Quantum entanglement distribution for secret key establishment in metropolitan optical networks

Einstein-Podolsky-Rosen (EPR) is the building block of entanglement-based and entanglement-assisted quantum communication protocols. Prior shared EPR pair and an authenticated classical channel allow two distant users to share a secret key. To build a network architecture where a centralized EPR source creates entangled states by the process of spontaneous parametric down-conversion (SPDC) then routes the states to users in different access networks. We present a metropolitan optical network (MON) architecture for entanglement distribution in a typical telecommunication infrastructure. The architecture allows simultaneous transmission of classical and quantum signals in the network and provides a dynamic routing mechanism to serve the entire MON. However, the strong launch power of the classical signals impairs the weak quantum signals when they coexist in the same optical fiber. Raman scattering Stokes-shift is the major physical impairment on the higher wavelength quantum signals which, caused by the lower wavelength classical signals. Therefore, we also study the physical impairments in the network to reduce the nonlinear effects and improve the quality of the signals. In our architecture, quantum and classical signals travel in the same optical fiber, but in different spectral bands. We show Raman Stokes-shift wavelength range and the peak power gain when simultaneous transmission of both signals occur in the same optical fiber. Reducing the physical impairments increases the traveling distance of the signals and the number of the access networks in the MON.