Apparatus for simulating optical transmission links

Abstract

A space-to-space or space-to-earth optical transmission link is simulated by positioning a linear optical modulator between an optical carrier source and a receiver for the carrier. The optical modulator is driven by an analog signal having random variations indicative of characteristics of the transmission link, as derived from an analog computer circuit. The analog computer circuit is responsive to a Gaussian random analog source. For certain types of links, the analog computer circuit is responsive to a pair of Gaussian analog signals which are derived by feeding a relatively wide band Gaussian analog source in parallel to a first low pass filter and to a heterodyne circuit that derives a beat frequency output that is passed through a second low pass filter having the same characteristics as the first low pass filter. For space-to-space transmission, transmitter pointing jitter is a dominant noise source and is simulated by deriving a beta statistical variation from the analog computer. For space-to-earth transmission, atmospheric scintillation is a dominant noise source and is simulated by driving the modulator with one of (1) a log normal, (2) Rayleigh, or (3) Ricean output of the analog computer circuit.