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24 August 2010 Aperture averaging in a laser Gaussian beam: simulations and experiments
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In terrestrial free-space laser communication, aside from pointing issues, the major problem that have to be dealt with is the turbulent atmosphere that produces irradiance fluctuations in the received signal, greatly reducing the link performance. Aperture averaging is the standard method used to mitigate these irradiance fluctuations consisting in increasing the area of the detector, or effectively increasing it by using a collecting lens with a diameter as large as possible. Prediction of the aperture averaging factor for Gaussian beam with currently available theory is compared with data collected experimentally and simulations based in the beam propagation method, where the atmospheric turbulence is represented by linearly spaced random phase screens. Experiments were carried out using a collecting lens with two simultaneous detectors, one of them with a small aperture to emulate an effective point detector, while the other one was mounted with interchangeable diaphragms, hence measurements for different aperture diameters could be made. The testbed for the experiments consists of a nearly horizontal path of 1.2 km with the transmitter and receiver on either side of the optical link. The analysis of the experimental data is used to characterize the aperture averaging factor when different values of laser divergence are selected.
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Ricardo Barrios, Federico Dios, Jaume Recolons, and Alejandro Rodriguez "Aperture averaging in a laser Gaussian beam: simulations and experiments", Proc. SPIE 7814, Free-Space Laser Communications X, 78140C (24 August 2010);

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