A kind of single-polarization single-mode photonic crystal fiber

A kind of single-polarization and single-mode totally internal reflection photonic crystal fiber (SPSM TIR-PCF) is proposed in this paper. It is a PCF structure with elliptical air holes in the cladding and four large holes in the first ring. A full-vector plane wave expansion method is employed to analyze this PCF structure. The numerical results show that this PCF structure can realize an ultra-broad SPSM bandwidth of 540?nm with a confinement loss less than 0.1?dB?km^?1, the broadest bandwidth to the best of our knowledge. Moreover, the structure that we proposed can realize a high nonlinear coefficient.     

一种高双折射低限制性损耗光子晶体光纤设计

本文设计了一种适用于长距离光纤通信的新型光子晶体光纤。该光纤包层内椭圆形和圆形空气孔呈交错排列,纤芯两侧为两个小椭圆空气孔。利用有限元分析方法对所设计光纤的传输特性进行分析并对其结构进行了优化,确定了最佳结构。结果表明,波长为1550 nm时,此新型光子晶体光纤在最佳结构下可提供高达3.51×10^-2的高双折射和低至1.5×10^-9 dB/m的限制性损耗。与现存的引入椭圆形空气孔的光子晶体光纤相比,本文中的光子晶体光纤的双折射系数有较大提高,限制性损耗系数降低了5个数量级。另外,本文还详细研究了光子晶体光纤的色散随光子晶体光纤结构的变化以及其布里渊增益特性,并分析了其可制造性。基于其高双折射和低限制性损耗特性,此种光纤可应用于长距离光纤通信系统。     

A single-mode highly birefringent dispersion-compensating photonic crystal fiber using hybrid cladding

Based on the hybrid cladding design, a single-mode photonic crystal fibre (PCF) is proposed to achieve an ultra-high birefringence and large negative dispersion coefficient using finite-element method. Simulation results reveal that with optimal design parameters, it is possible to achieve an ultra-high birefringence of 2.64 × 10^?2 at the excitation wavelength of 1.55 μm. The designed structure also shows large dispersion coefficient about ?242.22 to ?762.6 ps/nm/km over the wavelength ranging from 1.30 to 1.65 μm. Moreover, residual dispersion, effective dispersion, effective area, confinement loss and nonlinear coefficient of the proposed PCF are discussed thoroughly.     

新型辐射制冷器用纤维支撑系统的设计和分析

设计了1种新型辐射制冷器级间纤维支撑系统,介绍了其结构的设计,支撑材料的选择以及纤维接头的研制。利用MSC．Nastran有限元软件对系统进行准静态结构强度和纤维预紧力进行了分析。级间漏热的理论分析结果表明此纤维支撑系统为研制更大冷量的辐射制冷器提供了可能。     

聚合物SiON波导的可变光衰减器性能研究

利用弯曲聚合物SiON波导设计了一种新型可变光衰减器,该器件由输入、输出直波导,S型的弯曲波导,以及在聚合物SiON波导弯曲部位镀上的电极组成.通过外加电场的作用来调节波导覆盖层的折射率,从而达到衰减波导中光能量的目的.现采用光束传播法(BPM)对设计的新型光衰减器进行了仿真设计,结果表明,设计的光衰减器具有大的动态可调衰减范围(45.3 dB),低的插入损耗(0.8 dB).     

Design of single-polarization wavelength splitter based on photonic crystal fiber

A new single-polarization wavelength splitter based on the photonic crystal fiber (PCF) has been proposed. The full-vector finite-element method (FEM) is applied to analyze the single-polarization single-mode guiding properties. Splitting of two different wavelengths is realized by adjusting the structural parameters. The semi-vector three-dimensional beam propagation method is employed to confirm the wavelength splitting characteristics of the PCF. Numerical simulations show that the wavelengths of 1.3 μm and 1.55 μm are split for a fiber length of 10.7 mm with single-polarization guiding in each core. The crosstalk between the two cores is low over appreciable optical bandwidths.     

