High-Order Harmonic-Frequency Cross-Correlation Algorithm for Absolute Cavity Length Interrogation of White-Light Fiber-Optic Fabry-Perot Sensors

A novel high-order harmonic-frequency cross-correlation algorithm is proposed for the cavity length interrogation of white-light fiber-optic Fabry-Perot sensors. The algorithm uses the minimum value of a high-order harmonic-frequency cross-correlation coefficient to determine the sensor cavity length by fundamental cross correlation. This eliminates ambiguity in identifying the main peak of the fundamental cross-correlation coefficient, especially when the white-light source bandwidth is insufficient. The proposed algorithm was verified through simulation and experiment using a fiber-optic FP sensor with a cavity length of 79.175 μm. The reflection spectrum was obtained under illumination by an amplified spontaneous emission light source with a 3-dB bandwidth of 46 nm. The interrogation resolution of the algorithm was found to exceed 107.67 pm.