Design Of Humidity Sensing System Based On Tapered Optical Fiber

Environmental humidity plays an important role in traditional and emerging fields.In recent years,the requirements for humidity measurement have been increasing in various industries.Fiber optic humidity sensors have gradually become a hot research topic in the field of humidity sensing by virtue of anti-electromagnetic interference,small size,high sensitivity and corrosion resistance.Because of its unique structural characteristics,the tapered fibers have greatly improved the response speed of the fiber sensor,reduced the size of the device and expanded its application range compared to the ordinary fibers.In this paper,graphene oxide is chosen as a wet-sensitive material,and a new design of tapered fiber humidity sensing system is proposed.The main contents are as follows.Firstly,the classification of fiber humidity sensor is introduced.The development status of optical fiber humidity sensors is discussed.The transmission characteristics of light in tapered fibers are analyzed from the perspective of geometric theory and wave theory.The evanescent wave transmission is further analyzed,which lays the theoretical foundation for experimental research on humidity sensing.The different preparation methods of tapered fiber are discussed as well,and the fusion-pulled taper method is applied to prepare the double-tapered structured sensor optical fiber in the experimentSecondly,the special structure of graphene oxide determines its physical and chemical properties.Based on the internal structure,the basic principle of using graphene oxide as a wet-sensitive film is analyzed in this paper.Graphene oxide with interlayer structure contains a large number of oxygen-containing functional groups,which interacts with environmental humidity(absorbs or releases water molecules in the air),causing changes of its own refractive index and light transmission characteristics when combined with optical fibers.In the design,a titration method coating process was used to make a graphene oxide-tapered optical fiber sensing probe.Thirdly,a humidity-optical power experimental platform was set up to conduct humidity characteristic experiments.The experimental results show that the taper fiber with length of 18 mm and a tapered waist bending angle of 60°experienced more changes in power,and the sensitivity is 0.045dB/%RH.Finally,the design and implementation of the humidity sensor system are carried out.With the help of hardware circuit,STM32 single-chip microcomputer works as a controller,thus the real-time display of humidity value is realized after debugging the software and hardware.Then the performance of the whole system is tested.The experimental results shows that the design has a high stability in the measurement range of 20%-80%RH,with a resolution of 0.1%RH.The design can be applied to many fields in the future,such as smart home,smart agriculture,medicine storage,aviation and so on,which can detect humidity efficiently and quickly.