Asymmetric coupling between subradiant and superradiant plasmonic resonances and its enhanced sensing performance.

We present symmetric and asymmetric couplings within a pair of split-ring resonators (SRRs). The former shows a single transmittance dip, following the equivalent circuit model; yet, the latter introduces an additional transmittance peak, stemming from an asymmetrically coupled resonance (ACR) between the subradiant and superradiant modes. The mechanism of such induced transparency is elucidated well by the suppression of induced currents within the SRR element with a lower quality factor. Finally, the excitation of ACR is further associated with remarkable confinement of electromagnetic field, providing a compelling sensing performance based on its excellent sensitivity and figure of merit. (c) 2009 Optical Society of America