  Aluminum nitride is an appealing nonlinear optical material for on-chip
wavelength conversion. Here we report optical frequency comb generation from
high quality factor aluminum nitride micro-ring resonators integrated on
silicon substrates. By engineering the waveguide structure to achieve near-zero
dispersion at telecommunication wavelengths and optimizing the phase matching
for four-wave mixing, frequency combs are generated with a single wavelength
continuous-wave pump laser. The Kerr coefficient (n2) of aluminum nitride is
further extracted from our experimental results.
