Speckle contrast of the sum of N partially correlated speckle patterns.
In this paper a general method is presented for calculating the theoretical speckle contrast of a sum of correlated speckle patterns, motivated by the need to suppress the presence of speckle in laser projection displays. The method is applied to a specific example, where correlated speckle patterns are created by sequentially passing light through partially overlapping areas on a diffuser, before being projected onto a screen. This design makes it possible to find a simple expression for the correlation between speckle patterns. When the set of correlations involves symmetry, it is shown that the expression for the speckle contrast becomes simpler. The difference in performance between discretely and continuously varying speckle patterns is also investigated. In an example with speckle reduction by a rotating sinusoidal grating, it is found that continuous variation gives a speckle contrast that is 0.61 times the contrast obtained by discretely summing the maximum number of independent patterns.
Department of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim, Norway. sigbjoe@alumni.ntnu.no
Sigbjørn Vindenes
SV
Egge
Ulf
U
Österberg
Astrid
A
Aksnes