Slow optical vortices in multicoil fiber resonators

In this paper, we theoretically study the transmission of optical vortices (OVs) through a uniform N-turn coil of a multimode fiber. We suggest a scalar-approximation treatment based on coupled mode equations in slow amplitudes and study transformations of OVs and their orbital angular momentum (OAM) in such fiber resonators. We show that such resonators may exert super-efficient parametric control over the topological charge and OAM of the outcoming optical field. We study group delay time for transmittedOVs and show the possibility to implement on the basis of such coil resonators the delay lines forOAMlight beams. This property is potentially important for optical fiberOAMcommunications. (C) 2022 Optica Publishing Group