Plasmonic refractive index sensor based on a double concentric square ring resonator and stubs

A plasmonic refractive index sensor based on a metal-insulator-metal waveguide coupled with a double concentric square ring resonator is proposed and analyzed both theoretically and numerically. The theoretical and the numerical results are based on the transmission-line model and the finite difference time domain method, respectively. The theoretical results agree well with the numerical ones. A maximum sensitivity of 1250 nm per refractive index unit with a high figure of merit of 32.8 for the double concentric square ring resonator with one stub is obtained in the near-infrared region. Also, the double concentric square ring resonator with three stubs is simulated, and has a maximum sensitivity of 1270 nm per refractive index unit with a high figure of merit of 58. Our proposed plasmonic structures could find useful applications in sensing systems and integrated circuits in the near-infrared region.