Low harmonic distortion demodulation scheme for PMDI-TDM structure fiber-optic sensor array

The fiber-optic sensor array based on path-matched differential interferometry (PMDI)-time division multiplexing (TDM) offers the advantages of minimal channel crosstalk and high sensitivity. The 3 × 3 optical fiber coupler demodulation is the commonly employed scheme for PMDI-TDM. However, due to the non-ideal characteristics of the 3 × 3 optical fiber coupler and inconsistencies in multi-channel photodetectors, harmonic distortion occurs during signal demodulation. This paper proposes a low harmonic distortion signal demodulation scheme for PMDI-TDM structure fiber-optic sensor arrays based on multi-channel parameter fitting and tracking. This scheme utilizes the random sample consensus (RANSAC) algorithm to accurately obtain the parameters of the ellipse formed by the interference fringes of each element sensor in the system. Furthermore, the multi-channel parallel extended Kalman filter (MPEKF) is used to realize the real-time tracking of multi-channel demodulation parameters. The RANSAC-MPEKF scheme can suppress the influence of outliers, and effectively eliminate the non-ideal characteristics of 3 × 3 coupler and the non-consistency of photodetector, thereby suppressing harmonic distortion of the demodulation results of each channel. The experimental results demonstrate that the proposed scheme can suppress the influence of outliers, .and achieves a demodulation rate ≥500 kHz with minimal resource consumption, making it particularly suitable for large-scale multiplexing systems with a THD value better than 0.12%.