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

Abstract

Fiber Bragg gratings (FBGs) have emerged as important components and received intensive research attention in both fiber telecommunication and sensing fields. Bragg gratings in single mode fiber structure (SMFBGs) have been studied extensively. On the other hand, fewer studies have been reported on multimode fiber Bragg gratings (MMFBGs) despite of their potential applications in future optical access networks. In this paper, MMFBGs are studied in detail 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%. It is found that the spectra of MMFBGs depend strongly on fabrication conditions (e.g. modulation depth of the grating) and experimental conditions (e.g. mode excitation). Good agreement is obtained between the theoretical simulations and experimental measurements. Our simulations based on the developed MMFGB numerical model can provide quantitative explanations for the observed experimental phenomena. These explanations give a complete understanding of the nature of the interaction between the wave propagation and multimode fiber gratings. It is considered that the spectral simulations provide a theoretical guidance in design MMFBG based devices.