An improved 'plug & play' interferometric system for quantum key distr
ibution is presented. Self-alignment and compensation of birefringence
remain, while limitations due to reflections are overcome. Original e
lectronics implementing the BB84 protocol makes adjustment simple. Key
creation with 0.1 photon per pulse at a rate of 325 Hz with a 2.9% QB
ER, corresponding to a net rate of 210 Hz, over a 23 km installed cabl
e was realised.