同心椭圆柱-纳米管结构的双重Fano共振研究

提出了一种同心椭圆柱-纳米管复合结构,该结构由金纳米管中内嵌椭圆形金柱构成,利用时域有限差分法分析了尺寸参数、周围环境及纳米管内核材料对该结构光学性质的影响.结果表明,调节椭圆柱芯的旋转角度可产生双重偶极-偶极Fano共振,其主要是由椭圆柱芯的纵向或横向偶极共振模式与纳米管的偶极成键和反成键模式杂化形成的超辐射成键模式和亚辐射成键模式之间的相互作用产生的,且共振特性可通过调节复合结构的尺寸参数控制,随椭圆柱长轴或短轴的增大而红移,随纳米管外径的增大或整体尺寸的减小而蓝移,当纳米管内径增大时高频Fano共振随着红移,而低频Fano共振先蓝移再红移,同时其对外界环境的变化不敏感,但对纳米管内核材料变化有着较好的响应.利用等离激元杂化理论对该现象进行了解释.这些结果可为构造其他类型的多波段Fano共振二维或三维纳米结构提供一种新的方式.     

侧耦合谐振腔的多重独立可调谐Fano共振传感特性

基于表面等离极化激元在亚波长结构的传输特性,提出了一种含单挡板的金属-介质-金属(MIM)波导耦合双T型谐振腔的结构。在近场耦合作用下,单挡板形成的较宽连续态与单T型腔形成的较窄离散态,经过复杂的干涉相消形成非对称的双重Fano共振峰。基于耦合模理论,研究了单挡板MIM波导耦合单T型腔Fano共振的产生机理,并采用有限元分析法对该结构进行了模拟仿真。在此基础上,研究了含双T型腔结构的四重Fano共振形成过程,分析了上下T型腔结构参数对Fano共振峰的影响。结果表明,上下T型腔产生的Fano共振峰互不影响,且由单个T型腔可以实现两个Fano共振峰独立可调谐,故含金属挡板的MIM波导耦合双T型腔结构可以实现四个Fano共振峰独立可调谐。该结构可为差动传感器和波分复用器的设计提供有效的理论参考。     

基于半圆形与矩形谐振腔耦合结构的Fano共振

设计了一种基于金属-介质-金属波导的半圆形谐振腔与矩形谐振腔的耦合结构,采用有限元方法研究了该结构的传播特性.结果表明:透射光谱中产生一个类似Fano共振线型的共振谷,该Fano共振由半圆形谐振腔的宽谱共振和矩形谐振腔的窄谱共振相互耦合所导致.变化谐振腔的结构参量,发现该Fano共振谷位置依赖于矩形谐振腔的几何参量,而对两谐振腔相对位置的微小移动不敏感;同时,改变两谐振腔的并联方式,研究了两种衍生结构的传播特性,发现这些结构均可产生明显的Fano共振.此外,通过在谐振腔中填充不同折射率的介质材料,研究了三种结构基于Fano共振效应的折射率传感特性,其折射率敏感度最高达到750 nm/RIU.研究结果可为未来芯片上基于表面等离极化激元波导的高灵敏折射率传感器的设计提供理论依据.     

金纳米棒二聚体结构的Fano共振

等离激元金属纳米结构中的Fano共振,由于其在超灵敏传感、超材料、光开关和非线性光学器件等方面的潜在应用而引起了广泛的关注。但在单颗粒尺度下单个金属纳米二聚体结构的Fano共振的实验研究仍然很少。本研究基于单颗粒光谱技术从实验上探讨了二聚体结构产生的Fano共振现象。利用种子生长法制备了等离激元共振峰分别在1 060 nm和700 nm的一长一短金纳米棒,通过L-半胱氨酸分子的静电吸附自组装构建首尾相连的金纳米棒二聚体结构,在暗场显微系统中表征了金纳米棒二聚体耦合前后的散射光谱。结果表明,短金纳米棒的明偶极模式与长金纳米棒的暗四极模式间的相消干涉在660 nm处产生了明显的Fano共振谷,同时基于有限差分时域（FDTD）方法的理论模拟散射光谱与实验结果能够较好地符合。这种自组装金纳米棒二聚体在等离激元传感和探测等方面具有广阔的应用前景。     

三角缺口正三角形纳米结构的共振模式

设计了一个三角缺口三角形破缺纳米结构,它是从正三角形底边切掉一个三角切片所构成.应用离散偶极子近似方法研究了其消光光谱及表面电场分布.结果发现,该破缺纳米结构的消光光谱中出现了具有Fano共振的线形.分析表明,这个Fano共振线形是由绑定与反绑定混合表面等离激元模式相互作用所致.研究了三角缺口三角形纳米结构的结构参数对Fano共振的影响.     

