Simultaneous measurement of strain, temperature and refractive index based on a fiber Bragg grating and an in-line Mach–Zehnder interferometer

Abstract

Abstract A simple sensor for simultaneous measurement of strain, temperature and refractive index (RI) is proposed and demonstrated. The sensor is based on a fiber Bragg grating (FBG) combined with an in-line Mach–Zehnder interferometer (MZI). MZI is formed by introducing a section of thinned core fiber (TCF) between two segments of multimode fiber (MMF). The two MMFs act as couplers that can excite high-order modes and recouple core mode and high-order modes into lead-out SMF, the function of this structure is to form inter-modes interference. The maximum interference fringe visibility exceed 20 dB. By monitoring the wavelength shifts of FBG and interference dips, simultaneous measurement of strain, temperature and RI can be achieved. The experimental results show that the maximum sensitivity of the sensor for strain, temperature and RI are − 2.14 pm/ μ e , 35.2 pm/ ∘ C and 32.93 nm/RIU, respectively. The proposed sensor has the advantages of easy fabrication, high fringe visibility and high sensitivities. Therefore, it has potential applications in multi-parameters simultaneous measurement.