The imperfect components of a quantum key distribution (QKD) system will degrade its security. The highly attenuated
weak coherent laser source used in today's QKD system is vulnerable to PNS attacks due to multi-photon optical pulses.
Decoy State QKD, which is capable of beating PNS attacks and providing unconditional security, has been an attractive
scheme recently. We have used a one way Faraday-Michelson phase modulated QKD system to implement 123km
decoy state QKD in the lab. Furthermore a field decoy state QKD experiment of 32km dark fiber in Beijing is fulfilled.
The optical pulse repetition rate is 1MHz and the final secure key is 9.59×10<sup>-7</sup> (6.784×10<sup>-6</sup>) bit per pulse for 123km
(32km). The experiment result indicates that the decoy state scheme can be successfully used in real-life metropolitan
We have demonstrated a gated-mode single-photon detector at 1550 nm using two thermoelectrically cooled InGaAs/InP
avalanche photodiodes (APDs). Balanced outputs from the two APDs were used to cancel the charge and discharge
spikes, which were attributable to capacitive behavior in a gated mode. The avalanche signals were not attenuated during
the spike cancellation, which enable one to reduce the bias voltage applied to the APDs and thus reduce the dark count
probability. We obtained a quantum efficiency of 10.5% with a dark count probability of 4.8E-5 per gate at 212 K. A
single photon detector module that integrated APD and all necessary circuits into a compact bin has been performed.