Managing Self-Phase Modulation in Pseudo-Linear Multimodal and Monomodal Systems

We propose a new semi-analytical model, describing the bandwidth evolution of pulses propagating in dispersion managed (DM) transmission systems using multimodal graded-index fibers (GRIN) with parabolic index. The model also applies to monomodal fiber DM systems, representing the limit case where beam self-imaging vanishes. The model is successfully compared with the direct integration of the (1+1)D nonlinear Schrodinger equation for parabolic GRIN fibers, and to experimental results performed by using the transmission of femtosecond pulses over a 5 m span of GRIN fiber At the high pulse powers that are possible in multimodal fibers, the pulse bandwidth variations produced by the interplay of cumulated dispersion and self-phase modulation can become the most detrimental effect, if not properly managed. The analytical model, numerical and experimental results all point to the existence of an optimal amount of chromatic dispersion, that must be provided to the input pulse, for obtaining a periodic evolution of its bandwidth. Results are promising for the generation of spatio-temporal DM solitons in parabolic GRIN fibers, where the stable, periodic time-bandwidth behaviour that was already observed in monomodal systems is added to the characteristic spatial beam self-imaging.

Automated summary

A new semi-analytical model is proposed to describe the evolution of pulse bandwidth in dispersion managed transmission systems using multimodal and monomodal graded-index fibers. The model is compared with direct integration of the nonlinear Schrodinger equation and experimental results, showing the detrimental effects of dispersion and self-phase modulation interaction at high pulse powers. Promising results are found for spatio-temporal DM solitons in parabolic GRIN fibers.