Optical vortex dynamics in non-uniform twisted ring-core fibers

In this work, we present a thorough analysis of the propagation of fiber modes carrying orbital angular momentum in twisted, tapered, ring-core optical fibers. By generalizing the usual coupled-mode approach to include the effect of twisting and tapering, we discuss how it is possible to achieve efficient power transfer between modes carrying different amounts of orbital angular momentum. Our model presents, to the best of our knowledge, the first unified coupled-mode framework incorporating tapering, twisting, and arbitrary perturbations. In addition, our results allow us to get a clear insight into the dynamics of vortex modes propagating through twisted ring core fibers.