Long-distance QKD transmission using single-sideband detection scheme with WDM synchronization

We report a long-distance, polarization insensitive, quantum key distribution scheme using single-sideband (SSB) detection. The method uses an amplitude modulation to transmit photon in sidebands. The system acts as a fainted laser diode whose information quantum state is encoded in the phase difference between the main peak and its sidebands. Using the dispersion properties of the fiber, the relative phase between interacting quantum states can be reliably controlled by sending a reference signal over the physical link that transmits the quantum signal. Therefore, photon detection can be performed very accurately over long distances. Stability of the synchronization technique with respect to optical path variation is also discussed. The reconciliation process uses a LAN connection as public channel. Experiments were carried out in the C-band telecom window (1550 nm), over a 40-km standard single-mode fiber spool as well as over a 10-km deployed fiber.