Anisotropic Metasurface for Ultrafast Polarization Control via All-Optical Modulation

The ability to manipulate light polarization at an ultrafast speed is a challenging goal in the field of Photonics: sub-picosecond control of polarization is a fundamental functionality for a variety of applications, including the developement of free-space optical links for robust information encoding. To this aim, an important paradigm consists in employing metasurfaces as platforms which can be reconfigurable by all-optical means, i.e. upon illumination by an energetic femtosecond laser pulse. Here, we present giant all-optical modulations of dichroism in an anisotropic AlGaAs metasurface. An optimized design allows to exploit a sharp extended resonance of the nanostructure in the desired spectral range, where the pump-induced band-filling effect is the dominant process presiding over the ultrafast change of permittivity.