Surface modes in plasmonic Bragg fibers with negative average permittivity

TL;DR

This paper explores surface modes in plasmonic Bragg fibers, showing their existence depends on the sign of the average permittivity, with implications for topologically protected plasmonic surface modes.

Contribution

It demonstrates that surface modes in plasmonic Bragg fibers are determined by the sign of the averaged permittivity and explores their robustness and relation to surface plasmon polaritons.

Findings

Surface modes occur at interfaces with negative average permittivity.

Surface mode propagation constants approach those of planar surface plasmon polaritons.

Surface modes exhibit robustness against structural variations.

Abstract

We investigate surface modes in plasmonic Bragg fibers composed of nanostructured coaxial cylindrical metal-dielectric multilayers. We demonstrate that the existence of surface modes is determined by the sign of the spatially averaged permittivity of the plasmonic Bragg fiber, $\bar{% \varepsilon}$. Specifically, localized surface modes occur at the interface between the cylindrical core with $\bar{\varepsilon}<0$ and the outermost uniform dielectric medium, which is similar to the topologically protected plasmonic surface modes at the interface between two different one-dimensional planar metal-dielectric lattices with opposite signs of the averaged permittivity. Moreover, when increasing the number of dielectric-metal rings, the propagation constant of surface modes with different azimuthal mode numbers is approaching that of surface plasmon polaritons formed at the corresponding planar metal/dielectric interface. Robustness of such surface modes of plasmonic Bragg fibers is demonstrated too.