内嵌凹槽的金属亚波长狭缝共振透射特性分析

在亚波长金属狭缝内嵌入凹槽后,狭缝的透射峰发生红移、蓝移,也可能不变。本文利用有限时域差分法,详细讨论了内嵌凹槽深度对狭缝透射光谱的影响。通过与腔共振模式理论对比,我们发现内嵌凹槽的亚波长金属狭缝透射峰变化一方面来自于共振腔长度的增长,另一方面来自于透射峰所对应的共振模式数的增加。透射峰蓝移等变化均为共振模式数改变和共振腔长度增长共同作用的结果。     

一种新型亚波长光栅结构透射增强特性及机理研究

通过引入谐振腔,设计了一种具有较强透射特性的亚波长金属光栅。引入有耗Drude色散媒质模型,采用时域有限差分算法(Finite-Difference Time-Domain,FDTD),研究金属光栅的透射增强特性并分析了光栅几何参数对透射特性的影响。计算结果表明,所设计内壁刻有谐振腔的三层光栅比单层光栅具有更好的滤波效果,其透射光谱峰值可达84%,为带通滤波器的设计提供了参考。并利用波导Fabry-Perot(F-P)腔谐振效应分析了透射峰的漂移现象。     

1.5μm波段硅基金属光栅单向透射的研究

为了在硅衬底上制作全光逻辑元件,实现1.5μm波长的单向透射性,设计了一种基于硅衬底的复合金属光栅,利用光子在不同方向上入射到金属光栅表面时,耦合成表面等离子体的条件不同,通过FDTD数值仿真和优化,通过对光栅结构的优化和调节复合光栅的参数,实现了在1.5μm波段单向透射,正向入射光的透射率可达39%,对应的透射对比率可达9.4。这一研究成果可以应用于全光逻辑回路和全光二极管的设计。     

透射光谱法测光栅参数的可行性

利用透射光谱,结合正单纯形法来反演折射率调制光栅参数,首先利用光栅衍射傅里叶模式理论及RTCM算法得出在200nm~900nm波长范围内的透射光谱曲线,从上取5个点,作为理论计算值; 其次,在上述曲线上加入偏差不同的高斯噪声,以模拟透射光谱的测量曲线,再从每条曲线上各取5个对应点,获取模拟测量值;然后,假定光栅参数的初始值,代入评价函数,用正单纯形法不断进行迭代反演,得到光栅参数的计算模拟结果。此方法简单、快速、精确。     

亚波长金属光栅的共振吸收谱及其近场特性

通过对亚波长金属光栅的可见光波段的光谱特性及其近场强度分布进行研究,采用Comsol软件仿真了结构参数变化对光谱和强度分布的影响。研究结果表明,亚波长金属光栅具有共振吸收谱,在吸收率峰值处,表现出亚波长金属结构表面等离激元的驻波模式,并在适当的参数下,得到了一种暗中空光场模式,利用该暗中空光场模式可以实现基于亚波长光栅的原子囚禁与导引。研究结果为亚波长光栅的理论研究以及亚波长光栅器件研究的实用化提供了参考。     

透射式金属光栅耦合SPR传感器

用磁控溅射技术在双面抛光的蓝宝石衬底上沉积了20 nm Ti和100 nm Au的金属薄膜,通过标准光刻工艺制备出1.6和2.0μm两种周期结构的一维光栅表面等离子体共振(SPR)传感器。用时域有限差分算法(FDTD)模拟仿真并结合实验测试的透射光谱,研究分析了不同周期结构的金属薄膜光栅型SPR传感器的特性。基于金属光栅耦合,利用表面等离子体激元(SPP)的局域特性和光栅的选频特性,实现了SPR传感器的信号增强和滤波功能。研究结果表明,利用金属薄膜光栅表面介质的变化引起的光栅透射光谱中激发表面等离子体共振峰的位置变化,可以获得被测物体的物理、生物和化学等相关特征信息。     

金属狭缝阵列在电介质覆层下的TE波异常透射性

亚波长周期性结构具有不同于传统微结构的许多特异性质,利用这些性质可以设计新型纳米光子学器件。应用时域有限差分(FDTD)数值模拟方法,通过在亚波长周期性结构的金属上添加电介质覆层,发现了横电波(TE)偏振光激励下周期性调制金属狭缝的异常透射现象,并对金属薄膜左右表面和狭缝内添加电介质覆层对异常透射的作用和影响进行了分析讨论,得到金属的左右表面能激发一表面波,通过狭缝内的电介质波导的传输,产生异常透射增大的现象。     

表面修饰的亚波长金属Cu狭缝结构透射特性研究

为了深入研究表面修饰余弦凹槽的亚波长结构对太赫兹波透射特性的调控规律,提出一种表面修饰余弦凹槽的太赫兹亚波长金属Cu狭缝结构,基于时域有限差分法,对亚波长金属Cu狭缝结构的太赫兹波透射光谱特性进行模拟。仿真结果表明,通过改变金属Cu狭缝结构上下表面余弦凹槽的结构排布、数量、周期、深度及狭缝深度、宽度等参量,实现了对太赫兹波透射强度的调控。     

