Polarization singular patterns in modal fields of few-mode optical fiber

Structured light with isolated complex pi-symmetric polarization singular topologies such as lemon, star, and monstar is experimentally generated using few-mode optical fiber (FMF). These singularities, popularly known as C-points, are generated in the fiber modal field as a result of an inherent combination of orthogonally polarized Gaussian and vortex modes, excited simultaneously in FMF and controlled by input coupling conditions. The vortex charge, the state of polarization of the combining modes, and the relative phase difference between them are analyzed using Stokes polarimetry. Further, modal fields consisting of two opposite/similar index C-points are also generated, and the possible mode combinations that are responsible for such complex patterns are discussed. The helicity and index conservations in formation of dipoles also are discussed. (C) 2020 Optical Society of America