Quantum Cryptography with Polarized Photons in Optical Fibres

An all-fibre quantum cryptography set-up based on the polarization of single photon pulses is described. The feasibility of establishing a key over more than 1 km has been experimentally demonstrated. The limits due to the topological effects, the birefringence, and the polarization mode dispersion of fibres are discussed. A set-up using only two non-orthogonal polarization states and polarizers instead of analysers is proposed.