ABSTRACT
This chapter focuses on the new phenomenon which arises when the optically active material placed inside a cavity is in strong coupling with the cavity electromagnetic modes. The concept of strong light-matter coupling in microcavities arises from the central question: having a system whose excited states exhibits an irreversible decay because of the coupling to a thermostat, is it possible to recover a reversible behavior? Cavity-polariton dispersion curves can be calculated in different ways: A classical local Lorentz oscillator model can be included inside the FP cavity as a dispersive medium. Although applicable to atomic physics, this model is not suitable for a semiconductor microcavity: it is independent of the Lorentz oscillator position inside the cavity. Moreover, the coherent eigenstate is badly coupled to the outside photon states, because the random walk to the surface is very long compared to exciton destructive events and the transmission coefficient is most often very weak.
