低损耗、小模场太赫兹波导研究

发布时间：2018-02-01 15:01

本文关键词： THz波导模场宽度模式损耗表面等离激元　出处：《深圳大学》2017年硕士论文　论文类型：学位论文

【摘要】：太赫兹(Terahertz,简称THz)波是指频率在0.1~1 THz范围内的电磁波,位于红外与微波之间,处于宏观电子学向微观电子学的过渡阶段,因而具有许多独特的性质。在基础物理科学、超高速通信、高分辨率成像、安全检查、无损检测等方面具有重要的研究价值和广泛的应用前景。但目前缺乏低损耗、长距离传输的波导使得太赫兹的应用受到很大限制,开发低损耗、小模场的太赫兹波导对于推动太赫兹技术的实际应用具有十分重要的意义。由于现有的波导普遍存在低损耗与小模场难以同时实现的问题,由此,本文对传统波导的结构和材料进行可行性改进,分别提出了置于介质孔内的纳米金属线、石墨烯包裹的水滴状延拓纳米线、金属-缝隙-介质对称型波导,并利用数值分析软件与基于有限元方法的COMSOL商用软件研究了它们的传导特性。首先,利用COMSOL软件对置于介质孔内的金属线的表面等离激元模式进行仿真研究,并能与数值计算结果相互呼应。理论上很好地证明了置于介质孔内的金属线可以保持模式宽度与单金属线基本一致的情况下,将损耗降至极低。其主要原因是引入足够大的介质孔能够改变部分模场,在维持模式宽度基本不变的前提下,使得集中在金属线内的场能减小,从而缩小传输损耗。在工作频率为0.3 THz时,金属线半径为100 nm,损耗的理论值非常小,为0.42 m~(-1),同时模场宽度仅为纳米量级(290 nm)。其次,提出了利用石墨烯包裹的水滴状延拓纳米线传导THz表面等离激元。我们采用在太赫兹频段具有类金属性质的石墨烯材料包裹在水滴状延拓纳米线外,利用COMSOL求解,结果发现,该波导可以大大降低模式宽度。在工作频率为3 THz,底弧R为1μm时,在波导的楔形顶角出现宽度很小的亮斑,模式宽度为34 nm,其传输损耗为1.3 mm~(-1),即传播长度近800μm(相当于7λ0)。即该波导在保证传输损耗较低的前提下,实现了纳米聚焦。最后,提出金属-缝隙-介质对称型波导,主要包括两种类型:平板型和柱型,主要是利用插入电介质的方法改变了金属平板(或者金属空芯管)的模场特点。我们分别通过理论推导出TE模、TM模与HE模的色散方程。从数值计算结果直观地发现,模场更集中在介质层内,在模场宽度不增大的前提下,这种波导可以实现超低损耗传输THz波。当f为0.5 THz,平行平板DGM波导中两个金属层间距为b=λ/2时,TE1模和TM1模的最小损耗分别为0.21 m~(-1)和0.17 m~(-1);对于柱状DGM波导,金属铜管(内环)直径为2λ/3时,HE11模的最小损耗为0.20 m~(-1)。与不插入电介质的波导相比,它们的损耗均可以下降1~3个数量级。
[Abstract]:Terahertz (THz) waves are electromagnetic waves with a frequency of 0.1 THz, between infrared and microwave. At the stage of transition from macroelectronics to microelectronics, it has many unique properties. In basic physics science, ultra-high speed communication, high resolution imaging, security inspection. Nondestructive testing (NDT) has important research value and wide application prospect. However, the lack of low loss and long distance transmission waveguide make the application of terahertz to be greatly limited, and the development of low loss. THz waveguides with small mode field are of great significance to promote the practical application of THz technology. Because the existing waveguides are generally low loss and small mode field difficult to achieve at the same time. In this paper, the structure and materials of traditional waveguides are improved. Nanowires, water droplet extension nanowires, metal-crevice dielectric symmetric waveguides, which are placed in dielectric holes, are proposed respectively. Numerical analysis software and COMSOL commercial software based on finite element method are used to study their conduction characteristics. First of all. COMSOL software is used to simulate the surface of the metal wire in the dielectric hole. It is proved in theory that the metal wire placed in the dielectric hole can keep the mode width basically consistent with the single metal wire. The main reason is that the medium hole can change part of the mode field, and the field energy concentrated in the metal wire can be reduced under the premise of maintaining the mode width basically unchanged. Thus, the transmission loss is reduced. When the operating frequency is 0.3 THz, the wire radius is 100nm.The theoretical value of the loss is very small, which is 0.42 mm2 ~ (-1). At the same time, the width of the mode field is only about 290 nm ~ (-1) nanoscale. Water droplet extension nanowires coated with graphene were proposed to conduct isoexcitons on THz surface. Graphene materials with metal-like properties in terahertz band were used to encapsulate water droplet continuation nanowires. Using COMSOL solution, it is found that the mode width of the waveguide can be greatly reduced. When the operating frequency is 3 THZ and the bottom arc R is 1 渭 m, a small width bright spot appears in the wedge top angle of the waveguide. The mode width is 34 nm and the transmission loss is 1.3 mm / L, that is, the propagation length is nearly 800 渭 m (equivalent to 7 位 0), that is, the transmission loss of the waveguide is low. Finally, the metal-crevice dielectric symmetrical waveguide is proposed, which includes two types: plate type and column type. The mode field characteristics of metal plate (or metal hollow tube) are changed by the method of inserting dielectric. The dispersion equations of TM mode and HE mode. From the numerical results, it is found that the mode field is more concentrated in the dielectric layer and the width of the mode field does not increase. The ultra-low loss THz wave can be transmitted by this waveguide. When f is 0. 5 THZ, the distance between the two metal layers in the parallel plate DGM waveguide is b = 位 / 2:00. The minimum loss of TE1 mode and TM1 mode are 0.21 m-1 and 0.17 mG-1, respectively. For a cylindrical DGM waveguide, the minimum loss of the metallic copper tube (inner ring) is 0.20 m / m ~ (-1) in diameter of 2 位 / 3:00 ~ (-1) H _ (11) mode, compared with the waveguide without dielectric insertion. Their losses can be reduced by 1 ~ 3 orders of magnitude.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN814

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