80-Gbit/s 100-m Free-Space Optical Data Transmission Link via a Flying UAV Using Multiplexing of Orbital-Angular-Momentum Beams

Authors: Long Li^1*†, Runzhou Zhang^1†, Zhe Zhao¹, Guodong Xie¹, Peicheng Liao¹, Kai Pang¹, Haoqian Song¹, Cong Liu¹, Yongxiong Ren¹, Guillaume Labroille², Pu Jian²,Dmitry Starodubov¹, Robert Bock³, Moshe Tur⁴, Alan E. Willner^1*

¹Department of Electrical Engineering, University of Southern California, Los Angeles,
California 90089, USA.
²Cailabs, Rennes 35200, France.
³R-DEX Systems, Marietta, Georgia 30068, USA.
⁴School of Electrical Engineering, Tel Aviv University, Ramat Aviv 69978, Israel.
^*Correspondence to: longl@usc.edu, willner@usc.edu.
^†These authors contributed equally to this work.

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 station and 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: tracking errors, 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.