Superconducting nanowire single-photon detectors (SNSPDs) with very high efficiencies (80-90+%) near 1550nm have been recently used for many record-setting experiments in quantum optics, and high data-rate long-range optical communications. Much of the improvement in efficiency is due to the use of tungsten-silicide (WSi) as the superconducting material, which exhibits a higher device yield when fabricated in multi-layer stacks than traditional NbN or NbTiN-based detectors. In this talk, I will introduce SNSPDs and will describe the latest development of these devices at Photon Spot. The talk will also describe the closed-cycle cryogenic system that is used to cool down and operate these detectors.