IST Lunch Bunch

The development of techniques for confining photons efficiently on the deep sub-wavelength spatial scale will revolutionize scientific research and engineering practices.  Nanofocusing processes are essential for maximizing the performance of a new class of nanoscale optical/photonic devices as well as sub-diffraction-resolution imaging modules for medical and fundamental scientific research.  However, the efficient coupling of light into extremely small nanofocusing devices has posed a major challenge, especially in on-chip nanophotonics, due to the need to overcome various loss mechanisms as well as the nanofabrication challenges.

In this presentation, I will discuss the achievement of highly efficient nanofocusing in an Au-SiO₂-Au gap plasmon waveguide using a carefully engineered 3D taper.  The dimensions of the SiO₂ layer, perpendicular to the direction of wave propagation, tapered linearly below 100 nm.  Our simulations suggested that the 3D linear-tapering approach could focus 830 nm light into a 2-by-5 nm² area with ≤3 dB loss and an intensity enhancement of 3.0 × 10⁴.  In a two-photon luminescence measurement, our device achieved an intensity enhancement of 400 within a 14-by-80 nm² area and transmittance of 74%.