Spectral tailoring of Raman soliton generation via a dispersion-managed fiber Fabry-Pérot resonator.

Dissipative Raman solitons in passive Kerr resonators have emerged as a promising route to broadband coherent frequency comb generation. Yet, their center frequency has so far been mostly fixed near the Raman gain peak (13 THz downshifted from the pump center frequency in silica-based fibers), constraining spectral coverage and compatibility with standard optical amplifiers. This limitation arises because the frequency shift of Raman solitons that fulfill phase-matching and group-velocity-matching conditions has to fall within the Raman gain band, leaving little room for spectral tuning when using a single conventional optical fiber. Here, we demonstrate that dispersion management of the fiber Fabry-Pérot resonator, which allows us to directly shift the soliton center frequency. By combining two fibers with complementary dispersion profiles, we tailor the resonator's average dispersion to satisfy the phase-matching conditions for soliton formation at a target frequency downshifted by 7.8 THz from a pulsed pump, which is well outside the conventional 13 THz Raman gain band. This allows us to optically amplify the dissipative Raman soliton with a commercial L-band erbium-doped fiber amplifier and fully characterize its temporal profile via the frequency-resolved optical gating technique.