General theory and observation of Cherenkov radiation induced by multimode solitons

Advancements in computational capabilities along with the possibility of accessing high power levels have stimulated a reconsideration of multimode fibers. Multimode fibers are nowadays intensely pursued in terms of addressing longstanding issues related to information bandwidth and implementing new classes of high-power laser sources. In addition, the multifaceted nature of this platform, arising from the complexity associated with hundreds and thousands of interacting modes, has provided a fertile ground for observing novel physical effects. However, this same complexity has introduced a formidable challenge in understanding these newly emerging physical phenomena. Here, we provide a comprehensive theory capable of explaining the distinct Cherenkov radiation lines produced during multimode soliton fission events taking place in nonlinear multimode optical fibers. Our analysis reveals that this broadband dispersive wave emission is a direct byproduct of the nonlinear merging of the constituent modes comprising the resulting multimode soliton entities, and is possible in both the normal and anomalous dispersive regions. These theoretical predictions are experimentally and numerically corroborated in both parabolic and step-index multimode silica waveguides. Effects arising from different soliton modal compositions can also be accounted for, using this model. At a more fundamental level, our results are expected to further facilitate our understanding of the underlying physics associated with these complex “many-body” nonlinear processes.

Higher-order mode supercontinuum generation in dispersion-engineered liquid-core fibers

Supercontinuum generation enabled a series of key technologies such as frequency comb sources, ultrashort pulse sources in the ultraviolet or the mid-infrared, as well as broadband light sources for spectroscopic methods in biophotonics. Recent advances utilizing higher-order modes have shown the potential to boost both bandwidth and modal output distribution of supercontinuum sources. However, the strive towards a breakthrough technology is hampered by the limited control over the intra- and intermodal nonlinear processes in the highly multi-modal silica fibers commonly used. Here, we investigate the ultrafast nonlinear dynamics of soliton-based supercontinuum generation and the associated mode coupling within the first three lowest-order modes of accurately dispersion-engineered liquid-core fibers. By measuring the energy-spectral evolutions and the spatial distributions of the various generated spectral features polarization-resolved, soliton fission and dispersive wave formation are identified as the origins of the nonlinear broadening. Measured results are confirmed by nonlinear simulations taking advantage of the accurate modeling capabilities of the ideal step-index geometry of our liquid-core platform. While operating in the telecommunications domain, our study allows further advances in nonlinear switching in emerging higher-order mode fiber networks as well as novel insights into the sophisticated nonlinear dynamics and broadband light generation in pre-selected polarization states.

Gramian solutions and soliton interactions for a generalized (3 + 1)-dimensional variable-coefficient Kadomtsev–Petviashvili equation in a plasma or fluid

Plasmas and fluids are of current interest, supporting a variety of wave phenomena. Plasmas are believed to be possibly the most abundant form of visible matter in the Universe. Investigation in this paper is given to a generalized (3 + 1)-dimensional variable-coefficient Kadomtsev–Petviashvili equation for the nonlinear phenomena in a plasma or fluid. Based on the existing bilinear form, N -soliton solutions in the Gramian are derived, where N = 1, 2, 3…. With N = 3, three-soliton solutions are constructed. Fission and fusion for the three solitons are presented. Effects of the variable coefficients, i.e. h ( t ), l ( t ), q ( t ), n ( t ) and m ( t ), on the soliton fission and fusion are revealed: soliton velocity is related to h ( t ), l ( t ), q ( t ), n ( t ) and m ( t ), while the soliton amplitude cannot be affected by them, where t is the scaled temporal coordinate, h ( t ), l ( t ) and q ( t ) give the perturbed effects, and m ( t ) and n ( t ), respectively, stand for the disturbed wave velocities along two transverse spatial coordinates. We show the three parallel solitons with the same direction.