Curvature and Temperature Measurement Based on a Few-Mode PCF Formed M-Z-I and an Embedded FBG.

Hui Liu,Kok-Sing Lim,Yen-Sian Lee,Xueguang Qiao,Hangzhou Yang,Harith Ahmad,Xiaochong Liu,Yongqiang Wang

doi:10.3390/s17081725

Abstract

We have experimentally demonstrated an optical fiber Mach-Zehnder interferometer (MZI) structure formed by a few-mode photonic crystal fiber (PCF) for curvature measurement and inscribed a fiber Bragg grating (FBG) in the PCF for the purpose of simultaneously measuring temperature. The structure consists of a PCF sandwiched between two multi-mode fibers (MMFs). Bending experimental results show that the proposed sensor has a sensitivity of −1.03 nm/m−1 at a curvature range from 10 m−1 to 22.4 m−1, and the curvature sensitivity of the embedded FBG was −0.003 nm/m−1. Temperature response experimental results showed that the MZI’s wavelength, λa, has a sensitivity of 60.3 pm/°C, and the FBG’s Bragg wavelength, λb, has sensitivity of 9.2 pm/°C in the temperature range of 8 to 100 °C. As such, it can be used for simultaneous measurement of curvature and temperature over ranges of 10 m−1 to 22.4 m−1 and 8 °C to 100 °C, respectively. The results show that the embedded FBG can be a good indicator to compensate the varying ambient temperature during a curvature measurement.

Highlights

Optical fiber sensors have attracted significant research interest and have been widely used to monitor the health of smart engineering structures due to their unique advantages of compact size, low cost, high sensitivity, and immunity to electromagnetic interference [1,2,3,4].Curvature, bending, and strain of engineering structures are important parameters closely associated with the mechanical loading and health condition of the structures
Many sensors based on optical fibers have been proposed for bending or strain measurement, such as Long period Grating (LPG) [5,6], fiber Bragg grating (FBG) [7,8,9], and Mach-Zehnder interferometers [10,11,12,13], etc
We have reported a bending measurement device based on an Mach-Zehnder interferometer (MZI) structure

Summary

Introduction

Optical fiber sensors have attracted significant research interest and have been widely used to monitor the health of smart engineering structures due to their unique advantages of compact size, low cost, high sensitivity, and immunity to electromagnetic interference [1,2,3,4].Curvature, bending, and strain of engineering structures are important parameters closely associated with the mechanical loading and health condition of the structures. Many sensors based on optical fibers have been proposed for bending or strain measurement, such as Long period Grating (LPG) [5,6], FBG [7,8,9], and Mach-Zehnder interferometers [10,11,12,13], etc. Its sensitivity is lower than that of the LPGs in single-mode fibers [5]. It has been extensively studied [14] and improved in terms of accuracy and resolution [15]. For an optical fiber Mach-Zehnder interferometer (MZI) structure, two coupling elements in the structure will split and recombine the higher-order cladding modes to the core mode in order to form the interference pattern.

Methods

Results

Conclusion