Metasurfaces composed of designed nanoresonators arranged in a plane offer unique opportunities for controlling the properties of light fields. Such metasurfaces can e.g. impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front with high transmittance efficiency. However, most metasurfaces realized so far were passive and linear, and their optical response was permanently encoded into the structure during fabrication. Recently, a growing amount of research is concentrating on active metasurfaces, specifically on the integration of emitters and optical nonlinearities, as well as on obtaining dynamic control of their optical response.

This talk will provide an overview of our recent advances in nonlinear, tunable and light-emitting metasurfaces.

In particular, we have studied spontaneous and stimulated emission from metasurfaces incorporating various types of emitters, as well as second harmonic generation and spontaneous parametric downconversion in metasurfaces made of, or containing, materials with a high second-order nonlinear susceptibility. Our results show that both the directional, spectral and/or polarization properties of the generated light can be tailored by the metasurface design.

For dynamic tuning of the metasurface response, we make use of the strong spectral dispersion associated with the resonant optical response of the metasurfaces in combination with the sensitivity of the resonance properties on the refractive index of the dielectric environment or constituent material of the individual nanoresonators. Specifically, by integrating the semiconductor metasurfaces with nematic-liquid-crystals, responsive polymers, or two-dimensional semiconductors, we can dynamically tune their linear-optical response in the near-infrared spectral range using various stimuli as control parameters.