Patent ID: 7570420

Claim:
A system for transmitting, over a long-haul optical fiber network, classical signals having respective classical wavelengths representing a classical channel and quantum signals having a quantum signal wavelength representing a quantum channel, the system comprising: a demultiplexer adapted to separate the quantum channel and the classical channel; in the separate classical channel, an optical isolator, an optical amplifier optically coupled to the optical isolator, and a first narrow-band optical filter optically coupled to the optical amplifier and having a blocking bandwidth centered on the quantum signal wavelength but not extending to any of the classical signal wavelengths, so as to form filtered classical signals wherein the quantum signal wavelength is within 100 nm of one of the classical signal wavelengths; in the separate quantum channel, a second narrow-band optical filter adapted to substantially exclude non-quantum signal wavelengths, and a quantum key distribution (QKD) station optically coupled to the second optical filter and adapted to receive filtered first quantum signals therefrom and form relayed quantum signals; and a multiplexer adapted to recombine the classical and quantum channels onto a transmission optical fiber that carries both the filtered classical signals and the relayed quantum signals.