Research On Novel Waveguides And Devices Based Opon Surface Plasmon Polaritons

Surface plasmon polariton(SPP)offers promising strategies to realize highly compact circuits in nanotechnology because of their capability of confining electromagnetic waves at a scale beyond the diffraction limit.Hybrid plasmonic waveguide combines the advantages of the dielectric tube waveguide with the plasmonic polariton,which provide strong mode confinement with low propagation loss.Hybrid plasmonic waveguides provide a new idea for developing SPP waveguides with perfected performance and high integration in terahertz to mid-infrared bands.New artificial electromagnetic metamaterials,a kind of artificially structured EM materials,are usually composed of periodically arranged subwavelength microstructures or ?meta-molecules?,and have attracted great attention for their unique EM properties that the natural materials cannot realize.The application of electromagnetic devices,which combine the characteristics of the metallic metamaterials and the properties of localized SPP,involves many important research fields such as optical antenna,filter,detector,modulator,optical lens,thermal imaging,solar cells,absorbing materials and so on.However,traditional SPP waveguide and relative devices based on metallic structures cannot be changed once the structure is fabricated.To improve above situation,some actively controlled elements,such as liquid crystals,liquid metals and semiconductors,are applied in SPP waveguide and devices.Unfortunately,these tunable structures are unsuitable for compact integration.Recently,graphene,a flat monolayer of carbon atoms packed into a dense 2D honeycomb crystal lattice,has become a very promising material for its unique electrical properties,such as high electron mobility,flexible tunability,relatively low loss and tight field confinement.Graphene surface plasmons can work on the spectrum from THz to near infrared,with very strong mode confinement and low losses.The most attractive property is that the conductivity of graphene can be dynamically tuned by changing the Fermi energy through chemical doping or electrostatic gating.Therefore,the combination of graphene and SPP can provide an effective approach to achieve tunable and integrated waveguide and devices.To overcome the problems aforementioned,we investigated the proposed waveguide and relative devices by combing the semiconductor,graphene and new artificial electromagnetic metamaterials with surface plasmon polaritons.The main contents are divided into four parts shown as follows.1.A kind of new hybrid surface plasmonic waveguide working in the terahertz frequency range and based on uneven substrate structure was proposed.The proposed waveguide combines the advantages of the dielectric tube waveguide and the plasmonic polariton.SPP supported by the noble metals are weakly confined in the mid-infrared and terahertz regions,owing to the near-zero skin depth.To overcome this problem,InSb is used to replace the traditional noble metal in the hybrid waveguide for its plasma frequency loading in terahertz band.By comparing the mode properties of the multiple structured waveguide,such as the effective mode area,propagation length,figure of merit and energy ratio,we proposed a hybrid SPP waveguide based on uneven InSb substrate working at 1 THz.The results show that the proposed waveguide can reach the same propagation length with the traditional hybrid waveguide,while the mode area of the proposed structure is about 1/2000 of the diffraction-limited mode area in the free space,which indicates stronger mode confinement with similar propagation length.In addition,the possibility of lossless transmission is investigated by introducing gain materials into the hybrid.2.A single-mode graphene loaded double ridge plasmon waveguide(GDRW)with long propagation length and strong mode confinement was proposed.Based on Kubo formula,the different material properties of graphene working from terahertz to visible band are analyzed in detail.Graphene is introduced into the dielectric waveguide to replace the traditional noble metal and forms a hybrid plasmonic waveguide.Graphene SPP shows tighter mode confinement and lower propagation losses Compared with SPP modes on metal surface.Due to the investigations of the graphene loaded slab waveguide with different structures,we finally proposed a single-mode graphene loaded double ridge plasmon waveguide(GDRW)with long propagation length and strong mode confinement.High figures of merit and much lower crosstalk are obtained due to the dramatically suppressed interference between two parallel placed GDRWs with the nearest distance 120 nm,enabling thereby more tightly stacking in terahertz integrated circuits.Further investigation on fabrication errors,such as the horizontal misalignment of the two symmetric ridges,fabrication distortion of rectangular ridges,and variation of ridge tip curvature radius,indicates that the proposed structure has enough fabrication error tolerance.Tunable single-mode transmission with good performance can be realized either by chemical doping or electrostatic gating.3.Current metamaterial-based filters still suffers some problems,such as insufficient modulation depth,complex structure,difficulty in flexible design,and inability to tune in real time.Utilizing the properties of localized SPP characteristics,dynamically tunable band stop filter based on metal-graphene metamaterials is proposed and numerically investigated at mid-infrared frequencies.A stable modulation depth up to-23.26 dB can be achieved.Due to the cooperative effect of the “bright-bright” elements,the amount of the gold strips in each unit cell determines the number of the stop-bands,providing a simple and flexible approach to develop multispectral devices.Further investigations illustrate that the location of the stop bands not only can be adjusted by varying the length of gold strips,but also can be dynamically controlled by tuning the Fermi energy level of graphene,and deep modulation is acquired through designing the carrier mobility.With the sensitivity as high as 2393nm/RIU of the resonances to the varieties of surrounding medium,the structure is also enabled to be an index based sensor.4.Dynamically and independently tunable absorbers based on multilayer metal-graphene metamaterials are proposed to achieve multi-band and ultra-wide-band absorbing properties at mid-infrared frequencies.Multiple bands absorption can be arbitrarily customized by etching the appropriate number of tandem gold strips in each meta-molecule,as well as stacking multiple metal-graphene layers.Through tuning the Fermi energy level of the graphene in each metal-graphene layer separately,the multiple absorption resonances can be dynamically and independently adjusted.With side-by-side arrangement of the gold strips in each supercell,the proposed structure is rendered to be a promising candidate for ultra-wide-band absorber.The extreme bandwidth exceeding 80% absorption up to 7.5THz can be achieved with a dual-layered structure,and the average peak absorption is 88.5% in the wide-band range for lossless insulating interlayer.For a triplelayered structure,the average peak absorption is 84.7% from 27.5THz to 38.4THz with a minimum of 60%.All these results will benefit the integrated microstructure research with simple structure and flexible tunability.