Research On Temperature Measurement Method Based On Fiber Brillouin Dynamic Grating

Brillouin dynamic grating(BDG)sensing technology has been widely concerned by experts and scholars at home and abroad since it is proposed.Through a large number of experimental studies,it has found that,compared with the previous fiber optic sensing technology,it is has greatly improved multi-parameter simultaneous sensing,high precision and high spatial resolution measurement.In addition,it has many sensing characteristics,which is of great significance for the development of optical fiber sensing.This paper first expounded the BDG generation mechanism,and it theoretically derived the relationship between double refraction frequency shift and temperature and strain,which laid a theoretical foundation for the subsequent chapters.Then,the temperature and strain sensitivity of the polarization-maintaining fiber on the x and y axes were studied based on the temperature and strain sensing principle of the center wavelength of the fiber grating.The formula of relationship between the wavelength and the temperature and strain on the x and y axes of the polarization maintaining fiber was obtained.In addition,the relationship between the two-axis wavelength difference and temperature and strain was further studied.The results showed that the wavelength difference had a good linear relationship with temperature and strain.When the temperature increased by 10 °C and the strain increased by 10 ??,the wavelength difference decreased by 0.0045 nm and increased by 0.0001 nm,respectively.The theoretical derivation and numerical simulation on the relationship between fiber beat length and temperature and strain were carried out.The results showed that reciprocal of the beat length has a good linear relationship with temperature and strain,and it decreased and increased with the increase of temperature and strain.Based on the five-wave mixing equation,the relationship between the Brillouin dynamic grating reflectivity and the reflection spectrum and the grating length was studied and the derivation and numerical simulation of the correlation formula were carried out.The results showed that the reflectivity increased with the square of the grating length when the phase matching condition was equal to zero.When the phase matching condition was not equal to zero,the reflection linewidth and the maximum reflectivity became smaller as the grating length increased.At the end of this paper,temperature and strain(simultaneous)measurement error is analyzed based on the influence law of Brillouin dynamic grating double refraction frequency shift and Brillouin frequency shift measurement error.The results showed that the influence of the error in the single measurement by using the double refraction frequency shift on the error in the measurement results of temperature and strain is smaller compared with the Brillouin frequency shift and the simultaneous measurement.Related research provided a theoretical basis for further improving the measurement accuracy of fiber-based temperature and strain sensing systems.