Crosstalk interference synthesis and polarization switching hybrid interrogating method for inline interferometric fiber Bragg grating sensor arrays

Abstract

We presented a crosstalk interference synthesis and polarization switching (CIS-PS) hybrid interrogating method designed for inline interferometric fiber Bragg grating (FBG) sensor arrays, targeting the multi-reflection (MR)-induced time division multiplexing (TDM) crosstalk and polarization-induced signal fading simultaneously. The inline interferometric FBG sensor array, which has found wide applications in underwater sensing, generally consists of a series of FBGs written on a commercial single mode fiber (SMF), where the coupling of TDM crosstalk and polarization-induced signal fading often makes signal extraction difficult. In this paper, this coupling was modeled, and the principle of the CIS-PS hybrid method was demonstrated. Experiments showed that even though the FBG reflectivities were all larger than 5%, the measured MR-induced TDM crosstalk reached −50 dB, which was the lowest to the best of our knowledge. The background phase noises were lowered and polarization-independent due to efficient control of polarization-induced signal fading. The demodulation stability of the sensing signal was enhanced from ±2.25 dB to ±0.15 dB.