Ultrabroadband Supercontinuum Generation and Frequency-Comb Stabilization Using On-Chip Waveguides with Both Cubic and Quadratic Nonlinearities

Nanoscale aluminum nitride waveguides transform near-infrared laser light into a broad rainbow of colors, from midinfrared to visible frequencies. The asymmetric crystal structure of AlN endows the material with both χ⁽²⁾ and χ⁽³⁾ nonlinearities and allows the same color of light to be generated via different nonlinear pathways, enabling stabilization of the frequency comb and a rich, complex output spectrum. This development is of significant practical importance, as basing such waveguides on a lithography-compatible material allows for customization and mass production, greatly reducing their cost and boosting access to them worldwide.