An improved NPS algorithm for suppressing polarization fading in interferometric optical fiber sensing

There is polarization fading in interferometric distributed acoustic sensing (DAS) system, which leads to the situation that sensors cannot perceive the external signal. In order to improve the reliability and robustness of DAS system, an improved NPS algorithm for suppressing polarization fading based on malposition matched interference is proposed. According to the principle that the quadratic sum of the visibilities of two interference lights is one when two beams of light with orthogonal polarization interfere with another beam, the polarization related parameters can be eliminated by combining the two signals for phase demodulation, so as to suppress polarization fading. In this paper, the two signals are obtained by using the pulse group of specific states of polarization (SOP) for malposition matching interference, and then the joint NPS demodulation algorithm is used for demodulation, which ensures that the signal-to-noise ratio (SNR) of the signal is stable at about 37dB.