Normal-Mode Coupling In Planar Semiconductor Microcavities

Abstract

Scientists have realized for many years that it is possible to alter the spontaneous emission properties of a light-matter system by changing the boundary conditions[l]. Due to improvements in growth techniques for semiconductor structures, added emphasis has been placed upon tailoring the spontaneous emission characteristics of semiconductor quantum well heterostructures by enclosing them in distributed Bragg reflector (DBR) microcavities [2-8]. High fmesse microcavities can enhance the ratio of spontaneous emission into the cavity’s lasing mode to the total spontaneous emission, thereby reducing lasing threshold when the cavity transmission wavelength matches the emitter’s wavelength. One interesting and important side-effect of such high Q cavities is that the intracavity photon lifetime can be made quite large, so that the material in the cavity may have the chance via dipole coupling to absorb and reemit radiation several times before energy irreversibly escapes from the system. If this is the case, one is said to be in the strong coupling regime, where the light-matter coupling rate, Ω is greater than both the inverse photon lifetime, κ, and the polarization dephasing rate of the absorbing medium, λ. Further, this coupling serves to lift the degeneracy in the energy eigenstates of the uncoupled system. If one then diagonalizes the 2x2 interaction matrix to find the coupled system’s eigenenergies and eigenstates, one finds two new states which are split symmetrically in energy from the original state by a fi:equency which is characteristic of the coupling strength.