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

TL;DR

This paper develops a comprehensive quantum theory for exciton-photon interactions in photonic crystal slabs with embedded quantum wells, revealing conditions for polariton formation and their potential for nonlinear optical applications.

Contribution

It introduces a full quantum model for exciton-photon coupling in photonic crystal slabs, including losses and dispersion, and identifies new regimes of polariton states.

Findings

Identification of guided and radiative polaritons in photonic crystal slabs.

Energy minima of lower polariton branch near normal incidence.

Potential for polariton parametric interactions in these structures.

Abstract

A theoretical description of radiation-matter coupling for semiconductor-based photonic crystal slabs is presented, in which quantum wells are embedded within the waveguide core layer. A full quantum theory is developed, 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 quasi-particles called photonic crystal polaritons, which can occur in two situations: (i) below the light line, when a resonance between exciton and non-radiative photon levels occurs (guided polaritons), (ii) above the light line, provided 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.