Free-space optics (FSO) holds the potential for high bandwidth communication in situations where landline communication is not practical, with relatively low cost and maintenance. The short-wave infrared (SWIR) and midwave infrared (MWIR) bands contain atmospheric transmission windows spanning approximately 1.50-1.75 μm and 4.6- 4.9 μm, respectively. Transmission coefficients and losses were modeled using MODTRAN for optical path lengths of up to 2 km to for various atmospheric conditions. The determination of the refractive index structure parameter C_n ² is useful in calculating the time-dependent Fried parameter, r₀, which provides an indication of the magnitude of the phase distortion of an optical wavefront by scintillation in accordance with the Kalomogorov model. By better understanding the effects of turbulence and C_n ² on FSO transmission through modeling and experimental measurements, measures can be implemented to reduce the bit error rate and increase data throughput, enabling more efficient and accurate communication links. FSO beam optimization is achievable using a Shack-Hartmann wavefront sensor, whereby wavefront distortion of a transmitted beam is measured to compensate in real time for the effects of turbulence to provide optimized FSO reception. Using advanced techniques and compensation methods, limitations associated with infrared FSO transmission and reception in the evaporation layer may be overcome or circumvented to provide high bandwidth communication through turbulence and/or adverse weather conditions.

Date Published: 19 October 2012
PDF: 12 pages
Proc. SPIE 8540, Unmanned/Unattended Sensors and Sensor Networks IX, 85400C (19 October 2012);

Published in SPIE Proceedings Vol. 8540:
Unmanned/Unattended Sensors and Sensor Networks IX
Edward M. Carapezza; Henry J. White, Editor(s)