Theoretical And Experimental Investigation On The Surface Modified Micro-nano Optical Fiber Based Temperature And Gas Sensors

Micro-nanofiber(MNF) featured with miniature size, large evanescent field, high sensitivity, passive element, low loss, resistance to electromagnetic interference, suitable for harsh environment and ease of integration, is widely used in petrochemical industry, industrial production, medical security, smart home and other sensing fields. Meanwhile, the emergence of new materials such as graphene and molybdenum disulfide, makes the combination of MNF and materials possible, which not only greatly improves the detection sensitivity, but also widely increases the measureable parameters.In this thesis, we focus on high sensitivity temperature and gas sensing technologies for environmental monitoring Internet of Things. Theoretical and experimental investigation on the surface modified MNF based sensors are systematically carried on. The main work includes the following parts:(1) Based on the waveguide model of MNF, the model field distributions of different fiber are simulated and analyzed. In addition, the MNF fabrication process is experimentally studied.(2) The composite waveguide structure based on surface modified MNF with graphene is proposed, and then three modification techniques including optical-induced deposition, one-step-transfer method and graphene assisted method are investigated and implemented.(3) The temperature sensor based on the surface modified MNF with graphene is proposed and realized. The optical field of this composite waveguide is simulated by Comsol, and then the temperature sensing theory is analyzed in detail. Further, the temperature sensors based on the surface modified MNF with graphene particles deposition and graphene film assistance are respectively demonstrated. The experimental results prove the sensitivity of 0.1018dB/? in heating process and 0.1052dB/? in cooling process, as well as high resolution of 0.0098?.(4) The ammonia sensor based on surface modified MNF with graphene is proposed and demonstrated. Two detection schemes by using transmission power demodulation and spectral wavelength demodulation are designed and analyzed in theory, respectively. Through optical power demodulation, the sensitivity of 0.1352dB/100 ppm and the detect resolution of 0.74 ppm are experimentally demonstrated. In order to further improve the sensitivity, the surface modified MNF is inserted in a Mach-Zehnder interference configuration. Based on wavelength demodulation of the interference spectrum and accurately control the flow of ammonia with flow meter, high sensitivity up to 48.68pm/ppm, competitive detecting resolution of 0.021 ppm and fast response time of 76 s are realized.