本研究提出一種相位補償方式，使定向耦合器達到百分之百耦合。定向耦合器一定要透過適當的S型彎曲，使波導解耦合，然而非對稱型定向耦合器在S型彎曲的結構下會產生非同步耦合效應，縱使兩根完全相同波導，在彎曲半徑不同時，也會產生非同步耦合效應，進而無法百分之百耦合。藉由變化波導的寬度來調整波導的等效折射率，即使波導到處都沒有相位匹配，但利用相位補償機制，抑制非同步耦合效應，達成百分之百耦合，藉此改善定向耦合器的效能。

A high-performance directional coupler is proposed by utilizing phase compensation. In order to decouple waveguide from others, S-bends are necessary for directional coupler. However, without proper design, asymmetric S-bends are difficult to achieve synchronous coupling. Varying waveguide width changes mode index , which is the way we compensate for phase, inhibit asynchronous coupling and gat a high-performance directional coupler.