[Fiber monitoring network of methane concentration based on space division multiplexing in coal mine]

Methane explosion accidents occur frequently, and accurate and real-time detection and early warning of methane concentration are the effective means of preventing these accidents. The research was based on the spectrum absorption properties of methane, and a near-infrared tunable DFB laser diode of 1.65 microm wave band was used. With the mode-hopping features of laser diode, a differential absorption of double-wavelength and single-fiber optical sensor network was designed. Sixteen methane sensors were multiplexed in this system with space division multiple access technology and optical switch, and the key technologies of anti-dust in gas absorption cell were researched. All signals were gathered by the PCI data acquisition card, and information of each way was analyzed and displayed with virtual instrument. The results of experiment show that the method can reach the sensitivity of 0.05% even without using a phase-locked amplifier and the absorption light path is only 10 centimeters. Long-time accuracy and stability of all sensors could meet the practical demands, and the response time of each sensor was less than 1 seconds. With the replacement of lasers, the network can be used for the real-time detection of other gases.