Ultra-Sharp Resonances in THz Metamaterials

The performance of conventional metamaterial designs typically suffers from low quality (Q-) factors owing to ohmic and radiation losses. Hence, a drastic improvement is desired that can be achieved by novel and innovative structures for metamaterial unit cells. Asymmetric double split ring resonators (aDSRs) have been proposed at microwave and terahertz frequencies in order to achieve high Q-factors in a planar structure [1]. In this project, we show that a super cell made from four mirrored asymmetric single split ring resonators (mASRs) sustains an ultra-sharp inductive capacitive (LC) resonance feature that arises from the antiparallel currents excited in pairs of mASRs [2]. 




Fig. 1. (a) Simulated and (b) measured transmission spectra for the non-mirrored ASRs (dotted lines) and mirrored ASRs (solid lines) super cells. The insets in (b) depict the fabricated super cells with the electric (E) field orientation vertically polarized along the y-axis.



Figure 1 shows the measured and simulated results for the non-mirrored (dotted lines) and mirrored (solid lines) structures. The insets depict the unit cells of the fabricated structures when they are illuminated by an electric field polarized along the y-axis. The simulations agree quite well with the measurements. The results reveal a broad resonance for the non-mirrored metamaterial configuration with a full-width half-maximum (FWHM) bandwidth of 95 GHz and a Q-factor of 7.8. Interestingly, the mirrored design shows a much sharper resonance response, featured by a FWHM bandwidth of 29 GHz and a Q-factor of 24.2, which is nearly three times higher than that of the non-mirrored macrocell. This design concept can be applied for highly sensitive thin-film sensors, filters, and strong light matter interaction applications.


[1] V. A. Fedotov, M. Rose, S. L. Prosvirnin, N. Papasimakis, and N. I. Zheludev, “Sharp trapped-mode resonances in planar metamaterials with a broken structural symmetry,” Physical Review Letters, vol. 99, p. 147401, 2007.

[2] I. Al-Naib, R. Singh, C. Rockstuhl, F. Lederer, S. Delprat, D. Rocheleau, M. Chaker, T. Ozaki, and R. Morandotti, “Excitation of a high-Q subradiant resonance mode in mirrored single-gap asymmetric split ring resonator terahertz metamaterials,” Applied Physics Letters, vol. 101, no. 7, p. 071108, 2012.