Simultaneous quantum cryptographic key distributionand conventional data transmission over installed fibre using wavelength-divisionmultiplexing

Wavelength division multiplexing (WDM) is used to add a secure quantum key distribution channel (λ = 1300 nm) to a conventional 1.2 Gbit/s data channel (λ ~1550 nm) operating over 28 km of installed fibre in BT's London and East Anglia multi-service network testbed (LEANET). Error-free operation of the data channel is demonstrated with no degradation of the quantum channel performance.