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Comprehensive noise model impact for classical signals and CV-QKD coexistence in multi-core fiber

Haiyan Dai, bozhi wei, Ao Liu, Lanjian Chen, Chun Zhou, Li Yaping, Dong Chen, Zhang Zhenrong

Published Jun 5, 2026• 0 citations
Publisher

Abstract

Mitigating inter-core crosstalk is critical for the coexistence of classical optical signals and continuous-variable quantum key distribution (CV-QKD) in multi-core fibers (MCFs). In this work, a comprehensive excess-noise model is developed for MCF-based classical/CV-QKD coexistence, including direct inter-core crosstalk (ICXT), SpRS-ICXT, FWM-ICXT, and XPM-induced phase noise. Based on this model, we analyze the effects of classical launch power, channel spacing, inter-core coupling coefficient, and modulation variance on the secure key rate and total excess noise. A constrained optimization of classical launch power, channel spacing, and modulation variance is further performed under classical-link feasibility requirements, including receiver sensitivity, received-power margin, and implementation loss. The results show that ICXT is the dominant impairment under the considered MCF conditions, and that the optimized configuration achieves higher SKR and longer secure reach than fixed baseline settings while maintaining classical-channel availability. This work provides a theoretical noise-modeling and constrained-optimization framework for practical classical/CV-QKD coexistence in MCFs.

DOI
10.1364/oe.599124

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In this paper, the influence of noise induced by classical signals on independent core transmitting quantum key distribution (QKD) is studied over multicore fiber (MCF). We propose a theoretical model of the cascaded noise of spontaneous Raman scattering and inter-core crosstalk (SpRS-ICXT), and the cascaded noise of four-wave mixing and inter-core crosstalk (FWM-ICXT) considering modulation frequency over MCF. To analyze the effect of modulation frequency on QKD, we define and simulate the average power difference and power fluctuation difference of SpRS-ICXT and FWM-ICXT. Then, SpRS-ICXT and FWM-ICXT noises are simulated in two cases: (1) 1 or 3 classical channels and 1 km MCF; (2) 8 or 16 classical channels and 45 km MCF. For the latter case, SpRS-ICXT and FWM-ICXT noises have a serious impact on QKD. Therefore, the impact of noise on QKD is studied. A higher modulation frequency can improve QKD performance, and the secure transmission distance can be further extended by 15.2% when the modulation frequency is 10 GHz relative to ignoring the modulation frequency. However, inter-core crosstalk (ICXT), SpRS-ICXT and FWM-ICXT noises will shorten 52.2% secure transmission distance compared to only transmitting QKD. Finally, the noise of quantum channel is experimentally measured at different symbol rates and modulation formats of classical signals, and it is shown that increasing the symbol rate of data signals at the same optical power degrades the secure key rate of QKD system.
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.
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In this paper, the crosstalk-induced impact of coexisting dense-wavelength-division-multiplexed (DWDM) channels on continuous-variable quantum key distribution (CV-QKD) in practical communication environment is investigated. We analyze the nonlinear effect resulting from classical channels on the transmitted local oscillator in CV-QKD, while various existing studies mainly focus on the crosstalk-induced excess noise. We demonstrate that the generally ignored phenomenon of four-wave mixing in excess noise analysis is a visible factor causing local oscillator fluctuation characterized by the statistical properties of the power evolution of local oscillator. Besides, the impact of stimulated Raman scattering on local oscillator is derived in the same theoretical approach and experimentally investigated. Finally, by establishing a trusted model for local oscillator fluctuation we perform the security analysis to constrain the threshold of fluctuation. All of the above analysis should be taken into account as a supplementary for evaluating the performance of CV-QKD with coexisting DWDM system and optimal allocation of classical and quantum channels.
The feasibility of transmitting discrete-variable quantum key distribution channels with carrier-grade classical optical channels over multicore fibers is experimentally explored in terms of achievable quantum bit error rates, secret key rates as well as classical signal bit error rates. A coexistence transmission record of 11.2 Tb/s is achieved for the classical channels simultaneously with a DV-QKD channel over a 1 km-long 7-core multicore fiber. Coexistence over the same multicore fiber core is identified as a dominant factor for the performance of the quantum channel requiring optical bandpass filtering of 17 nm for the quantum channel to avoid the effect of Raman noise. Also, counter-propagation of classical channels and quantum channels probe more tolerance to noise proliferation than co-propagation. In addition, the performance of the quantum channel is maintained when more than three cores are used for the classical channels. Furthermore, by adding a second DV-QKD channel in the multicore fiber, the simultaneous transmission of classical channels as well as the generation of quantum-secured keys of two QKD channels is achieved with an operational range of 10 dB of launched power into the MCF.