数值研究一种基于腔共振和电共振的近红外双频段超材料吸收器（英文）

设计,数值模拟和讨论了一种具有两个宽带和扁平的吸收带的超材料吸收器,其中一个是腔共振吸收带,另一个是电共振吸收带.电共振的吸收带由于空腔尺寸(d)或者介质层厚度(H)的增加而蓝移,而腔共振吸收带则表现出红移的现象.同时,电共振和腔共振吸收带可以通过优化吸收器的结构设计耦合为一个吸收带.最后,数值模拟研究了入射角度的改变对电共振和腔共振吸收带的影响.利用不同波段的共振模式形成不同吸收带的方式提供了将双吸收带调制为单吸收带的可能性.     

基于局部表面等离子体激元的共振增强超材料吸收器的吸收性质

提出了一种在150～165 THz区域内的具有单峰吸收特性的高性能超材料吸收器。设计的吸波器包含两个阵列:双金属颗粒阵列和双空气孔阵列。金属层的阻尼常数在模拟中被优化。发现在模拟中使用2. 3倍的阻尼常数时,可以获得最大吸收率96%。吸收峰由局域表面等离子体(LSP)模式共振激发。为了揭示共振电磁机理,进行了两组模拟,研究结构参数变化对共振吸收峰的影响。发现随着垂直距离V的增加,吸收峰被增强,当V=160 nm时,获得新的吸收带。在第二次模拟中,对于水平距离H的增加,吸收峰也增强,并且当H=190 nm时获得另一个新的吸收带。电场强度分布结果表明LSP模式的激发和LSP模式之间的耦合效应导致吸收峰增强现象。     

基于局部表面等离子体激元的共振增强超材料吸收器的吸收性质（英文）

提出了一种在150～165 THz区域内的具有单峰吸收特性的高性能超材料吸收器。设计的吸波器包含两个阵列:双金属颗粒阵列和双空气孔阵列。金属层的阻尼常数在模拟中被优化。发现在模拟中使用2. 3倍的阻尼常数时,可以获得最大吸收率96%。吸收峰由局域表面等离子体(LSP)模式共振激发。为了揭示共振电磁机理,进行了两组模拟,研究结构参数变化对共振吸收峰的影响。发现随着垂直距离V的增加,吸收峰被增强,当V=160 nm时,获得新的吸收带。在第二次模拟中,对于水平距离H的增加,吸收峰也增强,并且当H=190 nm时获得另一个新的吸收带。电场强度分布结果表明LSP模式的激发和LSP模式之间的耦合效应导致吸收峰增强现象。     

基于SU8的远红外超材料完美吸收器理论研究（英文）

设计了一种基于SU8介质材料的工作波段为20-30微米范围内的的多层超材料吸收器.该吸收器由金属颗粒周期阵列、介质间隔层和金属底层组成.利用LC模型和FDTD数值模拟方法,通过对SU8介质层厚度、金属颗粒阵列周期、金属颗粒尺寸等参数的优化,实现了对20-30微米波段范围内入射波的接近100%的完美吸收.并在上述研究基础上进一步设计了具有双层谐振腔的双模完美吸收器.通过数值模拟发现,由于SU8介质间隔层厚度的增加,上下两个谐振吸收器可以分别独立实现对特定波长的完美吸收.相应的特征共振吸收波长符合LC模型的预测.同时,数值模拟结果进一步证实了共振吸收频率与入射角度无关.该完美吸收机制可以归因于入射光在金属底层-SU8介质层-金属颗粒层所组成的谐振腔内多次反射吸收.     

可用于农药传感的多带太赫兹超材料吸收器

多带太赫兹超材料吸收器是响应、操纵和调制太赫兹波的重要光子元件。本文基于周期性分裂环谐振器结构构建了一种多带太赫兹超材料吸收器。模拟和实验测试显示,在横磁(TM)极化情况下该超材料吸收器对0.918 THz和1.581 THz处的入射太赫兹波呈现出近似完美吸收。进一步,基于器件共振吸收峰的介电敏感特性,研究了负载不同浓度的多菌灵、三环唑、百草枯、塞苯隆4种农药溶液后超材料吸收器的传感性能,获得器件对4种农药的检测灵敏度分别为：1.06 GHz/ppm、0.65 GHz/ppm、0.67 GHz/ppm、2.07 GHz/ppm。结果表明该器件可实现对微量农药的传感检测,为今后食品质量安全控制提供了新的思路。     

基于等离子体共振1～10μm波段内可调节的双波段 超吸收研究

亚波长人工超构材料可以实现特定波长的近完美吸收,在红外光电器件应用中能够克服传统红外材料吸收效率低、厚度较大、工作波长受限于带隙等缺陷.本文利用金属/介质/金属结构构造了一种可大面积制备的亚波长结构,可以实现1-10μm波段内的双波段红外超吸收.通过时域有限差分法模拟和实验分析,我们认为该吸收器高频的吸收峰,主要来源F-P共振干涉增强吸收;而低频红外波段的吸收峰,主要得益于电偶极共振和磁共振模式的激发.利用退火工艺调节上层金颗粒的大小,可以有效地调节两个吸收峰的位置.     

