Heterodyne detection applied to the characterization of nonlinear integrated waveguides

Nonlinear optics has been a productive field of research and investigation for a few decades now, but the rapid progression of photonic integration platforms in recent years has opened up a whole new range of applications. On-chip integration of effective saturable absorbers and secondary sources including Brillouin laser, supercontinua, or frequency combs are few examples of the very wide possibilities offered by nonlinear nanophotonics. In this context, materials with large third-order optical nonlinearities become highly sought after, as they enable the development of nonlinear functionalities at low input powers. Given a large number of potential candidates as material for nonlinear nanophotonics, it becomes even more important to be able to measure their nonlinear optical response [1] . The two most common techniques for measuring the optical nonlinearity of materials are the Z-scan [2] and four wave mixing (FWM) [3] techniques. The Z-scan method can only be applied to bulk materials, and not to optical waveguides such as the ones used in nanophotonics. In contrast, FWM can measure nonlinearities in waveguides but requires a phase matching, long waveguides with low losses and important optical power.