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.