Optical path difference sensors

In a synthetic aperture system, three main kinds of optical path difference (OPD) sensors can be distinguished: sensors used for astronomy and sensors used for the real-time correction of OPD disturbances, fed either by a sta r or an internal source. To select the best implementation, a general analy sis of OPD measurement algorithms is made with a new vectorial formalism. F or any modulation, demodulation algorithms can be derived and compared in t erms of additive noise propagation and sensibility to systematic errors. Fr ee parameters (the modulation, the number of samples and the demodulation a lgorithm) can be optimized for each kind of sensor. For best performance, t hese sensors must use different implementations and thus be distinct. This should be considered in the instrument early design, as illustrated with tw o examples. (C) 2001 Academie des sciences/Editions scientifiques et medica les Elsevier SAS.