以極化差異法與PXI平台改善分佈式布里淵光纖感測系統

Abstract

大型結構物的維護與監測需仰賴各式感測器，將感測器鋪設在結構物上監控該處狀況。但結構物未來損害的位置不容易預測，而傳統式感測器只能做點狀式量測，無法反映結構物整體的狀況。本實驗室之光纖感測系統即是以光纖分佈式感測來作為結構物之神經系統。以此來偵測結構物之裂化並避免災害發生。 本研究室已建置出一套分佈式布里淵光纖感測系統(BOCDA)，其藉由控制泵光波(pump)與探測光波(probe)之間的相關性(correlation)來達到分佈式應變量測。在本文則是提出一極化差異法(polarization diversity)來減少因泵光波與探測光波極化態的改變所造成的量測誤差，先以一極化控制器將泵光波與探測光波之極化態調整成一致獲得最佳的布里淵增益，再利用一極化切換器以探測光波的正交極化態來補償極化態未調成一致的區段，降低量測誤差。並以PXI(PCI eXtensions for Instrumentation)平台來重新架構系統，以模組式介面卡取代傳統箱型儀器來縮小系統體積、提升傳輸效率及降低成本，使系統應用性更廣。

At present, the maintenance and monitoring of the large-scale structure are dependent on all kinds of sensors, we monitor the conditions of the locations where sensors are laid. However, due to the characteristics of conventional sensors, structural response can only be measured at specific locations. Since it’s very difficult to predict the future damage locations of the structure, the monitoring systems usually fail to reflect the conditions of the structures. Therefore, our lab’s fiber sensor system use the property of distributed sensing for establishing the nervous system of structures, in order to detect structure cracks and avoid accidents. Our lab have developed Brillouin Optical Correlation Domain Analysis (BOCDA) for distributed strain measurement. BOCDA can achieve distributed strain measurement by controlling a correlation between pump and probe lightwave. In this study, we propose a scheme for polarization diversity to reduce data fluctuation by polarization state change of pump and probe lightwave. First, we used a polarization controller(PC) and adjusted relative polarization state between the pump and probe lightwave to acquire the optimum Brillouin gain. Second, we introduced a polarization switch(PSW) that can generate vertical and horizontal linear polarization state and compensated for the sections that the relative polarization state are not optimum to decrease the measurement errors. And, we use a PXI(PCI eXtensions for Instrumentation) platform to reconstruct our system : replace conventional instruments by PXI modules for lightweight, upgrade transmission rate, cut down the installation cost and apply widely.