Experimental analysis of the effects of atmospheric parameters on performance of an optical communication link

Abstract

Performance of free-space optical communication links can be affected by spatial and temporal fields of the refractive index created by atmospheric turbulence. They result in wave front distortions and lead to performance degradation, which can be expressed quantitatively by reduction of the signal power and increase of the bit-error-rate (BER). Under severe turbulence conditions, these effects can be profound even in short-range links. While it is impossible to obtain closed-form solutions for instantaneous realizations of wave front distortions, several spectral models of atmospheric turbulence can be used to study statistical properties of the refractive index fluctuations and to find the scintillation index. This analysis can be further expanded to include communication performance of free-space optical links. From a practical stand point, it would be very beneficial to find a relationship between the expected system performance and specific variables responsible for wave front distortions, such as air temperature and pressure, temperature gradient, wind speed, cross wind, net radiation, soil-heat flux, etc. In this paper, we present the results of an experimental study and subsequent analysis that mathematically justifies some of these relationships after conducting a series of tests over an extended time period. This measurement data was obtained for a free-space laser communication link established between two fixed-point terminals and designed for transmitting a data stream using 1550 nm as the operating wavelength.