High Sensitivity of Balloon-Like Bent MMI Fiber Low-Temperature Sensor

A novel low cost and simple temperature sensor based on multimode interference (MMI) is formed by a successive singlemode fiber (SMF)-bent multimode fiber (MMF)-SMF structure. Due to the small curvature radius of bent MMF section mimicking a balloon shape, MMI effect from the core is spreading into coating. The high temperature sensitivity is mainly due to the large thermo-optical coefficient of the existing acrylate coating of the MMF fiber. A temperature sensitivity of up to −2060 pm/°C and −25.1 nW/°C for wavelength- and intensity-based interrogation, respectively, have been achieved in the range between 27 °C and 31 °C. This sensor is most suitable in high sensitivity and low-temperature application such as the measurement of human body temperature.