Accusto-optic time-integrating correlator for processing broadband doppler-shifted signals

摘要

This invention relates to an acousto-optic time-integrating correlator for processing broadband Doppler-shifted signals. The present invention uses a conical lens telescope to compensate, in one dimension, for the differences in the absolute values of Doppler shift occurring in broadband signals. A laser light beam is expanded to a sheet beam using a conventional beam expander. The sheet beam is split and redirected using a modified Koster's prism. The two sheet beams are them directed toward a SAW device. The SAW device contains two tilted transducers. The inputs to the SAW device are counterpropagating A Doppler-shifted sheet beam and an undiffracted sheet beam are processed by respective conical lens telescopes. The outputs of the conical lens telescopes are combined with associated unprocessed sheet beams and combined by respective modified Koster's prisms and imaged onto respective two-dimensional photodetectors. The output of one photodetector is subtracted from the other to reduce offsets. Three alternate embodiments are also disclosed which show how a conical lens telescope can be used to improve the broadband performance of prior art approaches that use cylindrical lenses.