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Implementing QKD over Multi-Fiber Ribbon Cables: How Dark is the "Dark Fiber"?

Florian Honz, Vana Pezelj, Theodor Strobl, Florian Kutschera, Valeria Saggio, Philip Walther, Hannes Hübel, Bernhard Schrenk

Published Mar 13, 2026• 0 citations
Publisher

Abstract

We identify inter-lane crosstalk as main cause for QKD degradation in 1×12 bend-loss insensitive fiber ribbon cables. Despite allocating QKD to unused fiber lanes, neighboring classical signals can lead to total saturation of single-photon detectors.
DOI
10.5281/zenodo.19005902

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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.