Peak wavelength tracking for enhanced measurement sensitivity and range in an fibre optic interferometric sensor

Spectral peak wavelengths observed in an Fabry-Perot interferometer (FPI) are proportional to the effective cavity length (ECL). Ambiguity in the tracking of the peak wavelength always occurs, an effect which limits the measurement range to half of the operation wavelength. In this work we propose a new demodulation method that can unambiguously recognize the spectral peak wavelengths. The evaluation of the ECL was realized by using the farthest-separated peak pairs, leading to a negligible integer rounding error in determining the peak order value. A new set of peak wavelengths could then be calculated based on the obtained ECL and peak order value. The difference between the measured and calculated peak wavelengths then was used as error correction factor to further improve the accuracy of the ECL and the peak order. Using this method, an accurate value of the peak order can be quickly obtained to achieve high measurement sensitivity and large dynamic range.