内嵌银纳米棒圆形银缝隙结构中的法诺共振现象

应用时域有限差分算法系统地研究了内嵌银纳米棒圆形银缝隙结构的透射特性. 由于倾斜银纳米棒破坏了圆形腔原有的对称稳态磁场分布, 该系统中产生了法诺共振现象. 此外, 透射光谱强烈地依赖于纳米棒的倾斜角度和纳米棒的形貌参数. 这些结果有助于设计复合结构滤波器, 满足特定的滤波需要. 关键词： 表面等离极化激元 法诺共振 时域有限差分算法     

ITO纳米棒结构红外波段消光特性模拟与分析

铟锡氧化物（ITO）作为一种高掺杂的半导体材料,其材料介电常数零点波长位于近红外波段,且其在近红外波段的吸收损耗较小,因此ITO可以成为近红外波段理想的局域表面等离激元共振效应（LSPR）材料。采用时域有限差分法模拟长方体状ITO纳米棒阵列的LSPR效应,通过调整ITO纳米棒的载流子浓度、尺寸、间距以及衬底折射率实现其红外波段LSPR共振峰的有效调节。这对于扩宽ITO纳米结构在红外波段LSPR效应的应用具有重要的研究意义。     

椭圆截面金纳米管的局域表面等离激元共振特性研究

基于时域有限差分方法研究了几何形状、入射电场偏振方向、管壁厚度及内核和包埋介质的变化对椭圆截面金纳米管局域表面等离激元共振特性的影响.研究发现,当长轴固定时,短轴的减小将导致纳米管消光峰红移;入射电场偏振方向与椭圆长轴夹角的增大将导致消光峰红移;当颗粒整体尺寸不变时,管壁厚度减小同样会使得消光峰红移.此外,内核及包埋介质介电常数的增大均导致消光峰红移.利用等离激元杂化理论及自由电子和振荡电子竞争机理对上述现象进行了理论分析. 关键词： 消光光谱 局域表面等离激元共振 金纳米管 时域有限差分方法     

D3h和D4h等离激元超分子的Fano共振光谱的 子集合分解解释

针对D_3h和D_4h对称构型金属纳米多颗粒集合即等离激元超分子表面等离激元共振光谱的子集合分解及其相对应的Fano共振光谱低谷的产生机理, 本文运用群论的方法做出了详细的分析研究. 运用与群论中求解分子简正振动模式类似的方法, 推导证实了在线偏振光入射时, D_nh环形多颗粒只有2个电偶极表面等离激元共振模式, 增加中心颗粒会使模式增加1个. 对D_3h和D_4h等离激元超分子的表面等离激元共振模式进行不可约表示基向量正交分解分析表明, Fano共振光谱低谷是由于两个起主要作用的相邻模式包含有共同的正交基向量, 并形成相消干涉而产生. 这进一步验证了Fano共振光谱低谷的起源除传统观点(即源自于宽频超辐射亮模式和窄频低辐射暗模式之间的耦合)之外的另一种解释视角.     

Tunable Fano resonances and plasmonic hybridization of gold triangle–rod dimer nanostructure

A gold dimer structure consisting of a notched triangle nanoslice and a rectangle nanorod is proposed to produce distinct Fano resonance. Owing to the coupling between the dipole plasmon mode of the nanorod and the dipole or quadrupole plasmon mode of the nanoslice, the extinction spectrum with a deep Fano dip is formed and can be well fitted by the Fano interference model for different geometry parameters. In addition, Fano resonance of the gold dimer nanostructure also intensely depends on the polarization direction of incident light. Moreover, Fano resonance of the triangle–rod trimer is also analyzed by adding another nanorod into the former dimer and exhibits the splitting of plasmonic resonant peak in high order coupling modes. The plasmonic hybridizations in these nanostructures have been analyzed for revealing the physical origin of the Fano resonance.     

Modulation of Fano resonances in symmetry-broken gold-SiO2-gold nanotube dimers

Fano resonances in the symmetry-broken gold-SiO2-gold(BGSG)nanotubes and the associated dimers have been investigated based on the finite element method.In the BGSG nanotube,the symmetry breaking induced the interactions of the inner gold core and outer gold nanoshell plasmons of all multipolar orders and hence the red-shifts of the plasmon resonance modes and the enhanced quadrupole mode peaks were observed.The interference of the quadrupole mode peak with the subradiant dipole mode caused a Fano-dip in the scattering spectrum.By increasing the core offset-value in the BGSG nanotube,the Fano dip with low energy showed a red-shift and became deeper.Unexpectedly the plasmon coupling between a GSG nanotube and a BGSG nanotube can lead to two strong Fano dips in the scattering spectra of the dimer.It was further noted that the thin side of the BGSG nanotube located at two sides of the dimer gap can lead to the strong near-field coupling between two BGSG nanotubes and hence a deeper and broader Fano dip.     

Fano resonances in heterogeneous dimers of silicon and gold nanospheres

We theoretically investigate the optical properties of dimers consisting of a gold nanosphere and a silicon nanosphere. The absorption spectrum of the gold sphere in the dimer can be significantly altered and exhibits a pronounced Fano profile. Analytical Mie theory and numerical simulations show that the Fano profile is induced by constructive and destructive interference between the incident electric field and the electric field of the magnetic dipole mode of the silicon sphere in a narrow wavelength range. The effects of the silicon sphere size, distance between the two spheres, and excitation configuration on the optical responses of the dimers are studied. Our study reveals the coherent feature of the electric fields of magnetic dipole modes in dielectric nanostructures and the strong interactions of the coherent fields with other nanophotonic structures.     

Fano resonances in semiconductor superlattices

We use semiconductor superlattices as a model system for the investigation of Fano resonances. In absorption the excitonic transitions of the Wannier–Stark ladder show the typical asymmetric line shape due to coupling to the continuum of lower-lying transitions. The unique feature of these Fano resonances is that they allow to continuously tune the key parameter – the coupling strength Γ between the discrete state and the degenerate continuum – by varying the bias voltage. Using this feature, we directly show that the Fano coupling leads to a fast polarization decay. We also investigate the dependence of the Fano parameters on the structure of the superlattice and compare with an extensive theoretical model of the resonances.     

金属半圆环/长板阵列的法诺共振特性

本文设计了金属半圆环/长板阵列,并应用有限元方法研究了该阵列的透射特性。研究表明:由于半圆环与长板之间的电场耦合,在该阵列中产生了法诺共振现象。法诺共振峰强烈地依赖于半圆环/长板的结构参数和相对位置,并且法诺共振峰对周围介质折射率有着较高的灵敏度,最高可以达到862.5 nm/RIU。这些结果有助于设计基于法诺共振的微纳光子学器件。     

椭圆截面金纳米管近场增强特性的研究

本文基于时域有限差分方法(finite difference time domain, FDTD)研究了入射光波长、入射光偏振方向、纳米管几何形状、 管壁厚度及内核和包埋介质的变化对椭圆截面金纳米管近场分布特征的影响. 研究发现, 入射光波长为纳米管等离激元共振波长时, 纳米管近场增强最大; 入射光偏振方向与椭圆长轴夹角的增加会导致管内的场强迅速增大; 椭圆管半短轴变大可以调节纳米管场强分布从两端高、中间低变化为均匀分布; 内核和包埋介质介电常数的增大均会使得纳米管内部及周围场强逐渐减弱.     

Fano resonances in complex plasmonic super-nanoclusters: The effect of environmental modifications on the LSPR sensitivity

In this study, gold nanodisk clusters in heptamer orientations as clusters were used to design a super-heptamer consisting of one central and six peripheral heptamers. We examined the position and movement of the plasmon and Fano resonances by sketching the spectral response of the superstructure for various nanodisk dimensions. The quality of the interference between the superradiant and subradiant plasmon resonance modes of the nanodisk clusters was found to depend strongly on the structural configuration and the refractive index of the environmental medium. We replaced the central heptamer with a nanodisk and probed the position of the Fano resonance by geometrically altering the nanodisk structure. Finally, the effect of the dielectric environment on the plasmon response of both of the studied structures was examined numerically and theoretically. The localized surface plasmon resonance sensitivity of the finite plasmonic structures to the presence of liquid substances was investigated and shown by plotting the linear figure of merit. The finite-difference time-domain method was used as a numerical tool to investigate the plasmon response of the structure.