Temperature and strain simultaneous sensing measurement based on an all-fiber Mach-Zehnder interferometer and fiber Bragg grating

We designed and fabricated what we believe to be a novel dual-parameter fiber optic sensor for simultaneous measurement of temperature and strain, which was composed of a femtosecond laser inscribed fiber Bragg grating (FBG), three segments of a single-mode fiber (SMF), and two segments of a multimode fiber (MMF), forming a SMF-MMF-FBG-MMF-SMF structure. The FBG and Mach-Zehnder interferometer (MZI) were present in this structure so that the changes of the temperature and strain parameters can be sensed by the shifts of the reflection center wavelength of the FBG and the interference valley wavelength of the MZI. We simulated the light field distribution of the sensor structure, compared the shapes of the interference spectra formed by the MZI structure with different sensing arm lengths of 25, 35, and 45 mm, and analyzed the spectra in the spatial frequency domain. The simulation results showed that the interference spectrum of the MZI structure with a 25 mm length sensing arm was clearer and more suitable for the experiment. The experimental results showed that the temperature sensitivity of the FBG and MZI was 14.81 and 43.54 pm/°C in the range of 80°C to 240°C, and the strain sensitivity was 1.49 and -2.58 pm/µε in the range of 0 to 1200 µε, with a high linearity and excellent repeatability. The sensor is economical, sensitive, and convenient to fabricate, and exhibits promising applications in the fields of biochemical medical detection and industrial production monitoring.