液晶聚合物小直径光缆挤塑工艺研究

基于液晶聚合物挤塑法,提出一种研制小直径光缆的技术途径。描述了液晶聚合物的基本特性,说明了液晶聚合物是小直径光缆的理想挤塑材料。研究了小直径光缆的挤塑工艺参数并根据液晶聚合物的材料特性给出了挤塑工艺流程。采用挤塑方式研制出外径为0.45mm的液晶聚合物小直径光缆,分析了该光缆的基本性能。试验结果表明：挤塑工艺对光纤几乎不产生附加损耗,在-60℃～＋80℃的温度范围内,光缆的附加损耗几乎为零。     

用于电响应红外反射窗的液晶聚合物薄膜特性研究

提出了一种红外反射器件,通过载体液晶在电场下的转向控制胆甾型液晶聚合物粒子在器件中的排布方向,实现红外反射与透射之间切换.其中,胆甾型液晶聚合物粒子是实现红外反射关键.介绍了胆甾型液晶聚合物薄膜的制备方法,并采用超声波破碎的方法制备液晶粒子.研究了液晶混合物中不同比例的交联剂液晶1对液晶聚合物薄膜脆性和反射波段的影响,发现当液晶1占100%时,液晶聚合物薄膜的脆性最大,且其清亮点最高,并且薄膜的反射波段随着液晶1比例的增加而向短波方向偏移.同时,研究了薄膜厚度对液晶聚合物粒子的影响,发现液晶薄膜厚度越小,制备的液晶聚合物粒子越小且越均匀,其制成的器件电驱动性更好.该研究有利于帮助电响应红外反射窗的性能优化.     

光纤传光束敛集率及其填充率的计算

采用二种方式推算了光纤采用六边形排列配用圆形端套光纤传光束的理论敛集率,其值为90.69%,这一值同光纤采用六边形排列配用长方形端套的传光束理论敛集率一致.而单根粗直径聚合物光纤和液芯光纤配用圆形端套制作的光纤传光束,其敛集率为100%,在可见光或紫外光范围内,选用单根粗直径聚合物光纤或液芯光纤传光束具有更多的优势.分析了皮层的厚度对光纤传光束或传像束填充率的影响,当光纤半径低于250 μm时,皮层厚度对细直径光纤传光束或传像束填充率影响明显,而当光纤半径大于等于500 μm,皮层厚度的影响相对较小.     

聚合物分散液晶增强散射的理想模型

介绍聚合物分散液晶技术新进展,应用光学原理对液晶微滴增强散射问题进行研究,提出液晶微滴最佳间距判据,液晶微滴间隔处聚合物材料光学厚度满足增反膜条件;提出液晶微滴最佳直径判据,液晶微滴直径满足双折射相消干涉条件;提出聚合物与液晶最佳配比的计算方法,应用晶体学原子堆积致密度知识给出最佳配比的计算结果.建立一种聚合物分散液晶增强散射的理想模型,进而从更基本的光学原理出发对异常散射理论模拟计算和实验上确定的液晶微滴最佳直径和聚合物与液晶最佳配比问题给出十分简单明确的理论解释.     

连续变焦的聚合物分散液晶电控透镜

介绍了一种基于聚合物分散液晶材料的连续调焦电控透镜.在聚合物分散液晶盒的上表面电极上刻蚀圆孔,形成一个非对称电极,在液晶盒上下极板之间,诱发一个非均匀电场,从而引起聚合物分散液晶材料的折射率非均匀分布,形成电控变焦透镜.阐述了聚合物分散液晶可调焦透镜的基本原理,分析了透镜孔径对聚合物分散液晶透镜焦距的影响,在直径3mm和6mm的圆孔条件下,分别测量了透镜焦距随电压的变化关系.结果表明:电压从50V加到170V的过程中,透镜焦距逐渐减短,刻蚀3mm圆孔的聚合物分散液晶盒焦距从1.361 63m到0.429 21m,刻蚀6mm圆孔的聚合物分散液晶盒焦距从1.769 92m到0.548 43m.     

