Research On Optical Fiber Relative-humidity Sensor Based On Fabry-perot Interferometer And Multilayer Porous Films

Different from traditional humidity sensor, optical fiber humidity sensor has many advantages of miniature, high sensitivity, fast response, good repeatability and immune to electromagnetic interference. In this paper, a novel optical fiber relative-humidity sensor(OFRHS) with porous thin films as sensing elements is proposed and demonstrated. The sensor, with coatings on the distal end of the multimode fiber by Electron Beam Physical Vapor Deposition(EB-PVD) process, is based on a nano Fabry–Perot configuration. The main contents are as follows,(1) This paper introduces the background information of optical fiber humidity sensor research, such as the significance of humidity sensor, the definition of humidity and relative humidity, the classification of OFRHS, the research progress of OFRHS, and the experimental scheme adopted in this thesis.(2) The moisture absorption principle of the porous humidity sensitive thin film was analyzed in detail, while the interference theory of multilayer coatings was explained. Moreover, the math theoretical simulation of the reflective spectra in different parameters(morphology, thickness, and refractive index of coatings) was calculated, which provides the theoretical foundation for sensor design and production.(3) The designs of multilayer thin films were demonstrated and introduced, meawhile, the advantages and disadvantages of each design were compared. The common preparation methods of the optical thin film were introduced, as well as the preparation process and equipment used in this research.(4) The experimental investigation of F-P type OFRHS based on porous TiO2/SiO2/TiO2 thin films was shown in this section. The preparation method of the sensor and the experimental methods were introduced; the humidity sensitivities of probes with different deposition process parameters(such as coating thickness, baking temperature, and air pressure) were explored; Besides, the sensing performance was investigated in detail, including the humidity response characteristics, repeatability, response time, cross-sensitivity of temperature; In the end of this paper, the most of attention was focused on the film morphology, moisture sensitivity, and heat treatment effect on the stability of the sensor. Furthermore, two Calibration and Test Reports were illustrated.One of the highlights in this paper is that multilayers coatings interference was applied to optical fiber sensor with Electron Beam Physical Vapor Deposition process. Further, the probe based on this type of F-P interference and porous thin films presents an excellent humidity response property, showing promising prospect in the low and middle humidity measurement.