Experimental Comparison Of Coherent Array Detection And Conventional Coherent Detection For Laser Radar And Communications

There is an upper bound on the effective size of receiving aperture for both the improvement in carrier-to-noise ratio and the reduction in signal fading of a conventional coherent detection system due to the atmospheric turbulence-induced finite transverse coherence length of the received laser field for laser radar and communications. But a coherent array detection system, which uses multiple independent apertures/receivers whose IF\u27s are electro-optically co-phased in real time and then added, can overcome the effective aperture limitation and mitigate the signal fading. This paper presents experimental comparison of the performance of an eight-aperture coherent array detection system and the conventional coherent detection system. The field tests were conducted over two-km range (round-trip). The carrier-to-noise ratio and the fade statistics of the IF signals were investigated for both systems. The results show a gain factor of up to six on the mean carrier-to-noise ratio of the IF signal from the eight-aperture coherent array detection system compared to the conventional coherent detection system even though the two systems collected the same power of laser signal. Also shown is a factor of 100,000 reduction in probability of fade of the IF signal