Highly Robust PGC Demodulation Scheme for Fiber Optic Interferometric Sensors

The quadrature signals in phase generated carrier (PGC) demodulation scheme inevitably introduce nonlinear errors degrading the robustness. A highly robust PGC demodulation scheme based on a Lissajous figure judging module and a renormalization ellipse fitting algorithm (R-EFA) is proposed for fiber optic interferometric sensors. As the Lissajous figure of quadrature signals is usually an ellipse arc, the judging module is designed based on the central angle calculation of the ellipse arc to overcome the failures of R-EFA under small signals. If the central angle of the ellipse arc is large than π/2, R-EFA is executed to calculate the ellipse correction parameters and the preset parameters are updated by the calculated parameters, otherwise, the ellipse correction parameters use the preset parameters. The quadrature signals are then corrected by the ellipse correction parameters and processed by the differential-and-cross-multiplying method. R-EFA remedies the large statistical bias of least squares ellipse fitting algorithm (LS-EFA) by iterative re-weighting and renormalization, especially when the input ellipse arc is short. Experimental results show that compared with PGC-LS-EFA, the signal to noise and distortion ratio and total harmonic distortion of the demodulated signal of the proposed algorithm are improved by 38.55 dB and 5.52%, respectively. Furthermore, the proposed algorithm is insensitive to phase modulation depth deviation and carrier phase delay. The mean demodulated amplitude is -21.89 dB in the frequency band of 500-5000 Hz with a standard deviation of 0.044 dB, the response linearity reaches 99.99% in a wide stimulating range of 0.1-9 V.