Programmable Dual‐Mode Ultrafast All‐Optical Switching via Symmetry‐Broken Plasmonic Metasurface

ABSTRACT All‐optical switches are fundamental to high‐speed information processing, yet their operational speeds are typically constrained by intrinsic material relaxation processes. Here, we demonstrate that the temporal trajectory of an ultrafast all‐optical switch can be deterministically programmed by pump polarization within a symmetry‐broken plasmonic metasurface. Femtosecond pump‐probe measurements identify two reversible operational regimes within a single meta‐atom, spanning a sub‐picosecond fast mode of 237 fs and a picosecond‐scale slow mode of 3.05 ps. A self‐consistent multiphysics framework, which couples electromagnetic field localization, nonequilibrium electron‐lattice energy exchange, and transient Drude renormalization, reveals that pump polarization dictates the nanoscale topology of optical absorption, thereby selectively activating distinct microscopic dielectric modulation pathways. Under one polarization state, absorption is strongly confined to nanoscale tips, triggering a localized, electron‐dominated nonequilibrium response that enables switching on a sub‐picosecond timescale. In contrast, orthogonal pumping redistributes energy toward extended regions of the meta‐atom, suppressing the tip‐confined electronic channel and promoting a lattice‐assisted relaxation process. These findings establish polarization‐controlled spatial mode engineering as a general principle for programming ultrafast optical dynamics, paving the way for reconfigurable photonic devices with in situ tunable temporal functionality.