Experimental Quantum Key Distribution over 14.8 km in a Special Optical Fibre

We present an experimental setup for quantum key distribution in a special optical fibre at the wavelength of 850 nm. The system employs the BB84 protocol to establish a secret key between Alice and Bob over 14.8 km. The key is encoded in the phase of very weak laser of average photon number 0.11 per pulse. The measured error rate is lower than 10%.