Multiple fano resonances in an end-coupled MIM waveguide system

In this paper, multiple tunable Fano resonances are firstly achieved in an end-coupled system composed of a rectangular cavity and an inverted U-shaped groove. Through increasing a coupling path, dual Fano resonances are tuned to four Fano peaks. High figure of merits (FOMs) and high refractive index sensitivities are obtained so that the proposed structure is preferred in the highly integrated optical sensing technology. Besides, a new Fano resonance with high performances occurs through cascading a horizontal rectangular cavity. Additionally, the phase shifts and the group delays are also investigated within the Fano resonant windows. These proposed structures are investigated and analyzed by 2D finite-difference time-domain (FDTD) method and multiple interference coupled mode theory (MICMT) method, respectively, and the results show enormous potential in highly integrated optical area.