Dissipative Kerr solitons in an active microcavity

Abstract The emergence of soliton microcombs has catalyzed significant advancements in a wide range of applications, including optical communication, precision metrology, and astronomical calibration. Despite the existing benefits, soliton microcombs generated in passive microcavities often face significant limitations in promoting comb power and nonlinear efficiency. On the other hand, generating soliton combs within active microresonators has remained challenging due to the confined cavity volume for doping and substantial opto-thermal effects. In this study, we successfully achieve dissipative Kerr solitons in an active microcavity by sintering erbium ions (Er3+) onto its surface. The introduction of Er3+ significantly boosts the power of the microcomb within the cavity, bypassing the traditional requirement for an external erbium-doped fiber amplifier (EDFA) and paving the way toward high quality soliton microcomb integration. By operating the system below the lasing threshold, the actively optical-assisted microcomb maintains the low-noise advantages of coherently driven solitons. Our research demonstrates that the optical excitation of Er3+ facilitates the tunability of cavity losses, thereby providing a method to dynamically control the soliton properties. This enables soliton operation at a lower threshold, with a larger soliton access range, wider comb span, and enhanced comb power. The increased intracavity power and enhanced Kerr nonlinear process also enable the generation of EDFA-free solitons in a low-Q microcavity, paving the way for simplifying microcomb devices. These findings open new avenues for the formation of active cavity solitons (ACSs), where the combination of coherent and incoherent pumping within a microcavity yields superior performance and increased practicality.