Research On Optical Fiber Sensors Based On Double Fabry-Pérot Structure

In recent years, fiber Fabry-Pérot interferometers(FPIs) play an important role in sensing because of the outstanding advantages, such as compact size, single, ability of high resolution, immunity to electromagnetic radiation, high sensitivity and remote monitoring. Fiber Fabry-Pérot interferometers based sensors have attracted more attentions for great potential applications, including monitoring refractive index, temperature, humidity, strain and bending. According to the properties of the polymer, such as ultraviolet photoresist(SU-8) and polydimethylsiloxane(PDMS), we designed and fabricated the polymer fiber Fabry-Pérot interferometers for sensing. The main of research work has been summarized as follow:Firstly, we have proposed and fabricated an ultra-compact double polymer-capped Fabry-Pérot interferometer(FPI), which could be used for simultaneous measurement of refractive index(RI) and temperature with extremely low cross sensitivity. The double polymer layers were fabricated by step-curing ultraviolet photoresist(SU-8) and polydimethylsiloxane(PDMS) on the end face of a traditional single-mode fiber(SMF). In theory, we analyzed the temperature and refractive index sensing properties of the double Fabry-Pérot interferometers sensor, and experimental results show that sensors have nice linear response of temperature and RI. Three samples were fabricated with different Fabry-Pérot cavity lengths. Experimental results show that the temperature is 689.68 pm/oC(based on the wavelength shift in the temperature range of 20oC-75oC) and RI sensitivities of the fabricated fiber-tip is-147.04 d B/RIU(based on peak intensity measurement in the RI range of 1.335-1.355). On the basis of this double Fabry-Pérot interferometers, we fabricated a humidity senso r by curing polyvinyl alcohol(PVA) on the end face of PDMS.Secondly, we have proposed and fabricated fiber Fabry-Pérot interferometer(FPI) with glycerinum sealed in a hollow core fiber cavity at the end face of fiber. The FPI is used to measure temperature and angle. Two kinds of microstructures were fabricated, one was the double FPIs, and the other was single FPI. The proposed FPIs were fabricated by fusion splicing a tiny segment of the hollow core fiber with diameter 50?m and filling with glycerinum. PDMS material was used to encapsulate the glycerol solution. We fabricated a single Fabry-Pérot interferometer sensor. And experimental results show that the temperature sensitivity is 2.993nm/oC and the lin earity is 99.131%. For increasing the sensitivity, we fabricated a double Fabry-Pérot interferometers sensor, experimental results show that it has a good linear response and the sensitivity of temperature is 4.823nm/oC. The linearity is 99.699%. The radian sensitivity is-31.5nm/rad, and it also has a good linear response. The linearity is 99.986%.