| As sensors, Fiber Bragg gratings(FBG) are widely used in the field of optical fiber sensing for structure health monitoring. How to realize the on-line monitoring of weak signal with high sensitivity has been always the focus of security field. In this paper, the sideband filtering system was designed and improved, and a demodulation scheme of multi-band filtering was proposed and the sensitivity of FBG sensing system was improved significantly.In this paper, the simulation model was built based on the demodulation principle and numerical analysis of multi-band filtering, which reflected the relationship between the slope, number of the side band and the sensitivity. By using this model, the effects of the slope, number of side band on the system detection sensitivity were investigated. Within the allowable range of optical power, the research found that the sensitivity of the system was directly related to both of the parameters. Supposing that the slope of linear region is constant, adding a side band filter, the sensitivity doubled. When considered the two parameters, the demodulation sensitivity of multiple filtering was 0.99685 times the sum of the slope.On the basis of the theory and simulation, an experimental platform of high sensitivity FBG demodulation system based on the Coarse Wavelength Division Multiplexer(CWDM) was built. The strain sensing experiment of demodulating FBG with CWDM was carried out, and the effects of slope and number on demodulation sensitivity were verified, the results showed that the experiments were very consistent with simulation trend. Then an experimental platform of FBG dynamic sensor system based on CWDM was set up, the demodulation sensitivities of first and second filtering were 0.151 m mV/pm and 0.268mV/pm, respectivety. And it can be concluded that the detection sensitivity of the system increased with increasing number of CWDM, the experimental results agreed with the theory trend. |
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