Study of two-dimensional diffractive optical element for the computed tomographic imaging spectrometer

電腦斷層影像光譜儀(computed tomographic imaging spectrometer﹐CTIS)是一種非掃描式儀器，可以從一個場景中的一張快照中獲得充分的空間與光譜的訊息。只需要幾秒鐘就能顯示出光譜圖，能夠對光波的能量、波長、頻寬等重要特徵進行精確分析，在恆星分類、生物醫學、軍事監測等方面有廣泛的應用。 在本研究中，進行電腦斷層影像光譜儀之二維繞射光學元件(diffractive optical element, DOE)的設計與製作。我們提出對光譜成像系統設計出將影像經由繞射方式產生二維色散所必須之色散片(disperser)，探討二維之繞射光學元件適用於CTIS系統。以二元光學(binary)技術為基礎，開發可對影像產生二維繞射與色散之相位光柵，目的為使二維之各繞射階產生均勻繞射。利用純量繞射理論分析其二維四階金字塔型光柵之繞射效率，並利用光學設計軟體與數值分析軟體進行分析結構深度與繞射效率之關係，實作部份我們利用微影蝕刻製程將二維繞射光學元件完成，接著驗證其光學繞射效率與設計所需求相符合，最後結合影像光譜儀之光學系統以做驗證在聚焦平面陣列(focal plane array, FPA)上產生二維之繞射影像。Computed tomographic imaging spectrometer (CTIS) is a non-scanning instrument which can acquire the spatial and spectral information from the snapshot of a scene. It can display the spectrum in a few seconds and precisely analyze the energy of the light waves, wavelength, bandwith, and other important characteristics. Therefore, it can be widely used in stellar classification, biomedicine, military surveillance, etc. This study consists of the design and production of a two-dimensional diffractive optical element (DOE) for the use of the CTIS. We propose the necessary disperser used for the spectral imaging system through the diffraction of a two-dimensional DOE. And, we discuss the application of the two-dimensional DOE for the CTIS. Based on the technology of binary optics, this study seeks to develop a phase grating which is capable of providing two-dimensional diffraction and dispersion for an image. The purpose is to produce uniform diffraction among the diffraction orders. Scalar diffraction theory is used to analyze the diffraction efficiencies of the two-dimensional four-level pyramid grating. Besides, the optical simulation software and numerical analysis software are employed to analyze the relation between the depth of structure and the diffraction efficiency. In fabrication, we use the lithography and etch processes to implement the DOE and to verify its optical diffraction efficiencies for being consistent with the design values. The final step is the test of the two-dimensional diffraction image produced on the focal plane array (FPA) by means of the optical system of the CTIS.摘要.......................................................I Abstract..................................................II 誌謝.....................................................III 目錄......................................................IV 圖目錄....................................................VI 表目錄....................................................IX 第一章 緒論................................................1 1.1研究背景................................................1 1.2文獻探討................................................2 1.3研究動機與目的..........................................6 1.4論文架構................................................7 第二章 基本理論............................................8 2.1光柵繞射理論............................................8 2.1.1繞射理論簡介..........................................8 2.1.2光柵之特性............................................9 2.1.3光柵形態分類.........................................10 2.1.4相位型光柵繞射效率...................................12 2.2光譜原理...............................................19 第三章 設計與模擬.........................................24 3.1系統簡介...............................................24 3.2光學系統設計...........................................25 3.2.1光譜解析度之分析.....................................25 3.2.2光譜成像系統設計.....................................27 3.3繞射元件設計...........................................30 第四章 元件製作...........................................35 4.1繞射元件製作...........................................35 4.1.1黃光微影技術.........................................35 4.1.2離子蝕刻技術.........................................38 4.2對準鍵的設計...........................................43 第五章 繞射效率量測.......................................47 5.1第一道製作之繞射光學元件量測...........................47 5.2第二道製作之繞射光學元件量測...........................50 5.3二維繞射光學元件量測...................................52 第六章 結論...............................................57 6-1結論...................................................57 6-2未來展望...............................................58 參考文獻..................................................5