  Modulational instability is a phenomenon that reveals itself as the
exponential growth of weak perturbations in the presence of an intense pump
beam propagating in a nonlinear medium. It plays a key role in such nonlinear
optical processes as supercontinuum generation, light filamentation, and rogue
waves. However, practical realization of these phenomena in the majority of
available nonlinear media still relies on high-intensity optical beams. Here,
we analytically and numerically show the possibility of necklace beam
generation originating from low-intensity spatial modulational instability of
vortex beams in engineered soft-matter nonlinear media.
