Quantum theory of exciton-photon coupling in photonic crystals slabs with embedded quantum wells

We report on a theoretical description of radiation-matter coupling for semiconductor-based photonic crystal slabs, in which quantum wells are embedded within the waveguide core layer. We develop a full quantum theory by quantizing both the electromagnetic field with a spatial modulation of the refractive index and the exciton center-of-mass field in a periodic piecewise constant potential. The second-quantized Hamiltonian of the interacting system is diagonalized with a generalized Hopfield method, thus yielding the complex dispersion of mixed exciton-photon modes including losses. The occurrence of both weak- and strong-coupling regimes is studied, and it is concluded that the new eigenstates of the system are described by quasiparticles called photonic crystal polaritons, which can occur in two situations as follows: (1) below the light line, when a resonance between exciton and nonradiative photon levels occurs (guided polaritons) and (2) above the light line, provided that the exciton-photon coupling is larger than the intrinsic radiative damping of the resonant photonic mode (radiative polaritons). For a square lattice of air holes, it is found that the energy minimum of the lower polariton branch can occur around normal incidence. The latter result has potential implications for the realization of polariton parametric interactions in photonic crystal slabs.