Fibre-Based Dynamic Speckle Generation for Emulation of Atmospheric Turbulence

Mitigating the impact of atmospheric turbulence induced speckle is a major challenge for free-space optical communications (FSOC). Such turbulence results in a multimodal, speckled beam which can be challenging to couple into the small active-area photoreceivers needed for high-bandwidth detection. Naturally, lab-based turbulence emulators are needed to benchmark FSOC system performance and develop turbulence mitigating subsystems. Common approaches to turbulence emulation include: rotating phase plates (PPs) [1], spatial light modulators (SLMs) [2] and turbulent-air generators [3]. In this work, we present a fibre-based, dynamic speckle generator, notable for its simplicity, cost-effectiveness (especially compared to SLMs and PPs), and unobtrusive in-lab use (compared to turbulent-air approaches). Unlike today's SLMs, which currently struggle to replicate the fast-changing distortion caused by high slew-rate Low-Earth-Orbit (LEO) satellite tracking, our all-fibre speckle generator can be easily scaled to faster modulation speeds (demonstrated here with a modest 230RPM).