Characteristics of Ultra-Long Deep Space FSO Downlinks Using Special Detector Technologies Like SNSPD

Free Space Optics (FSO) communication technology substantially increases its presence in the growing satellite constellations as well as for deep space applications. The current work provides an overview over a demonstration of deeper space optical links beyond Lunar distance, reaching planets Mars and Venus (that is partly accomplished in frame of ESA's Hybridised Optical/RF Payload Data Transmitter study). By means of Poisson point processes (PPPs), the introduced space-to-ground downlink is simulated in Matlab programming language and in a later phase, it is modeled with a self-developed laboratory testbed (implementing also different atmospheric effects and influences). In order to comply with CCSDS standards, the High Photon Efficiency (HPE) communication link relies on Nr-array Superconducting Nanowire Single-Photon Detector (SNSPD) unit. Along with BER performance, the dependence on SNSPD's recovery time and array size as well as Pulse Position Modulation (PPM) order and adverse atmospheric conditions are investigated, plotted and verified. The consistence of the theoretical predictions with the real downlink are tested based on laboratory FSO testbed investigating the performance of a 2-array SNSPD receiver unit. Apart from the SNSPD, an approach with space-to-ground downlink emulator based on fibre-coupled Variable Optical Attenuator (VOA) and a few fixed attenuators, which reproduce a Poisson channel, is considered and analysed.