Strong Modulation of Absorption and Third-Harmonic Generation in Resonant Metasurfaces based on VO2

Control of linear and nonlinear optical signals is of key importance in a variety of applications, including signal processing, optical computing and energy harvesting, to name just a few. Optical modulation and switching, and more generally tunability in photonic devices, are usually achieved in the visible and nearinfrared range by carrier injection, chemical or mechanical activation, or by deploying materials with large electro-optic or optical nonlinear coefficients. However, these mechanisms are inherently weak and therefore require intense control signals in order to produce significant modulation effects. Here we adopt a nanophotonic solution in which a resonant film of a volatile phase-change material, vanadium dioxide, is inserted between an array of antennas and a metallic backplane. Our design takes advantage of (i) the large refractive-index change of VO2 at its insulator-to-metal transition and (ii) the field enhancements available when the Fabry-Pérot resonance of the film and the plasmonic resonance of the antennas are exited. In response to the VO2 phase transition, not only does our metasurface provide a strong and broadband modulation of linear absorption and reflection but it also shows a drastic variation of third-harmonic generation, with a conversion-efficiency contrast higher than three orders of magnitude.