Large core-offset based in-fiber Michelson interferometer for humidity sensing

A humidity sensor based on Michelson interferometer (MI) is proposed and demonstrated. The sensor achieves intermodal interference by a large core-offset between two single mode fibers (SMFs) through arc fusion splicing. Experimental results show the sensor with a length of 25 mm and core-offset of 50 μm exhibits a linear humidity sensitivity of -0.083 dB/%RH in the humidity range of 35-95 %RH, which is comparable to that of intensity-modulated humidity sensors with coating humidity sensitive materials. The temperature response and stability is also investigated, a linear temperature sensitivity of 9.5 pm/°C in the temperature range of 20-180 °C is obtained. The low manufacturing cost, easy fabrication and good stability make the sensor has great potential in many applications.