Propagation of optical vortices in loop resonators on the basis of multimode optical fibers

In this paper we theoretically study the propagation of optical vortices (OVs) through a loop resonator (LR) on a multimode optical fiber. We demonstrate the presence in LRs of a resonance, which is in the inversion of the topological charge (TC) of the transmitted OV. We show that in the outcoming field the weights of the OVs with opposite TCs may be sensitive to wavelength variations of the LR's length. Near the resonance points this property can be used for super-efficient control over the TC and orbital angular momentum of the outcoming field. We discuss application of this effect for temperature sensing. We also demonstrate the resonance power spikes in the loop and show that the resonance loop fields are the Hermite-Gaussian modes. In addition, we study the spectral characteristics of OV transmission and show feasibility of LR-based comb filters and delay lines for OVs.