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

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

Numerical and experimental time-domain characterization of terahertz conducting polymers

A comprehensive framework for the theoretical and experimental investigation of thin conducting films for terahertz applications is presented. The electromagnetic properties of conducting polymers spin-coated on low-loss dielectric substrates are characterized by means of terahertz time-domain spectroscopy and interpreted through the Drude-Smith model. The analysis is complemented by an advanced finite-difference time-domain algorithm, which rigorously deals both with the dispersive nature of the involved materials and the extremely subwavelength thickness of the conducting films. Significant agreement is observed among experimental measurements, numerical simulations, and theoretical results. The proposed approach provides a complete toolbox for the engineering of terahertz optoelectronic devices

Ultrahigh-quality factor resonant dielectric metasurfaces based on hollow nanocuboids

In this work, a dielectric metasurface consisting of hollow dielectric nanocuboids, with ultrahigh quality factor, is theoretically proposed and demonstrated. The variation of the hole size of the cuboid allows for the tuning of the resonant anapole mode in the nanoparticles. The metasurface is designed to operate in two complementary modes, namely electromagnetically induced transparency and narrowband selective reflection. Thanks to the non-radiative nature of the anapole resonances, the minimal absorption losses of the dielectric materials, and the near-field coupling among the metasurface nanoparticles, a very high quality factor of =2.5×106 is achieved. The resonators are characterized by a simple bulk geometry and the subwavelength dimensions of the metasurface permit operation in the non-diffractive regime. The high quality factors and strong energy confinement of the proposed devices open new avenues of research on light-matter interactions, which may find direct applications, e.g., in non-linear devices, biological sensors, laser cavities, and optical communications.Research and Development Program through the Comunidad de Madrid (SINFOTON S2013/MIT-2790); Ministerio de Economia y Competitividad of Spain (TEC2013-47342-C2-2-R); mobility programs of Carlos III University and "Jose Castillejo" of the Ministerio de Educacion, Cultura y Deporte of Spain

Author Correction: Toroidal metasurface resonances in microwave waveguides

Correction to: Scientific Reports https://doi.org/10.1038/s41598-019-44093-7, published online 17 May 2019 This Article contains a typographical error in the Acknowledgements section. “the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R)”. should read: "the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R)"

Toroidal metasurface resonances in microwave waveguides

We theoretically investigate the possibility to load microwave waveguides with dielectric particle arrays that emulate the properties of infinite, two-dimensional, all-dielectric metasurfaces. First, we study the scattering properties and the electric and magnetic multipole modes of dielectric cuboids and identify the conditions for the excitation of the so-called anapole state. Based on the obtained results, we design metasurfaces composed of a square lattice of dielectric cuboids, which exhibit strong toroidal resonances. Then, three standard microwave waveguide types, namely parallel-plate waveguides, rectangular waveguides, and microstrip lines, loaded with dielectric cuboids are designed, in such a way that they exhibit the same resonant features as the equivalent dielectric metasurface. The analysis shows that parallel-plate and rectangular waveguides can almost perfectly reproduce the metasurface properties at the resonant frequency. The main attributes of such resonances are also observed in the case of a standard impedance-matched microstrip line, which is loaded with only a small number of dielectric particles. The results demonstrate the potential for a novel paradigm in the design of “metasurface-loaded” microwave waveguides, either as functional elements in microwave circuitry, or as a platform for the experimental study of the properties of dielectric metasurfaces.This work was supported by the European Union COST Action CA16620 "European Network for High Performance Integrated Microwave Photonics", by the Research and Development Program through the Comunidad de Madrid and FEDER Program under grants 2013/MIT-2790 and S2018/NMT-4326, the Ministerio de Economía y Competitividad of Spain (TEC2013-7342-C2-2-R), and the mobility programs of Carlos III University and "José Castillejo" of the Ministerio de Educación, Cultura y Deporte of Spain

Anapole Modes in Hollow Nanocuboid Dielectric Metasurfaces for Refractometric Sensing

This work proposes the use of the refractive index sensitivity of non-radiating anapole modes of high-refractive-index nanoparticles arranged in planar metasurfaces as a novel sensing principle. The spectral position of anapole modes excited in hollow silicon nanocuboids is first investigated as a function of the nanocuboid geometry. Then, nanostructured metasurfaces of periodic arrays of nanocuboids on a glass substrate are designed. The metasurface parameters are properly selected such that a resonance with ultrahigh Q-factor, above one million, is excited at the target infrared wavelength of 1.55 µm. The anapole-induced resonant wavelength depends on the refractive index of the analyte superstratum, exhibiting a sensitivity of up to 180 nm/RIU. Such values, combined with the ultrahigh Q-factor, allow for refractometric sensing with very low detection limits in a broad range of refractive indices. Besides the sensing applications, the proposed device can also open new venues in other research fields, such as non-linear optics, optical switches, and optical communications.This work was supported by the Research and Development Program through the Comunidad deMadrid (SINFOTON S2013/MIT-2790), the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R) and the funding from Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) for the Project TEC2016-77242-C3-1-R AEI/FEDER,UE

Description and Characterisation of a Large Array of Sensors Mimicking an Artifical Olfactory Epithelium

Biological olfactory systems show high sensitivity and exquisite discriminatory capacity to odorants. These characteristics are due to hierarchical signal processing of the large numbers of sensory inputs that occurs within the olfactory system. In testing realistic computational models of the olfactory system, large numbers of chemical sensor inputs are required. So far, sensory devices that may serve as model inputs to an artificial olfactory system do not exist. The development of a large scale array of chemical sensors able to mimic the olfactory receptor neurons is described, and these have been characterised in terms of their variability and degree of redundancy. Using this device it is possible to start testing computational hypotheses appropriate to biological chemosensory systems and adapt them to the artificial olfaction

All-dielectric toroidal metasurfaces for angular-dependent resonant polarization beam splitting

An all-dielectric metasurface exhibiting a strong toroidal resonance is theoretically designed and experimentally demonstrated as an angular-dependent resonant polarization beam-splitter in the microwave K-band. The metasurface is fabricated by embedding a square periodic array of high-permittivity ceramic cuboid resonators in a 3D-printed substrate of polylactic acid. It is demonstrated that by properly selecting the resonator geometry and by tuning the angle of incidence through mechanical rotation, the metasurface can switch between a polarization beam splitting and bandpass or bandstop operation. Such performance is achieved by exploiting the highly asymmetric Fano spectral profile of the toroidal resonance and the very low (high) dispersion of the associated p-(s-) polarized mode resulting from the resonant toroidal dipole mode's field profile, as evidenced by both full-wave and band structure simulations. Theoretically infinite extinction ratios are achievable for polarization beam splitting operation with very low insertion losses and adjustable bandwidth. The experimental demonstration of such a compact, all-dielectric metasurface expands the research portfolio of resonant metasurfaces toward not only the investigation of the intriguing physics of toroidal modes but also to the engineering of functional millimeter-wave components for polarization control, for instance, in the context of 5G wireless communication networks.This research was co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH CREATE INNOVATE (Project code: No. T1EDK-02784) and by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), and the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-107270RB-C21 and PID2019-109072RB-C31)