金属圆孔阵列的非共振增强透射

基于非共振原理的光异常透射现象(EOT)可以实现宽频带透射,对宽频带光收集与激发具有重要意义.为实现宽频透射,本文设计了亚波长金属圆孔阵列,并应用有限元方法研究了该结构的透射特性.结果表明,金属圆孔阵列可实现宽频透射.此外,本文还研究了入射光偏振方向、圆孔半径以及横向周期对金属圆孔阵列透射特性的影响.这些结果对设计非共振宽频透射的金属孔洞结构具有一定的指导意义.     

Microscopic theory of the extraordinary optical transmission

The phenomenon of extraordinary light transmission through metallic films perforated by nanohole arrays at optical frequencies was first observed a decade ago and initiated important further experimental and theoretical work. In view of potential applications of such structures--for example, subwavelength optics, optoelectronics devices, and chemical sensing--it is important to understand the underlying physical processes in detail. Here we derive a microscopic theory of the transmission through subwavelength hole arrays, by considering the elementary processes associated with scattering of surface-plasmon-polariton (SPP) modes by individual one-dimensional chains of subwavelength holes. Using a SPP coupled-mode model that coherently gathers these elementary processes, we derive analytical expressions for all the transmission spectrum characteristics--such as the resonance wavelength, the peak transmission and the anti-resonance. Further comparisons of the model predictions with fully vectorial computational results allow us quantitatively to check the model accuracy and to discuss the respective impacts of SPP modes and of other electromagnetic fields on producing the extraordinary transmission of light. The model greatly expands our understanding of the phenomenon and may affect further engineering of nanoplasmonic devices.     

Light in tiny holes

The presence of tiny holes in an opaque metal film, with sizes smaller than the wavelength of incident light, leads to a wide variety of unexpected optical properties such as strongly enhanced transmission of light through the holes and wavelength filtering. These intriguing effects are now known to be due to the interaction of the light with electronic resonances in the surface of the metal film, and they can be controlled by adjusting the size and geometry of the holes. This knowledge is opening up exciting new opportunities in applications ranging from subwavelength optics and optoelectronics to chemical sensing and biophysics.     

Transmission resonances through aperiodic arrays of subwavelength apertures

Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission. The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons (collective electronic excitations in the metal surface) mediate light transmission through the grating. In this picture, structural periodicity is perceived to be crucial in forming the transmission resonances. Here we demonstrate experimentally that, in contrast to the conventional view, sharp transmission resonances can be obtained from aperiodic aperture arrays. Terahertz transmission resonances are observed from several arrays in metallic films that exhibit unusual local n-fold rotational symmetries, where n = 10, 12, 18, 40 and 120. This is accomplished by using quasicrystals with long-range order, as well as a new type of 'quasicrystal approximates' in which the long-range order is somewhat relaxed. We find that strong transmission resonances also form in these aperiodic structures, at frequencies that closely match the discrete Fourier transform vectors in the aperture array structure factor. The shape of these resonances arises from Fano interference of the discrete resonances and the non-resonant transmission band continuum related to the individual holes. Our approach expands potential design parameters for aperture arrays that are aperiodic but contain discrete Fourier transform vectors, and opens new avenues for optoelectronic devices.     

亚波长孔阵透射增强特性的FDTD数值仿真

 推导出了一种基于有损耗的Drude色散媒质模型的三维时域有限差分法（FDTD）.用该方法对金属亚波长圆形周期孔阵的透射增强特性进行了研究.数值仿真计算了金属板厚度、孔的大小、基底介质、孔中填充不同折射率的介质和孔阵的周期等对孔阵透射率的影响.数值计算结果表明,亚波长孔阵的透射系数随孔的变大而增大,随孔阵周期的变大而减小,在金属前后介质匹配时最大,孔中填充高折射率的介质可以增强透射能力.     

