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Anisotropic Temporal Metasurfaces for Tunable Ultrafast Photoactive Switching Dynamics

Recent progress in miniaturized photonic devices has promoted the development of metasurfaces for multidimensional manipulation of optical light fields. One significant example is the polarization multiplexing metadevice, which has earned considerable attention because of its low crosstalk and tremendous polarization‐controlled functionalities for numerous applications, such as wavefront steering, holography, and display. Here, a novel metasurface platform is demonstrated for photoactive terahertz switching by encoding the temporal modulation dynamic into the polarization channels. Coupled plasmonic resonators with four‐fold symmetry are utilized to exhibit an isotropic plasmon‐induced transparency analog resonance. Unlike typical optically tunable metamaterials that are limited to a single switching speed, this temporal modulation is multiplexed into two sets of polarization profiles. Specifically, the switching dynamic can be alternated between a quasi‐steady state with a recovery time larger than 2 ns and an ultrafast transient state with a recovery time of <25 ps in the orthogonal polarization channels. This extraordinary performance is attributed to the high contrast in crystallinity between two photoactive islands embedded in one‐unit cell. The long‐standing bottleneck of invariant switching dynamics in all‐optical metadevices is addressed, which provides a new paradigm for the design of future switchable metamaterial devices.