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International Conference on Transparent Optical Networks

Quantum Key Distribution Technologies for Secured Passive Optical Networks

Alessandro Gagliano, Paola Parolari, Eliana Mazza, Pierpaolo Boffi, João Frazão, Aaron Albores-Mejía, Chigo M. Okonkwo, Michela Svaluto Moreolo, Paolo Martelli, Alberto Gatto

Published Jul 6, 2025• 0 citations
Publisher

Abstract

The integration of quantum key distribution (QKD) into passive optical networks (PONs) poses new challenges due to the specific characteristics of the access network, as the high losses from passive splitters and the spontaneous Raman scattering noise generated by classical channels co-propagating in the same optical fiber. In this paper, different QKD technologies and implementations are compared, taking into account both discrete-variable and continuous-variable QKD systems to maximize the achievable secret key rate performance in single-fiber bidirectional PONs.

DOI
10.1109/icton67126.2025.11125155

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The integration of quantum key distribution (QKD) into passive optical networks (PONs) poses new challenges due to the specific characteristics of the access network, as the high losses from passive splitters and the spontaneous Raman scattering noise generated by classical channels co-propagating in the same optical fiber. In this paper, different QKD technologies and implementations are compared, taking into account both discrete-variable and continuous-variable QKD systems to maximize the achievable secret key rate performance in single-fiber bidirectional PONs.
Fiber-based quantum key distribution (QKD) systems are mature and commercialized, but their integration into existing optical networks is crucial for their widespread use, in particular in passive optical networks (PONs) if end-to-end quantum-secured communications are to be addressed. While discrete-variable QKD coexistence with classical channels is well-studied in point-to-point links, its performance in point-to-multipoint topologies like PONs has received less attention. We thus developed a numerical tool to estimate quantum-available bandwidth and maximum link lengths for QKD systems in single-fiber PON architectures in coexistence with GPON, XG-PON, NG-PON2, and HS-PON standards. The QKD channel performance is obtained by setting thresholds on the quantum bit error rate and the secret key rate, ultimately limited by spontaneous Raman scattering noise and high optical distribution network losses. We perform a comparison between the performance obtained assuming the asymptotic infinite-key generation rate or taking into account actual implementations in the finite-key regime. We evidence that proper design rules can be obtained as a function of both classical and quantum system parameters to support end-to-end quantum security services in existing optical networks.
The access network segment represents the end point for the provision of quantum key distribution (QKD) services, offering secure communication to the end users. Yet the integration of QKD into legacy passive optical networks (PONs) is very challenging due to the high losses of the passive optical distribution network (ODN) and the presence of upstream and downstream classical channels belonging to many coexisting PON standards, which are the source of scattered Raman noise photons. In this study we evaluate the sustainability of discrete variable QKD services in access networks supporting one or more PON standards, evidencing the necessity of ODN architectures able to enhance the QKD performance and facilitate the key-exchange over the legacy PON links.
To achieve commercial scalability, fiber-based quantum key distribution (QKD) systems must be integrated into existing optical communication infrastructures, rather than deployed exclusively on dedicated dark fibers. Integrating QKD into optical access networks (OANs) would be particularly advantageous, as these networks provide direct connectivity to end users for whom security is critical. Such integration can address the inherent security vulnerabilities in current OANs, which are primarily based on time-division multiplexing passive optical networks (TDM-PONs). However, integrating QKD into PONs poses significant challenges due to Raman noise and other detrimental effects induced by PON signals, which intensify as the launched power of PONs increases to support higher transmission speeds. In this study, we review recent advancements in both QKD and access network technologies, evaluate the technical feasibility of QKD-OAN integration, and propose cost-effective strategies to facilitate the widespread deployment of QKD in future access networks.
It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in time-division multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks. In this paper, we address quantum key distribution (QKD) over passive optical access networks, which is an enabling technology required to cost efficiently deploy practical quantum encrypted data communication in the access area. We study different methods to integrate QKD systems in conventional optical access networks and quantitatively evaluate their suitability for a potential implementation.
We provide design guidelines for the integration of quantum key distribution (QKD) into legacy passive optical networks (PONs). Our study addresses the challenge of quantum coexistence with various PON standards in different network topologies. We develop a novel theoretical model to assess the impact of the passive optical distribution network on both the quantum signal and the generation of scattered Raman photons from classical signals. This work also includes an extensive Raman efficiency experimental evaluation over a wide frequency range. The study evaluates the integration of upstream QKD systems in 32- or 64-user PON scenarios, determining quantum-available bandwidths and maximum supported PON lengths. In single-fibre architectures the coexistence with standards having upstream and downstream classical channels in different telecommunication fibre windows (e.g. XG-PON) is extremely challenging due to the pervasive spectrum placement of the spontaneous Raman scattering noise. However dual-feeder architectures (i.e., placing the QKD receiver at the OLT-side of the protection feeder fibre) can significantly enhance QKD performance and support the key-exchange over the entire standardized PON length for most PON standards and even in case of two-PON standard presence. Finally, the dual-fibre topology allows the quantum coexistence in access networks where three classical standards share the same infrastructure.
Abstract Passive Optical Networks (PON) are widely used to deliver fixed line communication due to their cost effectiveness and potential for high data transfer rates. However, due to the nature of their operation, every user on a PON system has access to every other user’s downstream data. Current progress in quantum computing means that the classical encryption algorithms currently used to secure communication data, including PON data, may not be sufficient in the future and so, for total information security another encryption solution, such as Quantum Key Distribution, must be found. This paper outlines the different variations of QKD on PON that have so far been proposed and summarises the current state of the art of experimental demonstrations of QKD on PON.