Nonlinear interactions in multimode optical fibers

The limitations of single-mode fibers incite multimode fibers to meet the technological demands and explore new physics. Multimode fibers support many spatial modes which can interact with each other through various nonlinear processes and give rise to complex spatiotemporal dynamics. In this review paper, we address intermodal coupling based nonlinear phenomena in short and long pulse regimes. Ultrashort femtosecond pulse regime is dominated by four-wave mixing, self and cross-phase modulation, interpulse as well as intrapulse Raman scattering and provides strong platform for the realization of multitude of nonlinear phenomena such as multimode soliton formation, generation of intense combs of dispersive waves from the multimode soliton, beam clean-up, geometric parametric instability, and optical event horizon. On the other hand, long pulse regime exhibits strong stimulated Raman processes and provides natural tool for the investigation of nonlinear phenomena such as, cascaded Raman scattering, intermodal four-wave mixing based wideband frequency generation, transient grating formation and many others. This article reviews the recent developments in intermodal nonlinear interactions in multimode fiber for both the short and long pulse regimes and provides a roadmap for future research directions in the area of multimode nonlinear fiber optics.