A small, low-cost, turbulence profiling instrument for free-space optical communication

Abstract

Characterisation and mitigation of atmospheric turbulence is critical for free space optical communication that relies on adaptive optics such as high bit rate coherent modulation or quantum key distribution. Turbulence profiling, i.e. measuring turbulence at different altitudes, provides more detail than typical seeing monitors and supports sophisticated AO and the possibility to forecast conditions. We present the implementation of a Ring-Image Next Generation Scintillation Sensor (RINGSS) instrument that profiles turbulence with a novel approach of defocused ring images introduced by A. Tokovinin (2021) 1 . RINGSS is exceptionally low-cost, small, and fully automated, requiring significantly simpler equipment than previous turbulence profilers. We have demonstrated preliminary results that demonstrate the capability of this instrument for measurements of seeing and a low resolution turbulence profile. Future work is outlined that includes cross-calibration with a Stereo-SCIDAR instrument recently commissioned on the ANU 2.3m telescope at Siding Spring Observatory and plans for deployment at prospective optical ground station sites for an Australia-New Zealand optical network.

Measuring the vertical profile of atmospheric turbulence with the laser communication relay demonstration downlink at Table Mountain Facility

“…While Tokovinin (2021) can be referred to for an explanation on the operational principle behind RINGSS, it is important to note that this FSOC version does not require any polychromatic corrections which are typical and the weighting functions required are simpler. 6,9 Simplicity in the context of mathematics built on many weak-scintillation assumptions is critical to ensure accuracy in regimes such as daytime turbulence. This compounds with the weakening of turbulence with increasing wavelength, to allow RINGSS at 1.55 µm to avoid scintillation saturation (due to the relative 'slowing' of turbulence).…”

Deep space communication with the ANU optical communications ground station

“…Outages due to poor weather can be minimised by diversity in the ground station network to ensure there is always an available site for a link. 1 The small divergence of the optical signal also means the terminals require very precise pointing to maintain a link.…”

A transmitter and receiver for lunar communications on the ANU Optical Ground Station

“…Network diversity where the individual sites are not correlated can help mitigate the weather downtime by offering multiple link options. 3 With deep space links to the Moon and beyond network diversity across the entire globe is desirable so there are always sites that are visible to the spacecraft. If these sites have similar capability then performance can be consistent across the different ground terminals.…”