Organic Exciton in Strong Coupling with Long-Range Surface Plasmons and Waveguided Modes

In this Letter, we demonstrate experimentally the strong interaction between organic semiconductor excitons and long-range surface plasmons. For this purpose, a thin J-aggregated cyanine dye layer is deposited on a thin silver film bounded by two poly(vinyl alcohol) layers. An anticrossing between the long-range surface plasmon and the dye exciton is measured in the dispersion relation and confirmed in luminescence experiments, showing unambiguously the hybridization between the long-range surface plasmon and the dye exciton. The extension of the polaritonic states deduced from the dispersion curves is 50 μm, which represents an increase of more than 1 order of magnitude compared to usual surface plasmon-based polaritons. We believe that the extension of the polariton coherence length can have direct applications to the energy transfer between molecules over long distances in strong coupling, as well as in the modification of the properties of materials (conductivity, second harmonic generation). Strong coupling between an aggregated dye layer and guided modes is also experimentally evidenced in a similar structure. The hybridization between dye exciton and guided modes demonstrated here opens the way to the exploitation of polariton nonlinearities and switching already evidenced in cavities for integrated optics: the strong coupling now occurs directly on the guided mode.