以偏極保持光纖研製波導干涉儀的先導性研究

Abstract

波導干涉術(waveguide interferometry)之基本理論為使用全反射的原理將光限制於某一介質中行進，又由於全反射時所伴隨產生的漸逝波現象能反映出邊界上的性質變化，隨著感測樣本的折射率不同而會有不同的相位變化，同時可由干涉術以及演算法將相位變化量取出並反推樣本資訊，故相當適用於生物分子的檢測。 本論文的主要目的是對偏極保持光纖為主軸製作的光纖式波導干涉儀做初步的研究，並試圖改善上一代光纖式波導干涉儀所遇到的問題。晶片設計上使用鐵氟龍材料以機械加工方式製作雙層平板，上板為感測槽；下板設計V型溝槽以放置光纖，如此可解決前一代光纖晶片還需要另外鍍膜以定義感測區內的光偏極態的問題。在系統光路上可藉偏極板配合偏極控制器切換物光和參考光的偏極方向，達成雙偏極檢測的目的；在解相方面選用了楊氏干涉儀的架構配合旋轉偏極板相移法，以CCD拍攝干涉條紋的移動並傳送回電腦以五步相移演算法做相位分析。 在實驗驗證方面首先以去離子水進行穩定性實驗，確定訊號不會由於環境因素而有大幅度變動後再用去離子水以及十倍的PBS溶液交互測試進行再現性的測試，由結果知道雖然訊號還是會稍為飄動，但對於同一種溶液的光強和相位分佈圖可說是幾乎完全相同的。最後以不同濃度的PBS溶液做為檢測樣本，並使用兩種不同偏極方向之樣本光檢測，由量測並計算而得的相位資訊可知系統對折射率不同的樣本會有不同之相位改變值，因此可確定本系統具有判別不同濃度樣本的能力。

Waveguide interferometer is a sensor based on the characteristics of total internal reflection (TIRF). When a light beam propagates in a waveguide structure, the evanescent wave accompanies TIRF is very sensitive and can be used to sense the changes of the properties on the boundary. Therefore, we can combine the waveguide structure and interferometry together so as to utilize some appropriate algorithms to detect the phase change of different sample solutions. The information of phase change can then be applied to calculate the refractive index and thickness variations of the boundary. As a result, the waveguide interferometer is suitable for being a biosensor. The main purpose of this thesis is to pursue a preliminary research of a fiber-based waveguide interferometer, which I chose the polarization maintaining fiber to built the guide tunnels. Upon the design of the fiber chip, a double layer Teflon fiber fixture is fabricated by machining. In addition, the design can solve the problem of defining light polarizations while the light beam propagating through the sensing window. In order to accomplish the function of dual-polarization detection, I used the polarizer and the polarization controller to switch the light polarizations of reference beam and sample beam. The construction of Young’s interferometry is chose to be the optical path for phase analysis. Utilizing the CCD camera to catch the interference fringes and then rotated the analyzer to obtain five images. At last I used five step phase shifting method to get the phase distribution diagram. The system has proved its stability and reproducibility by DI water and 10X PBS solution. In order to make sure the fiber-based waveguide interferometer has the ability to recognize between the sample solutions with different concentrations, I used two light polarizations (which were orthogonal to each other) of the sample beam to detect the PBS solutions. By the results we knew that the system would have different phase changes with respect to measure the specimen which have individual refractive index themselves. In summary, the system has been proved that it has the fundamental ability to distinguish the sample solutions with different concentrations.