Spatio-temporal enhancement of Raman-induced frequency shifts in graded-index multimode fibers

We investigate the impact of intrapulse Raman scattering and third-order dispersion on the propagation of a pulsed optical beam inside graded-index (GRIN) fibers by solving an effective nonlinear Schrodinger equation that includes the spatial self-imaging effects through a periodically varying effective mode area. Numerical simulations are used to show that the Raman-induced frequency shift of the shortest fundamental soliton, created after the fission process, is enhanced considerably inside GRIN fibers compared to single-mode fibers for the same value of the soliton order. We also discuss the role of spatial-width contraction during each self-imaging cycle on the Raman-induced frequency shifts.