Plasmonic Ring Resonator Sensor With High Sensitivity and Enhanced Figure of Merit Using an Ag–Si–Ag Bus Waveguide

A plasmonic miniaturized ring resonator based on Ag-analyte-Ag ring cavity coupled with an Ag-Si-Ag input bus waveguide has been numerically analyzed for bulk refractive index and surface adlayer sensing applications. The opto-geometric parameters of the sensor structure have been thoroughly optimized to maximize field confinement in the sensing zone, which significantly improves the sensitivity. Using an Ag-Si-Ag input bus waveguide results in the reduction of propagation loss which offers an improved quality factor and figure of merit due to narrowing of full width at half maximum (FWHM) of the transmission spectrum. The average bulk refractive index sensitivity over biologically relevant refractive index range (1.33-1.38 RIU) and gas-sensitivity (1-1.01 RIU) values are 1757.71 nm/RIU with an FWHM of 37 nm, and 1787.14 nm/RIU with an FWHM of 24 nm, respectively. We have also investigated the optimized sensor's performance as an adlayer biosensor and the maximum adlayer sensitivity obtained is 2.72 nm/nm. We have also analyzed the sensor's optical tolerance by incorporating a 10% change in Ag's and Si's real part of dielectric constants. Owing to excellent sensitivity and high figure of merit the proposed sensor may find applications in designing highly sensitive on-chip nano-sensors with improved detection limit.