Nonlinear Nanostructures

Using the best materials available is crucial to the development of photonic devices. Nevertheless, there are additional mechanisms, such as nanostructuring and local-field effects, that one can implement to control and enhance the optical properties of materials. Within this research direction, we are exploring such mechanisms.

Local-field effects arise when neighbouring atoms and molecules change the local electric field driving an atomic transition. The modified local field is, in turn, responsible for the optical properties of the medium. The contribution to the local field at an emitter site from its immediate neighbours can also be electrostatically controlled by nanostructuring. Further, one can explore nanopatterning of metal, dielectric or semiconductor structures to form metasurfaces exhibiting resonant behaviour. These three mechanisms of control and enhancement of optical response could be combined with the design and material selection to achieve record-high nonlinearities and to enhance specific optical properties in patterned integrated photonic structures.

Much progress has been made by our group in collaboration with other researchers to establish the foundations of this research direction. We explored, both theoretically and experimentally, collective resonances of metasurfaces, which are 2D arrays of metamolecules made of metal and defined on top of a dielectric substrate, to enhance linear and nonlinear optical responses. Moreover, our group has developed a simple analytical model based on an equivalent RLC circuit, capable of accommodating a variety of metamolecules of different shapes and materials. Metasurfaces with tailored collective resonances hold promise for enhanced optical nonlinearities, and our simple analytical model provides additional means for tailoring nonlinear optical responses of structural elements of such arrays of metamolecules.