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. Mode conversion effects in Fibre Bragg Gratings (FBGs) are widely exploited in applications such as sensing and fibre lasers. However, when FBGs are inscribed into Few-mode optical Fibres (FMFs), the mode interactions become highly complex due to the increased number of guided modes, rendering. 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.