High resolution signal-processing method for extrinsic Fabry–Perot interferometric sensors

• The resolution of the cavity length is only 36.7 pm when the sampling points in the wavelength domain is only 512.
• Dynamic signal detecting based on white-light interferometry.
• The corresponding resolution of the cavity length is only 1 pm on the low frequency range below 420 Hz.

In this paper, a signal-processing method for optical fiber extrinsic Fabry–Perot interferometric sensors is presented. It achieves both high resolution and absolute measurement of the dynamic change of cavity length with low sampling points in wavelength domain. In order to improve the demodulation accuracy, the reflected interference spectrum is cleared by Discrete Wavelet Transform and adjusted by the Hilbert transform. Then the cavity length is interrogated by the cross correlation algorithm. The continuous tests show the resolution of cavity length is only 36.7 pm. Moreover, the corresponding resolution of cavity length is only 1 pm on the low frequency range below 420 Hz, and the corresponding power spectrum shows the possibility of detecting the ultra-low frequency signals based on spectra detection.