Low Coherent Fiber Optic Strain Measuring System & It's Application In Bridge Monitoring

In recent years, fiber optical sensors have moved out of the laboratory and assumed a significant role in sensing and measurement fields. Fiber optic interferometric sensors using low coherence length source process absolute measurement, improved dynamic range and represent an active area of research.In the thesis described here, firstly the partial coherence theory is introduced since most of the my work are based on the theory. And then analysis of the light intensity is given by using the Fourier transform which is based on the homogeneous coherence function. Applying the low coherence technology, we proposed a novel type of interferometer, which can be regarded as the combination of unbalanced Michelson interferometer and Fizeau interferometer. And the detection scheme is archived by scanning the static and dynamic optical paths. On the foundation of these previous works, a fiber optical strain sensor system is constructed to extract the inner and outer strain information of structures.In the paper, the principle and setup of the strain sensor system are presented. Experimentally the system is applied to measure the mechanical strain variables inside a bridge model and experimental data are acquired. Lastly the industrial promise of this fiber optical sensor is discussed and valued in the application field of structure mechanical properties measurement and monitoring.