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

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-1cm-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-1cm-2, can be achieved by reducing propagation losses.

III-nitride on silicon electrically injected microrings for nanophotonic circuits.

Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440 mW/cm2 output power density at 20 mA from such microrings with diameters of 30 to 50 µm. The first steps towards achieving an integrated photonic circuit are demonstrated.

Increasing the angular sensitivity of two-dimensional photonic crystal based sensors to arbitrary values.

A new design of photonic crystal (PhC) for optical sensing using guided mode resonance (GMR) is presented. We theoretically show that angular sensitivity is inversely proportional to the group velocity of the probed mode and can be made arbitrarily high in a properly designed PhC. PhCs made in polycrystalline diamond on insulator are fabricated. The angular sensitivity dependence is validated. We measured modes with group velocity of c/80 at a wavelength of 800 nm. A sensitivity in the order of 500 ° per refractive index unit is inferred, a value much larger than the one usually encountered in PhCs.