Research On Hybrid Plasmonic Waveguide Devices For Infrared Region Based On Graphene

Surface plasmon polaritons(SPP)refers to the interaction of electromagnetic waves in a medium or free space with the free electrons on the metal surface,which propagate along the interface and exponentially decay along the normal direction.Surface plasmons are widely used to enhance the interaction between device materials and electromagnetic waves due to their strong local field enhancement effect,which can break through the diffraction limit.In the 21st century,the electronic communication industry is booming and nanotechnology is becoming more mature.The demanding is increasing due to big data cloud computing,the arrival of 5G communication and the Internet of Things,the miniaturization of devices,high transmission rate,low power consumption,and communication bandwidth.The realization of the development of nanoscale high-quality optical information communication technology provides opportunities and challenges for the study of surface plasmon polaritons.Graphene is a honeycomb-like unique two-dimensional nanomaterial formed by sp2 hybridization of its single-layer carbon atoms.Because graphene itself has excellent mechanical,thermal,optical,and electromagnetic properties,it can effectively support terahertz and infrared light.The transmission of surface plasmons.At the same time,the electromagnetic properties of graphene can be dynamically adjusted by electrostatic doping and chemical doping,and are widely used in the study of tunable devices from terahertz to infrared.Waveguide devices based on graphene surface plasmons have low loss,low power consumption,ultra-wideband,high speed,high efficiency,small size,easy integration,and electrical adjustment.It is one of the most promising core devices in the field of optical communication in the future.The research content of this thesis is mainly based on the surface plasmon effect of graphene.Based on the traditional dielectric-metal waveguide,the mechanism of plasmon surface plasmon enhancement is analyzed to explore new waveguide devices with low loss,high efficiency,high bandwidth and strong coupled.Specific research content includes:1.Research on mid-infrared graphene hybrid plasmon waveguide.Through theoretical analysis of the interaction mechanism between single-layer graphene and electric field,a mid-infrared long-range waveguide based on symmetric double parabolic silicon substrate structure is proposed.Due to the symmetrical internal extension of the double parabolic silicon substrate,mostm of the electric field is confined to the center of the dielectric waveguide.At this time,the graphene is laid at the maximum of the electric field,which greatly enhances the plasmon effect between the graphene and the electric field.In the range of 10-20 THz,when the chemical potential of graphene is set to l eV,the propagation length of 12.1-16.7 ?m can be achieved,and the normalized effective mode area of the electric field can be compressed to the order of 10'4.At the same time,a modulation depth of up to 100%can be achieved in the process of changing the chemical potential of graphene from 0 to l eV.2.Research on strongly coupled broadband modulators based on graphene and metal nano strips.The basis of the conventional electro-optic modulator is the electro-optical effect,which changes the refractive index of the electro-optic crystal by external conditions(such as chemical doping)to achieve the purpose of modulation.Combining graphene with a modulator enables electrical tunability to be achieved only by static biasing,and the modulation efficiency and bandwidth can be substantially enhanced due to the plasmon effect of graphene.However,due to the characteristics of graphene's own material,only its in-plane conductivity can be adjusted by static bias,and the absorption rate of near-infrared light is only 2.3%.In response to such problems,the combination of graphene and dielectric-metal hybrid waveguide is proposed.To achieve the purpose of enhancing the near-infrared-graphene interaction,the coupling and binding properties of the staggered metal nano-strips on the electric field are used to enhance the electric field component parallel to the graphene surface,thus achieving polarization matching between graphene and electric field.In the process of adjusting the graphene chemical potential from 0 to 0.65 eV,a modulation depth higher than 3.12 dB/?m(peak 11.3 dB/?m)can be achieved with a modulation bandwidth of 380 GHz,and the device also has a small size(1.8 ?m2),low power consumption(29.39 fj/bit).3.Research on the mid-infrared broadband gradual coupling structure based on graphene.A GaAs-TOPAS dielectric waveguide is used to design a reasonable double parabolic gradient transition structure,and electromagnetic waves are coupled to the graphene layer to excite surface plasmons.Under this structure,it is possible to achieve a peak value of T=0.75 at ?=2130 cm-1(f=63.9 THz),and an ultra-wideband transmission with T>0.5(S21<-3 dB)is completed within the range from ?=1960 cm-1(f?58.8 THz)to?=2320 cm-1(f?69.6 THz),and more than 90%coupling efficiency can be achieved in a specific frequency range.Therefore,this dielectric-semiconductor-graphene surface plasmon broadband gradual coupling structure is great significance for exciting the mid-infrared graphene surface plasmon and low-loss long-range transmission.