Research On Surface Plasmon Wave Directional Excitation Based On Nanoantenna

The emission and control of surface plasmon wave(SPW)is one of the important research topics in the field of plasmonics and plays an important role in the related applications of plasmonics.Due to momentum mismatch,traditional SPP excitation schemes depend on total internal reflection of prisms or grating diffraction,or evanescent wave generated by waveguide and convergent beam.However,such schemes are not suitable for compact and highly integrated photonic devices.In this respect,the excitation of SPW by nanoantennas,including subwavelength slits,apertures and nanoparticles,represents a more feasible method.The unidirectional excitation of SPW by the nanoantenna is based on the directional correlation interference effect.For example,SPWs excited by asymmetric slits have different spatial phase distributions,so constructive or destructive interference occurs in specific directions.However,such interference requires the combination of multiple nanomaterials,which are also limited in size.Therefore,maintaining coherent electromagnetic dipole nanoparticles is a good candidate for unidirectional SPW launchers.Considering the electric dipole and magnetic dipole,coherent interaction can be realized in different ways.Or circularly polarized dipole is essentially a coherent dipole,and the direction of SPW can be controlled by the helicity of incident plane wave.However,despite the existence of a large number of such directionally coherent nanoantennas,few single nanoantennas are useful for directionally selective excitation of SPW.Based on the existing research results and theoretical technology,this paper will study the coupling between nanoantenna and SPW,and explore the feasibility of directional excitation of SPW using asymmetric near-field in wavevector space of nanoantenna.Based on electromagnetic multipole expansion theory,near-to-far-field transformation technology based on Lorentz reciprocity theorem and field distribution angular spectrum representation,the near-field and far-field distribution of Huygens dipole and circular polarized dipole will be discussed in position space and wavevector space,starting from the study of near-field coupling between ideal point source and SPW.The research results of point source will be extended to the actual nano antenna.For Huygens dipole,a dual-band multilayer metal-dielectric-metal(MDM)antenna is proposed to unidirectionally excite SPW.For circularly polarized dipole,a 1/4 tapered nanoantenna is designed to control the excitation direction of SPW.We will carry out finite element full-wave numerical simulation of point source or nanoantenna,near-field-far-field transformation technology and near-field angular spectrum verification,and study the directional excitation characteristics of two practical antennas to SPW,including energy characteristics,parameter control characteristics and so on.The combination of nanomaterials and SPW will provide a variety of design and development methods for surface plasmon devices.