| Fiber-optic acoustic sensor has high sensitivity and wide dynamic range compared with the traditional electric microphone. It detect the acoustic signal with high quality in a harsh environmental. Now, the study on fiber-optic acoustic sensor has become a highlight field of optical fiber sensing.In this paper, demodulation methods and performances of fiber-optic microphone based on Fabry-Perot Interferometer have been studied. The main work is shown as follows:1. Analyzed the ideal phase generates carrier algorithm, verified feasibility of the ideal algorithm by using Simulink tools. Determined the relationship between the modulation frequency, sampling rate, filter excessive bandwidth and dynamic range of demodulation. Verified the relationship’s correctness through large amounts of simulation data.2. For engineering applications, appeared some harmonic demodulated signal for ideal PGC demodulation by using DFB laser in the modulation scheme. Improved the method of using double and triple carrier frequency to do demodulation and eliminated the multiple harmonic. In addition, solved the effects of system latency using phase compensation, and verified the group delay characteristics of demodulated signal in multi-frequency demodulation case.3. Designed the hardware for fiber optic microphones demodulation system, Programmed drivers for FPGA and algorithms for DSP. Restricted the laser working current and temperature in Laser driving circuit to protect the laser out of damage. Ensured real-time demodulation through the core circuit that capture data, process algorithms, output audio signals.4. Tested the demodulation system’s performance. Through lots of experiments, the audio output signal linear response is well and the error is 0.21%; And the frequency response range is less than 3dB at 3kHz-10kHz; When working in 1kHz, the system can detect minimum sound pressure is 2mPa(-54dB@1kHz). Experimental results show that this system meet the basic measurement requirements. |
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