  We report on the strong coupling between the Bloch surface wave supported by
an inorganic multilayer structure and $J$-aggregate excitons in an organic
semiconductor. The dispersion curves of the resulting polariton modes are
investigated by means of angle-resolved attenuated total reflection as well as
photoluminescence experiments. The measured Rabi splitting is 290 meV. These
results are in good agreement with those obtained from our theoretical model.
