We propose all-dielectric metasurfaces that can be actively re-configured using the phase-change material Ge 2 Sb 2 Te 5 (GST) alloy. With selectively controlled phase transitions on the composing GST elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase-change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near-field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta-devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.

The toroidal dipole is a localized electromagnetic excitation independent from the familiar magnetic and electric dipoles. It corresponds to currents flowing along minor loops of a torus. Interference of radiating induced toroidal and electric dipoles leads to anapole, a nonradiating charge-current configuration. Interactions of induced toroidal dipoles with electromagnetic waves have recently been observed in artificial media at microwave, terahertz, and optical frequencies. Here, we demonstrate a quasi-planar plasmonic metamaterial, a combination of dumbbell aperture and vertical split-ring resonator, that exhibits transverse toroidal moment and resonant anapole behavior in the optical part of the spectrum upon excitation with a normally incident electromagnetic wave. Our results prove experimentally that toroidal modes and anapole modes can provide distinct and physically significant contributions to the absorption and dispersion of slabs of matter in the optical part of the spectrum in conventional transmission and reflection experiments.

Split-ring resonators (SRRs) have been the subject of investigation as plasmonic sensors that operate by sensing plasmon resonance shift δλ when exposed to a medium with a refractive index change δn. However, conventional planar SRRs have their plasmon fields spread into the substrates, reducing accessible sensing volume and its sensing performance. Such a limitation can be eradicated with vertical SRRs in which the plasmon fields localized in SRR gaps are lifted off from the substrate, allowing for greatly enhanced sensitivity. Here, we demonstrate the highest sensitivity among reported SRR-based sensors in optical frequencies.

This paper proposes a 1D plasmonic multilayer structure as a high-contrast mid-infrared thermal emitter with three distinct resonant wavelengths. The three resonance modes, based on the localized surface plasmon, provide an omnidirectional thermal emission. The emissivity spectrum reveals high polarization and strongly angle-independent properties. The resonance-assisted emissivity can be as high as 19.5 dB relative to off-resonant sideband emissivity. Such extremely low sideband emissivity makes the proposed plasmonic thermal emitter an efficient, high-contrast emitter, which will be useful for thermophotovoltaic and thermal sensing applications.

We experimentally and theoretically study the interplay between capacitive electric and inductive magnetic couplings in infrared metamaterials consisting of densely-packed three-dimensional (3D) meta-atoms. The meta-atom is made of metal-stress-driven assembled 3D split-ring resonators to exhibit strong bi-anisotropy, where electric and magnetic resonances occur simultaneously. By varying the spatial arrangement of the arrayed meta-atoms, the mutual coupling between meta-atoms dramatically modifies their mode profiles and resultant spectral responses. The corresponding numerical simulations evidently retrieved current densities and magnetic field strengths, as well as the transmittance, to reveal the important resonant behavior in the coupled meta-atom systems. We conclude that the mutual electric coupling between the neighboring meta-atoms plays a crucial role to the scattering behaviors of the bi-anisotropic metamaterials.