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29 September 2011 Effects of evaporation layer on free-space optical communication links near sea surface at 1.55 μm
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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. For FSO communication in maritime environments, laser beams propagating through the evaporation layer near the sea surface are affected by turbulence, the scattering coefficients of the water particles, and the salt water itself. To better gauge and understand the effects of turbulence on FSO communication, the refractive index structure parameter C2n, which relates to scintillation strength, is determined from database of environmental parameters experimentally measured near the sea surface. A high speed Shack-Hartmann wavefront sensor is utilized to measure wavefront distortion of a beam transmitted though the evaporation layer, and thus determine the extent of turbulence encountered along the optical pathway. Through the use of adaptive optics, the wavefront of a transmitted beam is modulated in real time to compensate for turbulence, thereby providing optimal FSO reception. The Kalman filter method is also employed to reconstruct an original undistorted image from a series of sequential transmitted images altered by turbulence. In addition, atmospheric, free-space, and scintillation losses are analyzed and predicted for extended optical path lengths in view of their impact on FSO data transfer and communication. Furthermore, the effects of weather conditions on FSO transmission are investigated through MODTRAN based modeling at 1.55 μm wavelength, where multiple elevation angles are considered. Using advanced techniques, many limitations associated with infrared FSO transmission and reception in the evaporation layer may be overcome or circumvented.
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John Zeller and Tariq Manzur "Effects of evaporation layer on free-space optical communication links near sea surface at 1.55 μm", Proc. SPIE 8184, Unmanned/Unattended Sensors and Sensor Networks VIII, 81840C (29 September 2011);

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