Visible Phase-Locked Microcombs Generation in High-Index Doped Silica Glass Micro-Ring Resonators

The development of integrated microcomb in the visible light region attracts considerable interest due to their potential applications ranging from bioimaging to quantum systems. However, apart from the handful of reports of phase-locked microcombs, the realization of a phase-locked visible microcomb in the visible region has so far been elusive. Here, visible phase-locked microcombs are experimentally demonstrated by frequency conversion of a near-infrared (NIR) energetic soliton crystal microcomb in a high-index doped silica glass (HDSG) integrated micro-ring resonator. Two-color (green-NIR) and even tri-color (green-red-NIR) phase-locked microcombs are produced by the combined Pockels (chi(2)) and Kerr (chi(3)) parametric processes. The results show that bright green and yellow microcombs can be alternately produced via scanning the continuous-wave pump laser over the C + L bands. The visible microcomb power is found to be simultaneously reinforced to their maximum when the NIR microcomb evolves within the soliton crystal state. The coordinated behavior of the power evolution of descending soliton staircase between the visible and NIR microcombs is also observed, indicating the joint soliton formation and phase locking characteristics. These findings confirm the HDSG micro-ring resonator a promising integrated solution for broadband and phase-locked visible microcomb generation linking the frequency from visible green to NIR.