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

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. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement