A very high-resolution refractive index sensor based on hybrid topology of photonic crystal cavity and plasmonic nested split-ring resonator

In this paper, an optical refractive index (RI) sensor based on a photonic crystal and plasmonic (PhC-P) hybrid topology is designed. The sensor's structure is composed of nested circular metallic split-ring resonators (NCMSRR), which are embedded inside a hexagonal cavity in a rod-type photonic crystal (PhC) structure. The finite-difference time-domain (FDTD) method is used for the numerical simulation of the sensor. The obtained results show that by the cooperative coupling between the surface plasmon polaritons (SPP) induced by the NCMSRR and resonant PhC cavity modes, a hybrid PhC-P mode is created. The hybrid mode provides unique opportunities, not only for incrementing the sensitivity but also for obtaining a much higher figure of merit (FoM) compared to modes belonging to purely plasmonic or purely PhC sensors. The simulation results demonstrate a fairly high sensitivity of 1250 nm/RIU and an excellent FoM of 2083 RIU-1 when the proposed sensor is exposed to hazardous gases. These results show considerable improvement compared to the works published in the literature. Accordingly, the sensor proposed in this paper has tremendous potential to be used for high-sensitivity and high-resolution sensing applications at optical communication wavelengths.