Experimental observation of self-frequency-shifting Raman quasi-solitons in a fiber Fabry-Perot resonator

Abstract: We report the generation of self-frequency-shifting Raman quasi-solitons in a pulse-pumped high-Q fiber Fabry-Perot resonator in the weak normal dispersion regime. They are induced by modulation instability mediated by fourth-order dispersion in a regime where the Raman gain overwhelms the cavity losses. The resulting spectrum, spanning over 50 THz, is reminiscent of the supercontinuum generated in single-pass waveguides. For the first time to our knowledge, we clearly identify this process using a dispersive Fourier transform experiment. Additionally, we demonstrate the suppression of modulation instability by tuning the synchronization mismatch between the pump repetition rate and the cavity roundtrip time, enabling the generation of a standard dissipative Kerr soliton in this system. These observations align remarkably well with numerical simulations based on a generalized Lugiato-Lefever equation, incorporating the Raman response of the optical fiber.