High-Capacity Free-Space Optical Communications Between a Ground Transmitter and a Ground Receiver via a UAV Using Multiplexing of Multiple Orbital-Angular-Momentum Beams

TLDR

The study investigates using OAM‑multiplexing to boost free‑space data transmission capacity to moving platforms while potentially reducing interception risk. The authors experimentally establish an OAM‑multiplexed FSO link between ground stations via a UAV and evaluate its performance under static, hovering, and moving conditions, examining misalignments, airflow, power loss, crosstalk, and BER. The system achieves 80 Gbit/s over a 100‑m round‑trip by multiplexing two 40‑Gbit/s QPSK OAM modes, with hovering causing 2.1 dB power fluctuation and −19 dB crosstalk, moving causing 4.3 dB fluctuation and −10 dB crosstalk, and crosstalk further reducing as OAM mode spacing increases.

Abstract

Abstract We explore the use of orbital-angular-momentum (OAM)-multiplexing to increase the capacity of free-space data transmission to moving platforms, with an added potential benefit of decreasing the probability of data intercept. Specifically, we experimentally demonstrate and characterize the performance of an OAM-multiplexed, free-space optical (FSO) communications link between a ground transmitter and a ground receiver via a moving unmanned-aerial-vehicle (UAV). We achieve a total capacity of 80 Gbit/s up to 100-m-roundtrip link by multiplexing 2 OAM beams, each carrying a 40-Gbit/s quadrature-phase-shift-keying (QPSK) signal. Moreover, we investigate for static, hovering, and moving conditions the effects of channel impairments, including: misalignments, propeller-induced airflows, power loss, intermodal crosstalk, and system bit error rate (BER). We find the following: (a) when the UAV hovers in the air, the power on the desired mode fluctuates by 2.1 dB, while the crosstalk to the other mode is −19 dB below the power on the desired mode; and (b) when the UAV moves in the air, the power fluctuation on the desired mode increases to 4.3 dB and the crosstalk to the other mode increases to −10 dB. Furthermore, the channel crosstalk decreases with an increase in OAM mode spacing.