Performance improvement of refractometric sensors through hybrid plasmonic-Fano resonances

Abstract: In this paper, we present a plasmonic refractometric sensor that works under normal incidence; allowing its integration on a fiber tip. The sensor's material and geometry exploit the large scattering cross-section given by high-contrast of the index of refraction subwavelength dielectric gratings. Our design generates a hybrid plasmonic-Fano resonance due to the interference between the surface plasmon resonance and the grating response. We optimize the sensor with a merit function that combines the quality parameter of the resonance and the field enhancement at the interaction volume where the plasmon propagates. Our device shows a high sensitivity (1000 nm/RIU) and a high Figure of Merit (775 RIU$^{-1}$). Degradation in performance is negligible through a wide dynamic range up to 0.7 RIU. These quantitative parameters overperform compared to similar plasmonic sensors.