Dielectric metasurfaces for switchable nonlinear optics

Dielectric nanostructures are cherished because of their great potential for low-loss optical devices. Achieving strong optical resonances in dielectric nanostructures is the key to realizing practical dielectric metadevices. In particular, the exploration of new mechanisms for high quality (Q) factor resonances in dielectric architectures provides the basis for actively tunable responses and nonlinearities. In this work, we study the switchable optical responses from dielectric/plasmonic hybrid systems and the nonlinearities in pure dielectric nanostructures supporting optical resonances associated with the bound states in the continuum (BICs). First, we show that, under optical excitations, hybrid metasurfaces based on a dielectric nanoantenna array of active materials (such as silicon (Si) and zinc oxide (ZnO)) on a plasmonic (e.g., silver (Ag)) backplane exhibit broadly tunable topological properties. Accordingly, enormously strong polarization manipulation of near-infrared light in the vicinity of the topological features is observed. Second, we study the efficient second harmonic generation (SHG) from asymmetric lithium niobate (LN) metasurfaces. Third, based on the large Kerr nonlinearities of silicon, we explore the nonlinear chiroptical response from a planar Si metasurface supporting high Q-factor guided mode resonances (GMRs) at near-infrared wavelengths. Fourth, leveraging the momentum-space polarization vortices observed in photonic structures, we investigate the switchable and nonlinear optical vortex generation from Si photonic crystal slabs. Our work shows that dielectric nanostructures which support high-Q resonances via careful nanoengineering can serve as a transformative platform for active and nonlinear photonics.