A Differential Phase Shift Scheme for Quantum Key Distribution in   Passive Optical Networks
  We propose a scheme for quantum key distribution (QKD) in a passive optical network (PON) based on differential phase shift (DPS) coding. A centralized station including all expensive components serves many users, making it suitable for a true multi-user network in a local environment with moderate distances on the order of a few kilometers. The emphasis lies on an asymmetric design for cost effective implementation of network end points. 
Michael Hentschel, Andreas Poppe, Bernhard Schrenk, Momtchil Peev,   Edwin Querasser, Roland Lieger
quant-ph