Orbital Angular Momentum Resonances Arising from Mode Coupling in Hollow-Core Fibers

Abstract

It is known that the growth of the orbital part of the angular momentum of the fundamental air core mode of the negative curvature hollow-core fibers (NCHCFs) with circular polarization occurs at the edge of the transmission bands due to the spin–orbit interaction. In this paper, we consider the resonant behavior of orbital angular momentum (OAM) for a linearly polarized fundamental air core mode in straight and bent NCHCF. The resonant growth of OAM is associated with coupling between the linear polarized fundamental air core mode and the cladding capillary wall modes. The coupling between the modes arises due to crossing and anti-crossing. This OAM growth can be explained by a complex interaction of energy fluxes of the coupled modes under crossing. This phenomenon may be useful for a deeper understanding of the processes arising from mode coupling in fiber optics and nanophotonics, as well as for generating and transmitting OAM modes in micro-structured optical fibers.