Robust Multimode Waveguide Design for Avoided Mode Crossing-Suppressed Microresonators

Microresonator-based optical frequency combs enable many potential applications, from frequency metrology to optical communication. Soliton comb generation relies on dispersion control. For bright soliton generation, it is required to have anomalous group velocity dispersion. However, the avoided mode crossing in the microresonator can disturb the local dispersion and may prevent the soliton formation. Although the avoided mode crossing may enable dark soliton generation, the unintended avoided mode crossing distorts the comb spectrum. Here, we present a robust multimode waveguide design against intermodal coupling to suppress unintended avoided mode crossing. By engineering the waveguide dimension, the phase mismatch between coupling modes can be increased, which will significantly reduce the modal coupling strength. We experimentally demonstrated the avoided mode crossing-suppressed microresonators in the AlGaAs-on-insulator platform.