Broadband Plasmon Resonance Enhanced Third-Order Optical Nonlinearity in Refractory Titanium Nitride Nanostructures

Ultrafast control of light by light at the nanoscale may enable numerous long-awaited applications in nanophotonics. However, traditional plasmonic materials suffer from low optical thresholds that limit their usages. Titanium nitride has shown superior properties such as thermal stability, low cost, and a CMOS-compatible fabrication process. Even though titanium nitride is a prominent alternative plasmonic material, little is known about its optical nonlinearities and underlying mechanisms. Specifically, the third-order nonlinearity results in modifications of the refractive index, allowing all-optical modulation and switching functionalities. Here, we experimentally obtained the third-order optical susceptibility of the titanium nitride nanoparticles in an unprecedented wide bandwidth range and compared it to those of traditional materials. The experiments show a much broader nonlinear enhancement compared to gold and silver nanoparticles. This work demonstrates that titanium nitride is a valid alternative plasmonic material for efficient active nanophotonics devices in the near-infrared region without the need for complex nanostructures.