Observation of synthetic moving effect in metamaterials

When light propagates through a flowing transparent fluid, the refractive index it experiences depends on its propagation direction relative to the flow direction. This leads to different phase delays for light traveling along or against the flow. The moving effect, which results from the cross-coupling between electric and magnetic responses in a specific way, is only detectable over a considerable distance within the moving medium, because the fluid's velocity is much smaller than the speed of light c in realistic systems. In the context of metamaterials - artificial subwavelength structures - it may be possible to manipulate electromagnetic fields to mimic the moving medium without physical motion. Here we demonstrate a passive metamaterial that achieves a significant synthetic moving effect. The metamaterial is composed of artificial metallic structures and gyromagnetic materials, and is meticulously designed based on symmetry and electromagnetic considerations to achieve significant pure bianisotropic moving coupling. Our experiment reveals for the first time a gigantic moving response of the metamaterial with an effective velocity reaching 0.3c. The inherent strong non-reciprocity of this moving response opens the door to a variety of photonic devices, like polarization-independent gyrators and isolators.