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IET Quantum Communication

Investigation of Nonlinear Raman Scattering in Optical Quantum Communication Systems

Flóra Viktória Kárpát, Eszter Udvary

Published Jan 1, 2025• 2 citations

Abstract

ABSTRACT In this paper, we introduce an improved spontaneous Raman scattering (SRS) model to accurately determine the quantum communication channel's quality when integrated into a Dense Wavelength Division Multiplexing (DWDM) network. To assess the degradational effect of counter‐propagating SRS, we carried out laboratory experiments to analyse the impact of different variables, namely the input power, fibre length and channel arrangement. Based on the measurement results, we developed a new model for defining SRS within the C‐band, which provides more precision in describing the impact of SRS compared to the previously used simplified V‐shape model. A 96‐channel DWDM use case, including one quantum and 90 classical channels, is modelled to identify the optimal channel wavelength allocation strategy. Using the revised model, we concluded that the optimal channel layout, where the channel numbering is based on the ITU‐T standard, is with the quantum channel being the 88th (1533.4 nm), or the 96th (1530.2 nm) if we consider the classical capacity. In contrast, if the V‐shape model is used for defining the optimal channel allocation, the quantum channel would be the 59th (1545 nm). The results show the importance of accurately modelling SRS, as determining the right channel placement is essential for the coexistence of quantum and classical channels.

DOI: 10.1049/qtc2.70004

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ABSTRACT In this paper, we introduce an improved spontaneous Raman scattering (SRS) model to accurately determine the quantum communication channel's quality when integrated into a Dense Wavelength Division Multiplexing (DWDM) network. To assess the degradational effect of counter‐propagating SRS, we carried out laboratory experiments to analyse the impact of different variables, namely the input power, fibre length and channel arrangement. Based on the measurement results, we developed a new model for defining SRS within the C‐band, which provides more precision in describing the impact of SRS compared to the previously used simplified V‐shape model. A 96‐channel DWDM use case, including one quantum and 90 classical channels, is modelled to identify the optimal channel wavelength allocation strategy. Using the revised model, we concluded that the optimal channel layout, where the channel numbering is based on the ITU‐T standard, is with the quantum channel being the 88th (1533.4 nm), or the 96th (1530.2 nm) if we consider the classical capacity. In contrast, if the V‐shape model is used for defining the optimal channel allocation, the quantum channel would be the 59th (1545 nm). The results show the importance of accurately modelling SRS, as determining the right channel placement is essential for the coexistence of quantum and classical channels.

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 a quantum communication channel with classical optical communication is a cost-effective, deployment-friendly solution to provide secure data transmission over optical fibres. However, the noise introduced by intense classical signals into the quantum channel severely impacts the performance of quantum communication. This paper evaluates the impact of optical attenuation and Spontaneous Raman Scattering in the quantum communication system. A hybrid Dense Wavelength Division Multiplexing (DWDM) and Coarse Wavelength Division Multiplexing (CWDM) solution is investigated by combining experimental and theoretical work. The optimal wavelength allocation strategy is defined.

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.

Including Quantum Key Distribution service into classical high-speed optical data transmission networks applying a dense wavelength division multiplexing technique via one joint fibre is a cost-effective solution to improve the network’s security. Several noise sources degrade the quality of the quantum channel in this multichannel system. Optical filtering cannot eliminate the optical nonlinear effects, like Spontaneous Raman Scattering caused by the classical optical channels. The paper thoroughly investigates this nonlinear optical effect with different combined classical and quantum system topologies. The applied model uses experimental values of Spontaneous Raman Scattering.

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.

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.