臺灣博碩士論文加值系統

當一外加介質--其折射率高過波導或光纖核的折射率--靠近核時，此波導即成為洩漏型波導。本論文討論到光能量在洩漏型波導中的衰減量。我們提出了一種新的方法-洩溢波導模-來分析上述的波導。此洩溢波導模的概念是來自於消逝場激發（evanescent-field excitation）的概念而得來的。消逝場激發的方式是由我們實驗室學長所提出。我們可以想像一光束從無損耗波導的最外側覆膜入射，假如能得到一個非常低的反射(機近於零)，則從此相對應的角度，可找出此特定模之傳輸常數，依此方法與傳統的方法需要解馬克斯威爾方程式與代入邊界條件所得到的結果 一樣。以此觀念延伸應用到洩漏型波導，我們亦可找出其相對應的傳輸常數，所不同的是此傳輸常數為複數，其虛數部分代表損耗。依此方式找到的模就是洩溢波導模。此方法想當簡單且直觀，只要檢測多層結構的反射率，再用圖示的方式來找出洩溢波導模，不需要用到複雜的數學運算式。
用這樣的方式來評估傳輸效能與修正過後的LZT方法，可以看出兩者的結果是相當令人滿意的，不管是在弱耦合或在強耦合的情行下，兩種方法均能得到相當接近的結果。LZT方法也是由我們實驗室所提出，而在本論文做修正。此洩溢波導模的概念不僅適用於多層結構，且其不需要額外的數值運算。本論文針對方向耦合器的轉瞬反應（transient response）做了分析，也發現有相當好的結果。本論文的主要貢獻即是提供這樣一個簡單直觀的方式來分析各種不同波導結構。

Discussed are the light transmission and their characteristics in a leaky step-index planar waveguide. In this waveguiding structure, an input guided mode will couple to continuous radiation modes, located in the leaky section. The major contribution of this thesis is to introduce a new concept - the leaky bound mode - to analyze the previous problem. The methodology is as follows. We are visionally incident a light ray from one side of the cladding to the leaky waveguide. If we can obtain extreme reflection, this condition corresponds to a new kind of bound modes, namely the leaky bound mode. This new method is straightforward and simple. Knowing the familiar light transmission and reflection by a multilayered structure are sufficient while this new method is actually originated from the evanescent field excitation, proposed by our predecessors.
In this thesis, we also investigate the light throughput in leaky waveguides. Two methods based on the leaky bound mode and a ray-optic approach are presented and compared. Excellent agreement between the two methods is found. Our method is very useful and efficient in analyzing multilayered structures and no numerical technique, e.g., finite element method, is required.

Acknowdements
Abstract
Table of contents
List of figures
Chapter 1 Introduction
1.1 Motivations of this thesis works
1.2 Contributions of this thesis
1.3 Organization of this thesis
Chapter 2 The Modified LZT method
2.1 Leaky planar waveguide
2.2 The LZT method and its modified version
2.3 Brief of the leaky quasi-modes
2.4 Results and comparisons
Chapter 3 The Leaky Bound Modes
3.1 Introduction
3.2 Examples and numerical results
4.2 Conclusions
Chapter 4 Analyzing Losses in Directional Coupler
4.1 The directional couplers
4.2 Conclusions
Chapter 5 Summary and suggested future work
5.1 Summary
5.2 Suggested future work
List of References
Appendix A
Appendix B
Vita

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