Theoretical investigation of quality factor and light-speed reduction in a plasmon-induced transparency device

In this study, the group index and the quality factor of a plasmon-induced transparency structure, introduced recently, have been investigated in detail with the aim of narrowing the frequency transparency window and obtaining a higher quality factor. The structure consists of an Al₂O₃ grating and metallic film (silver or gold) coated onto SiO₂/TiO₂/SiO₂ layers. The induced transparency occurred due to the wave vector matching between the surface plasmon polaritons and guided mode in the high refractive index layer (TiO₂) in a terahertz regime. This phenomenon can reduce the group velocity of the light. Group index at its highest has been estimated theoretically to be about 298 and 393, respectively, using gold and silver as metals in such an induced transparency system.