Designs And Effects In Novel Electromagnetic Metamaterials And Metasurfaces

How to manipulate the propagation of electromagnetic waves to study the interaction between light and matters always attracts enormous research interests.Exhibiting extraordinary physical properties unobtainable in nature,artificial electromagnetic microstructures have played a key role in the development of many fields including material science,electromagnetic and optical device designs.In this thesis,based on effective medium theory,artificial electromagnetic microstructures are designed to realize novel materials including complementary media and gauge field materials.Their peculiar manipulabilities to electromagnetic waves are studied and novel applications as polarization-dependent optical beam splitters and high-efficient directional collimators are achieved.More intriguing properties in these systems are also explored.The following aspects are discussed in the thesis:1.Complementary media using dielectric photonic crystalsBy accidentally tuning the filling ratio of a dielectric photonic crystal with a square lattice,triply-degenerate Dirac-like cone photonic band diagram appears at the center of the Brillouin zone.At the corresponding Dirac frequency,this photonic crystal can be effectively described as a material with simultaneous zero permittivity and permeability.Keeping the filling ratio while scaling the lattice constant,double-zero-index property can be tuned to other frequencies.With linear dispersions of effective parameters close to Dirac frequency,we successfully construct two photonic crystal structures with effective permittivity and permeability of the same magnitude but different sign,and thus the complementary media are implemented.Using microwave experiments,the unique space cancellation effect of complementary media is verified.2.Gauge field Material using anisotropic metamaterial designThrough theoretical derivation,we find that when the effective permittivity tensor of an anisotropic metamaterial meets certain criteria,its iso-frequency contour is of the shape of two circles shifted in opposite directions.Orthogonal pseudospins associated to each circle will deflect when propagating inside such a gauge field material.The effective vector potential in such a system is the reason such a split iso-frequency contour is constructed.A polarization dependent optical beam splitter is thus designed and experimentally demonstrated.Using the same design principle,we successfully extend the artificial gauge field material to optical frequencies.3.Zitterbewegung-like phenomenaDue to the interference between electrons at different energy levels,the trajectory of electrons will have a trembling motion,which is a direct proof of the wave property of electrons.First proposed by Schrodinger in the name of Zitterbewegung in the 1930s,the phenomena have never been directly observed as the periodicity of motion is on the order of de Broglie wave.Efforts are made in this thesis to observe this trembling motion in both photonic crystals with Dirac-like cone dispersion and anisotropic metamaterials.The electromagnetic wave pulses will suffer a pulse reshaping when propagating inside photonic crystals with a Dirac-like cone dispersion due to the fact that the frequency close to Dirac frequency is filtered.Only appearing in the frequency domain,this pulse reshaping cannot be the optical analogy of Zitterbewegung as not occurring in the space.In contrast,in a homogeneous medium constructed by anisotropic metamaterials,we experimentally observe the oscillations of an optical beam,the optical Zitterbewegung,which is also consistent as predicted by non-Abelian gauge field theory.4.High-efficient sub-wavelength hole collimatorDue to the grating structure used,a traditional sub-wavelength hole collimator suffers from low diffraction efficiency because of the simultaneous excitations of all diffraction orders.Using a gradient metasurface to replace the grating structure,we can customize the diffraction order needed and suppress all others.A selective scattering of electromagnetic waves in the desired direction is demonstrated in microwave experiments with high efficiency.By careful designs of artificial electromagnetic microstructures,we hope that more peculiar electromagnetic materials can be discovered and more methods to manipulate light can thus be grasped.The discovery of these intriguing properties can pave the road to the development of optical devices.