Platicons in lithium niobate microresonators with the photorefractive effect

Platicon microcombs have been demonstrated on various material platforms, offering wide spectral bandwidth, excellent spectral flatness, and efficient power conversion, which are of interest for numerous applications. Lithium niobate (LN) with its Pockels and Kerr effects has become a promising platform for both generating and controlling microcombs. The photorefractive (PR) effect intrinsic to LN significantly influences the dynamics of Kerr frequency comb generation in microresonators. Here, we experimentally and theoretically analyze platicons in a LN microresonator, demonstrating that the PR effect promotes comb generation during scans from the red-detuned side but hinders it when scanning from the blue-detuned side. We also report platicon microcombs generated in normal-dispersion LN microresonators, which span over 250 nm and achieve a conversion efficiency of 13.5%. This Letter expands the understanding of LN microresonators with the PR effect and highlights their potential as platforms to develop highly efficient and flat optical comb sources.