Abstract
Quantum key distribution (QKD) systems have already reached a reasonable level of maturity. However, a smooth integration and a wide adoption 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 optical transmitters, amplifiers and nonlinear effects in fibers, is presented and discussed. We determine and characterize impairments on quantum channels caused by many classical telecom channels at practically used power levels coexisting within the same fiber. Extensive experimental results are presented and indicate that a practical integration of QKD in conventional optical metro networks is possible.
Highlights
The idea to utilize the quantum nature of optical phenomena to encrypt transmitted data is not substantially new, it was already introduced in the early 1980’s [1], practical Quantum key distribution (QKD) systems that can be smoothly and economically integrated in conventional optical networks are still not available
Similar to the QKD combiner/separator units required to realize the co-existence approach, these are necessary to realize the transparent QKD overlay nodes. The influence of such additional components on the quantum channel needs to be considered in the QKD overlay design because these determine the quantum signals reach, which in turn limits the span of the transparent sections and the QKD overlay’s reach
We proposed and investigated an approach for reliable exchange of quantum keys over existing fiber infrastructures in coexistence with many classical data channels operated at usual power levels
Summary
The idea to utilize the quantum nature of optical phenomena to encrypt transmitted data is not substantially new, it was already introduced in the early 1980’s [1], practical QKD systems that can be smoothly and economically integrated in conventional optical networks are still not available. A first step to make QKD systems more economical is to find a way to transmit weak QKD signals together with strong conventional optical signals over the same optical fiber Such an option, referred to as coexistence scheme, has attracted particular interest in recent years. We address perspectives and limitations of a smooth QKD integration in conventional metropolitan area networks and aim to find a wavelength range that best suits to allocate quantum channels. For this purpose, we analyze the impairments on quantum channels that result from many strong classical signals.
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