Tunable compact nanosensor based on Fano resonance in a plasmonic waveguide system.

An ultracompact plasmonic refractive index sensor based on Fano resonance is proposed. The sensor comprises a metal-insulator-metal waveguide with a stub and a side-coupled split-ring resonator. The effect of structural parameters on Fano resonance and the refractive index sensitivity of the system are analyzed in detail by investigating the transmission spectrum. Simulation results show that Fano resonance has different dependences on the parameters of the sensor structure. The reason is further discussed based on the field pattern. The peak wavelength and lineshape can be easily tuned by changing the key parameters. Furthermore, dual Fano resonance effects with different frequency intervals are obtained, which are mainly induced by the symmetry breaking of the structure. The proposed sensor yields sensitivity higher than 1.4×103  nm/RIU and a figure of merit of 1.2×105. The sensitivity and figure of merit can be further improved by optimizing the geometry parameters.