Patent ID: 7130258
Filing Date: 2006-10-31
Classification: G11B

Abstract:
1. An optical head for scanning an optical record carrier having an information layer, the head comprising a radiation source for generating a radiation beam comprising a plurality of simultaneous diffraction subbeams, each of the plurality of simultaneous diffraction subbeams having a different angle of diffraction as compared to each other of the plurality of simultaneous diffraction subbeams, an optical system for simultaneously converging each of the plurality of simultaneous diffraction subbeams to a focus on corresponding portions of the information layer, the optical system imparting a field angle-dependent first wavefront deviation to the radiation beam, and a compensator arranged in the radiation beam for compensating the first wavefront deviation, wherein the compensator includes a phase structure of a material having field angle-dependent properties, the phase structure having the form of annular areas forming a non-periodic pattern of optical paths of different, field angle-dependent lengths, the optical paths forming a second wavefront deviation compensating the field angle-dependent first wavefront deviation, wherein the first wavefront deviation is field curvature.