Highly efficient NbTiN nanostrip single-photon detectors using dielectric multilayer cavities for a 2-m wavelength band

We report superconducting nanostrip single-photon detectors (SNSPDs) with di-electric multilayer cavities (DMCs) for a 2-& mu;m wavelength. We designed a DMC composed of periodic SiO2/Si bilayers. Simulation results of finite element analysis showed that the optical absorptance of the NbTiN nanostrips on the DMC exceeded 95% at 2 & mu;m. We fabricated SNSPDs with an active area of 30 & mu;m x 30 & mu;m, which was sufficiently large to couple with a single-mode fiber of 2 & mu;m. The fabricated SNSPDs were evaluated using a sorption-based cryocooler at a controlled temperature. We carefully verified the sensitivity of the power meter and calibrated the optical attenuators to accurately measure the system detection efficiency (SDE) at 2 & mu;m. When the SNSPD was connected to an optical system via a spliced optical fiber, a high SDE of 84.1% was observed at 0.76 K. We also estimated the measurement uncertainty of the SDE as & PLUSMN;5.08% by considering all possible uncertainties in the SDE measurements.& COPY; 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement