本文提出使用漸進式折射率分布的三維微光流體分束器，使光束分束後向中央平面聚焦、提高傳輸。以氯化鈣水溶液與去離子水作為包覆流體與核心流體，包覆流體注入口深度較核心流體注入口淺，兩流體注入後會在主流道形成馬鞍形折射率分布，使入射光向兩側分束後向中央平面聚焦、提高傳輸。本文使用數值模擬軟體模擬速度及濃度場，再自行開發C++程式模擬光線在不同流道幾何與流動參數下，受折射率分布影響之軌跡，並使用Matlab的最佳化工具尋求主流道長度、注入口深度比、流率比與總流率之最佳參數組合，得到微光流體分束器的最好傳輸。本文使用微影製程製作分束器，選用最佳參數組合進行實驗，以數位單眼連接可變焦顯微觀察系統，由流道上方進行觀察與拍攝，並使用光纖於流道後方量測光束分束後聚焦的能量大小，由實驗結果與數值模擬結果相近，得知模擬可靠。模擬結果顯示三維流道形成之折射率分布使其傳輸比二維流道大。深度越淺的包覆流體注入口有越好的傳輸，但過淺的深度會使光線無法完全進入主流道。主流道長度對光束分束與傳輸影響不大，但光線在越長的主流道受漸進式折射率影響時間越長，偏折程度越大。越小的流率比會有越大的分束角度。總流率對傳輸有明顯影響，適當的總流率會使傳輸更好。各項參數組合起來的微光流體分束器，無法同時得到最大的分束角度與傳輸，但傳輸最高與最低時分束角度差距不大。

In this work, we proposed a three-dimensional (3D) micro optofluidic beam splitter based on liquid gradient refractive index. Calcium chloride solution and deionized water are applied as cladding and core fluids, respectively. The depth of cladding fluid inlet is set to be shallower to form saddle-like refractive index distribution, which splits the incident beam into two beams and the split beams converge to the middle horizontal plane. ANSYS Fluent and self-developed codes are used to simulate flow field and light propagation under different geometry and flow parameters. Optimization tools of Matlab are used to optimize the parameters to enhance the transmission. Validity of simulations is shown by experiment. We find the following trends from the results. (i) 3D structure of a splitter is necessary for improving transmission. (ii) Lower depth ratio and proper total flow rate causes higher transmission, lower flow rate ratio causes higher split angle, and length of main channel does little influence on transmission and split angle. (iii) The largest split angle and the highest transmission cannot be obtained at the same time, but the difference of split angle is not significant for a case with the highest or lowest transmission.

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