All‐Dielectric High‐Q Dynamically Tunable Transmissive Metasurfaces

Active metasurfaces, which are arrays of actively tunable resonant elements, can dynamically control the wavefront of the scattered light at a subwavelength scale. To date, most active metasurfaces that enable dynamic wavefront shaping operate in reflection. On the other hand, active metasurfaces operating in transmission are of considerable interest as they can readily be integrated with chip-scale light sources, yielding ultra-compact wavefront shaping devices. Here, designs for all-dielectric low-loss active metasurfaces which can dynamically manipulate the transmitted light wavefront in the near-infrared wavelength range are reported. The active metasurfaces feature an array of amorphous silicon (a-Si) pillars on a silica (SiO₂) substate, which support resonances with quality factors (Q-factors) as high as 9800. The high-Q resonance dips observed in transmission can be transformed into transmission resonance peaks by positioning a-Si pillar resonators at a prescribed distance from a crystalline Si substrate. The design of metasurface geometry with realistic interconnect architectures that enable thermo-optic dynamic beam switching with switching times as low as 7.3 µs is reported. Beam switching is observed for refractive index differences between neighboring metasurface elements as low as 0.0026. It is shown that the metasurface structures with realistic interconnect architectures can be used for dynamic beam steering.