Authors:
Margherita Marni
and
Domenico de Ceglia
Affiliation:
Department of Information Engineering, University of Padova, Italy
Keyword(s):
Metasurfaces, Nonlinear Optics, Harmonic Generation, Nanoantennas, Tunable Devices, Nanophotonics, Phase-change Materials.
Abstract:
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 near-infrared 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.
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