Fabrication and measurement of AIN cladding AIN/GaN multiple-quantum-well waveguide for all-optical switching devices using intersubband transition

We measured intersubband (ISB) absorption in high-mesa waveguides consisting of AIN cladding layers and AIN/GaN multiple quantum wells (MQW). Inductively coupled plasma (ICP) dry etching for waveguide fabrication was optimized to reduce propagation loss by achieving vertical and smooth sidewalls. We changed the ICP/RF power and introduced intervals during the etching process in order to overcome the induction time of the etching rate and the instability of plasma observed from long etching experiments. The ISB absorption greater than 20 dB was clearly observed at around 1.5 pm. The insertion loss of an 800-mu m-long waveguide was 5-1OdB including the coupling loss between a fiber and the end of the waveguide. With this low-loss waveguide, we observed a saturation of 10dB in the ISB absorption with 100pJ probe light introduced to the waveguide. We thus demonstrated the possibility of achieving all-optical switching devices with low loss using the ISB transition of AIN-based materials.