Single photon detection system for visible and infrared spectrum range.

We demonstrate niobium nitride based superconducting single-photon detectors sensitive in the spectral range 452-2300 nm. The system performance was tested in a real-life experiment with correlated photons generated by means of spontaneous parametric downconversion, where one photon was in the visible range and the other was in the infrared range. We measured a signal to noise ratio as high as 4×104 in our detection setting. A photon detection efficiency as high as 64% at 1550 nm and 15% at 2300 nm was observed.