左右手材料光子晶体带隙及表面波局域电场特性

为研究与设计新型光波导和光学传感器，通过参数匹配，并利用平面波展开的传输矩阵理论及布洛赫定理，研究左右手材料光子晶体的能带结构、表面波局域电场分布等，结果表明:零平均折射率左右材料光子晶体能带中存在的半封闭状和封闭状禁带结构，且通带中的能级曲线由高频向低频方向振荡衰减并简并。添加表面覆盖层介质后，部分半封闭状及封闭状禁带中出现正向波和反向波分立能级，分立能级随覆盖层厚度增大向波矢减小方向移动，半封闭状禁带中的分立能级在覆盖层厚度达到一定数值时出现分裂现象。禁带中正向表面波局域电场极大值均处于覆盖层与光子晶体表面交界处附近，并随覆盖层厚度增大或远离交界处而衰减，封闭状禁带对应的局域电场极大值对覆盖层厚度的响应灵敏度弱于半封闭状禁带。禁带中的反向表面波局域电场及其极大值均处于光子晶体内部，而且随覆盖层厚度增大而增强，封闭状禁带对反向表面波的局域限制作用、表面波与入射光的耦合作用、局域电场对覆盖层厚度的响应灵敏度等强于半封闭状禁带。     

采用TiO_2薄膜增强光子晶体光纤表面等离子体共振生物传感器灵敏度的建模分析

提出一种采用TiO_2膜增强双纤芯单通道光子晶体光纤表面等离子体共振生物传感器灵敏度的设计方案:在传感器银膜表面增加一层TiO_2薄膜,不仅可以隔绝氧气,防止银氧化,而且可提高传感器的灵敏度;采用全矢量有限元法数值分析传感器的耦合特性及其性能。结果表明,在待测介质折射率为1.33~1.38时,待测介质折射率与传感器的共振波长呈线性关系,线性相关度为0.9806,传感器的平均灵敏度为4200nm·RIU-1。此外,进一步分析了光子晶体光纤空气孔大小、银膜厚度、TiO_2厚度等参数对传感器性能的影响。结果表明,改变结构参数可以优化生物传感器的输出光谱、改善传感器的性能。     

铬过渡层对银膜光学性质及附着力的影响

研究了在玻璃基底上采用不同厚度的铬膜作过渡层,对银膜的光学性质及其附着力的影响。光谱测量结果表明,随着铬膜层厚度的增加,银膜的反射率先增大后减小。与直接镀在玻璃基底上的银膜的反射率相比,铬膜层厚度为8~14nm时,银膜的反射率较低;铬膜层厚度为17~21nm时,银膜的反射率得到提高,其中铬膜厚度为17nm时,银膜的反射率最高;继续增加铬膜层的厚度,银膜的反射率又降低,说明采用一定厚度的铬膜作过渡层可以提高银膜的反射率。X射线衍射(XRD)结构分析表明,一定厚度的铬膜改善了银膜的结晶程度,使薄膜的晶粒度增大,晶界散射及缺陷减少,从而使应变减小。剥落实验证明薄膜与玻璃基底之间的附着力也得到了提高。     

一维函数型光子晶体的光学传输特性

研究了一维正弦函数型光子晶体的透射特性和缺陷层对透射特性的影响,同时分析了光在正弦函数型光子晶体中的光学传输特性,即电场在正弦函数型光子晶体中的分布。对正弦函数型光子晶体,在缺陷层处的场强既可局域增强,也可局域减弱。这与缺陷层介质的折射率大小有关。当缺陷层对场强的作用是增强或减弱时,缺陷层位置越靠前,它对其后场强的增强或减弱作用越大。这些结论对光子晶体的设计与应用具有一定指导意义。     

镜像耦合一维光子晶体窄带滤波器设计研究

文章提出准周期一维光子晶体的概念,把一维时域有限差分方法用于一维二元准周期光子晶体构成镜像耦合结构的窄带滤波特性设计研究.数值结果表明,用此结构能实现窄带滤波.进一步研究表明,要实现同一波长的滤波,在其他条件不变时,耦合层的折射率越大,则镜像耦合层厚度越小;在耦合层介质一定时,耦合层厚度决定窄带的位置与带宽;在其他条件一定时,入射角大小决定窄带的位置,入射角度越大,窄带位置越向短波方向移动.     

