A phase demodulation algorithm based on fast Fourier transfer for extrinsic Fabry-Perot interferometer sensor

A phase demodulation algorithm based on the fast Fourier transform (FFT) extrinsic Fabry-Perot interferometer (EFPI) is proposed in this paper. The EFPI is usually of low reflectivity at the fiber end face, and the optical model is simplified as two-beam interference. For fiber optic sensors, the signal information is mainly concentrated in a few spatial frequencies. The proposed phase demodulation method uses a variable step-size fast Fourier transform (VFFT) to accurately extract phase changes. The FFT demodulation algorithm uses data from the entire interference spectrum to calculate the phase at intrinsic spatial frequencies. The VFFT phase demodulation algorithm considers the problem of nonperiodic sampling under different initial cavity length conditions. The signal demodulation performance is simulated and analyzed to verify the reliability of the proposed demodulation algorithm. The results show that the demodulation precision of the VFFT is higher, and the adaptability to the same cavity length and reflectivity is better than that of the FFT. From the perspective of engineering practice, the demodulation algorithm has more stable performance and provides more technical support for the realization of ocean detection.