Epsilon-near-zero media coupled with localized surface plasmon modes

Bilge Can Yildiz,Humeyra Caglayan

doi:10.1103/physrevb.102.165303

Abstract

Epsilon-near-zero (ENZ) media are an emerging platform, embracing the great potential for novel nanophotonic phenomena. One method to obtain an ENZ medium is to operate at the cutoff wavelength of the fundamental mode of a plasmonic waveguide. Control over this mode is limited to the waveguide's material and size properties. Here, we demonstrate that a plasmonic nanostructure (nanorod) can be strongly coupled to the plasmonic waveguide, providing two new hybrid resonance modes exhibiting characteristics of both guided ENZ modes and localized surface plasmon modes. Strong coupling gives rise to a Rabi splitting of 300 meV, which is demonstrated by finite-difference time domain simulations where we calculate the decay rate enhancement of a dipole emitter located in the coupled system. The hybrid modes are retrieved using the analytic coupled harmonic oscillator model. This suggested method via hybridization of modes can be used to generate and manipulate ENZ media where the unique ENZ property of wavelength extension enables effectively shrinking spatially long distances down to optically short distances.

Highlights

There has been a lot of interest in epsilonnear-zero (ENZ) materials, a new class of materials having vanishing permittivity at a certain frequency range [1,2,3]
As a proof of concept, that the fundamental (TE10) mode of a rectangular plasmonic waveguide strongly couples with the localized surface plasmon resonance of a metal nanorod placed in the core of the waveguide at its cutoff wavelength, resulting in two hybrid modes
We studied coupling between the fundamental mode of a rectangular plasmonic waveguide providing an ENZ medium at its cutoff wavelength and the localized plasmon resonance of a gold nanorod located at the center of the waveguide

Summary

INTRODUCTION

There has been a lot of interest in epsilonnear-zero (ENZ) materials, a new class of materials having vanishing permittivity at a certain frequency range [1,2,3]. In the deep subwavelength-thickness limit, metal or TCO films were recently demonstrated to support so-called ENZ modes [17,18] These are essentially a special case of long-range surface plasmon polariton modes in which the mode frequency ω is equal to the plasma frequency ωp for a wide range of wave numbers, which corresponds to the electric permittivity, ε = 0, very within the framework of the Drude model [ε = 1 − ω2p/(ω2 + iγ ω)]. As a proof of concept, that the fundamental (TE10) mode of a rectangular plasmonic waveguide strongly couples with the localized surface plasmon resonance of a metal nanorod placed in the core of the waveguide at its cutoff wavelength, resulting in two hybrid modes These modes exhibit mixed-field profiles of both ENZ and dipolar localized surface plasmons and provide enhanced density of optical states, demonstrated by the decay rate enhancement of a dipole emitter located near the nanorod

FUNDAMENTAL MODE OF THE PLASMONIC WAVEGUIDE AT THE CUTOFF

DECAY RATE ENHANCEMENT IN THE ENZ REGIME

COUPLED WAVEGUIDE-PLASMON MODES

DISCUSSION AND CONCLUSIONS