Performance metrics and design considerations for a free-space optical orbital-angular-momentum–multiplexed communication link

Abstract

The capacity of free-space optical (FSO) communication links could potentially be increased by the simultaneous transmission of multiple orbital angular momentum (OAM) beams. For such an OAM multiplexing approach, one requires the collection of adequate power as well as proportion of the phase front for a system with minimal crosstalk. Here we study the design considerations for an OAM-multiplexed free-space data link, analyzing the power loss, channel crosstalk, and power penalty of the link in the case of limited-size receiver apertures and misalignment between the transmitter and the receiver. We describe the trade-offs for different transmitted beam sizes, receiver aperture sizes, and mode spacing of the transmitted OAM beams under given lateral displacements or receiver angular errors. Through simulations and some experiments, we show that (1) a system with a larger transmitted beam size and a larger receiver aperture is more tolerant to lateral displacement but less tolerant to the receiver angular error, and (2) a system with a larger mode spacing, which uses larger OAM charges, suffers more system power loss but less channel crosstalk; thus, a system with a small mode spacing shows a lower system power penalty when system power loss dominates (e.g., a small lateral displacement or receiver angular error), whereas that with a larger mode spacing shows a lower power penalty when channel crosstalk dominates (e.g., a larger lateral displacement or receiver angular error). This work could be beneficial to the practical implementation of OAM-multiplexed FSO links.

Quantum features in the orthogonality of optical modes for structured and plane-wave light

“…In this Letter, we re-examine the key commutation relation, and show that a different formulation is entirely consistent with quantum principles. Moreover, the new formulation has special relevance for the propagation character, and potential informationconveying capacity, of structured light [6]. The motivations behind the study are to highlight the importance of a correct photon commutation relation, to explore a connection to beams endowed with orbital angular momentum (OAM) [7], Letter Vol.…”

Recent advances in high-capacity free-space optical and radio-frequency communications using orbital angular momentum multiplexing

“…This suggests that OAM-multiplexed links may require a more precise system alignment than non-OAM, single-beam communication links [24]. To date, most of the OAMbased free-space SDM systems rely on line-of-sight (LOS) connection between the transmitter and receiver [25,26].…”

“…These factors need to be carefully considered in the choice of the link parameters of an FSO system using OAM multiplexing. A simulation model was established in [24] to investigate signal power and crosstalk effects for received OAM channels over pure free-space propagation. modes chosen for transmission, system misalignment tolerance, transmitted beam sizes, aperture sizes and link distance were explored.…”

Propagation of structured light beams after multiple reflections in a spiral phase plate

“…Optical beams with OAM have structured wavefronts and are frequently referred to as complex light beams or structured light beams. [47][48][49][50] In fact, in the generation of optical vortices at millimeter wavelengths, the device of choice is still SPPs 8,29,39,40 compared with other devices that can generate optical vortices. An example of a device used to create a complex light beam is a spiral phase plate (SPP).…”