Eccentric coaxial gap-plasmon aperture arrays for enhanced extraordinary optical transmission and applications

The eccentric coaxial metal waveguide is similar to concentric coaxial structure, which has been studied extensively in the plasmonics community. Compared to the concentric structure, the eccentric structure has many benefits, including: (1)stronger subwavelength field localization around the narrowest gap, (2) improved optical coupling to the lowest order mode due to linear polarization, and (3) an increased effective index due to the gap plasmon. Yet, there have been no reports on the plasmonic aspects of this structure so far. This paper investigates on focussed-ion beam fabricated arrays of eccentric coaxial structures. An effective index method is used to analyze the field localization and enhancement. The gap plasmon is assumed dominant over conformal effects which can play an important role. Results show that the analytic theory agrees very well with a commercially-available finite-difference mode-solver(FDMS). Based on the simulations, strong modification to the extraordinary optical transmission peak is expected, with increased transmission over the concentric coaxial and cylindrical structures.