In this work, we demonstrate vertical GaN, AlN, and InN hollow nano-cylindrical arrays (HNCs) grown on Si substrates using anodized aluminum oxide (AAO) membrane templated low-temperature plasma-assisted atomic layer deposition (PA-ALD).
Vortex beams acquire increasing attention due to their unique properties. These beams have an annular spatial profile with a dark spot at the center, the so-called phase singularity. This singularity defines the helical phase structure which is related to the topological charge value. Topological charge value allows vortex beams to carry orbital angular momentum. The existence of orbital angular momentum offers a large capacity and high dimensional information processing which make vortex beams very attractive for free-space optical communications. Besides that, these beams are well capable of reducing turbulence-induced scintillation which leads to better system performance. This chapter introduces the research conducted up to date either theoretically or experimentally regarding vortex beam irradiance, scintillation, and other properties while propagating in turbulent mediums.
This study aims to develop a deep-learning-based approach that is able to detect turbulence-induced mode distortion in orbital angular momentum-based free-space optical communication links. The proposed and tuned deep learning-based models have been trained with a dataset that is created based on the intensity beam profiles that propagate 5 Km in four different levels of turbulent atmosphere. The random search algorithm has been adopted for conducting a hyperparameter tuning process to select the best structures for two groups of deep learning models each of which contains three different deep learning model. The proposed approach is able to not only distinguish the distorted beams but also to recognize the level of distortion. The provided results indicate that the utilized fine-tuned models have 100% classification accuracy in terms of detecting the distorted beams. Besides that, the proposed and tuned models obtained a very high classification accuracy reached 97, 94.99, and 97.78% in terms of assessing the amount of distortion exposed by the transmitted beams. We believe that the obtained results will be a milestone in free-space optical communication systems that utilize orbital angular momentum.
The averaged received intensity of hollow higher-order cosh-Gaussian (HHOCG) beam propagating in oceanic turbulence is derived based on extended Huygens–Fresnel integral. In detail, the effect of beam parameters and oceanic turbulence parameters on the received intensity is analyzed. Interestingly, beam has a focusing nature along propagation. Our results indicate that received intensity distribution is not affected from the variation in source field parameters. Beam size at the receiver plane can vary according to the changes in turbulence nature. Accordingly, the provided results will contribute to the improvement of both underwater optical communication and imaging systems.
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