Optical Fiber Relative Humidity Sensor Based on Inline Mach–Zehnder Interferometer With ZnO Nanowires Coating

A simple optical fiber relative humidity (RH) sensor was proposed and demonstrated using a dumbbell-shaped inline Mach-Zehnder interferometer (IMZI) as a probe. The humidity sensor was constructed by coating the tapered waist region of the IMZI with ZnO nanowires. Based on an optical interferometric technique, the response of the sensor probe was examined by changing the RH within a range of 35%-60% RH. A wavelength shift of 0.490 nm was achieved for a humidity variation from 35% to 60% RH. It was also found that the sensitivity of IMZI-based sensor improved from 0.0002 to 0.020 nm/%RH with the ZnO coating.