An end-to-end demonstration of a receiver array based free-space photon counting communications link

TLDR

NASA anticipates a significant demand for long‑haul communications service from deep‑space to Earth in the near future. The study aims to demonstrate key technologies for a deep‑space optical receiver by building an end‑to‑end free‑space photon‑counting testbed. The testbed uses two Geiger‑mode avalanche photodiode detector arrays, aggregates their photon arrivals with hardware, and decodes the combined stream in real time using a hardware turbo decoder. The system achieved error‑free communication at up to 14 Mbps, within 1 dB of channel capacity and with an efficiency exceeding one bit per incident photon.

Abstract

NASA anticipates a significant demand for long-haul communications service from deep-space to Earth in the near future. To address this need, a substantial effort has been invested in developing a free-space laser communications system that can be operated at data rates that are 10-1000 times higher than current RF systems. We have built an end-to-end free-space photon counting testbed to demonstrate many of the key technologies required for a deep space optical receiver. The testbed consists of two independent receivers, each using a Geiger-mode avalanche photodiode detector array. A hardware aggregator combines the photon arrivals from the two receivers and the aggregated photon stream is decoded in real time with a hardware turbo decoder. We have demonstrated signal acquisition, clock synchronization, and error free communications at data rates up to 14 million bits per second while operating within 1 dB of the channel capacity with an efficiency of greater than 1 bit per incident photon.