A piezoelectric 3D hexahedral curvilinear finite element based on the space fiber rotation concept

The paper is focused on a piezoelectric 3D hexahedral finite element formulation on the basis of the space fiber rotation concept. The proposed electromechanical finite element has eight nodes and is animated by the virtual rotation of an elementary spatial fiber that creates an additional mechanical displacement enhancing the classical one generally considered to formulate the standard solid elements. The mechanical strain tensor and the electric field vector are expressed in a curvilinear coordinate system to handle the transverse isotropy behavior of piezoelectric materials. Numerical examples demonstrate that the proposed electromechanical element is less sensitive to mesh distortion than the standard piezoelectric solid elements. Besides, it is shown that the developed element response is better than those of the standard first‐order piezoelectric elements. Copyright © 2011 John Wiley & Sons, Ltd.     

基于激光超声二次谐波技术检测纤维增强树脂复合材料加固混凝土结构剥离损伤

纤维增强树脂(FRP)复合材料加固混凝土结构的早期剥离损伤往往趋向于闭合状态,传统线性超声技术对这种剥离损伤不敏感.本文提出了基于连续激光激发窄带超声波技术结合非线性超声二次谐波法检测FRP复合材料加固混凝土剥离损伤的方法,该方法通过强度调制激光技术在加固结构的表面激励窄带超声表面波,在超声波的扰动下,依据弹簧模型的接...     

Ultra-flattened negative dispersion for residual dispersion compensation using soft glass equiangular spiral photonic crystal fiber

Abstract

We present a numerical investigation of an equiangular spiral photonic crystal fibre (ES-PCF) in soft glass for negative flattened dispersion and ultra-high birefringence. An accurate numerical approach based on finite element method is used for the simulation of the proposed structure. It is demonstrated that it is possible to obtain average negative dispersion of –526.99 ps/nm/km over 1.05–1.70 μm wavelength range with dispersion variation of 3.7 ps/nm/km. The proposed ES-PCF also offers high birefringence of 0.0226 at the excitation wavelength of 1.55 μm. The results here show that the idea of using the proposed fibre can be potential means of effectively directing for residual dispersion compensation, fibre sensor design, long distance data transmission system and so forth.     

含紧固件碳纤维增强树脂复合材料在雷电流A分量下的损伤特性

为深入分析雷电环境下含紧固件碳纤维增强树脂（CFRP）复合材料的损伤机制及尺寸对损伤面积的影响规律,对两种不同尺寸含紧固件CFRP进行雷电损伤试验和仿真研究。根据热电耦合理论在ABAQUS中建立含紧固件CFRP的热-电耦合模型,得到单一雷电流A分量作用下CFRP的温度场分布规律;雷电损伤试验中采用超声C扫描方法评估试件损伤特性。试验和仿真结果表明:此雷击条件下,雷电流通过紧固件扩散到CFRP层合板整个厚度,试件在雷电流峰值不太大的情况下损伤面积较小,但随电流峰值的增大,损伤面积剧增、分层损伤严重。电流相近情况下不同尺寸的含紧固件CFRP的损伤分层、损伤形态及面积相近,尺寸对试件的损伤特性影响较小。试验和仿真研究为CFRP的结构设计提供一定的仿真和试验数据支撑。      

Surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber

A surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber has been designed and simulated by finite element method. The square-lattice airholes are first coated with a calcium fluoride layer to provide mode confinement, then a nanoscale gold layer is deposited to excite the plasmon mode, and finally, the sample is infiltrated into the holes. The numerical results reveal that the resonance properties are easily affected by many parameters. The refractive index resolution of corresponding sensor can reach 4.3 × 10^?6 RIU when the optimum parameters are set as the radius of curvature of the airhole r = 2 μm, the thickness of the core struts c = 200 nm, the auxiliary dielectric layer s = 1 μm, and the gold film d = 40 nm. In addition, the effective area and nonlinear coefficient are calculated.     

