Optimization of Mechanically Induced Long-Period Fibre Grating Transmission Spectrum

A new double-layer grating template is designed to reduce the out-of-band loss as much as 1.8dB when the loss of LPo3 reaches 10.2 dB. Meanwhile, we propose a method to remove the sidelobes in the transmission spectra by the adjustment of the thickness of pressure plates. The plate-thickness-induced shift of resonant wavelength and the attenuation of loss peak intensity when removing sidelobes can be modified by the fibre distance and contact point on the pressure plates.     

手性噁唑硼烷结构与还原苯基乙基甲酮的对映选择性研究~≠

本文以苯基乙基甲酮为还原底物,研究了原地(in situ)制备的在3、4、5位具有不同取代基的手性1,3,2-(口恶)唑硼烷催化剂的结构与不对称催化效应关系。研究结果表明,在不对称催化硼烷还原反应中(CBS方法),产物的构型和对映选择性主要受手性(口恶)唑硼烷的4位取代基控制。     

WO3中单斜相/六方相异相结的构建及提高光催化降解罗丹明B活性

光催化技术被认为有可能成为解决环境污染和能源危机的有效手段之一,引起了各国政府和科学家的极大兴趣.以TiO2,WO3和Bi2O3等半导体为催化剂的光催化反应受到广泛关注.WO3是一种典型的n型半导体材料,具有电致变色、气敏和光催化等性能,在电致变色器件、气敏传感器和光催化剂等方面有着广泛应用前景.由于WO3具有高的太阳能利用率、良好的可见光响应性和较强的抗光腐蚀性,是一种极具开发潜力的半导体光催化材料,所以在光解水制氢及催化降解有机污染物等领域中得到广泛应用.然而,WO3半导体表面上较高的光生电子-空穴复合效率是影响其光催化性能的主要因素之一,从而限制了WO3在光催化领域的工业应用.研究发现,TiO2材料在从锐钛矿向金红石转变的过程中,通过精细调变焙烧温度,可以在两种晶相的界面形成TiO2异相结.形成的锐钛矿-金红石异相结能有效促进电子-空穴分离.目前,构建异相结已成为改善光催化剂电子-空穴分离效率的有效方法之一.近年来,人们先后成功构建了α-Ga2O3/β-Ga2O3,α-Bi2O3/β-Bi2O3和WO3/WO3·H2O等异相结,这些异相结催化剂在光催化降解水产氢和降解污染物反应中显示了比单一晶相更高的光催化活性.WO3是一种多晶相材料,具有正交、六方、单斜和四方等多种晶体结构,其中六方晶相(h-WO3)由于具有开放结构而在气体传感器和电池电极等领域显示了突出性能,而单斜晶相(m-WO3)具有合适的带宽和良好的可见光响应性,因而广泛应用在光催化领域.而且,h-WO3的导带和价带均低于m-WO3的导带和价带,所以在WO3材料中有可能通过构建单斜/六方异相结(m-WO3/h-WO3)来提高WO3的光催化性能.本文借鉴半导体异相结概念,采用固相热分解法,试图通过调节焙烧温度和焙烧时间以构建m-WO3/h-WO3异相结催化剂.利用X射线衍射(XRD)、高分辨透射电镜(HRTEM)、扫描电镜(SEM)、X射线光电子能谱仪(XPS)和N2吸附-脱附等方法对WO3样品的晶相结构、形貌和元素组成等进行了表征.以光催化降解罗丹明B(RhB)为模型,研究了不同晶相WO3材料的光催化性能,考察了WO3晶相和异相结对其光催化性能的影响,从而为WO3材料中异相结的构建提供思路、方法和理论指导.结果表明,采用偏钨酸铵固相热分解制备WO3的过程中,焙烧温度为600-700℃时,样品为单斜晶相,随着焙烧温度升高至800℃时,样品中开始出现六方晶相.随着焙烧温度升高,h-WO3的含量没有明显变化,当温度升至1000℃时,h-WO3的含量有所减少.SEM和HRTEM结果验证了m-WO3/h-WO3异相结的形成,小的m-WO3粒子分布在棒状h-WO3上,并且两者紧密接触.为了进一步证实WO3的异相结效应,将偏钨酸铵在800℃焙烧不同时间(8-30 h).结果表明,通过改变焙烧时间可有效控制m-WO3和h-WO3混合晶相比例,800℃焙烧8h时m-WO3为主要晶相,焙烧12h时h-WO3含量明显增加,当焙烧时间延长至24和30h时h-WO3含量减少.SEM结果同样显示,在800℃焙烧12h样品中棒状h-WO3显著增多,与小的m-WO3粒子接触几率增大,即m-WO3/h-WO3异相结数量增加.不同晶相WO3样品光催化降解RhB的结果表明,具有m-WO3/h-WO3异相结结构的WO3催化剂具有较高光催化活性.荧光光谱结果表明,单斜相/六方相异相结的形成提高了电子-空穴分离效率,从而提高了其光催化降解RhB的活性.而在具有m-WO3/h-WO3异相结结构的WO3催化剂中,随着焙烧温度升高或焙烧时间延长,h-WO3含量有所减少,从而导致暴露的m-WO3/h-WO3异相结数量减少,因而使得活性有所降低.本文采用固相热分解法通过调变焙烧温度构建了m-WO3/h-WO3异相结光催化剂,显著提高了光催化降解RhB的活性,这对设计合成高效WO3基光催化剂具有一定借鉴.     

