Nonlinear Anisotropic Dielectric Metasurfaces for Ultrafast Nanophotonics

We report on the broadband transient optical response of anisotropic, amorphous silicon nanobricks that exhibit Mie-type resonances. A quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely, two-photon absorption, free-carrier relaxation, and lattice heating. We reveal a set of operating
windows where ultrafast all-optical modulation of transmission is achieved with full return to zero in 20 ps.