基于纤维束增强树脂基复合材料测试的单向层合板层间剪切性能的预估方法

纤维束增强树脂基复合材料（FBC）及其单向层合板在标准Iosipescu剪切实验中表现出非常相似的破坏特征,然而测量得到的剪切强度却有明显差异。本文使用两种碳纤维和两种环氧树脂制备了3种FBC和单向层合板,对FBC剪切强度和单向层合板层间剪切强度进行了测量与分析。应用界面单元方法分析了纤维束与基体之间的界面应力场,发现FBC剪切试件中纤维束/基体界面附近的应力状态为拉剪耦合,而单向层合板中界面处于纯剪切应力状态,这一差异导致FBC剪切实验测量的强度低于单向层合板的剪切强度。本文基于Yamada-Sun强度理论建立了FBC剪切强度与单向层合板剪切强度之间的关系模型,应用该模型预测的单向层合板剪切强度与实测强度之间达到良好的一致性,相对偏差为10%左右。根据本文提出的方法,通过制样较简单的FBC试验能够预测和评估相应单向层合板的层间剪切性能。     

Dispersion-compensating photonic crystal fiber with wavelength tunability based on a modified dual concentric core structure

We present a 5-layer air-hole dispersion-compensating photonic crystal fiber (PCF) with a modified dual concentric core structure, based on central rod doping. The finite element method (FEM) was used to investigate the structure numerically. If the structural parameters remain unchanged, a high degree of linear correlation between the central rod refractive index and the operating wavelength can be achieved in the wavelength range of 1.5457–1.5857 μm, which suggests that the operating wavelength can be determined by the refractive index of the centre rod. A negative dispersion coefficient between –5765.2 ps/km/nm and –6115.8 ps/km/nm was obtained by calculation and within the bandwidth of 108 nm (1.515–1.623 μm) around 1.55 μm, a dispersion coefficient of –3000 ps/km/nm can be ensured for compensation. In addition, this proposed PCF also has the advantage of low confinement loss, between 0.00011 and 0.00012 dB/m, and ease of fabrication with existing technology. The proposed PCF has good prospects in dispersion-compensating applications.     

SiC陶瓷纤维高聚物先驱体的研究进展

先驱体转换法是迄今为止高性能SiC陶瓷纤维最为成功的一种工业化方法，而高聚物先驱体的结构与性能则是该法的关键。本文主要综述了国内外SiC陶瓷纤维高聚物先驱体分子设计方面的研究动态及最近的发展趋势。     

基于宏微观分析的碳纤维增强高分子复合材料强度性能表征

微观力学强度理论(MMF)是一种新型的基于物理失效模式的复合材料强度理论。通过对碳纤维/树脂(UTS50/E51)复合材料单向层合板进行纵向、横向静载拉伸、压缩和弯曲试验, 得到层合板的基本力学性能和宏观强度指标。建立了碳纤维增强树脂基复合材料微观力学模型, 获取树脂基体和纤维不同位置的机械载荷应力放大系数和热载荷应力放大系数。结合获取的应力放大系数及试验测得的单向层合板宏观强度, 计算出层合板组分的MMF强度特征值。绘制了基于MMF强度理论的层合板破坏包络线, 并与Tsai-Wu失效准则预测结果进行对比。实现了对UTS50/E51层合板MMF强度特征值的表征。     

A finite element model of shape memory polymer composite beams for space applications

Structures made of shape memory polymer composite (SMPC), due to their ability to be formed into a desired compact loading shape and then transformed back to their original aperture by means of an applied stimulus, are an ideal solution to deployment problems of large and lightweight space structures. In the literature, there is a wide array of work on constitutive laws and qualitative analyses of SMP materials; dynamic equations and numerical solution methods for SMPC structures have rarely been addressed. In this work, a macroscopic model for the shape fixation and shape recovery processes of SMPC structures and a finite element formulation for relevant numerical solutions are developed. To demonstrate basic concepts, a cantilever SMPC beam is used in the presentation. In the development, a quasi‐static beam model that combines geometric nonlinearity in beam deflection with a temperature‐dependent constitutive law of SMP material is obtained, which is followed by derivation of the dynamic equations of the SMPC beam. Furthermore, several finite element models are devised for numerical solutions, which include both beam and shell elements. Finally, in numerical simulation, the quasi‐static SMPC beam model is used to show the physical behaviors of the SMPC beam in shape fixation and shape recovery. Copyright © 2015 John Wiley & Sons, Ltd.     

