1310-nm quantum key distribution system with up-conversion pump wavelength at 1550 nm.

We show that the performance of a 1310-nm quantum key distribution (QKD) system with up-conversion detectors pumped at 1550 nm is comparable with or better than that of current 1550-nm QKD systems with a pump at shorter wavelength. The nonlinearly-induced dark counts are reduced when the wavelength of the pump light is longer than that of the quantum signal. We have developed a 1550-nm pump up-conversion detector for a 1310-nm QKD system, and we experimentally study the polarization sensitivity, pump-signal format, and various influences on the dark count rate. Using this detector in a proof-of-principle experiment, we have achieved a secure key rate of 500 kbit/s at 10 km and 9.1 kbit/s at 50 km in a 625-MHz, B92, polarization-coding QKD system, and we expect that the system performance could be improved further.