Intrinsic polarity inversion in III-nitride waveguides for efficient nonlinear interactions

Abstract

III-nitrides provide a versatile platform for nonlinear photonics. In this work, we explore a new promising configuration – composite waveguides containing GaN and AlN layers with inverted polarity, i.e., having opposite signs of the χ (2) nonlinear coefficient. This configuration allows us to address the limiting problem of the mode overlap for nonlinear interactions. Our modelling predicts a significant improvement in the conversion efficiency. We confirm our theoretical prediction with the experimental demonstration of second harmonic generation with an efficiency of 4%W -1 cm -2 using a simple ridge waveguide. This efficiency is an order of magnitude higher compared to the previously reported results for III-nitride waveguides. Further improvement, reaching a theoretical efficiency of 30%W -1 cm -2 , can be achieved by reducing propagation losses.