石墨烯及其异质结的非线性表面等离子体激元研究

发布时间：2018-01-18 16:10

本文关键词：石墨烯及其异质结的非线性表面等离子体激元研究　出处：《深圳大学》2017年博士论文　论文类型：学位论文

【摘要】：石墨烯作为第一种被发现的二维材料,自出现开始就受到人们广泛的关注。石墨烯相对于传统的材料具有许多优良的特性,包括:非常高的非线性折射率和吸收系数;快速的响应时间;非常大的工作带宽;光与石墨烯的强相互作用;方便灵活的调控方式等。这使得石墨烯在光电子领域具有广阔的应用前景。目前针对石墨烯在光电子领域的研究方兴未艾。其中,石墨烯表面等离子体激元成为一个研究的热点。因为石墨烯和贵金属相比,在支持表面等离子体激元方面具有以下优势:首先,石墨烯中的表面等离子体激元的损耗要比在贵金属中小,因此传输长度大于贵金属中的表面等离子体激元,同时石墨烯中表面等离子体激元具有更高的局域性,电磁场能被很好地限制在石墨烯表面附近。其次,更重要的一个优点是,石墨烯的电导率可以通过外加电场或化学掺杂被调制,可以利用石墨烯的这种特性设计制作相应的光电子器件。围绕探索石墨烯表面等离子体激元的独特特性,以期应用于新型的光电子器件,本文进行了一系列研究,并取得了如下的成果:1.我们研究了各向异性的晶体位于两层石墨烯之间时的表面等离子体激元的特性,结果表明所研究晶体的光轴的不同的放置方向,对于奇模式和偶模式表面等离子体激元特性具有不同的影响。对于奇模式,当晶体光轴与交界面平行时有效折射率最大,而晶体光轴与交界面垂直时有效折射率最小。当两层石墨烯间隔超过某一阈值时,晶体光轴与交界面平行对应的表面等离子体激元传输长度最大。偶模式的特点则刚好与奇模式相反。我们通过分析电磁场分布,揭示了其原因在于不同的晶体光轴朝向会影响模式电磁场的分布,并分析了各向异性晶体位于不同位置时对石墨烯表面等离子体激元的影响。2.我们研究了一种非线性表面声子-等离子体激元的特性,这种表面声子-等离子体激元存在于石墨烯介于六方氮化硼(hBN)和非线性介质之间的结构中。理论研究表明,可以通过控制石墨烯的化学势能、层数和弛豫时间等参数来调节表面声子-等离子体激元的特性。同时发现介电常数非线性部分对于其传播常数的影响很大:低频模式传播常数的实部随着正值介电常数的非线性部分增加而增加;在上剩余射线带,虚部则随着正的介电常数的非线性部分增加而减小,在下剩余射线带则几乎保持不变,而带外的低频模式的虚部则随之增加。本文的结果有助于石墨烯-hBN的异质结结构在实际中的应用。3.我们研究了双层石墨烯两侧为对称的非线性介质,中间夹层为线性介质时的TE极化表面等离子体激元,所研究波长为中红外和太赫兹波段。与单层石墨烯介于无限大的非线性材料和线性材料的结构相比,该结构中的TE极化表面等离子体激元能够获得更灵活的调控方式,更强的光场局域性。我们分析了该结构条件下偶对称和奇对称TE模式的存在条件。研究表明当中间介质介电常数小于非线性材料介电常数的线性部分时,同一个非线性变化量可以对应两个不同的偶对称模式分支;而当中间介质介电常数大于非线性材料介电常数的线性部分时,只存在一个偶对称模式分支。并发现了当中间的线性介质的介电常数大于非线性材料介电常数的线性部分,且两层石墨烯的间隔足够大时,存在奇对称的TE极化表面等离子体激元,这种奇对称TE模式在类似的金属结构中是不存在的。并且我们研究了石墨烯的费米能级对于TE极化表面等离子体激元的传播常数以及模式电场的峰值位置的影响。此外文中还阐明了石墨烯本身的损耗和非线性对于色散特性的影响。4.我们设计了一种石墨烯-介质-石墨烯的双稳态结构,该结构可以非常方便地通过外加偏置电压实现对结构的特性进行调节,并且获得非常小的双稳态阈值功率。我们首先利用传输矩阵法分析了该结构的反射系数,进一步找出该结构的表面等离子体激元对应的衰减全反射(ATR)入射角度。通过分析发现,随着波长的增加或者石墨烯费米能级的增加,都会导致激发表面等离子体激元对应的ATR入射角度减小,而ATR谱的宽度也相应减小,同时棱镜和石墨烯之间的最佳的间隔增加。同时随着两层石墨烯之间的间隔增加时,会导致激发表面等离子体激元对应的入射角度增加,ATR谱峰值的宽度相应增加,而棱镜和石墨烯之间的最佳的间隔则是先减小而后增加。基于此结论,我们优化结构的参数,计算结果发现随着石墨烯间隔的减小,双稳态的阈值功率减小,但是当石墨烯的间隔小于一定值时,石墨烯间隔对于双稳态的影响比较小。此外,随着石墨烯费米能级的增加,或者石墨烯弛豫时间的增加,或是上下石墨烯层数的增加,都会导致双稳态的阈值功率的减小。最终相对于单层石墨烯结构,我们所设计的上下多层石墨烯夹心结构,双稳态阈值降低了4个数量级。
[Abstract]:Graphene as a first discovered two-dimensional material since the beginning has been widespread concern. Compared with traditional materials, graphene has many excellent properties, including high nonlinear refractive index and absorption coefficient; fast response time; very large bandwidth; light and strong interaction of graphene convenient and flexible; regulation mode. This makes graphene has wide application prospect in the field of optoelectronics. The graphene research in the field of photonics just unfolding. Among them, the graphene surface plasmon becomes a hot research topic. Because graphene and precious metals, has the following advantages in supporting surface plasmon yuan: first, the plasmon loss in graphene surface plasma should be smaller than that in precious metals, so the transmission length is greater than the precious metals in surface plasmon polaritons At the same time, graphene has localized surface plasmon higher, electromagnetic field can be well confined near the surface of graphene. Secondly, a more important advantage is that the conductivity of graphene can be doped by external electric field or chemical is modulated, the fabrication of optoelectronic devices designed this characteristic can use stone graphene. Exploring graphene surface plasmon unique characteristics, applied in optoelectronic device model, this paper conducted a series of studies, and achieved the following results: 1. we study the anisotropic crystal in the plasmon characteristics between two layers of graphene surface plasma, results show that the study of optical axis of different crystal orientations, have different effects on the odd mode and even mode surface plasmon characteristics. For the odd mode, when the optical axis of the crystal and the interface Parallel to the effective refractive index, and the optical axis of the crystal and the interface of vertical effective refractive index is minimum. When the two layer graphene interval exceeds a threshold, the optical axis of the crystal and the interface of the corresponding surface plasmon transmission characteristics. The maximum length is just the odd and even mode mode instead. We analyze the electromagnetic field distribution the reason is that, reveals the different orientations of the optical axis of the crystal will affect the distribution pattern of the electromagnetic field, and analyzes the