Research On The Mechanism Of Optoelectronic Manipulation Based On Typical Materials/Structures Including Graphene

High efficiency,high speed,and high integration are the development tendencies of future photonic devices.To achieve these goals,massive research work has been done and new subjects such as silicon photonics and plasmonics have been developed.However,the performances of photonic devices are limited by the intrinsic disadvantages of silicon and metal materials,e.g.,the problems of realizing integrated light source and spectral converter remain unsolved.The emergence of novel optoelectronic materials,including rare earth ions,quantum dots,graphene,and metamaterials,has a great impact on the existing research of photonic devices.Since they are of low losses,easy to be fabricated,and artifically controllable,these materials are very suitable for the design of photonic devices.They are becoming the research hotspots in recent years.In particular,the light-matter interactions in graphene materials are extraordinary,providing a new and promising platform for the radiation control of light source.In this thesis,we have studied several new optoelectronic materials including graphene and designed controllable optoelectronic devices based on them.It has been demonstrated that the new devices break the limits of traditional photonics and are of great potential to be applied in photovoltaics,optical communication,optical computing,etc.The work is supported in part by the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of China,and Natural Science Foundation of China.The detailded contents are listed as follows:1.Research on solar spectral conversion based on quantum cuttingThe quantum cutting in photoluminescence process is utilized to turn ultraviolet and blue violet light in solar spectrum into near infrared light which can be absorbed more easily by single crystal silicon solar cell.The photovoltaic conversion efficiency is therefore elevated.1)Through the energy transfer between Yb²⁺and Yb³⁺ions,the Yb²⁺-Yb³⁺codopedsystem can move the energy near 310 nm in the solar spectrum to 980 nm where singlecrystal silicon solar cells are most sensitive to incident photons.Numerical resultsshow that the Yb²⁺-Yb³⁺codoped spectral converter can improve the solar cellconversion efficiency by about 3%.2)Due to the multiexciton generation effect in quantum dot,the silicon quantum dotdoped glass can divide a single photon of high energy in solar spectrum into severalphotons of lower energy which are better for single crtstal silicon solar cell absorption.By optimizing quantum dot radius,the detailed balance limit of efficiency can beincreased by about 6%.2.Research on enhanced spontaneous emission in graphene-based nanostructuresSince graphene surface plasmons have the property of field enhancement and ultrahigh photonic density of states,we have designed two graphene-based nanostructures to enhance the light-matter interaction.As a result,the spontaneous emission of quantum emitter embedded in the structures is greatly enhanced.1)Gate voltages are applied to the graphene double layers to form the centralwaveguiding region.The energy of electric dipole located between graphene layers willbe released in the form of directed graphene surface plasmons.The maximum Purcellfactor can reach 2.127×10⁶ with a primary excitation of symmetric monopole mode inthe waveguide.2)Radiation fields of electric dipole are confined by chemically doped graphene ingraphene-glass film-graphene hybrid structure.The maximum Purcell factor can reach1.286×10⁶.Compared to double-layer graphene waveguide,it can work without stavoltage and its fabrication is simpler.3.Research on single-photon switch and wavelength conversion waveguide based ongrapheneOwing to ultrahigh mobility of electrons and third order nonlinear coefficient,graphene becomes an ideal platform to realize high speed optical switch and ultra-compact wavelength conversion waveguide.1)An electrically controllable single-photon switch based on graphene is designed.Themodulation speed can be as high as tens of GHz theoretically.Numerical results provethat the maximum extinction ratio is 20.8 dB with a 3-dB bandwidth of 600 GHz.2)A graphene-silicon nitride-silicon hybrid photonic crystal waveguide is proposed andstudied.With the excitation of proper mode in photonic crystal waveguide and thebuffering effect of silicon nitride layer,we can concentrate the field energy in graphene.It is demonstrated that the four-wave mixing conversion efficiency is 19.66 dB higherwith graphene than in the same structure without graphene.4.Research on extraordinary quantum interference effect based on quantum vacuumengineeringBy manipulating anisotropic quantum vacuum and anisotropic quantum emitter,we can achieve extraordinary quantum interference between two orthogonal transitions via quantum vacuum engineering.1)We propose a system with an anisotropic quantum dot near hyperbolic metamaterial.The quantum vacuum near hyperbolic metamaterial is strongly anisotropic.Togetherwith the anisotropy of quantum dot,we can achieve extraordinary quantum interferencewhose strengh of interference is greater than that of decoherence.In this way,the decayof excited state population in quantum dot is tremendously slowed down andnonexponential decrease can be observed due to interference.The work could be usefulfor the implementation of quantum logic gates based on semiconductor quantum dotwhich are the basic units of scalable quantum computing and quantum informationprocessing module.