Enhancing the Sensitivity of a Temperature and Relative Humidity Sensor Utilizing Fe₂O₃-Coated Tapered Optical Fiber

This article presents the development and experimental verification of a temperature and humidity sensor featuring a stable structure and high sensitivity. The sensor utilizes a Mach-Zehnder interferometer (MZI) formed by coating a layer of Fe2O3 nanorods onto the surface of a tapered coreless fiber (NCF) via water bath method. The nanostructures formed on the NCF silver film exhibit remarkable stability and strength. Variations in external temperature and humidity alter the permeability of the Fe2O3 nanorods, leading to changes in their refractive index (RI) and a linear shift in the MZI’s resonance wavelength. Experimental findings reveal a temperature sensitivity of 0.454 nm/°C within the range of 25 °C–60 °C and a humidity sensitivity of 0.3332 nm/%RH within the range of 40%RH–70%RH. To enhance measurement sensitivity and accuracy, the MZI sensor is cascaded with a fiber Bragg grating (FBG) to mitigate cross-sensitivity between temperature and humidity.