Performance of an optical heterodyne receiver for various receiving apertures

The results of an experimental study, dealing with the coherent detection of an optical signal after propagation over a 2.6-km atmospheric path, are presented. The average receiver output power was measured at the intermediate frequency for various receiving aperture diameters. The measured values were compared with predicted values calculated on the basis of no atmospheric degradations. The asymptotic approach of the received signal-to-noise ratio to a constant value for increasing aperture diameters is demonstrated and shown to be due to the turbulence in the propagation path. Typical values of the spatial coherence area are discussed.