Studies Of Novel Partially Coherent Beams Propagation Through Turbulent Atmosphere

With the deve;opment of information technology, the amount of information and the data transmission rate are increasing. As a technology providing high bandwidth wireless communication links over a distance of several kilometers using unlicensed optical wavelengths, free space optical (FSO) communication has increasingly attracted much attention with a variety of applications. However, atmospheric turbulence induced effects including intensity fluctuations (scintillations), phase fluctuations, beam spreading, beam wander and beam jitter can severely degrade the link performance of free space optical communications.Oriented to high-speed and long-distance free space optical communication through atmospheric turbulence, the novel theories and methods deduced from the spatial coherence degree of light source and the spatial coherent length of atmospheric turbulence are investigated to suppress the complex atmospheric turbulence effects. In order to mitigate the intensity fluctuations and amplitude distortions induced by atmospheric turbulence, we propose to study the generation and propagation characteristics of a partially coherent Airy beams in atmospheric turbulence and optimize the beam parameters for free space optical communications. In order to conquer the inhomogeneity and anisotropy of atmospheric turbulence, we plan to investigate the spatial diversity techniques based on MIMO configuration, multi-wavelength and multi-rate FSO communications. We propose to investigate the statistical model of partially coherent Airy beam arrays propagation through non-Kolmogorov moderate-strong atmospheric turbulence, and analyze the effects of atmospheric turbulence on the performance of free space optical communication.The satistic model for a Gaussian beam wave propagation through non-Kolmogorov turbulent atmosphere is derived in strong fluctuation regime, using non-Kolmogorov spectrum with a generalized power law exponent and the extended Rytov theory with a modified spatial filter function. The analytic expressions are obtained and then used to analyze the effect of power law, refractive-index structure parameter, propagation distance, phase radius of curvature, beam width and wavelength on scintillation index of Gaussian beam under the strong atmospheric turbulence. The free space optical communication performance for a Gaussian beam wave of scintillation index, mean signal-to-noise ratio<SNR>, and mean bit error rate<BER>, have been derived by extended Rytov theory in non-Kolmogorov strong turbulence. And then the influence of wind speed variations on free space optical communication performance has been analyzed under different atmospheric turbulence intensities. There exist optimal value of radius of curvature and beam width for minimizing the value of scintillation index and long wavelength for mitigating the effect of non-Kolmogorov strong turbulence on link performance.Experimental studies on performance of Gaussian beams propagation in atmospheric turbulence medium. Atmospheric turbulence generator design, setup atmospheric turbulence generator experimental platform to evaluate the refractive index structure constant, experimental measurements intensity fluctuations and spectral characteristics of Gaussian beams in atmospheric turbulence, to explore the effective measures to compensate atmospheric turbulence.We study statistic model of spatially partially coherent Airy beam in atmospheric turbulence. We investigate the scintillation properties of partially coherent beams, and study the effects of partial coherence on the propagation and generation of partially coherent Airy beams. We investigate the intensity evolution of partially coherent Airy beam through non-kolmogorov turbulent atmosphere, and study the effects of partial coherence and atmospheric turbulence on the propagation of partially coherent Airy beams.Generation experiment on partially coherent Airy beams in turbulent atmosphere. Study the self-bending and self-reconstruct propagation property of Ariy beams; generate the partially coherent Airy beams by using a spatial light modulator.Optimization of propagation characteristics of partially coherent Airy beams for free space optical communications. Performance optimizations as a function of beam parameters and turbulence parameters. The results will mitigate atmospheric turbulence induced scintillations and improve the FSO system performance.We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The proposed optical receiver not only can provide a60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere.We investigate the performance of wide field-of-view MIMO optical receiver for free space optical communications in atmospheric strong turbulence. The proposed scheme can help to reduce scintillations and improve BER performance. Optimization of correlation length and spatial separation for wide FoV diversity receiver apertures provide a further BER performance improvement for MIMO FSOC system propagating through moderate to strong turbulence.We study the average capacity performance for MIMO FSO communication systems using multiple partially coherent beams propagation through non-kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gammagamma random variables for multiple independent partially coherent beams. The closed-form expressions of the scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law a, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. There exist optimal values of spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions.