New Fiber Bragg Grating Dynamic Strain Demodulation System

Fiber Bragg grating (FBG) sensors have become one type of most important fiber-optic sensors. The sensing mechanism of a FBG sensor is always based on the precise detection of its resonant wavelength. Comparing with traditional electronic transducers, FBG sensors possess some important advantages, e.g. immuring to electromagnetic field and remoting and multiplexing sensing capability, and have a widely applications in civil or industrial areas.Signal demodulation technology of sensor decides the work mode, sensing application and performance. Therefore, it is very important research topic to develop new signal demodulation technology, and design new type of high-performance FBG sensors.Based on the FBG's spectrum tailoring capability, we develop a FBG-based triangular filter, and employ this filter to realize a new type of FBG based dynamic-strain interrogation system. In our experiments, a FBG triangular filter is fabricated by introducing the chirp in grating period and the apodization in index modulation, This FBG triangular filter has been utilized to demodulate the dynamic-strain signal of another wavelength-matched FBG sensor. Through a comparison with the results measured by the strain gauge, this system exhibits a good performance in the measurement of dynamic strain. The system is simple, compact, passive, and can be integrated as a portable demodulation module.The contributions of this thesis are:(1) After a brief summary of the principles of FBG sensors, the sensing features and demodulation techniques of FBG sensors have been comprehensively analyzed.(2) Propose a new type of demodulation technique based on FBG triangular filter,and numerically analyze the spectra of FBG based triangular filter.(3) Give a summary of grating fabrication techniques, and fabricated a chirped andapodized FBG triangular filters based on a beam scanning techniques.(4) Based on the fabricated FBG triangular filter, experimentally evaluate the performance of measurement of dynamic strain.(5) Summarize experimental results, and propose several future applications.