Split Ring Resonators-Based Plasmonics Sensor With Dual Fano Resonances

Abstract

Plasmonics is garnering the attention in the field of optical sensing due to the unique interaction of light with noble metals which enables sub-wavelength confinement. Here in this paper, a Plasmonic sensor based on coupled split ring resonators is proposed. The interaction between split resonators is theoretically studied and numerically investigated using Finite Difference Time Domain method. Dual Fano resonances are observed in the transmission spectrum with an ultra-narrow line width ( $\Delta \lambda = 7$ nm) and large Quality factor (Q = 185). The resonant wavelength demonstrates a linear dependence with the refractive index of the sensing region. An intriguing feature of the designed sensor is that both the Fano peaks exhibit different value of sensitivities i.e. $\text{S}_{I}=1050$ nm/RIU and $\text{S}_{II}=1965$ nm/RIU for peak I and II respectively which is beneficial in terms of optical sensing. The performance of sensor is also studied for variation in geometrical parameters such as the gap between the split ring resonators. High Figure of Merit (FOM) of 328 RIU−1 is obtained from the structure with a gap of 20 nm. Sensitivity is stable with respect to fabrication tolerances (±10%) of gap (g). The proposed structure can be useful in designing optical glucometer with better sensitivity and resolution. The structure can be modified to finds its applicability in chemical sensing and different biological applications.