Orbital Angular Momentum of Partially Coherent Beams through Turbulence

The orbital angular momentum of light is a promising candidate as an information carrier in optical communication systems to enhance the capacity of data channels. However, the effects of atmospheric turbulence significantly degrade the quality of light beams, thereby imposing limitations on the range of reliable data transmission. To address this issue, researchers have been actively seeking methods to enhance the resilience of light against fluctuations of refractive index due to the atmospheric turbulence. It has long been recognized that partially coherent beams exhibit greater robustness in propagation through turbulence. Consequently, transitioning from full coherence to partial coherence has been suggested as a solution. Conversely, in OAM-based communications, reducing coherence results in broadening of the OAM spectrum, thus increasing cross-talk between adjacent channels. Therefore, utilizing partially coherent beams in free space communications entails both Benefits and drawbacks.
The main objective of this dissertation is to explore various classes of partially coherent beams through analytical approaches in order to identify a robust OAM spectrum in the presence of atmospheric turbulence. The results are presented in three different articles. The first article introduces a simplified version of the extended Huygens-Fresnel principle which is a widely used method of turbulence propagation. The discoveries outlined in the first article substantially alleviate the mathematical complexity associated with propagation in random media, thereby enabling analytical exploration of the propagation of partially coherent beams in random media.
The second article presents an optimization criterion associated with a specific class of partially coherent beams, substantially enhancing their resistance against turbulence. Finally, the third article thoroughly investigates the behavior of three categories of partially coherent beams in interaction with atmosphere, providing a detailed comparison of their respective resistance. The compilation of these three articles presents a comprehensive study of the impact of atmospheric fluctuations on the orbital angular momentum spectrum of partially coherent beams.