Gap Plasmon Enhanced Second Harmonic Generation in Epsilon-Near-Zero Nanolayers

With the ability to confine light to subwavelength volumes, plasmonic nanostructures and metamaterials have proven to be powerful tools for nanophotonic applications. For nonlinear processes, however, the small dimensions of nanophotonic devices can become problematic, as phase-matching techniques—designed to increase interaction lengths—are no longer applicable. In this work, we utilize the field confining properties of plasmonic nanoparticles in a modified metal-insulator-metal (MIM) patch nanoantenna to efficiently couple to an epsilon near zero (ENZ) mode in a nanolayer film of indium tin oxide (ITO). The modified MIM device differs from traditional MIM structures in that the insulator spacing layer makes use of a low index, 12 nm nanolayer ITO film on top of a higher index SiO2 layer, allowing for highly confined electric fields. Combined with the enhanced nonlinear response at the ENZ point of the ITO film, we are able to achieve second harmonic generation (SHG) enhancements of up to 50,000 relative...