High-Sensitivity Optical Fiber Humidity Sensor Based on Iridescent Chiral-Oriented Cellulose Nanocrystals/Polyethylene Vinyl Oxide Composite Film

In this article, a new optical fiber humidity sensor based on the iridescent chiral-oriented cellulose nanocrystals (CNCs)/polyethylene oxide (PEO) (referred as CP) nanocomposite films was proposed. The CP composites were prepared by evaporation-induced self-assembly (EISA), and the material characteristics of the composites were performed by fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), polarizing optical microscope (POM), scanning electron microscope (SEM), and ultraviolet–visible spectroscopy (UV-vis). The CP films exhibited uniform structural color of the nematic liquid crystal regulated by the content of PEO. Then, CP composite as humidity sensing material was deposited on the sensing fiber. Based on the Mach–Zehnder structure, the as-fabricated optical fiber humidity sensor produced an interference peak intensity movement associated with the change of refractive index (RI) and thickness of sensitive material. The structure and principle of the fiber sensor were described in detail, and the humidity sensing performances, including humidity sensitivity, response time, and stability, were comprehensively studied and the humidity sensing mechanism was discussed. An ultrahigh sensitivity of 0.64 dB% RH in the range of 30%–85% RH can be obtained, which is superior to other optical fiber humidity sensor. Additionally, the sensor has the advantages of fast response and recovery, good stability, and easy to fabricate and has potential applications in the field of remote online humidity monitoring.