Investigation of the transmission properties of a plasmonic MIM waveguide coupled with two ring resonators

Transmission characteristics of a plasmonic MIM waveguide coupled with two ring resonators are investigated both numerically and analytically. It is shown that due to the field-driven interactions between the two ring resonators, the second-order resonant mode of the directly-coupled ring resonator is split into two resonances, and as a result, a clear transmission dip emerges on the transmission spectrum. Simulations also show that the splitting is not only sensitive to the geometry parameters, but also sensitive to the refractive index of the dielectrics filled in the ring resonators. The group index can be varied from positive to negative, and thus indicates the properties of normal and abnormal dispersion related to the slow- and fast-light feature. The proposed structure is not only helpful to the application of nanoscale plasmonic filters and nano sensors with its sensitivity up to 685 nm/RIU in the area of highly integrated optical circuits, but also paves a new way towards the realization of controlling the light speed.