Theoretical Model of Inter-Core Four-Wave Mixing in Quantum and Classical Coexistence Systems Over Homogeneous and Heterogeneous Multicore Fibers

In the quantum and classical coexistence system, the classical noises can affect the performance of quantum key distribution (QKD). Among these noises, forward intercore four-wave mixing (FIC-FWM) noise has a serious impact. However, the current analytical theories of FIC-FWM are not yet fully developed. In this paper, we derive an analytical equation for FIC-FWM based on correlation functions (termed FICFWM-CF). The FIC-FWM-CF model can be applied in both homogeneous and heterogeneous multicore fibers (MCFs) with low computational complexity. Then, we analyze the effect of FIC-FWM noise on QKD performance in the quantum and classical coexistence system, revealing that frequency spacings should exceed 75 GHz for homogeneous MCFs and 50 GHz for heterogeneous MCFs to effectively mitigate FIC-FWM noise interference. Finally, we experimentally investigate the impact of FIC-FWM noise on QKD and demonstrate that the FIC-FWMCF model can accurately predict the resulting trends in QKD performance.