Beaconless Auto-Alignment for Single-Wavelength 5 Tbit/s Mode-Division Multiplexing Free-Space Optical Communications

TL;DR

This paper introduces a beaconless alignment system for single-wavelength 5.14 Tbit/s mode-division multiplexed free-space optical links, achieving higher accuracy and faster setup without additional beacon beams, simplifying calibration and enhancing performance.

Contribution

The paper presents a novel beaconless alignment method that improves accuracy, reduces complexity, and enables ultra-high data rates in mode-division multiplexed free-space optical communications.

Findings

Achieved record-high 5.14 Tbit/s line rate.

Demonstrated higher alignment accuracy and faster acquisition.

Eliminated need for beacon beams, reducing system complexity.

Abstract

Mode-division multiplexing has shown its ability to significantly increase the capacity of free-space optical communications. An accurate alignment is crucial to enable such links due to possible performance degradation induced by mode crosstalk and narrow beam divergence. Conventionally, a beacon beam is necessary for system alignment due to multiple local maximums in the mode-division multiplexed beam profile. However, the beacon beam introduces excess system complexity, power consumption, and alignment errors. Here we demonstrate a beaconless system with significantly higher alignment accuracy and faster acquisition. This system also excludes excess complexity, power consumption, and alignment errors, facilitating simplified system calibration and supporting a record-high 5.14 Tbit/s line rate in a single-wavelength free-space optical link. We anticipate our paper to be a starting point for more sophisticated alignment scenarios in future multi-Terabit mode-division multiplexing free-space optical communications for long-distance applications with a generalised mode basis.