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

VO2 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 VO2'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 VO2 all-optical modulation with a dramatically low pump fluence utilizing the composite structure of a self-supported VO2 film on a gold nanoshell grating. Plasmonic hot electrons in the gold excited by femtosecond pulses are injected into the VO2 film and trigger its phase transition, reducing the pump fluence threshold for the structural transformation to only 147.8 mu J/cm2. 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.