查看文章

Optical frequency combs enable state-of-the-art applications including frequency metrology, optical clocks, astronomical measurements, and sensing. Recent demonstrations of microresonator-based Kerr frequency combs or microcombs pave the way to scalable and stable comb sources on a photonic chip. Generating microcombs in the short-wavelength range, however, has been limited by large material dispersion and optical loss. Here we demonstrate a scheme for efficiently generating microcombs near the edge of the visible spectrum in a high- aluminum nitride microring resonator. The enhanced Pockels effect strongly couples infrared and near-visible modes into hybrid mode pairs, which participate in the Kerr microcomb generation process and lead to strong Cherenkov-like radiation in the near-visible band an octave apart. A surprisingly high on-chip conversion efficiency of 22% is achieved from a …