镀膜长周期光纤光栅的单峰宽带滤波特性

镀膜长周期光纤光栅(LPFG)工作于相位匹配转折点时纤芯模与高次包层模的耦合产生单个宽带损耗峰,其3 dB带宽取决于纤芯模和包层模之间的色散差、光栅长度以及中心波长.研究表明,薄膜折射率和厚度的变化将影响纤芯模与包层模之间的色散差,从而影响损耗峰的3 dB带宽,同时损耗峰中心波长亦随之移动.薄膜折射率为1.57,厚度为350 nm时,损耗峰带宽可达302 nm.减小光栅长度在保证中心波长损耗大于6 dB的前提下可使损耗峰3 dB带宽增大至334 nm.进一步研究表明,在均匀LPFG中偏离光栅中点的适当位置引入单个π相移可以使带宽增大至372 nm以上.     

有限包层半径光纤Bragg光栅的理论研究

采用光纤波导三层模型,对有限包层半径光纤Bragg光栅导模有效折射率的改变进行了理论分析,结果表明:当包层直径小于16μm时,单模光纤Bragg光栅(纤芯直径为8.3μm)的导模有效折射率才开始发生明显变化.在包层外添加外包层,通过改变外包层的折射率可以实现对光栅Bragg反射波长的调谐,同时对不同芯子直径的光栅Bragg波长移动进行了数值计算.在保证光纤归一化频率不变的前提下,芯径越小Bragg波长调谐范围越大,当包层厚度为1μm时,芯径为a＝2.2μm的光栅Bragg波长调谐范围约为3.9μm.     

双包层手性光纤中导模的光功率特性

在对W型阶跃双包层手性光纤进行解析求解的基础上,对几个低阶导模的功率特性进行了仔细的研究.对典型的内包层厚度,计算了几个低阶模留在纤芯中的光功率随纤芯和内外包层的手性参数的变化关系曲线,讨论了纤芯和内外包层的手性参量以及内包层厚度对不同符号模式的功率特性的影响.内包层厚度越大,功率越被限制在纤芯中.随着纤芯中手性参量的增大, HE－11模和HE－21模（HE01模）限制在纤芯中的光功率缓慢增加,而HE11模和HE21模（HE02模）限制在纤芯中的光功率则逐渐减小.包层手性参量的作用正好与此相反.     

聚合物波导型表面等离子体共振传感器的特性研究

基于表面等离子体共振理论,将SU-8作为波导芯层材料,以聚甲基丙烯酸甲酯(PMMA)为下包层材料,设计了一款聚合物波导型SPR传感器。理论计算了波导芯层折射率、被测物折射率、不同金属薄膜及其厚度等因素对表面等离子体共振曲线的影响。分析结果表明,在可测试范围内,被测物折射率越大,灵敏度越高;波导芯层折射率减小,共振峰向长波方向移动,被测物检测范围整体向折射率小的方向偏移,波导芯层折射率增大则相反。     

微结构聚合物光纤中高双折射可调效应研究

通过在纤芯附近引入两个直径较大的空气孔诱导纤芯局部双折射,在包层减小x方向的孔间隔诱导包层双折射,设计实现了一种高双折射随波长可调效应的微结构光纤.采用全矢量平面波方法,以聚合物甲基丙烯酸甲酯为基材,对其偏振特性和基模模场进行了研究.结果发现,该光纤基模双折射在光通信波段呈现两个最大值,且最大双折射大小和位置随光纤结构和波长的变化可以进行调节.通过调节光纤结构参数,模拟得到了该光纤具有高双折射和零偏振模色散的最佳设计参数. 关键词： 导波与光纤光学 双折射可调 聚合物 全矢量平面波法     

