Research On Optical Fiber Strain Sensor Based On Vernier Effect

Optical fiber sensor is widely used in the measurement of strain,temperature,refractive index and other external physical parameters,because of its simple structure,small size,strong resistance to electromagnetic interference,high sensitivity and high resolution.Optical fiber Fabry-Perot(F-P)sensor stands out with its simple and compact structure.However,for some high-precision measurement fields,the conventional optical fiber F-P sensor can not meet the demand.Therefore,on the basis of the interference principle of optical fiber F-P cavity,the optical vernier effect is introduced to improve the sensitivity of the sensor.Finally,a separate double F-P cavity strain sensing structure based on bubble cavity is designed to realize double-cavity reflection spectrum multiplication,and fiber bragg grating(FBG)is introduced for temperature demodulation to eliminate the influence of temperature cross-sensitivity.The main research contents are as follows.Firstly,the sensing mechanism of optical fiber F-P cavity is introduced,and its interference spectrum characteristics are studied.Through the analysis of the sensing principle of FBG,the FPI-FBG model is introduced.And the sensitization mechanism of optical vernier effect is described in detail,which lays a theoretical foundation for the research work.Secondly,the technology of preparing bubble cavity by single mode fiber(SMF)arc discharge is described in detail,and the interference spectrum characteristics of bubble cavity are analyzed.The relationship between cavity length and interference free spectrum range is consistent with the simulation results.The strain and temperature sensing characteristics of the bubble cavity are studied by experiments.And the process of making reference cavity by casing method is described.Thirdly,the theoretical model of separated double F-P cavity strain sensing is proposed and established,and the spectral characteristics of double-cavity vernier interference are simulated by MATLAB.The sensor is prepared and the strain measurement platform is built to explore the strain sensitivity and vernier amplification factor of the sensor under different structural parameters.And the repeatability of the sensor is studied.Finally,a temperature measurement platform is built to study the temperature cross-sensitivity of the sensor,and the influence of optical vernier effect on temperature cross-sensitivity is analyzed.Two schemes to eliminate temperature cross-sensitivity are demonstrated,and the scheme of introducing FBG to eliminate temperature cross-sensitivity is verified experimentally.The optical fiber strain sensor designed in this paper has good linearity and repeatability,and can be used to measure micro-strain.The research results provide a new idea for the design of optical fiber strain sensor based on optical vernier effect.