Nonreciprocal spatio-temporal modulated metasurfaces*

Spatio-temporal modulated metasurfaces (STMMs) are dynamic two-dimensional arrays of sub-wavelength resonators with arbitrary reflection amplitude and phase reconfigurability, and have the potential to revolutionize fundamental and applied photonics. Just as their static counterparts, STMMs can also enable arbitrary wave-front engineering with the key advantage of on-demand reconfigurability and control of the frequency and momentum harmonic contents of scattered waves. In this talk I will report our recent theory and experimental advances in STMMs for dynamical wave-front shaping and nonreciprocal propagation of free space electromagnetic waves. Our experimental measurements reveal on-demand wave-front control of frequency conversion processes. We also demonstrate maximum violation of Lorentz reciprocity in both beam steering and focusing due to nonreciprocal excitation of surface waves. We develop an analytical generalized Bloch-Floquet theory valid for arbitrary modulations, providing excellent agreement with the experiments.