Study On The Transmission Characteristics Of Surface Plasmon Waveguides And The Optical Chirality Of Metal Nanoarrays

Surface plasmons(Surface Plasmons,SPs)are the collective oscillations of free electrons on the metal surface.The collective oscillation of free electrons on the surface of noble metal nanoparticles produces the unpropagated electromagnetic waves,known as localized surface plasmon(Localized Surface Plasmon,LSP).LSP can realize local electric field enhancement,improve the efficiency of many optical processes,is widely used in surface enhanced spectroscopy and biological sensing.Surface plasmons popagate along the interface between metal and dielectric is called surface plasmon polaritons(Surface Plasmon Polaritons,SPPs).SPPs are regarded as the suitable information carrier for guiding light in nano-photonic integrated circuits due to that they can confine and guide light in nanoscale beyond the diffraction limit.In this paper,the transmission characteristics of the surface plasmon waveguides and the chiral response of the metal nanostructures are studied by the finite element method(FEM).The main research works of this paper are listed as follows:1.In this disseration,a silver cross nanowire waveguide was designed and the several different modes of SPPs splitting characteristics at the visible wavelength ? ?532 nm were numerically investigated,the effect of geometrical parameters on the splitting characteristics of different modes SPPs was discussed.The numerical results show that the mode effective index,the propagation length,and the mode area of the SPPs modes supported by silver cross nanowire waveguide are strongly dependent on the geometric parameters.In addition,the distributions of output transmittance of different modes SPPs in the three branches of the cross nanowire waveguide have different trends.The study also found that there is a periodic electric field distributionsat some branches of the cross structure due to the superposition of the electric fields of different SPPs modes,and the period of the electric field depended on the geometricalparameters.This silver cross nanowire SPPs waveguide has potential application in the field of optical interconnects and nanophotonic integrated circuits.2.In this disseration,a V-shaped silver nanowire hybrid plasmonic waveguide was proposed and its propagation properties at the telecommunication wavelength ?=1550 nm were investigated by the finite element method,the effect of geometrical parameters on propagation properties of SPPs was discussed.The numerical resultsshow that the proposed hybrid plasmonic waveguide could achieve very small effective mode area and long propagation length.It is found that the strong field confinement are due to the field enhancement around the tip of V-shaped silver nanowire and the lateral confinement.In addition,the propagation properties of SPPs mode were strongly dependent on the geometric parameters.The dependence of the propagation properties on the geometrical parameters was analyzed by calculating the energy confinement ratio of the SPPs mode field in the low-index cladding(SiO2),metal(Ag)and semiconductor(Si)substrate.Our proposed structure is potential for building ultra-compact plasmonic devices and highdensity photonic integrated circuits.3.In this disseration,a periodic L-shaped metal nanostructure arrays above a dielectric substrate was proposed and the circular dichroism(Circular Dichroism,CD)effect of "extrinsic chirality" of the achiral metal nanostructure arrays at obliquely incident circularly polarized light was investigated,the influence of light incident direction and geometrical parameters on the CD effect were discussed.Results show that the L-shaped nanostructure arrays can achieve strong and broad bandwidth CD under the obliquely incident circularly polarized light irradiation,and the CD effect is tunable:its sign and magnitude are controlled by light incident direction.In addition,the broad CD band can be tuned by changing the geometrical parameters.Importantly,this type of tunable CD occurs in simple planar structure designs that are ideally suited for well-established planar manufacturing technologies.These results have certain reference significance for the design of broad bandwidth circular polarizer.4.In this disseration,a kind of planar chiral nanostructure arrays which composed of a S-shaped nanostructure next to a nanorod was proposed and the asymmetric transmission(Asymmetric Transmission,AT)effect of the composite arrays was investigated,the influence of geometrical parameters on the AT effect were discussed.Results show that the metal nanorods and S-shaped metal nanostructures combined arrays can achieve strong AT effect for normally incident circularly polarized light.The AT effect is robust:when the gap between the nanorod and the S-shaped nanostructure varied within a certain range,the magnitude and spectral band range of AT effect almost unchanged.These results have certain reference significance for the design of polarization converter.