Study On Asymmetric Transmissions Based On Anisotropic Metallic Micro/nao Structures

Metamaterial is a new word in the 21 st century.Generally,it means the periodically or randomly arranged artificial structures with subwavelength sizes.The metamaterials have supernormal physical properties unavailable naturally occurring,such as,toroidal dipole response,asymmetric transmissions,anomalous refractions and so on.Because of these fascinating properties,metamateriales result in extensive attention in the field of scientific research.As a result,metamateriales will produce far-reaching effects in communication,detection,imaging and sensing.With the development of metamaterial,metasurface(metamaterial with ultrathin thickness)is proposed recently,which has shown great potential in applications.The anisotropic metallic micro/nano structure is a kind of metamaterial,whose physical properties are related to the polarization directions of the incoming electromagnetic waves.The works of this thesis are based on simulation and experiment.Firstly,this thesis researched the asymmetric transmissions of anisotropic metamaterial,which lay the foundation of optical diode,optical isolator,polarization switch and so on;Secondly,this article researched the unidirectional propagation of surface plasmon polariton(SPP)induced by metasurface which makes it possible to manipulate the propagation trajectories of electromagnetic waves,freely.It is found that the spin state of incoming electromagnetic waves can also control the propagations of SPP.As a result the metasurface has an important meaning in the research of photo-electronics.Then,the main contents of thesis are as follows:(1)A bilayer chiral metamaterial with long and short naobars are designed.Here the chiral structural arrangement destroys the rotational and translational symmetries in all directions,which result in asymmetric transmissions for linearly and circularly polarized incident lights.Importantly,the ultra-broad band linearly polarized asymmetric transmissions,mainly depending on the bar length,originate from the subwavelength plasmon coupling between long-and short-bar dipole-like responses;(2)A bilayer cross-shaped metamaterial with the long-and short-arms arranged orthogonally is designed,by which a broadband linearly polarized asymmetric transmission is realized numerically and experimentally in microwave wavelength.As a result,the work further evidences that the resonance coupling between long-and short-bars can induce broadband asymmetric transmission;(3)A metamaterial with trilayer twisted nanobars are proposed which could transform y(x)-polarized incident light to x(y)-polarized transmissions in a unidirectional manner.Besides,when the trilayer is increased,the band of polarization conversion is broadened.The asymmetric polarization conversions can also be called an asymmetric transmission;(4)When the twisted angle in part(3)is changed to ?=22.5°,the x-polarized incident light can be transformed to right circularly polarized light(RCP)or left circularly polarized light(LCP)in +z or –z direction,respectively;(5)In order to enhance the asymmetric transmissions at a near-infrared regime,a continuous omega-shaped metamaterial is proposed,and then it is demonstrated that the maximum value of the high-efficiency asymmetric transmission effect can reach up to 0.8.In addition,the works also present the physical mechanism of the high-efficiency asymmetric transmission effect and the influence of different geometric parameters.At last we experimentally demonstrate the asymmetric transmissions at this near-infrared band;(6)An elliptical nano-slit shaped structure with doubly degenerate geometrical charge is designed,which could induce two kinds of localized surface plasmons by different polarized lights.Next,the single elliptical nano-slit shaped structure is arranged particularly in a periodic metasurface and then realized a spin-controlled directional SPP propagations.