OBJECTIVE, OPTICAL PICKUP APPARATUS AND OPTICAL INFORMATION RECORDING AND/OR REPRODUCING APPARATUS

摘要

An objective optical system by which spherical aberration correction necessary for achieving compatibility among a high density optical disc, DVD and CD can be well performed without sacrificing characteristics, such as wavelength dependency of spherical aberration and tracking characteristic, and an optical pickup device and optical information recording/reproducing device using such objective optical system are provided. The objective optical system (OL) is provided for the optical pickup device (PU), which reproduces and/or records information from/in first to third optical information recording medium having a protection layer with a thickness of t1-t3 by using first to third luminous fluxes of a first wavelength (lambda1) to a third wavelength (lambda3) emitted from a first light source (LD1) to a third light source (LD3). The objective optical system (OL) is provided with a first diffraction structure (DOE1) whose diffraction order where the diffraction efficiency is maximum is the same for any of the first to the third luminous fluxes; and a second diffraction structure (DOE2) which diffracts the second luminous flux but not the first luminous flux nor the third luminous flux.