Abstract-Terahertz multiple modes defined by fractal symmetry in complementary meta-atoms

Zhidong Gu, Zhenyu Zhao, Hui Zhao, Wei Peng, Jianbing Zhang, Hongwei Zhao, Rajour Tanyi Ako, and Sharath Sriram

 Schematic representation of CSRR design. (a) Fractal meta-atoms of CSRR under different symmetric conditions: O-gap, U-gap, and C-gap, respectively, and fractal levels. (b) Pattern direction of fractal meta-atom, of which the z direction is the <100>-crystallographic orientation of SI-GaAs. P: lattice period, g: gap-size, r1: outer-radius, r2: inner-radius. (c) The top-view optical image of meta-atom. (d) Diagram of terahertz transmission spectroscopy

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-10-4138

Low quality (Q) factors of the intrinsic inductive–capacitive (LC) mode as well as the parasitic dipole oscillation mode restrict high-resolution sensing using split-ring resonators (SRR). Although the trapped Fano-mode of the high-Q factor is found in asymmetric SRR, the conventional design limits the scaling down of resonators. As such, excitation and manipulation of multiple trapped modes of SRR is significant for driving innovative designs of terahertz metamaterials and metasurfaces. In this work, we present a novel approach to manipulating multiple terahertz modes by increasing the fractal levels as well as the geometric symmetry of complementary SRR. It is found that the multiple trapped modes become achievable only in the case that the gap of adjacent fractal SRR opposes each other. By increasing the fractal level, the intrinsic resonance modes change slightly, and more trapped modes appear in between the frequency range of the two major intrinsic modes. The map of surface currents and magnetic field distribution reveal that intrinsic LC resonance in the first or second level SRR dominates the intrinsic modes. By contrast, the trapped mode arises from the hybridization of high-order localized dipole oscillation as well as the multiple localized LC resonances. These findings create new design opportunities for scalable metasurfaces across the terahertz spectrum and beyond, with ability to create high-resolution sensors.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Dielectric meta-atom with tunable resonant frequency temperature coefficient

• Lingling Wu, 
• Xiaoqing Xi, 
• Bo Li & 
• Ji Zhou

https://www.nature.com/articles/s41598-017-02974-9

In this paper, we present a proof-of-concept of a new approach to achieving tailored resonant frequency temperature coefficients in dielectric meta-atoms. The technique involves introducing a thermally expanding or contracting material joining the active high permittivity dielectric absorbers. Both simulation and experiment show that by careful design of the element size and appropriate choice of thermomechanical intermediate layer material, increased or decreased resonant frequency shift temperature sensitivity is possible. Once the active dielectric material is chosen, and a meta-atom design determined, we show the resonant frequency shift depends on the thermal expansion coefficient of the intermediate layer. This work demonstrates the feasibility of manipulating the blue or red shift of metamaterial devices by introducing temperature responsive intermediate layers into meta-atoms.Furthermore, this method could also be applied in the Terahertz, infrared or even optical frequencies on scaled meta-atoms.

Abstract-Manifestation of PT Symmetry Breaking in Polarization Space with Terahertz Metasurfaces

Mark Lawrence, Ningning Xu, Xueqian Zhang, Longqing Cong, Jiaguang Han, Weili Zhang, and Shuang Zhang

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.093901

By utilizing the vector nature of light as well as the inherent anisotropy of artificial meta-atoms, we investigate parity time symmetry breaking in polarization space using a metasurface with anisotropic absorption, whose building blocks consist of two orthogonally orientated meta-atoms with the same resonant frequency but different loss coefficients. By varying their coupling strength, we directly observe a phase transition in the eigenpolarization states of the system, across which the long axis of the eigenpolarization ellipses experience a sudden rotation of 45°. Despite the lack of rotational symmetry of the metasurface, precisely at the phase transition, known as the exceptional point, the eigenmodes coalesce into a single circularly polarized state. The PT symmetric metasurfaces are experimentally implemented at terahertz frequencies.

DOI: http://dx.doi.org/10.1103/PhysRevLett.113.093901

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• Published 28 August 2014
• Received 14 April 2014

© 2014 American Physical Society

Abstract-Multistability and switching in a superconducting metamaterial

                                                        Switching of a 54 SQUID array

P. Jung,  S. Butz,  M. Marthaler,  M. V. Fistul,  J. Leppäkangas, V. P. Koshelets  A. V. Ustinov,

http://www.nature.com/ncomms/2014/140428/ncomms4730/full/ncomms4730.html

The field of metamaterial research revolves around the idea of creating artificial media that interact with light in a way unknown from naturally occurring materials. This is commonly achieved using sub-wavelength lattices of electronic or plasmonic structures, so-called meta-atoms. One of the ultimate goals for these tailored media is the ability to control their properties in situ. Here we show that superconducting quantum interference devices can be used as fast, switchable meta-atoms. We find that their intrinsic nonlinearity leads to simultaneously stable dynamic states, each of which is associated with a different value and sign of the magnetic susceptibility in the microwave domain. Moreover, we demonstrate that it is possible to switch between these states by applying nanosecond-long pulses in addition to the microwave-probe signal. Apart from potential applications for this all-optical metamaterial switch, the results suggest that multistability can also be utilized in other types of nonlinear meta-atoms.