In recent years, there is a growing demand on lightweight optical components for novel applications like augment reality. The project studied fundamental properties of optical nanostructured surfaces, so called metasurfaces, with potential applications in holography and imaging. During the project, we focused our research on the development of nonlinear metasurfaces for functional elements, like nonlinear holograms and nonlinear metalenses. Here, nonlinear optical metasurfaces means that the used systems will transform the wavelength of the light during the interaction. Within our studies, we investigated the possibilities to increase the information capacity of metasurface holograms consisting of ultrathin layers of nanostructured materials. Therefore, new design algorithms and suitable structure design of the unit-cells were developed. Such algorithms are necessary for obtaining high-quality holographic images and information recovery from the metasurfaces when they are illuminated by particular light states.
Furthermore, we studied the performance of plasmonic, hybrid, and purely dielectric metasurfaces for nonlinear light conversion. In such a way, the illuminating light at a particular frequency can be converted to two or three times the frequency, allowing to go from near-infrared light to the visible. For that, we developed a concept that can tailor the spatial phase of this conversion process, which is mandatory for nonlinear beam shaping and holography. First, metasurfaces were fabricated and tested for their optical performance. With some impressive experiments, we were able to show for the first time some imaging of objects by a nonlinear metalens, which led to the conclusion that the traditional lens equation for linear ray optics can be modified to include nonlinear optical effects.
Another part of the project studied the potential of active materials for dynamically tunable or switchable optical metasurface holograms. Such metasurfaces can reveal different information by externally stimulated by some trigger. We showed that chemical processes, as well as temperature, can be used to obtain such behavior when particular materials are combined.
Finally, we proved that optical metasurfaces can act as high numerical aperture lenses for optical trapping in liquid environment. For that we demonstrated metasurface lenses that can trap particles and transfer orbital angular momentum to particles. Such metalenses are easy to integrate into microfluidic systems.
The project also tested new concepts of topological photonic systems, in particular topological photonics crystals for light guiding and manipulation. These systems have to potential to be robust against fabrication tolerances and can be integrated in optical chips for diverse applications.
