OPTICAL SCANNING DEVICE

摘要

An optical scanning device for scanning of a first, second and third type of optical record carrier with radiation of a first wavelength lambda₁, a second wavelength lambda₂ and a third wavelength lambda₃, respectively, where the three wavelengths are substantially different. The device comprises: a radiation source for emitting a beam of said radiation, an objective system for converging the beam on a selected one of the optical record carriers, and a phase structure arranged in the path of the beam, the phase structure comprising a plurality of phase elements of different heights, forming a non-periodic stepped profile of optical paths in the beam, and is characterised in that the stepped profile substantially approximates a flat wavefront at the first wavelength lambda₁, a spherical aberration wavefront at the second wavelength lambda₂, and a flat or spherical aberration wavefront at the third wavelength lambda₃.