Similarity relations and their experimental verification for strong intensity fluctuations of laser radiation

Gracheva, Maria E.; Gurvich, A. S.; Kashkarov, S. S.; Pokasov, VI V.

doi:10.1007/3540088121_18

Cited by 23 publications

(15 citation statements)

References 11 publications

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“…The σ 2 R values were calculated from the path-averaged refractive index structure constant, C 2 n , measured during the experiments, according to σ 2 R = 1.23C 2 n k 7/6 L 11/6 (k = wave number, L = propagation distance). These values cover the range from relatively weak turbulence (σ 2 R = 0.2) to the scintillation saturation regime [21] (σ 2 R = 10). The irradiance values, I, were normalized by their respective average, I , in order to allow for an easier comparison of the curves.…”

Section: Experimental System Arrangement and Componentsmentioning

confidence: 98%

Free-space laser communications with adaptive optics: Atmospheric compensation experiments

Weyrauch

Vorontsov

2004

J Optic Comm Rep

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Refractive index inhomogeneities of the turbulent air cause wave-front distortions of optical waves propagating through the atmosphere, leading to such effects as beam spreading, beam wander, and intensity fluctuations (scintillations). These distortions are responsible for severe signal fading in free-space optical communications systems and therefore compromise link reliability. Wave-front distortions can be mitigated, in principle, with adaptive optics, i.e., real-time wave-front control, reducing the likeliness of signal fading. However, adaptive optics technology, currently primarily used in astronomical imaging, needs to be adapted to the requirements of free-space optical communication systems and their specific challenges.In this chapter we discuss a non-conventional adaptive optics approach that has certain advantages with respect to its incorporation into free-space optical communication terminals. The technique does not require wave-front measurements, which are difficult under the strong scintillation conditions typical for communication scenarios, but is based on the direct optimization of a performance quality metric, e.g., the communication signal strength, with a stochastic parallel gradient descent (SPGD) algorithm.We describe an experimental adaptive optics system that consists of a beamsteering and a higher-resolution wave-front correction unit with a 132-actuator MEMS piston-type deformable mirror controlled by a VLSI system implementing the SPGD algorithm. The system optimizes the optical signal that could be coupled into a single-356 Thomas Weyrauch and Mikhail A. Vorontsov mode fiber after propagating along a 2.3-km near-horizontal atmospheric path. We investigate characteristics of the performance metric under different atmospheric conditions and evaluate the effect of the adaptive system. Experiments performed under strong scintillation conditions with beam-steering only as well as with higherresolution wave-front control demonstrate the mitigation of wave-front distortions and the reduction of signal fading.

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Section: Experimental System Arrangement and Componentsmentioning

confidence: 98%

Free-space laser communications with adaptive optics: Atmospheric compensation experiments

Weyrauch

Vorontsov

2004

J Optic Comm Rep

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“…The elaboration consists in evaluating, ever 5 min of recording, the centred moments m i up to the fifth order and the statistical coefficients y i up to the third order The results of the elaboration are shown in figure 2, plotted against time . The choice of the 5 min duration is justified both by the intent of reducing the error source indicated in [10] and by the analysis developed in [14] and [15] (see also [8]) .…”

Section: Downloaded By [University Of Otago] At 02:21 03 January 2015mentioning

confidence: 99%

“…As a matter of fact, several phenomena occur at detection that may distort the revealed signal, and hence its statistics and its variance <X 2 >, with respect to the incident signal . Gracheva et al [10] indicated the possible effects of the finite duration of the measurement time . In previous papers [8,11,12], we studied the effects of the non-linearity of the detecting system, reaching the conclusion that the experimental data could be explained, more than qualitatively, in terms of a log-normally distributed incident signal distorted at detection [8] because of the non-linearity of the detecting system .…”

Section: Introductionmentioning

confidence: 98%

Evidence of Log-Normally Distributed Intensity Fluctuations of an Atmospherically Degraded Laser Beam

Ciolli

Consortini

Pandolfini

et al. 1979

Optica Acta: International Journal of Optics

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“…Specifically, for 07 2 > 1 the irradiance variance saturates, that is, it reaches a peak (referred to as the strong-focusing regime) and then slowly decreases with increasing total turbulence. 3 Over the past decade considerable progress has been made in understanding the saturation of scintillation, in particular for horizontal propagation through homogeneous turbulence. For example, the role of the inner scale has been elucidated 4 and has been found to have a greater significance for spherical waves than for plane waves.'"'…”

Section: Introductionmentioning

confidence: 99%

Stellar scintillation and the atmosphere’s vertical turbulence profile

Camparo

2001

J. Opt. Soc. Am. A

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Similarity relations and their experimental verification for strong intensity fluctuations of laser radiation

Cited by 23 publications

References 11 publications

Free-space laser communications with adaptive optics: Atmospheric compensation experiments

Free-space laser communications with adaptive optics: Atmospheric compensation experiments

Evidence of Log-Normally Distributed Intensity Fluctuations of an Atmospherically Degraded Laser Beam

Stellar scintillation and the atmosphere’s vertical turbulence profile

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