1维光子晶体微腔的光子局域特性分析

为了研究光子晶体的光局域特性,采用传输矩阵法计算了1维缺陷光子晶体微腔中缺陷模的局域场强分布,建立了相对局域化长度的概念,它表征光子局域程度的强弱,局域化长度越小,光子局域程度越强,反之亦然。结果表明,缺陷层两侧排列为高折射率介质层的结构局域光的能力比两侧为低折射率介质层的强;考察前一种结构,且满足共振布喇格散射条件或共振米散射条件范围时,相对局域化长度可获得较小值。     

1维光子晶体微腔的光子局域特性分析

为了研究光子晶体的光局域特性,采用传输矩阵法计算了1维缺陷光子晶体微腔中缺陷模的局域场强分布,建立了相对局域化长度的概念,它表征光子局域程度的强弱,局域化长度越小,光子局域程度越强,反之亦然.结果表明,缺陷层两侧排列为高折射率介质层的结构局域光的能力比两侧为低折射率介质层的强;考察前一种结构,且满足共振布喇格散射条件或共振米散射条件范围时,相对局域化长度可获得较小值.     

AlGaN/GaN HEMT中电场分布的ATLAS模拟

用Silvaco的ATLAS软件模拟了栅场板参数对AlGaN/GaN HEMT中电场分布的影响.模拟结果表明,场板的加入改变了器件中电势的分布情况,降低了栅边缘处的电场峰值,改善了器件的击穿特性;场板长度(LFP,length of field plate)、场板与势垒层间的介质层厚度t等对电场的分布影响很大.随着LFP的增大、t的减小,栅边缘处的电场峰值Epeak1明显下降,对提高器件的耐压非常有利.通过对相同器件结构处于不同漏压下的情况进行模拟,发现当器件处于高压下时,场板的分压作用更加明显,说明场板结构更适合于制备用作电力开关器件的高击穿电压AlGaN/GaN HEMT.     

液晶染料填充一维光子晶体局域模的电场调控及其光激发特性研究

基于液晶的电场调控特性及激光染料作为增益介质的增益模型,通过传输矩阵法理论研究了液晶染料填充一维光子晶体局域模的电场调控及其光激发特性。数值结果表明:随着垂直入射光和电场方向的夹角θ的增大,局域模波长向短波方向移动;当角度θ在(0°,90°)范围内变化时,局域模波长最大调控量达56.7nm;激光染料泵浦后不改变局域模的位置,但局域模的透射率变大了;随着增益系数的增大,局域模透射率先增大后减小,不同局域模对应不同的泵浦阈值,并且随着夹角θ的增大局域模对应的泵浦阈值将减小。     

波导层介质对二维光子晶体反射光谱的影响

构建了基底介质为SiO2、表面覆层介质为TiO2 的二维光子晶体,采用严格耦合波法分析了二维光子晶体的窄带光学传输特性。分析了二维光子晶体的晶格周期、波导层的折射率及厚度对其反射光谱的影响。分析结果表明:当光子晶体的晶格周期和波导层介质厚度为常数时,随着波导层介质折射率的增大,光子晶体的反射峰值波长红移,且波导层折射率与反射峰值波长呈线性关系。当光子晶体波导层介质折射率为常数时,波导层厚度增大或光子晶体晶格周期的增大都会引起光子晶体反射峰值波长增大,但这两个参数与反射峰值波长只是在一定的变化范围内为线性关系。此种结构的二维光子晶体覆层表面吸附分布不均匀的介质时,通过分析光子晶体的呈现光谱可获得其表面吸附介质的不均匀特性。     

Plasmonically enhanced lasing by different size silver nanoparticles-silver film hybrid structure

