3D Nanofocusing plasmonic waveguide

We have demonstrated experimentally a highly efficient on-chip three-dimensional (3D) linearly tapered metal-insulator-metal (MIM) nanoplasmonic photon compressor (3D NPC) with a final aperture size of 14 × 80 nm². An optimized and linearly tapered MIM gap plasmon waveguide could theoretically reduce the excessive losses that would occur during nanofocusing processes. In simulation study, this approach could enable nanofocusing into a 2 × 5 nm² area with the coupling loss and maximum E2 enhancement of 2.5 dB and 3.0 × 10⁴, respectively. We fabricated the 3D NPC on a chip employing electron beam-induced deposition and demonstrated its highly localized light confinement using a two-photon photoluminescence (TPPL) technique. From the TPPL measurements, we experimentally estimated an intensity enhancement of 400 within a 14 × 80 nm² cross-sectional area and a coupling efficiency of -1.3 dB (or 74% transmittance).