High-index dielectric nanoparticles supporting a distinct series of Mie resonances have enabled a new class of optical antennas with unprecedented functionalities. The great wealth of multipolar responses has not only brought in new physical insight but also spurred practical applications. However, how to make such a colorful resonance palette actively tunable is still elusive. Here, we demonstrate that the structured phase-change alloy Ge2Sb2Te5 (GST) can support a diverse set of multipolar Mie resonances with active tunability. By harnessing the dramatic optical contrast of GST, we realize broadband (Δλ/λ ~ 15%) mode shifting between an electric dipole resonance and an anapole state. Active control of higher-order anapoles and multimodal tuning are also investigated, which make the structured GST serve as a multispectral optical switch with high extinction contrasts (>6 dB). With all these findings, our study provides a new direction for realizing active nanophotonic devices.

Recent attempts to synthesize hybrid perovskites with large chirality have been hampered by large size mismatch and weak interaction between their structure and the wavelength of light. Here we adopt a planar nanostructure design to overcome these limitations and realize all-dielectric perovskite metasurfaces with giant superstructural chirality. We identify a direct spectral correspondence between the near- and the far- field chirality, and tune the electric and magnetic multipole moments of the resonant chiral metamolecules to obtain large anisotropy factor of 0.49 and circular dichroism of 6350 mdeg. Simulations show that larger area metasurfaces could yield even higher optical activity, approaching the theoretical limits. Our results clearly demonstrate the advantages of nanostructrure engineering for the implementation of perovskite chiral photonic, optoelectronic, and spintronic devices.

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All-dielectric metasurface absorbers are good candidates for realizing near-unity light absorption within subwavelength-thin nanostructures. However, only moderate quality factor (Q-factor, e.g., Q ∼ 10) all-dielectric metasurface absorbers have been demonstrated due to high radiative loss of the supported Mie resonances. Here, we theoretically propose a high-Q crystalline silicon metasurface superabsorber with near-unity absorption in the near-infrared region by utilizing the dipole quasi bound states in the continuum (quasi-BIC) resonances with engineered radiative loss. The designed all-dielectric metasurface superabsorber shows high-Q (∼640) near-unity absorption in the near-infrared region. Moreover, when the superstrate refractive index is different from that of the substrate, the anticrossing behavior of the induced dipole quasi-BIC resonances can be observed in the absorption spectra. This design applies to arbitrary high-refractive-index low-loss materials at various working bands, enabling practical applications of high-Q all-dielectric ultrathin superabsorbers in optical sensing, optical filtering, and photon detection.

Strong near‐infrared absorption in ultrathin semiconductor layers is essential for increasing the speed and efficiency of photocarrier extraction in optoelectronic devices. However, the absorption of a free‐standing ultrathin film can never exceed 50% in principle. In this article, an all‐dielectric germanium metasurface absorber in the near‐infrared region (800–1600 nm) is proposed theoretically and experimentally. Near‐unity absorption can be achieved in such a subwavelength‐thin (≈0.13 λ0) layer of nanostructures based on the destructive interference between simultaneously excited electric and magnetic dipoles inside each element in the backward direction in combination with the destructive interference between the scattered field and the incident field in the forward direction. Its response is both polarization‐independent and angle‐insensitive, with over 80% absorption at an incident angle up to 28°. This ultrathin and flexible design paves the way for realizing next generation optoelectronic devices aimed for high‐speed photon detection and energy harvesting.

The ability to continuously tune the emission wavelength of mid-infrared thermal emitters while maintaining high peak emissivity remains a challenge. By incorporating the nonvolatile phase changing material GeSbTe (GST), two different kinds of wavelength-tunable mid-infrared thermal emitters based on simple layered structures (GST-Al bilayer and Cr-GST-Au trilayer) are demonstrated. Aiming at high peak emissivity at a tunable wavelength, an Al film and an ultrathin (∼5 nm) top Cr film are adopted for these two structures, respectively. The gradual phase transition of GST provides a tunable peak wavelength between 7 μm and 13 μm while high peak emissivity (>0.75 and >0.63 for the GST-Al and Cr-GST-Au emitters, respectively) is maintained. This study shows the capability of controlling the thermal emission wavelength, the application of which may be extended to gas sensors, infrared imaging, solar thermophotovoltaics, and radiative coolers.

The study of all-dielectric nanoantennas has become an emerging branch of the study of optical nanoantennas in recent years, with all-dielectric nanoantennas having an outstanding ability to tailor forward and backward unidirectional scattering arising from interference mainly between electric dipoles and magnetic dipoles induced simultaneously inside a nanoparticle. To further control their radiation properties, we demonstrate the off-normal scattering, by a silicon stair-like nanoantenna, of an incident near-infrared plane wave due to multipolar interference. The radiation angle could be tailored over a 20-degree range by tuning the geometric parameters of the nanoantenna. A multipolar model was adopted to interpret the interference among one electric dipole, two magnetic dipoles and one electric quadrupole induced inside the nanoantenna. The maximum radiation angle reached 20° at a wavelength near 1550 nm. Such a stair-like nanoantenna sets a good example for further flexible manipulation of multipolar resonances inside all-dielectric nanoparticles, which is an essential step towards practical application of all-dielectric nanoantennas in the near future.

The Rashba effect, i.e., the splitting of electronic spin‐polarized bands in the momentum space of a crystal with broken inversion symmetry, has enabled the realization of spin‐orbitronic devices, in which spins are manipulated by spin–orbit coupling. In optics, where the helicity of light polarization represents the spin degree of freedom for spin–momentum coupling, the optical Rashba effect is manifested by the splitting of optical states with opposite chirality in the momentum space. Previous realizations of the optical Rashba effect relied on passive devices determining the surface plasmon or light propagation inside nanostructures, or the directional emission of chiral luminescence when hybridized with light‐emitting media. An active device underpinned by the optical Rashba effect is demonstrated here, in which a monolithic halide perovskite metasurface emits highly directional chiral photoluminescence. An all‐dielectric metasurface design with broken in‐plane inversion symmetry is directly embossed into the high‐refractive‐index, light‐emitting perovskite film, yielding a degree of circular polarization of photoluminescence of 60% at room temperature.