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Performance Analysis of Classical Channel Power for CV-QKD Integration in Full C-band WDM Networks

Ryosuke Matsumoto, Alireza H. Derkani, Ana Risnoveanu, Fausto Gomez-Agis, Satoshi Suda, Jeffrey Lee, Chigo M. Okonkwo, Aaron Albores-Mejía

Published Jan 1, 2026• 0 citations
Publisher

Abstract

We analyzed the launched power constraints required for optimal integration of CV-QKD and WDM channels in full C-band transmission. Simulations prove the feasibility of 75-km coexistence transmission with 23.6-Tb/s classical data through power optimization.
DOI
10.1364/cleo_at.2026.jtu.108

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We demonstrate experimentally the feasibility of continuous variable quantum key distribution (CV-QKD) in dense-wavelength-division multiplexing networks (DWDM), where QKD will typically have to coexist with several co-propagating (forward or backward) C-band classical channels whose launch power is around 0 dBm. We have conducted experimental tests of the coexistence of CV-QKD multiplexed with an intense classical channel, for different input powers and different DWDM wavelengths. Over a 25 km fiber, a CV-QKD operated over the 1530.12 nm channel can tolerate the noise arising from up to 11.5 dBm classical channel at 1550.12 nm in the forward direction (9.7 dBm in backward). A positive key rate (0.49 kbits s −1 ) can be obtained at 75 km with classical channel power of respectively −3 and −9 dBm in forward and backward. Based on these measurements, we have also simulated the excess noise and optimized channel allocation for the integration of CV-QKD in some access networks. We have, for example, shown that CV-QKD could coexist with five pairs of channels (with nominal input powers: 2 dBm forward and 1 dBm backward) over a 25 km WDM-PON network. The obtained results demonstrate the outstanding capacity of CV-QKD to coexist with classical signals of realistic intensity in optical networks.
We demonstrated the coexistence of an S-band CV-QKD signal with fully loaded C+L-band classical signals for the first time. The secret key rate of the S-band QKD system was 986 kbps with the C+L-band WDM signals transmitted through a 20 km G.654.E fiber link. We also revealed that the S-band CV-QKD performance limiting factor under the C+L-band WDM condition is the spontaneous Raman scattering light similar to the C-band CV-QKD performance limiting factor, confirming the validity of estimating the wavelength dependency of the secret key rate under the WDM condition from the fiber loss and the spontaneous Raman scattering light power. These results show that the CV-QKD performance under the C+L band WDM conditions becomes comparable to that under the C-band WDM conditions by wavelength design in the S-band.
In this paper, we explored various physical-layer parameters affecting the coexistence of continuous-variable quantum key distribution (CV-QKD) and classical channels (CCs) within dense wavelength division multiplexing (DWDM) in the C-band. These parameters include the number of transmitted quantum symbols , power levels of CCs , quantum channel (QC) allocation within the C-band , power distribution among CCs, channel spacing between CCs and the QC, and CC power ranges suitable for both CCs and the QC . These insights provide valuable guidance for a software-defined networking (SDN) control system to manage CV-QKD and CC coexistence effectively. We observed that, for short distances and lower key rates, the number of quantum symbols exchanged does not need to reach the asymptotic convergence limit. However, achieving the asymptotic regime on a 10 km link requires transmitting approximately 1×10 13 quantum symbols. CC power significantly impacts CV-QKD performance. For example, in a DWDM setup with 37 dummy CCs on a 100 GHz grid, CV-QKD can support up to 11 dBm total launch power over a 10 km link when the QC is positioned at 193.2 THz and a 200 GHz channel spacing between the QC and CCs is maintained. Strategic placement of the QC within the C-band also enhances performance. Placing the QC at higher frequency channels relative to CCs improves both the secret key fraction and the maximum supported power of CCs. For instance, placing the QC at 195.9 THz provides better performance than positioning it at 193.2 or 192.2 THz. However, when the QC is placed at 192.2 THz, the maximum supported CC power reduces to 9.8 dBm. Additionally, the relationship between power distribution and power concentration is complex and requires careful consideration. It depends on the number of active CCs, the power of CCs, and their spectral placement relative to the QC. We also analyzed the case of 8×200G modulated CCs and found that placing them 100 GHz from the QC introduces nonlinear noise but still allows a positive secret key fraction. Increasing the spacing to 200 GHz further improves CV-QKD performance. Joint performance analysis revealed that, at a 100 GHz spacing and a 30 dB optical signal-to-noise ratio for CCs, a launch power range of −16.96 to 9.03 dBm supports both error-free CC recovery and positive key rate generation over a 10 km link. This comprehensive analysis highlights the interplay between CV-QKD and CCs, offering practical strategies for optimizing their coexistence in DWDM systems through an SDN control system .