Tunable Fano resonance analysis in plasmonic waveguide side-coupled multiple Taiji resonators

Abstract

In this paper, we first propose and analyze tunable Fano resonance based on indirect interaction between two Taiji resonators which both side-couple with a MIM (metal–insulator–metal) waveguide. An S-shaped branch waveguide embedded in the Taiji ring can tailor the propagating modes and then varying the number of whispering-gallery (WG) modes in the Taiji resonator, leading to the convenient tuning of Fano resonance lineshape. By covering monolayer graphene on the waveguide, Fano resonance lineshape can be all-optically tuned with relatively low pump intensity because of the optical Kerr effect of graphene; by coating UV-glue on the proposed structure, temperature sensing with high sensitivity of −0.23 nm/°C is obtained because of large negative thermo-optic coefficient of UV-glue. Furthermore, up to 16 Taiji resonators are designed and coupled with a common MIM waveguide to observe and analyze Fano lineshape variation, finally realizing the optical band-stop filter with maximal bandwidth of 49.5 nm and optical band-pass filter with maximal bandwidth of 45.3 nm. This ultra-compact micro-structure of plasmonic waveguide coupling multiple Taiji resonators demonstrates good potential applications in the nonlinear optics, optical modulation, and high-sensitivity biochemical sensors.