FFT Algorithm-Assisted Polarimetric Twist Sensor

We propose a polarimetric twist sensor based on fast Fourier transforms (FFT) algorithm-assisted spectrum demodulation of single-mode fiber coupler (SMFC). Theoretically, when tapering the coupling area of the SMFC to an extremely tiny extent, the coupling coefficient difference of orthogonal fundamental modes pair appears larger and the output spectra oscillates with an envelope. What is more, the shape of the output spectrum is tuned by twisting the input fiber of the SMFC, because of the principal axes alignment between the torsional input fiber and the SMFC. To demodulate torsion-induced variation of the orthogonal fundamental modes pair on the input single-mode fiber in experiment, FFT algorithm is utilized to analyze the output spectrum. The experimental results are corresponding to the theoretical analysis. The proposed fiber twist sensor can be used to measure twist angles from 0 degrees to 180 degrees. Meanwhile, we provide a new method to investigate the polarization components in sensor and communication system.