Self-locked broadband Raman-electro-optic microcomb

Optical frequency combs (OFCs), composed of equally spaced frequency lines, are essential for communications, spectroscopy, precision measurement, and fundamental physics research. Recent developments in integrated photonics have advanced chip-scale OFCs, enabling on-chip OFC generation via the Kerr or electro-optic (EO) effect. However, these nonlinear processes can occur simultaneously and are often accompanied by parasitic effects, like Raman scattering, which may impede broadband and low-noise microcomb generation. Here, we harness these interactions to demonstrate a novel OFC, the self-locked Raman-electro-optic (REO) microcomb in a lithium niobate microresonator. By leveraging the collaboration of EO, Kerr and Raman scattering, the REO microcomb spans over 300 nm (~1400 lines) with a 26.03 GHz repetition rate, achieving low-noise operation without external feedback. Our approach points to a direction for improving the performance of microcombs and paves the way for exploring new nonlinear physics, such as new laser locking techniques, through the multi-nonlinear synergy.