Fourth-order Jameson–Schmidt–Turkel FDTD scheme for non-magnetised cold plasma

A fourth-order finite-difference time-domain (FDTD) scheme is proposed for the solution of Maxwell's equations in cold plasma (Drude medium), based on the multistage method of Jameson, Schmidt and Turkel, which was originally introduced in the framework of fluid dynamics. First, the system of governing differential equations is formed as a general first-order, operator-based approach, and then a four-stage algorithm is established. The accuracy of the method is verified in benchmark problems compared with analytical solutions and with the conventional second-order FDTD algorithm

Long-range plasmonic directional coupler switches controlled by nematic liquid crystals

A liquid-crystal tunable plasmonic optical switch based on a long-range metal stripe directional coupler is proposed and theoretically investigated. Extensive electro-optic tuning of the coupler's characteristics is demonstrated by introducing a nematic liquid crystal layer above two coplanar plasmonic waveguides. The switching properties of the proposed plasmonic structure are investigated through rigorous liquid-crystal studies coupled with a finite-element based analysis of light propagation. A directional coupler optical switch is demonstrated, which combines very low power consumption, low operation voltages, adjustable crosstalk and coupling lengths, along with sufficiently reduced insertion losses. © 2013 Optical Society of America

Recent advances in strongly resonant and gradient all-dielectric metasurfaces

We provide a critical overview of recent advances in all-dielectric, strongly resonant and gradient metasurfaces, as their performance is pushed to the extreme in view of emerging flat-optics applications

Event-Triggered Islanding in Inverter-Based Grids

The decentralization of modern power systems challenges the hierarchical structure of the electric grid and requires the implementation of automated schemes that can overcome adverse conditions. This work proposes an adaptive isolation methodology that can segregate a grid topology in autonomous islands that maintain stable and economic operation in the presence of deliberate (e.g., cyberattacks) or unintentional abnormal events. The adaptive isolation logic is event-triggered to avoid false positives, improve detection accuracy, and reduce computational overheads. A measurement-based stable kernel representation (SKR) triggering mechanism inspects distributed generation controllers for abnormal behavior. The SKR notifies a machine learning (ML) ensemble classifier that detects whether the system behavior is within acceptable operational conditions. The event-triggered adaptive isolation framework is evaluated using IEEE RTS-24 bus system. Simulation results demonstrate that the proposed framework detects anomalous behavior in real-time and identifies stable partitions minimizing operating costs faster than traditional islanding detection techniques

Plasmon resonance optical tuning based on photosensitive composite structures

This paper reports a numerical investigation of a periodic metallic structure sandwiched between two quartz plates. The volume comprised between the quartz plates and the metallic structure is infiltrated by a mixture of azo-dye-doped liquid crystal. The exposure to a low power visible light beam modifies the azo dye molecular configuration, thus allowing the wavelength shift of the resonance of the system. The wavelength shift depends on the geometry of the periodic structure and it also depends on the intensity of the visible light beam

Time-domain modeling of dispersive and lossy liquid-crystals for terahertz applications

A numerical framework based on the finite-difference timedomain method is proposed for the rigorous study of electro-optically tunable terahertz devices based on liquid crystals. The formulation accounts for both the liquid-crystal full-tensor anisotropy and the dispersion of its complex refractive indices, which is described via modified Lorentzian terms. Experimentally characterized liquid-crystalline materials in the terahertz spectrum are fitted and modeled in benchmark examples, directly compared with reference analytical or semi-analytical solutions. In addition, the efficiency of broadband time-domain modeling of the proposed technique is also demonstrated by accurately reproducing time-domain spectroscopy measurements. © 2014 Optical Society of America