Adaptive-optics-based simultaneous pre- and post-turbulence compensation of multiple orbital-angular-momentum beams in a bidirectional free-space optical link

TLDR

Orbital angular momentum can enable multiplexing of multiple data‑carrying beams to increase transmission capacity, but atmospheric turbulence poses a critical challenge in free‑space optical communications. The study experimentally demonstrates simultaneous pre‑ and post‑turbulence compensation of multiple OAM beams in a bidirectional free‑space optical link using a single adaptive optics system. Each 100‑Gbit/s OAM beam traverses emulated turbulence, while a Gaussian‑beam‑based adaptive optics system at one link end performs wavefront sensing and correction. The adaptive optics system simultaneously pre‑ and post‑compensates OAM beams, reducing adjacent‑mode crosstalk by over 12 dB and achieving bit‑error rates below 10⁻³ in both link directions, demonstrating its potential for high‑capacity bidirectional FSO links.

Abstract

As a recently explored property of light, orbital angular momentum (OAM) has potential in enabling multiplexing of multiple data-carrying beams, to increase the transmission capacity and spectral efficiency of a communication system. For the use of OAM multiplexing in free-space optical (FSO) communications, atmospheric turbulence presents a critical challenge. In this paper, we experimentally demonstrate simultaneous pre- and post-turbulence compensation of multiple OAM beams, in a bidirectional free-space optical communications link, using a single adaptive optics (AO) system. Each beam carries a 100  Gbit/s signal, and propagates through an emulated atmospheric turbulence. A specifically designed AO system, which utilizes a Gaussian beam for wavefront sensing and correction, is built at one end of the bidirectional link. We show that this AO system can be used to not only post-compensate the received OAM beams, but also pre-compensate the outgoing OAM beams emitted from the same link end. Experimental results show that this compensation technique helps reduce the crosstalk onto adjacent modes by more than 12 dB, achieving bit error rates below the forward error correction limit of 1×10−3, for both directions of the link. The results of work might be helpful to future implementation of OAM multiplexing, in a high-capacity FSO bidirectional link affected by atmospheric turbulence.