Study On PGC Demodulation Of Optical Fabry-Perot Acoustic Sensor Based On Film

The conventional extrinsic Fabry-Perot Interferometric(EFPI) optical fiber sensor based on film is hard to ensure the reproducibility with short cavity. In general, it has bad temperature-resistant ability. In case of this situation, we design a new structure of EFPI optical fiber acoustic sensor with long cavity and propose a demodulation system of analog and digital mixture based on PGC detecting technology. The experiment is conducted to test the feasibility, reproducibility and temeperature-resistant ability. The main content of research works are as following:1. The operational principle of Fabry-Perot Interferometer and multiple beam interference are analysed in detail. The math deduction of PGC demodulation schme is introduced, based on which the change of signal is easily observed in the spectrum during the demodulation process. It is discussed how to determine the sampling and phase-carrier frequency. The simulation of PGC demodulation algorithm is conducted, which can work as the reference of the following demodulation system design.2. A new structure of EFPI optical fiber acoustic sensor is proposed with long cavity, whose advantage is detailedly analysed. The simulation of the stucture is experimented, proving that the sturcture is able to interfere with two-beam lights.And the sensor is fabricated in the laboratory, also the reflectivity of two reflectors are tested,which are 2.74% and 1.73%.3. The PGC demodulation system of analog and digital mixture is designed and realized. The analog circuit of PGC demodulation system is designed, including the photoelectric conversion circuit, amplifying circuit and analog-to-digital conversion circuit. The timing sequence of AD7610 is also tested. The software program of PGC demodulation system is designed, including the design of low pass filter, the design of integrator and differentiator.4. The PGC demodulation system is tested and analysed. The noise of demodulation is tested. The signal-noise ratio of electrical noise and the entire-system noise are 33 d B and 58 d B. Demodulation system is tested by play sound. The signal-noise ratio of demodulated result reaches 40 d B at frequency of900 Hz. The cavity length of the sensor is changed with 1 centimeter and the sensor is tested then at 900 Hz. The result show no change of signal-noise ratio.