光纖式波導干涉儀之設計與研製

Abstract

波導干涉術(Waveguide Interferometry)的基本精神是利用當光由高折射率入射至低折射率時產生全反射的特性，將耦合入波導的光侷限在同一介質中傳遞，再藉由與樣本接觸之樣本光以及參考光進行干涉並擷取出待測物中所需資訊。由於全反射在垂直界面方向上會產生漸逝波，所以光波對於界面上的特性變化相當靈敏，隨著不同的特性將會對光造成不同的相位變化，相對的就可在干涉訊號中看見這些來自於樣本所造成的變化。 本研究主要目的是為了建構出一光纖式波導干涉儀系統，主軸在於設計並製備出可與光纖式馬赫-曾德架構結合之光纖晶片。晶片方面有鑑於以往製程步驟繁瑣且高成本，故在此希望以光纖進行蝕刻來取代，論文中以鐵氟龍材質設計出放置光纖的平台，除了固定光纖方便蝕刻的設計外更將防止扯斷光纖的樣本流道一並考慮，特色是架構簡單、製備容易且低成本，此外，在論文中亦對光纖製備常遇到的問題做了完整的分析與討論，期望能夠提高晶片製備的良率。解相部份由於光纖耦合器可將樣本光與參考光完全的疊合，故元件由以往的CCD擷取影像變成使用光偵測器偵測單一光強値來得到干涉後訊號，如此不僅僅降低了系統元件成本更實現了縮小化的目的。由於光纖的可撓性特質大幅降低了波導干涉儀體積，加以系統具有簡單、快速與高靈敏度等特性，所以未來相當適合朝向縮小化機構繼續前進。 本論文實驗中首先以酒精與空氣進行重現性試驗，經實驗結果可知系統訊號雖然會受環境影響稍為飄動，但是仍然可以區分出此二樣本，並且對相同樣本有著相同的光強反應。接著採用不同濃度之酒精以及葡萄糖(Glucose)水溶液做為檢測樣本，結果可發現干涉後之光強値會隨著樣本濃度變化而改變，因此可得知本系統的確具有判斷不同濃度樣本的能力。

The fundamental theory of Waveguide Interferometry is the characteristics of total reflection and sensing by the evanescent wave. When coupling a light beam into a waveguide structure, we can get the information of the specimen from the interference signal produced by the reference and sample beams. The evanescent field is sensitive to the surface of guiding layer and different environment will induce different phase change of the light beam, so we can apply this property to detect the surface condition of dielectric media. In this dissertation, a fiber-based waveguide interferometer system that includes low-cost optical fiber based guiding tunnel was built. The principal goal is trying to design a fiber based chip that can be combined with the traditional Mach-Zehnder system. In order to simplify complicated steps before, I design a Teflon fixture that can fix fiber to make etching easier. Besides, there is a flow tunnel design to prevent that specimen pull apart the sensing fiber. This chip has many characteristics including simple structure、easy to fabricate and low-cost. In order to promote the yield of chip making, completely analysis so as to foster the fabrication process was made in this thesis. Because fiber coupler can couple the light beam completely, interference signal will be a single spot of light and need one photo detector to capture signal only. This method not only reduces the cost of system components but also realizes the goal to minimum system volume. The property of flexible of fiber make the volume of system smaller than before and system gets simpler, faster, and has higher sensitivity, so it has the potential to extend the current system into a handheld meter in the future. This fiber-based waveguide interferometry system has been proved to have ability of differentiating between different sample by using air and alcohol solution as the specimen. By way of experimental verifications, we can find that proper signal level change was found with respect to different alcohol and glucose concentrations solutions. In summary, this system was verified experimentally to be able to detect the refractive index changes on the waveguide surface.