Field curvature reduction for optical system

摘要

An optical head ( 1 ) for scanning an optical record carrier ( 2 ) is provided with a compensator ( 16 ) for compensating the field curvature aberration of the objective system ( 18 ) caused by operation of the optical head at a different field angles. A surface of the compensator ( 16 ) comprises a phase structure in the form of annular areas ( 52, 53, 54, 55, 56 ), the areas forming a non-periodic pattern of optical paths of different lengths. The optical paths change as a function of field angle and form a field angle-dependent wavefront deviation that compensates field curvature of the optical head.