Enhancing Detection Efficiency by Applying an Optical Cavity Structure in a Superconducting Nanowire Single-Photon Detector

We report on the enhancement of system detection efficiency in a superconducting nanowire single-photon detector (SNSPD) by applying the optical cavity structure. The nanowire was made using 4nm-thick NbN thin films and covered with an SiO cavity and Au mirror designed for 1300–1600 nm wavelengths. The device is mounted into fibercoupled packages, and installed in a practical multichannel system based on GM cryocoolers. System detection efficiency depends on the absorptance of cavity structure, and reached 28% and 40% at 1550 nm and 1310 nm wavelengths, respectively. These values were considerably higher than an SNSPD without optical cavity. key words: single photon detector, superconducting nanowire, quantum information and communications, NbN thin films