Realizations Of Anisotropic Waveguide Metamaterials Based On Structural Dispersions Of Metallic Waveguides

Electromagnetic metamaterials have attracted much attention of researchers due to their abilities of controlling light propagation.People realized metamaterials with different functionalities by all kinds of methods.In recent years,novel waveguide metamaterials(WMMs)constructed by metallic waveguides have become a focusing topic.Researchers can realize effective media with negative permittivities by exploiting structural dispersions of metallic parallel-plate waveguides(PPWs)(or metallic rectangular waveguides)with TEm modes.And some interesting applications,such as effective surface plasmonic polaritons(SPPs)and plasmonic cloaking,were demonstrated in waveguides.However,metallic WMMs are usually isotropic and anisotropic metallic WMMs(e.g.,hyperbolic WMMs and anisotropic zero-index WMMs)are rarely in deep researches.In this paper,we will discuss realizations of hyperbolic metamaterials(HMMs)and anisotropic zero-index metamaterials(AZIMs)based on metallic waveguides.In addition,we will study applications of perfect absorption by zero-index metamaterials.The main results are as follows:1.Realizations of hyperbolic WMMs based on structural dispersions of metallic waveguidesHMMs are known as their hyperbolic dispersions,having important applications of controlling electromagnetic waves.We alternately stack two kinds of dielectrics A and B filling in a metallic PPW with thin metal wires connected to the upper and lower metal plates.Then,we can regard the whole waveguide system as a two-dimensional anisotropic medium to further realize hyperbolic WMMs by exploiting structural dispersions of the metallic PPW.We demonstrate the equal frequency contours(EFCs)of the unit cell of the WMM describing hyperbolic functions and two typical phenomena of HMMs—negative refraction and cone-like emission pattern by simulations.Moreover,we design a microwave experiment to demonstrate the phenomenon of negative refraction.2.Realizations of anisotropic zero-index WMMs based on structural dispersions of metallic waveguidesWe periodically stack two different dielectrics A and B with thin metal wires connected to the upper and lower plates in a metallic PPW or rectangular waveguides.Then,based on structural dispersions of metallic waveguides with TEm modes,we can regard the whole waveguide system as a two-dimensional anisotropic zero-index media(AZIM)around the higher cutoff frequencies.We demonstrate the EFCs describing flat elliptical functions and hyperbolic functions around the cutoff frequency,which are typical dispersion relations of AZIM.Furthermore,we demonstrate directive emissions and realize nearly perfect wave transmission in exotic waveguides and subwavelength energy focusing by simulations.3.Photonic-doped epsilon-near-zero media for coherent perfect absorptionCoherent perfect absorption increases light absorption to 100%via appropriate interference of waves.According to photonic doping theory of epsilon-near-zero media(ENZM),ENZM with defects can be homogenized as effective media.We find that the lossless defects can tune the effective permeability to be near zero,and the lossy defects can further tune the effective permeability to be a pure imaginary value to realize the coherent perfect absorption by theoretical analyses.Moreover,we show that the doping scheme enables many ways to control absorption,such as multiple channels and multiple doping defects,etc.Our work reveals a unique approach for advanced coherent perfect absorption.