Generation of Kerr Frequency Combs in Resonators with Normal GVD
  We show via numerical simulation that Kerr frequency combs can be generated in a nonlinear resonator characterized with normal group velocity dispersion (GVD). We find the spectral shape of the comb and temporal envelope of the corresponding optical pulses formed in the resonator. 
Andrey B. Matsko, Anatoliy A. Savchenkov, and Lute Maleki
physics.optics