Analysis of Propagation/Leakage transition of fiber cladding modes for processing of data from dielectric tilted fiber Bragg grating sensors

Abstract

Tilted fiber Bragg gratings (TFBGs) possess promising characteristics for refractometric purposes. However, their complex spectral response containing a large number of features makes the sensor’s output relevance highly dependent on data demodulation and interpretation. We propose a method for processing sensor data based on a detailed analysis of the system’s behavior during the transition of cladding modes from propagation to leakage into the environment. We regarded this transition as an exceptional point, which made it possible to obtain an analytical expression for leakage losses of cladding modes in the proximity of the leakage condition. As a result, we built a regression model with good performance ensuring the determination of changes in the refractive index with an accuracy of 2.1 × 10^-5 RIU.