Sensing Application in Fano Resonance With T-Shape Structure

A T-shape plasmonic structure, consisting of a stub resonator coupled with bus waveguide and cavity, has been investigated numerically and theoretically. Due to the near-field coupling mechanism between bright and dark modes, plasmon induced transparency can be observed in transmission spectrum. Moreover, it is demonstrated theoretically that the first order resonance mode can exist or not in the cavity by adjusting lateral displacement (S), which leads to the appearance or disappearance of the narrow transmission dip together with a steep Fano resonance in reflection spectrum. The effects of different parameters on a figure of merit (FOM) are investigated in detail. In sensing applications, the T-shape structure yields a sensitivity of similar to 1090 nm shift per refractive index unit and a FOM of 33340. The results indicate that the width of cavity (w(c)) is more sensitive than the distance (g) and length (L) for FOM. The transparency and Fano resonance effects may have potential applications in optical switch, slow-light devices, and nano sensor in highly integrated optical circuits.