Research on weak signal demodulation algorithm of orthogonal Fabry-Perot cavity fibre optic acoustic sensor

The ellipse fitting (EF) algorithm has attracted extensive attention in phase demodulation schemes for eliminating nonlinear errors. When the amplitude of the phase change of the interference spectrum caused by the signal to be measured is weak, the error of EF results is large, which leads to the failure of EF and differential-cross-multiplying (EF-DCM) demodulation. This paper proposes a presetting ellipse parameters and differential-cross-multiplying (PEP-DCM) demodulation scheme based on an orthogonal Fabry–Perot fibre optic acoustic sensor. When the sensing system is sensitive to strong sound pressure signals, a set of reliable elliptic parameter solution results are utilised as the preset values of elliptic fitting parameters for correcting the EF results of weak signals, which in turn improves the demodulation effectiveness of weak sound pressure signals. The scheme and the EF-DCM algorithm are simulated for demodulation. The two algorithms' effectiveness for demodulating weak sound pressure signals are compared and analysed. The feasibility of the PEP-DCM scheme for demodulating weak signals is verified through experiments. The experimental results show that the PEP-DCM algorithm is more accurate and stable for demodulating weak signals.