Hot-Electron-Assisted Femtosecond All-Optical Modulation in MXene-Based Heterostructures

All-optical modulators are essential for photonic circuits, yet their limited nonlinearity and high fabrication complexity have hindered the scalable implementation. In this work, we present a lithography-free, ultracompact heterostructure based on Ti₃C₂T_x MXene, enabling plasmon-driven femtosecond modulation of both visible and near-infrared light with a broadband response and low energy consumption. Upon photoexcitation, surface plasmon resonances facilitate the generation of hot electrons, which are subsequently relaxed by injection into a thin electron-accepting indium tin oxide layer in an ultrafast process, functioning as an all-optical switch. By optimization of the hot-carrier excitation and relaxation pathways, a switching time as low as 126 fs and a large modulation depth of up to 21.6% are realized. This work introduces a cost-effective and facile high-performance all-optical platform, holding great promise for future on-chip nanophotonics.