Towards a smooth integration of quantum key distribution in metro networks

Quantum key distribution (QKD) systems have already reached a reasonable level of maturity. However, a smooth integration of commercial QKD systems in metropolitan area networks has still remained challenging because of technical and economical obstacles. Mainly the need for dedicated fibers and the strong dependence of the secret key rate on both loss budget and background noise in the quantum channel hinder a practical, flexible and robust implementation of QKD in current and next-generation optical metro networks. In this paper, we discuss these obstacles and present approaches to share existing fiber infrastructures among quantum and classical channels. Particularly, a proposal for a smooth integration of QKD in optical metro networks, which implies removing spurious background photons caused by lasers, amplifiers and nonlinear effects in optical fibers, is presented and discussed.