【作者】 孙璐；

【导师】 姜淳；

【作者基本信息】 上海交通大学 ， 通信与信息系统， 2016， 博士

【摘要】 高效、高速和高集成是未来光子学器件的发展趋势。为实现这些目标,人们做了大量的研究并由此衍生了许多新兴学科,例如硅基光子学和表面等离子激元学。然而,硅材料和金属材料自身固有的缺陷限制了光子学器件某些性能的提升,例如集成光源和集成光波长转换器的实现仍需进一步的研究。新型光电材料的出现强烈冲击着现有的光子学器件的研究,其中包括稀土离子、量子点、石墨烯和超材料等等。它们具有低损耗、易于集成和人为可调控等优点,非常适用于光子学器件的设计,所以近年来逐渐成为国际上该领域的研究热点。特别是石墨烯材料特殊的光与物质相互作用为基于新型光电材料的光源辐射调控提供了崭新且富有潜力的实验平台。本论文研究了以石墨烯为首的几种新型光电材料并设计了基于这些材料的光电调控器件,事实证明新器件突破了传统光子学存在的瓶颈,非常有希望应用于光电转换、光通信和光计算等诸多领域。本论文完成的过程中受到了教育部科学技术研究重大项目培育基金和国家自然科学基金的资助。具体的研究内容如下:1.基于量子剪裁的太阳光谱变换研究论文利用粒子光致发光过程中普遍存在的量子剪裁效应将太阳光谱中的紫外光和蓝紫光变成更利于单晶硅太阳能电池吸收的近红外光,从而提升太阳能电池的光伏转换效率。1)Yb²⁺-Yb³⁺共掺系统通过Yb²⁺离子和Yb³⁺离子之间的能量转移,将太阳光谱中310nm附近的能量变换到980 nm附近,更利于单晶硅太阳能电池的吸收。数值结果表明,添加Yb²⁺-Yb³⁺共掺光谱变换层可使太阳能电池的光伏转换效率提升3%。2)硅量子点掺杂玻璃利用量子点中的多激子产生效应,将太阳光谱中的高能光子切割成适合单晶硅太阳能电池吸收的低能光子。计算结果表明,通过优化量子点半径最高可使太阳能电池的细致平衡效率提升6%。2.基于石墨烯微纳结构的自发辐射增强效应研究论文利用石墨烯表面等离子激元的光场增强特性和超高空间态密度,设计了两种微纳结构有效增强了光与物质之间的相互作用,使置于其中的量子光源的自发辐射速率得到大幅提升。1)双层石墨烯波导利用外加电压形成中央导波区域,置于其中的电偶极子能量会以石墨烯表面等离子激元的形式定向传播。其珀塞尔因子最大可达2.127×10⁶,而且激励起的主要是“对称单极模式”。2)石墨烯-玻璃薄膜-石墨烯混合结构采用经过化学掺杂的石墨烯层来束缚电偶极子光场,其珀塞尔因子最高可达1.286×10⁶。相比于双层石墨烯波导,其优势在于不需外加静态电压,因而制备起来更为简单。3.基于石墨烯的单光子开关和波长转换波导研究由于石墨烯具有超高的电子迁移率和三阶非线性系数,所以非常适合用来设计高速光开关和集成光波长转换波导。1)设计了一种基于石墨烯的可通过外加电压控制的单光子开关,其调制速率理论上可达几十GHz。数值计算表明,开关状态下的消光比最高可达20.8 dB,且在中心波长附近消光比的3 dB带宽可达600 GHz。2)设计了一种石墨烯-氮化硅-硅光子晶体混合波导,通过选取合适的光子晶体波导模式和添加氮化硅缓冲层可将光场能量集中在石墨烯层上。研究结果表明,其中的四波混频效率比不加石墨烯的同类结构提升了19.66 dB。4.基于量子真空调控的反常量子干涉效应研究通过调控各向异性量子真空和各向异性量子光源,我们可以实现两个正交跃迁之间的反常量子干涉效应。1)设计了一种置于双曲超材料附近的各向异性量子点系统。双曲超材料附近的量子真空具有很强的各向异性,配合上量子点自身的各向异性,我们可实现干涉强度大于退相干强度的反常量子干涉效应。此时,量子点中激发态粒子数衰减将被大大延缓,可观察到由干涉引起的粒子数非指数形式衰减。该成果有望应用于基于半导体量子点的量子逻辑门,实现可扩展的量子计算与量子信息处理模块。更多还原

【Abstract】 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.更多还原