least one of surfaces of the objective lens includes a first area for attaining the numerical aperture required for recording data to and/or reproducing data from the third optical disc, and a second area located outside the first area. The first area includes an inner area including an optical axis of the objective lens, and an outer area located outside the inner area. The outer area is configured to converge the third light beam on a data recording layer of the third optical disc with an amount of an aberration being substantially zero. The objective lens satisfies a condition: 0.75<h/h<0.87 . . . (1), where hrepresents an effective radius of the first area, and hrepresents an effective radius of the inner area.