单向纤维增强聚合物复合材料压缩渐进破坏单向纤维增强聚合物复合材料压缩渐进破坏

复合材料结构在承压时破坏如何演化,是其强度破坏分析的基础和核心任务。本文提出了基于连续介质损伤力学（CDM）的单向纤维增强聚合物复合材料压缩破坏渐进损伤分析（PDA）模型。建模中考虑了材料非线性行为、失效判断及损伤演化中材料性能退化等基本问题,分别对应于拉压不对称弹塑性本构关系、Puck准则、LaRC05准则及考虑破坏面方向的刚度退化方法。该模型通过用户材料子程序接口VUMAT引入到有限元软件ABAQUS中实现了有限元求解。对文献中提供的纵向、横向及偏轴压缩案例进行了数值计算并与试验数据对比。数值分析结果与试验数据吻合较好,证明了该方法的合理性和有效性,对开展多向层合板压缩破坏分析富有参考价值。      

基于深度信念网络的玄武岩纤维增强树脂复合材料耐久性预测

采用紫外线老化试验箱模拟大气环境中的紫外线进行加速老化试验,对玄武岩纤维增强树脂复合材料（BFRP）及环氧树脂在紫外线环境中的耐久性进行了研究。通过BFRP及环氧树脂经紫外线老化后的拉伸强度、弹性模量、断裂延伸率的变化,结合深度信念网络（DBN）的方法,预测BFRP及环氧树脂拉伸强度、弹性模量的变化趋势;并提出以同批次非破坏性试件的弹性模量作为BFRP耐久性的评价指标。结果表明,随着老化时间的延长,BFRP及环氧树脂的拉伸强度及断裂延伸率均先提高后下降,但弹性模量趋于平缓下降; DBN得到的预测值与试验值相对误差基本在10%以内,表明DBN进行BFRP及环氧树脂耐久性预测的有效性;以非破坏性试件的弹性模量来评价BFRP的耐久性更具科学性。      

聚合物光纤光谱损耗特性的研究

截断法测量聚合物光纤 ( POF)的光谱特性是研究其损耗的一种有效方法 .用平面光栅单色仪对聚合物光纤聚甲基丙烯酸甲酯 ( PMMA)和聚苯乙烯 ( PS)的损耗光谱进行了测量 ,结果 PMMA芯 POF有三个传输窗口 ,分别为 5 2 0 nm,5 74nm,65 0 nm.在 5 2 0 nm,5 74nm处的损耗较小 ,且特性较为平坦 ,有很好的应用前景 . PS芯 POF窗口分别为 5 5 0 nm,5 80 nm,63 0 nm,670 nm,73 3 nm和 780 nm.在 5 5 0 nm,5 80 nm处同样有较好的应用前景     

Evaluation of prestressed basalt fiber and hybrid fiber reinforced polymer tendons under marine environment

This paper studies the degradation of the tensile properties of prestressed basalt fiber-reinforced polymer (BFRP) and hybrid FRP tendons in a marine environment. Two levels of prestressing toward typical prestressing applications were applied in the experiment. The variations of tensile strength, elastic modulus and the relevant coefficient of variation (CV) were first investigated. The effect of prestressing on tensile property degradation was discussed. The characteristics of prestressed hybrid FRP tendons in a marine environment simulated by a salt solution were clarified. Moreover, a prediction model of BFRP tendons with different levels of prestressing in a marine environment was proposed. The results show that the BFRP tendons’ superior resistance to salt corrosion and the degradation rate of their tensile strength is nonlinearly proportional to the prestressing ratios, whereas the elastic modulus remains constant regardless the prestressing ratio and aging duration. Although prestressing on BFRP tendons accelerates degradation, it can still lower the variation of the strength of the BFRP tendon. Hybridization can lower the degradation rate of basalt and carbon FRP (B/CFRP) without prestressing, whereas basalt and steel-wire FRP (B/SFRP) exhibit much faster degradation due to the internal corrosive steel wires. The model regression by the Napierian logarithm equation well represents the degradation trend of BFRP tendons under different levels of prestressing.