Mode interaction aided excitation of dark solitons in microresonators constructed of normal dispersion waveguides

摘要

Kerr frequency combs from microresonators are now extensively investigated asa potentially portable technology for a variety of applications. Most studiesemploy anomalous dispersion microresonators that support modulationalinstability for comb initiation, and mode-locking transitions resulting incoherent bright soliton-like pulse generation have been reported. However, someexperiments show comb generation in normal dispersion microresonators;simulations suggest the formation of dark pulse temporal profiles. Excitationof dark pulse solutions is difficult due to the lack of modulationalinstability in the effective blue-detuned pumping region; an excitation pathwayhas been demonstrated neither in experiment nor in simulation. Here we reportexperiments in which dark pulse combs are formed by mode-interaction-aidedexcitation; for the first time, a mode-locking transition is observed in thenormal dispersion regime. The excitation pathway proposed is also supported bysimulations.