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Quantized conical waves in multimode optical fibers

Multimode optical fibers has emerged as the platform that will bridge the gap between nonlinear optics in bulk media and in single-mode fibers. However, the understanding of the transition between these two research fields still remains incomplete despite numerous investigations of intermodal nonlinear phenomena and spatiotemporal coupling. Some of the striking phenomena observed in bulk media with ultrashort and ultra-intense pulses (i.e., conical emission, harmonic generation and light bullets) require a deeper insight to be possibly unveiled in multimode fibers. Here we generalize the concept of conical waves described in bulk media towards structured media, such as multimode optical fibers, in which only a discrete and finite number of modes can propagate. The modal distribution of optical fibers provides a quantization of conical emission (e.g., quantized X-waves) through phase-matched resonant radiations (i.e., dispersive waves) seeded by optical shocks or ultrashort wave structures during spatiotemporal compression stages. Such quantized dispersion- and diffraction-free waves are generated when a rather intense short pulse propagates nonlinearly in a multimode waveguide, whatever the dispersion regime and waveguide geometry. Future nonlinear experiments in commercially-available multimode fibers could reveal different forms of conical emission and an easy control of supercontinuum light bullets.