一维光子晶体与光学多层介质膜

本文阐述了一维光子晶体和光子禁带的概念,对比了一维光子晶体与光学多层介质膜在结构和特性方面的联系和差别,运用薄膜光学的理论和方法讨论了多层介质膜的高反射带与光子禁带和膜系结构参量的关系.     

利用电磁感应透明介质调控一维光子晶体带隙结构

应用传输矩阵法研究了由电磁感应透明材料构成的一维光子晶体带隙结构.计算结果表明:通过改变控制光的拉比频率可以调控一维光子晶体的禁带宽度.随着拉比频率的增加,EIT原子气体的相对折射率也随着增加.随着拉比频率的逐渐加大,光子晶体的禁带宽度变得越来越窄,但变化变得越来越慢,即增加相同大小的拉比频率其影响越来越小.     

基于MoO_3/Au/MoO_3透明电极的有机太阳能电池

以透明导电薄膜Mo O3/Au/Mo O3代替铟锡氧化物(ITO)作为有机太阳能电池(OSCs)的阳极,研究了一系列结构为Mo O3/Au/Mo O3的透明电极和Mo O3(y nm)/Au(x nm)/Mo O3(y nm)/Cu Pc(25 nm)/C60(40nm)/BCP(8 nm)/Al(100 nm)的有机太阳能电池。研究表明,Mo O3/Au/Mo O3电极的光电特性可通过改变各层薄膜厚度加以调控,在Mo O3薄膜厚度为40 nm、Au薄膜厚度为10 nm时性能最优,且以该薄膜为电极的有机太阳能电池器件的性能接近于电极为ITO的有机太阳能电池器件。     

二维介质柱光子晶体波导的优化设计

通过改变靠近导光区域介质柱的直径和周期,优化设计了二维介质柱光子晶体波导.结果表明：单独增大和减小柱的直径以及增大柱的周期不能提高波导的传输特性;单独减小柱的周期能提高波导的传输特性,获得传输系数小于1 dB,带宽80 nm的波谱;同时减小柱的直径及周期能够极大的提高波导的传输特性,得到了带宽为150~250 nm,传输系数小于1 dB的波谱.     

一维金属/介质光子晶体用于BaF2晶体闪烁光谱修饰

利用一维金属/介质光子晶体对BaF2晶体闪烁光谱进行修饰. 以Al2O3/MgF2/Al/ MgF2为周期构成光子晶体，讨论了周期数、金属层的厚度以及在低折射率层中的相对位置、入射角度等与光子晶体能带特性的关系及其对BaF2晶体闪烁光谱进行修饰的效果. 结果表明，在所考虑的发射角范围，光子晶体对快成分的衰减小于5倍，对慢成分的相对抑制比超过20倍，采用合适的探测角度，可使对慢成分的相对抑制比提高到100以上.     

透明导电电极对聚合物太阳能电池光学性能的影响北大核心CSCD

采用传输矩阵法研究了基于MoO3/Ag/MoO3(MAM)透明导电电极和ITO电极的聚合物太阳能电池的光学性能。分别对电池耦合层厚度、活化层厚度和金属电极进行了优化,得到了优良效率的结构。结果表明,MAM与ITO有机太阳能电池在不同活性层厚度和不同光学间隔层厚度条件下有明显的光学性能差异;对于薄活性层MAM电极器件(100nm),最大短路电流密度可达到16.85mA/cm^2,比ITO器件提高了7.3mA/cm^2,而对于厚活性层MAM电极(270nm),ITO电极器件的光学性能明显优于MAM器件;还通过改变光学间隔层LiF的厚度进行计算,得出本仿真条件下两种结构性能差异的临界光学间隔层厚度为30nm。     

多缺陷结构的一维磁光多层膜隔离器

由磁光介质（M）和电介质（G）周期性排列构成的磁光光子晶体会出现很强的光 局域性，最近用它来实现磁光隔离器引起人们广泛的兴趣.给出了一种可用于计算 偏振光在各向异性介质传播问题的传输矩阵方法.并用该方法计算了对称多缺陷结构磁光多 层膜隔离器的光学性质，发现随着缺陷数目的增多，旋转角及透过率的频谱响应得到改善. 当缺陷增加到一定数目时，不需要额外的反射层即可实现反射型磁光隔离器的要求. 关键词： 光隔离器 磁光效应 多层膜 光子晶体     

