太赫兹金属线表面等离子体激元特性研究
文献类型：学位论文
| 作者 | 杨洁 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 周常河 ; 曹清 |
| 关键词 | 表面等离子体激元 波导 太赫兹 金属线 |
| 其他题名 | Research on properties of metal wire plasmon of terahertz wave |
| 中文摘要 | 太赫兹技术是近年来研究的热门课题之一，特别是在太赫兹通信方面。2004年Mittleman教授领导的研究小组发现，太赫兹金属线波导有许多独特的优点，如低的传输损耗、低的色散、大的模式场等特征。该实验一经报道就引起了科学界的广泛关注，许多关于太赫兹金属线波导的理论和实验研究都开展起来了，但是该报道侧重于实验描述。曹清教授在第一时间提供了太赫兹金属线波导的理论解释，并确认该波导效应来自于方位角偏振的表面等离子体激元。在该工作中，作者通过对本征方程进行数值计算的方法得到了有效折射率的值，从而解释了实验中出现的各种物理现象。因此可以看出，有效折射率的求解对于研究金属线表面等离子体激元的性质起着至关重要的作用。目前该领域的许多理论工作都是基于数值计算的方法。这种方法虽然具有较高的精度，但是同时也具有计算效率低，物理图像不清晰等缺点。因此寻找有效折射率的显式势在必行。针对太赫兹金属线表面等离子体激元的特性，本博士论文主要做了以下几个方面的工作： 1）建立了一系列精度不同的有效折射率的显式表达式。 a)在充分研究了金属线表面等离子体激元特性的基础上，我们将含有贝塞尔函数的本征方程近似为简单的一元二次方程，最终方便地得到有效折射率的近似表达式，经数值测试发现所得结果在金属半径大于100mm时是适用的。该工作在2009年第八届环太平洋激光与光电子国际会议上做了口头报告。 b)在充分利用金属的介电常数在太赫兹频段下值很大的特点的基础上，并使用贝塞尔函数的性质和适当的泰勒展开方法，推导出了有效折射率的显式表达式。经过严格的数值测试发现，对于11种被测试的非磁性金属（Al铝，Ag银，Au金，Mo钼，W钨，Pd钯，Ti钛，Pb铅，Pt 铂，V钒，Cu铜），该公式在整个太赫兹频谱内，可以方便地描述半径从10微米到无穷粗的太赫兹金属线的表面等离子体激元，并且保证最大偏差小于5%，该项工作发表在[Optics. Express 17, 20806-20815(2009)]上。 c)由于上述工作得到的是非循环计算的结果，相对偏差还比较大。随后，我们推导出了精度极高的有效折射率的循环计算公式，经测试发现，对于测试的11种非磁性金属，在整个太赫兹频谱内，对半径从10微米到无穷粗的太赫兹金属线，该循环计算公式经过四次循环计算最大偏差小于2.1×10-6。该工作发表在[J. Opt. Soc. Am. A 27, 1608-1612 (2010)]上。这些有效折射率的近似表达式可以方便地用于分析和设计太赫兹金属线表面等离子体激元。 2）探寻纳米尺度的太赫兹金属线的传输特性。太赫兹频段下，表面等离子体激元研究的一个重要尺度就是金属的肌肤深度。本论文研究了当金属线的尺度逐步缩小至纳米尺度时，金属表面等离子体激元特别是在半径为亚肌肤深度的情况下的传输特性。 a)我们给出了有效折射率的近似表达式，经数值测试，该近似公式对11种非磁性金属，在整个太赫兹频谱内，在半径为5nm到500nm的范围内，最大偏差小于3%。 b)有效折射率的显式表达式可对研究纳米金属线的传输特性起到一定的帮助作用，我们发现该特性与纳米金属线的半径R和复波数k的乘积有关。另外，当金属线的半径小于肌肤深度时，模式场的尺度和金属线的半径成简单的正比关系。这些由解析解推导的简单特性都经过了严格的数值验证，这些结果可用于太赫兹波在亚肌肤深度尺度的纳米金属线上传输特性的分析和设计。该工作发表在[Optics Express 18 18550-18557 (2010)]上。 综上所述，本论文主要包含了我们在太赫兹金属线表面等离子体激元特性方面的研究工作，重点阐述了有效折射率的显式近似表达式的推导以及传输性质的研究。研究的范围覆盖了从几个纳米到无穷粗的金属线，这些研究结果有利于太赫兹金属线波导的设计和分析工作。 |
| 英文摘要 | In resent years, terahertz technology becomes one of the hot research issuses, especially in the aspect of terahertz communication. In 2004, Wang and Mittleman found that metal wires could be used as effective terahertz waveguide with many special advantages, such as low loss, low dispersion and wide modal field. Great interests were arised as soon as the experiment was reported. Since then, many theoretical and experimental works on metal wire teraherz waveguide have been carried out. But Wang and Mittleman focused on the report of experimental observations. Professor Cao gave a deep theoretical explanation for the first time and pointed out that the terahertz waveguide effect of metal wire came from the azimuthally polarized surface plasmon. In the report, Professor Cao explained the experimental results by effective index, which was obtained by using numerical techniques to sovle the related eigen-value equation. As a result, the effective index is very important for study of properties of metal wire plasmon of terahertz wave. Up to now, numerical techniques are still the basis of the theoretical works. The method of numerical techniques has high accuracy, but with low efficiency and without a clear physical image at the same time. So an explicit approximate formula for the effective index is useful. Several research aspects on properties of metal wire plasmon of terahertz wave are included in this doctoral dissertation: 1) A series of explicit formulas with different accuracy for effective index are established. a) Based on the properties of metal wire plasmon, we obtain a simple approximate expression from eigen-equation, which is a simple quadratic equation of one variable, and finally get the approximate expression