Strong plasmon-exciton coupling in MIM waveguide-resonator systems with WS₂ monolayer

The room-temperature strong plasmon-exciton coupling is first investigated in a metal-insulator-metal (MIM) waveguide-resonator system with WS₂ monolayer. Finite-difference time-domain (FDTD) simulated results exhibit that the Fabry-Pérot (F-P) cavity is realized by the MIM plasmonic waveguide with two separated metal bars. When the F-P resonance is tuned to overlap with the A-exciton absorption peak of WS₂ monolayer, the strong plasmon-exciton coupling is obtained at visible wavelengths. As a result, the spectral splitting response confirmed by the coupled-mode theory (CMT) appears in the transmission spectrum. Intriguingly, the switching response is handily witnessed by tuning the orientation of WS₂ monolayer along the cavity, and the coupling strength is dynamically tuned by changing the position of the WS₂ monolayer. Simultaneously, the anticrossing behavior with the Rabi splitting up to 109 meV is achieved by small changes in the length of the F-P cavity and the refractive index of dielectric in the cavity, respectively. The underlying physics is further revealed by the coupled oscillator model (COM). The proposed strong plasmon-exciton coupling can find utility in highly integrated plasmonic circuits for optical switching.