Cascaded four-wave mixing in tapered plasmonic nanoantenna

We theoretically study the cascaded four-wave mixing (FWM) in broadband tapered plasmonic nanoantennas. In comparison with nonlinear bulk medium they demonstrate a 300-fold increase in nonlinear frequency conversion detected in the main lobe of the nanoantenna far-field pattern. This is achieved by tuning the elements of the nanoantenna to resonance frequencies involved in the FWM interaction. Our findings have a potentially broad application in ultrafast nonlinear spectroscopy, sensing, on-chip optical frequency conversion, nonlinear optical metamaterials, and photon sources.