Research On A System Composed By Two Fabry-Perot Sensors To Improve Sensitivity Based On Vernier Effect

Optical fiber sensor,because of its simple structure,free from electromagnetic interference and other advantages,widely used in the sensing field.Among all kinds of optical fiber sensors,the fiber optic Fabry-Perot(F-P)sensor can send and receive optical signals at a single end,with high contrast of interference spectrum and rapid response,so is widely used in the measurement of pressure,temperature and other sensing quantities.In recent years,a variety of fiber optic sensors based on F-P interference principle have been designed and manufactured.With the in-depth study of fiber optic F-P sensor,how to improve the sensor measurement sensitivity has become one of the most concerned research directions.In this paper,a separated double F-P structure is designed based on the vernier effect,which can improve the sensitivity of the fiber F-P sensor without changing the original sensor structure.The sensor cavity and auxiliary cavity with the same structure can eliminate the influence of cross sensitivity on the spectrum.The main work of this paper is as follows:Firstly,the research history of fiber optic sensor is introduced,and the research achievements of scholars in fiber F-P structure,demodulation method and sensitivity improvement over the years are introduced in detail.Secondly,the expression of F-P interference light intensity is studied,and the relationship between the free spectral range and the cavity length is analyzed,as well as the relationship between the interference spectrum drift and the cavity length change in the same order.The theoretical model of the separated double F-P structure is presented,and the interference spectrum expression of the double cavity modulation is obtained.In addition,the relation between the deformation and pressure of the diaphragm type fiber-optic F-P sensor is analyzed.Thirdly,the basic characteristics of fiber F-P are studied through theoretical simulation and experiment,which verifies the theoretical analysis of the basic characteristics of fiber F-P in this paper.And then,the relationship between the interference spectrum and pressure of the diaphragm type fiber F-P sensor was studied by simulation,and a group of diaphragm type fiber F-P sensors were prepared.Thetheoretical analysis of the diaphragm type fiber sensor in this paper was verified by water depth experiments.Finally,the interference spectrum of the separated double F-P is obtained by theoretical simulation,which proves that the separated double F-P structure can improve the sensor sensitivity and eliminate the influence of cross sensitivity on the sensor.Two groups of separated double F-P structures were prepared for temperature and pressure experiments,respectively.The experimental results showed that the pressure sensitivity and temperature sensitivity of the separated double F-P structure were increased by 9times and 5 times without changing the original sensor structure.The experimental results show that the influence of temperature on the interference spectrum can be eliminated if the double cavity is in the same temperature environment with temperature as the cross sensitive quantity.The structure has certain application value in improving the sensitivity of the interferometric sensor.