Intensity Fluctuation Dynamics in XPM

Cross-Phase Modulation (XPM) constitutes a critical nonlinear impairment in high-capacity Wavelength Division Multiplexing (WDM) systems, significantly driven by intensity fluctuations (IFs) that evolve due to chromatic dispersion. This paper presents an enhanced XPM model that explicitly incorporates frequency-domain IF growth along the fiber, improving upon prior models that focused primarily on temporal pulse deformation. A direct correlation between this frequency-domain growth and XPM-induced phase distortions is established and analyzed. Results demonstrate that IF evolution, particularly at lower frequencies, profoundly affects XPM phase fluctuation spectra and phase variance. Validated through simulations, the model accurately predicts these spectral characteristics across various system parameters. Furthermore, the derived phase variance enables accurate prediction of system performance in terms of Bit Error Ratio (BER). These findings highlight the necessity of modeling frequency-domain IF evolution to accurately characterize XPM impairments, offering guidance for the design of advanced optical networks.