Behavier Contral Of Surface Plasmon Polaritions In The Structure Of Metal Slit

Surface Plasmon Polaritions Wave (SPPs Wave) are quasi-two-dimensionalelectromagnetic modes which has been caused by the coupling of free electron andphoton on the metal surface and propagate along a metal–dielectric interface. It has aexponential decay of the fields in the directions normal to the interface. Even thoughSPPs were the first observed more than100years ago, the potential to generate,manipulate and ultimately use them to practical ends have only recently been madepossible by the advances in the nanometre-scale fabrication and characterizationtechniques. In fact, SPPs have been identified to be the major physical mechanisminvolved in the enhanced light transmission through metallic hole and slit arrays.What is more, it will have an impact on some research field’s development, such asoptical storage technology, renewed light source, bio-photonics, and so on. Byaltering the structure of the metal’s surface, the dispersion relation, coupling andother properties of SPPs can be significantly changed. The unique nature and noveleffect of SPPs is become the current hot spots. SPPs also allow sub-wavelengthconfinement that has remarkable ability to break the diffraction limit, they, therefore,are ideal candidates for the construction of nano-optical devices (such as waveguide,lense, reflector, filter, and photovoltaic devices) and the next generation ultracompactintegrated photonic circuits. But before such applications are possible, it is vital thatthe relatively poor light-SPP coupling should be improved and SPPs would beefficiently generated with high flexibility to control the interaction between light andthe matters.In this thesis, we designed two kinds of asymmetry metal plasmonic structurebased on a simple and classic nanoslit with bump to study the performance ofunidirectional excitation of surface-plasmon-polaritons (SPPs). We employ ourtwo-dimensional finite-difference time-domain (2D-FDTD) program codes tosimulate the optical phenomenon and the interaction between the metal and incidentwave. It demonstrated that the introduction of dielectric layer and microcavity cancause the enhancement of SPPs excitation and coupling efficiency, ultimately, toachieve unidirectional excitation of SPPs. The contents include:(1) The coupling structure consists a metal film with a barely slit and a planar,dielectric layer on the slit-exit side of the metal film could achieve the directional excitation and coupling. It is demonstrated that the SPPs generation efficiency can beinfluenced under different conditions by changing the distance between the slit andbump, or the medium environment on the metal surface. We also explored theinfluence of the thickness of dielectric layer on the power flow (normalized to thepower flow of incident light). Different thickness of dielectric layer could havedifferent power flow distribution, even shows a modulation pattern. For this reason,we could select the appropriate thickness of dielectric layer to enhance the SPPpropagation efficiency.(2) Based on the above reaserches, we introduced an asymmetry microcavitystructure to further enhance the property of unidirectional excitation of SPPs. It isknown that the SPP generation efficiency can be adjusted by changing the slit width,and, owing to the dielectric layer, the the wave vector of SPPs confined on the metalsurface is significantly affected. In order to compare the maximum excitationefficiency of SPPs in different structures, we chose the optimal slit width for eachstructure to achieve the maximal of SPPs coupling efficiency. The introduction ofmicrocavity could cause the enhancement of the transmission through slit, moreelectro-magnetic energy is transferred into SPP modes propagating along the exitsurface. It is worth noting that the current density and the power flow are sensitive tothe open position and width of the cavity and the thickness of dielectric layer. Toachieve the larger current density and power flow, one should carefully choose theabove parameters. When we select appropriate above parameters, the metalmicrocavity would resonate and the current density and power flow would reach themaximizing to realize the enhancement of unidirectional transmission. We hope thatour findings will provide more theoretical support and reference for designingultracompact plasmonic coupler/generator and pave the way for using them in thepractical application.