Advanced Progress on χ⁽³⁾ Nonlinearity in Chip-Scale Photonic Platforms

χ⁽³⁾ nonlinearity enables ultrafast femtosecond scale light-to-light coupling and manipulation of intensity, phase, and frequency. χ⁽³⁾ nonlinear functionality in micro-and nano-scale photonic waveguides can potentially replace bulky fiber platforms for many applications. In this Review, we summarize and comment on the progress on χ⁽³⁾ nonlinearity in chip-scale photonic platforms, including several focused hot topics such as broadband and coherent sources in the new bands, nonlinear pulse shaping, and all-optical signal processing. An outlook of challenges and prospects on this hot research field is given at the end.