介质光学厚度对一维光子晶体缺陷模的影响

利用传输矩阵法理论,研究介质光学厚度对一维光子晶体（AB）5（ACB）2（AB）5缺陷模的影响,结果表明：随着介质A、B或C的光学厚度按奇数倍、偶数倍增大时,光子晶体主禁带中的缺陷模均向禁带中心移动,出现缺陷模向禁带中心简并的趋势,且光学厚度按奇数倍增加时简并的趋势更明显,同时缺陷模移动速度以A介质光学厚度奇数倍增大时为最快;当介质A、B或C的光学厚度按奇或偶倍数增大到一定数值时,均出现对称分布于禁带中心两侧的新缺陷模,而且光学厚度按偶数倍增大时出现的新缺陷模要比偶数倍增大时的快。介质光学厚度对光子晶体缺陷模的影响规律,对光子晶体设计窄带多通道光学滤波器件、高灵敏度光学开关等具有积极的参考意义。     

飞秒激光与透明介质的相互作用

随着飞秒激光技术的不断成熟,飞秒激光器不但在实验室能产生小于10fs的光脉冲,啁啾放大后的飞秒光脉冲的聚焦峰值功率密度可达到10的21次方W/cm2以上,而且飞秒激光系统已实现全固体、小型化结构,其稳定性和可靠性大大提高,因此在科学技术研究中的应用越来越广.文章重点介绍飞秒激光的主要特性和它与透明介质［如熔融石英、光学玻璃、对激光透明的高分子聚合物(PMMA)等］的相互作用过程,分析它们之间的非线性相互作用过程引起的材料特性或结构变化的物理机制和可能的应用,尤其在高密度大容量三维存储和微光子器件制造等方面的应用可能性.     

一维金属-介质周期结构的自准直特性和亚波长成像

计算了一维金属-介质周期结构(1DMD)的色散曲线，利用传输矩阵法模拟了该结构对入射高斯光束的自准直作用，着重讨论了金属层吸收的影响；对该结构在半波长厚度时近场成像特性进行了分析，单光源的成像分辨率为λ/8，达到亚波长分辨效果；分辨率随着光源逐渐远离近场范围而降低. 双狭缝的成像模拟进一步验证了1DMD结构的近场亚波长成像能力，分辨率达到λ/3.     

Simulation on effect of metal/graphene hybrid transparent electrode on characteristics of GaN light emitting diodes

In order to decrease the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals(silver(Ag), golden(Au), nickel(Ni), platinum(Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers(TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered(L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet(UV) or near-UV LEDs.     

ITO/Au/ITO multilayer thin films for transparent conducting electrode applications

Transparent and conducting ITO/Au/ITO multilayered films were deposited without intentional substrate heating on polycarbonate (PC) substrate using a magnetron sputtering process. The thickness of ITO, Au and ITO metal films in the multilayered structure was constant at 50, 10 and 40 nm, respectively.Although the substrate temperature was kept constant at 70 °C, ITO/Au/ITO films were polycrystalline with an (1 1 0) X-ray diffraction peak, while single ITO films were amorphous. Surface roughness analysis indicated ITO films had a higher average roughness of 1.76 nm, than the ITO/Au/ITO film roughness of 0.51 nm. The optoelectrical properties of the ITO/Au/ITO films were dependent on the Au thin film, which affected the ITO film crystallinity. ITO/Au/ITO films on PC substrates were developed with a resistivity as low as 5.6 × 10⁻⁵ Ω cm and a high optical transmittance of 71.7%.     

Optical bistability of planar metal/dielectric nonlinear nanostructures

We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the light by light in all-optical nanoscale devices and circuits.     

Coupled edge plasmon modes of metal/dielectric multi-wedges

We present a metallic/dielectric multi-wedge model to investigate the coupled edge plasmon modes （CEPMs）, where all wedges have a common edge and the wave propagates along the edge direction. A general theoretical method valid to many practical structures is presented. The analytical dispersion relations of CEPMs in these structures are obtained and the CEPM properties are discussed with numerical results and the dispersion relations. For all structures mentioned in this paper, we find that the structures containing an even number of metallic wedges have four CEPMs and those with an odd-number of metallic wedges have two CEPMs. Further, the periodic structures containing any odd number of periods and any even number of periods possess their common CEPMs, respectively.     

