Approaching single-photon detection in near-infrared region

We have implemented a single-photon detection system in the 1.55-μm region, based on frequency up-conversion in MgO-doped periodically poled LiNbO3 waveguide. We have subsequently reached a record-low dark count rate of 45 counts per second. The detectable signal photon rate, i.e., the rate for counting the up-converted photons corrected by the dark counts, noises, and losses, reaches a record-low value of 81 photons per second. Through free-space coupling, we have eliminated the dark counts induced by parametric fluorescence.