White light interference demodulation of optical fiber Fabry-Perot micro-pressure sensors based on the Karhunen-Loeve transform and singular value decomposition

In this paper, the Karhunen-Loeve transform (KLT) and wavelength domain interferometric spectral singular value decomposition (SVD) are used for the first time to demodulate the pressure of an optical fiber Fabry-Perot (F-P) micro-pressure sensor, and the feasibility of the proposed method is demonstrated experimentally. The eigenvalue decomposition of the dominant frequency part of the beam-domain interferometric spectrum after the fast Fourier transform (FFT) is performed using KLT, and the singular value decomposition of the wavelength domain interferometric spectrum is additionally performed using SVD. Both methods use high-order eigenvalues as a new metric and then derive the relation between the new metric and the reference pressure. The two demodulation methods are experimentally compared, and we used an optical fiber F-P pressure sensor with unknown structure and material for pressure measurements. Even though the interferometric spectral signal is acquired using a coarse spectrometer (2.5 nm wavelength resolution), one can still achieve high demodulation accuracy with both algorithms. However, the SVD demodulation accuracy decreases significantly after reducing the spectral data points in the wavelength domain from 1566 to 783. KLT still has high demodulation accuracy and linearity after spectral data points are reduced from 1024 to 256 in the wavenumber domain. The satisfactory linearity of the measured pressure versus reference pressure and low reading errors validate the feasibility of the proposed demodulation algorithm.