Long Propagation Nanowire Waveguides With Highly Confinement Based On Surface Plasmon Polariton

Surface plasmon polaritons(SPPs)are electromagnetic field from the coupling between the light and the free electrons on the metal surface.Their fields are strongly confined on the metal surface,and decay exponentially when departing away from the metal surface.Due to their subwavelenght field confinement and local field enhancement,SPPs have wide applications in nano-optics and nonlinear optics.This paper present the basic theory of SPPs and applications,also the properties of typical nanowire waveguide.The novel nanowire waveguides have been proposed.Specific content as follows:1.The paper introduce the theory of SPPs,such as dispersion relations,SPPs stimulating method,related physical mechanism and so on.This article reviews recent progresses in plasmonic waveguides.2.Extensive studies have been carried out on nanowire waveguides,including single nanowire waveguide,nanowire-SiO2 substrate waveguide and nanowire-Si substrate waveguide.For practical applications,free-standing nanowires should be supported by substrates,the introduction of the substrates breaks the symmetry and confines the energy to the interface between the nanowire and the substrate.3.Then the mode characteristics of the novel nanowire waveguide are studied,nearly all(>98%)the evanescent fields of the SPP mode are tightly confined in the outside of the metallic nanowire waveguide by comparing with the conventional nanowires on dielectric substrate.Simulation shows that the SPP mode can be confined in the outside of the ridge waveguide with an area(Am=0.07?2-0.38?2)while the propagation length(Lm=23 ?m-480 ?m)is still about ten times of the plasmon wavelength.Thus this waveguide is more suitable for application in nano photonic and other information transmission equipment.4.The Ag nanowires is separated from the Ag film by the cover a MgF2 layer,the variation of the effective refractive index of the SPP mode is large,and its value is greater than the refractive-index change of the surrounding medium when the surrounding medium waveguide refractive index change is 0.001.The outside fields are very sensitive to the surrounding.By comparing with the metallic nanowire directly placed on the dielectric substrate,the proposed nanowire waveguide exhibits much higher sensing performances.5.The paper proposes a novel horizontal symmetric hybrid plasmonic waveguide(HSHPW)in the following work,the waveguide consists of a cylindrical Ag nanowire and high-index dielectric layers Si,and the substrate is Si02.It combines the advantages of hybrid SPP,long-range SPP and wedge SPP for the nanoscale confinement and guiding of light on a chip.The waveguide could remarkably minimize the energy attenuation resulting from Ohmic losses while retaining highly confined modes guided in the low-index nanoscale gaps between the Ag nanowire and the high-index Si.The geometric dependence of the mode characteristics on the proposed structure is analyzed in detail,showing long propagation lengths beyond 7.8 mm with mode areas about 0.02?2 and our design also features an overall advantage of large improvement of Figure of Merit(FOM)than any other properties of HPW structures published in recent years.Thus the HSHPW is very helpful for building high-density photonic integrated circuits.