Adaptive optics compensation of multiple orbital angular momentum beams propagating through emulated atmospheric turbulence

Abstract

We propose an adaptive optics compensation scheme to simultaneously compensate multiple orbital angular momentum (OAM) beams propagating through atmospheric turbulence. A Gaussian beam on one polarization is used to probe the turbulence-induced wavefront distortions and derive the correction pattern for compensating the OAM beams on the orthogonal polarization. By using this scheme, we experimentally demonstrate simultaneous compensation of multiple OAM beams, each carrying a 100 Gbit/s data channel through emulated atmospheric turbulence. The experimental results indicate that the correction pattern obtained from the Gaussian probe beam could be used to simultaneously compensate multiple turbulence-distorted OAM beams with different orders. It is found that the turbulence-induced crosstalk effects on neighboring modes are efficiently reduced by 12.5 dB, and the system power penalty is improved by 11 dB after compensation.

Massive individual orbital angular momentum channels for multiplexing enabled by Dammann gratings

“…In this case, the crosstalk between the input and adjacent OAM channels is above the EFEC threshold and the error bits cannot be corrected. Therefore, under the moderate and strong turbulence conditions, we need to adopt some adaptive optics approaches 34 to compensate for the fluctuations of OAM-based long-distance free-space communication.…”

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

“…An AO system that uses a separate Gaussian beam to probe turbulence-induced wavefront distortions was recently proposed to overcome these problems [49]. As depicted in figure 4a, a Gaussian beam coaxially propagates with the OAM beams through the turbulent atmosphere.…”

A flexible cross-talk simulator for multiple spatial-mode free-space optical communication

“…The LG modes have received considerable interest because they carry orbital angular momentum (OAM) [6,7]. Theory has shown, however, that they are unitarily equivalent to the HG modes [4], hence any free-space optical communication advantage they might enjoy over HG modes would be one of implementation simplicity rather than one of a fundamental nature [5].…”

“…These studies have considered operation both with and without adaptive optics, and explored three possible spatialmode sets: focused-beam modes, Hermite-Gaussian modes, and Laguerre-Gaussian modes. Table-top experiments, using orbital angular momentum modes-specifically the Laguerre-Gaussian modes with lowest-order radial dependence-have measured cross talk and communication performance with and without adaptive optics for simulated thin (phase-screen) turbulence [6,7].…”

“…Whereas the theory from [4,5] would be exceedingly tedious to repeat for arbitrary distributions of turbulence along the propagation path, and the experiments from [6,7] have been limited to one mode set and thin turbulence, our proposed simulator can realize arbitrary path distributions for the turbulence, and it can be used with arbitrary mode sets. Moreover, it can be readily implemented.…”