One-way Electromagnetic Propagation Properties In Artificial Media Made Of Layered Structures

Artificial media is a new kind of composite structure or media,such as metamaterial,photonic crystals,spoof surface plasmon polaritons structure and so on.The novel properties of artificial media include anomalous refractions,super-resolution imaging,electromagnetic stealth and so on,which are manual and unavailable in nature.As a result,the artificial media may provide potential applications on communication,imaging and military.One-way electromagnetic propagation refers that electromagnetic waves are transmitted only in a specific direction,and completely suppressed in the opposite direction,which is immune to backscattering.In this thesis we have studied one-way electromagnetic propagation properties based on artificial media made of layered structuresFirstly,nonreciprocal light phenomena,including one-way wave propagation along an interface and one-way optical tunneling,are presented at terahertz frequencies in a system of magnetically controlled multi-layered structure.By varying the surface termination and the surrounding medium,it is found that the nonreciprocal bound or radiative Tamm plasmon polartions(TPPs)can be supported,manipulated,and well excited.Nonreciprocal bound TPPs could be supported with a top magnetic layer for the multi-layered structure,giving rise to the observation of one-way wave propagation at the surface of semi-infinite layered structure.Such non-reciprocity can be attributed to the contribution of direct magnetization effect of surface magnetic layer.By varying the top layer of the proposed structure to the dielectric and the other side of the interface by metallic materials,radiative TPPS with non-reciprocity could be seen.The radiative mode solutions can be well excited directly by incident plane waves,which enables us to see one-way optical tunneling through a finite-size structure.Calculations on the asymmetrical dispersion relation of surface modes,field distribution,and transmission spectra through the structure are employed to confirm the theoretical results,which may potentially impact the design of tunable and compact optical isolators.Next,a nonreciprocal layered waveguide structure is designed,allowing for of unidirectional electromagnetic transmission in the terahertz regime,which realizes the truly “trapped rainbow”effect,that is,electromagnetic waves of different frequencies are stopped at different positions of the waveguide.Under gradient magnetic field,“trapped rainbow”effect is observed in a three-layer waveguide composed of a metal-homogeneous medium-magneto-optical media.At the same time,by adjusting the intensity of the applied uniform magnetic field,the“trapped rainbow”can be flexibly modulated in the nonreciprocal waveguide with a gradual permittivity of the core layer.Moreover,the proposed structure is immune to backscattering,which overcomes the difficulty of coupling forward and backward modes in the previous coneshaped electromagnetic stopped waveguide.The electromagnetic waves transmitted within the structure are also robust and insensitive to obstacles in the waveguide.This“trapped rainbow”backscatting-immune waveguide with dynamic modulation will provide great application in terahertz sensing and storage.