Fiber Optic Fabry-Perot Interferometer(FPI)is a kind of optical measuring device with high resolution and high sensitivity,which can be used for long distance and noncontact measurement.It has been widely used in many fields such as filters,fiber lasers,fiber sensors and antennas.Among them,the optical fiber FPI sensor is a sensor based on the principle of optical interference,with high reliability,good temperature resistance,strong anti-interference ability and strong scalability.Therefore,it plays an important role in temperature,pressure,strain,liquid level,vibration,electric field,etc.However,there are still two great challenges in the practical application of fiber optic FPI sensor.On the one hand,this is due to the complicated structural design,cumbersome preparation and high cost of the sensors.On the other hand,there is still much room for improving their sensitivities.The aim of thesis is to investigate the structural design,fabrication methods and how to improve the sensitivities of optical fiber sensors.Thesis presents a highly sensitive epoxy resin(ER)-filled FPI pressure sensor with simple structure and low preparation cost,which is prepared by connecting a single-mode fiber(SMF)to a short section of hollow-core fiber(HCF)and filling the end face of the HCF with a layer of ER film by capillary action.Theoretical analysis and experimental results show that shortening the length of Fabry-Perot(F-P)cavity or reducing the thickness of reflective film are two effective methods to improve the pressure sensitivity.Between 200 k Pa and 300 k Pa,the pressure sensitivities of the sensing structures with the shortest F-P cavity length and the thickest film thickness are-387.18 pm/k Pa and-530pm/k Pa,respectively.To further improve the sensitivity,the vernier effect is introduced into the optical fiber sensor,and the ER-filled FPI sensing structure is cascaded with air reference cavity in a separated manner.In the local pressure measurement range of 233-257 k Pa,the pressure sensitivity is amplified to 2.526 nm/k Pa,which is 5.79 times that of a single FPI sensing structure(-435.95 pm/k Pa).In thesis,a new polymer-filled fiber optic probe for temperature sensing is proposed,which is simple to prepare and consists of only a section of SMF and a polymer-filled HCF spliced together.The F-P cavity media is filled with three different polymers: ER,ultraviolet(UV)and polydimethylsiloxane(PDMS).The experimental results show that when the temperature is increased from 50 ℃ to 70 ℃,the sensitivity of the PDMS-filled FPI temperature sensing probe is the highest,reaching 1.858 nm/°C.In addition,the sensitivity is amplified by shortening the length of the F-P cavity and the Vernier effect.The maximum temperature sensitivity is up to 10.202 nm/℃ in the temperature range of44-52 ℃. |