We reported on the enhanced lasing in organic dyes based on plasmonic hybrid structure of Ag nanoparticles (NPs)-Ag film, the diameters of Ag NPs ranged from 20 nm to 100 nm. The lowest lasing threshold was achieved by the optimal size Ag NPs-Ag film hybrid structure, which was reduced by 5.2 times than that of the neat gain medium. Comparing to the separate Ag NPs or Ag film, the hybrid structure presented the more intense local electric field due to the plasmonics coupling between the localized surface plasmons of Ag NPs and the surface plasmon polariton of Ag film, and the stronger scattering due to the reinjection of the leaking photons by external feedback of Ag film. The effects of different sizes Ag NPs-Ag film hybrid structures on lasing were investigated. It found that when the Ag NPs in hybrid structure is small (diameter≤40 nm), the enhanced localized electric field plays a major role on enhanced lasing; with the increase of Ag NPs size, the enhanced electric field and scattering have comparable contribution on enhancing lasing; for the larger size Ag NPs-Ag film (diameter≥80 nm), the scattering effect is the dominant mechanism for random lasing. Then the lowest threshold was dominated by the balance of enhanced localized electric field and scattering effect. Our results could provide us a unique idea to effectively enhance the lasing of organic dyes, and realize the lower pumped threshold and stronger lasing.     

Tailoring the Plasmonic Modes of a Grating‐Nanocube Assembly to Achieve Broadband Absorption in the Visible Spectrum

Engineered metal‐dielectric‐metal nanostructures with broadband absorbing properties in the visible spectral range are fabricated by combining the plasmonic resonances of different noble metal nanostructures. Silver nanocubes and gold nanogratings couple to each other using a dielectric polymer spacer with controllable thickness, resulting in a large multiplicative enhancement of absorption properties across a broad spectral range. Narrow, long nanogrooves in a gold film are first fabricated using electron beam lithography, after which a polymer spacer layer with a controllable thickness ranging from 4 to 12 nm is assembled by spin‐assisted layer‐by‐layer assembly. Finally, silver nanocubes with different surface coverages ranging from 12% to 22% are deposited using the Langmuir–Blodgett technique. The individual plasmon resonances of these different nanostructures are located at significantly different optical frequencies and are tuned in this study to allow a significant increase of light absorbance of the original gratings to an average value of 84% across the broad wavelength range of 450–850 nm.     

介质隔层金属光栅的局域磁共振场增强特性研究

使用LC等效电路模型和严格耦合波(RCWA)法分析了磁共振局域场增强介质隔层金属光栅的电磁特性,研究了光栅周期、脊宽和介质隔层厚度等参数对磁共振波长的影响.研究表明,当入射光波长为2.38μm时(θ=20°,∧=800 nm,w=400 nm,h=20 nm,d=30nm),由于入射光与介质隔层金属光栅阻抗能够很好地耦...     

参量变化对长程表面等离子体波特性的影响

为了掌握长程表面等离子体波的共振角度、共振峰半峰全宽以及衰减峰深度等重要特性,采用棱镜耦合激发介质-金属薄膜-介质对称结构中的长程表面等离子体波,研究了金属膜材料、厚度、介质折射率及介质厚度等参量变化时对长程表面等离子体波特性的影响。结果表明,实验中激发的长程表面等离子体波的衰减峰半峰全宽比传统的窄1~2个数量级;当介质膜厚度为500nm和1300nm时,激发的表面等离子体波的衰减深度只有薄膜厚度为700nm和1000nm时的1/2左右;随着介质膜厚度的增加,半峰全宽减小,金属膜越薄,衰减深度越深,衰减峰的半峰全宽值越小;介质膜折射率的改变对于半峰全宽的影响不明显;金属膜参量的变化将改变共振峰的位置。该研究为长程表面等离子体波的激发及应用于传感领域提供了有效依据,有利于其在波导和生物传感等方面的应用。     

Dual electric and magnetic frequency tuning of coupled oscillations in a composite magnetodielectric resonator

The possibility of dual magnetic and electric tuning of resonance frequencies of the electrodynamic structure consisting of dielectric resonator and the epitaxial film of Yittrium-Iron Garnet (YIG)- lead zirconate titanate (LZT) heterostructure has been shown. The coupled electromagnetic-andspin oscillations of dielectric resonator and epitaxial YIG film were theoretically and experimentally investigated. The experiments revealed the possibility of implementing the electric frequency tuning of coupled oscillations of a composite magnetodielectric resonator. This possibility is determined by induced elastic stresses in the epitaxial YIG film. A theoretical model is proposed for calculating the frequency shift of coupled oscillations caused by the electric field applied to the piezodielectric layer. It is shown that the basic Q-factor of composite resonator and the range of electric frequency tuning of hybrid oscillations increase with the reduction of the magnetic bias field.     

