Scintillation fluctuations of optical communication lasers in atmospheric turbulence

Abstract

The purpose of this research is to evaluate scintillation fluctuations on optical communication lasers and evaluate potential system improvements to reduce scintillation effects. This research attempts to experimentally verify mathematical models developed by Andrews and Phillips [1] for scintillation fluctuations in atmospheric turbulence using two different transmitting wavelengths. Propagation range lengths and detector quantities were varied to confirm the theoretical scintillation curve. In order to confirm the range and wavelength dependent scintillation curve, intensity measurements were taken from a 904nm and 1550nm laser source for an assortment of path distances along the 1km laser range at the Townes Laser Institute. The refractive index structure parameter (Cn²) data was also taken at various ranges using two commercial scintillometers. This parameter is used to characterize the strength of atmospheric turbulence, which induces scintillation effects on the laser beam, and is a vital input parameter to the mathematical model. Data was taken and analyzed using a 4-detector board array. The material presented in this paper outlines the verification and validation of the theoretical scintillation model, and steps to improve the scintillation fluctuation effects on the laser beam through additional detectors and a longer transmitting wavelength. Experimental data was post processed and analyzed for scintillation fluctuations of the two transmitting wavelengths. The results demonstrate the benefit of additional detectors and validate a mathematical model that can be scaled for use in a variety of communications or defense applications. Scintillation is a problem faced by every free space laser communication system and the verification of an accurate mathematical model to simulate these effects has strong application across the industry.