Single Photon Detector at Telecom Wavelengths for Quantum Key Distribution

Using InGaAs/InP avalanche photodiodes as sensors and coaxial cables as reflection lines to reject spike signals, we have firstly employed the ``timing filtering'' gates to pick out avalanche signals and have realized the single photon detection at 1550nm in the temperature range of thermoelectric cooling. A ratio of the dark count rate to the detection efficiency was obtained to be 9×10^-5 at 223K. When the detector is applied to a practical quantum key distribution system, the transmission distance can reach 89.5km and the repetition rate can reach 0.33MHz.