Impact of cross-phase modulation on modulation instability in nonlinear oppositely directed coupler

This study investigates the significant impact of cross-phase modulation (XPM) on modulation instability (MI) in a nonlinear tunnel-coupled oppositely directed coupler, with a focus on its practical applications in nonlinear optical systems. Our linear stability analysis reveals that XPM substantially enhances MI, leading to a considerable increase in the maximum gain and bandwidth of the instability gain spectrum. This enhancement is particularly pronounced when nonlinearity is concentrated in both channels of the coupler, making it an essential consideration for the design of optical devices. Furthermore, our analysis demonstrates that XPM induces instability breakup in the gain spectra, resulting in optical wave breaking. As MI is often a precursor to soliton formation, understanding the role of XPM in controlling soliton dynamics is crucial for predicting and manipulating soliton behavior in various applications, such as optical communication systems, ultrafast optics, and photonics. By elucidating the interplay between XPM and MI, this study provides valuable insights for the development of advanced nonlinear optical devices and systems, enabling the creation of stable and controllable soliton sources for a wide range of applications.