Patent ID: 7130134

Claim:
An optical scanning device ( 1 ) for scanning an information layer ( 2 ) of an optical record carrier ( 3 ) by means of a radiation beam ( 4 ), including: a radiation source ( 6 ) for providing said radiation beam, a lens system ( 7 ) for transforming said radiation beam to a converging radiation beam ( 16 ) so as to form a scanning spot ( 17 ) in the position of the information layer, the lens system including a first objective lens ( 18 ) having an optical axis ( 12 ), and a wavefront modifier ( 30 ) arranged between said radiation source and the position of said scanning spot, the wavefront modifier including a first element ( 301 ) having a first aspheric surface ( 301 b ) and a second element ( 302 ) having a second aspheric surface ( 302 a ), said first and second elements being mutually movable in a plane perpendicular to said optical axis for introducing a wavefront modification W 1 in said converging beam, characterized in that said first and second aspheric surfaces are shaped so that a mutual rotational displacement of said first and second elements over an angle of rotation (Φ) about an axis of rotation (Z A ) which is parallel to said optical axis ( 12 ) generates said wavefront modification W 1 .