（英）基于SU8的远红外超材料完美吸收器理论研究

设计了一种基于SU8介质材料的工作波段为20-30微米范围内的的多层超材料吸收器。该吸收器由金属颗粒周期阵列、介质间隔层和金属底层组成。利用LC模型和FDTD数值模拟方法,通过对SU8介质层厚度、金属颗粒阵列周期、金属颗粒尺寸等参数的优化,实现了对20-30微米波段范围内入射波的接近100%的完美吸收。并在上述研究基础上进一步设计了具有双层谐振腔的双模完美吸收器。通过数值模拟发现,由于SU8介质间隔层厚度的增加,上下两个谐振吸收器可以分别独立实现对特定波长的完美吸收。相应的特征共振吸收波长符合LC模型的预测。同时,数值模拟结果进一步证实了共振吸收频率与入射角度无关。该完美吸收机制可以归因于入射光在金属底层-SU8介质层-金属颗粒层所组成的谐振腔内多次反射吸收。     

一种基于耦合共振的太赫兹双频超材料吸收器设计

以两个相耦合的非对称十字金属条带结构作为基元,设计了一种新型双频带太赫兹超材料吸收器。该吸收器由周期性排列的基元、金属接地板以及介质层组成。通过基元之间的耦合,可利用单一基元实现太赫兹波段的双频带吸收特性。仿真结果表明,设计的超材料吸收器在具有基频共振所形成的吸收峰外,还具有耦合共振所形成的耦合吸收峰。通过调节耦合强度、介质层厚度和金属条带的对称性,可以在保持磁共振模式的耦合共振峰频率基本稳定的同时,对基频共振峰频率进行调控,以满足不同的吸收要求。此外,该超材料吸收器也展现出对气体折射率变化的敏感性,灵敏度可达2.5 THz/RIU,使这种吸收器在气体传感方面具有巨大的潜力。     

超短激光脉冲在共振光子带隙结构中的存储

采用时域有限差分方法求出了麦克斯韦-布洛赫方程的孤子解,数值模拟了由共振吸收原子按布拉格结构所排列而形成的″主动光子晶体″中产生″慢光子″和″静止光子″的方法.结果证明,如果使入射脉冲面积等于一个合适的值,无须对介质作任何初始激发,具有一定包络形状的脉冲可以在共振光子带隙结构中演化为空间局域化的振荡间隙孤子或静止间隙孤子.此外,理论上也模拟了间隙孤子分裂的情况.我们研究的结果证明,多个间隙孤子可以连续地自发局域化于同一结构中,因此,有效的光能就能以原子相干态的形式在共振光子带隙结构中存储,响应时间为亚皮秒的光子操控将有可能实现.     

基于石墨烯超材料的三频段可调谐完美吸收器

为进一步降低太赫兹频率下高性能调控器件的结构复杂度,提出一种三频段可调谐超材料完美吸收器. 该吸收器由图案化的石墨烯层和经Si介质层隔开的Au接地平面组成,利用太赫兹下的石墨烯表面等离子体共振以及图案化石墨烯与电场耦合提供的电偶极子共振形成多个吸收峰. 数值仿真结果表明,在0.489 THz、1.492 THz和2.437 THz处实现了对入射波的共振吸收,各峰值处的幅值均大于99.9%. 由于吸收峰处的幅值可以通过外部施加的偏置电压改变石墨烯的费米能级进行控制,因而所提出的吸收器结构的工作状态可在反射器和吸收器之间灵活切换. 同时,通过对吸收器单元结构的对称设计实现了对极化角度的不敏感特性,且在宽入射角范围内仍能保持良好的吸收性能. 因此,所设计的基于石墨烯的太赫兹超材料功能器件在调制和传感方面具有巨大的潜力.     

