Intersubband cavity polaritons: The role of higher photonic modes

We present a theoretical analysis of the consequence of coupling between higher photonic modes and intersubband excitations in microcavities with embedded multiple quantum wells (MQWs). The polariton dispersion relations and angle-resolved absorption spectra are calculated numerically using a semiclassical approach based on a transfer-matrix formulation and effective-medium approximation. The obtained results are interpreted employing a multiple coupled harmonic-oscillator model supplemented by the input-output formalism. We show that when the MQW occupies a large fraction of space between cavity mirrors the coupling with higher photonic modes cannot be considered as a negligibly small perturbation in formation of the intersubband cavity polariton modes. When appropriate conditions are fulfilled the coupling between higher photonic modes and so-called dark intersubband electronic excitations can lead, in accordance with experimental results, to the formation of complex multiple-peaked absorption spectra.