In-fiber Mach–Zehnder interferometer based on multi-core microfiber for humidity and temperature sensing

Abstract

A novel relative humidity (RH) sensor based on in-line microfiber interferometer(MFI) is proposed and demonstrated by experiment. The microfiber interferometer isfabricated by tapering multi-core fiber（MCF）down to micrometer scale in diameter, thecoupling occurs between the center core mode and the multiple side core modes. To makesensing performance enhanced, the microfiber sensor is fixed as U-shape. The variation ofRH is monitored by observing the wavelength shift of transmission spectrum. Theexperimental results show that the sensor has a good linear response to RH. A thinnerdiameter of 8.52μm of MFI can offer the better RH sensitivity of 59.8pm/(%RH) in the rangeof 35∼95%RH. When temperature changes from 35℃ to 85℃, the temperature sensitivity ofthe sensor is 4.2pm/℃, which demonstrates that the sensor is insensitive to temperature. Thesimultaneous measurement of temperature and RH can be realized by cascading with fiberBragg grating（FBG）. The microfiber sensor is easy to fabricate and does not has anyfunctional coating, which makes it widely used in accurate measuring relative humidity.