Scintillation index for two Gaussian laser beams with different wavelengths in weak atmospheric turbulence

Peleg, Avner; Moloney, Jerome V.

doi:10.1364/josaa.23.003114

Cited by 44 publications

(28 citation statements)

References 29 publications

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“…This research derived for the first time the optimal angular separations for multiple transmitter systems for airborne FSOC systems. A majority of previous research on multiple transmitters focused on satellite communications (where the turbulence is only present over a small part of the propagation path) or constant turbulence strength C 2 n paths [4,5,29,59,60,68]. The angular separations for all three airborne geometries (air-to-air, air-to-ground, and ground-to-air) are determined.…”

Section: Summary Of Main Resultsmentioning

confidence: 99%

“…Much of the research has focussed on multiple Rxs. Some research has been accomplished on multiple-Tx systems, but surprisingly little research can be found on the theoretical angular separation required to take full advantage of these spatial diversity techniques, especially for the airborne application [34,58,59,68]. Rather, most literature on differential statistics for angular separations is concerned with an isoplanatic angle (relatively similar paths) for sensing and wavefront control.…”

Section: Diversity Techniquesmentioning

confidence: 99%

“…For example, spatial diversity could be accomplished at the receiver by a single large aperture (larger than ρ c or multiple small apertures [3]. Some researchers have studied multiple-transmitter approaches [34,58,59,68] for the space-to-ground and the ground-to-ground scenarios, but few have studied the air-to-air scenario. Much of the spatial diversity research has focused on MIMO techniques or just multiple receivers to reduce signal fades, without defining the requisite separation distance.…”

Section: Diversity Techniquesmentioning

confidence: 99%

“…Then, techniques are devised to overcome these effects by applying multiple uncorrelated realizations. In the second approach, typically, or ground-based constant-turbulence-strength paths [4,5,30,40,59,60,68]. Here, this work presents these angular separations for three airborne geometries (air-to-air, air-to-ground, and ground-to-air) through extended turbulence and determines practical configurations.…”

Section: Assessment Of Best Areas For Further Researchmentioning

confidence: 99%

“…At this separation, the hot spots and signal drop outs due to strong scintillation across the aperture are "averaged out." Research has been done to determine this requisite separation distance [4,5,59,60], but it has not been accomplished for air-to-air scenarios and not put in terms of the correlation width ρ cw . The optimal Tx separation distance for reducing BER was 1-3 times ρ c for the air-to-air and ground-to-air scenarios.…”

Section: Anisoplanatic Effectsmentioning

confidence: 99%

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Integrated approach to airborne laser communication

Louthain¹

2008

SPIE Proceedings

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Lasers offer tremendous advantages over RF communication systems in terms of bandwidth and security due to their ultra-high frequency and narrow spatial beamwidth. Unfortunately, atmospheric turbulence significantly increases the received power variation and bit error rate (BER) in free-space optical communication (FSOC) systems. Further, airborne optical communication systems require special considerations in size, complexity, power, and weight.If two or more laser beams are sufficiently separated so that their turbulence effects are uncorrelated (i.e. anisoplanatic), they can effectively "average out" turbulence effects. This requisite separation distance is derived for multiple geometries, turbulence conditions, and optical properties. In most cases and geometries, the angles ordered from largest to smallest are: phase uncorrelated angle (equivalent to the tilt uncorrelated angle and phase anisoplanatic angle), tilt isoplanatic angle, phase isoplanatic angle, scintillation uncorrelated angle (or scintillation anisoplanatic angle), and scintillation isoplanatic angle (θ ψ ind > θ T A > θ 0 > θ χ ind > θ χ 0 ). Conventional adaptive optics (AO) systems only correct for phase and cannot correct for strong scintillation, while multiple-transmitter systems use several transmission paths to "average out" effects of the strong scintillation by incoherently summing up the beams in the receiver.Since all three airborne geometries (air-to-air, air-to-ground, and ground-toair) are studied, a comparison of multiple-beam airborne laser communication system performance is presented for the first time. Wave optics simulations show that a combination of transmitter diversity, receiver and transmitter trackers, and adaptive thresholding can significantly reduce BER in an air-to-air FSOC system by over 10,000 times. As demonstrated in this work, two transmitters alone separated by only 31 cm (100 km path length, 1.55 µm wavelength, 4 km in altitude) provide a significant iv BER improvement over one transmitter, especially for the strong turbulence regime where the required SNR for a fixed BER is reduced by 9 dB. Including the tracking and adaptive thresholding techniques, resulted in a 13 dB overall improvement.Two beams also reduce the fade length, suggesting even greater improvement can be obtained when interleaving and forward error correction coding is implemented. Major Schmidt also knew when to hand me water and how to keep me on the road, since he had just finished his marathon.

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Section: Summary Of Main Resultsmentioning

confidence: 99%

Section: Diversity Techniquesmentioning

confidence: 99%

Section: Diversity Techniquesmentioning

confidence: 99%

Section: Assessment Of Best Areas For Further Researchmentioning

confidence: 99%

Section: Anisoplanatic Effectsmentioning

confidence: 99%

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Integrated approach to airborne laser communication

Louthain¹

2008

SPIE Proceedings

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Characterization of atmospheric optical turbulence for laser propagation

Mahalov¹,

Moustaoui

2010

Laser & Photonics Reviews

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The performance of imaging or transmission systems is limited by atmospheric inhomogeneities and fluctuations. Temperature and pressure variations associated with turbulent eddies cause random fluctuations of the refractive index structure constant (C 2 n ), which distort optical waves. The distortions may lead to significant blurring, scintillations, broadening and wander of the laser beam. High resolution nested numerical simulations are used to predict and characterize Optical Turbulence (OT) induced by jet streams and gravity waves under various local atmospheric conditions. Non-homogeneous, anisotropic, non-Kolmogorov patchy shear-stratified turbulence in the Upper Troposphere and Lower Stratosphere (UTLS) requires that a fine mesh be used to resolve stiff velocity and temperature gradient profiles. Computational approach is based on nesting and refined vertical gridding in nested mesoscale/microscale codes. This methodology is applied to the analysis of field data from observations. Local distributions of simulated optical turbulence in the UTLS are obtained using very high resolution explicit simulations and parametrization formula. They show strongly laminated structures with thin layers of high values of the refractive index. These optical layers are characterized by steep vertical gradients of potential temperature and are located at the edges of relatively well mixed regions produced by shear instabilities and wave breaking.Streamwise-altitude and spanwise-altitude cross-sections for C 2 n from high resolution simulations. Z is the altitude.

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