| 摘要: | 在積體光學以及通訊領域中，耦合器將一道訊號光分到不同的通道中，為一重要的積體光學元件，而傳統的定向耦合器有著較差的製程容忍度以及對不同波長的響應限制其發展空間，而三波導絕熱耦合器的結構設計有效的解決了在定向耦合器的問題，而鈮酸鋰晶體有著良好的電光係數與非線性係數，在鈮酸鋰基板上發展三絕熱耦合器之結構，在未來作為主動性元件有著良好的前景展望。
本研究在Z切鈮酸鋰基板上利用Stimulated Raman adiabatic passage(STIRAP)的概念去製作鈦擴散式三波導絕熱耦合器之結構，在不同的波導參數設計下，量測其結構對中央波導偏移量有著0.6μm的容忍度，分光特性在波長在1495nm到1600nm範圍時，在不同波導長度在TM偏振態得到小於7.5%變動量，在TE偏振態得到小於4%的變動量。
在本研究所設計的波導參數下，我們嘗試去得到STIRAP所預期的結果，但量測結果並不符，而在研究後期探討STIRAP的效應以及歸納原因為兩外側波導的耦合效應以及入射條件的問題。在此分析各種參數並提出新的設計參數的方式，且使用BeamPROP軟體去進行模擬驗證。當入射偏振為TM和TE偏振，在波導長度L=20mm，兩外側波導間距S=22μm，傾斜度ΔS=10μm時有良好的分光比模擬結果，而新設計晶片的研究與製備正在持續當中。
;In integrated optics and communications, a coupler is the important devices to divide signal light into different channels. Unfortunately, the most common coupler, directional coupler nowadays, has the worst fabricated tolerance and wavelength dependent of optical property. However, the three waveguides adiabatic coupler is able to solve these problems including the disadvantage of directional coupler. Lithium Niobate is an attractive substrate material with high electro-optics and nonlinearity, which benefits the studies and usage related to active devices to build up a more compact and multi-functional device.
In this work, a three-Ti-diffused-waveguide adiabatic coupler was design and fabricated by stimulated Raman adiabatic passage (STIRAP) method on lithium niobate crystal. In the experiment, the tolerance from the fabrication error of the middle waveguide could reach to 0.6 μm. In addition, the deviation of the crossover-state division ratio was less than 7.5 % for TM polarization as well as 4 % for TE polarization in the operating wavelength range of 1495 nm to 1600 nm.
However, the prior experimental result, the complete energy coupling/ transferring, didn’t follow the design properly, which could be caused by some issues, such as a initially excited and unexpected mode and unwanted coupling effect between two sides waveguides are also discussed. In order to deal with and analysis different waveguide parameters in a three-waveguide adiabatic coupler, a commercial software, BeamPROP, is utilized to simulate and develop the designed parameters, and prove that the design is comparable with others research works. In the future, the new design will be kept improving and fabricating. |
