Conditions for Fano resonance occurrence in combined fiber quasiperiodic structures

Subject of study . This study investigates combined interferometric quasiperiodic structures incorporating a fiber Bragg grating and Fabry–Pérot interferometer (FPI). Aim of study. The aim of this study is to identify the regularities governing the occurrence of asymmetric Fano resonance in combined interferometric fiber structures (CIFSs). Method. Mathematical modeling of quasiperiodic fiber-optic structures is performed based on a model describing the propagation of planar electromagnetic waves through media composed of homogeneous layers. Within each layer, the permittivity and magnetic permeability are assumed to be constant. Main results. The conditions for the occurrence of asymmetric Fano resonance in CIFSs are investigated. The development of Fano resonance is facilitated in such structures when there is a decrease in the ratio of the maximum reflection coefficients of the fiber Bragg grating and FPI (typically less than 12 dB). When the length and/or induced refractive index of the Bragg grating are excessively reduced, the Fano resonance weakens owing to the insufficient contribution of the grating to its occurrence. Practical significance. The results of the study provide a foundation for the development of CIFSs with specific spectral response properties, suitable for use as sensitive elements for measuring various physical fields. They also open up possibilities for improving the metrological characteristics of systems based on such structures through the use of narrowband components in their spectral response.