Detection efficiency of large-active-area NbN single-photon superconducting detectors in the ultraviolet to near-infrared range

We report our studies on spectral sensitivity of meander-type, superconducting NbN thin-film single-photon detectors (SPDs), characterized by GHz counting rates of visible and near-infrared photons and negligible dark counts. Our SPDs exhibit experimentally determined quantum efficiencies ranging from similar to0.2% at the 1.55 mum wavelength to similar to70% at 0.4 mum. Spectral dependences of the detection efficiency (DE) at the 0.4 to 3.0-mum-wavelength range are presented. The exponential character of the DE dependence on wavelength, as well as its dependence versus bias current, is qualitatively explained in terms of superconducting fluctuations in our ultrathin, submicron-width superconducting stripes. The DE values of large-active-area NbN SPDs in the visible range are high enough for modern quantum communications. (C) 2002 American Institute of Physics.