Harmonic information transitions of spatiotemporal metasurfaces

Facilitated by ultrafast dynamic modulations, spatiotemporal metasurfaces have been identified as a pivotal platform for manipulating electromagnetic waves and creating exotic physical phenomena, such as dispersion cancellation, Lorentz reciprocity breakage, and Doppler illusions. Motivated by emerging information-oriented technologies, we hereby probe the information transition mechanisms induced by spatiotemporal variations and present a general model to characterize the information processing capabilities of the spatiotemporal metasurface. Group theory and abstract number theory are adopted through this investigation, by which the group extension and independent controls of multiple harmonics are proposed and demonstrated as two major tools for information transitions from the spatiotemporal domain to the spectra-wavevector domain. By incorporating Shannon's entropy theory into the proposed model, we further discover the corresponding information transition efficiencies and the upper bound of the channel capacity of the spatiotemporal metasurface. The results of harmonic information transitions show great potential in achieving high-capacity versatile information processing systems with spatiotemporal metasurfaces. Metamaterials: Heightened harmonics from moving metasurfaces The generation of light harmonics by rapidly-changing metasurfaces could provide exciting new methods of information processing. Metasurfaces made from metal or semiconducting nanostructures have opened up new ways of manipulating electromagnetic waves, but most are static in nature. More recently, spatiotemporal metasurfaces have emerged, in which the 'meta-atoms' that affect the waves can be rearranged periodically, through electrical or mechanical forcing. Now, Tie Jun Cui and co-workers at Southeast University in Nanjing and Peking University in Beijing have explained how several useful information transitions can be induced by spatiotemporal metasurfaces. Through a theoretical model and a proof-of-principle demonstration with microwaves, the researchers show how spatiotemporal metasurfaces can generate multiple harmonics from incoming waves. These harmonics represent processed information that could benefit new technologies such as intelligent computational imaging and sixth-generation (6G) wireless networks.