Monolithic LiNbO<inf>3</inf> metasurface for steering and polarization-encoding of second-harmonic generation in the visible

Nonlinear metasurfaces are a key-asset in nanophotonics, given their ability to scale down nonlinear optics to sub-µm thicknesses. To date, they are mainly realized using small-gap semiconductors, which hampers applications in the visible (VIS) range. High refractive-index transparent materials, such as lithium niobate (LiNbO 3 ), could be used to circumvent this limitation [1] , [2] , [3] , but efficient operation in this strategic spectral window is hindered by nanofabrication challenges. Here we show the first monolithic nonlinear metasurface based on LiNbO 3 for second-harmonic generation (SHG) in the VIS range with efficiency comparable to recent work in the near-infrared [3] . By tuning the pump polarization, we demonstrate efficient steering and polarization encoding of SHG, opening novel opportunities for nonlinear meta-optics.