Effect of Raman scattering on soliton interactions in optical fibers

We investigate numerically the effect of Raman scattering on the interaction of two temporally separated pulses with identical spectra that propagate inside a single-mode fiber as fundamental solitons. We take into account all interpulse Raman scattering terms in the generalized nonlinear Schrodinger equation and study the interplay between the Kerr, intrapulse Raman, and interpulse Raman effects. We observe considerable differences from the well-known two-soliton interaction behavior caused by the Kerr nonlinearity. We study in detail the mechanism for a net energy transfer from the leading pulse to the trailing pulse caused by the delayed nature of the Raman response in the case of two identical in-phase solitons. Long-range interactions, where the pulses do not temporally overlap, are found to not cause any energy transfer between the pulses, but solitons are still shown to affect each others’ phase owing to the long tail of the Raman response function. We also study and compare how a phase difference between two otherwise identical solitons affects the interaction scenario and changes the collision dynamics, both in the presence and in the absence of the Raman effect. Finally, we look at the effect of changing the relative amplitude of the two interacting solitons by a small amount.