Azimuthal Kerr combs with predictable mode spacing in surface nanoscale axial photonic microresonators

Optical frequency combs were generated for the first time in surface nanoscale axial photonic microresonators (SNAPRs) using continuous-wave light pumping. These SNAPRs were created in silica optical fibers through a localized heating process. The frequency combs created from fibers with different diameters (220 µm, 440 µm, and 660 µm) exhibited consistent spectral spacing that was in agreement with the theoretical spacing for untreated fibers of their respective sizes, without the need for fine-tuning the fabrication recipe.