Efficient and low-noise single-photon avalanche photodiode for 1.244-GHz clocked quantum key distribution

An efficient and low-noise 1.244-GHz gating InGaAs single-photon avalanche photodiode (SAPD) was developed for a high-speed quantum key distribution (QKD) system. An afterpulsing probability of 0.61% and a dark count probability per gate of 0.71 ×10-6 were obtained at a detection efficiency of 10.9% for 1.55-µm photons. Furthermore, our SAPD successfully coped with high detection efficiency (≤ 25%) and quite low afterpulsing noise (≤ 3% for ≤ 25% efficiency) at the same time. Its potential was verified using the actual QKD setups installed over a metropolitan area network.