Exciton polaritons in periodic nanostructures

A unified picture is presented to describe exciton-photon hybrid modes, or exciton polaritons, propagating in bulk crystals, regular multiple-quantum- well structures and periodic three-dimensional arrays of quantum dots. The corresponding three dispersion equations are displayed and compared. For a finite system of quantum wells which is open to radiate, exciton-photon int eraction leads not only to the energy renormalization but also to the radia tive decay. The resonant Bragg structures represent a particular case where among N eigenmodes only one is radiative, its oscillator strength being N times greater than that for an exciton in a single quantum well. Consequenc es of the exciton-photon coupling are discussed as well for a planar array of quantum dots.