Double Fano resonance based on Fabry-Perot mode and asymmetric waveguide mode

Abstract

Fano resonance effect has potential applications in many nanophotonics devices, Such as switch, sensor, and modulators. To realize double Fano resonance effect, in this paper, we present a novel coupling mechanism in a multi-layer metamaterial structure. The structure consists of periodic TiO2 grating covered with MgF2-TiO2-Ag multilayer with a MgF2 substrate. Results show that one of the two Fano resonance is caused by the interference between a broad Fabry-Perot (FP) mode and a dark waveguide mode (WG), and the other Fano resonance is caused by the asymmetric waveguide mode of the MgF2-TiO2-Ag layer. The effect of structural parameters on transmission is also studied, the field distribution of the proposed nanostructure is presented to illustrate the mechanism. We achieve a refractive index sensitivity of 73.5 nm/RIU, and temperature sensitivity of 0.0915nm/°C, the ultra-narrow transmission bandwidth leads to the high FOM*. The results will pave the way towards the design of double band Fano resonance, which may have potential application in high signal-to-noise ratio measurement, plasmonic modulator and refractive index sensor or temperature sensor.