Ultrathin 90-degree sharp bends for spoof surface plasmon polaritons.

Yihao Yang,Sanshui Xiao,Jingjing Zhang,Hongsheng Chen,N Asger Mortensen

doi:10.1364/oe.23.019074

Abstract

At low frequencies outside the plasmonic range, strongly confined surface waves can be achieved on periodically structured metal surfaces, thereby allowing for the design of compact electromagnetic guiding devices. Here, we propose an approach to realize highly efficient transmission of spoof surface plasmons around 90-degree sharp bends on ultrathin metallic films in the microwave regime. We demonstrate that by judiciously engineering the structure, the dispersion relation can be designed to reduce the scattering. Furthermore, the reflection can be suppressed by proper structural decoration at the bending corner. A one-dimensional scattering theory is employed to understand and verify the transmission properties of our waveguide bend structure. Our design scheme is not restricted to the specific structure we propose here but can be applied to other guiding components built up on two dimensional metal surfaces.

Highlights

At optical frequencies, surface electromagnetic waves can sustain at the interface between noble metals and air, due to the interaction between surface-charge oscillation and the electromagnetic (EM) fields, which is the so-called surface plasmon polaritons (SPPs) [1]
At low frequencies outside the plasmonic range, strongly confined surface waves can be achieved on periodically structured metal surfaces, thereby allowing for the design of compact electromagnetic guiding devices
The reflection can be suppressed by proper structural decoration at the bending corner

Summary

Introduction

Surface electromagnetic waves can sustain at the interface between noble metals and air, due to the interaction between surface-charge oscillation and the electromagnetic (EM) fields, which is the so-called surface plasmon polaritons (SPPs) [1]. One of the most important properties of SPPs is the confinement of light in subwavelength scale, which is promising for various applications, such as biosensing [2], photonic circuits [3, 4], surface-enhanced Raman scattering [5, 6], photovoltaics [7], nonlinear optics [8], broadband light localization [9,10,11,12,13] etc. The surface waves are demonstrated to propagate on a planar structured waveguides with a thickness of only 0.4 mm (relative to a wavelength of around 150 mm) over a broad frequency band in microwave spectrum. The high transmission efficiency is achieved by enhancing the confinement of spoof SPPs to suppress the scattering and reducing the reflection at the bend corner with proper design. High transmission with a maximum of almost 100% is observed at several frequencies for 90-degree sharp bends, and a transmission of no less than 85% is achieved over a bandwidth of 2.1 GHz

Theory and unit cell design

Simulations and models