| Summary: | On the basis of the photoelectric properties and hydrophilicity and multimode interference of Graphene Oxide (GO), this study proposes an all-fiber humidity sensor. Two core-offset regions are constructed with a fiber fusion splicer, and a GO film is coated on a single-mode fiber (SMF) between the core-offset regions to form a humidity-sensitive Mach–Zehnder interference structure. As the external humidity environment changes, the refractive index of the GO changes, and the light in the SMF is modulated by humidity. External humidity is measured by detecting the changes in the wavelength of the transmission spectrum of the sensing structure. A saturated salt solution is used to build a stable humidity environment. The sensitivity of the sensor is 0.05 nm/% relative humidity (RH) at 35.3%–95.8% RH, and the linear relationship between the characteristic wavelength and RH is 88%. In addition, the linear relationship between the light intensity and the RH of the sensor at a single wavelength at 1571 nm is analyzed, and the linearity is 97.45%. According to this finding, photoelectric conversion is used to convert the light intensity signal into a voltage signal. The data are processed by a computer to achieve the real-time and visual monitoring of the humidity environment. The fiber optic humidity sensor proposed in this work has a simple structure, simple production, low cost, and high sensitivity. This work provides a new method for humidity sensing.
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