以光子晶體的能帶隙概念，選擇具螺旋結構之膽固醇液晶作為探討對象。此薄膜在頻譜特性上會顯現選擇性光散射，可用來設計一種特性猶如電子二極體的光學元件，使特定波長的光能在一個方向上通過，但在反方向上卻無法通過。本文由兩個模型來說明，並以數值模擬來驗證。最後以當作色彩分離器為例，討論將其整合到光機電系統時，可作為色彩分離機構使用。

In the article, the concept of photonic band-gaps (PBGs) is used to design a novel optical component. Among many substances having PBG structures, cholesteric liquid crystals (ChLCs) with periodic helical structures are chosen to discuss their applications.
The selective reflection in the spectral properties of ChLC thin films can be used to design an optical device that permits the propagation of a band of wavelengths in one direction and blocks it in the other, acting as an optical diode (OD) analogous to an
electric diode. In the research, two models are proposed to demonstrate the diode behavior and are verified by the numerical simulations. Finally, two examples to produce a color-separating mechanism used for display projectors are given to discuss the possibility of combing the OD with an opto-mechatronics system. The OD can serve as a color splitter.