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Optics Letters

Coexistence of 1 Tbps classical optical communication and quantum key distribution over a 100.96 km few-mode fiber

Tianqi Dou, Song Gao, Chengliang Zhang, Jiangang Tong, Rende Liu, Lei Shen, Juhao Li, Zhengjun Pan, Min Liao, Jianjun Tang, Shibiao Tang

Published Aug 28, 2023• 12 citations
Publisher

Abstract

The integration of quantum key distribution (QKD) and classical optical communication has attracted widespread attention. In this Letter, we experimentally demonstrate a real-time co-propagation of 1 Tbps for 10 classical channels with one discrete-variable QKD channel in the weakly coupled few-mode fiber (FMF). Based on the selection of optimal device parameters and wavelength assignment of classical channels, as well as the optimization of equipment performance, a secure key rate of as high as 2.7 kbps of coexistence transmission of QKD and classical optical communication can be achieved using a 100.96 km weakly coupled FMF. Therefore, this study is a step toward realizing long-distance quantum-classical coexistence transmission.

DOI
10.1364/ol.500406

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The integration of quantum key distribution (QKD) and classical optical communication has attracted widespread attention. In this Letter, we experimentally demonstrate a real-time co-propagation of 1 Tbps for 10 classical channels with one discrete-variable QKD channel in the weakly coupled few-mode fiber (FMF). Based on the selection of optimal device parameters and wavelength assignment of classical channels, as well as the optimization of equipment performance, a secure key rate of as high as 2.7 kbps of coexistence transmission of QKD and classical optical communication can be achieved using a 100.96 km weakly coupled FMF. Therefore, this study is a step toward realizing long-distance quantum-classical coexistence transmission.
Integrating quantum key distribution (QKD) with classical optical communication is a deployment-friendly and cost-effective approach to advancing QKD network implementation. However, the noise introduced by intense classical signals into the quantum channel severely impacts the performance of the QKD system, presenting challenges for long-distance coexistence transmission. In this paper, we successfully demonstrate the simultaneous propagation of QKD and optical transport network (OTN) in the C-band over distances exceeding 100 km. We establish a coexistence transmission system based on a commercial OTN equipment and QKD device equipped with the Fabry-Perot filters, demonstrating the feasibility of combining QKD with 11 Tbps (110×100 Gbps) classical data over a 101.86 km fiber. To investigate longer transmission distances, we employ an optimized wavelength allocation method and conduct the co-propagation of QKD and 1 Tbps classical data over a 152.34 km fiber. To the best of our knowledge, these results are the first time that report the integration of QKD and large-capacity classical communication over hundred-kilometer scale fiber. Our works represent a significant advancement in developing OTN networks incorporating QKD systems.
Quantum key distribution (QKD) is one of the most practical applications in quantum information processing, which can generate information-theoretical secure keys between remote parties. With the help of the wavelength-division multiplexing technique, QKD has been integrated with the classical optical communication networks. The wavelength-division multiplexing can be further improved by the mode-wavelength dual multiplexing technique with few-mode fiber (FMF), which has additional modal isolation and large effective core area of mode, and particularly is practical in fabrication and splicing technology compared with the multi-core fiber. Here, we present for the first time a QKD implementation coexisting with classical optical communication over weakly-coupled FMF using all-fiber mode-selective couplers. The co-propagation of QKD with one 100 Gbps classical data channel at -2.60 dBm launched power is achieved over 86 km FMF with 1.3 kbps real-time secure key generation. Compared with single-mode fiber using wavelength-division multiplexing, given the same fiber-input power, the Raman noise in FMF using the mode-wavelength dual multiplexing is reduced by 86% in average. Our work implements an important approach to the integration between QKD and classical optical communication and previews the compatibility of quantum communications with the next-generation mode division multiplexing networks.
Integrating quantum key distribution (QKD) with classical optical networks is essential for the large-scale deployment of quantum-secure communication. However, the nonlinear impairments induced by classical signals pose significant challenges to co-propagation systems based on single-mode fiber. Although hollow-core fiber (HCF) offers low nonlinearity and low transmission loss, non-uniform attenuation and residual nonlinear effects still degrade the performance of the coexistence transmission system. To address these issues, we construct a co-propagation system based on HCF and propose a quantum-classical joint optimization (QCJO) scheme that effectively minimizes nonlinear noise and enhances the overall robustness of the system. In addition, we demonstrate the co-propagation of a commercial QKD system and an optical transmission network with 40 Tbps (50×800 Gbps ) classical communication capacity over a 101.6 km HCF link. The result represents the recorded classical capacity in fiber-based quantum-classical coexistence transmission and the secure key rate of 9.56 kbps satisfies the fundamental requirements for secure encryption. This work marks significant progress toward massive quantum network deployment and lays a foundation for inherent-security and high-capacity telecommunication infrastructures.
Quantum key distribution (QKD) provides information-theoretic security based on the laws of quantum mechanics. The desire to reduce costs and increase robustness in real-world applications has motivated the study of coexistence between QKD and intense classical data traffic in a single fiber. Previous works on coexistence in metropolitan areas have used wavelength-division multiplexing, however, coexistence in backbone fiber networks remains a great experimental challenge, as Tbps data of up to 20 dBm optical power is transferred, and much more noise is generated for QKD. Here we present for the first time, to the best of our knowledge, the integration of QKD with a commercial backbone network of 3.6 Tbps classical data at 21 dBm launch power over 66 km fiber. With 20 GHz pass-band filtering and large effective core area fibers, real-time secure key rates can reach 4.5 kbps and 5.1 kbps for co-propagation and counter-propagation at the maximum launch power, respectively. This demonstrates feasibility and represents an important step towards building a quantum network that coexists with the current backbone fiber infrastructure of classical communications.
Experimental Demonstration of 47×800Gbps47 \times 800 \text{Gbps}47×800Gbps Classical Communication and QKD Coexistence Over 101.6 Km HCF
We experimentally demonstrate 37.6 Tbps (47×800Gbps47 \times 800 \text{Gbps}47×800Gbps) classical optical communication and quantum key distribution coexisting over a 101.6 km hollow-core fiber, achieving a record capacity and distance to the best of our knowledge. Sustained secure key rate can be maintained at around 5 kbps. ©2025 The Author(s)