Abstract
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.