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arXiv:1412.1403 · New Journal of Physics

Coexistence of continuous variable QKD with intense DWDM classical channels

Rupesh Kumar, Hao Qin, Romain Alléaume

Published Apr 15, 2015• 221 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1088/1367-2630/17/4/043027

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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.
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 .
Integrating quantum key distribution (QKD) with classical data transmission over the same fiber is crucial for scalable quantum-secured communication. However, noise from classical channels limits QKD distance. We demonstrate the longest-distance continuous-variable QKD (CV-QKD) over 120 km (20 dB loss) in the asymptotic regime, and over 100 km (17 dB loss) in the finite-size regime, both coexisting with a fully populated coarse wavelength division multiplexing system. Natural mode filtering of the local oscillator and phase noise mitigation enabled this without additional filtering or wavelength reallocation. Benchmarking against a commercial discrete-variable QKD system and considering finite-size effects confirms the feasibility of CV-QKD as a plug-and-play solution for typical 80-100 km long-haul optical networks. Our results set a record fiber distance for CV-QKD, showing its potential for cost-effective, large-scale deployment in existing network infrastructure.
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).
Quantum Key Distribution (QKD) offers a secure method for generating cryptographic keys crucial for 6G future networks. It relies on quantum mechanics principles to guarantee protection against potential threats from quantum computers. However, QKD signal is fragile and can be easily degraded by external noise sources. Therefore, integrating QKD into existing networks poses a challenge, as it must seamlessly coexist with classical channels, in optical fiber links utilizing wavelength division multiplexing (WDM). Continuous-variable QKD (CV-QKD), which leverages optical coherent technology, is seen as a promising solution for this integration within current telecom infrastructure. Additionally, Software-Defined Networking (SDN) presents opportunities for enhancing efficiency and facilitating dynamic management in coexistence scenarios. This paper reports key noise sources that degrade CV-QKD performance in coexistence and the parameters contributing to these noise sources such as classical channel (CC) power, separation between CC and quantum channel (QC) and position of QC. We also report strategies for effectively managing coexistence scenarios using SDN. We focus on the coexistence of CVQKD in presence of classical channels spaced according a 100 GHz ITU-T grid over a 10 km link length, providing guidelines to optimize the performance.
Abstract Integration of quantum key distribution (QKD) into existing optical transport network is one of the important problems that should be solved to expand the applicability of QKD systems and to develop quantum networks. When multiplexing a quantum channel with classical ones, researchers and engineers are faced with a high background count rate caused by spontaneous Raman scattering. This paper presents the results of Raman noise measurement in the O-band at different distances and launched power of the C-Band channels. Based on this data, the 1310 nm QKD system capable to integrate into DWDM optical network was developed. Its performance has been experimentally confirmed in testing on coexistence with intense C-band signals. The experiments were carried out on the propagation of classical and quantum signals in the same fiber as well as in the opposite directions. As a result, the stable QKD over a distance up to 60 km with a total launched power of classical channels up to 20 mW has been demonstrated.
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.