Patent ID: 7184387

Claim:
An optical scanning device for scanning an optical record carrier comprising an information layer, the device comprising a radiation source for generating a main radiation beam and a subsidiary radiation beam, and a lens system, located between the radiation source and the information layer, for converging the main beam and the subsidiary beam to respective spots on the information layer, the main beam spot having a side-lobe, wherein the device includes: a phase modulating arrangement for generating a non-rotationally-symmetric phase profile in a subsidiary radiation beam, the subsidiary radiation beam being of a predetermined wavelength, the phase profile varying with an azimuthal angle measured about the optical axis of the beam portion, the phase profile varying such that successively different phases are introduced in at least five locations which are each at successive azimuthal angles (φ 1 , φ 2 , . . . φ N ) and each at a given radial distance from the optical axis, wherein the phase profile is such that the phases introduced, when taken in modulo 2π form, successively cycle through 0 to 2π at least twice, in each cycle taking at least a relatively low value and a relatively high value, whereby the subsidiary beam spot is provided with an intensity distribution on the information layer which overlaps that of the main beam spot side-lobe.