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

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

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

Recent Advances in Adaptive Liquid Crystal Lenses

An adaptive-focus lens is a device that is capable of tuning its focal length by means of an external stimulus. Numerous techniques for the demonstration of such devices have been reported thus far. Moving beyond traditional solutions, several new approaches have been proposed in recent years based on the use of liquid crystals, which can have a great impact in emerging applications. This work focuses on the recent advances in liquid crystal lenses with diameters larger than 1 mm. Recent demonstrations and their performance characteristics are reviewed, discussing the advantages and disadvantages of the reported technologies and identifying the challenges and future prospects in the active research field of adaptive-focus liquid crystal (LC) lenses.This work was supported by Comunidad de Madrid and FEDER Program under grant S2018/NMT-4326 and the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R)

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

Engineering aspheric liquid crystal lenses by using the transmission electrode technique

The transmission electrode technique has been recently proposed as a versatile method to obtain various types of liquid-crystal (LC) lenses. In this work, an equivalent electric circuit and new analytical expressions based on this technique are developed. In addition, novel electrode shapes are proposed in order to generate different phase profiles. The analytical expressions depend on manufacturing parameters that have been optimized by using the least squares method. Thanks to the proposed design equations and the associated optimization, the feasibility of engineering any kind of aspheric LC lenses is demonstrated, which is key to obtain aberration-free lenses. The results are compared to numerical simulations validating the proposed equations. This novel technique, in combination with the proposed design equations, opens a new path for the design and fabrication of LC lenses and even other types of adaptive-focus lenses based on voltage control.This work was supported by 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), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-107270RB-C21 and PID2019-109072RB-C31)