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金纳米结构等离激元透镜的聚焦特性的研究

发布时间:2018-01-11 08:32

  本文关键词:金纳米结构等离激元透镜的聚焦特性的研究 出处:《南京大学》2017年博士论文 论文类型:学位论文


  更多相关文章: 表面等离激元 透镜 相位调控 亚波长聚焦 相长干涉 时域有限差分法


【摘要】:表面等离激元是一种特殊电磁场,可以由光和金属表面自由电子相互作用而激发。它沿介质和金属表面传播,高度局域于金属和介质表面,具有比激发光波长短的波长及独特的场增强效应,因而引起很多研究者的兴趣。利用表面等离激元可以实现突破衍射极限的光子器件。随着微纳光学理论研究的深入以及微加工制备技术的进步,基于表面等离激元的亚波长光子器件可满足小型化和集成化的需求,在近年来得到极大的发展。其中,金属纳米结构(孔、缝、槽及它们的组合)由于在空间场调控和亚波长聚焦上独特的能力,引起了研究者们的特别关注。本文基于表面等离激元的基本理论,利用数值模拟方法研究了几种单个及阵列状金纳米结构等离激元透镜的远场超分辨亚波长聚焦行为,并对其物理机制进行了分析。本论文工作的主要创新如下:1.提出了一种介质填充型二次柱面等离激元透镜。该透镜由二氧化硅填充金膜纳米狭缝阵列组成,金膜的出射表面为二次柱面。表面等离激元在狭缝入口处激发并沿狭缝传输,在狭缝出口转变为带有一定相位延迟的自由空间传播的光波。通过对透镜结构参数的控制,可以调节来自各狭缝的光波间的相对相位,使它们在设定的焦点处进行相长干涉,从而实现聚焦效果。用时域有限差分法数值计算了二次柱面等离激元透镜的聚焦特性。数值模拟结果表明,所设计的孔径为2μm的透镜,能够实现微米级焦距和焦深、且焦斑半高宽低至0.4倍波长的亚波长聚焦。该表面等离激元透镜结构简单紧凑、尺寸小,有利于光子器件的集成。2.提出了一种基于单环纳米孔阵列与双同心槽金膜等离激元透镜。它由一个单环纳米孔阵列和二个包围环孔阵列双侧的同心槽构成,纳米孔穿透金薄膜;这是一种特殊的对称的结构,可以用圆偏振光照明来实现聚焦。以往的对称结构,多用径向偏振光照明,但径向偏振光不易获得,而且径向偏振光并不能适用于所有的对称结构。本文所设计的这种对称结构,用圆偏振光照明就可较好地实现远场聚焦。通过数值计算,找到了从凹槽和纳米孔发出的光之间的相位差与凹槽位置之间的关系,再通过线性拟合,确定了在实现指定焦距处聚焦所需的凹槽位置参数。时域有限差分数值模拟得到了这种等离激元透镜的电场分布,呈现出明显的远场聚焦现象。计算结果表明这种等离激元透镜能够实现中心轴对称的亚波长紧聚焦效果,焦斑的半高宽小于半个照明光波长并且获得长焦深,达到了用同心槽改善远场聚焦的目的,其聚焦性能显著优于常规的单环纳米孔结构等离激元透镜。我们还进一步研究了等离激元透镜阵列中相邻两个等离激元透镜间的聚焦相互作用,通过数值模拟找到了相邻两个等离激元透镜间的距离对最终聚焦特性的影响规律,提供了一个改善等离激元透镜阵列聚焦特性的新途径。3.提出了一种基于双椭圆孔阵列与多同心环槽的金膜等离激元透镜。该透镜是由多重同心槽和双椭圆形纳米孔阵列构成的金属薄膜结构,其中的椭圆形纳米孔沿阿基米德螺旋线分布。设计的纳米孔使得入射线偏振光与表面等离激元耦合并向同心环槽传播,而环槽可以有效地散射表面等离激元使之在金膜出口表面处转换成在自由空间可传播的波,从而实现亚波长的聚焦。我们对等离激元透镜的聚焦特性进行了理论和数值研究。该透镜能产生有趣的超分辨和长焦深焦场,比如光针或光管。值得注意的是,该透镜即使在线偏振光照明下也能产生中心对称的焦斑。4.提出了一种基于单环纳米孔阵列与三个同心环形狭缝的宽光谱金膜等离激元透镜。设计了单个及阵列状等离激元透镜,单个透镜为单环纳米孔阵列和三个位于单环孔内同心狭缝的金纳米透镜,纳米孔和狭缝均穿透金薄膜;阵列状透镜是以单个透镜为单元按不同阵列大小构建而成。用较易获得的圆偏振光照明;由时域有限差分法模拟得到等离激元透镜及其阵列的电场分布,呈现明显地远场聚焦现象;实现了中心轴对称亚波长聚焦。已报导的纳米结构等离激元透镜存在一些缺点,例如,传输光场发散以及精心设计的纳米结构只对特定的波长聚焦。而本文所设计透镜及其阵列可以实现宽光谱聚焦,本文透镜虽是针对660 nm光波设计,但在560 nm-760 nm范围内对任一波长光波均可实现良好的远场聚焦。通过分析瑞利-索末菲积分找到了"入射光波长越大,焦距越小。"的原因。进一步研究了阵列中相邻两个单元之间的聚焦相互作用;通过数值模拟找到了相邻两个单元之间距离、照明光工作波长及阵列大小对最终聚焦特性的影响规律;提供了一个设计符合实际需要的透镜阵列的依据。
[Abstract]:Surface plasmon is a special electromagnetic field can be determined by the interaction between light and metal surface free electron excited. It along the dielectric and metal surface spread, highly localized in metal and dielectric surface, compared with the length of the excitation light wavelength and unique field enhancement effect, so it attracts many researchers interested in using surface. Plasmonic photonic devices can break the diffraction limit. With the in-depth study of micro nano optical theory and micro fabrication technology, surface plasmon polaritons sub wavelength devices can meet the requirements of miniaturization and integration based on the great development in recent years. Among them, the metal nano structure (hole, groove joints, and their combination) due to the regulation in the space field and sub wavelength focusing unique ability, particularly attracted the attention of researchers. In this paper, the basic theory of surface plasmon polaritons based on Li Study of several arrays and single shaped gold nanostructures plasmonic lens by numerical simulation method of far-field super-resolution subwavelength focusing behavior, and the physical mechanism is analyzed. The main contributions of this dissertation are as follows: 1. put forward a two cylindrical dielectric filled plasmonic lens. The the lens is made of silica filled gold film nanogap arrays of gold film exit surface for two times. The cylindrical surface plasmon in the entrance slit along the slit excitation and transmission, in the exit slit into the light with the free space propagation phase delay. By controlling the lens structure parameters, can adjust the relative phase the light from the slit between them, so long in the focal point set interference, so as to realize the focusing effect. Calculated the two cylinder focusing the plasmonic lens characteristics calculated by using FDTD . the numerical simulation results show that the designed lens aperture of 2 m, can achieve micron focal length and focal depth, subwavelength focusing and focal spot width as low as 0.4 times the wavelength of the surface plasmon. The lens has simple and compact structure, small size, have integrated photonic devices for.2. a plasmonic lens single ring nano hole array with dual concentric grooves on gold film based on. It consists of a single ring nano hole array and two ring hole