Isopropanol-sealed multimode microfiber for temperature sensing

This paper presents a low-cost and high-sensitivity temperature sensor based on an isopropanol-sealed multimode microfiber (MMMF). Isopropanol is a kind of material with a high thermo-optic coefficient. Refractive index (RI) of isopropanol changes with the surrounding temperature variation allowing high-sensitivity temperature sensing. By inserting the MMMF into an isopropanol-sealed capillary, a simple and highly sensitive fiber temperature sensor is implemented. Theoretical and experimental results demonstrate that the tapered multimode fiber can efficiently excite high-order cladding modes, the MMMF can enhance the multimode interference and increase the interaction between the evanescent wave and the isopropanol. The characteristics of the measured transmission spectra under different conditions are evaluated. Experimental results demonstrate that the temperature sensitivity increases with the decreasing diameter of MMMF. The maximum temperature sensitivity of −4.12 nm/°C is obtained over the range of 30 °C–50 °C. This packaging technology not only offers a more stable structure but also improves the temperature sensitivity for the thermo-optic effect of isopropanol and the thermal expansion effect of packaging materials.