Spatially engineered nonlinearity in resonant metasurfaces

Spatial engineering of the nonlinear susceptibility χ 2 in resonant metasurfaces offers a new degree of freedom in
the design of the far-field response of second-harmonic generation (SHG). We demonstrate this by applying
electric field poling to lithium niobate (LN) thin films, which inverts the spontaneous polarization and thus
the sign of χ 2 . Metasurfaces fabricated in periodically poled LN films reveal the distinct influence of the
χ 2-patterning on the spatial distribution of the second harmonic. This work is a first step toward far-field
engineering of SHG in metasurfaces with electric field poling.