High-sensitivity and large-range fiber optic temperature sensor based on PDMS-coated Mach-Zehnder interferometer combined with FBG.

Although numerous efforts have been dedicated towards developing fiber sensors with high performances, challenges still remain in achieving high-quality temperature sensors with high sensitivity, large measurement range and high stability. This study proposes a compact fiber optic temperature sensor based on PDMS-coated Mach-Zehnder interferometer (MZI) combined with FBG, and it can realize both high-sensitivity and large-range temperature measurement. The MZI is based on Thin No-Core Fiber (TNCF) with lateral-offset. Owing to the high refractive index sensitivity of MZI and the high thermo-optic coefficient of PDMS, the sensor can achieve a high temperature sensitivity (>10 nm/°C). Besides, by optimizing the TNCF length, the cascaded FBG can be used to locate different temperature intervals in units of approximately 10 °C, and therefore the detectable temperature range is largely extended. The experimental test demonstrates that the average sensitivities of 11.19 nm/°C, 8.53 nm/°C, 7.76 nm/°C, 7.27 nm/°C are achieved at the temperature around 30 °C, 40 °C, 50 °C and 60 °C, and it shows excellent consistency and repeatability during the thermal cycle tests.