anisotropic crystals at different positions on the graphene surface plasmon effect.2. we developed a nonlinear surface phonon plasmon properties, the surface phonon plasmon in graphene between six boron nitride (hBN) structure and nonlinear medium. The theory research shows that can control the chemical potential of graphene layers, and relaxation The characteristics of time and other parameters to adjust the surface PHONON-PLASMON. At the same time it was found that the dielectric constant for the nonlinear part of the propagation constant: the real part of the low-frequency mode propagation constant increased with the nonlinear part of positive dielectric constant increased; in the reststrahlen band, the imaginary part is decrease with nonlinear dielectric constant is the increasing in reststrahlen band is almost the same, while the low-frequency modes of the imaginary part of the band is increased. The application of.3. heterojunction structure, the results of this paper contribute to graphene -hBN in practice, we study the bilayer graphene on both sides of the symmetric nonlinear medium, the middle layer is linear medium TE polarized surface plasmon, the wavelength of infrared and terahertz. Compared with the structure and material nonlinearity of linear material and graphene is infinite. The structure of the TE polarization, the surface plasmon can obtain control more flexible, more local light field. We analyzed the existence condition of the structure under the condition of even and odd symmetry TE mode. The results show that when the intermediate dielectric constant is less than the nonlinear dielectric constant of the linear part, change the amount of the same nonlinear can correspond to two different branches of symmetric mode; and when the linear part of the middle dielectric constant greater than the nonlinear dielectric constant of the material, there is only one symmetric mode branch. We found the linear part of the dielectric constant when the linear medium intermediate is greater than the dielectric constant of the material nonlinear, and the two layer graphene interval is large enough, there are odd symmetric TE polarized surface plasmon, the odd symmetric TE mode does not exist in the metal structure similar. And we research The Fermi level of graphene for the peak position of TE polarized surface plasmon propagation constant and the mode field effect. In addition the paper also illustrates the loss and nonlinear effects on the graphene dispersion characteristics of.4. we designed a bistable structure of graphene - medium - graphene, the structure you can easily through the bias voltage on the structure characteristics of regulation, and the bistable threshold power is very small. We first analyzed using transfer matrix method. The reflection coefficient of the structure, to further identify the surface plasmon corresponding to the structure of the attenuated total reflection (ATR) incident angle. The analysis found that with the increase of the wavelength increases or graphene Fermi level, will lead to the ATR incident angle corresponding to the excitation of surface plasmons decreases, while the ATR spectrum width The corresponding decreases, the optimum interval between the prism and graphene increased. At the same time with the interval between the two layers of graphene increased, will lead to the incident angle of the excitation of the surface plasmon corresponding increase, ATR peak width increases, and the optimum interval between the prism and the graphene is decreased at first and then increased. Based on this conclusion, we optimize the structure parameters, the calculation results show that with the decrease of graphene interval, the bistable threshold power decreases, but when the graphene interval is less than a certain value, the graphene interval is relatively small impact on bitable. In addition, with the increase of Fermi energy of graphene, graphite or increase by relaxation time, or is on the increase of graphene layers, will lead to reduce the threshold power bitable. Finally compared with single-layer graphene structure, the upper and lower layers stone we designed With the sandwich structure, the bistable threshold is reduced by 4 orders of magnitude.

【学位授予单位】：深圳大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ127.11

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