Strong exciton-plasmon coupling in dye-doped film on a planar hyperbolic metamaterial

We experimentally demonstrate the direct strong coupling between the S₀→S₁ absorption transition of rhodamine 6G (R6G) dye molecules and the surface plasmon polaritons of a hyperbolic metamaterial (HMM) substrate. The surface plasmon mode was excited by a guided mode of the R6G-doped polymer thin film on the HMM. The coupling strengths of the interactions between the surface plasmon and two molecular exciton modes are greater than the average linewidths of the individual modes indicating a strong coupling regime. This is the first, to the best of our knowledge, experimental demonstration of the direct strong coupling between the resonance mode supported by the HMM and the dye molecules on the HMM surface, not embedded in the HMM structure. The study may provide the foundation for the development of novel planar photonic or electronic devices.