VORRICHTUNG ZUM ABTASTEN EINER INFORMATIONSFLAECHE MITTELS OPTISCHER STRAHLUNG.

摘要

An apparatus is described for scanning an optical record carrier (1) in which a radiation beam (b) emitted by a source (4) is focussed by a lens system (6) and in which radiation reflected by the record carrier is focussed in two radiation spots (V1, V2) each co-operating with a separate detector pair (18, 19; 20, 21). Acombined beam-separating and beam-splitting element is constituted by a diffraction grating (9) comprising two sub-gratings (12, 13) with different grating parameters. The sub-gratings have varying grating periods (p1, p2) and curved grating strips (14, 15) so that less stringent requirements are imposed on the mutual positions of the source (4) and the detectors (18, 19; 20, 21).