Superconducting nanowire single-photon detectors ͑SNSPDs͒ have emerged as a highly promising infrared single-photon detector technology. Next-generation devices are being developed with enhanced detection efficiency ͑DE͒ at key technological wavelengths via the use of optical cavities. Furthermore, new materials and substrates are being explored for improved fabrication versatility, higher DE, and lower dark counts. We report on the practical performance of packaged NbTiN SNSPDs fabricated on oxidized silicon substrates in the wavelength range from 830 to 1700 nm. We exploit constructive interference from the SiO 2 / Si interface in order to achieve enhanced front-side fiber-coupled DE of 23.2 % at 1310 nm, at 1 kHz dark count rate, with 60 ps full width half maximum timing jitter. © 2010 American Institute of Physics. ͓doi:10.1063/1.3428960͔Infrared single-photon detectors are a key enabling technology for a host of scientific applications. Advanced photon-counting applications place stringent demands on detector performance, and new detector technologies are rapidly being developed, evaluated, and deployed.1 Superconducting nanowire single-photon detectors ͑SNSPDs͒ ͑Refs. 2-4͒ offer wide spectral range ͑from visible to midinfrared wavelengths͒ with free-running operation, low dark counts, short reset times, and low timing jitter. SNSPDs have begun to have a significant impact on applications, such as quantum key distribution, 5 time-of-flight ranging, 6 high bit-rate ground-to-space communications, 7 and optical quantum information processing.8 Recent work on SNSPDs has concentrated on increasing detection efficiency ͑DE͒ through improved materials, device layout, and optical architecture. 3,4,[9][10][11][12] Optical cavities increase the absorption of photons in the active device layer 9-11 and nanopositioning systems are employed to maximize coupling efficiency to the device area. 12The ϳ1300 nm wavelength range is important for quantum information experiments using telecom-wavelength quantum-dot single-photon sources 13 and medical applications such as singlet oxygen detection at = 1273 nm.14 In this paper we report on enhanced device efficiency in a NbTiN SNSPD ͑Ref. 15͒ with a cavity reflection from the oxidized Si substrate optimized for ϳ1300 nm wavelength. The devices are front-side fiber-coupled in a fixed package without the need for nanopositioners or thinning of the substrate used in backside illumination architectures. 9,10,12 In this paper, we describe device performance as a function of wavelength, with reference to the device architecture. We demonstrate the highest published efficiency in a practically packaged SNSPD at = 1310 nm with frontside fiber illumination, comparable to results achieved with backside illumination.Devices used in this study 15 are based on high quality films of NbTiN deposited by reactive dc magnetron sputtering at room temperature on a Si substrate with a 225 nm SiO 2 layer. 16 Further device fabrication details are given in Ref. 15. The devices studied consist of a 10...