Polariton optics of semiconductor photonic dots: weak and strong coupling limits

Abstract

We develop coherent optics of dipole-active, dispersionless excitons in sphericalsemiconductor photonic dots (PDs). In the absence of any incoherent scattering,both the strong and weak coupling regimes can intrinsically be realized simplyby changing the parameters of the dot and surrounding medium. A criterion,which attributes the transition between these two regimes to a discrete topologicalchange of the relevant dispersion curves, is found and approximated by an analyticexpression. The transition depends upon the intrinsic radiative lifetime of the PDphoton eigenstates, i.e. it is determined by the parameters of the structure (theoscillator strength of the exciton–photon interaction, PD radius and the ratio of thebackground dielectric constants inside and outside of the dot). We propose the use ofhigh-precision modulation spectroscopy in order to visualize the above ‘phase’transition between a well-developed polariton picture (the strong coupling regime) andweakly-interacting exciton and PD photon states (the weak coupling regime). It is shownthat the radiative decay of optically dressed PD excitons, coherently distributedamong the relevant PD eigenstates, is non-monotonous against the dot radiusa: a size-dependent increase of the effective oscillator strength at smalla saturates at , and with a increasing further towards the optical lifetime of excitons starts to increase proportionally toa, reflecting the ballistic escape of nearly bulk polaritons from the PD. The numericalsimulations are scaled to dispersionless excitons in PDs fabricated from cyanine dyeJ aggregates.