Hard and soft excitation regimes of Kerr frequency combs

We theoretically study the stability conditions and excitation regimes of hyperparametric oscillation and Kerr frequency comb generation in continuously pumped nonlinear optical microresonators possessing an anomalous group velocity dispersion. We show that both hard and soft excitation regimes are possible in the microresonators. Selection between the regimes is achieved via change in the parameters of the pumping light.