ZnO/Ag/ZnO multilayer transparent electrode for highly-efficient ITO-Free polymer solar cells

Ultrathin metal film (UTMF) with a ZnO/Ag/ZnO hybrid structure was used as transparent electrode in a high-efficiency bulk heterojunction system for the fabrication of ITO-free polymer solar cells. The performance of the devices was carefully tuned through optical simulation using transfer matrix method by varying the thickness of ZnO seed layer and thin absorber layer. By employing appropriate device architecture, polymer solar cells fabricated using this UTMF-based electrode show efficiency as high as 9.49%, which is slightly higher compared to that of ITO-based device. From good agreement between the external quantum efficiency and optical modeling, it was found that the optimized microcavity configuration formed in UTMF-based device can greatly enhance the absorbance of the BHJ layer at longer wavelength as well as the favored exciton distribution for better charge transport and collection.     

Numerical analysis and design of patterned electrode liquid crystal microlens array with dielectric slab

The phase profile of hole patterned electrode liquid crystal (LC) microlens array (MLA) was studied by a numerical method. It indicated that the formation of inverse domain and tilt wall in the liquid crystal cell limits the optical performance of the microlens array. The physical mechanism that determines the formation of inverse domain and tilt wall was elucidated by analyzing the phase profile and the liquid crystal director distribution. According to our numerical results, a new configuration for hole patterned electrode liquid crystal microlens array was proposed by introducing a dielectric slab between the patterned electrode and the liquid crystal. The physical parameters that influence the optical performance of this new configuration LC MLA were studied, which provide fundamental information for the design. The results indicate that the phase profile and focusing power of the new configuration is greatly improved.     

Splitting the surface wave in metal/dielectric nanostructures

We investigate a modified surface wave splitter with a double-layer structure, which consists of symmetrical metallic grating and an asymmetrical dielectric, using the finite-difference time-domain (FDTD) simulation method. The metal/dielectric interface structure at this two-side aperture can support bound waves of different wavelengths, thus guiding waves in opposite directions. The covered dielectric films play an important role in the enhancement and confinement of the diffraction wave by the waveguide modes. The simulation result shows that the optical intensities of the guided surface wave at wavelengths of 760-nm and 1000-nm are about 100 times and 4～5 times those of the weaker side, respectively, which means that the surface wave is split by the proposed device.     

Active modulation of plasmonic signal with a subwavelength metal/nonlinear dielectric material/metal structure

<正>Light propagation through a metal/nonlinear dielectric material/metal(M-NL-M) structure is numerically studied.The design parameters of the M-NL-M structure are found with the waveguide theory so that the structure only supports the symmetric surface plasmon polaritons(SPP(0)) mode and the antisymmetric surface plasmon polaritons(SPP(1)) mode.The coupling between the two modes within the M-NL-M structure is exploited.Through controlling the propagation constants of the two modes with the intensity-dependent dielectric constant of the nonlinear Kerr material,an effective all-optical control of plasmonic signal modulator can be realized with this M-NL-M structure.     

Surface plasmon-polariton waveguiding characteristics of metal/dielectric quasi-coplanar structures

A novel metal-dielectric structure for efficient confinement and guiding of surface plasmon-polaritons is proposed. The proposed quasi-coplanar geometry achieves a trenchlike mode confinement over a wide range of spectrum by substituting a trench structure with two patterned metal layers, which will simplify the fabrication steps significantly. Using the finite-element method, the modal characteristics and the impact of waveguide structural parameters on them were investigated.     

金属/电介质颗粒复合介质的非线性交流响应

推广T矩阵法来研究二组分颗粒复合介质的非线性交流响应，解析推导出基频、三次及五次谐波频率下的有效线性介电常数及三阶和五阶非线性极化率的解析表达式.当组分颗粒的介电常数为实数时，表达式同以前微扰理论完全一致.进一步数值计算了金属-电介质复合介质的有效非线性交流响应，数值结果表明，体系的三阶、五阶非线性极化率在表面等离子共振频率附近有明显增强，而且，随着体积分数提高，共振峰增强且伴随着共振频率红移现象.还进一步讨论了维度效应对体系非线性交流响应的影响. 关键词： T矩阵方法 复合介质 非线性交流响应