Tunable Metasurface Inverse Design for 80% Switching Efficiencies and 144° Angular Deflection

Abstract

Tunable metasurfaces have demonstrated the potential for dramatically enhanced functionality for applications including sensing, ranging and imaging. Liquid crystals (LCs) have fast switching speeds, low cost, and mature technological development, offering a versatile platform for electrical tunability. However, to date, electrically tunable metasurfaces are typically designed at a single operational state using physical intuition, without controlling alternate states and thus leading to limited switching efficiencies (<30%) and small angular deflection (<25°).Here, we use large-scale computational "inverse design" to discover high-performance designs through adjoint-based local-optimization design iterations within a global-optimization search. We study and explain the physics of these devices, which heavily rely on sophisticated resonator design to fully utilize the very small permittivity change incurred by switching the liquid-crystal voltage. The optimal devices show tunable deflection angles ranging from 12°to 144°and switching efficiencies above 80%, exhibiting 6× angular improvements and 6× efficiency improvements compared to the current state-of-the-art.

Tunable Metasurfaces: The Path to Fully Active Nanophotonics

“…Adapted with permission. [ 112 ] Copyright 2020, American Chemical Society. d) Schematic of beam switching between nematic and isotropic phase LCs.…”

“…[ 111 ] Using an computational inverse design method, beam steering at a working wavelength of 1550 nm of up to 114°, with diffraction efficiency into the ±1 orders of 78% between the on and off states, has been proposed (Figure 4b). [ 112 ] To ensure that the grating structures exhibits the desired beam switching into the ±1 diffraction orders with high efficiency, an adjoint‐based optimization method was used for the inverse design.…”

Intelligent designs in nanophotonics: from optimization towards inverse creation

“…Furthermore, for a systemically design of tunable meta-gratings depicted in Fig. 7 (d), Chuang [89] developed a combination framework comprised of the adjoint-based local-optimization with a global-optimization search (i.e., PSO). Here, the liquid crystal (LC) was aligned perpendicular to TE-mode electric fields once the voltage turned on, while the LC became parallel to TE-mode on the condition of voltage-off, thereby maximizing the effective refractive-index change of the LC.…”

Fundamental limits to multi-functional and tunable nanophotonic response

“…We consider periodic grating structures with the active designable medium comprising a liquid crystal (LC). (More realistic models with a LC filling a patterned material such as silicon can be similarly modeled [80].) For a period Λ and grating thickness L (as shown in the top of Fig.…”