Intrinsic power oscillations generated by the backaction of continuum on solitons and its implications on the transfer functions of a mode-locked laser.

Soliton mode locking is an essential technique for building compact mode-locked lasers with multigigahertz repetition rates. In this scheme, pulses behave like dissipative solitons due to the presence of gain, loss, frequency filtering, and nonlinear absorption in the cavity. The continuum waves that radiate from the perturbed soliton act back on the soliton, resulting in periodic changes in the electric field of the pulse. We find that, in the presence of gain filtering or two-photon absorption, this field modulation is converted to power modulation, which is observable from the radio-frequency spectrum of the laser's output power. We investigate its physical origin in the context of soliton perturbation theory. For comparison, we also perform numerical simulations and experiments.