Fiber-coupled near-infrared single-photon spectrum analyzer based on a InGaAs/InP avalanche photodiode single-photon detector

A highly sensitive fiber-coupled single-photon spectrum analyzer is built based on a InGaAs/InP avalanche photodiode single-photon detector operated in Geiger mode. This device is capable of analyzing weak light signals with less than 3.6 10-4 photon pulse-1 in the spectral range from 1390 to 1600 nm. We have used it to measure the spectrum of the weak nonlinear signal of the fiber caused by the clock pulse in the quantum key distribution experiment. The spectral information will help to eliminate the nonlinear background in the fiber and improve the performance of the system.