APPARATUS FOR OPTICALLY SCANNING AN INFORMATION PLANE

摘要

An optical scanning apparatus is described, which comprises a radiation source (7) supplying a scanning beam (b1), an objective system (8) for focusing the scanning beam (b1) to a scanning spot (S1) in an information plane (2) to be scanned and a first diffraction element (9) for deforming the beam reflected by the information plane (2) in such a way that a focus-error signal can be derived therefrom. The apparatus further comprises a second diffraction element (10) for forming two auxiliary beams (b2,b3) by means of which a tracking-error signal can be derived, which second diffraction element has such a size and is arranged at such position that the beams originating from the first diffraction element (9) do not traverse the second diffraction element.