Systems and methods for transmitting quantum and classical signals over an optical network
View Patent ↗Systems and methods for transmitting quantum and classical signals over an optical network are disclosed, wherein the quantum signal wavelength either falls within the classical signal wavelength band, or is very close to one of the classical signal wavelengths. The system includes a deep-notch optical filter with a blocking bandwidth that includes the quantum signal wavelength but not any of the classical signal wavelengths. The deep-notch optical filtering is applied to the classical signals prior to their being multiplexed with the quantum signals to prevent noise generated by the classical signals from adversely affecting transmission of quantum signals in the transmission optical fiber. Narrow-band filtering is also applied to the quantum signals prior to their detection in order to substantially exclude spurious non-quantum-signal wavelengths that arise from non-linear effects in the optical fiber. The present invention allows for the quantum and classical signals to have wavelengths within just a few nanometers of one another, which has benefits for both classical and quantum signal transmission on a common transmission optical fiber.
1. 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.
2. The system of claim 1 , wherein the first narrow-band optical filter has a blocking bandwidth such that at least one of the classical signal wavelengths transmitted by the first narrow-band optical filter is within 10 nm of the quantum signal wavelength.
3. The system of claim 1 , wherein the blocking bandwidth is 5 nm or less.
4. The system of claim 1 , wherein the blocking bandwidth is 1 nm or less.
5. The system of claim 1 , wherein the quantum signal wavelength is between two classical signal wavelengths.
6. The system of claim 1 , wherein the classical signal wavelengths include wavelengths of about 1552.52 nm and 1546.12 nm, and wherein the quantum signal wavelength is about 1549.32 nm.
7. The system of claim 1 , wherein the optical amplifier is an erbium-doped amplifier (EDFA).
8. The system of claim 1 , wherein the first narrow-band optical filter has a 3 dB blocking bandwidth in the range from about 0.2 nm to about 100 nm.
9. The system of claim 1 , wherein the first narrow-band optical filter has a 3 dB blocking bandwidth in the range from about 0.2 nm to about 10 nm.
10. The system of claim 1 , wherein the second narrow-band optical filter comprises at least one Fabry-Perot filter and at least one thin-film filter.
11. The system of claim 1 , wherein the first narrow-band optical filter comprises two or more blocking filters.