Scattering of open vortex beams: Applications towards free space optical communications

The topological charge (TC) of optical vortex beams can be measured using various interferometric and non-interferometric techniques in both coherent and partially coherent domains. However, these methods are not suitable for obstructed vortex beams, also known as open optical vortex (OOV) beams. Recently, several methods for studying open optical vortex (OOV) beams, have recently been proposed and demonstrated based on interferometry, phase retrieval, spatial coherence analysis, which limit their applicability in the presence of significant perturbations or long-distance propagation. In this study, we propose and experimentally demonstrate an efficient method for measuring both the magnitude and sign of the topological charge (TC) of OOV beams using the auto-correlation distribution after scattering through a rough surface. We generated the OOV beams using partially blocked computer-generated holograms. Although the rings or zero points present in the auto-correlation are broken, the number of rings is equal to the TC. Further, we have utilized the radius of the first ring and its divergence with propagation distance, which can be easily observed for all orders, for finding the TC of higher orders. We can measure the sign of the topological charge solely through intensity measurements using the rotation of the autocorrelation profile with the help of blocking parameter. Furthermore, we demonstrate that the characteristics of OOV beams derived from our proposed method align well with the propagation characteristics of unobstructed OV beams. The results confirm the efficacy of optical vortex beams for free-space optical communication.