本論文旨在改善定向耦合器在非對稱 S型彎曲架構下的同步耦合效能 本論文設計 一根直線傳播的波導，與固定曲率半徑的 S型彎曲波導，藉由改變直線傳播波導的寬度來匹配彎曲波導的模態折射率 ，使其能達到相位匹配 條件 。 在 此 定向耦合器 是 以 兩個鏡像 S型彎曲組成的 當兩 根波導 模態折射率相同 時 能 使 此定向耦合器達到百分之百的 同步 耦合效果 。

This paper aims to improve the coupling efficiency of directional couplers in an asymmetrical S-bend configuration. The paper designs a straight waveguide and an S-bend waveguide with a fixed curvature radius. By changing the width of the straight waveguide to match the mode index of the curved waveguide, phase matching conditions can be achieved. The directional coupler is composed of two mirrored S-bends, and when the mode indices of the two waveguides are identical, the directional coupler can achieve 100% synchronous coupling efficiency.