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International Conference on the Design of Reliable Communication Networks (DRCN)

Crosstalk-induced Impact of Coexisting DWDM Network on Continuous-variable QKD

Binjie Chu, Yichen Zhang, Yijia Zhao, Yifan Xu, Xing Chen, Xiangyu Wang, Song Yu

Published Mar 1, 2020• 1 citation
Publisher

Abstract

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.

DOI
10.1109/drcn48652.2020.1570604589

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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.
Integrating quantum key distribution (QKD) on the existing optical fiber network through dense wavelength-division multiplexing (DWDM) can greatly reduce the costs of quantum channels and improve the scalability and flexibility of the quantum communication network. In the scenarios of an access network or local area network with a large number of users, the connected optical fibers are relatively short and the quantum signal can be adjacent to the classical channels. In this case, the four-wave-mixing noise generated by the classical lights will have a severe impact on the performance of the QKD. We establish a theoretical model to characterize the excess noise in continuous-variable QKD induced by the four-wave mixing, and experimentally demonstrate the validity of the theoretical predictions. In addition, the influence of cross-phase-modulation noise between the carrier of the quantum signal and classical data channels on the QKD is investigated. To suppress the effect of the four-wave-mixing noise, an unequal channel spacing technique is employed. We realize coexistence of entangled state-based continuous-variable QKD and five adjacent DWDM classical channels with 10 dBm launch power and nonreturn-to-zero on-off-keying modulation at 2.5 Gb/s (10 Gb/s).
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.
Theoretical research and numerical simulation of the noise influence caused by spontaneous Raman scattering, four-wave mixing, and linear channel cross talk on the performances of quantum key distribution (QKD) systems were conducted. Three types of QKD systems were considered: a coherent one-way QKD protocol, subcarrier-wave QKD system, and continuous-variable QKD integrated with classical dense wavelength division multiplexing (DWDM) channels. We calculate the secure key generation rate for the systems mentioned addressing different channel allocation schemes (i.e., configurations). A uniform DWDM grid is considered with a quantum channel located in the C-band and O-band (at 1310 nm) of a telecommunication window. The systems’ performances are analyzed in terms of the maximal achievable distance values. Configurations for further analysis and investigation are chosen optimally, i.e., their maximal achievable distances are the best.
Numerically, a theoretical analysis of the noise impact caused by spontaneous Raman scattering, four-wave mixing, and linear channel crosstalk on the measurement-device-independent continuous variable quantum key distribution systems is conducted.The analysis considers symmetry and asymmetry of system paths, as well as possible channel allocation schemes, for a quantum channel located in C-and O-bans.Mathematical models for MDI CV-QKD system and the contributing noises' description are provided.The secure key generation rate is estimated to state features of protocol operation when integrated with existing DWDM systems in the context of its implementation into telecommunication networks.
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 .