Research On Optical Fiber Fabry-perot Air Pressure Sensor System

With the rapid development of the aviation industry,the real-time and accurate monitoring of the air pressure at critical positions of the aero engine compressor plays a key role in improving its propulsion performance and ensuring a safe working environment.Optical fiber F-P sensors are suitable for atmospheric pressure testing in harsh environments such as engines due to its advantages of anti-electromagnetic interference and high temperature resistance.However,the existing sensor structures and demodulation methods are difficult to take into account the advantages of large range,high accuracy,high sensitivity,and easy reuse.Therefore,in order to meet the needs of accurate pressure measurement in high-temperature and high-pressure environments,this paper proposes a coaxial sealed optical fiber F-P sensing structure to establish a model of air pressure-cavity length-output spectrum,and designs a demodulation scheme based on the principle of polarization low coherent interference,which tracks the extremum locations of the fringe to achieve high precision and high stability demodulation.The main research contents include:Firstly,the principle of optical fiber F-P interference is analyzed,and the air pressure sensor model with cavity length sensitivity is designed with the reflected light as the output.It meets the requirements of large range,high sensitivity,temperature insensitivity and high linearity.The mechanical properties,thermal properties and coupling loss characteristics of the sensor structure are theoretically analyzed,and the structural parameters are set,and then the packaging structure is designed to encapsulate the sensor structure.Based on the structural design,the key processing technology is explored wherein the CO2 laser welding method is adopted to realize the sealing welding of the optical fiber and the tube.The welding optical path and the mechanical control platform are built,and the welding control program is designed.Secondly,the demodulation method of the output spectrum of the sensing structure is explored,thus a low-coherence interference demodulation model with a birefringent crystal wedge as the main body is established,and the interference fringe distribution form introducing crystal dispersion is analyzed.The effects of light source spectrum,wedge angle and noise on the output fringe are discussed.A data processing scheme based on fringe envelope and location search of specified order extremum is designed,in which the wavelet tool is introduced to extract fringe valuable information,so as to realize the accurate demodulation of F-P pressure sensing structure.Finally,the finite element simulation is used to verify the pressure sensing characteristics and temperature response characteristics of the sensing structure.Through the test of the CO2 laser welding effect of optical fiber and casing,it is concluded that the welding power of 3.75 W can achieve sealed welding,and the optical fiber can pass light well.At the same time,a polarization low-coherence interference demodulation optical path iss built.A piezoelectric ceramic is used to simulate the change of the F-P cavity to test the demodulation performance.The test results show that within the range of 3?m cavity length,the repeatability of demodulation reaches 2.66 nm and the resolution reaches 4.0nm.The above work realizes the design of optical fiber F-P air pressure sensing system,which can take into account the advantages of high precision,high sensitivity,large range,and high robustness.The feasibility of the design scheme is verified,and it can be applied to the high-precision testing of air pressure in the high-temperature and high-pressure environment of aeroengines.