Plasmons are an interesting alternative to cavities in order to confine the electromagnetic field. Their coupling to semiconductor excitons (GaAs quantum wells) is the purpose of the ANR project SCOP. Metallic nano-particles possess a localized surface plasmon mode which energy depends on their size and geometry. Those modes can interact with GaAs or organic semiconductor excitons. The modelling and the optimization of dedicated structures allowed us to specify geometrical constraints for the realisation of the strong coupling regime. We observe the formation of mixed states between localized plasmons and excitons, with a clear anti-crossing and a giant Rabi splitting of 450 meV (to our knowledge, the largest reported Rabi energy). This research started with the recruitment of Joël Bellessa (professor) in September 2007. The activity, and especially its theoretical part, is continued in interaction with him, despite his leave for Lyon (LPMCN) in September 2008.