Temporal encoding to reject background signals in a low complexity, photon counting communication link

Communicating information at the few photon level typically requires some complexity in
the transmitter or receiver in order to operate in the presence of noise. This in turn incurs expense
in the necessary spatial volume and power consumption of the system. In this work we present
a self-synchronised free-space optical communications system based on simple, compact and low
power consumption semiconductor devices. A temporal encoding method, implemented using
a gallium nitride micro-LED source and a silicon single photon avalanche photo-detector (SPAD)
demonstrates data transmission at rates up to 100 kb/s for 8.25 pW received power, corresponding
to 27 photons per bit. Furthermore, the signals can be decoded in the presence of both constant
and modulated background noise at levels significantly exceeding the signal power. The system’s low power consumption and modest electronics requirements are demonstrated employing it as a
communications channel between two nano-satellite simulator systems.