Systems and methods for transmitting quantum and classical signals over an optical network

A method of transmitting classical signals and quantum signals over an optical fiber, comprising:

• generating classical signals at respective classical signal wavelengths;
• generating quantum signals at a quantum signal wavelength that is between at least two of the classical signal wavelengths;
• filtering the classical signals to block wavelengths that include the quantum signal wavelength but not the classical signal wavelengths, thereby forming filtered classical signals;
• multiplexing onto the optical fiber the filtered classical signals with the quantum signals;
• demultiplexing the filtered classical signals and the quantum signals;
• and
• filtering the quantum signals just prior to their detection to substantially exclude non-quantum signal wavelengths.

An optical network system, comprising:

• a classical optical communications system adapted to generate and receive classical signals having respective classical signal wavelengths;
• a quantum key distribution (QKD) system having QKD stations ALICE and BOB respectively adapted to generate and receive quantum signals having a quantum signal wavelength;
• a transmission optical fiber adapted to carry both the classical signals and the quantum signals from a transmission side of the network to a receiver side of the network;
• a first optical blocking filter arranged so as to filter only the classical signals over a narrow spectral band that surrounds the quantum signal wavelength but that does not extend into the classical signal wavelengths so that the quantum signal wavelength is within 100 nm of one of the classical signal wavelengths;
• a multiplexing element arranged to combine the quantum signals and classical signals at the transmitter side of the network and a de-multiplexing element arranged at the receiver side of the network to separate the quantum signals and the classical signals at the receiver side of the network;
• and
• a narrow-bandpass filter adapted to filter the quantum signals at the receiver side of the network just prior to their detection to substantially exclude non-quantum signal wavelengths.