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 1550 nm in the temperature range of thermoelectric cooling. A ratio of the dark count rate to the detection efficiency was obtained to be 9 x 10(-5) at 223K. When the detector is applied to a practical quantum key distribution system, the transmission distance can reach 89.5 km and the repetition rate can reach 0.33 MHz.