Light with a complex amplitude structure has been successfully investigated in fundamental and applied optical sciences. Mature devices such phase modulating spatial light modulators (SLM) have allowed a myriad of experimental findings in classical as well as quantum optics. However, state transformations that are more complex than simple phase manipulation are still hard or even impossible to realize.
We show that controlled scattering of structured light can be seen as a novel tool to achieve transformations, which haven’t been possible before. By adapting recently developed techniques to control a complex, random scattering process and using a feedback signal, we demonstrate for example how an appropriate phase front shaping can lead to a programmable, custom-tailored mode sorting. We are able to sort up to 7 different orbital angular momentum (OAM) modes with accuracies of up to 98% to arbitrarily chosen spots and verify the coherence between the sorted positions, an essential feature for future applications in quantum experiments. Additionally, we successfully demonstrate the sorting of more complex light modes, such as superpositions of OAM modes and different p-modes, modes with different radial structure, a task which was not demonstrated before. We also investigate the possibility to send structured light modes through otherwise opaque material and test multi-mode fibers as scattering devices to increase transformation efficiencies. Our findings can be seen as first step to use a controlled coherent scattering process as a novel tool for complex transformations of structured light.
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