Exciton-lattice polaritons in multiple-quantum-well-based photonic crystals

However, when the emitters are not only periodically arranged as in refs 2 to 4, but are also placed in a periodically modulated dielectric environment, the interaction between them is carried by the electromagnetic Bloch waves of the photonic crystal 7,8 . Here we report the first observation of this effect using a periodic arrangement of GaAs/AlGaAs quantum wells. The formation of coherently coupled photonic-crystal excitonic-lattice polaritons manifests in our experiments through enhanced reflectivity and reconstruction of the photonic bandgap in the vicinity of the excitons. Experimental evidence of hybrid light hole–heavy hole excitonic-lattice polaritons is also presented. Coherent coupling between excitons and Bloch waves is established through comparisons of the experimental results with theory. Finally, we demonstrate the tuning of these polariton states by an electric field. Modification of the optical properties of emitters by confining their electromagnetic field in structures such as microcavities and photonic crystals have been studied extensively. Another method of manipulation of optical properties is based on the possibility of coherent radiative coupling between a collection of emissive species. R. H. Dicke showed 1 that if the spacing between the emitters was much smaller than their emission wavelength, the emitters became coherently coupled by the common radiative field. As a result, new collective states are formed, with one of them exhibiting the effect of superradiance. A similar phenomenon can also be realized when the emitters are arranged periodically in a uniform dielectric background or vacuum with the period equal to half of the emission wavelength 2 .