Channel plasmon subwavelength waveguide components including interferometers and ring resonators

Photonic components are superior to electronic ones in terms of operational bandwidth, but the diffraction limit of light poses a significant challenge to the miniaturization and high-density integration of optical circuits. The main approach to circumvent this problem is to exploit the hybrid nature of surface plasmon polaritons (SPPs), which are light waves coupled to free electron oscillations in a metal that can be laterally confined below the diffraction limit using subwavelength metal structures. However, the simultaneous realization of strong confinement and a propagation loss sufficiently low for practical applications has long been out of reach. Channel SPP modes--channel plasmon polaritons (CPPs)--are electromagnetic waves that are bound to and propagate along the bottom of V-shaped grooves milled in a metal film. They are expected to exhibit useful subwavelength confinement, relatively low propagation loss, single-mode operation and efficient transmission around sharp bends. Our previous experiments showed that CPPs do exist and that they propagate over tens of micrometres along straight subwavelength grooves. Here we report the design, fabrication and characterization of CPP-based subwavelength waveguide components operating at telecom wavelengths: Y-splitters, Mach-Zehnder interferometers and waveguide-ring resonators. We demonstrate that CPP guides can indeed be used for large-angle bending and splitting of radiation, thereby enabling the realization of ultracompact plasmonic components and paving the way for a new class of integrated optical circuits.     

基于金属表面等离子激元的侧耦合半圆形腔-波导透射谱分析

设计了一种新型的基于金属表面等离子激元（Surface Plasmon Polaritons,SPPs）的亚波长金属-介质-金属型滤波器.该滤波器由一个半圆形谐振腔和一个直波导组成.使用时域耦合模理论和传输变换矩阵方法对结构进行理论分析,并通过时域有限差分方法(the finite difference time domain method,FDTD)进行数值模拟得出光谱响应.讨论了几何参数对透射曲线的影响, 并设计了一种双腔结构来获得高对比度的透射曲线.     

汽车用防声材料的SEA参数预测

声学特性的预测工具已经被应用于计算声音包对声腔阻尼的影响.文中基于转移矩阵法,提出一种能够预测多层结构防声材料声学特性的方法.该方法通过考虑绝缘部分与结构的非均匀特性,允许在统计能量分析SEA软件外计算多层绝缘元件的数量.将该方法用于预测修正元件的传播损耗,结果表明预测结果和实验结果符合较好.     

亚波长十字型MIM等离子波导滤波器

运用时域有限差分方法(FDTD)方法数值研究了一种亚波长十字型金属—绝缘体—金属(MIM)等离子波导结构的透射属性.结果表明该结构的透射极小值与十字型切口的长度密切相关,表现出良好的滤波性质.十字型切口被直MIM等离子波导分为上下两段,每一段独立构成一个驻波谐振腔.当各段长度独立满足驻波谐振条件时,该结构均会产生透射极小值.     

M型钡铁氧体的制备及其吸波性能表征

采用溶胶凝胶自蔓延合成工艺制备了六角晶系M型钡铁氧体微粉BaFe12O19.用X射线衍射仪,振动样品磁强计和矢量网络分析仪对粉末的结构、磁性能以及电磁波吸收性能进行了表征.结果表明,BaFe12O19既能产生磁损耗,又能产生介电损耗,是一种宽频微波吸收材料.     

超短脉冲在纳米金属缝中的传输特性

根据Drude模型和时域有限差分法（FDTD）编制程序包,通过模拟计算研究超短脉冲经纳米金属缝衍射的时域信号的分布特性．讨论了透射脉冲的时域分布与超短脉冲有效驰豫时间的演化关系,借助于其谱域分布对时域波形进行了解释．     

镧六方铁氧体Ba1-xLaxFe12O19的电磁 性能与吸波特性

研究了掺稀土六方铁氧体Ba_{1-xLaxFe12O1 9的合成条件, 测试了其结构、 形貌、 电磁性能与吸波特性. 结果表明, 稀土离子 La³⁺的加入, 降低了钡铁氧体的磁化强度、 矫顽力和顽磁性, 其磁特性接近 软磁铁氧体材料; 在1.65~2.95 GHz的频率范围内, 具有良好的吸波性能.}     

基于IEEE 802.11a的E1无线传输系统及其应用

在分析IEEE 802.11a和E1传输两种技术各自特点的基础上,介绍了基于802.11a的E1无线传输系统的系统构成,提出了该系统几种典型的应用模式,并与传统的E1微波传输系统做了比较。基于802.11a的E1无线传输系统具有频段无需申请、组网方式灵活多样、可同时传输E1数据和IP数据以及成本低廉等优势,可作为传统E1微波传输系统的替代和补充而广泛应用。     