对透射闪耀光栅的傅里叶分析

一般的透射光栅光谱的缺点是,没有色散的零级主极大占去了入射能量中的很大一部分,剩下的能量又要分配到正负各级主极大上,造成用来分析的有色散的那些谱线中只分配到很小的能量。在实际的应用中,要设法把能量集中分配到所要利用的那级光谱中,闪耀光栅就是为此目的设计的。研究从不同方向入射透射闪耀光栅的透射函数,利用傅里叶光学,从理论上分析透射闪耀光栅衍射图样的复振幅和光强分布与闪耀角及波长的关系。     

透射光栅谱仪光谱法测量ICF辐射温度

辐射温度是间接驱动ＩＣＦ研究中一个非常重要的参量。利用透射光栅谱仪,结合光谱还原技术对辐射温度进行测量,并对辐射输运过程作细致的研究。本文介绍了透射光栅光谱还原技术的一般方法,以及在重复频率脉冲激光等离子体Ｘ射线光源上进行ＸＵＶ二极管标定和光栅标定的一般过程。     

Effects on extraordinary transmission of TE wave through varying structure of sub-wavelength metallic gratings without host media

A model of sub-wavelength metallic grating without host media is proposed. Under the excitation of TE polarized light, the extraordinary transmission is also found, and their transmission energy distributions corresponding to different structural parameters of this model are calculated systematically by using finite difference time domain (FDTD) method. The influence of slit width, grating thickness and grating period on the location of transmission peak is obtained. By studying these relations, it is found that Fabry-Perot-like (FPL) effect of the slit is the main physical reason of this extraordinary transmission. Varying the slit width can cause the change of reflection phase transition at both ends, and then the characteristics of FPL resonance of slit cavity are affected. The surface mode of metallic gratings has less effect on the location of transmission peak.     

On Light Addressing Within Subwavelength Metallic Gratings

We consider a zero-order diffraction metallic grating having two subwavelength rectangular slits per period. The electromagnetic behavior of this system is studied theoretically in the resonance spectral domain of the cavities. We show that, by choosing judicious opto-geometrical parameters, we can perform the selective excitation of one or the other category of cavities with a very appreciable quality factor, illustrating then a switch effect. The results open the way to the quantitative light addressing on passive metallic micro/nano-structures. In particular, for transmitting gratings, we can force light to cross each subwavelength channel doublet through a determined aperture, reconsidering in some extent the Young's slits experiment.     

THz波微结构器件特性的研究

在电磁波谱中所处的特殊位置使得THz波在在物理、化学、生物医学、电子科学、材料科学、环境监测等领域有着广泛的应用前景。综述了THz波微结构器件特性方面的研究工作。亚波长金属周期微结构器件的THz波谱选择增强透射现象,亚波长环形槽金属线上的THz等效表面等离子体激元,以及THz光子晶体光纤。     

单层和多层有缝金属板电磁波透射的FDTD分析

采用在入射波一侧的总场边界处同时引进入射波和反射波作为激励源的FDTD方法来分析斜入射时单层和多层有缝金属板电磁波透射问题.通过计算金属板缝隙附近的散射场,提取缝隙口径面上的等效面磁流,进而得到透射截面.计算机仿真结果证实了算法的有效性.数值计算结果表明,两金属板上所开缝隙的相对偏移以及两板间插入介质板将会改变屏蔽效应.该方法可以有效分析平面波斜入射时多层金属板上任意形状缝隙的散射和透射,包括缝隙内或金属板之间填充有介质情形.     

A novel in-service surveillance scheme for optically amplified transmission systems

We propose here a novel surveillance scheme for an optically amplified transmission system which allows simultaneous in-service fault identification for fiber and optical amplifiers. While requiring additional fiber Bragg gratings of designated wavelengths to be integrated with optical amplifiers, the monitoring light source is derived from the unused spectra of ASE and no dedicated light source is needed as in conventional OTDR technique. We have further demonstrated the scheme's feasibility with a 100-km, three-EDFA optical transmission system.     

Wide-band Fabry-Perot-like filters in optical fiber

We report the fabrication and characterization of wide-band Fabry-Perot-like resonators in optical fiber. Using Bragg gratings with variable detuning, resonators that operate ever a wavelength span in excess of 140 nm have been produced, with free spectral ranges between 0.09 nm and 11.27 nm. Numerical and experimental results for two typical resonators are presented, showing good agreement between the two     

Gold nanohole arrays for biochemical sensing fabricated by soft UV nanoimprint lithography

We report on results of fabrication and optical characterisation of sub-250 nm periodic gold nanohole arrays on glass by using UV nanoimprint lithography (UV-NIL) combined with both reactive ion etching (RIE) and Cr/Au lift-off processes. The transmission spectra of the fabricated nanohole gratings were measured for different hole diameters and periods. We also show preliminary results of chemical sensing after surface modification of the gold hole arrays. In agreement with the theoretical prediction, we found that any change in the dielectric index of the surrounding environment of the metallic array produces a transmission peak red shift.     

Efficient Linearly Polarized Lamp for Liquid Crystal Displays

We propose a new optical design to produce linearly polarized illumination for liquid crystal displays. The operation mechanism is based on polarization conversion due to induced surface plasmon polariton on metallic gratings in conical diffraction. This linearly polarized lamp integrates an unpolarized light source and a light recycling scheme inside the lamp housing. Its structure is simple and, moreover, its optical efficiency reaches 92% in emitting a linearly polarized light.