RESUMEN
We show that a dielectric nanowire (NW) with a rectangular cross section can effectively be modeled as a Fabry-Perot cavity formed by truncating a dielectric slab waveguide. By calculating the mode indices of the supported waveguide modes and the reflection phase pickup of the guided waves from the end facets, we can numerically predict the spectral locations of optical, Mie-like resonances for such NWs. This type of analysis must be performed twice in order to account for all resonances of these structures, corresponding to light propagating in the vertical or horizontal directions. The model shows excellent agreement with full-field simulations. We show how the refractive index of both the NW itself and neighboring materials and substrates impact the resonant properties. Our results can aid the development of NW-based optoelectronic devices, for which rectangular cross sections are much simpler to fabricate using top-down fabrication procedures.
RESUMEN
Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag_{4}In_{3}Sb_{67}Te_{26}. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales-faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.
RESUMEN
The increased importance of plasmonic devices has prompted a sizable research activity directed toward the development of ultracompact and high-performance couplers. Here, we present a novel scheme for efficient, highly localized, and directional sourcing of surface plasmon polaritons (SPPs) that relies on the excitation of leaky mode optical resonances supported by high-refractive index, semiconductor nanowires. High coupling efficiencies are demonstrated via finite difference frequency domain simulations and experimentally by leakage radiation microscopy. This efficiency is quantified by means of a coupling cross section, the magnitude of which can exceed twice the geometric cross section of the nanowire by exploiting its leaky resonant modes. We provide intuition into why the SPP coupling via certain wire modes is more effective than others based on their symmetry properties. Furthermore, we provide an example showing that dielectric scatterers may perform as well as metallic scatterers in coupling to SPPs.
RESUMEN
The success of semiconductor electronics is built on the creation of compact, low-power switching elements that offer routing, logic and memory functions. The availability of nanoscale optical switches could have a similarly transformative impact on the development of dynamic and programmable metasurfaces, optical neural networks and quantum information processing. Phase-change materials are uniquely suited to enable their creation as they offer high-speed electrical switching between amorphous and crystalline states with notably different optical properties. Their high refractive index has already been harnessed to fashion them into compact optical antennas. Here, we take the next important step, by showing electrically-switchable phase-change antennas and metasurfaces that offer strong, reversible, non-volatile, multi-phase switching and spectral tuning of light scattering in the visible and near-infrared spectral ranges. Their successful implementation relies on a careful joint thermal and optical optimization of the antenna elements that comprise a silver strip that simultaneously serves as a plasmonic resonator and a miniature heating stage. Our metasurface affords electrical modulation of the reflectance by more than fourfold at 755 nm.