Plasmonic Hot-Electron Injection Driving Ultrafast Phase Transition in Self-Supported VO₂ Films for All-Optical Modulation

VO 2 has been widely used in optical modulation devices due to its large change in permittivity across its first-order metal–semiconductor phase transition. People have proved that VO 2 ’s phase transition can be driven by plasmonic hot-electron injection, providing a new approach to realizing ultrafast all-optical devices with a low pump fluence. Here, we report on ultrafast VO 2 all-optical modulation with a dramatically low pump fluence utilizing the composite structure of a self-supported VO 2 film on a gold nanoshell grating. Plasmonic hot electrons in the gold excited by femtosecond pulses are injected into the VO 2 film and trigger its phase transition, reducing the pump fluence threshold for the structural transformation to only 147.8 μJ/cm 2 . With a pump fluence above this threshold, ultrafast phase transition can be triggered within 1 ps, and a high modulation depth of 50% can be achieved. Moreover, an ultrafast modulation with an on–off time of 650 fs can also be achieved using a pump fluence below the threshold. This work may explore new applications of plasmonic hot-electron-driven phase transition in optical modulation devices and configurable devices.