  We demonstrate niobium nitride based superconducting single-photon detectors
sensitive in the spectral range 452 nm - 2300 nm. The system performance was
tested in a real-life experiment with correlated photons generated by means of
spontaneous parametric down conversion, where one of photon was in the visible
range and the other was in the infrared range. We measured a signal to noise
ratio as high as $4\times 10^4$ in our detection setting. A photon detection
efficiency as high as 64% at 1550 nm and 15% at 2300 nm was observed.