一种波长可调的近红外波段完美吸收体

一般将电磁波完美吸收体简称为完美吸收体,它可用于很多行业。用有限时域差分法研究了一种可以在近红外波段工作的完美吸收体。模拟结果表明,这种完美吸收体可以实现98%的单峰1400 nm左右宽谱吸收,或者可以实现90%以上的1320 nm和1640 nm波长的双峰吸收效率。通过调节共振腔结构的大小可以调节吸收波长和吸收宽度。电磁波完美吸收体是一种背靠背双共振腔模式的完美吸收体,有非常广泛的应用前景。     

Electrical Conductivity, Thermoelectric Power, and Optical Properties of Organo-Soluble Polyaniline Organic Semiconductor

The electrical conductivity, thermoelectric power (TEP), and optical properties of organo-soluble polyaniline doped with HCl have been investigated. The electrical conductivity and TEP of the sample increase with increasing temperature. The electrical conductivity and TEP results of the polymer suggest that it is a p-type semiconductor. The fundamental absorption edge in the polymer is formed by the direct allowed transitions, and the optical band gap value was found to be 2.79 eV. The absorption spectra for an acidic solution of the polymer indicate two new absorption bands, which are due to polaron formation. The polaron bands are responsible for the conductivity of the polymer. The TEP results indicate that the conductivity mechanism of the polymer is controlled by the large polaron hopping model.     

微量Co2+掺杂ZnO粉体的结构和光学性能研究

采用球磨法制备了Zn1-xCoxO(x=0,0.004,0.008)纳米粉体,分别利用XRD,PL光谱和紫外-可见吸收光谱对样品进行了表征。XRD图谱显示样品呈六方纤锌矿结构,随着Co2+离子掺杂量的增加,晶格常数和平均晶粒尺寸略有减小。在PL光谱上观察到三个发光带:370nm处的本征发光峰、468nm附近的强蓝光发光峰,以及533nm附近的绿光发光峰。和球磨样品相比,1 200℃退火的样品的发光强度明显增强,这归因于退火使样品晶粒长大。在紫外-可见吸收谱上可以观察到两个吸收带:由ZnO的带隙吸收引起的360～388nm的强紫外吸收带和由Co2+离子的d-d跃迁引起的565nm附近的可见光吸收带。因此通过调节Co2+掺杂量和选择适当的退火温度可制备高质量的发光材料。     

一种带宽展宽的等离子体超材料吸波体的设计

为了在TE波下获得带宽可展宽（11GHz~14GHz频带内）且可调谐的吸收曲线，提出了一种新型超材料吸波体，其周期性结构单元采用蜂窝状特有的六边形结构。对该吸波体的参量分析图进行了计算，研究了变量g和d的数值不同时，对吸波体吸收频带及吸收带宽的影响，并解释了蚀刻"十"字形结构吸波体带宽展宽的成因。结果表明，该吸波体在9.17GHz~9.5GHz低频频域的吸收率达到90%以上，当不同的等离子体谐振区域被激励时，可以实现吸波体的分时分频域吸收以及改善吸波体的吸收性能，改变变量g和d可以实现对吸收频带的动态调控；可以通过在方形结构中蚀刻"十"字形结构的方式拓宽高频频域的吸收带宽，其在12.08GHz~13.91GHz频域的吸收率高于90%，改变变量s可以明显展宽吸收频带，且该吸波体对入射电磁波的角度不敏感。该吸波体的设计思路为拓宽吸波体的吸收带宽提供了一种有效的方法。     

Design of Tri-Band Filters With Improved Band Allocation

A new design method for tri-band filters with improved band allocation is proposed. The design concept treats different band allocations with different methodologies. For the bands assigned to adjacent frequency regions, transmission zeros are introduced to split one of the single bands into two. For the bands that are assigned separately, different harmonic modes of stepped-impedance resonators are used to realize different passbands. Two design examples with different responses and band allocations are given, and were verified by experiments, as well as full-wave simulation results.      

Consolidation-atmosphere influence on drawing-induced defects inpure silica optical fibers

Drawing-induced paramagnetic defects (E'centers and oxygen-associated hole centers (OHCs)) and optical absorption bands at 630 nm and in the UV region are investigated for optical fibers. These fibers are drawn from pure silica glass preforms consolidated in atmospheres containing O₂ and Cl₂. UV absorption bands at 245 nm and 275 nm are clearly observed through deconvolution of the absorption spectra of optical fibers. The defects and absorption bands are influenced by the atmosphere in the consolidation process: (1) the OHCs and the absorption bands at 630 nm and 275 nm increase the intensity with increasing O₂ content and with decreasing Cl ₂ content; (2) the E' centers decrease under the same conditions; and (3) the absorption band at 245 nm is independent of the atmosphere     