Long-range surface plasmon polaritons with subwavelength mode expansion in an asymmetrical system

Long-range surface plasmon polariton (LRSPP) modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoretically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thicknesses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.     

Global adaptive synchronization of chaotic systems with uncertain parameters

We propose a novel adaptive synchronization method for a class of nonlinear chaotic systems with uncertain parameters.Using the chaos control method,we derive a synchronizer,which can make the states of the driven system globally track the states of the drive system asymptotically.The advantage of our method is that our problem sctting is more general than those that already exist,and the synchronizer is simply constructed by an analytic formula,without knowledge in advance of the unknown bounds of the uncertain parameters.A computer simulation example is given to validate the proposed approach.     

Global synchronization of Chua＇s chaotic delay network by using linear matrix inequality

Global synchronization of Chua‘s chaotic dynamical networks with coupling delays is investigated in this paper.Unlike other approaches, where only local results were obtained, the network is found to be not linearized in this paper.Insteat, the global synchronization is obtained by using the linear matrix inequality theory. Moreover, some quite simple linear-state-error feedback controllers for global synchronization are derived, which can be easily constructed based on the minimum eigenvalue of the coupling matrix. A simulation of Chua‘s chaotic network with global coupling delays in nodes is finally given, which is used to verify the theoretical results of the proposed global synchron izationscheme.     

一类含参数不确定性混沌系统的自适应控制

基于Lyaponov函数,对一类含参数不确定性混沌系统,当系统的不确定性参数具有未知界时,给出了自适应控制器的设计方法和构造控制器的解析式.构造混沌控制器直接代入控制器的参数化公式即可.方法简单,无需拼凑,能够使系统消除混沌并渐近稳定到任何期望的光滑轨道上.而整个设计过程无需预先知道未知参数的估计值和精确值.仿真验证了其有效性 关键词： 混沌系统 自适应混沌控制 Lyaponov函数 参数不确定性     

光纤损耗对抽运消耗光纤参变过程的影响分析

在各向同性高非线性光纤中同时考虑光纤损耗和抽运消耗对单抽运四波混频参变过程的影响,得到了导波光之间功率转化关系所满足的椭圆方程,计算结果与OptiSystem软件仿真的结果一致。利用该椭圆方程分析了基于四波混频的全光2R再生器的性能,研究表明,光纤损耗系数的增加不但会劣化再放大性能,还会分别减小和增加高低电平上的输入噪声容限。     

Bending Loss Calculation of a Dielectric-Loaded Surface Plasmon Polariton Waveguide Structure

Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide （DLSPPW） based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators （WRRs） and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.     

Ultrafast Third-Order Nonlinear Optical Response of Organic-Inorganic Hybrid Materials （C19H25N2）7Hn [P2Mo18-n Vn O62]

We have measured the third-order optical nonlinearity of the organic-inorganic hybrid materials of supermolecules (C19H25N2)7Hn [P2Mo18-n Vn O62] (n = 1, 2, 4, 5) and their reactants (C19H25N2) Br and Hn 6[P2Mo18-n Vn O62] by using the ultrafast optical Kerr effect at 830 nm wavelength, with time resolution of 115fs. By comparing the γ values of the supermolecules and their reactants, it is concluded that the charge-transfer eahanced remarkably the third-order optical nonlinearity of the compounds. With the increment of the number of the vanadium atoms,the electron distribution changed strongly and the γ value decreased dramatically.