Investigation Of Sensing Based On The Brillouin Dynamic Grating In A Polarization Maintaining Photonic Crystal Fiber

Though it has been only 20 years since the distributed Brillouin sensor was born,this technology is being widely used to monitor the temperature and strain of large architectures. Traditional distributed Brillouin sensor is complicated and lack of accuracy; besides, sensors based on fiber Bragg grating can only achieve quasi-distributed measurement with the shortcoming that parameters of the grating are difficultly altered once it is etched. It is necessary to study a new kind of sensor that can easily realize dual-parameter sensing with high accuracy and resolution. This dissertation proposes a distributed Brillouin optical fiber sensor that monitors temperature at the same time by the Brillouin dynamic grating and stimulated Brillouin scattering in a single polarization maintaining photonic crystal fiber.First, we discretize the coupling wave equation by the finite difference time and space method based on the present theoretical model, building the programmatic expressions. Then the characterization of the reflective spectrum of the Brillouin dynamic grating and influence of pump depletion on the Brillouin dynamic grating is simulated using Fortran to get optimized pump power. The birefringence frequency shift of the fiber and the mode field is calculated combining with the Comsol software, which lays the foundation of the experiment.Second, a Brillouin optical time domain analysis system is established to measure the temperature and strain coefficient of Brillouin frequency shift respectively. Afterwards, the experimental setup that generates and reads the BDG is set up, then the Brillouin dynamic grating is stimulated and detected and the temperature and strain coefficient of birefringence frequency shift is got separately.The results show that the relationship between birefringence frequency shift and temperature is piecewise linear at the range of-40~10 ?C and distributed dual-parameter sensing namely temperature and strain sensing is realized with 20 cm spatial resolution; while at the range of 10~80 ?C the birefringence frequency shift of this kind of fiber has no obvious change, strain sensor which is insensitive totemperature is created.