被動式雷射光斑之模擬和量測分析

The Study of Simulation and Measurement of Objective Laser Speckles

周民俊(Min-Chun Chou)

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(2011年)

https://doi.org/10.6841/NTUT.2011.00474

摘要

光斑（speckle）現象是所有使用同調光源的光電成像系統的共同問題，從全像術到現代的雷射投影技術中，最終的成像都因含有光斑使得影像品質降低，因此減低光斑的影響成了長久以來此一領域的共同目標。也因此，正確地評量同調影像中光斑現象的方法不僅可以提供成像系統客觀的比較參考，更可以為抑制光斑的方法提供正確的依據。評估光斑影響程度的參數，一般為光斑對比值（speckle contrast），它是影像中的光強平均值和標準差的比值，然而擷取影像時各項參數會造成光斑對比值的差異，例如入射光的功率、擷取光斑影像的系統參數（放大率，CCD像素大小），和偏極片的使用等。
本論文之目的在於釐清過去文獻中光斑影像的量測參數，期望能建立一個合理的被動式光斑量測方法，被動式光斑量測指的是量測是不使用透鏡成像的光斑量測技術。研究的數值模擬中，我們發現入射光的最大訊號值和CCD像素飽和值的比必須在0.09~1.3之間；而光斑大小和CCD像素大小的比必須在16/5之上擷取的影像才能提供正確地光斑對比值。然而從實際的實驗結果，我們發現入射光的最大訊號值和CCD像素飽和值的比僅能約略等於1。此外，本研究主要針對單一光強的光斑影像進行研究，未來將針對灰階影像進行進階的研究。

關鍵字

光斑 ； 光斑對比值 ； 繞射光學

並列摘要

For all optical imaging systems using coherent light source, speckles always occur in the final display, and degrade the image quality. From holography to laser projection systems, the reduction of the influence of speckles has been a key issue for all the research in the field. Therefore, evaluating correctly the method of speckle phenomenon in coherent image can not only provide the imaging system with an objective suggestion, but also provide correct basis for the method of reducing speckle. It is of importance to quantize or evaluate the influence of speckles in an image. The most frequently-used parameter to evaluate the speckles is speckle contrast, which is defined as the ratio of the intensity average and the standard deviation. However, each system parameter will affect the speckle contrast of the displayed image, e.g. the power of the incidence light, the system parameter for capturing the speckle images (magnification and the pixel size of CCD), and the use of the polarizer, etc.
The purpose of the thesis is to clarify the parameter of the measurement of the speckle images in previous literatures. We expect to build a reasonable method for the measurement of objective speckle. The measurement of objective speckle means the measurement technology of speckle without a lens. In the value simulation of our study, we found the ratio of the maximum signal value of incident light to the saturation value of CCD must be between 0.09~1.3. The captured image can provide correct speckle contrast when the ratio of speckle size to CCD pixel size is above 16/5. However, from the actual experimental results, we found that the ratio of the maximum signal of incident light to the saturation of CCD can only be about 1. In addition, our study mainly focuses on the speckle image of single intensity to carry on researches, and we will focus on gray image to proceed advanced researches in the future.

並列關鍵字

Speckle ； Speckle contrast ； Diffractive optics

參考文獻

[1] P. Janssens and K. Malfait, "Future prospects of high-end laser projectors," Proc. SPIE, vol. 7232, 2009, p. 72320Y.

[2] J. W.Goodman, Speckle phenomena in optics: theory and applications. Roberts & Company, 2007.

[3] J. I. Trisnadi, "Speckle contrast reduction in laser projection displays," Proc. SPIE, vol. 4657, 2002, pp. 131-137.

[4] J. C. Dainty, editor. Laser Speckle and Related Phenomena. Springer Verlag, 1975.

[5] J. W. Goodman, "Some fundamental properties of speckle," J. Opt. Soc. Am., vol. 66, 1976, pp. 1145-1150.