Phase demodulation of interferometric fiber sensor based on fast Fourier analysis

A demodulation method for interferometric fiber sensors (IFSs) is proposed in this article. The phase variation induced by the measurands can be estimated by calculating the Fourier phase at the intrinsic spatial frequencies of the fiber sensor. Theoretical analysis of the demodulation method is discussed in detail. Numerical simulations are put forward to demonstrate the consistency of the demodulation results under different wavelength sampling interval and noise level, showing a better stability compared with the conventional peak wavelength tracking technique. The proposed method is also experimentally demonstrated by an inline multimode interferometer based on a single-mode fiber (SMF) offset-splicing structure. Experimental results indicate that the phase response of different cladding modes can be analyzed simultaneously. Simultaneous measurement of strain and temperature is realized in our confirmatory experiment by analyzing the phase sensitivities of two selected cladding modes.