Topological charge conversion and localization in defected heterogeneous multihelicoidal optical fibers

In this paper, we have theoretically studied the processes of topological charge conversion in heterogeneous, that is, with an alternating chirality, multihelicoidal fibers in the presence of twist defects. We have shown that two-part and three-part multihelicoidal fibers of that type can be used as compact topological charge all-fiber inverters and comb filters for optical vortices. Also, we have studied the emergence of topologically charged states localized on twist defects in such fibers. We have demonstrated that such states can emerge only in multihelicoidal fibers comprising three parts with alternating chirality. The obtained results can be readily scaled to the terahertz range. (paper)