Upconversion single-photon detectors based on integrated periodically poled lithium niobate waveguides [Invited]

We demonstrate upconversion single-photon detectors based on integrated periodically poled lithium niobate waveguides that incorporate two mode filters and a directional coupler. The two mode filters are optimized for the fiber-waveguide coupling efficiencies for 1550 and 1950 nm, respectively, while the directional coupler plays the role of wavelength combiner, making the overall system portable and low cost. The two wavelengths pump each other in our detection system. We achieve detection efficiencies of 28% for 1550 nm and 27% for 1950 nm, respectively. This scheme provides an efficient integrated single-photon detection method for any two well-separated spectral bands in the whole low-loss range of lithium niobate waveguides.