In our recent experiment, we have designed a novel single-photon detecting module for quantum key distribution using an InGaAs/InP avalanche photodiode with gate-mode quenched photo-detection. At a repetition rate of 100 kHz and the working temperature of -60°C, we obtained the detection efficiency η higher than 10% and 20% at the dark probability Pd about 1.3×10-5 and 1.6×10-5 per nanosecond, respectively. Also at 100 kHz,
we got the best ratio of Pd/η as 1.7×10-3 per pulse (20 ns). And at a lower repetition such as 10 kHz, we obtained
Pd/η as 8.9×10-4 per pulse.
This report proposes a “Plug and Play” quantum key distribution system using differential phase shift, in which any birefringence effects and polarization-dependent losses in the telecom fiber are automatically compensated by using a Faraday mirror. In this system, a light pulse is split into three pulses after traveling through four couplers and a light intensity feedback servosystem is plugged into this system in order to adjust the phase shifter to compensate the variation of these three pulses. The efficiency of key creation in this system is 8/3 higher than the conventional cryptosystem based on the BB84 protocol.