Sensor óptico de variações de índice de refração baseado em interferência multimodal

Abstract

This work presents the development, theoretical modeling, and experimental validationofarefractive index sensor based on multimode interference, employing a Singlemode–No-Core–Singlemode (SNCS) interferometric structure. The proposed approach explores multimodeinterference and the self-imaging phenomenon in optical fibers, with emphasis on theuseofano-core fiber as the multimode region in order to enhance the interaction betweentheevanescent field and the surrounding medium. Initially, the fundamental principles of opticalwaveguiding, multimode interference, and SMS-type configurations are reviewed, togetherwith the main theoretical models reported in the literature. Subsequently, the spectral responseof the SNCS structure is analyzed through numerical simulations implementedinPython,reproducing previously reported results and validating the adopted theoretical framework.Experimentally, the structure was fabricated by direct fusion between standardtelecomsingle-mode fibers and a no-core fiber segment, and characterized using a broadbandopticalinterrogator. Refractometric measurements were performed by immersing the sensorinaqueous glycerin solutions with different concentrations, revealing linear and reproduciblespectral shifts as a function of the external refractive index. The results demonstratehighsensitivity and structural simplicity, confirming the potential of the SNCS configurationforrefractometric sensing applications, particularly in environmental monitoring andliquidsolution control.