Generation of Correlated Photon Pairs in the 1550-nm Band Using a Periodically Poled Lithium Niobate Waveguide

摘要

Long-distance communication is important for practical quantum key distribution. From the viewpoint of transmission distance, generation of single photons at 1550 nm is desirable for fiber transmission. Making use of parametric down-conversion (signal and idler photons) as a single photon source for quantum key distribution can obtain communication distance longer than using a conventional weak coherent pulse. The reason for this is that the arrival time of the idler photon can be known by the detection of signal photon and therefore the dark count probability can be reduced by operating Bob's detector for a very short time around the photon arrival. In this paper, we report on the generation of the correlated photon pairs in the 1550-nm band using a periodically poled lithium niobate waveguide which has a high conversion efficiency. Our measurements are in agreement with a Poissonian photon-pair distribution. We have deduced that the probability of multi-photon-pair generation is sufficiently reduced when the pump is lower than 5 μW with a repetition rate of 800 kHz. We also demonstrated a two-photon interference experiment using a Mach-Zehnder interferometer to confirm the quantum-mechanical nature of the correlated photon pairs. We found that that visibility was decreased when the pump power was increased due to the multi-photon-pair contribution.