Compactly packaged superconducting nanowire single-photon detector with an optical cavity for multichannel system

We developed superconducting nanowire single-photon detectors with an optical cavity (OC-SNSPDs) for multichannel systems. For efficient coupling, the devices were installed in compact fiber-coupled packages after their substrate thickness was reduced from 400 to 45 $\mu$m. The measured detection efficiency (DE) measurement at different substrate thicknesses and the estimation of optical coupling efficiency indicated that ~98% of the input light beam could be radiated on a 15x15 $\mu m^2$ nanowire area from behind the substrate. The DEs of a NbN OC-SNSPD system were observed to be 9.5% and 25% at 1550 nm and 1310 nm, respectively (dark-count rate: 100 c/s).