Université Côte d’Azur, CNRS, CRHEA, rue Bernard Grégory, Valbonne, France, Université Côte d’Azur, CNRS, IN?NI, Parc Valrose, Nice, France, Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bâtiment 220, Rue André Ampère, Orsay, France, Université Grenoble Alpes, CEA, LETI, MINATEC Campus, Grenoble, France

We demonstrate low-loss GaN/AlGaN planar waveguides grown by molecular beam epitaxy on sapphire substrates. By using a proper AlGaN cladding layer and reducing surface roughness we reach &lt,1dB/cm propagation losses at 633nm. These low propagation losses allow an efficient second harmonic generation using modal phase matching between a TM0 pump at 1260nm and a TM2 second harmonic at 630nm. A maximal power conversion of 2% is realized with an efficiency of 0.15%·W?1cm?2. We provide a modelling that demonstrates broadband features of GaN/AlGaN platform by showing second harmonic wavelengths tunability from the visible up to the near-infrared spectral region. We discuss drawbacks of modal phase matching and propose a novel solution which allows a drastic improvement of modal overlaps with the help of a planar polarity inversion. This new approach is compatible with low propagation losses and may allow as high as 100%·W?1cm?2 conversion efficiencies in the future. © 2017 Optical Society of America.

Aluminum alloys, Efficiency, Gallium nitride, Harmonic analysis, Harmonic generation, Infrared devices, Molecular beam epitaxy, Nonlinear optics, Phase matching, Photosensitivity, Sapphire, Surface roughness, Waveguides, Low propagation loss, Modal phase matching, Near-infrared spectral regions, Polarity inversion, Power conversion, Propagation loss, Sapphire substrates, Second harmonics, Gallium alloys