Research Of Terahertz Surface Plasmons By Metasurfaces

Free-space light can be coupled into propagating electromagnetic surface waves at a metal-dielectric interface,known as surface plasmons(SPs).Last decade,twodimensional forms of artificial electromagnetic materials,i.e.,the metasurfaces,have emerged as an ideal platform for the coupling and manipulation of SPs.The works reported in this theis were carried out in terahertz frequencyies,which focus on the study of universal SP manipulation schemes based on metasurfaces,and explore some general underlying physcis which are applicable to visible lights but can hardly be directly demonstrated due to the limitations of current technology.The main contents are summarized as follow:1.Through controlling the orientation angle of a pair of slit resonators under circular polarization incidence,the amplitude and phase of the excited SPs can be freely manipulated.Take such slit pair as basic element,the design scheme and optimization method of SP holography are proposed.By specially designing the interference between the SPs excited by different circular polarizations,some polarization-controlled complex SP launchings are demonstrated.2.By introducing the dark mode coupling mechanism into the SP metasurface design,an exotic asymmetric excitation design scheme is proposed.Based on coupledmode theory,matehematical models are builed to describe the excitation details of the coupled resonator pair.In addition,functional devices such as SP metalens and SP vortex launcher composed by coupled resonator pairs are demonstrated.3.Employing C-shaped slit resonators as unit elements,an efficient SP metacoupler design scheme is demonstrated by cleverly applying the generalized Snell's law.The performances of different kinds of metacoupler design schemes are systematically analyzed and compared.By carefully altering the geometrical parameters and the rotation angles of the C-shaped slit resonators,the phase and amplitude of the excited SPs can be simultaneously manipulated.As a proof of concept,single-and dual-order SP diffractions are demonstrated both theoretically and experimentally.