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Minet J.,University of Dayton | Vorontsov M.A.,University of Dayton | Wu G.,Optonicus | Dolfi D.,Thales Alenia
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

In long-range situations, the performance of free-space optical (FSO) communication links is strongly impacted by atmospheric turbulence. In this paper we compare efficiency of turbulence effects mitigation in FSO communication links using spectral (wavelength) and spatial diversity techniques. Numerical analysis of both techniques is performed considering FSO communication setting with single-mode fiber-collimator transceivers. In the case of spectral diversity setting, the fiber-collimators are based on the use of photonic crystal fibers that provide single-mode operation for three distinct wavelengths (532, 1064 and 1550nm). In the spatial diversity communication setting, analysis is performed using multiple-transceiver configurations. Analysis includes both received signal's statistical and temporal spectral characteristics. © 2013 Copyright SPIE.


Vorontsov M.,University of Dayton | Weyrauch T.,University of Dayton | Lachinova S.,Optonicus | Gatz M.,University of Dayton | Carhart G.,U.S. Army
Optics Letters | Year: 2012

Maximization of a projected laser beam's power density at a remotely located extended object (speckle target) can be achieved by using an adaptive optics (AO) technique based on sensing and optimization of the target-return speckle field's statistical characteristics, referred to here as speckle metrics (SM). SM AO was demonstrated in a targetin- the-loop coherent beam combining experiment using a bistatic laser beam projection system composed of a coherent fiber-array transmitter and a power-in-the-bucket receiver. SM sensing utilized a 50 MHz rate dithering of the projected beam that provided a stair-mode approximation of the outgoing combined beam's wavefront tip and tilt with subaperture piston phases. Fiber-integrated phase shifters were used for both the dithering and SM optimization with stochastic parallel gradient descent control. © 2012 Optical Society of America.


Weyrauch T.,University of Dayton | Vorontsov M.A.,University of Dayton | Carhart G.W.,U.S. Army | Beresnev L.A.,U.S. Army | And 3 more authors.
Optics Letters | Year: 2011

We demonstrate coherent combining (phase locking) of seven laser beams emerging from an adaptive fibercollimator array over a 7 km atmospheric propagation path using a target-in-the-loop (TIL) setting. Adaptive control of the piston and the tip and tilt wavefront phase at each fiber-collimator subaperture resulted in automatic focusing of the combined beam onto an unresolved retroreflector target (corner cube) with precompensation of quasi-static and atmospheric turbulence-induced phase aberrations. Both phase locking (piston) and tip-tilt control were performed by maximizing the target-return optical power using iterative stochastic parallel gradient descent (SPGD) techniques. The performance of TIL coherent beam combining and atmospheric mitigation was significantly increased by using an SPGD control variation that accounts for the round-trip propagation delay (delayed SPGD). © 2011 Optical Society of America.


Filimonov G.A.,University of Dayton | Filimonov G.A.,Zuev Institute of Atmospheric Optics | Vorontsov M.A.,University of Dayton | Lachinova S.L.,Optonicus
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The phase noise that originates in the multi-channel master-oscillator power amplifier (MOPA) system of a coherent tiled fiber-array beam director may drastically impact the efficiency of laser beam projection on a remotely located target in the atmosphere. The recently proposed near-field phase locking (NFPL) technique mitigates the MOPA-induced phase noise and gives an opportunity for programmable control of local (on-subaperture) piston and tip/tilt phases of the outgoing fiber-array beams (beamlets). In the present paper, we evaluate the influence of both NFPL and programmable phase control on the beam director performance for different laser beam propagation paths and atmospheric turbulence conditions. Our analysis is based on wave-optics numerical simulation. © 2014 SPIE.


Lachinova S.L.,Optonicus | Vorontsov M.A.,Optonicus | Vorontsov M.A.,University of Dayton | Lemaster D.A.,Air Force Research Lab | Trippel M.E.,Air Force Research Lab
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

Computational efficiency and accuracy of wave-optics-based Monte-Carlo and brightness function numerical simulation techniques for incoherent imaging through atmospheric turbulence are evaluated. Simulation results are compared with theoretical estimates based on known analytical solutions for the modulation transfer function of an imaging system and the long-exposure image of a Gaussian-shaped incoherent light source. © 2016 SPIE.


