Ultra-pure RF tone from a micro-ring resonator based optical frequency   comb source
  We demonstrate a novel mode locked ultrafast laser, based on an integrated high-Q micr-oring resonator. Our scheme exhibits stable operation of two slightly shifted spectral optical comb replicas. It generates a highly monochromatic radiofrequency modulation of 60MHz on a 200GHz output pulse train, with a linewidth < 10kHz 
Alessia Pasquazi, Marco Peccianti, Brent E. Little, Sai T. Chu, David   J. Moss, and Roberto Morandotti
physics.optics