Increasing the Link-distance of Free-space Quantum Coherent Communication with Large Area Detectors

Abstract

A large area photo-diode based homodyne detector for free-space quantum coherent communication is reported. The detector's performance is studied in terms of the detection bandwidth and electronic noise for shot-noise limited quantum signal detection. Using large area photo-diodes increases the signal collection efficiency from turbulent atmospheric channels, in comparison with thetypical fibre-based free-space homodyne detectors. Under identical atmospheric turbulence and receiver aperture conditions, over a 700-km free-space link at 90° elevation angle, our homodyne detector based on a diameter of 1mm photo-diode experiences 0dB loss due to turbulence, while a 10-um fibre-based detector experiences 13.5dB of signal loss.