Abstract: A low-cost fiber Bragg grating (FBG) sensing system for coal-mine security monitoring is proposed in this paper. Based on the coherence multiplexing (CM) and spatial division multiplexing (SDM) techniques, this hybrid sensing network can support more than 40 sensors for quasi-distributed detection. It is demonstrated experimentally that the multiplexed sensing signal of each sensor can be clearly distinguished by an optical low-coherence reflectometry (OLCR). Methane concentration is detected with maximum sensitivities of an intensity variation of 10.92% and a concentration variation of 1%, using a well-designed sensor structure. Strain and temperature are also detected by this system, which also exhibits good results in the experiment.

Key words: Fiber Bragg grating, Coherence multiplexing, Spatial division multiplexing, Optical low-coherence reflectometry, Methane concentration

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