In this study, the behavior of FBGs under varying temperatures is modeled using Coupled Mode Theory (CMT), which provides an analytical framework for the coupling of forward and backward propagating modes within a periodic refractive index structure. Fiber Bragg Gratings (FBGs) have emerged as one of the most versatile and reliable optical fiber sensors, particularly for temperature and strain monitoring in aerospace, civil, and biomedical applications. The temperature sensitivity of FBGs originates from two intrinsic effects: the thermo-optic. Abstract— The spectral characteristics of superstructure fiber Bragg gratings are analyzed numerically based on the coupled mode theory, simultaneously taking into account the counterdirec-tional guided mode coupling, codirectional and counterdirectional claddings mode coupling. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a.
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