Investigation On The Characteristics Of Photon Transportation In The Near-zero Anisotropic Metamaterials

Metamaterials are artificial microstructures with unusual properties not readily available in nature.Typically,the metamaterial is a sub-wavelength structure whose structural average cell size is much smaller than the guided wavelength,that is the structure unit is less than one quarter of an operating wavelength.One prominent class of metamaterials is anisotropic metamaterials,the material parameters of which are not scalars but tensors,with their principle components taking different values.This property causes the dispersion relations to display elliptic or hyperbolic shapes.And the propagation characteristics of electromagnetic waves in the so-called anisotropic metamaterials are related to their propagation direction in the media.When only a few components of the permittivity or permeability tensor are close to zero,they are called near-zero anisotropic metamaterials?NZAMMs?.NZAMMs have been extensively studied by scholars at home and abroad due to their unique electromagnetic wave manipulation characteristics.In this paper,near-zero index hyperbolic metamaterials?HMM?and elliptic metamaterials with near-zero permittivity are designed,and the characteristics of photon transportation in which are studied.The main work and results in this paper are summarized as follows:In chapter 1,the concepts of metamaterials,anisotropic metamaterials,hyperbolic metamaterials and anisotropic nearly zero-index metamaterials are introduced,as well as the research background and current research progress in this field at home and abroad.In chapter 2,we mainly studied the theory of composite right/left-handed transmission line?CRLH TL?,which be used to realize near-zero index hyperbolic metamaterials.According to transfer matrix method,Bloch theory and homogenization theory,we can obtain the equivalent circuit model of composite right/left-handed transmission line,the wave-vector dispersion relation for the TE,effective permeability and permittivity.We realized the hyperbolic metamaterials at microwave frequencies.Hyperbolic metamaterials composed of double zero materials with both permittivity and permeability near zero are designed by loading shunt inductors.Meanwhile,inductors enlarge the adjustable range of frequency.All of these are designed to achieve a very flat hyperbolic wave-vector iso-frequency dispersion diagram over a wide frequency range.In chapter 3,we present theoretical and experimental studies of the highly directive emission and subwavelength focusing based on near-zero index hyperbolic metamaterials.The highly-directive emission samples contain a rectangular part?HMM?and a wedge part?isotropic medium?,in which the EM waves with different incident angles were refracted in a direction instead of were scattered in isotropic medium.The experimentally obtained data exhibits excellent agreement with the simulation.Furthermore,the HMM allows us to control the direction of emission of a source and collect all the energy in the normal direction.We showed that the focusing resolution of the HMM at microwave frequencies.The subwavelength focusing with the narrowest full width half maximum?FWHMs?of about₂)?31 and₂)?11 at 0.95 GHz and1.5 GHz was demonstrated in the work.The realization of the subwavelength focusing which derives from the canalization regime.We show that the focusing effect does not change with the transmission distance.Finally,it is proved that the designed subwavelengthfocusing metamaterialhas super-resolution characteristics.The theoretical simulation results obtained in this chapter are in good agreement with the experimental results.In chapter 4,we propose a novel method using a concave axicon consisting of anisotropic epsilon-near-zero material?AENZ?to generate Bessel beam in visible region.Firstly,we show that the physics behind the AENZ concave axicon generated Bessel beam is different from the refractive principle of ordinary axicon.Through theoretical analysis,it is proved that concave AENZ axicon can also generate Bessel beam.Then,by reasonably designing the structural parameters of Ag/SiO₂ multilayers,the permittivity which perpendicular to the anisotropy axis is near zero,so that anisotropic epsilon-near-zero material?AENZ?can be realized.Due to very little spatial phase change in the AENZ metamaterials,we can arbitrary steer the output beams by tailoring the edge of structures.The transport properties of electromagnetic waves which emitted from the AENZ concave prism with different concave angles are studied.It is found that the electromagnetic waves emitted from each point in AENZ metamaterials are perpendicular to the tangential plane of the radiation boundary forever.Therefore,we use AENZ metamaterials with 10 degrees and 5 degrees concave angles form concave axicon with a mirror symmetry,respectively.We can observe that concave AENZ axicon can generate Bessel non-diffractive beam propagating in a straight line for a long distance.The self-healing property of Bessel beam was also observed when an obstacle was embedded on the beam path.In this chapter,we propose a novel optical element that can generate Bessel beam,which provides a new passive method for realizing non-diffractive propagation.Our results extend the application of zero refraction materials for highly efficient beam steering.