Localization of optical vortices in nonlinear hexagonal multicore fibers

We investigate the existence and stability of vortexlike collective excitations in nonlinear (NL) multicore fibers (MCFs). We focus on realistic cored and coreless hexagonal MCFs where every core operates in the single-mode regime while displaying polarization degeneracy. We model the propagation dynamics of vortex fields in such MCF structures by NL discrete Schrödinger equations, finding families of homogeneouslike NL vortex fields with constant power distribution over peripheral cores. By analyzing the stability of such collective modes with distinct topological charges against perturbations, we find that they are all unstable. We further investigate the existence and stability of inhomogeneous NL vortex fields, finding only one stable nonspinning localized NL mode with vanishing topological charge in a narrow power range only for cored hexagonal MCFs. Our results are relevant for the manipulation and control of collective excitations in NL MCFs, indicating that self-organization into stable localized collective modes can be exploited in innovative MCF-based communication systems.