(Al,In)GaN waveguides with low losses for blue light photonic integrated circuits

Our work is concentrated on developing a reliable waveguide technology for transmitting blue light, that can be integrated on the bulk GaN substrate together with the nitride emitters. We utilise the strong relationship of indium incorporation into InGaN layers and the substrate off-cut to locally modify the absorption edge of InGaN quantum wells. This allows us to use the same epitaxial structure to create laser diodes and waveguides (in dedicated positions on the substrate). Our approach gives a huge advantage over hetero-integration: the perfect alignment of the elements and mechanical stability. The newest improvements of our technology are devoted to lowering the scattering at the connection between the laser and the waveguide areas. Thanks to the optimised geometry, we were able to demonstrate an output optical power of above 20 mW from our waveguide. While treating a test waveguide (500 μm) as a passive section of the laser diode cavity (500 μm gain section), the system shows the same slope efficiency as a 500 μm laser and an increase of threshold current from 55mA to 85 mA.