Phase-change Materials in Multifunctional Reconfigurable Metasurfaces

Metasurfaces, 2D periodic subwavelength electromagnetic resonant structures, enable diverse optical responses in ultrathin geometries. By integrating phase-change materials (PCMs) with optically or thermally tunable material properties into the unit cell geometries, multiple functionalities can be achieved in a single reconfigurable device. However, the extra degrees of freedom offered by PCMs also presents a difficulty, especially since each state of the PCM requires a unique combination of multiple resonances to achieve a desired functionality. To this end, multi-objective optimization algorithms offer the possibility to directly inverse design reconfigurable devices by enabling multiple functionalities to be simultaneously optimized. These devices usually consist of counterintuitively complicated structures that provide novel resonance mechanisms.