Improving detection efficiency of superconducting nanowire single-photon detector using multilayer antireflection coating

Optical cavity with backside optical coupling is one of the prevalent optical structures for superconducting nanowire single photon detector. A single layer anti-reflection coating (ARC) on the backside of the substrate is often adopted to enhance the transmittance to the substrate. We here apply a multilayer ARC to further increase the transmittance from 94.5% to 99.5%. An NbTiN SNSPD made on such a substrate with cavity structure presents a system detection efficiency of 90.1% at a dark count rate (DCR) of 100 Hz, which is the best value reported for backside optical coupled SNSPD at 1550 nm. It shows a timing jitter of similar to 40.7 ps and the recovery time constant of similar to 22.9 ns. (C) 2018 Author(s).