A. Armitage

Cavity-polariton dispersion and polarization splitting in single and coupled semiconductor microcavities

Recent theoretical and experimental work on linear exciton-light coupling in single and coupled semiconductor microcavities is reviewed: emphasis is given to angular dispersion and polarization effects in the strong-coupling regime, where cavity-polariton states are formed. The theoretical formulation is based on semiclassical theory. The energy of single-cavity modes is determined by the Fabry-Pérot frequency ωc as well as by the center of the stop band ωs of the dielectric mirrors; the phase delay in the dielectric mirrors carries a nontrivial angle-and polarization dependence. The polarization splitting of cavity modes depends on the mismatch between ωc and ωs, and increases with internal angle as sin2θeff. Interaction between the cavity mode and quantum-well (QW) excitons is described at each angle by a two-oscillator model, whose parameters are expressed in terms of microscopic quantities. Weak and strong coupling regimes and the formation of cavity polaritons are described. Comparison with experimental results on a GaAs-based cavity with In0.13Ga0.87As QWs shows that a quantitative understanding of polariton dispersion and polarization splitting has been achieved. Coupling of two identical cavities through a central dielectric mirror induces an optical splitting between symmetric and antisymmetric modes. When QW excitons are embedded in both cavities at antinode positions, the system behaves as four coupled oscillators, leading to a splitting of otherwise degenerate exciton states and to separate anticrossing of symmetric and antisymmetric modes. These features are confirmed by experimental results on coupled GaAs cavities with In0.06Ga0.94As QWs. An analysis of reflectivity lineshapes requires the inclusion of the effect of resonance narrowing of cavity polaritons. Finally, the polarization splitting in a coupled cavity depends both on the single-cavity factors and on the angle-and polarization dependence of the optical coupling between the cavities. Inclusion of all these effects provides a good description of the experimental findings.

Exciton polaritons in single and coupled microcavities

Recent work on strong coupling exciton–polariton phenomena in single and coupled microcavities is presented. We describe experiments for single cavities where the strong coupling nature of the excitations manifests itself. It is also shown that coupled cavities enable optically induced coupling between macroscopically separated exciton states to be achieved, and polaritons with strongly anisotropic properties to be realised. Results for both inorganic and organic microcavities are presented.

Modelling of asymmetric excitons in organic microcavities

The behaviour of strongly coupled optical and excitonic states has been observed experimentally in microcavities containing organic semiconductors. Due to the asymmetry of the exciton absorption, modifications to existing models are necessary. Presented here are revised linear dispersion and quantum mechanical models, which are used to verify the observed phenomena.

Excitons and Polaritons in Semiconductor Microcavities

We review various aspects of the behaviour of semiconductor microcavities, focusing on the important role that polaritons play in determining their optical properties. The review covers angular dependent measurements of cavity polariton dispersions, the effects of motional narrowing on the inhomogeneous line widths, and the possibilities for observing consequences of Bose-Einstein statistics in microcavities.

Strong Coupling in Organic Semiconductor Microcavities Based on J-Aggregates

We report a room temperature study of the strong coupling regime in a planar microcavity, using ‘J-aggregates’ of cyanine dyes. The characteristic features of energetic anticrossing between photon and exciton clearly observed, indicating the formation of cavity polaritons. Rabi-splittings as large as large 80 meV are measured. We generate polariton emission via non-resonant excitation and find that emission from the lower polariton branch dominates. We present light emitting diodes (LEDs) based on J-aggregates/polymer composite films, indicating that electrically generated polariton emission may also be possible.