Electromagnetic Wave Manipulation Via Low Dimensional Metamaterials And Its Applications

Electromagnetic metamaterials consisting of artificial subwavelength metaatoms possess unsusal electromagnetic parameters and/or spatial parameter distributions and hence exhibit unprecedented ability to manipulate electromagnetic waves.By utilizing metamaterials,numerous intriguing phenomena and applications are enabled such as negative refraction,optical cloaking,perfect lens and wave tunneling.In this thesis,we study on electromagnetic wave manipulating functionality of lower dimensional elctromagnetic metamaterials including transparent metasurfaces and gradient wire structure and investigate the potential applications such as ultrathin invisibility cloaks,high-efficiency wave maniputaltion on an interface,propagating waves-guided waves conversion and so on.The main content,motivations and innovations are summarized as follows:1.A hybrid invisibility cloak based on integration of transparent metasurfaces and zero-index materialsThe invisibility cloak,a long-standing fantastic dream for humans,has become more tangible with the development of metamaterials.Recently,metasurface-based invisibility cloaks have been proposed and realized with significantly reduced thickness and complexity of the cloaking shell.However,the previous scheme is based on reflection-type metasurfaces and is thus limited to reflection geometry.In this chapter,by integrating the wavefront tailoring functionality of transparent metasurfaces and the wave tunneling functionality of zero-index materials,we have realized a unique type of hybrid invisibility cloak that functions in transmission geometry.The principle is general and applicable to arbitrary shapes.For experimental demonstration,we constructed a rhombic double-layer cloaking shell composed of a highly transparent metasurface and a double-zero medium consisting of dielectric photonic crystals with Dirac cone dispersions.The cloaking effect is verified by both full-wave simulations and microwave experimental results.The principle also reveals exciting possibilities for realizing skin-thick ultrathin cloaking shells in transmission geometry,which can eliminate the need for spatially varying extreme parameters.Our work paves a path for novel optical and electromagnetic devices based on the integration of metasurfaces and metamaterials.2.A hybrid invisibility cloak based on integration of transparent metasurfaces and antireflection coatings.In the previous chapter,by integrating the wavefront tailoring functionality of transparent metasurfaces and the wave tunneling functionality of zero-index materials,we have realized a unique type of hybrid invisibility cloak that functions in transmission geometry.However,zero-index materials consisting of dielectric photonic crystals with Dirac cone dispersions are relatively thick,hindering the realization of ultrathin cloaking shells.Here,we propose a unidirectional cloaking scheme that cloaks dielectric of almost arbitrary shapes by using cloak shells composed of two metasurfaces and an antireflection coating sandwiched between them.By the action of the cloaking shells,incident plane wave enters and passes through the dielectric and recovers its wave front at the exit boundary.Beside conventional antireflection coatings,we also adopt ultrathin gain/loss antireflection coatings to form ultrathin cloaking shells.Cloaking shell with parity-time symmetry is constructed and one-way cloaking effect is observed.Besides,3.Gradient antireflection metasurface:tailoring electromagnetic wave on an interface with high efficiencyGradient metasurfaces as the 2D counterpart of metamaterials have shown great power in manipulating the electromagnetic waves by using artificial micro-structures over the scale of subwavelength.High-efficiency gradient metasurfaces working in the reflection geometry can be designed by using a mirror substrate.While high-efficiency gradient metasurfaces working in the transmission geometry can be realized by adopting transparent metaatoms.However,these transmission-type high-efficiency metasurfaces is usually considered to working in homogeneous materials e.g.,free space.Here,we propose a new concept of antireflection gradient metasurface which can manipulate transmission waves on an interface between two different media with near unity transmission coefficient.To demonstrate this concept,a specific gradient antireflection metasurface that can eliminate the reflection and refraction effects simultaneously is designed,fabricated and measured.This gradient antireflection metasurfaces can be applied to forming an ultrathin invisibility cloak.Antireflection gradient metasurfaces may inspire numerous high-efficiency devices working on interfaces such as wave-front steering,beam transformation,polarization conversion and could find a wide range of applications in various realms including optics,holography,opto-electronics,microwave therapy.4.Propogating wave-guided wave conversion via quasi one-dimensional gradient wire structureBy introducing abrupt phase changes,gradient metasurfaces have demonstrated the ability to convert propagating waves into surface waves that propagate along the metasurfaces which has been verified by microwave and optical experiments.Exhibiting a two-dimensional structure geometry,metasurfaces are usually designed for plane incident waves.However,in certain circumstances,smaller devices of lower dimensionality are desired.Here,we propose a method for the design of gradient wire structures which are capable of converting propagating waves into guided waves along the wire.We demonstrate that two types of gradient wire structures,with either a gradient permittivity and a fixed radius,or a gradient radius and a fixed permittivity,can both be designed to realize such a wave conversion effect.Besides,we demonstrate two types of meta-couplers that can convert propagating waves into guided waves along wire waveguides(e.g.,metal wires and optical fibers)by manipulating either reflected waves or transmitted waves in a noninvasive way.The principle and metacoupler demonstrated in our work has potential applications in various areas including plasmonics,nano-photonics,silicone photonics,and optical communication.