Excitation mechanisms of multiple Er3+ sites in Er-implanted GaN

Site-selective photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies carried out at 6K on the ∼1540 nm ⁴I_13/2→⁴I_15/2 emissions of Er³⁺ in Er-implanted GaN have revealed the existence of four different Er³⁺ sites and associated PL spectra in this semiconductor. Three of these four sites are excited by below-gap, impurity- or defect-related absorption bands, with subsequent nonradiative energy transfer to the Er³⁺ 4f electrons; a fourth site is excited by direct Er³⁺ 4f shell absorption. PLE spectra obtained by selectively detecting Er³⁺ PL from each of the three sites pumped by broad below-gap absorption bands are compared with the PLE spectra of broad PL bands attributed to implantation damage-induced defects in the Er-implanted GaN. This comparison enables us to distinguish broad-band, below-gap optical excitation processes for Er³⁺ emission that are attributable to (1) absorption due to implantation damage-induced defects; (2) absorption due to defects or impurities characteristic of the as-grown GaN film; and (3) an Er-specific absorption band just below the band gap which may involve the formation of an Er-related isoelectronic trap. The two sites excited by impurity-or defect-related absorption bands are also strongly pumped by above-gap excitation, while the sites pumped by the Er-related trap and direct 4f shell absorption are not. This observation indicates that excitation of Er³⁺ luminescence in crystalline semiconductor hosts by either optical or electrical injection of electron-hole pairs is dominated by trap-mediated carrier capture and energy transfer processes. These trap-mediated processes may also control the thermal quenching of Er³⁺ emission in semiconductors.     

High Power, Magnetic Field Controlled Microwave Gas Discharge Switches

A new type of gas discharge switch is described, It is electronically controllable, broadband, and capable of rapidly switching high power pulsed microwaves from either of two waveguide input ports to a single waveguide output port, or from one waveguide input port to either of two waveguide output ports. The electronic control is achieved by turning on or off a magnetic field set for cyclotron resonance. An approximate analysis is given of the operation of the active element of the switch and the results are compared with experiment. An analysis of the effects of frequency scaling indicates that, with the exception of the magnetic flux density which increases with increasing frequency, the switch parameters either improve or remain unchanged in going to higher frequencies. Two different switch configurations are investigated, one a Y-junction switch for operation at S band and the other a balanced top-wall hybrid coupler switch for operation at K/sub u/ band. Their electrical characteristics are described.     

Single silicon waveguide MRR based Fano resonance in the whole spectral bands

To improve the integration of Fano devices, we design a T-shaped waveguide coupling micro-ring resonator (MRR) structure to achieve a single cavity with Fano resonance in the whole spectral bands. The mathematical relationship between the phase factor, the coupling coefficient of the bus waveguide, and the Fano resonance slope extinction ratio (ER) is established. The electron beam exposure process is used to obtain a device with an insertion loss of ~3 dB. The maximum ER of the Fano lineshape exceeds 15 dB, and the slope ratio (SR) is 251.3 dB/nm. This design improves the compactness of the Fano resonant device.     

Spectral encoding on Gold Nanorods Doped in a Silica Sol–Gel Matrix and Its Application to High‐Density Optical Data Storage

Metallic nanorods exhibit fascinating optical properties due to surface plasmons—collective oscillation of the electron cloud within a particle. They exhibit two principle absorption bands that correspond to surface plasmon resonance (SPR) along the longitudinal and transverse directions of the nanorod. Most importantly, the longitudinal band can be tuned with the aspect ratio of the rod, making it a spectrally tuneable optical material, which can be applied to a variety of devices from bioimaging to high‐density optical storage. Here, spectral encoding for high‐density optical storage applications is demonstrated on two sizes of gold nanorods (aspect ratios of three and five) doped in a silica sol–gel matrix by femtosecond pulsed laser irradiation. It is widely known that high‐power pulsed laser irradiation causes metal nanorods to undergo shape transformations via the process of melting or fragmentation. The process is enhanced if the laser wavelength is tuned at the longitudinal surface plasmon resonance peak of the nanorods, which results in a significant reduction or shift in the surface plasmon resonance peak. As such a shape change occurs only on the subpopulation of rods that have a longitudinal plasmon band matching the laser wavelength, a size‐ or spectrum‐selective shape transition is possible in a rod mixture with varying aspect ratios. The current spectral encoding technology can be incorporated into existing optical disc technology, such as three‐dimensional bit‐by‐bit and holographic, and can increase the capacity limit by utilizing the spectral domain.