Abstract: An optical scanning device is for scanning an information layer (2) with a radiation beam (4). It includes: a radiation source (6) for providing said radiation beam, a lens system (7) for transforming said radiation beam to a scanning spot (17) on said information layer, and a wavefront modifier arranged between said radiation source and said scanning spot. The modifier including two elements (301, 302) having each an aspheric surface (301b, 302a) and being mutually linearly movable for introducing a wave-front modification in said second radiation beam. According to the invention, the aspheric surfaces are shaped so that: a first mutual linear displacement of the elements (301, 302) introduces a first wavefront modification (Wa) along a first axis (XO) in said second radiation beam, and a second mutual linear displacement of the elements introduces a second wavefront modification (Wb) along said second axis (YO) in said second radiation beam.

Abstract: 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.

Abstract: A holographic mask comprises a plurality of pixels each imparting a calculated phase and/or amplitude change to the projection beam to provide an image that is parallel to the mask. The holographic mask is used displaced from the best object plane of the projection lens.

Abstract: The invention relates to an optical scanning device (1) for scanning an information layer (2) by means of a radiation beam (4). The device includes: a radiation source (6) for providing said radiation beam, a lens system (7) for transforming said radiation beam to a converging beam (16), and a wavefront modifier including a first element (301) and a second element (302) having each an aspheric surface and being mutually movable in a plane perpendicular to an optical axis (12) of said lens system for introducing a wavefront modification (W1) in said converging beam. According to the invention, the aspheric surfaces of said first and second elements are shaped so that a mutual rotational displacement of the elements about an axis of rotation (ZA) which is parallel to said optical axis (12) generates said wavefront modification (W1).