Study On Surface Plasmon Micro-nano Optical Devices And Enhanced Raman Substrates

The material itself and the diffraction limit,have limited the miniaturization and integration of traditional optical devices.The appearance of surface plasmon(SP)provides possibilities for the manipulation of light at the nanoscale.The surface plasmons is a free electron gas collective oscillation in the metal nanostructure under light excitation.It not only breaks through the optical diffraction limit,but also achieves the high concentrated local field.In this paper,the graphene sandwiched long-range plasmonic waveguide based on the properties of the SP that could break the diffraction limit is designed.On this basis,a multilayer graphene polymer waveguide TM polarizer is also proposed.At the same time,the surface enhanced Raman scattering(SERS)substrate of Au nanocube is designed using the local electric field enhancement propertiy of surface plasmon.At last,the local electric field enhancement of metal nanostructures is also studied.Firstly,this paper systematically analyzes the relationship between its optical parameters and the Fermi level of two-dimensional graphene.By applying voltage or doping,the Fermi energy of graphene is adjusted,which can achieve changes in the optical properties of graphene.When the graphene Fermi energy satisfies certain conditions,the graphene exhibits the properties of a metal material,supporting surface plasmon.On this basis,a plasmonic waveguide based on graphene material is designed.The influences of the buffer layer thickness,dielectric ridge width and dielectric ridge height on physical parameters,such as mode effective index,attenuation constant,mode width,and figure of merit are analyzed,which achieves the optimization of waveguide geometry size.In addition,when two identical waveguides approach each other,the coupling can be generated to constitute a direction coupler.The relationship between coupling length and separation is furtherly analyzed.Then,based on the graphene photoelectric effect,a multi-layer graphene polymer waveguide is studied on the basis of the graphene sandwiched waveguide,and an optical device of TM polarizer is designed by exploiting this structure.The TM polarizer is composed of multilayer graphene and silicon nitride inserted into the dielectric ridge.After optimization of the architecture and analysis of performance parameters,an optical polarizer with wide bandwidth,high extinction ratio,and low insertion loss can be obtained.Based on the COMSOL Multiphysics software,theoretical analysis of electric field enhancement has been performed on some common surface-enhanced Raman scattering(SERS)substrates.The relationships between the electric field enhancement and the excitation wavelength of various Au nanostructures are analyzed.The local electric field enhancements of different metal structures are closely related to the incident wavelength and nanogap.The variations in the gold nanospheres distance will change the local electric field enhancement factor and the resonant wavelength also shifts.For different metal structures,the corresponding optimal excitation wavelength and change regulation are also different.Therefore,in the experimental process,the appropriate excitation wavelength should be selected according to the different metal architecture to acquire the best enhancement effect.In addition,the influence of the excitation manner on Au nanorod structure's electric field enhancement factor is also evaluated.Finally,Au nanocube microarray structure SERS substrate is designed.The relationships between separation,excitation wavelength,and enhancement factor are analyzed theoretically.It is verified that the structure can be used as a SERS substrate to realize the detection of the sample.Compared with the traditional SERS substrate,theoretical analysis shows that the uniformity of the electric field enhancement of the nanocube array structure is very good.