Algorithms And Multiplexing Of Fiber Fabry-Perot Strain Sensor

The fiber optic Fabry-Perot strain sensing is a new strain measurement invented at the end of 1980.It has become a hot point in the area of "smart structure" in foreign countries since it has the advantage of simple structure and low sensitivity towards temperature. For a fiber optic Fabry-Perot strain sensing system, algorithms used to demodulate the strain information contained in the output of the sensor is the key technology, while the multiplex is the technique used to lower its cost. The thesis is to study the demodulation algorithms and multiplex technology of the phase modulated Fabry-Perot sensor. The main points of the thesis are as follows:1. At the beginning of this thesis, the principle of fiber Fabry-Perot strain sensor is presented briefly, and the influence on the results of the peak-to-peak algorithm, brought by the spectrum distribution of light source, wavelength quantification or the noise in the output of the Fabry-Perot sensor is investigated. The limitation of the peak-to-peak algorithm is pointed out.2. The output of the low finesse Fabry-Perot sensor is approximated as two-beam interferogram. The DFT (Discrete Fourier Transform) method is use to demodulate the gap length of the low finesse Fabry-Perot sensor.3. The accuracy of the results of DFT algorithm is analyzed. Zero-padding on the output data of the Fabry-Perot sensor and Gauss interpolation on their DFT frequency domain can be use to improve the accuracy.4. As the spectrometer sample the output signal of the Fabry-Perot sensor uniformly in wavelength domain, so not uniformly in frequency domain, the DGT algorithm is put forward. A peak search method named golden search rule is applied to reduce the computation intensity.5. Multiplexing technology of fiber Fabry-Perot strain sensor is studied. The frequency domain algorithms are adopted for demodulating sensors connected in parallel. The capability of this multiplexing method is analyzed.6. Experiments are carried out to demonstrate the validity of algorithm improvement and Multiplexing technology.