for effective index. By using numerical test, we find that this result can be used for the metal wire plasmon of terahertz wave with metal radius larger than 100mm. This work is reported by oral at 2009 Conference on Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics. b) On the basis of the huge relative permittivities of nonmagnetic metals in the spectral region of terahertz wave, and by using some important properties of modified Bessel functions, and a suitable Taylor expansion, we derive an explicit formula for effective index. The obtained formula is further checked by many numerical tests. We find that, for all 11 tesetd nonmagnetic metals（Al, Ag, Au, Mo, W, Pd,Ti, Pb,Pt,V,Cu）, for the whole spectral region of terahertz wave, and for the wide radius range from 10μm to infinity, the relative deviation for the effective index is always smaller than 5%. This work is published [Optics. Express 17, 20806-20815(2009)]. c) The above work is non-recurrent and the relative deviation is still large. Later, we derive an analytical recurrence formula with extremely high accuracy. The recurrence formula after four recurrences is numerically tested for the 11 nonmagnetic metals, for the whole spectral region of terahertz wave and for the wide radius range from 10μm to infinity, the relative deviation for the effective index is always smaller than 2.1×10-6。This work is published [J. Opt. Soc. Am. A 27, 1608-1612 (2010)]. These explicit formulas for effective index can be conveniently used for the analysis and design of metal wire plasmon of terahertz wave. 2）The propagation properties of terahertz plasmon of a metallic nanowire with sub-skin-depth diameter are revealed. A very important size for a plasmon in the spectral region of terahertz wave is the skin-depth. In this dissertation, we investigate the properties of terahertz plasmon of a metallic nanowire with sub-skin-depth radius. a) The approximate expression for effective index is firstly established. The maximum relative deviation of the formula is always less than 3% for all 11 tested nonmagnetic metals in the whole spectral region of THz wave when the radius of metal wire is in the wide range from 5 nm to 500 nm. b) The explicit formula is helpful for the research of propagation properties. It is shown that the main propagation properties are closely related to the product of the radius of the metallic nanowire and the complex wave number of the mtal. In addition, when the radius of the metal wire is smaller than the skin-depth, the size of the modal field is simply proportional to the radius of the metal wire. We also carefully verify these analytical predictions with rigorous numerical simulations.The obtained results can be used for the fast analyses and design of the terahertz plasmon of a metallic nanowire with a sub-skin-depth diameter. This work is published [Optics Express 18 18550-18557 (2010)]. In conclusion, this dissertation includes our researches on the properties of metal wire plasmon of terahertz wave, mainly about the deviations of the explicit formula for effective index, and the discusions on the properties of transmission. The wide radius range is from several nanometers to infinity. These researches will be helpful for the analysis and design of metal wire plasmon of terahertz waves. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15661]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 杨洁. 太赫兹金属线表面等离子体激元特性研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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