Nonlinear Chiral Meta-Mirrors: Enabling Technology for Ultrafast Switching of Light Polarization.

Photonic nanostructures that realize ultrafast switching of light polarization are essential to advancements in the area of optical information processing. The unprecedented flexibility of metasurfaces in light manipulation makes them a promising candidate for active polarization control. However, due to the lack of optical materials exhibiting a fast as well as large refractive index change, photonic metadevices capable of ultrafast polarization switching remain elusive. Here, an ultrathin nonlinear chiral meta-mirror consisting of an array of amorphous silicon (α-Si) split-ring resonators on top of a silver backplane is demonstrated as a feasible platform for picosecond all-optical polarization switching of near-infrared light at picojoule-per-resonator pump energies. This success was made possible by the high-quality-factor resonances of the proposed meta-atoms that enable the mirror to exhibit strong chiro- and enantioselectivity. Experimental results confirm that our meta-mirrors can be used to facilitate high-speed and power-efficient polarization-state modulators.