Quantum Communication in Optical Networks: an Overview and Selected Recent Results

We discuss recent work in quantum communication, and in some details present a bright, narrowband, portable, quasi-phase-matched two-crystal source generating polarization-entangled photon pairs at 809 nm and 1555 nm. We also show how the single-photon quantum channel at 1555 nm and a classical synchronization signal gating the single photon detector at the receiving side can be multiplexed in the same optical fiber of length 27 km by means of wavelength division multiplexers (WDM) having 100 GHz (0.8 nm) spacing between channels. This illustrates how single-photon quantum communication applications is compatible with current high-speed optical networks.