Study On Hybrid Surface Plasmon Wave-Guide

Hybrid surface plasmon waveguide(HSPWG)and long-range hybrid surface plasmon waveguide(LRHSPWG)combining characteristics of all-dielectric coupled silicon waveguide and surface plasmon waveguide(SPWG)to confine optical mode in the low-loss gap region beyond the diffraction limit,is the basic element of integrated plasmonic device and regarded as a promising candidate for biological detection,nonlinear data processing,compact optoelectronic devices and any other applications.Traditional HSPWG and LRHSPWG supporting hybrid mode which coupled dielectric mode with surface plasmon polariton(SPP)and long range surface plasmon polariton(LRSPP)mode,respectively.Owing to the property of electric filed distribution of HSPWG and LRHSPWG's mode,HSPWG and LRHSPWG has relative high ohmic loss and large optical mode area,respectively.And their mode confinements or figure of merits could not meet the requirement of high performance and integrated plasmonic devices.In addition,hybrid mode is changed to be a complicated asymmetric mode under relative large fabrication errors of waveguide.Owing to its relative weak coupling strength,the asymmetric mode may have relative strong light confinement.Hence,it is necessary to study its mode properties because the asymmetric mode can be used to improve the plasmonic devices' integration density.For the issues aforementioned,in this thesis,rib metal structure with small optical mode area and slot region with little loss combined with the property of all-dielectric coupled silicon waveguides and plasmonic waveguides,are used to design HSPWG with strong optical mode confinement and LRHSPWG with high figure of merit,respectively,then the coupled mode theory is adopted to analyze the influence of designed waveguide's mode properties with varied structures' parameters.In addition,many kinds of asymmetric waveguides are designed in this thesis by varying structures' parameters,in order to study the influence of mode properties under relative large fabrication errors and their effects in the improvement of performance for waveguide.Then,FEM is used to discuss the mode properties of asymmetric structures and the reasons of changed mode properties are explained,further.The main contributions of the thesis are as follows:1.The single interface SPP mode which is existed in the interface of metal and dielectric and the LRSPP mode or short-range SPP(SRSPP)mode that is existed in the dielectric-metal-dielectric(DMD)structure governing wave equations are derived based on physical procedure of the SPP effect and principle.After that,Drude model is used to obtain permittivity of some metals in light wave and near-infrared wave band,all of which can be applied to investigate the dispersion relation of three kinds of SPP modes.In addition,two sorts of normal methods related to excite SPP mode are introduced and the key factors for mode properties of SPP modes are given to evaluate their transmission performance.2.Due to the analytical solution of SPWGs' wave equations is not available for inhomogeneous medium,multilayers medium and multimode interactions,the plasmonic mode provided by SPWG is obtained by the numerical method-FEM or finite difference time domain(FDTD)method which is applied to solve SPWGs' wave equations,respectively.On one hand,owing to strong field localizations exploited in plasmonic modes and SPWG's curved region,simultaneously,FEM with 2-order basis function and curved triangle elements are used to simulate objects of SPWG;On the other hand,due to SPWG consisting of metal region,FDTD with Drude model are used to simulate objects of SPWG.The effectivity of FEM and FDTD methods are validated by the single SPP mode,the traditional HSPWG and LRHSPWG cases,respectively.3.In order to improve the performance of HSPWG for high density of plasmonic devices,HSPWG with strong mode confinement are designed.One the one hand,an easy-to-fabricate convex rib HSPWG(CRHSPWG)is designed by changing the height of metal rib structure.On the other hand,combining of rib metal structure with small optical mode area and mode energy distribution property of slot-dielectric region with high-index contrast and little-loss,a rib-slot-rib HSPWG(RSRHSPWG)with strong mode confinement is proposed in this thesis.Moreover,FEM is used to the investigate influences of these two waveguide's mode properties with varied structures' parameters.And coupled mode theory is applied to explain the changed plasmonic modes of CRHSPWG and RSRHSPWG with varied parameters,respectively.The simulation results show that CRHSPWG and RSRHSPWG with proper parameters have 10 and 100 times stronger capacity of light filed confinement than that of traditional HSPWG,respectively.4.In order to improve the figure of merit of LRHSPWG for high performance compact plasmonic devices,a LRHSPWG with high figure of merit is proposed in this thesis.In details,a so called center-slot LRHSPWG(LRCSHSPWG)is proposed by combing the characteristics of metal tip with relative small mode area and mode energy distribution property of slot-dielectric region with high-index contrast and little-loss.Moreover,FEM is used to investigate influences of LRCSHSPWG's mode properties with varied structures' parameters.And coupled mode theory is applied to explain the changed plasmonic modes of LRCSHSPWG with varied parameters.Compared with traditional LRHSPWG,the propagation distance and the mode confinement of our designed LRCSHSPWG are improved,simultaneously.In details,LRCSHSPWG has one order stronger capability of confining light field and 3 times higher figure of merit than its traditional LRHSPWG counterpart.5.In order to study the mode properties of waveguides with relative large fabrication errors,it is necessary to analyze the performance of asymmetric waveguides by varying parameters of dielectric waveguides,gap region and their locations,and further to study their performance which can be used to improve performance of HSPWG or LRHSPWG.In details,the center asymmetric structures of CRHSPWG,RSRHSPWG are proposed.On the other hand,the center symmetric the Si nano-line circular waveguide asymmetric structure,the gap asymmetric structure and the center asymmetric structure of LRHSPWG and LRCSHSPWG are proposed.In addition,FEM is used to study the mode properties of these asymmetric structures,further.Compared to the symmetric structures,the asymmetric RSRHSPWG or CRHSWG's capabilities of mode confinement or of long-distance information transmission is improved with proper parameters;the simulation results show that our designed asymmetric LRHSPWG and LRCSHSPWG have stronger capability of mode confinement with proper parameters.