Nonlinear interactions and wavefront manipulation using nonlocal silicon metasurfaces

Despite the undeniable importance of silicon in the semiconductor industry, its nonlinear optical properties have not been fully exploited. We combine the rotational symmetry of the meta-atoms and the Pancharatnam–Berry principle to enable the generation of the fundamental, second, and third harmonics, as well as polarization and wavefront manipulation in silicon metasurfaces. Both the surface and bulk electric field distribution are enhanced, leading to the corresponding enhancement of the surface and bulk contributions of the nonlinear second-order polarization beyond the electric dipole approximation. We experimentally realize the second harmonic and sum-frequency generation in such silicon metasurface in the visible wavelength range.