Experimental Verification of Beam Wander, Beam Spread and Scintillation in an Optical Laser Link through a Turbulent Atmosphere

Abstract

Laser satellite communications for ground-to-ground and ground-to space links is influenced by atmospheric turbulence. Typically, theoretical models are used to predict link performance and the influence of the atmosphere on variables such as beam wander, spot size and scintillation at the receiver. These variables are used as input for system design. However, the models, which predict the individual variables have not yet been empirically verified for their individual contributions. Therefore, this paper focuses on retrieving the individual variables estimated by theoretical models from measurements representing these variables. These measurements have been retrieved in a 10 km uplink path, ground-to-ground field test. In this test, the receiver plane is imaged. The spot location and size and the longitudinal, radial and on-axis scintillation indices are estimated from the measurements. Also, turbulence strength is measured along the path and are used as inputs for the theoretical models. For weak turbulence conditions the theory and test results fall within the same order of magnitude. For all effects, except on-axis scintillation, the values predicted by theory lie at a slightly higher value than retrieved with the field test for the weak turbulence regime. For strong turbulence conditions the difference in results between theory and data grows, up to order one. To the authors’ knowledge, this is the first time the turbulence variables have been experimentally investigated in so much detail. It is clear from the differences, that both the experimental setup and theory for horizontal ground-to-ground links need attention to close the gap between them, especially for turbulence conditions outside the Rytov approximation range.