This coherent conversion of the pump laser to a frequency comb takes place inside an optical resonator which is typically of micrometer to millimeter in size and is therefore termed a microresonator.
One important property of Kerr frequency combs, which is a direct consequence of the small dimensions of the microresonators and their resulting large free spectral ranges (FSR), is the large mode spacing of typical Kerr frequency combs.
For mode-locked lasers this mode spacing, which defines the distance in between adjacent teeth of the frequency comb, is typically in the range of 10 MHz to 1 GHz.
[3] More recent research has expanded the range of available platforms further which now includes diamond,[4] aluminum nitride, [5] lithium niobate,[6] and, for mid-infrared pump wavelengths, silicon.
[7] Because both use the nonlinear effects of the propagation medium, the physics of Kerr frequency combs and of supercontinuum generation from pulsed lasers is very similar.