Terahertz Self-Induced Dynamic Slow-Light Behavior in Metasurfaces

Dynamically reconfigurable metasurfaces are complex to realize because they require exotic materials, external stimuli, or both. However, with the advent of intense THz transients, these conventional preconditions can be bypassed. Strong THz fields are capable of invoking modulation of the electronic configuration in materials through impact ionization. In this context, we report the diligent intertwining of strong THz field-induced nonlinearities and the structural interactions of near-field coupled metastructures. We experimentally demonstrate a well-established metal-on-silicon metasurface framework to achieve reconfigurability that is devoid of any exotic materials or external stimuli. Aided by meta-geometry, intense THz transients modify the dispersion of the silicon substrate, leading to self-induced nonlinear modulations in conductivities. Altering the conductivity through impact ionization results in dynamically reconfigurable electromagnetically induced transparency (EIT) effects in a self-sustained manner, controlling the slow-light characteristics (group delay and the group velocity) by more than 6 times. These outcomes could potentially enable versatile applications in upcoming 6G technologies and on-chip silicon-based integrated photonics.