Bifunctional Spatiotemporal Metasurfaces for Incident Angle-Tunable and Ultrafast Optically Switchable Electromagnetically Induced Transparency.

Advances in tunable metamaterials/metasurfaces facilitates their utilization in novel optical components, and lead to many breakthroughs in light tailoring by giving birth to diverse spatiotemporal dynamics. In the ascendant field of terahertz (THz) photonics, the ultrafast modulation is the fundamental process of technological advancements in high-speed wireless communications, sensing, and imaging. However, the current research efforts have been mainly devoted to studies of single functionality under the control of one stimulus, which has plateaued in terms of innovative new features. Here, building on the incident angle-induced C symmetry breaking of split ring pairs, we experimentally demonstrate extremely versatile, ultrafast THz switching behaviors at continuously alterable resonant states. The direction-controlled resonance hybridization provides another excellent degree of routing freedom, owing to its robustness, simplicity, and wide tunability. By leveraging such virtues, single LC mode and EIT-like resonance under normal and oblique incidence conditions are both effectively switched-off by means of photon injection. Considering the ultrashort lifetime of free carriers in MoSe crystal, the corresponding transient dynamics show an ultrafast recovery time within 700 ps. The strategy proposed here is a viable pathway for multidimensional THz wave manipulation, which gears up a crucial step for diversified functionalities in deployable metaphotonic devices.