Theoretical analysis of tunable double plasmon induced transparency in three-ellipse-shaped resonator coupled waveguide

The tunable double plasmon-induced transparency (PIT) effects are investigated in a waveguide coupled by the three ellipse-shaped resonators. By the finite element method, we study the influences of coupling modes of the three ellipse-shaped resonators, waveguide structure parameters and the refractive indices of dielectric in three ellipse-shaped resonators on double PIT effects. The waveguide structure consists of three ellipse-shaped resonators, and is similar to a four-level structure of the atomic system. The bottom ellipse-shaped resonator can be named a bright mode, the middle and top ellipse-shaped resonators each can be seen as a dark mode. In order to obtain an ideal double PIT transparency window, we also numerically analyze the optical transmission characteristics of structures of several three-ellipse-shaped resonator coupled waveguides. Furthermore, we mainly discuss the transmission spectra in the better three-ellipse-shaped resonator coupled waveguide structure as a function of the radii of the long axis in ellipse-shaped resonators, the coupling distance between the bottom ellipse-shaped resonator and the bus waveguide, the coupling distance between ellipse-shaped resonators, and the symmetry broken degree. In addition, we also consider the effect of the refractive indices of dielectric in three ellipse-shaped resonators on double PIT spectra. It is found that the transmission spectra in the threeellipse-shaped resonator coupled waveguide have obvious red shift when the refractive indices of dielectric in the three ellipse-shaped resonators increase. All the simulation results may provide the theoretical basis for the potential application of multiple PIT in plasma switches and sensors.