Raman-assisted high-efficiency soliton microcombs in a SiO₂ microsphere

Soliton microcombs, generated in high-Q microresonators, have revolutionized integrated photonic technologies such as optical clocks, spectroscopy, and telecommunications. However, conventional pump schemes suffer from low pump-to-soliton conversion efficiency and high power threshold. Besides, parasitic nonlinear processes such as stimulated Raman scattering (SRS) may also affect the generation and stabilization of soliton states. Here, we realize a high-efficiency soliton microcomb with a low power threshold by exploiting the synergistic interplay between SRS and four-wave mixing (FWM) in a high-Q SiO2 microsphere. A dual-pump strategy-where a primary pump triggers the Raman gain and a secondary pump initiates soliton microcomb formation-enables 21.8% conversion efficiency from the pump laser to the soliton state. Experimental evidence reveals that the introduction of the secondary pump allows the tuning of the center frequency of the Raman soliton microcomb within the Raman gain region. This approach not only reduces the soliton formation threshold but also enables robust soliton stabilization via dynamic Raman gain compensation and thermal suppression. Our work provides a universal pathway for energy-efficient nonlinear photonics in Raman-active microresonators.