Orbital angular momentum and beyond in free-space optical communications

Abstract Orbital angular momentum (OAM), which describes tailoring the spatial physical dimension of light waves into a helical phase structure, has given rise to many applications in optical manipulation, microscopy, imaging, metrology, sensing, quantum science, and communications. Light beams carrying OAM feature two distinct characteristics, i.e., inherent orthogonality unbounded states principle, are suitable for capacity scaling In this paper, we give an overview beyond free-space The fundamentals OAM, concept communications using modulation (OAM based on modulator, high-speed modulation, array modulation), multiplexing (spectrally efficient, high capacity, long distance), multicasting (adaptive multicasting, N -dimensional multicasting), turbulence optics, digital signal processing, auto-alignment system), structured (Bessel beams, Airy vector beams), diverse robust (multiple scenes, turbulence-resilient communications, intelligent communications) comprehensively reviewed. prospects challenges also discussed at end. future, there will be more opportunities exploiting extensive advanced from general light.