Theoretical And Experimental Study Of Fiber Bragg Grating Sensors

Since emerged in the late of 1970's, as an optical filter, fiber Bragg grating (FBG) has been widely applied to optical fiber communications. Also it has been applied to optical fiber sensors and optical measurements because it is sensitive to strain and temperature. In this dissertation, fiber Bragg gratings which act as quasi-distributed sensors and distributed sensors are studied theoretically and experimentally.First, the key technology (wavelength demodulation technique) of the quasi-distributed strain sensor systems was studied theoretically and experimentally. By using a wavelength tunable fiber laser as the light source to enhanced the signal energy, digital signal processing techniques to enhance the resolution, LabView + data acquiring board to acquire, analyze and display the data, also combining the familiar wavelength division technique, the quasi-distributed strain sensor demodulation system with 4Hz demodulation speed, strain resolution of 1μstrain, channel spacing of 1nm and C band operating wavelength range was developed.By combining the advantages of etching fiber Bragg grating by HF and packaging it in an aluminum tube, an temperature sensitivity imhanced fiber Bragg grating was achieved, which was proved theoretically and experimentally. The experimental results showed that when this technology was employed, the equivalent temperature-sensitivity of the packaged fiber Bragg grating was about5.53 times of the unpackaged fiber Bragg grating, in the temperature range of to 90 . This kind of package could not only enhance the temperature sensitivity, but also could adjust the temperature sensitivity in a range by changing the package material or adjusting the etching process. So the package method satisfied the most requirements. 20°C°CThe distributed fiber Bragg grating sensors was analyzed theoretically, In order to analyze the spectra of fiber Bragg grating sensor under inhomogeneous strain fields, the difference between the transfer matrix method and the Runge-Kutta method were analyzed. By combing the merits of both methods, the method to analyze fiber Bragg grating spectra was improved; Also the spectra synthesizing technique based on the simulate annealing evolutionary algorithm and the adaptive genetic algorithm were bring forward, which were suitable for fiber Bragg grating distributed strain senor demodulation. And the fiber Bragg grating distributed sensing could be applied on the fields of structural damage identification and internal stress mapping of material. Finally, By the principle of the cladding mode resonances of fiber Bragg grating is sensitive to the external refractive index in some condition, a new refractive index sensing scheme based on the cladding modes of fiber Bragg grating (FBG) was developed for the first time and studied theoretically and experimentally. The results showed that in the refractive index range of 1.33~1.4584, the resonance wavelength of cladding mode shifts to longer wavelength with the increasing of the external refractive index and a higher sensitivity can be achieved when the external refractive index is close to that of fiber cladding's. The maximum refractive index sensitivity reaches 172nm/riu (refractive index unit).