The effect of Raman scattering in Kerr comb generation in a silica toroidal microcavity

We investigated the interaction between the stimulated Raman scattering (RS) and four-wave mixing (FWM) occurring during the Kerr comb generation in a silica toroidal microcavity. While both Raman lasing and frequency comb generation have already been demonstrated, the effect of the interaction between these two phenomena is still unclear. Due to the broad Raman gain bandwidth in silica, multiple longitudinal modes are excited from single wavelength pump. Since the multiple modes interact each other via FWM, the behavior becomes complex. Figs. 1(a) and (b) show the experimental results of the cascaded generation of RS light, where we obtained 4th order RS light. As shown Fig. 1(c), two different sets of longitudinal modes were excited in a cavity. To understand this result, we developed a model based on the Lugiato-Lefever to simulate the mode interaction, such as, equation where, t R is the round-trip time, α 1 , α 2 are the intrinsic cavity losses, k is the coupling loss, δ 1 , δ 2 are the detuning of the input wavelength, L is the cavity length, β k1 , β k2 are the dispersion at each modes, γ 1 , γ 2 are the nonlinear coefficient and S 1 , S 2 are the input power. ƒ R is the fractional contribution of the delayed Raman response. h is the Raman response function. B is mode overlapping. C is mode interaction coefficient.