Strain Measurement Of Optical Fiber Fabry-perot Sensor Based On Blackbody Light Source

Aircraft engines,nuclear power engines,supercritical generators and other special large-scale equipment usually work in high temperature and high pressure or other harsh environments.It is important to monitor its structural health,in order to avoid the vicious accidents and economic losses.Fiber Fabry-Perot sensorsare suitable for health monitoring of such large equipment in harsh environments,because of their promising characteristics,such as miniaturization,thermal stability,and a corrosion resistant nature.In an optical fiber Fabry-Perot sensing system,the broadband light source is often needed to supply energy for sensing and demodulation.While at high temperature,the blackbody radiation energy of materials is strong,so it has the great potential to become the light source of an optical fiber sensing system.In this way,the optical fiber sensing system architecture can be simplified and system cost can be reduced.In this paper,the blackbody radiation cavity is designed to provide the input light source for the fiber Fabry-Perot sensing system,and the theoretical analysis and experiments based on the blackbody light source are carried out.It includes the following several aspects:(1)The fiber Fabry-Perot sensing system based on blackbody light source is designed,and the theoretical feasibility of strain sensor based on blackbody light source is analyzed.(2)The coated and casing type of blackbody cavity are designed,the efficiency of the blackbody light coupled into the optical fiber has been analyzed.The effects of fiber numerical aperture,fiber core area,blackbody cavity length and blackbody cavity radius on the efficiency of the blackbody light coupled to the optical fiber have been investigated.Output intensity of blackbody radiation based on two types of blackbody cavity have been investigated experimentally.The results show that the emission intensity of the coated blackbody cavity is better than that of the casing blackbody cavity.(3)The principle of the correlation algorithm for demodulating the fiber Fabry-Perot sensoring signal based on the blackbody light source is analyzed.The effects of the center wavelength,spectral bandwidth,the temperature of the blackbody light source,the length of the sensor cavity and the inclination of the fiber in the sensor on the signal demodulation accuracy are also analyzed.The results show that the sensor cavity length is better between 8?m to 18?m,the higher the temperature of the blackbody light source,the wider the spectral response bandwidth,the closer the spectral center wavelength is to 900 nm,and the higher the demodulation accuracy of the sensor signal.(4)The fiber Fabry-Perot sensing system based on blackbody light source is designed and constructed.Under the condition of different temperature of the blackbody light source,repeated strain loading and unloading experiments of several fiber Fabry-Perot sensor were carried out.The results show that the strain information can be effectively demodulated when the temperature of the blackbody cavity is higher than or equal to 900oC.When the measured is in the range of 7.5?m ~ 16?m,the demodulation error is less than 2.26%.Fiber Fabry-Perot sensing system based on blackbody light source can accurately measure strain and can be used in high temperature environment.