Topological transformations of speckles

Deterministic control of coherent random light is highly important for information transmission through complex media. However, only a few simple speckle transformations can be achieved through diffusers without prior characterization. As recently shown, spiral wavefront modulation of the impinging beam allows permuting intensity maxima and intrinsic +/- 1-charged optical vortices. Here, we study this cyclic-group algebra when combining spiral phase transforms of charge n, with D-3- and D-4-point-group symmetry starlike amplitude modulations. This combination allows for statistical strengthening of permutations and controlling of the period to be 3 and 4, respectively. Phase saddle points are shown to complete the cycle. These results offer new tools to manipulate critical points in speckles. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement