Simultaneous restoration of a non-smooth strain distribution and temperature of an optical fiber Bragg grating based on its intensity spectrum

Abstract

This paper presents the implementation and results of simultaneous restoration of a non-smooth strain distribution and temperature acting on a uniform fiber Bragg grating (FBG) based on its intensity spectrum. It is to be noted that only a part of the grating is subject to strain, preferably not less than half of its length. To accomplish this task, the transfer matrix method and the Nelder-Mead nonlinear optimization algorithm were used. At a test stand, measurements were taken of the intensity spectrum of the beam reflected by the FBG, which was subject to the simultaneous effects of the two above-mentioned measurands. Based on the measured FBG spectrum, calculations were carried out for the simultaneous restoration of the strain distribution and the temperature value. The obtained restoration results correspond well with the set temperatures and strain gradients. The relative error of reproducing the temperature value and the strain gradient does not exceed 4.4 % and 5.6 %, respectively.