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 × 10 −5 at 223 K. 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.