Decoupling Crossover in Asymmetric Broadside Coupled Split Ring Resonators at Terahertz Frequencies

TL;DR

This study explores how asymmetric broadside coupled split ring resonators (ABC-SRRs) behave under in-plane displacement at terahertz frequencies, revealing a decoupling transition and mode splitting crucial for metamaterial design.

Contribution

It provides the first detailed analysis of the electromagnetic response of ABC-SRRs as a function of displacement, highlighting the transition to dual resonance modes and their dependence on asymmetry.

Findings

Decoupling occurs at a displacement of 0.375Lo in ABC-SRRs.

Asymmetry increases the oscillator strength of the new mode.

Symmetric BC-SRRs do not exhibit mode splitting up to 0.75Lo.

Abstract

We investigate the electromagnetic response of asymmetric broadside coupled split ring resonators (ABC-SRRs) as a function of the relative in-plane displacement between the two component SRRs. The asymmetry is defined as the difference in the capacitive gap widths (\Delta g) between the two resonators comprising a coupled unit. We characterize the response of ABC-SRRs both numerically and experimentally via terahertz time-domain spectroscopy. As with symmetric BC-SRRs (\Delta g=0 \mu m), a large redshift in the LC resonance is observed with increasing displacement, resulting from changes in the capacitive and inductive coupling. However, for ABC-SRRs, in-plane shifting between the two resonators by more than 0.375Lo (Lo=SRR sidelength) results in a transition to a response with two resonant modes, associated with decoupling in the ABC-SRRs. For increasing \Delta g, the decoupling transition begins at the same relative shift (0.375Lo), though with an increase in the oscillator strength of the new mode. This strongly contrasts with symmetric BC-SRRs which present only one resonance for shifts up to 0.75Lo. Since all BC-SRRs are effectively asymmetric when placed on a substrate, an understanding of ABC-SRR behavior is essential for a complete understanding of BC-SRR based metamaterials.