  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.
