Study On Interrogation Of Fiber Bragg Grating Sensors With A Broadband Source

The thesis focuses on the study on interrogation of fiber Bragg grating (FBG)sensors with a broadband source. FBG sensors are a kind of wavelength-encodedoptical sensor; they have all the advantages normally attributed to optical sensors,such as light weight, small size, high sensitivity, etc. In addition, the FBG sensors areinsensitive to the power fluctuation of the light source and easily multiplexed along asingle fiber; they also use the absolute measurement method. On the basis ofintroducing the most commonly used interrogation method of FBG sensors, the thesisstudy on the interrogation method of wavelength-dependent device method, opticalfilter method, interferometric method and FBG sensors network in detail. The thesis analyses the noise properties, including light source noise, shot noiseand thermal noise of the photo detector, of wavelength-dependent device method andoptical filter method, and derives the formulas for predicting noise-limited strainresolution for uniform FBG sensors. The thesis reports a FBG dynamic signal analyzer for multi-point, dynamicstrain or temperature measurement. The analyzer uses a combination of anunbalanced fiber interferometer and phase locked loops and is capable of measuringdynamic signals. The thesis also analyses the noise properties, including light sourcenoise and photo detector noise, of heterodyne demodulation system and derives theformulas for predicting noise-limited strain resolution for uniform FBG sensors. The thesis reports a new method for the chirped FBG distributed sensing by theuse of simulated annealing algorithm. The numerical simulations and experimentsshow that, the algorithm is capable of determining the strain profiles along the FBG.Simulations and experiments demonstrate a strain detection accuracy of a fewmicrostrains in various types of strain profile. The spatial resolution is tetermined bythe numbers of the FBG sections in the matrix method and is now 0.2 mm. The thesis uses some optimization techniques, including step search method, - II -英 文 摘 要genetic algorithm, simulated algorithm and self-organization network, to improve theperformance of a FBG FBG sensors network. For the given light sorce, thesetechniques can be used to extend the measurement range of each sensor and/orincrease the number of FBG sneosr in the network.