Patent ID: 7292517

Claim:
An optical scanning device for scanning of a first, second and third type of optical record carrier with radiation of a first wavelength λ 1 , a second wavelength λ 2 and a third wavelength λ 3 , respectively, the three wavelengths being substantially different, the device comprising: 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, wherein the stepped profile substantially approximates a flat wavefront at the first wavelength λ 1 , a spherical aberration wavefront at the second wavelength λ 2 , and a flat or spherical aberration wavefront at the third wavelength λ 3 and wherein an attainable number of substantially different phases for different heights of a phase element at the wavelength λ 2 is different from an attainable number of substantially different phase steps for different heights of a phase element at the λ 3 , wherein |λ 1 -λ 2 |, |λ 2 -λ 3 | and |λ 1 -λ 3 | are each larger than 50 nm.