Abstract
A simple acousto-optic system is described that is capable of
demodulating frequency- and phase-modulated signals using a bicell
photodetector. A summary of an analytical study of the system is provided,
describing its main performance characteristics. Results from a
Mathcad model of the system are presented showing that, by taking the
sum and difference of the outputs from the two bicell elements, it is
possible to identify and demodulate a wide range of different types of
modulation without any a priori information. Thus the technique is well
suited for surveillance receiver and electronic support measures (ESM)
applications. In particular, it is shown that biphase shift keying (BPSK),
quaternary phase shift keying (QPSK), offset-keyed QPSK, differential
QPSK, continuous phase frequency shift keying (FSK) [including minimum
shift keying (MSK)], and ordinary FSK all give unique and easily
identifiable signatures. Experimental results are presented, which are in
good agreement with both theoretical and modeled results.
