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International Conference on Transparent Optical Networks

On the impact of launch power control on the performance OF QKD networks

Lidia Ruiz, Juan Carlos García-Escartín

Published Jul 6, 2025• 0 citations
Publisher

Abstract

Quantum Key Distribution is increasingly being integrated into existing classical communication networks. However, the coexistence of classical traffic with quantum signals introduces noise due to nonlinear effects, which can degrade the performance of the quantum channel. In this work we analyze the impact of launch power control protocols on network resource allocation algorithms in mitigating this interference. Our study aims at enhancing the quality of the quantum channel in hybrid QKD-classical optical networks.

DOI
10.1109/icton67126.2025.11125383

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Quantum Key Distribution is increasingly being integrated into existing classical communication networks. However, the coexistence of classical traffic with quantum signals introduces noise due to nonlinear effects, which can degrade the performance of the quantum channel. In this work we analyze the impact of launch power control protocols on network resource allocation algorithms in mitigating this interference. Our study aims at enhancing the quality of the quantum channel in hybrid QKD-classical optical networks.
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The demand for the integration of quantum key distribution (QKD) and classical optical communication in the same optical fiber medium greatly increases as fiber resources and the flexibility of practical applications are taken into consideration. To satisfy the needs of the mass deployment of ultra-high power required for classical optical networks integrating QKD, we implement the discrete variable quantum key distribution (DV-QKD) under up to 25 dBm launch power from classical channels over 75 km on an ultra-low-loss (ULL) fiber by combining a finite-key security analysis method with the noise model of classical signals. To the best of our knowledge, this is the highest power launched by classical signals on the coexistence of DV-QKD and classical communication. The results exhibit the feasibility and tolerance of our QKD system for use in ultra-high-power classical communications.
As quantum key distribution networks grow in size and complexity, resource assignment has become increasingly important. In passive optical networks without wavelength conversion, we need to assign a full route between origin and destination with the same wavelength from a finite set. This problem is computationally intensive and the common solution in classical optical networks is using heuristics. We adapt these heuristics to hybrid quantum networks where the quantum channel can share some of the optical links with classical channels. In this quantum–classical multiplexing, nonlinear effects can become the limiting factor in the range of the network. The signal in the classical channels can be subject to Raman Scattering or Four-Wave-Mixing and produce light in the quantum channels. While these processes are not efficient, even a single photon can ruin the quantum channel. We propose heuristics for the routing and wavelength assignment problem for hybrid quantum–classical networks with power control for the classical channels. By keeping the transmitted power to its bare functional minimum, we can reduce the interference to the quantum channels. We study their efficiency under different scenarios.
The co-existence of quantum key distribution (QKD) signals with classical optical signals in a single fiber enables substantial fiber resource savings and reduces the deployment costs of QKD networks. However, conventional approaches to mitigate the impact of strong classical signals on QKD performance typically involve reducing classical optical power, which inherently conflicts with standard optical communication network specifications and impedes the widespread adoption of QKD networks. In this work, we explore the feasibility of integrating QKD networks with high-capacity classical optical networks without significant modifications to existing infrastructure and validate wavelength allocation strategies for their co-existence in field-deployed shared fibers. Notably, we demonstrate co- propagation of QKD with high-power classical signals (21.75 dBm total launch power) over 81 km of commercial backbone fiber, covering 90% of China Telecom's inter-site links. Leveraging a 400 Gbps optical transport network (OTN) system, we first, to the best of our knowledge, achieve a classical optical capacity of 15.7 Tbps. Additionally, we introduce single-fiber optical supervisory channel (OSC) configurations in quantum-classical co-existence experiments for the first time, further validating the feasibility of integrating QKD networks with classical networks requiring high-precision clock synchronization. The system achieves secure key rates (SKRs) of 2.2 kbps and 1.35 kbps under two-fiber and single-fiber OSC configurations, respectively. This study marks a significant step towards the practical deployment and maturity of QKD networks.
As the limitations of classical cryptographic systems become increasingly evident in the face of advancing quantum algorithms, Quantum Key Distribution (QKD) emerges as a vital paradigm for securing information in next-generation networks. This paper explores the theoretical foundations and protocol architectures underpinning QKD, including BB84, E91, and newer hybrid approaches designed for scalable integration into existing infrastructures. Performance metrics such as key generation rate, error thresholds, and resistance to various attack models are critically examined across both fiber-optic and free-space implementations. Furthermore, the study delves into real-world deployment challenges—ranging from synchronization errors and quantum channel noise to cost-efficiency and interoperability with classical systems. By offering a comparative analysis and proposing optimization strategies, this work aims to pave the way for robust quantum-secure communication protocols suited for large-scale, heterogeneous network environments.
This paper presents an experimental evaluation of the impact of optical switching equipment on the integrity of sensitive quantum signals, which are fundamental components of quantum networks. Focusing on switching in a Quantum Key Distribution (QKD) network as one example of a quantum network scenario, this study highlights how the impairments introduced by optical switches can significantly degrade the quality of quantum signals, resulting in a noticeable increase in the Quantum Bit Error Rate (QBER). This signal degradation poses serious challenges to the reliability and efficiency of the quantum networks. However, by accurately modeling the effects of switching-induced impairments, designing and implementing an ideal digital twin becomes feasible, which can cut QBER by up to 90% by identifying and addressing root causes and enabling proactive measures. Hybrid quantum-classical networks can benefit from such digital twins through improved quality and scalability.