Investigation of Nonlinear Raman Scattering in Optical Quantum Communication Systems

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.