OPTICAL SCANNING DEVICE

摘要

The invention relates to an optical scanning device and to an optical wavefront modifier for use therein, for scanning an optical record carrier, such as an optical disk comprising an information layer. The device comprises a radiation source (9) for emitting an incident radiation beam; a detection system comprising an information signal detector (25) arranged to receive radiation reflected from the information layer and to detect an information signal therein; an optical system (14, 12) for focusing the incident radiation beam to a spot on in the record carrier, and for directing the reflected radiation beam onto the information signal detector; and an optical wavefront modifier (10) arranged in the path of the incident radiation beam and the reflected radiation beam. The incident radiation beam has a first wavefront shape at a given location (L) prior to its incidence on the optical wavefront modifier and the reflected radiation beam has a second wavefront shape at the given location after passing through the optical wavefront modifier. In embodiments of the invention, the optical wavefront modifier is arranged to perform wavefront modification on the incident and reflected radiation beams such that the second wavefront shape is substantially different to the first wavefront shape. The second wavefront shape is of such a form that the optical path of the reflected radiation beam is less than the optical path of the incident radiation beam so that the optical scanning device can be further miniaturised.