使用負相關影像在雷射光班消除上的研究

Speckle Suppression by Integrated of Fully Developed Negatively Correlated Patterns in Coherent Imaging

朱翊麟(I-Lin Chu)

指導教授 ： 徐巍峰

國立臺北科技大學/機電學院/機電科技研究所/博士(2012年)

摘要

在一個同調光學成像系統中，當物體先成像於作動中的擴散片上，而後便能投影一張已經過光斑抑制的圖形出來。當我們使用一個空間光調變器(SLM) 來取代持續作動的擴散片時，也可以達到消光斑的功用且不需要額外的運動機制。所以把M個隨機相位陣列以特定順序及在特地時間內撥放於空間光調變器上，當播放時間控制於一個檢知器的積分時間內時，我們可以得到一個累加影像強度，此影像強度來自於M個無關連的影像所加總而來，同時此累加影像的相關係數Cf 被有效的降低至1/√M，藉此便能達到光斑抑制的效果。
本篇論文展示了，在理論上和模擬上，當兩個為"完全散射光斑"的基元光斑圖樣被賦予彼此為負相關特性時，我們可以在其加總的圖樣上得到一個被大幅降低的相關係數Cf 。因此我們達到了一個很好的目標，在相關係數位於[-0.3, -0.25]的範圍內所找出的基元圖樣，其疊加10張負相關圖樣後得到的Cf，比相同數量疊加但彼此為非相關的圖樣，數值小了48%以上。
關於負相關的圖樣， 我們可以利用空間光調變器及繞射光學元件來實現它。而且應用範圍可用於抑制光斑雜訊在數位全像術，雷射投影顯示器及全像投影顯示器上，都能得到很有效的結果。

關鍵字

雷射光斑 ； 光斑消除 ； 空間光調變器 ； 完全散射光斑

並列摘要

A coherent imaging system images a frame or an object onto a changing diffuser and projects the resulting pattern which generally contains speckles. Using a spatial light modulator (SLM) as the changing diffuser, the speckles in the pattern are suppressed without the need for any other mechanisms. With M random phasor arrays being displayed in the SLM during the integration time of a detector, a suppression factor (Cf) of speckles, 1/√M, is achievable in the projected pattern, which is the sum of the intensity of M uncorrelated patterns.
This paper shows both theoretically and in simulations that the correlation coefficient Cf of the sum pattern was considerably reduced when two elementary patterns with fully developed speckles were negatively correlated. With the correlation coefficients of the elementary patterns found at the range of [-0.3, -0.25], the Cf of the sum of 10 negatively-correlated speckle patterns was achieving a 48% lower than the Cf of the sum of 10 uncorrelated speckle patterns.
The negatively correlated patterns can be implemented by using spatial light modulators or diffractive optical elements, and are used to suppress speckle noise in digital holography, laser projection display, and holographic display projections with relatively high efficiency.

並列關鍵字

Laser Speckle ； Speckle Suppression ； Spatial Light Modulator ； Fully Developed Speckle

參考文獻

[1] Goodman, J. W., “Some fundamental properties of speckle,” Journal of Optical Society America, Vol. 66, 1145-1150, 1976.

[2] Silverstein, S. D. and M. O’Donnell, “Theory of frequency and temporal compounding in coherent imaging: speckle suppression and image resolution,” Journal of Optical Society America A, Vol. 5, 104-113 (1988).

[3] Goodman, J. W., Speckle Phenomena in Optics: Theory and Applications (Roberts & Co., 2007).

[4] Rojas, J. A. M., J. Alpuente, E. Bolivar, P. Lopez-Espi, S. Vignote, and M. I. Rojas, “Empirical characterization of wood surfaces by means of iterative autocorrelation of laser speckle patterns,” Progress In Electromagnetics Research, Vol. 80, 295-306, 2008.

[5] Iwai, T. and T. Asakura, “Speckle reduction in coherent information processing,” Proceedings of The IEEE, Vol. 84, 765-781, 1996.