Towards Magnetically Tunable Extraordinary Optical Transmission*

Extraordinary optical transmission (EOT) is the transmission of electromagnetic radiation through an
array of subwavelength holes with an area-normalized transmittance exceeding unity. Basic
conceptualizing of transmission cannot explain such an anomalously high transmittance. Since its
discovery, there have been many attempts to make EOT actively tunable (e.g. chemical or electrical
means). There remains, however, an opportunity for advancements in the realm of magnetic tuning.
Magnetic tuning offers advantages over other means in being potentially contactless, remote, and low-
power. It comes with its own challenge--magnetic materials are generally slow to respond and have a
magnetic permeability around unity at optical frequencies. However, this difficulty could be overcome
by magnetically sensitizing either the coupling between the propagating surface plasmon polariton
modes and the modes localized to the holes; thus possibly enabling a Fano resonance, coupling light to
dark modes, or their modal frequencies. The magnetic sensitization can be realized with an ultrathin
layer of magnetic nanoparticles over the surface or along the rim of the hole, taking advantage of the
greatly intensified near-field. This work reports on our endeavor to realize such a tuning.