  Kerr frequency combs generated from microresonators are the subject of
intense study. Most research employs microresonators with anomalous dispersion,
for which modulation instability is believed to play a key role in initiation
of the comb. Comb generation in normal dispersion microresonators has also been
reported but is less well understood. Here we report a detailed investigation
of few-moded, normal dispersion silicon nitride microresonators, showing that
mode coupling can strongly modify the local dispersion, even changing its sign.
We demonstrate a link between mode coupling and initiation of comb generation
by showing experimentally, for the first time to our knowledge, pinning of one
of the initial comb sidebands near a mode crossing frequency. Associated with
this route to comb formation, we observe direct generation of coherent,
bandwidth-limited pulses at repetition rates down to 75 GHz, without the need
to first pass through a chaotic state.
