Atmospheric compensation with a speckle beacon in strong scintillation conditions: Directed energy and laser communication applications
Intelligent Optics Laboratory, Institute for Systems Research, University of Maryland, College Park, Maryland 20742, USA.Applied Optics (Impact Factor: 1.78). 11/2005; 44(30):6388-401. DOI: 10.1364/AO.44.006388
Wavefront control experiments in strong scintillation conditions (scintillation index, approximately equal to 1) over a 2.33 km, near-horizontal, atmospheric propagation path are presented. The adaptive-optics system used comprises a tracking and a fast-beam-steering mirror as well as a 132-actuator, microelectromechanical-system, piston-type deformable mirror with a VLSI controller that implements stochastic parallel gradient descent control optimization of a system performance metric. The experiments demonstrate mitigation of atmospheric distortions with a speckle beacon typical for directed energy and free-space laser communication applications.
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ABSTRACT: A concept of a Hybrid Wavefront-based Stochastic Parallel Gradient Decent (WSPGD) Adaptive Optics (AO) system for correcting the combined effects of Beacon Anisoplanatism and Thermal Blooming is introduced. This system integrates a conventional phase conjugate (PC) AO system with a WSPGD AO system. It uses on-axis wavefront measurements of a laser return from an extended beacon to generate initial deformable mirror (DM) commands. Since high frequency phase components are removed from the wavefront of a laser return by a low-pass filter effect of an extended beacon, the system also uses off-axis wavefront measurements to provide feedback for a multi-dithering beam control algorithm in order to generate additional DM commands that account for those missing high frequency phase components. Performance of the Hybrid WSPGD AO system was evaluated in simulation using a wave optics code. Numerical analysis was performed for two tactical scenarios that included ranges of L = 2 km and L = 20 km, ratio of aperture diameter to Fried parameter, D/r0, of up to 15, ratio of beam spot size at the target to isoplanatic angle, thetaB/theta0, of up to 40, and general distortion number characterizing the strength of Thermal Blooming, Nd = 50, 75, and 100. A line-of-sight in the corrected beam was stabilized using a target-plane tracker. The simulation results reveal that the Hybrid WSPGD AO system can efficiently correct the effects of Beacon Anisoplanatism and Thermal Blooming, providing improved compensation of Thermal Blooming in the presence of strong turbulence. Simulation results also indicate that the Hybrid WSPGD AO system outperforms a conventional PC AO system, increasing the Strehl ratio by up to 300% in less than 50 iterations. A follow-on laboratory demonstration performed under a separate program confirmed our theoretical predictions.Proceedings of SPIE - The International Society for Optical Engineering 01/2007; DOI:10.1117/12.735721 · 0.20 Impact Factor
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ABSTRACT: The tensile strain on a submarine optical-fiber cable may reach a nonlinear elastic region when recovered from the sea floor. In this paper, a method is shown to characterize cable elongation up to the nonlinear plastic region by extending wire theory previously developed to evaluate cable strain in the elastic linear region. The results of applying this method to several optical-fiber cables agrees well with tensile test results of the cables when cable ends are prevented from twisting, as well as when they are free to rotate. Also, by evaluating the dependence of cable strain on cable materials, such as stranded-strength members and pressure-resistant conductor pipe, a practical submarine optical-fiber cable structure for deep-sea use is determined.Journal of Lightwave Technology 03/1985; DOI:10.1109/JLT.1985.1074151 · 2.97 Impact Factor
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