Abstract-Terahertz electromagnetically-induced transparency of self-complementary meta-molecules on Croatian checkerboard

Zhenyu Zhao, Xiaobo Zheng, Wei Peng, Jianbing Zhang, Hongwei Zhao, Wangzhou Shi

https://www.nature.com/articles/s41598-019-42038-8

A terahertz (THz) electromagnetically-induced transparency (EIT) phenomenon is observed from two types of self-complementary meta-molecules (MMs) based on rectangular shaped electric split-ring resonators (eSRR) on Croatian checkerboard. Each MM contains a couple of identical size eSRRs and a couple of structural inversed eSRRs twisted π/2 in checkerboard pattern. In the first type of MM (type-I), the gap is in the middle line of eSRR. In the second type of MM (type-II), the gap is on the two arms of eSRR. Both types of MMs exhibit EIT effect. A maximum 20 ps group delay is observed at the transparency window of 0.63 THz in type-I MM; while a maximum 6.0 ps group delay is observed at the transparent window of 0.60 THz in type-II MM. The distribution of surface currents and electrical energy reveals that only CeSRR contribute to the transparency window as well as the side-modes in type-I MM, where the current leakage via contact point contributes to the low-frequency side-mode, and the coupled local inductive-capacitive (LC) oscillation in CeSRRs contributes to the high-frequency side-mode. In type-II MM, however, the localized dipolar oscillator of CeSRR contributes to the low-frequency side-mode; while the hybridization of dipole oscillation on eSRR and LC resonance on CeSRR contributes to the high-frequency side-modes. Our experimental findings manifest a new approach to develop THz slow-light devices.

Abstract-Tuning the terahertz trapped modes of conductively coupled Fano-resonators in reflectional and rotational symmetry

Xiaobo Zheng, Zhenyu Zhao, Wei Peng, Jianbing Zhang, Hongwei Zhao, and Wangzhou Shi

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-1-105&origin=search

We experimentally investigate the terahertz (THz) response of conductively coupled asymmetric split ring resonator-based meta-molecules in the layout of reflection and rotational symmetry. In the reflectional symmetry case, the horizontally polarized THz excites a couple of trapped modes: the low-order one is a coupled Fano-resonance, and the high-order one is a decoupled dipole oscillator. The vertically polarized THz excites an inductive-capacitor resonance as a low-order trapped mode below the frequency of a high-order intrinsic mode. The quality factors (Q factors) of trapped modes decrease with the displacement of top-and-bottom gap increasing. In the rotational symmetry case, the horizontally polarized THz excites a single trapped mode owing to coupled Fano-resonance. The vertically polarized THz excites a high-order trapped mode of coupled multiple dipole oscillations beyond the frequency of intrinsic low-order dipole oscillation. The Q factors of trapped modes increase with the displacement of the top-and-bottom gap increase. For the first time, our results reveal the trapped modes’ evolution owing to the interaction of Fano-resonators conductively coupled under different symmetry.

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