Analysis on real-time phase delay in an interferometric FBG sensor array using polarization switching and the PGC hybrid processing method.

The polarization switching and phase generated carrier (PS-PGC) hybrid method is typically adopted to control signal fading induced by fiber birefringence and to precisely demodulate signals in interferometric fiber Bragg grating (FBG) sensor arrays. Unlike simple PGC demodulation, the real-time phase delay between the detected interference and the PGC carrier in the hybrid method has more adverse effects as both demodulation accuracy and background noise can be deteriorated, which may invalidate the polarization switching (PS) method. Aiming at this issue, the real-time phase delay and its compensation method were analyzed in detail in this paper. The features of the real-time phase delay in the PS-PGC hybrid method were summarized and the differences among polarization channels were investigated. Theoretical analysis indicated that the real-time phase delay mainly affected the interference complex synthesis (ICS) procedure, ultimately bringing about errors in the PS-PGC algorithm. The method for demodulating the real-time phase delay from sampled interference was presented, which provided the key compensation parameter. Experimental results showed that the compensation method could greatly improve the stability of the demodulated signal and suppress the sensor background phase noise. The amplitude of the demodulated signal was stabilized with a fluctuation less than ± 0.75dB and a noise suppression of 5dB. The acceptable compensation error was also analyzed.