The coupling of the two oscillators, photons modes in the semiconductor optical microcavity and excitons of the quantum wells, results in the energy anticrossing of the bare oscillators, giving rise to the two new normal modes for the system, known as the upper and lower polariton resonances (or branches). The energy shift is proportional to the coupling strength (dependent, e.g., on the field and polarization overlaps). The higher energy or upper mode (UPB, upper polariton branch) is characterized by the photonic and exciton fields oscillating in-phase, while the LPB (lower polariton branch) mode is characterized by them oscillating with phase-opposition. Microcavity exciton-polaritons inherit some properties from both of their roots, such as a light effective mass (from the photons) and a capacity to interact with each other (from the strong exciton nonlinearities) and with the environment (including the internal phonons, which provide thermalization, and the outcoupling by radiative losses). In most cases the interactions are repulsive, at least between polariton quasi-particles of the same spin type (intra-spin interactions) and the nonlinearity term is positive (increase of total energy, or blueshift, upon increasing density).
Recently, researchers measured the long-range transport in organic materials coupled to optical micro-cavities and showed that exciton-polaritons propagate over several microns. The members of the team associated with the experiment were Georgi Gary Rozenman, Katherine Akulov, Adina Golombek and Tal Schwartz from Tel-Aviv University.
^Georgi Gary Rozenman; Katherine Akulov; Adina Golombek; Tal Schwartz (2018). "Long-Range Transport of Organic Exciton-Polaritons Revealed by Ultrafast Microscopy". ACS Photonics. 5 (1): 105–110. doi:10.1021/acsphotonics.7b01332.