BST薄膜的膜厚与铁电性能关系研究

采用射频磁控溅射法制备了Ba.6Sr0.4TiO3(BST)薄膜,研究了不同膜厚的BST薄膜的介电偏压特性曲线和电滞回线。结果表明,当膜厚从250nm增加到650nm时,BST薄膜的εr、εr的电压变化率和最大极化强度分别从195,9%,4.7×10–6C/cm2逐渐增加到1543,19%,30×10–6C/cm2,而矫顽场强随膜厚的变化较复杂。进一步分析发现,膜厚通过影响矫顽场强和最大极化强度进而影响铁电薄膜的电压非线性。     

吸收式气敏传感空芯光纤的设计和制备

研发了红外波段吸收式气敏传感空芯光纤.空芯光纤的内面镀有银膜和介质膜,在目标波长提高反射率从而降低损耗.银膜和介质膜分别采用化学银镜反应法和液相镀膜法成膜.优化介质膜的材料和膜厚.光纤在可见光到中红外波段实现了低损耗特性.空芯光纤不仅可以用作气体传感的光吸收气室,而且也可用作红外光的传输媒介.初步实验结果显示这种空芯光纤可以替代普通的气体吸收气室,实现传感系统小型化.     

Photocurrent enhancement in thin film amorphous silicon solar cells with silver nanoparticles

Silver nanoparticles embedded in a dielectric material have strong scattering properties under light illumination, due to localized surface plasmons. This effect is a potential way to achieve light trapping in thin‐film solar cells. In this paper we study light scattering properties of nanoparticles on glass and ZnO, and on silver coated with ZnO, which represent the back reflector of a solar cell. We find that large nanoparticles embedded in the dielectric at the back contact of amorphous silicon solar cells lead to a remarkable increase in short circuit current of 20% compared to co‐deposited cells without nanoparticles. This increase is strongly correlated with the enhanced cell absorption in the long wavelengths and is attributed to localized surface plasmons. We also discuss the electrical properties of the cells. Copyright © 2010 John Wiley & Sons, Ltd.     

多元等离子体共振纳米结构的飞秒激光加工与拉曼检测应用

以多元金属纳米薄膜(金、银)为基底,利用飞秒激光加工技术制备得到多元等离子体纳米结构,并研究了其局域表面等离子体共振效应(Local Surface Plasmon Resonance,LSPR)和表面增强拉曼散射(Surface Enhanced Raman Scattering,SERS)性能。利用时域有限差分(Finite Difference Time Domain,FDTD)软件模拟了不同情况下(单层金膜、金银双层金属薄膜的平面以及阵列结构)的电场分布情况。根据仿真结果,相较于平面金属膜来说,飞秒激光制备的微纳结构阵列附近区域产生电磁场增强,集中在结构边缘处,且其强度变化与预期结果基本保持一致。此外,使用浓度为10-4 M和10-6 M的罗丹明(R6G)溶液进行SERS性能测试。测试的结果表明,单层平面金膜基本没有SERS峰值信号出现,而单层金膜上制备的等离子体纳米结构附近出现峰值信号,双层金属薄膜上制备的等离子体纳米结构展现出更高的SERS峰值信号。多元金属等离子体纳米结构展示出更强的局域表面等离子体共振效应,从而在表面增强拉曼散射、光催化、生物传感等领域具有广泛的应用。     

The strong absorption characteristics of ternary one-dimensional photonic crystals with silver layer

In order to achieve broadband and efficient optical absorption, the multiple silver nanolayer was introduced into the photonic crystals to form a one-dimensional ternary periodic symmetric structure. The effects of thickness of each layer on the band range, absorption bandwidth, absorbance and absorption energy field distribution of the solar spectrum high absorption band were studied by the transfer matrix method. The absorption band with wavelength range from 724 nm to 1 188 nm, spectral width of 464 nm, and average absorbance of 0.78 was obtained by structural adjustment. The absorbed energy is mainly distributed in the first half of the symmetrical structure of the photonic crystal. When the thickness of the silver layer decreased from 30 nm to 15 nm, the local energy in each period increased significantly. At the same time, the distribution and transfer of energy in silicon and MgF2 layers can be controlled. The results of this paper can be used to improve the absorption of solar radiation, and provide an important basis for the design of photonic crystal and their application in solar energy utilization.