Efficient Intermodal Third-Harmonic Generation in Adiabatic Silica Nanofiber

We successfully fabricate silica nanofibers that permit adiabatic transmission of the higher-order spatial modes by tapering wet-etched optical fibers. Phase-matched intermodal third-harmonic generation in a 760-nm-thick nanofiber is demonstrated with an efficiency higher than 1.05*10-4.