A Novel Polyaniline/Graphene Oxide Composite Film-Coated Humidity Sensor Based on a Mach–Zehnder Interferometer With Thin-Core Fiber

In this article, a novel humidity sensor based on Mach–Zehnder interferometer (MZI) was proposed and experimentally demonstrated. The sensor was constructed by fusion splicing of three sections of thin-core fiber (TCF) and two sections of single-mode fiber (SMF). Experiment and simulation results of the sensor exhibit consistent good response characteristics in the refractive index (RI) range of 1.3330–1.3645 and 1.3645–1.3982, respectively. A thin film made of alternating polyaniline (PANI) and graphene oxide (GO) layers was selected as sensitive coating, which was deposited on the surface of a TCF by the layer-by-layer (LbL) self-assembly method. The morphological and compositional properties of PANI/GO composite films were examined by means of FTIR spectrometer, Raman spectroscopy, UV–vis absorption spectroscopy, and SEM. External humidity changes the RI and dimension of PANI/GO, causing the wavelength changes in the interference pattern. The humidity sensing properties of the GO/PANI nanocomposite based on optical fiber sensor were investigated by exposing to a broad range of 20%RH–85%RH. The results show that the monitoring peak shows a redshift with the increase in humidity. The proposed sensor was linearly responsive to relative humidity (RH) within the range of 20%RH–65%RH and 65%RH–85%RH, with sensitivity of 20.21 and 67.31 pm/%RH, respectively. What is more, the proposed sensor has the advantages of easy fabrication, low cost, wide measurement range, and good stability in RH measurement, and it has potential applications in the detection of low and medium humidity.