Design and Fabrication of Lithium Niobate Blue-Laser Directional Couplers

由於藍光雷射可成功地積體化，因此積體光學應用的波段可延伸至更短波長。短波長可應用於軍事用光通信，但相較於長波長會有明顯的光折效應，而可能造成系統的損害，因此如何製作出可操作在藍光波長下的元件，並了解其與長波長操作下之差別便成為重要的課題。 本論文利用鈦擴散式鈮酸鋰光波導，在Z-cut的基板上製作出方向耦合器，使其操作在藍光波段(473nm)且導單模態，製作時並成功地抑制了鋰離子外散。量測結果發現，在波導寬度2微米、波導間距2微米時，其耦合長度為0.694mm。此外，在模擬中計算單模態線寬與方向耦合器耦合長度之關係，結果發現量得之耦合長度與模擬結果0.69mm非常接近。在光折效應的量測中，發現相較於態擴散式波導，鋅鎳共同擴散式波導具有較好的抗光折效應。Because blue laser can now be successfully fabricated and integrated, the range of wavelength in the applications of integrated optics can thus be extended to shorter one. The short-wavelength operation can be applied to optical communication of military affairs. However, the photorefractive effects, which are more remarkable when compared with longer wavelength, will be harmful to the system. Therefore, it is important to fabricate devices that can be operated at blue-laser wavelength and to know the differences when they were once operated at longer wavelength. In this thesis, Ti-diffused lithium niobate directional coupler has been successfully fabricated using Z-cut substrate and can be operated at blue-laser wavelength with single mode. Besides, lithium out-diffusion is suppressed. The coupling length is 0.694mm at a waveguide width of 2 micrometer and a gap of 2 micrometer. The experimental coupling length is also compared with simulation results, and the former is very close to the later. When measuring the photorefractive effects, the Zn-Ni:LiNbO3 waveguide is found to be more resistant than Ti:LiNbO3 waveguide.第一章 序論 1 1-1 研究背景 1 1-2 研究動機 2 1-3 內容簡介 3 第二章 基本原理 5 2-1 光波導耦合原理 5 2-2 光折效應原理 8 第三章 理論模擬 11 3-1 模擬方法 11 3-1.1 鈦擴散濃度分佈 11 3-1.2 折射率分佈 13 3-1.3 光束傳播法 14 3-2 驗證 15 3-3 模擬結果 16 3-3.1 單模態藍光波導之線寬 16 3-3.2 方向耦合器之耦合長度 18 第四章 元件設計與製作 20 4-1 藍光方向耦合器光罩之設計 20 4-2 製作流程 21 4-3 製作瓶頸 24 4-4 量測系統 26 第五章 實驗結果與討論 28 5-1 製程條件 28 5-2 實驗結果 29 5-2.1 光場模態之觀測 29 5-2.2 耦合長度之量測 30 5-3.3 光折效應之觀測 31 5-3 結果討論 34 第六章 結論與未來展望 37 6-1 結論 37 6-2 未來展望 37 參考文獻 39 中英文名詞對照表 4