Design and Fabrication of AlGaAs-on-Insulator Microring Resonators for Nonlinear Photonics

Recent advances in integrated nonlinear material platforms and low-loss optical microresonators enabled a broad range of chip-scale optical applications, such as optical frequency combs, quantum photonics, and optical signal processing. The aluminum gallium arsenide-on-insulator (AlGaAsOI) platform exhibiting high nonlinearity, strong light confinement, and negligible two-photon absorption has motivated research in realizing highly efficient nonlinear components. Low loss and dispersion engineering are essential for nonlinear processes in waveguides as the former allows for a long nonlinear interaction distance while the latter ensures good phase matching. Constructing waveguides into microresonators can bring the nonlinear efficiency of the device to an unprecedented level but also requires extra considerations concerning the excess losses induced by waveguide bend and coupler, and the dispersion perturbation induced by intermodal coupling. This paper presents the fabrication process and its critical aspects for high Q AlGaAsOI microresonators. We report the highest Q for high-confinement III-V microring resonators that are fabricated using an electron-beam lithography-based patterning process. We also present an efficient coupler that simplifies the post-processing step for fiber-chip coupling. Moreover, we present generic design methods to suppress the avoided mode crossing (AMX) or dispersion defects in microresonators and demonstrate AMX-free AlGaAsOI microresonators.