Point-to-point wireless communication using partially coherent optical fields

Coherent light launched into an atmospheric channel experiences substantial degradation in spatial coherence as it traverses the channel, resulting in beam wander and intensity scintillation at the receiver. Launching partially coherent light with well-defined "beam-like" properties into the channel may exploit the spatial and frequency diversity properties of the atmospheric path so that acceptably low levels of system bit error rate performance can be obtained at fiber-optic data rates. To better understand the properties of partially coherent light in an atmospheric channel, here we develop an analytic expression for the second moment of a partially coherent lowest-order Gaussian beam propagating in the presence of isotropic, homogeneous atmospheric turbulence. From the second moment equation expressions for the average intensity, beam size, complex degree of coherence, and lateral coherence length are derived. These results are valid for any beam type: focused, collimated, divergent, and the limiting cases of the plane and spherical wave. Expressions obtained here exactly reduce to the diffractive equivalents for a fully coherent beam when full coherence and the absence of turbulence are assumed. In addition, results correspond to expressions obtained previously for a partially coherent collimated beam in the absence of turbulence.