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Environmentally Adaptive Free-Space Optical Communication



OBJECTIVE: Develop an approach to free-space optical communication (FSOC) that adapts to environmental conditions based on an estimate of current conditions impacting optical propagation (optical turbulence, extinction, jitter, etc.), via direct or indirect measurements, to improve communication performance.

DESCRIPTION: The military and commercial sectors have increasing needs for high-speed data transmission over long atmospheric paths.Due to their high directivity and high oscillation frequency, optical beams can transmit data over free space much faster than radio and microwave frequencies.Over the past couple of decades, there have been significant advances in optical source and receiver technology to reduce source power requirements, extend link distances, and increase link margins.Unfortunately, optical beams are much more susceptible to weather, clouds, turbulent fluctuations in the air’s refractive index, and spatial motion in transmit and receive platforms [1].Still, a FSOC system on a mobile platform will likely need to operate over a very broad range of conditions, e.g., link distance, geographic location, and time of day.In the past few years, there have been significant improvements in modeling environmental factors that affect the transmission of optical beams through the open air.This is especially true for the lower atmosphere in the boundary layer [2,3].If environmental information, such as GPS coordinates, time of day, and meteorological measurements are available in real time, and the models can calculate optical turbulence parameters quickly, the FSOC system could adapt itself to improve its performance.This would provide additional resilience beyond that provided by the margin of the link power budget without resorting to a secondary radio frequency (RF) channel.The end goal of this SBIR topic is to develop (Phase I and II) and demonstrate (Phase III) an approach to adapting a FSOC only system within engineering constraints combined with sufficient environmental modeling for a diverse range of geographic sites, times of day, and link paths in the atmosphere.A Phase I effort will develop a concept for adapting a FSOC system and identify the required model and input data. A Phase II effort would involve developing a fast modeling code and demonstrating the FSOC adaptation concept in computer simulation.Conducting laboratory or outdoor field experiments would be a plus.A Phase III effort would demonstrate the full prototype adaptive FSOC system in the field at multiple sites in day and night times.

PHASE I: Devise an initial approach to adapting a FSOC system (beam properties, wavelength, encoding, etc.).Identify a set of inputs needed to drive that adaptation and likely sources of the basic data (sensors, databases, etc.).This step will ensure that the developed approach is ready for a Phase II effort.

PHASE II: Using the results from Phase I, with validation and uncertainty estimates for phase II, finalize the FSOC design and demonstrate its use in extensive computer simulations.The simulations should be done with an emphasis on determining which parameters and inputs contribute most to improving system performance.Conduct relevant experiments, either in a laboratory or the open air, to validate correlation of computer simulations with empirical results.The correlation must include an estimate of uncertainty of the computer simulations for a variety of parameters and inputs.This step shall ensure that the developed approach is ready for a Phase III effort.In this manner, the FSOC prototype will provide initial validation of an optical communications performance.

PHASE III: Military application: Demonstrating the developed approach in a field environment at distances greater than 1 km with a moving transmitter or receiver platform.This step shall ensure that the developed approach is ready for realistic operations. The FSOC prototype will be used in field conditions to provide effectiveness predictions of optical communications in a variety of combat environmental conditions.Commercial Application: The successfully demonstrated FSOC approach could be applied to commercial aircraft, vehicles, and trains where high speed data transmission is required.

KEYWORDS: communication, lasers, meteorology, sensing


S. Karp and L.B. Stotts, Fundamentals of Electro-Optic System Design, Cambridge University Press, Cambridge, UK (2013).; T.C. Farrell, D.J. Sanchez, P. Kelly, A. Gallegos, W. Gibson, D. Oesch, E.J. Aglubat, A.W. Duchane, D.F. Spendel, T. Brennan, “Characterizing Earth’s Boundary Layer (CEBL),” Proc. OSA, Propagation Through and Characterization of Distributed Volume Turbulence (2014).; A. Belmonte and J. M. Kahn, "Sequential Optimization of Adaptive Arrays in Coherent Laser Communications", J. of Lightwave Technol., vol. 31, no. 9, pp. 1383-1387, May 1, 2013; D.H. Tofsted, “Modeling Turbulence Generation in the Atmospheric Surface and Boundary Layers,” U.S. Army Research Laboratory report, ARL-TR-7503 (2015).

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