Robust measurement of orbital angular momentum of a partially coherent vortex beam under amplitude and phase perturbations

Abstract

The ability to overcome the negative effects, induced by obstacles and turbulent atmosphere, is a core challenge of longdistance information transmission, and it is of great significance in free-space optical communication. The spatial-coherence structure, that characterizes partially coherent fields, provides a new degree of freedom for carrying information. However, due to the influence of the complex transmission environment, the spatial-coherence structure is severely damaged during the propagation path, which undoubtedly limits its ability to transmit information. Here, we realize the robust far-field orbital angular momentum (OAM) transmission and detection by modulating the spatial-coherence structure of a partially coherent vortex beam with the help of the cross-phase. The cross-phase enables the OAM information, quantified by the topological charge, hidden in the spatial-coherence structure can be stably transmitted to the far field and can resist the influence of obstructions and turbulence within the communication link. This is due to the self-reconstruction property of the spatial-coherence structure embedded with the cross-phase. We demonstrate experimentally that the topological charge information can be recognized well by measuring the spatial-coherence structure in the far field, exhibiting a set of distinct and separated dark rings even under amplitude and phase perturbations. Our findings open a door for robust optical signal transmission through the complex environment and may find application in optical communication through a turbulent atmosphere.

The Spiral Spectrum of a Laguerre–Gaussian Beam Carrying the Cross-Phase Propagating in Weak-to-Strong Atmospheric Turbulence

“…To study the impact of a turbulent atmosphere on vortex beams, the first matter to deal with is the generation of the turbulence. One can consider using a hot plate [54,55] or random complex phase screens [31] to OAM detection underpins almost all aspects of the advances in vortex beams, such as communication. Although this paper is only a theoretical work, the direction of future experimental research can be envisioned as follows.…”

“…To study the impact of a turbulent atmosphere on vortex beams, the first matter to deal with is the generation of the turbulence. One can consider using a hot plate [54,55] or random complex phase screens [31] to simulate the turbulent environment in the laboratory. The former can effectively achieve quantitative control over the strength of turbulence by adjusting the hotplate temperature (the specific quantitative relationship can be inverted using the scintillation index [54] or Fried's coherence length [56]).…”