  High-index dielectric nanoparticles have become a powerful platform for
modern light science, enabling various fascinating applications, especially in
nonlinear nanophotonics for which they enable special types of optical
nonlinearity, such as electron-hole plasma photoexcitation, which are not
inherent to plasmonic nanostructures. Here, we propose a novel geometry for
highly tunable all-dielectric nanoantennas, consisting of a chain of silicon
nanoparticles excited by an electric dipole source, which allows tuning their
radiation properties via electron-hole plasma photoexcitation. We show that the
slowly guided modes determining the Van Hove singularity of the nanoantenna are
very sensitive to the nanoparticle permittivity, opening up the ability to
utilize this effect for efficient all-optical modulation. We show that by
pumping several boundary nanoparticles with relatively low intensities may
cause dramatic variations in the nanoantenna radiation power patterns and
Purcell factor. We also demonstrate that ultrafast pumping of the designed
nanoantenna allows unidirectional launching of surface plasmon-polaritons, with
interesting implications for modern nonlinear nanophotonics.
