Highly robust demodulation algorithm for fiber optic interferometric sensors

We propose a phase demodulation algorithm in interferometric fiber-optic sensing systems based on 3 × 3 coupler demodulation with high robustness and strong disturbance resistance, which incorporates spectral decomposition into the three-dimensional ellipsoid fitting algorithm. This algorithm employs the least squares method to solve the ellipsoid parameters, then uses spectral decomposition to calculate the principal axis components for two-dimensional projection, and finally integrates the ATAN algorithm with phase unwrapping technology to achieve signal demodulation. Experimental results show that this algorithm improves the demodulation performance of the traditional ellipse fitting algorithm, achieving a linearity of 99.98% even when the amplitude of the excitation signal is below π/4. The algorithm was validated through experiments in different environments, under conditions with a maximum disturbance amplitude of 321 rad, its THD remains stably below 1% and the average SINAD is improved by approximately 13.8 dB, demonstrating enhanced robustness.