Optimization And Integration Of Brillouin-Based Distributed Fiber-Optic Sensing System With High Spatial Resolution

Structural health monitoring technology can be used for early damage detectionand disaster prevention for infrastructure. For over two decades, distributedfiber-optic sensors based on Brillouin scattering have gained significant interest fortemperature or stain measurements in structural health monitoring, due to the uniqueadvantage of distributed measurement of strain and temperature along an optical fiberunder test.In this thesis, we propose an optimized scheme of Brillouin optical correlationdomain analysis (BOCDA) for distributed fiber-optic sensor, which measures the netBrillouin spectrum between Brillouin gain and Brillouin loss effects. The thesis isorganized as follows:1) The proposed scheme of the optimized BOCDA system combining Brillouingain and loss effects is presented. And the improvement of signal-to-noise ratio (SNR)by two-fold is proved theoretically.2) The principle and experimental setup of the scheme is demonstrated. Adual-parallel MZ modulator (DP-MZM) is used to generate the light waves for bothBrillouin gain and loss process. The two-fold SNR improvement for the feasibility ofdistributed strain sensing is experimentally verified. Compared to traditional BOCDAscheme, the scheme system needs fewer devices, showing cost-effectiveness.3) A prototype of the optimized BOCDA system is developed, which iscomprised of DP-MZM, two-level EDFA, polarization scrambler, optimized circuit design and data acquisition technique. The prototype ensures distributed sensingability with the nominal spatial resolution of1.6cm and the measurement accuracyof10or0.5℃.4) The developed prototype is adopted to monitor the spatial and temporaldistribution of strain in the Jiangyin Bridge. It is proved the feasibility andpracticability of this prototype for structural health monitoring of nowadays bridges.