Strong coupling of an EIT-like metamaterial with photons in a photonic crystal cavity

We report strong coupling between a plasmonic dark mode of an EIT-like metamaterial (EIT: electromagnetically induced transparency) with the photons of a 1D photonic crystal cavity in the terahertz frequency range. The coupling between the dark mode and the cavity photons is mediated by a plasmonic bright mode, which is proven by the observation of a frequency splitting which depends on the strength of the inductive interaction between the plasmon bright and dark modes of the EIT metamaterial. In addition, since the plasmonic dark mode strongly couples with the cavity dark mode, we observed four polariton modes. The frequency splitting by interaction of the four modes (plasmonic bright and dark mode and the two eigenmodes of the photonic cavity) can be reproduced in the framework of a model of four coupled harmonic oscillators.