Temporal soliton and optical frequency comb generation in a Brillouin laser cavity

Temporal cavity soliton generation in fiber cavities or microresonators has achieved great breakthroughs and found significant applications in many fields. Despite recent advances in soliton frequency comb generation via external driving or pump light, it remains challenging to identify a versatile approach for driving the cavity coherently, tuning the mode spacing of soliton frequency combs largely, and achieving long-term operation. Here, instead of using external pump light to drive the cavity coherently, intra-cavity pumping is proposed to drive a Kerr-nonlinear optical cavity for generating temporal solitons and soliton frequency combs. By introducing the Brillouin gain into the cavity, the generated intra-cavity Brillouin lasers are used as the pump light to drive the cavity coherently for generating temporal solitons. In contrast to previous works, the soliton pulses form spontaneously via intra-cavity pumping without the need for fine-tuning the external pump light (to match the cavity resonance), which enables the generation of soliton frequency combs via cascaded four-wave mixing between multiple wavelength intra-cavity Brillouin lasers. Furthermore, by varying the frequency separation of multiple wavelength intra-cavity Brillouin lasers, the soliton pulses with a pulse width of hundreds of femtoseconds and a repetition rate of gigahertz (GHz) to terahertz (THz) are achieved via intra-cavity pumping, corresponding to the generation of soliton frequency combs with step tunable mode spacing from GHz to THz.