The central goal in optical wave control is to manipulate light fields so that they fulfil a certain function, such as for imaging, detection and efficient transmission across complex photonic media. To reach this goal, different techniques have been considered, either for shaping an incoming wavefront or for shaping the medium itself. This talk covers two novel insights for both of these two contrasting approaches and their application to disordered media.
In the first part of this talk I will speak about how to control wave scattering by delicately designing the refractive index of a scattering medium. In particular, I will show how to completely eliminate the highly fluctuating intensity profile inside a disordered material by adding a tailored gain and loss profile to it. The resulting constant-intensity waves in such non-Hermitian scattering landscapes are free of any backscattering and feature perfect transmission even through highly disordered media .
In the second part of this talk, I will present a novel approach for shaping a wave incident on a disordered medium to achieve a focus deep inside of it. This approach is based on a prior measurement of the system's transmission matrix and its derivative with respect to a shift of the target one aims to focus on. I will explain the connection of this novel approach to the concept of "principal modes" and present an experimental realization in the microwave regime .
 Konstantinos G Makris, Andre Brandstötter, Philipp Ambichl, Ziad H Musslimani, and Stefan Rotter. Wave propagation through disordered media without backscattering and intensity variations. Light: Science & Applications 6, e17035 (2017); doi: 10.1038/lsa.2017.35
 Philipp Ambichl, Andre Brandstötter, Julian Böhm, Matthias Kühmayer, Ulrich Kuhl, and Stefan Rotter. Focusing inside disordered media with the generalized Wigner-Smith operator. Phys. Rev. Lett. accepted article; arXiv:1703.07250