Reasearch And Application Of High-Speed Demodulation System Of FBG-EFPI Hybrid Sensor

In recent years,people pay more attention to the research of optical fiber sensing technology.Fiber optic sensors have been developed successfully in structural health monitoring and fault diagnosis.In the field of structural health condition detection,such as hydraulic piping,the monitoring system is often more complex.Not only is the sensor required to measure both temperature and strain,which solve the influence of temperature and strain cross sensitivity on actual condition monitoring,but the system requires a dynamic demodulation frequency higher than the high frequency component of the device.For this reason,the paper proposes a composite fiber optic sensor array demodulation system based on Fourier domain mode locking(FDML)laser,the main contents are as follows:(1)Fabrication,study on sensing mechanism and multiplexing capacity of composite fiber optic sensor array.An extrinsic fabry-perot interference cavity is designed and fabricated,which is cascaded with fiber Bragg gratings to form a composite fiber optic sensor.The mathematical expressions of reflection spectra of composite optical fiber sensors are derived and the sensing mechanisms of temperature and strain are analyzed.The multiplexing technology of composite optical fiber sensor is studied,and the multiplexing capacity of the sensor is improved by improving the spectral frequency demodulation precision of the sensor,so as to form a quasidistributed sensor network.(2)Research on high-speed demodulation system of composite fiber optic sensor array.A high speed demodulation system based on FDML sweep laser for composite fiber sensor array is proposed.On the one hand,the construction principle of the modelocked sweep laser in the Fourier domain and the spectral simulation of the light source are studied,and the optical device driver module is designed to construct a high-speed sweep frequency light source with a sweep frequency of 40 kHz.On the other hand,the optical characteristics of comb filter and single-peak filter are studied,the nonlinear effect of tunable fabry-perot filter in frequency sweeping is analyzed,the spectral wavelength information calibration module is designed,the spectral information of the sensor is restored,and the decoupling algorithm of the high-precision composite optical fiber sensor is studied.(3)The temperature and strain of the composite fiber optic sensor were calibrated by static temperature and strain measurement experiments.The temperature,static strain and vibration of the pipeline were measured simultaneously by building a performance test bench of the composite fiber optic sensor array.The experimental results show that the composite fiber optic sensor can not only measure the temperature and strain at the same time with high precision,but also the high-speed demodulation system based on FDML frequency sweep laser can achieve the high-speed demodulation of 40 kHz and realize the quasi-distributed sensor measurement.