分色光柵的設計製作之研究

Abstract

在單片式液晶投影顯示系統中，利用彩色濾光片作為分光元件是主要的方式，濾光片之穿透效率不高再加上孔徑比率的關係，使得整體效率不超過30％，這是濾光片的最大缺點，而且由於濾光片為穿透式會使系統有發熱的問題。 利用繞射光柵作為單片式投影系統的分光元件稱為分色光柵法，以反射式光柵加上微透鏡代替濾光片。由於所設計之分色光柵的光柵週期已經小於可見光波長，因此理論上必須以向量繞射理論作為分析的基礎，本論文我們使用嚴格耦合波理論來分析一維表面刻紋型光柵。 在光柵的設計上，主要是決定符合設計要求的光柵參數，製作上由於光柵線寬十分細小，我們使用電子束微影技術來製作光柵。根據設計的光柵參數，我們製作出四階表面刻紋型光柵，最小線寬達到0.15μm。最後對光柵繞射效率量測的結果我們證明出嚴格耦合波理論的正確性。

In the single-panel liquid crystal projection system, the color filter is the common device used for separating light. Because of the low transmitted efficiency of the color filter, the total efficiency of the system is less than 30%. And the transmitted filter has the problem of heat dispersing in the system. Using diffraction gratings for separating light is called the Color Grating Method. This method uses the reflected grating and micro lens instead of the filter. We analyze the one-dimensional surface relief grating by the vector diffraction theory, this is because the line-width of the grating is same order of magnitude as the wavelength of light. The theory is also called the rigorous coupled-wave theory (RCWT). We design the color grating by determining parameters of the grating and an optimization program by the RCWT is made. The line-width of designed gratings is so small that we made them with E-beam lithography techniques. In this paper, we have made four-level gratings with line-width about 0.15um. Finally, we measure the diffraction efficiency of the grating and show that the RCWT is correct.