Experimental Characterization of Optical Turbulence Using Custom-Built Atmospheric Chamber for FSO Applications

Abstract

Free-space optical (FSO) communication has emerged as a promising solution for high-speed, high-bandwidth wireless transmission, overcoming the spectrum congestion and licensing constraints associated with radio frequency (RF) systems. However, the performance and reliability of FSO links are significantly influenced by atmospheric conditions, particularly atmospheric turbulence. Atmospheric turbulence induces random variations in the refractive index of air, resulting in beam wander, scintillation, and wavefront distortion, which collectively degrade signal quality and increase the bit error rate (BER). This study experimentally characterizes the turbulence generated within an atmospheric turbulence generation (ATG) chamber to better understand its behavior and controllability under varying operating conditions. This paper presents an experimental investigation conducted in an in-house fabricated atmospheric chamber of 0.58 × 1 × 0.31 meters, designed to emulate diverse turbulence scenarios. By precisely modulating the internal temperature profile, airflow dynamics, and humidity, various atmospheric conditions were simulated. Turbulence was characterized using the refractive index structure parameter (C2n) and the Fried parameter (ro), which describe the strength and spatial coherence of optical wavefront distortions. A 520 nm laser beam was used to evaluate turbulence-induced fluctuations in beam propagation. The inertial subrange of the airflow was analyzed to determine the scaling behavior of turbulence, while micrometeorological and macrometeorological methods were applied to assess the energy distribution and refractive index variations under different flow conditions. This work provides experimentally derived insights into the primary drivers of optical turbulence, supporting the development of more accurate predictive models and robust FSO communication systems.