All‐Optical Modulation with Dielectric Nanoantennas: Multiresonant Control and Ultrafast Spatial Inhomogeneities

The transient optical response of multiresonant all-dielectric nanoantennas via a combination of broadband ultrafast reflectivity experiments and nonlinear optics nanoscale modeling is studied. Ultrafast all-optical control of the reflectivity is demonstrated in variably sized Al.18Ga.82As nanoantennas over four distinct Mie resonances (including Fano-like resonances), spanning a broad spectral range, from the red to the near-infrared. A spatially inhomogeneous dynamical model, which accounts for diffusion of the photogenerated carriers inside the semi- conductor, is introduced and exploited to isolate the physical phenomena leading to the overall transient response, namely, Drude plasma formation and Pauli blocking following band filling and thermo-optical effect. The results pave the way to the development of multiwavelength all-optically reconfigurable filters for next- generation ultrafast add/drop multiplexing.