High-Resolution FBG-Based Inclination Sensor Using Eigen Decomposition of Reflection Spectrum

This article addresses the analysis and design of a high-resolution and temperature-insensitive inclination sensor using fiber Bragg grating (FBG). The sensor uses a pendulum-based structure with FBG attached to its cantilever arm. Initially, strain analysis of the proposed inclination sensor is carried out using the finite-element method (FEM) to optimize the structure and materials for its fabrication. Experimental analysis is carried out on the inclination sensors by varying the inclination angle, and its results are compared with the FEM-based results. The shift in Bragg wavelength of FBG due to the generated strain at the cantilever arm is observed on optical interrogator. To measure the subpicometer wavelength shift with enhanced resolution and lower uncertainty, eigen decomposition of the reflection spectrum using Karhunen-Loève transform (KLT) is implemented. The range of measurement of tilt angle is found to be 0°-3° with a resolution of 0.0008°. The satisfactory linearity of the measured angle versus true angle, excellent repeatability, and very high resolution validates the feasibility of the proposed inclination sensor.