Study On All-fiber Detecting System Of Methane Based On The Hollow-core Photonic Bandgap Fiber

Environmental protection has been the focus of global concern, and methane is one of the main pollution gases, which brings the life safety and health problems and also causes the greenhouse effect. The real-time online detection of methane concentration would be in relation to the production safety and healthy life. This paper adopts the hollow core photonic bandgap fiber to fabricate the gas sensor, and combines with the optical fiber detection technology, harmonic detection technology and other weak signal detection technology to design new methane all optical fiber detection system, which would get experienced truth and accuracy. The main research work is as follows:(1) The absorption database of methane gas is built, and the calculation model of methane gas concentration is established after analysising molecule spectrum theory. According to the newest Hitran 2012 Database, the paper exhibits the methane molecular absorption spectra build the mathematical model of methane gas concentration.(2) A new design scheme is proposed by using the hollow core photonic bandgap fiber as the gas sensing probe, to detect methane gas concentration in the all fiber optic detection system. The paper rsearchs the characteristic of the hollow core photonic bandgap fiber, such as transmission characteristic, bandgap effect and diffusion characteristic, which lays a theoretical foundation for the construction of optical fiber gas chamber. The appropriate parameters of hollow core photonic bandgap fiber is selected to establish different gas chambers by comparing the diffusion time according to two different diffusion end model.(3) A data acquisition system is established, which is based on Labview as the virtual instrument, to realize the detection of methane gas concentration. It carries methane gas spectra experiment, absorption experiment, and evaluation experiment and so on. The experimental results the all-fieber detecting system of methane based on the hollow core photonic bandgap fiber fesisble and accurate.(4) The weak signal detection in gas detection is researched. And the main research is foucsed on the Empirical Mode Decomposition(EMD) and its improved algorithm Ensemble Empirical Mode Decomposition(EEMD) used in optical signal detection. Compared to wavelet algorithm, it turns the data processing effect in both the spectrogram by subjective evaluation and parameter calibration by objective evaluation.