Optical Kerr Frequency Comb Generation in Overmoded Resonators
  We show that scattering-based interaction among nearly degenerate optical modes is the key factor in low threshold generation of Kerr frequency combs in nonlinear optical resonators possessing small group velocity dispersion (GVD). The mode interaction is capable of producing drastic change in the local GVD, resulting in either a significant reduction or increase of the oscillation threshold. It is also responsible for the majority of observed combs in resonators characterized with large normal GVD. We present results of our numerical simulations as well as supporting experimental data. 
A. B. Matsko, A. A. Savchenkov, W. Liang, V. S. Ilchenko, D. Seidel,   and L. Maleki
physics.optics