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Research On On-chip Integrated Waveguides And Waveguide-based Functional Devices

Posted on:2016-04-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:W XuFull Text:PDF
GTID:1318330536467176Subject:Optical Engineering
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Photonic integrated circuits are the effective ways to fulfill the increasing demands of optical communication bandwidth,and to solve the problems caused by electrical interconnection in high-performance computers.In this thesis,with integrated optical waveguides as the starting point,several novel integrated optical waveguide-based functional devices have been proposed theoretically.Our research mainly includes the following contents and results.(1)Metal surface plasmon polaritons applied to the mode control of SOI nanowire waveguides are explored.The mode control of SOI nanowire waveguides,which has great applications in the polarization division multiplexing and multimode spatial-division multiplexing technology,is the fundamental thesis in photonic integrated circuits.Firstly,the mode characteristics of SOI nanowire waveguide and metal surface plasmon polaritons are simply analyzed.Then silicon-metal hybrid waveguide is proposed to control the modes of SOI nanowire waveguides.The principle is based on multimode interference,and the key point is subtly designing the electric field distribution of eignmodes in the hybrid waveguide.Two different hybrid waveguides are proposed,based on which ultracompact waveguide TE-like and TM-like polarization converter,and fundamental TE-like mode and the first order TE-like mode converter are realized,respectively.Simulation results show that at the wavelength of 1.55 ?m,the polarization extinction ratio is up to 26.5 d B;however,the converter length is only 6.5 ?m.And the fundamental TE-like mode and the first order TE-like mode converter show an extinction ratio of 30 d B with the converter length of 1.1 ?m.(2)The existing graphene plasmonic waveguide structures are improved.Firstly,the graphene optical conductivity,the relationship between graphene Fermi energy level and the bias voltage,and the dispersion relation of graphene plasmonic modes are attentively analyzed.Then dielectric loaded graphene plasmonic waveguide is proposed.This waveguide does not need to pattern or local doping the graphene sheet.Moreover,it is easy to be fabricated and inetegrated,which may be the fundamental device in graphene plasmonics.Effective-index method is applied to analytically solve the dispersion relation of the dielectric loaded graphene plasmonic waveguide.Then,the mode effective index,propagation loss,cutoff wavelength of higher order modes,single-mode operation region and the tunability of the modes are discussed.Based on these analyses,the directional coupling between dielectric loaded graphene plasmonic waveguides was further studied.We found that when varying the Fermi energy level,the power coupling ratio between waveguides could be effective controlled,which could applied to design electrically controllable optical switch.Simulation results show an on-off ratio of 16 d B at the wavelength of 10.5 ?m.(3)The enhancement of visible and near-infrared light-graphene interaction by nanobeam cavity is proposed.The nanobeam cavity has both the advantage of waveguide and cavity.The coupling between graphene and nanobeam cavity takes advantage of the electric field enhancement of cavity,along with the accessibility in waveguide integration.A simple design method of nanobeam cavity is firstly proposed.Then temporal coupled-mode theory is used to theoretically analyze the nanobeam cavity-graphene coupling system.We found that as for the symmetric input and output waveguide,the maximal absorptivity of graphene is 50%.However,for asymmetric input and output waveguide,the maximal absorptivity of graphene could be 100%,provided that the critical coupling conditions are satisfied.Based on these theoretically analyses,ultracompact on-chip integrated graphene electro-optical modulator is realized by the symmetric structure.Simulation results show that the electro-optical modulator achieves a modulation depth of 7 d B at the wavelength of 1.55 ?m.However the total length of the modulator is only 6.5 ?m.Furthermore,the on-chip integrated graphene nearly perfect absorber is firstly realized by the asymmetric structure,with the design process is discussed in detail.Simulation results show that the absorptivity of graphene is raised up to 97% with a length of only 1.7 ?m.
Keywords/Search Tags:On-chip Photonic integrated circuits, SOI nanowire waveguide, Surface plasmon polaritons, Waveguide modes conversion, Graphene, Electro-optical modulator, Perfect absorber
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