Error Analysis and Experimental Research of Temperature/Strain Sensing Based on Few-Mode Fiber Bragg Grating

Abstract

ABSTRACT To solve the temperature/strain cross-sensitivity problem, simultaneous measurement of temperature and strain can be achieved by using the two spectra of LP01 mode and LP11 mode in few-mode fiber Bragg grating (FM-FBG). However, in the same fiber the temperature/strain sensitivity difference is small, so the sensing accuracy is limited greatly. In this paper, we calculate the relation between sensing accuracy and sensitivity-difference and obtain that the enlarged sensitivity difference could improve the sensing accuracy. FBGs are engraved on two kinds fibers single-mode (SM) and few-mode (FM) with different geometrical dimensions; the sensing coefficients of LP01 mode in SM-FBG and LP11 mode/LP01 mode in FM-FBG are calibrated firstly and then are used to sense the temperature/strain. The experimental results show that parallelly using LP01 mode in SM-FBG and LP11 mode in FM-FBG achieves simultaneous measurement of temperature and strain, and error is reduced greatly compared with the sensing results using LP11 mode and LP01 mode in FM-FBG or using LP01 mode in SM-FBG and LP01 mode in FM-FBG, where the wavelength-temperature/strain coefficient difference is maximum. The temperature measurement error is 1.64°C, and the strain measurement error is 20.04 με, which is consistent with the theoretical analysis. The sensing results provide technical reference for FBG multi-parameter sensing measurement and the practical engineering application.