A Highly Precise Demodulation Method for Fiber Fabry-Perot Cavity Through Spectrum Reconstruction
A highly precise demodulation method based on spectrum sampling and reconstruction for optical fiber extrinsic Fabry–Perot interferometer (EFPI) sensor is proposed and experimentally evaluated. A tunable laser and an optical power meter were used to sample the response of the EFPI sensor discretely. The full spectral response of the EFPI sensor is obtained through a nonlinear least squares fitting between the measured data and the theoretical model. An EFPI sensor was experimentally tested to verify the performance of the proposed demodulation method. The demodulation fluctuation range of the cavity length was within 0.84 nm, during 50 continuous measurements. The demodulation resolution of 4.59 nm was achieved for the change of cavity length around  $112~\mu \text{m}$  in a strain sensing experiment. Furthermore, the maximum measurement fluctuation of the cavity length just increased from 0.84 to 1.27 nm, when the number of sampling points decreased to one-third by increasing the sampling step from 0.4 to 1.2 nm. This demodulation method may be applied to a wide range of interference spectrum demodulation applications for the high precision and simplicity.