Tunable metasurfaces

Abstract

Metasurfaces, composed of arrays of subwavelength nanostructures, offer a powerful means to manipulate light-matter interactions with high precision. While most early designs functioned as static devices, a central challenge is to achieve dynamic control, enabling reconfigurable and adaptive optical functionalities. This thesis develops a comprehensive framework for tunable metasurfaces by exploring three complementary tuning mechanisms, each based on distinct material platforms and physical effects.

The first approach relies on applying an external electric field, which modifies the intrinsic optical properties of Lithium Niobate and consequently enables controlled modulation of its optical response. Amplitude control is achieved through Mie resonances and phase control via high-Q quasi-bound states in the continuum, establishing electrically driven metasurfaces as a versatile platform for active nanophotonics.

The second approach relies on thermo-optic tuning of lithium niobate metasurfaces. By harnessing guided-mode and quasi-BIC resonances, small temperature-induced changes in refractive index are amplified into large spectral shifts. Through Brillouin zone-folding and symmetry-breaking designs, sharp thermal responses are achieved and experimentally validated, confirming the potential of thermal control for high-Q metasurface devices.

The final approach develops all-optical tuning in semiconductor metasurfaces. Ultrafast pump--probe spectroscopy is used to track photo-excited carrier dynamics, which induce a transient Drude response and thereby modulate multipolar resonances and polarisation conversion on femtosecond timescales. This mechanism enables ultrafast control of chirality and nonlinear optical switching.

Together, these results demonstrate electrical, thermal, and optical routes for the dynamic control of metasurfaces, establishing a foundation for reconfigurable flat optical devices. The concepts presented in this thesis open pathways toward adaptive imaging, high-speed communication, quantum photonics, and ultrafast information processing.