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arXiv:2505.05351 · International Conference on Transparent Optical Networks

Quantum-Aware Network Planning and Integration

Cédric Ware, Mounia Lourdiane

Published Jul 6, 2025• 0 citations
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Abstract

In order to broaden the adoption of highly-demanded quantum functionalities such as QKD, there is a need for having quantum signals coexist with classical traffic over the same physical medium, typically optical fibers in already-deployed networks. Beyond the experimental point-to-point demonstrations of the past few years, efforts are now underway to integrate QKD at the network level: developing interfaces with the software-defined-network ecosystem; but also network planning tools that satisfy physical-layer contraints jointly on the classical and quantum signals. We have found that in certain situations, naïve network planning prioritizing quantum traffic drastically degrades classical capacity, whereas a quantum-aware wavelength assignment heuristic allows coexistence with minimal impact on both capacities. More such techniques will be required to enable widespread deployment of QKD and other future quantum functionalities.

DOI
10.1109/icton67126.2025.11125476

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In order to broaden the adoption of highly-demanded quantum functionalities such as QKD, there is a need for having quantum signals coexist with classical traffic over the same physical medium, typically optical fibers in already-deployed networks. Beyond the experimental point-to-point demonstrations of the past few years, efforts are now underway to integrate QKD at the network level: developing interfaces with the software-defined-network ecosystem; but also network planning tools that satisfy physical-layer contraints jointly on the classical and quantum signals. We have found that in certain situations, naïve network planning prioritizing quantum traffic drastically degrades classical capacity, whereas a quantum-aware wavelength assignment heuristic allows coexistence with minimal impact on both capacities. More such techniques will be required to enable widespread deployment of QKD and other future quantum functionalities.
Modern optical networking techniques have the potential to greatly extend the applicability of quantum communications by moving beyond simple point-to-point optical links and by leveraging existing fibre infrastructures. We experimentally demonstrate many of the fundamental capabilities that are required. These include optical-layer multiplexing, switching and routing of quantum signals; quantum key distribution (QKD) in a dynamically reconfigured optical network; and coexistence of quantum signals with strong conventional telecom traffic on the same fibre. We successfully operate QKD at 1310 nm over a fibre shared with four optically amplified data channels near 1550 nm. We identify the dominant impairment as spontaneous anti-Stokes Raman scattering of the strong signals, quantify its impact, and measure and model its propagation through fibre. We describe a quantum networking architecture which can provide the flexibility and scalability likely to be critical for supporting widespread deployment of quantum applications.
Continuous-variable quantum key distribution (CV-QKD) could allow QKD and classical optical signals physically sharing the same optical fibers in existing networks. However, Raman scattering imposes a limit on the optical power, which in turn impacts the network capacity for classical traffic in presence of CV-QKD. Network-planning simulations indicate that maxing out the CV-QKD capacity in an optical link can adversely impact its classical capacity. Although preliminary, these results show that designing a mixed classical and CV-QKD network will require dedicated planning heuristics and tools that specifically seek a compromise between classical and CV-QKD traffics.
Modern optical networking techniques have the potential to greatly extend the applicability of quantum communications by moving beyond simple point-to-point optical links, and by leveraging existing fibre infrastructures. We experimentally demonstrate many of the fundamental capabilities that are required. These include optical-layer multiplexing, switching, and routing of quantum signals; quantum key distribution (QKD) in a dynamically reconfigured optical network; and coexistence of quantum signals with strong conventional telecom traffic on the same fibre. We successfully operate QKD at 1310 nm over a fibre shared with four optically amplified data channels near 1550 nm. We identify the dominant impairment as spontaneous anti- Stokes Raman scattering of the strong signals, quantify its impact, and measure and model its propagation through fibre. We describe a quantum networking architecture which can provide the flexibility and scalability likely to be critical for supporting widespread deployment of quantum
QKD technology is mature enough to be used beyond the usual single, point to point, link by creating networks. Quantum ad hoc networks, where a separate, quantum-only network, is running in parallel to a classical network have been demonstrated in several occasions. Having to, essentially, duplicate the network to introduce quantum communications is very expensive and, beyond niche use-cases, fully integrated quantum-classical networks is what the industry demands to accept quantum technologies as a serious networking technology, ready for a broad market uptake.Recently we have reported on the successful deployment of the Madrid Quantum Network. This network is novel because it has been the first installed in production sites of a Telecommunications operator and moreover it is managed through a Software Defined Networking (SDN) structure that integrates classical and quantum channels. The network was operating for four months and we could demonstrate several technologies utilizing the integration of quantum and classical networks. Here we report on some implementation aspects and its usage in several use cases, in particular to secure the management of the SDN control plane as a critical infrastructure.
As a prototype of quantum communications, quantum key distribution (QKD) is recommended for integration into the existing optical infrastructures to enable scalable quantum networking. This necessitates the development of supporting resource allocation strategies for carrier-grade operations. In this work, we propose a quantum-aware RWA framework with dual-granularity power control (QRA-PC) to mitigate quantum-classical interference under hybrid network constraints. In a 9-node mesh network with 1 GHz discrete-variable QKD systems coexisting in the C-band, QRA-PC with local power control mode achieves an average SKR of 891.9 kb/s at a traffic load of 50 erlangs, compared to the first-fit baseline of 50.4 kb/s. This result is achieved without incurring any classical traffic blocking.
The growth of communication networks and the innovation in technology have driven a rising need for advanced security solutions. With the rise of quantum technologies, traditional communication networks could potentially become vulnerable, posing challenges for academia, research, and industry. Quantum Key Distribution (QKD) has emerged as a promising quantum-safe solution, but its integration into existing infrastructures requires extensive study due to challenges in real-world scenarios. This paper presents an innovative quantum-safe infrastructure deployment and an in-depth analysis of co-propagation, using polarization-entangled QKD in the C-band, coexisting with classical data at 100 Gbps via Dense Wavelength Division Multiplexing (DWDM), and employing production-ready equipment within a real infrastructure. Results validate the coexistence of data and quantum channels within the same fibers, demonstrating the adaptability of traditional networks toward future quantum-safe ecosystems. In addition, the paper provides insights and lessons learned for similar deployments.