Numerical analysis of the F-P TCFBG strain sensor spectral response and its multiplexation capabilities achieved with DSP and FFT analysis

Abstract

This work presents a numerical spectral properities analysis of a chirped-Bragg-grating-based Fabry–Perot (F-P CTFBG) cavity written in tapered fiber together with its application for strain monitoring. The work focuses on analyzing the structure’s sensing performance and spectral response for codirectionally and counter-directionally written reflectors for various manufacturing process parameters (reflector lengths, phase mask chirp ratios, and positions on the linear transition of tapered fiber). In turn, it is shown that by manipulating the Bragg wavelength distribution of the cavity’s reflectors, it is possible to control strain sensitivity character (i.e., positive or negative). The discussion also focuses on signal processing of the acquired spectrum through analytical derivation of the digital filter parameters that allows for unambiguous extraction of the cavity length for a given axial force applied to the each sensor irrespectively. Finally, a sensing system consisting of two cavities with either co-directionally or counter-directionally written reflectors is discussed.