Accelerating and locked Raman solitons in micro-ring resonators: Role in supercontinuum generation

Generation of broad spectra in micro-ring cavities is particularly important for self-referencing frequency combs [1]. Wide supercontinuum (SC) generation has been demonstrated in these systems [2] but the role of the Raman effect, known to enhance spectral broadening in fibers [3], has only been recently explored numerically by means of an extended Lugiato-Lefever equation [4]. In the latter theoretical frame we found that in the presence of Raman effect cavity solitons that are locked to the frequency of the external pump (parametrized by h) do not exist for arbitrarily small losses, γ, or arbitrarily large quality factors, Q=τωp/γ (τ is the roundtrip time and #p is the optical frequency of the pump). The existence of this cut-off in Q (or γ) is entirely due to the Raman effect because locked solitons are known to exist in the γ =0 limit under higher order dispersion (HOD) terms [5].