Modulational instability and solitons in excitonic semiconductor waveguides

TL;DR

This paper theoretically investigates nonlinear light propagation in excitonic semiconductor waveguides, revealing strong modulational instability and soliton formation due to exciton-exciton interactions near resonance.

Contribution

It introduces a new analysis of modulational instability and soliton formation in excitonic waveguides, highlighting the impact of large excitonic nonlinearities near resonance.

Findings

Unconventional modulational instability observed near exciton resonance.

Formation of solitary waves inside and outside the polaritonic gap.

Spectral broadening of light pulses in the waveguide.

Abstract

Nonlinear light propagation in a single-mode micron-size waveguide made of semiconducting excitonic material has been theoretically studied in terms of exciton-polaritons by using an analysis based on macroscopic fields. When a light pulse is spectrally centered in the vicinity of the ground-state Wannier exciton resonance, it interacts with the medium nonlinearly. This optical cubic nonlinearity is caused by the repulsive exciton-exciton interactions in the semiconductor, and at resonance it is orders of magnitude larger than the Kerr nonlinearity (e.g., in silica). We demonstrate that a very strong and unconventional modulational instability takes place, which has not been previously reported. After reducing the problem to a single nonlinear Schr\"odinger-like equation, we also explore the formation of solitary waves both inside and outside the polaritonic gap and find evidence of spectral broadening. A realistic physical model of the excitonic waveguide structure is proposed.