Nanoscale Engineering of Optical nonlinearity Based on a Metal Nitride/Oxide Heterostructure

The abilities to modulate linear and nonlinear optical response of materials in the nanoscale are of central importance in the design and fabrication of photonic devices for applications like optical modulators. Here, based on a simple transition metal oxide/nitride (TiO₂/TiN) system, we show that it is possible to tune the optical properties by controlling the nanoscale architecture. Through controlled oxidation of the plasmonic TiN nanoparticle surfaces, we observe a continuous change of linear and nonlinear optical (NLO) properties with the increase of the thickness of the oxide layer in the TiN/TiO₂ heterogeneous architecture. The NLO response is manifested by the strong saturable absorption with a structurally tunable negative NLO absorption coefficient. The variation in the NLO absorption coefficient by up to 7-fold can be connected to the relative change in the volume fraction of the metallic core and the dielectric shell. We demonstrate further that the optimized TiN-TiO₂ heterostructures can be used to drive an optical switch for pulse laser generation in the 1.5 μm wavelength region. Our results delineate a topochemical process for optimization of the NLO properties of common plasmonic materials for photonic applications based on simple materials chemistry.