Research On The Characteristics Of Rectangle-Analogy FBG Sensing

FBG sensing is one of the important fiber optic sensors. Birefringent fiber gratings become the research hotspot of birefringent fiber gratings sensing technique as they have two different centre reflect wavelengths on their X,Y direction. Rectangle-analogy FBG in this dissertation differs from other birefringent fiber gratings in the sensing characteristics due to its different structure, and especially has obvious advantages over other birefringent fiber gratings on the two-parameter measurement. Theoretical and experimental researches on birefringent and sensing characteristics of rectangle-analogy FBG have been reported in the dissertation, which includes several aspects as follows:1. Theoretical researches on birefringent characteristics of rectangle-analogy FBG. have been done. Due to its speciality of structure, we obtained the stress firstly in core and stress areas and then we added the two stresses to get the total stress. The relations between birefringence and envelope radius,birefringence and core radius,birefringence and the area of stress are simulated. The conclusion that the birefringence increases with the core radius and stress area is drawn.2. The excursion coefficients of FBG wavelength with temperature and stress have been obtained based on theoretical model of the sensing characteristics of rectangle-analogy FBG temperature and stress. Experimental researches on the temperature and stress sensing characteristics of rectangle-analogy FBG have been done, and the typical values of the FBG temperature and stress sensitivities of X,Y directions are 10.25 pm 0 C and 12.46 pm 0 C, 14.85 pm g and 14.88 pm g, respectively.3. The experiments that temperature and stress two parameters were measured simultaneously with FBG have been done as the application of rectangle-analogy FBG sensing characteristics. The error of the experimental results is below 10%. With rectangle-analogy FBG, the measurements of polarization-maintaining fiber beat length have also been done, and the measured beat length of the fiber is about 16.6mm.