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Multimode optical fiber Bragg gratings: modeling, simulation, and experiments

Fiber Bragg gratings (FBGs) have emerged as important components and received intensive research attention in both fiber telecommunication and optical sensing. Bragg gratings in a multimode fiber structure (MMFBGs) are studied in this paper both theoretically and experimentally. A comprehensive numerical model is developed for MMFBGs based on the coupled mode theory and applied to analyze measured transmission and reflection spectra from MMFBGs with reflectivities ranging from 78% to 99%. Good agreement is obtained between the theoretical simulations and experimental measurements. It is found that the spectra of MMFBGs depend strongly on fabrication conditions and experimental conditions. The theoretical investigations and the physical explanations for the observed experimental phenomena give a complete understanding of the nature of the interaction between the propagating wave and multimode fiber gratings. It is considered that the spectral simulations provide a theoretical guidance in design MMFBG based optical devices.