| In recent years,optical fiber sensors have attracted much attention due to their unique advantages over traditional sensors,such as small size,light weight,high sensitivity,strong electromagnetic interference resistance,fast response speed,and high chemical and thermal stability.As one of the most representative members,optical fiber Fabry-Perot sensors,especially extrinsic optical fiber Fabry-Perot sensor based on sensitive diaphragm have been widely used in many fields such as petrochemicals,power systems,medicine,environmental monitoring,civil engineering,etc.and have achieved very outstanding achievements.With the development of optical fiber communication technology and the continuous improvement of new materials and related processing technologies,more and more materials were used in the preparation of sensitive diaphragm of optical fiber sensors.Silicon has become one of the most commonly used materials due to its excellent mechanical,chemical and thermal stability.In addition,because the bonding process between silicon and pyrex glass has very high bonding strength and relatively simple process steps,the silicon diaphragm based fiber optic sensor has a great advantage.Nowadays,a large number of ultra-thin materials such as silver films,polymer materials,and two-dimensional materials were also used in the preparation of sensitive diaphragms for fiber sensors.Relying to the small Young's modulus and very thin thickness of the material itself,high sensitive optical fiber Fabry-Perot sensors were obtained.The method of analyzing the optical signal of the optical fiber sensor was divided into intensity demodulation method,phase demodulation method,frequency demodulation method,etc.according to its analysis object.Different demodulation methods have their own unique advantages and disadvantages.In different application fields and commercialization processes,a suitable sensor demodulation method is selected according to their own needs.So far,most of the research on Fabry-Perot fiber optic sensors have been in the laboratory stage,only a small number of sensors have been commercialized.Many key technologies and principles still need continuous experimental exploration,so the principle research of the optical fiber Fabry-Perot sensor is the most important part at this stage.In this dissertation,the pressure and temperature test performance of silicon thin film Fabry-Perot fiber optic sensors are studied from theoretical analysis,finite element simulation,experimental testing,and applications.The main work of the dissertation is summarized as follows:1.Finite Element Analysis and Pressure Experimental Test of Optical Fiber Fabry-Perot SensorsThe COMSOL software was used to perform two-dimensional modeling of the sensor interference cavity with relevant material parameters and boundary conditions.The parameterized scanning of the model's wavelength was performed by appropriate meshing to obtain the energy field distribution in the sensor interference cavity and the sensor reflection spectrum under different pressures.The simulated pressure sensitivities of silicon diaphragm thickness between 1 to 10 micron of optical fiber sensors were obtained by setting different silicon diaphragm thicknesses.In subsequent experiments,pressure tests were performed on optical fiber Fabry-Perot sensors of the same structure size and compared with the results of finite element analysis.It was found that the two results are in agreement well,and accurate design and prediction of the pressure test performance of the sensors were achieved through finite element analysis.2.Analysis and Simulation of Thermal Stress on Silicon Diaphragm and Its Impacton Sensor Temperature Test Performance The relationship between the thermal stress of the silicon diaphragm generated by the high temperature cooling process with the bonding temperature and the cooling time during anodic bonding was studied.Finite element simulations showed that when the bonding temperature was 450?,the surface thermal stress of the silicon diaphragm was 2-6 MPa,and the thermal stress at the center and edge positions of the silicon film was relatively large.Furthermore,by introducing the thermal stress model into the interference model,the temperature simulation sensitivities of the sensors in different sealed cavity's initial pressures(0.01 MPa,0.03 MPa,0.04 MPa,0.05 MPa)were 0.032 nm/?,0.087 nm/?,0.107 nm/?,C,and 0.125 nm/?,respectively.Temperature tests were performed on samples with different initial intracavity pressures to obtain sensor temperature test sensitivities of 0.037 nm/?,0.080 nm/0.104 nm/?,and 0.116 nm/?C,respectively.It can be seen from the results that compared with the theoretical analysis,the results obtained by the finite element simulation are closer to the experimental values,and the temperature sensitivity and linearity are in good agreement with the experimental results.3.Pressure and Temperature Cross Test Coefficient Correction of Optical Fiber sensors and Application ResearchThe pressure test of the optical fiber Fabry-Perot sensor at different temperatures were performed,the intensity demodulation method and the phase demodulation method were used to analyze the pressure and temperature test expressions and correction coefficients,which realizing accurate measurement of body cavity pressure within a small range of temperature variation in medical tests.In the dissertation,the testing equipment for the sensor was designed and built,and the vulnerability of the sensor' s silicon diaphragm was analyzed by ultrasonic test.It was obtained that when the thickness of the silicon diaphragm is 7 to 8 microns,it can meet the requirements of the strength of the silicon diaphragm in practical applications and the higher test sensitivity was obtained.Finally,the pressure gradient test and the small-scale temperature-varying pressure test of the sensor in the simulation environment were carried out,and the biocompatibility of the sensor was further discussed and analyzed. |
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