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European Conference on Optical Communication

Quantum Key Distribution over a 143 km Heterogeneous SMF-MCF Infrastructure with Co-existing Classical Traffic

Joakim Argillander, C. Lei, Martin Clason, M. Ahmadian, Ming Tang, Rui Lin, GUILHERME BARRETO XAVIER

Published Sep 28, 2025• 0 citations
Publisher

Abstract

We demonstrate QKD transmission over heterogeneous network infrastructure consisting of a long-distance deployed single-mode fibre link connected to a multicore fibre-based access network, while showing dynamic co-existence with classical traffic within the multicore fibre, enabling one-to-many quantum and classical services.
DOI
10.1109/ecoc66593.2025.11263078

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Quantum key distribution (QKD) is increasingly considered for deployment in realistic communication networks, where long distances, heterogeneous fiber infrastructure, and coexistence with classical traffic present substantial challenges. Here, we demonstrate trusted-node QKD between Linköping University and the Stockholm hub of the Swedish national quantum communication infrastructure over 270 km of deployed single-mode fiber, extended by a 33 km multi-core fiber (MCF) segment emulating a metropolitan access link, for a total distance of 303 km. The two sub-links use commercial QKD systems whose receivers are interfaced with external superconducting nanowire single-photon detectors, enabling operation at losses beyond those supported by standard internal gated-mode detectors. We operate the link while actively switching the QKD channel between two MCF cores, with co-propagating Ethernet traffic and injected broadband optical noise in the other cores. The results demonstrate the integration of commercial QKD into demanding, dynamically reconfigurable fiber infrastructure relevant to future hybrid quantum-classical networks. Finally, using the generated secret keys, we illustrate how limited and time-varying QKD throughput affects one-time-pad-protected image transmission: image fidelity depends strongly on the available QKD-generated key budget and the choice of compression algorithm, highlighting application-level challenges for QKD-based encryption in realistic scenarios.
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Quantum key distribution (QKD) allows authenticated communicating entities to generate and distribute random keys with security guaranteed by the principles of quantum mechanics. Usually, the deployment of optical fibre-based QKD links requires a dark fibre for the quantum channel of the QKD link. However, the availability of dark fibre is scarce for field deployments and involves higher capital expenses. In this paper, we propose a QKD solution where the quantum channel and classical channel of the QKD link are multiplexed on the same fibre carrying a data traffic of 100 Gbps using wavelength division multiplexing (WDM). The solution will facilitate rapid upgradation of existing communication networks with quantum security, especially in metropolitan networks.
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