Orbital angular momentum of light for communications

Structured light, especially beams carrying orbital angular momentum (OAM), has gained much interest due to its unique amplitude and phase structures. In terms of communication systems, multiple orthogonal OAM can be potentially utilized for increasing link capacity in different scenarios. This review describes challenges, advances, perspectives on aspects the OAM-based optical communications, including (a) generation/detection (de)multiplexing, (b) classical free-space links, (c) fiber-based (d) quantum (e) communications frequency ranges, (f) using integrated devices, (g) novel structured communications.