基於 Fresnel 繞射原理的深度資訊辨識技術

Abstract

在本篇論文中,本研究提出一種可獲得深度資訊的光學成像系統,利用不同物 距的光源,在不同位置聚焦後,經過尺寸為微米等級的微小孔洞產生繞射的發散程 度將會有所差別,可藉由量測在感光元件上的光束寬來判斷。 此系統相對於其他可獲得深度資訊的光學成像系統的優點為不需額外發射微 波,移動載具和複雜的後端運算,並且在長物距下(公里等級),聚焦點相差微米 等級時仍能作用。模擬時以傅立列光學中的 Fresnel 繞射原理為基礎,搭配 Matlab 軟體來建構此系統的模擬模型來驗證次光學深度辨識系統。 在模擬中選擇了光源為單顆點光源,以及二維正方形非同調光源,相當於模擬 了光源為完全同調(coherent)與完全不同調(incoherent)的情形,取樣光波發散 資訊的孔洞則使用了幾何形狀為圓形和矩形的圓形針孔與單狹縫。 並且藉由改變模擬中各項元件的參數來預測繞射圖形變化,如調整單狹縫與 圓形針孔孔徑的大小,觀察面的距離,透鏡的焦比值(f-number)大小,觀察繞射 圖形變化的趨勢,以及分析以上參數的改變如何影響兩不同物距的光源,經過孔 洞繞射後在感光元件上的光束寬大小,提供建議如何設計實驗的相關光學元件。

This thesis presents an innovative optical imaging system which can detect the depth information of objects in the same time. It utilizes the wave property of light that light from different object has different divergence after the focus and this difference can be measured by adding an aperture to diffract the light, which means analyzing the spot size on the charged-coupled device (CCD). Advantages of this system compared to other depth-detecting optical imaging systems are no need to emit extra microwave, move vehicle, and conduct complex back end calculating. This system can work under the condition that objects are in long distance (kilometer scale). Numerical simulation is constructed in Matlab software and the central idea is based on the Fresnel diffraction theory. This thesis simulates light sources as point source and two dimensional incoherent square light, equally completely coherent and incoherent, aperture shape as single slit and circular pinhole. By adjusting the variables of optical elements in simulation, diffraction pattern can be predicted. Relation between diffraction pattern and diameter of circular pinhole and single slit, distance between CCD and aperture and f-number of lens are discussed. In the end, suggestions about how to design this system are proposed.