Performance analysis and verification of passive demodulation for the fiber-optic Fabry–Perot interferometric sensor

Abstract A three-wavelength passive demodulation method for the fiber-optic Fabry–Perot acoustic sensor is proposed in this paper. The applied acoustic signal is recovered by three interfering signals with different wavelengths. The performance of this demodulator is analyzed and verified through simulations and experiments. Acoustic signals of varying amplitude from 0.1 rad to 8 rad can be extracted, demonstrating the ability of this algorithm to achieve a wide demodulation range. It is also possible to recover acoustic signals of different frequencies. The potential demodulation errors caused by the initial cavity length deviation and laser operating wavelength shift are calculated respectively, and the results show that the demodulation algorithm maintains high accuracy even under environmental disturbances or long-term laser operation. A linear demodulation range test system has been built. The amplitude of the demodulated cavity length variation shows a linear increase with increasing acoustic pressure and the acoustic pressure sensitivity of the EFPI sensor used in the experiment is 3 nm Pa −1 . Meanwhile, the demodulation system can still extract all the frequency information when the EFPI sensor is excited by a multi-frequency acoustic signal. Finally, the static and dynamic demodulation stability of the demodulation system has been tested. During 10 h of continuous excitation of the acoustic signal, the demodulation error does not exceed 10%. With two cycles of increasing/decreasing acoustic pressure, the demodulation results are repeatable. This demodulation technique has high accuracy, wide dynamic range, repeatable and stable demodulation, making it suitable for demodulating EFPI working in complex engineering application scenarios.