Research On Highly Sensitive And Low Temperature Sensor Based On Fiber F-P Cavity

Low temperature environment is closely related to human life,industrial and agricultural production and scientific research.In high altitude frozen soil areas,it is of great significance to take effective long-term monitoring of frozen soil temperature field to provide reference information for dealing with potential disasters.Fiber Fabry-Pérot Interferometer(FPI)temperature sensor has the advantages of small volume,light weight,anti-electromagnetic interference and electrical insulation.Based on the application background of frozen soil low temperature monitoring technology,this paper researches the new method of fiber F-P cavity low temperature sensing,which mainly includes the following aspects: research on sensing mechanism and sensitization technology of FPI,design and implementation of F-P cavity temperature sensor,study on the response characteristics of F-P cavity temperature sensor in low temperature environment,etc.The main work of this paper includes:(1)Research on temperature sensing mechanism and sensitization technology of fiber F-P cavity.The sensing mechanism of FPI is theoretically studied.The interference spectrum and main characteristic parameters of FPI are analyzed,and the variation of interference spectrum with the length of resonator and the reflectivity of end face is analyzed.On this basis,the theoretical model of fiber F-P cavity is established,the sensitization mechanism of fiber F-P cavity temperature sensor is studied,and the sensitization technology of optical fiber F-P cavity temperature sensor is discussed.(2)A low temperature sensor based on polymer filled F-P cavity is designed and developed.A sensitization scheme combining thermal material and F-P cavity is proposed.The working principle of the sensor is theoretically analyzed,the sensor sample is developed,and the low temperature response characteristics of the sensor are experimentally studied.The results show that the sensor has a temperature sensitivity of 1.485 nm/℃ and a linearity of 99.5% in the temperature range of-3℃ to 3℃.(3)A double F-P cavity cascaded fiber temperature sensor based on Vernier effect is designed and developed.The mechanism of Vernier effect in cascaded F-P cavities is studied theoretically,and the relationship between the amplification factor of the Vernier envelope sensitivity and the optical path difference of two F-P cavities is analyzed.The design idea of high sensitivity fiber F-P cavity based on the Vernier effect is proposed.The cascade temperature sensor model of quartz fiber cavity and polymer cavity with Vernier effect is constructed.The sensor samples are developed and experimentally studied.The experimental results show that the sensor has an ultra-high sensitivity of-80.449 nm/℃ in the range of-40.00℃ to-39.44℃,and has a good linear relationship between temperature and wavelength,with a linearity of99.9%.(4)A wide range and highly sensitive low temperature sensor based on "FPI+FBG" is proposed and developed.In view of the restrictive relationship between the sensitivity and measurement range of fiber F-P cavity temperature sensor,the design idea of "FPI+FBG" sensor with large range and high sensitivity is proposed.The relationship between the sensitivity,measurement range and free spectrum of F-P cavity temperature sensor is analyzed theoretically.The sensor sample is made,and the temperature response characteristics of the sensor are experimentally studied.The experimental results show that the main scale sensitivity of the sensor is 10.2 pm/℃,the Vernier sensitivity is-4.665 nm/℃,and the linearity is 99.9%.It can effectively realize wide range,high sensitivity and low temperature measurement.