  We demonstrate Kerr-frequency-comb generation with nanofabricated Fabry-Perot
resonators with photonic-crystal-reflector (PCR) end mirrors. The PCR
group-velocity-dispersion (GVD) is engineered to counteract the strong normal
GVD of a rectangular waveguide fabricated on a thin, 450 nm silicon nitride
device layer. The reflectors provide the resonators with both the high optical
quality factor and anomalous GVD required for Kerr-comb generation. We report
design, fabrication, and characterization of devices in the 1550 nm wavelengths
bands, including the GVD spectrum and quality factor. Kerr-comb generation is
achieved by exciting the devices with a continuous-wave (CW) laser. The
versatility of PCRs enables a general design principle and a
material-independent device infrastructure for Kerr-nonlinear-resonator
processes, opening new possibilities for manipulation of light. Visible and
multi-spectral-band resonators appear to be natural extensions of the PCR
approach.
