In this paper, a theoretical comparison is made of the mean carrier-to-noise ratio (CNR) for a coherent (heterodyne detection) equal gain (EG) optical array receiver system with that predicted by a conventional single-aperture monolithic coherent detector system. Our analysis shows that the mean CNR for an EG array receiver system improves significantly over that of a single aperture system. Experimental data taken from a recent outdoor experiment over a range up to 1 lan between target and transceiver are also presented and compared with the theory for a particular eight-element EG system developed at the University of Central Florida. Optical signals received by the EG receiver array are launched into eight single mode optical fibers. Phase compensation between the individual receivers is accomplished by wrapping the fibers around PZT cylinders that are controlled by phase compensating electronics.

The detection and processing of laser communication signals are affected by the fading induced onto these signals by atmospheric turbulence. One method of reducing this fading is to use an array of detectors in which each of the detector outputs are added together coherently. We present experimental verification and theory of a 1.06 mum eight-element coherent receiver used to mitigate the effects of fading over a 1-km outdoor range. The carrier-to-noise ratio (CNR) was measured on a single channel and was then compared with the CNR obtained from the coherent sum of the eight channels. The increase of the mean CNR for the coherent sum as compared with a single aperture was observed proportional to the number of the apertures under different conditions of atmospheric turbulence. The measured mean CNR gain fitted the theoretical prediction well when the laser intensity fluctuations followed the gamma distribution.