以雙繞射光學元件串接組合將繞射圖案作空間擴展之實現

Implementation of Expansion of Spatial Patterns by Use of Cascaded Diffractive Optical Elements

鄭閔中(Min-Chung Cheng)

指導教授 ： 徐巍峰

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2010年)

https://doi.org/10.6841/NTUT.2010.00254

摘要

以繞射光學元件(Diffractive optical element,DOE)產生二維空間影像時， 其影像為遠場之第零階繞射，故繞射影像的大小和產生位置是由波長、元件-成像面距離或透鏡焦距和元件之關鍵(臨界)尺寸(Critical dimension,CD)所決定， 其中以元件之關鍵尺寸為最重要之因素。當繞射光學系統以市售的液晶空間光調變器(Liquid crystal spatial light modulator,LC-SLM)為輸入元件時，其關鍵尺寸偏大，而繞射影像則太小，應用有限。本論文中，我們在LC-SLM(即第一片DOE)後再串接一片DOE,第一片DOE之圖案是電腦輸入，而第二片DOE是固定圖案的。藉由正確的計算，我們可將第一片DOE的繞射圖案由第二片DOE擴展至較大之空間區域，其作用如同二維摺積(Convolution)運算，而非直接將影像放大，因此影像之空間頻率(週期)得以維持不變。這樣的繞射光學系統是用於空間中物體的三維輪廓之測量與重建的應用，本系統不僅滿足該類應用之要求，更因為LC-SLM的使用而提供了多樣的空間圖案和解析度。

關鍵字

繞射光學元件 ； 關鍵尺寸 ； 液晶空間光調變器

並列摘要

When the diffractive optical element (DOE) is used to generate the two-dimensional (2D) spatial image in the far field, the image occur mainly in the zeroth-order. The size and the location of the image is determined by the wavelength, the distance from the DOE to the image plane (or the focal length of the lens), and the critical dimension of the DOEs. When the liquid crystal spatial light modulator as the input element in a optical system, its critical dimension is so large that the diffractive image is too small to be well applied. In this paper, we cascaded another DOE behind the first DOE (realized by LC-SLM), to duplicate the diffraction pattern of the first DOE by the second DOE, which corresponds to a 2D convolution of the diffractive fields of the two DOEs.
By using the cascaded compound DOEs, we can extend the diffraction pattern without reducing the spatial frequency of the image. This diffractive optical system can be applied in the spatial 3-D profile measurement and reconstruction. The advantage of the proposed system include the effective extension of the spatial patterns, the high resolution of the pattern, the flexibility of changing the basic pattern by different DOE, and the low calculation complexity in the design of DOEs.

並列關鍵字

Diffractive optical elements ； Critical dimension ； Liquid crystal spatial light modulator

參考文獻

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