一种新型双层PBG结构带阻滤波器

本文介绍了一种双层结构的基于衬底打孔的PBG结构带阻滤波器,采用了周期结构与微带电路分离的设计,解决了传统的打孔结构的导带加工问题,并且有利于电路的加工和修改.最后给出了利用HFSS理论仿真和实际测量的结果,论证了这种结构的可行性     

一种新型双层PBG结构带阻滤波器

本文介绍了一种双层结构的基于村底打孔的PBG结构带阻滤波器，采用了周期结构与微带电路分离的设计。解决了传统的打孔结构的导带加工问题，并且有利于电路的加工和修改。最后给出了利用HFSS理论仿真和实际测量的结果，论证了这种结构的可行性     

单阶梯调制金属狭缝中的磁场及能量分布

本文利用时域有限差分(FDTD)算法,研究了由亚波长向非亚波长过渡时,单阶梯调制狭缝内的磁场及能量分布的变化情况.理论计算表明,当结构处于亚波长范围内时,结构中只有零阶模式即SPP传播,I区和II区由于反射场的存在,z方向上呈现振荡的场分布,而III区中没有反射场,其振幅沿z方向上是一常量.当结构处于非亚波长范围内时,除了SPP外,还有高阶模式的存在,它们之间的相互作用及与反射场的相互作用使得缝内场和能量分布变得复杂.     

Plasmon-assisted transmission of entangled photons

The state of a two-particle system is said to be entangled when its quantum-mechanical wavefunction cannot be factorized into two single-particle wavefunctions. This leads to one of the strongest counter-intuitive features of quantum mechanics, namely non-locality. Experimental realization of quantum entanglement is relatively easy for photons; a starting photon can spontaneously split into a pair of entangled photons inside a nonlinear crystal. Here we investigate the effects of nanostructured metal optical elements on the properties of entangled photons. To this end, we place optically thick metal films perforated with a periodic array of subwavelength holes in the paths of the two entangled photons. Such arrays convert photons into surface-plasmon waves--optically excited compressive charge density waves--which tunnel through the holes before reradiating as photons at the far side. We address the question of whether the entanglement survives such a conversion process. Our coincidence counting measurements show that it does, so demonstrating that the surface plasmons have a true quantum nature. Focusing one of the photon beams on its array reduces the quality of the entanglement. The propagation of the surface plasmons makes the array effectively act as a 'which way' detector.     

水平管气液环状流在新型分配器中的分配研究

设计了一种新型三通型两相分配器，该分配器主管侧壁均匀分布着直径均为3．5mm的8个小孔，主管中的气液混合物通过安装在主管外壁上的环室进入侧支管．通过在空气一水实验台上对水平管气液环状两相流通过该分配器进行的实验研究发现：与传统三通分配器的分配特性不同，该分配器的液相会优先进入侧支管．建立了相分配模型，认为对于环状流，通过管壁小孔的液膜将被小孔捕获，从而进入侧支管．该模型还提出了分配影响区修正系数，实验发现该系数与入口干度成线性关系．预测的气液相分流系数、主管出口与直通管间压力损失与实验结果吻合得很好，最大误差为7．24％．     

频率可调磁感应波器件的微波透射性能

研究了由双层磁化铁氧体构成的磁感应波器件的微波透射性能以及场致频率可调特性,并探讨了结构参数对微波性能的影响.两磁化铁氧体平板样品平行放置,由于间隙处表面波共振模强烈耦合产生磁感应波透过样品,在铁磁共振产生的微波禁带频率范围内产生一个显著的通带.通带的中心频率随着偏置磁场的增强而单调上升,显示出很好的场致频率可调性.随着两铁氧体之间间距的增加,界面耦合作用减弱,透射通带的半高宽逐渐降低,损耗增加.     

圆孔与三极子组合单元频率选择表面研究

应用谱域法分析了圆孔与三极子组合单元频率选择表面(FSS)的频率响应特性。分析了组合单元的结构参数、电磁波极化和入射角度对其稳定性的影响。研究结果表明,该组合单元的频率响应特性曲线具有明显的两个阻带和一个通带,且具有良好的极化稳定性和角度稳定性。在结构参数中,圆孔大小对频率响应特性曲线的位置影响较大,极子长度对传输带宽影响较大,而极子宽度影响较小。通过单元结构参数调整,可获得良好的宽带传输和陡峭下降边缘特性,实现相临波段信号分离和多波段通讯。该结构FSS可应用于卫星通讯、雷达罩及其他相关领域。