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International Conference on Software, Telecommunications and Computer Networks (SoftCOM)

Investigation of Nonlinear Effects on a Quantum Key Distribution System in DWDM Scenarios

Benjámin Ott, Márton Czermann, Áron Szabó, Eszter Udvary, Benedek Kovács

Published Sep 18, 2025• 0 citations
Publisher

Abstract

Integrating quantum communication technologies, such as Quantum Key Distribution (QKD) into existing optical infrastructures is critical to improve their scalability, being a cornerstone of their practical implementations. Since installing optical fibers dedicated for QKD proves to be a costly solution, wavelength division multiplexing (WDM) appears to be a viable alternative. This paper investigates viable wavelength selections for the quantum channel in WDM systems. In this research, disturbances from nonlinear effects arising from conventional optical communications are introduced. Four-Wave Mixing (FWM) and Spontaneous Raman Scattering (SpRS) is modeled in various communication scenarios using OptiSystem and VPIphotonics modeling environments. Results from these simulations are evaluated, based on which guidelines are given for optical system design with QKD integration. Techniques for suppressing the noise components from the abovementioned nonlinear effects are proposed. In addition, the noise tolerance of a self-developed plug-and-play QKD architecture - implementing the BB84 protocol - was experimentally investigated to support the modeling.

DOI
10.23919/softcom66362.2025.11197446

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Integrating quantum communication technologies, such as Quantum Key Distribution (QKD) into existing optical infrastructures is critical to improve their scalability, being a cornerstone of their practical implementations. Since installing optical fibers dedicated for QKD proves to be a costly solution, wavelength division multiplexing (WDM) appears to be a viable alternative. This paper investigates viable wavelength selections for the quantum channel in WDM systems. In this research, disturbances from nonlinear effects arising from conventional optical communications are introduced. Four-Wave Mixing (FWM) and Spontaneous Raman Scattering (SpRS) is modeled in various communication scenarios using OptiSystem and VPIphotonics modeling environments. Results from these simulations are evaluated, based on which guidelines are given for optical system design with QKD integration. Techniques for suppressing the noise components from the abovementioned nonlinear effects are proposed. In addition, the noise tolerance of a self-developed plug-and-play QKD architecture - implementing the BB84 protocol - was experimentally investigated to support the modeling.
Quantum key distribution (QKD) provides information-theoretic security based on quantum mechanics. Integrating QKD with classical data traffic by using wavelength division multiplexing (WDM) techniques in a single fibre is a cost-efficient way to improve security in legacy infrastructure. In such a system, the main noise source to the quantum channel is spontaneous Raman scattering (SRS) caused by the classical channels. In this letter we introduce a channel allocation strategy for both quantum and classical signals to minimize the SRS noise. A use case that quantum and classical channels co-exist in a dense WDM system is investigated. The results show >26% increase of achievable transmission distance for the QKD system when implementing the introduced channel allocation strategy. Moreover, a network updating plan is proposed, which provides a guideline to light the new wavelengths for classical communications while minimizing the SRS noise to 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).
In this paper we study the performance of subcarrier-wave quantum key distribution (SCW QKD) in the presence of classical channels of optical transport network utilizing dense wavelength division multiplexing (DWDM). We consider the impact of spontaneous Raman scattering noise as well as the four-wave mixing and channel isolation efficiency. We calculate quantum bit error rate as well as the secure key generation rate of SCW-QKD protocol for different parameters of DWDM system and quantum channel allocations. Our calculations show, that quantum channel allocation at the wavelength of 1310 nm is preferable to allocation at C-band due to lower nonlinear noise, despite fiber's larger attenuation at this wavelength.
In this letter, we report on the advances toward the integration of our developed continuous variables (CV) quantum key distribution (QKD) system in existing optical infrastructure and wavelength division multiplexed (WDM) networks. First, we investigate the tolerance of the CV-QKD system to spontaneous Raman scattering (SRS) noise, the latter being the most dominant impairment in a WDM co-existence environment for QKD. In particular, we investigate by experiment the impact of a WDM10×1010\times 1010×10Gb/s ON–OFF-keying signal in terms of induced SRS noise in the QKD channel. The spontaneous SRS noise influence is assessed for different transmission scenarios, i.e., for various optical launch powers of the WDM signal, and for different transmission links of 20, 40, 60, and 80 km. Based on the experimental data and on the measured system’s parameters, we estimate the key rates and reach capabilities of the proposed CV-QKD system. The scheme supports a key rate of 90 kbit/s over 20 km, for an ideal QKD system multiplexed with 2-mW optical power. A step further, we demonstrate for first time the use of the aforementioned CV-QKD system to encrypt a 10GE client service over deployable optical transport network legacy equipment over 20 km. Our results prove the feasibility of the integration of our proposed scheme with legacy telecom equipment in existing WDM optical networks.
Integrating Quantum Key Distribution service with classical high-speed optical data transmission using a dense wavelength division multiplexing technique in a fiber is a cost-effective solution to improve the network's security. In this multichannel system, several noise sources degrade the quality of the quantum channel. The dominant degradation effect is determined by modeling in different cases. Optical filtering cannot decrease spontaneous Raman Scattering caused by the classical optical channels. So this nonlinear optical effect is investigated in detail with different system parameter setups. The optimal channel allocation and the required bandgap between the classical and quantum channels are determined.
Abstract Integrating quantum key distribution (QKD) into optical networks is a crucial step toward the adoption of quantum technologies in existing telecommunication fiber infrastructures. However, state-of-the-art solutions face significant challenges, including sensitivity to classical noise, particularly spontaneous Raman scattering, limited transmission distances, and varying network conditions. In this work, we present a novel discrete-variable QKD system running a time-bin BB84 protocol operating in the O-band (1295.56 nm), where the impact of dominant noise sources is effectively reduced. Combined with passive narrow-spectral filtering at the receiver, our system demonstrates robustness across diverse dense wavelength-division multiplexing scenarios, making it practical for real-world deployments. We validate its performance through extensive testing, showing stable key generation coexisting with different classical traffic conditions up to 17 dBm of total launch power. These results represent a significant advancement toward the integration of QKD into existing fiber networks, paving the way for secure quantum communication on a large scale.