surrounded by concentric array of bilateral grooves, nanoporous gold film penetration; this is a special kind of symmetrical structure, can be used circularly polarized light focusing is achieved. The symmetric structure in the past, with radially polarized illumination, but radially polarized light is not easy to get, and the radially polarized light and not applicable to all symmetric structure. The symmetric structure is designed in this paper, using circularly polarized lighting can achieve better far-field poly Coke. Through numerical calculation, find out the relationship between the phase between the groove and the hole from the poor and the position of the groove, and then through the linear fitting, groove position parameters in achieving the desired specified focal distance focusing was determined. The finite difference time domain numerical simulation to get the plasmonic lens field distribution, showing a far field focusing phenomenon obviously. The calculation results show that the effect of tightly focused subwavelength plasmonic lens can realize axis symmetry, half width of the focal spot is less than half of a wavelength of light illumination and long focal depth, to improve the far field focus on the purpose of using concentric groove, plasmonic lens the focusing performance is significantly better than the conventional single loop nano pore structure. We further studied the plasmon polaritons in adjacent lens array two plasmon lens focusing interaction, through the numerical simulation to find the phase Influence of two adjacent plasmonic lens and the distance between the final focusing characteristics, provides a new way of.3. plasmonic lens array focusing characteristics of an improvement, proposed a plasmonic lens double elliptical holes array and multiple concentric ring groove based on gold film. The lens is a metal film the structure is composed of a plurality of concentric grooves and double elliptic nano hole array, the oval nano hole along the Archimedes spiral line. The distribution of linearly polarized light with surface plasmon coupling and concentric ring groove to spread nano hole design makes, and the ring groove can effectively scattering surface plasmon to export in the gold film surface can be converted into the wave propagation in free space, so as to realize the sub wavelength. We focus on equivalence focusing properties of plasmonic lens are studied theoretically and numerically. The lens can produce high resolution and long focal depth and focal field interesting For example, light or light pipe. It is worth noting that, even if the lens focal spot.4. online under polarized illumination can also produce symmetrical presents a single ring nano hole array based on three concentric ring slit wide spectrum of gold film plasmonic lens. The design of single and array plasmon element lens, a single lens is a single ring nano hole array and three in single hole concentric ring slit gold nano lens, nano hole and slit are penetrating the gold thin film; array lens is formed by a single lens unit is constructed. According to the different array size obtained by circularly polarized light lighting is easy; simulation etc. from the electric field excitation lens and lens array distribution by FDTD method, showing obviously far field focusing phenomenon; the central axis symmetric subwavelength focusing. Reported nanostructured plasmonic lens has some shortcomings, for example, light field The divergence and nano structure carefully designed only for specific wavelength. And the design of focusing lens and lens array can achieve a wide spectrum of focus, this paper is aimed at the 660 nm optical lens design, but the realization of far field focusing on any good wavelength wave can be 560 nm-760 in the range of nm. Through the analysis of the Rayleigh Sommerfeld integral find the wavelength of incident light increases, the smaller focal length. The reason. To further study the interaction between the two adjacent unit array focusing; through numerical simulation to find the distance between the two adjacent unit, influence of wavelength and light illumination on the final size of array focusing characteristics; provides a design to meet the according to the actual needs of the lens array.

【学位授予单位】:南京大学
【学位级别】:博士
【学位授予年份】:2017
【分类号】:TB383.1;O441

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