Vorontsov M.A.,Optonicus | Vorontsov M.A.,University of Dayton | Lachinova S.L.,Optonicus | Majumdar A.K.,U.S. Navy
Applied Optics | Year: 2016

A new target-in-the-loop (TIL) atmospheric sensing concept for in situ remote measurements of major laser beam characteristics and atmospheric turbulence parameters is proposed and analyzed numerically. The technique is based on utilization of an integral relationship between complex amplitudes of the counterpropagating optical waves known as overlapping integral or interference metric, whose value is preserved along the propagation path. It is shown that the interference metric can be directly measured using the proposed TIL sensing system composed of a single-mode fiber-based optical transceiver and a remotely located retro-target. The measured signal allows retrieval of key beam and atmospheric turbulence characteristics including scintillation index and the path-integrated refractive index structure parameter. © 2016 Optical Society of America.


Vorontsov M.A.,University of Dayton | Lachinova S.L.,Optonicus
Optics InfoBase Conference Papers | Year: 2014

A new target-in-the-loop (TIL) atmospheric sensing concept for in-situ remote measurement of major atmospheric parameters is discussed. The proposed technique is based on utilization of integral relationships between complex amplitudes of the counter-propagating waves, whose values are preserved along the propagation path, for atmospheric turbulence characterization. We show that these relationships, referred to here as the remote sensing invariants, can be directly measured using a TIL sensor composed of a single-mode fiber-based optical transceiver and a remotely located small-size retro-reflector. The measured signals allow retrieval of key turbulence characteristics along the target line of sight, including refractive index structure parameter and scintillation index. The discussed concept allows practical development of a compact TIL atmospheric sensor that does not require installation of an additional transmitter/receiver device at the other end of the laser beam propagation path. © 2014 OSA.


Lachinova S.L.,Optonicus | Vorontsov M.A.,Optonicus | Vorontsov M.A.,University of Dayton
Journal of Optics (United Kingdom) | Year: 2013

A new approach for engineering a variety of unconventional laser beams with complex spatio-temporal characteristics using coherent (coherently combinable) fiber-array laser transmitter systems is proposed and analyzed through numerical simulations. These laser beams, referred to here as exotic beams, include beams with periodic, quasi-periodic, and stochastic spatio-temporal phase modulation. We show that exotic laser beams can be generated in fiber arrays using feedback control systems of different architectures based on a network of beam-tail interference sensors and fiber-integrated phase shifters. Due to the extremely short (nanosecond time scale) response time of these phase shifting elements, the proposed technique permits generation of laser beams with controllable spatial coherence which can be used for mitigation of speckle effects in various applications including directed energy, laser communications, active imaging, and wavefront sensing. Results of analyses and computer simulations of exotic beams are presented for the fiber-array system with seven subapertures. © 2013 IOP Publishing Ltd.


Weyrauch T.,University of Dayton | Vorontsov M.,University of Dayton | Mangano J.,Darpa | Ovchinnikov V.,Optonicus | And 3 more authors.
Optics Letters | Year: 2016

We demonstrate coherent beam combining and adaptive mitigation of atmospheric turbulence effects over 7 kmunder strong scintillation conditions using a coherent fiber array laser transmitter operating in a target-in-the-loop setting. The transmitter system is composed of a densely packed array of 21 fiber collimators with integrated capabilities for piston, tip, and tilt control of the outgoing beams wavefront phases. A small cat's-eye retro reflector was used for evaluation of beam combining and turbulence compensation performance at the target plane, and to provide the feedback signal for control of piston and tip/tilt phases of the transmitted beams using the stochastic parallel gradient descent maximization of the power-in-the-bucket metric. © 2016 Optical Society of America.


Lachinova S.L.,Optonicus | Vorontsov M.A.,Optonicus | Vorontsov M.A.,University of Dayton
Journal of Optics (United Kingdom) | Year: 2016

In the wave-optics numerical simulations of laser beam propagation in volume atmospheric turbulence, we observe irregular appearance of giant intensity spikes with amplitudes exceeding the diffraction-limited intensity value by a factor of ten or even more. The presence of giant spikes may explain the existing significant difference between the scintillation index theoretical prediction and the results obtained in numerical simulation and experimental measurements. The giant spikes' physics-based origin, probability of appearance, and impact on irradiance scintillation index are analyzed. © 2016 IOP Publishing Ltd.

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