Propagation of structured light in cascaded fiber Sagnac resonators

In this paper, we have addressed the propagation of structured light in cascaded Sagnac loop resonators (SLRs) based on multimode fibers. In the frameworks of developed scalar-approximation theory, we have studied propagation of optical vortices (OVs), as well as even and odd Laguerre–Gaussian (LG) modes in such cascades. We have shown that cascades of SLRs are capable of generating in the transmitted field frequency combs for both OVs and even and odd LG modes. This property is potentially useful in information orbital angular momentum photonics. Arrays of SLRs can invert topological charges of incoming vortex beams. We have also demonstrated that such arrays are capable of operating as all-fiber delay lines for structured beams. In addition, we have studied the sensitivity of this system to variations of its geometric parameters and have shown that the presence of defects in the cascade enables one to engineer its modal–spectral response with respect to both transmittance and reflectance.