Study On High-speed Demodulation And Key Technologies For Huge-capacity Fiber Bragg Grating Network

The development trends towards next generation of optical fiber sensing network are huge capacity, long distance and high sensitivity. The paper mainly concentrates on the development of multiplexing and demodulation techniques for optical fiber sensing network with huge capacity. In 2013, our team successfully on-line wrote no-weld friber Bragg grating(FBG) with reflectivity lowing to-50 dB from drawing tower. It made the suitable sensing cell and got rid of big loss, low strength in trandional series connection method in the process of large-scale FBG network. Then, it is the facing key issue to research a high-sensitivity and high-speed demodulation methord for weak sensor signal in hybrid network of time division multiplexing(TDM) and wavelength division multiplexing(WDM).It needs lower reflectivity FBG to improve the multiplexing capability and transmission distance for FBG sensing network. With the aim to solve key problems of multiplexing and demodulation in huge-capacity ultra-weak hybrid network of TDM and WDM, this proposal investigated mathematics model of sensor noise interference in ultra-weak FBG array in theory. Firstly research work was conducted on the spectrum and demodulation electrical signal characteristics, optical noise generation mechanism, superimposed effect and removal methods. Further investigation concentrated on the creation mechanism, interfering effect and elimination method of optical noise. Finally it realized ultra-weak sesing singal demodulation with huge-capacity and high-precision for FBG sensing network. Following are the main contents and obtained results.(1) Study and simulation of ultra-weak FBG sensing characteristics. Combining coupled mode theory and calculation methord of FBG, the reflected spectrum expression of ultra-weak FBG was deduced and simulated.(2) Comparative spectrum analysis of the experiment between different sensing network with different FBG peak reflectivity. At same time the sensing characteristics in huge-capacity ultra-weak FBG network was studied by combing its interference mathematics model.(3) The advantages and limitations of present multiplexing and demodulation method in huge-capacity FBG network were compared. In order to lower optical noise in FBG array, the phase shift pulse high-speed imaging spectrum demoluation was realized for huge-capacity FBG network. The basic ideas were to separat the valid FBG sensing signals with restrain noise, greatly reducing the amount of data processing. The system prototype was developed. And the system control strategy and algorithm performance were analyzed.(4) The deformation and temperature measurements were experimented in lab. The study for building ultra huge-capacity FBG sensing network was performed by using the hybrid WDM/TDM and TDM/SDM scheme.(5) The methord for on-line measuring FBG reflectivity based on ultra-weak FBG sensing array was proposed. It did not need any human intervention and lab instruments, but the measure speed was just the same as system demodulation speed.(6) A real-time sensing signal zoom setting change methord was studied to expand its scope of application for adapting to different reflectivity FBG sensing array. And a self-adptive FBG reflected power compention scheme was proposed. In this way, all FBG sensing signals were at the best sampling position of sampling window, and solved the issue of unfitted FBG sensing signal wavelength caused by reflectivity inconsistency.