Nanofocusing of Toroidal Dipole for Simultaneously Enhanced Electric and Magnetic Fields Using Plasmonic Waveguide

Optical toroidal dipole and electromagnetic field enhancement have attracted much interest owing to their interesting physical features and various potential nanophotonic applications. In this paper, novel antireflective nanofocusing methods to deliver and squeeze toroidal dipole moment with simultaneous enhancement of electric and magnetic fields are suggested. By coupling the two fundamental modes of a metal-insulator-metal waveguide with a partial mirror in a waveguide and a nanocavity, resonant squeezing of longitudinal and perpendicular toroidal dipoles in an ultracompact nanocavity (~λ²/190) is achieved at the near-telecom wavelengths. Moreover, electric and magnetic field enhancements occur simultaneously in a designated nanocavity. We expect that the proposed scheme would pave a way to engineer nanophotonic waveguide based light-matter interactions by enhancing both electric and magnetic fields. This study would interest both nanophotonics and quantum optics communities.