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We fabricated superconducting nanowire single-photon detectors (SNSPDs) made of NbTiN and NbN thin films in the same fabrication batch. Various parameters, such as critical temperature, resistivity, switching current, and kinetic inductance, were compared between the two types of SNSPDs. These data indicate that NbTiN SNSPD surpasses NbN SNSPD in many aspects, including a shorter recovery time due to smaller kinetic inductance, a lower timing jitter due to higher switching current, and better uniformity. Based on the measurement of 28 out of 121 NbTiN SNSPDs on a 2-in Si wafer, 71% of detectors show a system detection efficiency of over 50% at a dark count rate of 100 Hz, with the maximum efficiency being 77.5%. [ABSTRACT FROM AUTHOR]

We report the characterization of optical coupling efficiency and the absorption coefficient of fiber-coupled superconducting nanowire single photon detector with an optical cavity, which limit the system detection efficiency. The small lenses were applied to compact fiber-coupled package and the efficient optical coupling higher than 95% were confirmed experimentally. The absorption coefficient was also verified and reached to \sim60% at 1550 nm wavelength and optimum polarized condition. The system detection efficiencies at 1550, 1310 and 810 nm were 28, 40 and 3%, respectively, which are related to the absorptance dependencies on wavelengths. [ABSTRACT FROM AUTHOR]