US Patent 7489448 Optical scanning device

An optical scanning device provides a radiation source (2,200), a collimator lens (4,40), an objective (7,90) for converting a beam (5,30′) to a scanning spot at the position of an information layer (101) of a record carrier (1,100). The device also includes an electrowetting cell (6). The electrowetting cell (6) acts such that a beam (5,30′) enters the objective (7,90) at a predetermined height of an entrance pupil of the objective (7,90) independent of the position of the objective (7,90) and that the beam (5,30′) forms a predetermined angle at the entrance pupil of the objective (7,90) with the optical axis (8). In this way the rim intensity may be kept constant over the entrance pupil of the objective (7,90).