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.

Lamellar gratings are investigated via temporal coupled-mode theory and numerical simulations. Total absorption can be achieved by an optimized grating with shallow grooves under normal incidence and the full width at half-maximum (FWHM) is only 0.4 nm. For certain wavelengths, the structure shows high absorption only within an ultra-narrow angle, which suggests that it can be used as a highly directional thermal emitter according to Kirchhoff’s law. Besides, the resonant wavelength is sensitive to the refractive index of the environmental dielectric. The large sensitivity ($1400\mathrm{nm}/\mathrm{RIU}$) and simultaneous small FWHM result in a huge figure-of-merit of $2300/\mathrm{RIU}$, which enables the structure to have great potential in plasmonic sensing.

An ultra-narrow band absorber consisting of continuous silver and alumina films is investigated. Owing to Fabry–Pérot resonance and silver's inherent loss, an ultra-narrow spectral range of light can be entirely trapped in the structure. By varying thicknesses of metallic and dielectric films, absorption peak shifts in visible and near-infrared regions. When two such metal-insulator-metal stacks are cascaded, experimental results show that an ultra-narrow absorption bandwidth of 7 nm is achieved, though theoretical results give that of 2 nm. Features of high-efficiency and ultra-narrow band absorption have huge potential in optical filtering, thermal emitter design, etc.

MEMS inductors are used in a wide range of applications in micro- and nanotechnology, including RF MEMS, sensors, power electronics, and Bio-MEMS. Fabrication technologies set the boundary conditions for inductor design and their electrical and mechanical performance. This review provides a comprehensive overview of state-of-the-art MEMS technologies for inductor fabrication, presents recent advances in 3D additive fabrication technologies, and discusses the challenges and opportunities of MEMS inductors for two emerging applications, namely, integrated power electronics and neurotechnologies. Among the four top-down MEMS fabrication approaches, 3D surface micromachining and through-substrate-via (TSV) fabrication technology have been intensively studied to fabricate 3D inductors such as solenoid and toroid in-substrate TSV inductors. While 3D inductors are preferred for their high-quality factor, high power density, and low parasitic capacitance, in-substrate TSV inductors offer an additional unique advantage for 3D system integration and efficient thermal dissipation. These features make in-substrate TSV inductors promising to achieve the ultimate goal of monolithically integrated power converters. From another perspective, 3D bottom-up additive techniques such as ice lithography have great potential for fabricating inductors with geometries and specifications that are very challenging to achieve with established MEMS technologies. Finally, we discuss inspiring and emerging research opportunities for MEMS inductors.

Three different types of polarization-sensitive perfect absorbers are designed and numerically investigated. The bottle-like and the cup-like absorbers are narrowband absorbers, which strongly absorb light of a specific polarization and reflect almost all light of another polarization. By varying the geometric parameters, their absorption peaks can be tuned from 1300 nm to 2300 nm and 700 nm to 1400 nm, respectively. The broadband absorber is polarization-sensitive as well, exhibiting an average absorption efficiency of 88% over a wide range of wavelength (700-2300 nm). The proposed absorbers may have potential applications in polarization detectors, polarizers etc.