共路徑非等光程偏極干涉儀之研究

本論文提出一套創新的偏極干涉儀，它屬全光纖共路徑非等光程類型，可高靈敏、高穩定地量測波長漂移。干涉儀含參考與量測光路。參考光路包含一參考光，它直接經一旋轉光遮斷器後，被光感測器接收，形成參考信號。量測光路包含一量測光，它經線性極化光纖、光纖極化控制器、保偏光纖、光纖λ/4波板、及一與光遮斷器同步旋轉分析板後，被光感測器接收，形成量測信號。透過觀察量測訊號和參考訊號之間的相位差變化，可求得量測波長的漂移量。量測光之光程差乃由保偏光纖產生，實驗架構採用有5m及10m兩種保偏光纖；它們令干涉儀分別具有297.87°/nm及598.53°/nm的靈敏度，且穩定度分別為4.73×10-3 nm及6.77×10-3 nm。應用上，本干涉儀被用來量測布拉格光纖光柵(FBG)承受靜態和動態負荷下之應變。靜態量測為FBG 貼附於四點彎曲樑上後，該樑承受靜負載，藉由相位變化量及干涉儀的靈敏度，換算而求得波長漂移量，即可求得FBG因受力而產生的應變。該應變也同步地被應變規量出，以作為量測參考標準。實驗發現量測結果與參考標準值具有相當的一致性，也證實本論文所提出偏極干涉儀的準確性。動態量測為將FBG貼於PZT驅動的結構上，當PZT產生動態伸縮時，干涉儀量測出FBG所承受之動態應變。最後本干涉儀被應用到分時與分波多工的FBG應變感測上，實驗結果可證實本干涉儀在FBG的動態與靜態的多工感測具有可應用性與實用性。

關鍵字

波長漂移；布拉格光纖光柵(FBG) ；光纖極化控制器；光纖λ/4波板

並列摘要

This thesis proposed a novel polarization interferometer for measuring wavelength shifts. It possesses the characteristics of full fiber design, common-path, and non-equal optical path length, so it is with the preformance of compact optical setup, high measurement sensitivity, and high measurement stability. The interferometer comprises a reference and measurement pathes. The lightwave of the reference path passes through a rotating optical chopper to generate a reference signal on directly, and it is received by an optical sensor and became reference signal. Whereas the beam of the measurement path travels through a fiber linear polarizer, fiber polarization controller, polarization maintaining fiber, fiber quarter-wave plate, and an analyzer coaxially mounted on the chopper, this beam is then incident on an optical sensor to generate a measurement signal. By comparing the measurement and reference signals, the wavelength shift of the lightbeam can be obtained. The optical path difference of measurement path comes from the birefringent effect of the polarization maintaining fiber. In this research, there were polarization maintaining fibers of 5m and 10m. They made interferometer be with sensitivities of 297.87 °/nm and 598.53 °/nm, and stabilities of 4.73×10-3 nm and 6.77×10-3 nm, respectively. In application, the interferometer was adopted to detect dynamic and static strains on fiber-optic Bragg gratings (FBGs). In the static detection, a FBG and strain gage were attached onto the opposite sides of a four-point bending beam loaded by a static force. The wavelength shift of the wave reflected from the FBG was examined by the interferometer, and the measured shift was transferred into the strain of the beam, which is consistent with that measured by the gage. In the dynamic measurement, a FBG was affixed onto a structure driven by a PZT, the interferometer performed the ability to examine the strain of the structure while it was loaded periodically by PZT. Finally, the proposed interferometer is conducted to inspect the strains of FBGs in a TDM and WDM systems, the experiment results demonstrate the applicability of the interferometer.