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 $4times 10^4$ in our detection setting. A photon detection efficiency as high as 64% at 1550 nm and 15% at 2300 nm was observed.
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