Theory Of Tilted Hyperbolic Metamaterials For Field Discontinuity,Field Enhancement And Polarization Beam Splitting

Metamaterials offer new technological opportunities to desirably manipulate the electromagnetic waves.Among all types of metamaterials,hyperbolic metamaterials(HMMs)have attracted significant scientific attention due to their extreme anisotropy for extraordinary propagating waves.The current HMM based world is only partially served by investigations that incorporate only some limited version of anisotropy.As we know,even modest deviations of the optical axis from the main propagation axis resulting new phase shifts,which affect the absorption,reflection and transmission.Thus,in order to develop new pathways,the constructive manipulation of the optical axis position is required.In this thesis we focus on the optical properties of tilted-HMMs that satisfies ?=?_c,where ? is the tilted angle and ?_c represents the critical angle between the asymptotic line of hyperbolic isofrequency contour and the optical axis.By establishing the electromagnetic field solutions of waves interacting with tilted-HMMs,we propose the concepts and designs of field discontinuity,field enhancement as well as polarization beam splitting via tilted-HMMs.The main works of this thesis are detailed as follow:(1)The electromagnetic field solutions of waves interacting with tilted-HMMs satisfying ?=?_c are established.The detailed calculations reveal that,at this specific condition,when a transverse magnetic(TM)polarized wave is incident from a tilted-HMM to a dielectric medium,tangential component of electric fields is expected to be discontinuous at the interface.Extraordinary surface voltages are induced at the inner boundary of the tilted-HMM,which allow the total transmission of electromagnetic waves.This alternative behavior of induced extraordinary surface voltages enriches the understanding of continuity across the boundary and provides guidance for their realizations among multiple experimental platforms.(2)Enhancing the light-matter interactions(most of them focus on the electric field)is one of the major challenging task to realize practical and market-oriented on-chip optical devices.Here,we propose a similar design of a tilted-HMM as for field discontinuity and demonstrate it with real-life materials which could achieve strong field enhancement within small volume at deep-subwavelength scale.Both effective and realistic structures are demonstrated in order to well understand the field enhancement in the tilted-HMM.Strong field enhancement can be realized along the interface of tilted-HMM satisfying ?= ?_c.However,for a realistic tiltedHMM,new phase shifts are introduced to affect the tilted angle which can be explained according to the nonlocal corrections of effective medium theory.Remarkably,this study opens up a new frontier for field enhancement and the findings are promising for propelling nanophotonic technologies and research endeavors.(3)The ability to control the polarization of light at the extreme nanoscale has long been a major scientific and technological goal for photonics.We predict the phenomenon of polarization splitting through tilted-HMM(i.e., ??0 and ?_z?0).First,the phenomenon of polarization beam splitting is theoretically observed from such tilted-HMM.Second,based on this theoretical observation,at the mid-infrared region,an ultrathin HMM design is proposed with 2D van der Waals heterostructure composed of graphene-h BN.Such graphene-h BN heterostructure can be designed to be transparent to the transverse electric(TE)waves while opaque to the transverse-magnetic(TM)waves.This polarization beam splitting is insensitive to incident angles without resorting to the interference effect.Moreover,the predicted phenomenon is robust to the design of polarization beam nano-splitters and the exploration of superscattering for TM waves while zero scattering for TE waves from deep subwavelength nanostructures.