We report electrically tunable nonlinear optical metasurfaces for Second Harmonic Generation (SHG) based on coupling of intersubband transitions with plasmonic nanocavity. In the structure, conversion efficiency, spectral bandwidth, and local nonlinear phase of SHG can be controlled by the nonlinear response of the constituent meta-atoms. Experimentally, we demonstrate over 2900% of SHG intensity modulation depth, SHG beam diffraction, and SHG beam steering by applying electrical bias voltages. In addition, we propose a new meta-atom structure with full 2π phase tunability, which can be used to construct electrically tunable nonlinear flat optics.
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