We propose a noise-aware wavelength allocation scheme enabling stable twin-field QKD and classical communication coexistence over hollow-core fibers. By interleaving channels and minimizing nonlinear noise, our approach significantly improves transmission distance and power compatibility for hybrid quantum-classical networks.
In this paper, we investigate the impact of classical optical communications in quantum key distribution (QKD) over hollow-core fiber (HCF), multi-core fiber (MCF) and single-core fiber (SCF) and propose wavelength allocation schemes to enhance QKD performance. Firstly, we theoretically analyze noise interference in QKD over HCF, MCF and SCF, such as spontaneous Raman scattering (SpRS) and four-wave mixing (FWM). To mitigate these noise types and optimize QKD performance, we propose a joint noise suppression wavelength allocation (JSWA) scheme. FWM noise suppression wavelength allocation and Raman noise suppression wavelength allocation are also proposed for comparison. The JSWA scheme indicates a significant enhancement in extending the simultaneous transmission distance of classical signals and QKD, reaching approximately 100 km in HCF and 165 km in MCF under a classical power per channel of 10 dBm. Therefore, MCF offers a longer secure transmission distance compared with HCF when classical signals and QKD coexist in the C-band. However, when classical signals are in the C-band and QKD operates in the O-band, the performance of QKD in HCF surpasses that in MCF. This research establishes technical foundations for the design and deployment of QKD optical networks.
With the development of quantum key distribution (QKD), integration with classical communications has become one of the future development trends. In this paper, in order to solve the problems of fiber resource waste and noise interference in twin-field QKD (TF-QKD) where servo signals exist, we design a high-security and fiber-saving classical-quantum coexistence architecture that ensures both high security and efficient utilization of fiber resources, which is designed to be seamlessly compatible with quantum signals, servo signals of TF-QKD, and bidirectional classical signals over multicore fiber (MCF). Subsequently, an in-depth analysis of noise on the quantum channels is conducted. Furthermore, a quantum-priority core and wavelength allocation (QPCWA) scheme is proposed, which effectively reduces the noise interference from servo signals and classical signals to QKD, improving the performance of QKD. Simulation results show that the QPCWA scheme can extend the secure transmission distance up to nearly 300 km compared with the benchmark scheme. Experimental results show that the QPCWA scheme can effectively reduce noise photons by 50.8%. This research establishes a technical foundation for the integrated deployment of QKD and classical communications.
The integration of quantum key distribution (QKD) with classical optical networks has emerged as a pivotal strategy for building secure communication infrastructures. However, achieving their coexistence in silica-core fibers faces inherent limitations due to nonlinear interference, particularly under high classical signal power. In this paper, we experimentally demonstrate the coexistence of classical optical transport networks and QKD over 101.6 km of hollow-core fiber (HCF) with classical power exceeding 20 dBm for the first time to the best of our knowledge. Through systematic theoretical analysis, we characterize HCF’s transmission loss and nonlinear noise generation mechanisms, revealing its unique compatibility with high-power classical–quantum coexistence compared to conventional fibers. To address spectral interference from HCF’s absorption peaks and nonlinear effects, we propose a spectrally optimized multi-stage allocation (SOMA) scheme that coordinates low-loss channel selection and noise suppression. Experimental validation shows that, under the SOMA scheme, coexisting classical signals achieve 19 dBm in single-wavelength configuration and 21 dBm in multi-wavelength configuration, while maintaining a secure key rate above 10 kbps. This breakthrough establishes HCF as a viable platform for simultaneous high-capacity classical communication and quantum-secured data transmission, overcoming critical power limitations of existing fiber-based coexistence systems.
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.
The convergence of quantum key distribution (QKD) with classical optical networks represents a pivotal advancement in secure communication technologies. This paper presents an experimental investigation of a resource allocation framework for co-transmitting QKD and classical signals through multicore fiber (MCF). We first analyze theoretical model characterizing inter-core noise interference mechanisms between classical and quantum channels over MCF. Building on this analysis, a noise-aware spatial-spectral resource allocation scheme is proposed, coordinating resources across two dimensions: core allocation via a Cartesian coordinate-based hierarchy ensures universal compatibility with arbitrary MCF configurations, while adaptive wavelength assignment dynamically suppresses single or dual noise sources. Experimental validation demonstrates the scheme's superior noise suppression capabilities and enhanced secure key rates compared to benchmark approaches, achieving reductions of ⩾ 4.2 dB in noise photons and improvements of ⩾ 10 kbps in secure key rate. This work establishes a practical foundation for implementing QKD networks within existing fiber infrastructure, advancing the realization of scalable quantum-classical coexistance.
Quantum key distribution (QKD) is approaching industrial maturity, but its integration with high-power classical signals in shared optical fiber is hindered by noise from nonlinear effects like spontaneous Raman scattering and four-wave mixing. Hollow-core fiber (HCF) offers a promising solution by inherently suppressing these nonlinearities. However, a comprehensive noise analysis for pure HCF or standard single-mode-fiber–HCF hybrid links, validated experimentally under realistic high-power conditions, remains unavailable. This work bridges that gap through a thorough theoretical and experimental investigation of an HCF-featured coexistence system. We demonstrate a silicon-photonics-based QKD system operating with an optical transport network (OTN). The system achieves multiplexed launch powers of 20 dBm for counter-propagation and 14 dBm for co-propagation, meeting the highest requirements of modern OTNs. Over a 10 km HCF link, it simultaneously supports 12×583 Gbps classical channels across the C-band and achieves secure key rates of 5.7 kbps (counter-propagation) and 2.5 kbps (co-propagation) over a 1550 nm quantum channel. Our results provide critical benchmarks and a practical framework for deploying HCF-based quantum-classical networks, paving the way for future inherently secure telecommunications.