High-Q Active Metasurfaces Enabled by ITO Integration

In this talk, we report designs of active metasurfaces that dynamically control the wavefront of transmitted or reflected light in the near-infrared wavelength range. Our active all-dielectric transmissive metasurfaces consist of arrays of amorphous silicon localized guided mode resonant (L-GMR) structures, supporting resonances with quality factors ranging from 1,000 to 10,000, depending on the specific design parameters. The dynamically tunable optical response of the designed metasurfaces is achieved by integrating a 5 nm-thin indium tin oxide (ITO) layer into the resonant structure and gating the ITO layer. By introducing asymmetry into the L-GMR structure, we excite localized modes, which exhibit a significant component of the electric field normal to the ITO layer. First, we analyze the performance of the designed metasurfaces in transmission. Our simulations show that this approach yields dynamically tunable phase shift >240^o in transmission with transmittance between 4% and 15%. We observe that ~50% of the incoming light is reflected in the designed transmissive metasurfaces. To attain metasurfaces that exhibit higher optical efficiencies, we explore the performance of the designed asymmetric L-GMR metasurfaces in reflection. We boost the optical efficiency of the reflective L-GMR metasurfaces by introducing a gold back reflector and placing the L-GMR structures at the prescribed distances from gold. Finally, we use the temporal coupled mode theory to interpret the simulation results and establish efficiency limits for the designed metasurfaces.
The designed active metasurfaces can readily be integrated with chip-scale light sources, yielding ultra-compact wavefront shaping devices.