Octave-spanning frequency comb generation in a silicon nitride chip
  We demonstrate a frequency comb spanning an octave via the parametric process of cascaded four-wave mixing in a monolithic, high-Q silicon nitride microring resonator. The comb is generated from a single-frequency pump laser at 1562 nm and spans 128 THz with a spacing of 226 GHz, which can be tuned slightly with the pump power. In addition, we investigate the RF-noise characteristics of the parametric comb and find that the comb can operate in a low-noise state with a 30-dB reduction in noise as the pump frequency is tuned into the cavity resonance. 
Yoshitomo Okawachi, Kasturi Saha, Jacob S. Levy, Y. Henry Wen, Michal   Lipson, and Alexander L. Gaeta
physics.optics