Macromolecular composites of extruded thermotropic polymer sheets

Using two types of thermotropic liquid-crystal polymers, experimental results reconfirmed previous reports that the relaxation time of extruded liquid-crystal polymers is much longer than that of conventional polymers. The initial modulus and elongation of sheets extruded with liquidcrystal polymers were found to be strongly dependent on the gauge length. In addition, it was observed, for the first time, that the mechanical properties of the extruded thermotropic copolyesters follow the general equations for fiber-reinforced composites such that the angular dependence of the tensile strength of the extruded liquid-crystal polymeric sheets obeys the Tsai-Hill theory, while the angular dependence of the initial modulus follows the Lees equation. These results suggest that the highly oriented liquid-crystal domains may be considered as reinforcing fibers in the extruded articles, and their mechanical properties can be predicted using existing composite theories.     

Effect of matrix yield properties on fragmentation behavior of single fiber composites

Experimental and theoretical investigations have been conducted to study the dependence of fiber fragmentation behavior on matrix yielding properties. The cured Epikote 828 resins with two types of curing agents have almost similar elastic moduli, but different tensile yield strengths. The interfacial chemistry between fiber and epoxy resin is unchanged due to the same constituent of the epoxy resin. The experimental results indicate that the fragmentation behavior of the fibers embedded in the matrix is significantly different for the tested glass fiber treated by γ-glycidoxypropyltrimethoxysilane. The average fragment length decreased with increasing tensile yield strength of resin, which suggests that the interfacial shear strength determined in the fragmentation test should be different depending on the tensile yield strength of resin used. The important phenomenon observed is the transition of the micro-damage mode from matrix crack to interfacial debonding. An elastoplastic shear-lag model was used to calculate the shear stress and fiber tensile stress distributions considering different plastic behaviors of the matrices. The theoretical results indicate that the plastic behavior of the matrix has a large influence on stress transfer. Based on elastic and plastic properties of the matrix, the fiber fragmentation behavior in the matrix is predicted. Experimental and theoretical results are favorably compared.     

Optical fiber cables using V-grooved cylindrical units: High performance cables

Some practical and theoretical aspects of a V-grooved cylindrical cable (high performance optical fiber cable) are now being developed in several countries. Design of cables is important, because bendings may cause distortions. In order to limit micro-bending losses in an optical fiber cable, it is possible to modify parameters relating to the fiber or the cable. Some of the possibilities are: to decrease the core diameter in order to decrease the attenuation coefficient; to increase the diameter of the cladding so as to increase the tension above which micro-bendings occur; to increase the continuous bending radius due to cabling; to decrease the effects of roughness (μ); to integrate the effects of roughness as much as possible by decreasing the Young modulus of the coating and of the cable material and by increasing the cladding thickness; and to suppress the tension T of the fiber in the cable. The cabling element is made of a V-grooved cylindrical core, in which the fiber with an outside diameter d_e (outside diameter or primary coating) are laid without tension, with a slight excess length. The slots with a depth h are helical or alternated helical, providing the possibility of additional excess length, and the fiber can be “cabled” directly without stresses. A central strength member with a diameter Dp reinforces the cylindrical rod, ensuring the mechanical and thermal qualities.     

Optical fiber cables using V-grooved cylindrical units: High performance cables

Some practical and theoretical aspects of a V-grooved cylindrical cable (high performance optical fiber cable) are now being developed in several countries. Design of cables is important, because bendings may cause distortions. In order to limit micro-bending losses in an optical fiber cable, it is possible to modify parameters relating to the fiber or the cable. Some of the possibilities are: to decrease the core diameter in order to decrease the attenuation coefficient; to increase the diameter of the cladding so as to increase the tension above which micro-bendings occur; to increase the continuous bending radius due to cabling; to decrease the effects of roughness (μ); to integrate the effects of roughness as much as possible by decreasing the Young modulus of the coating and of the cable material and by increasing the cladding thickness; and to suppress the tension T of the fiber in the cable. The cabling element is made of a V-grooved cylindrical core, in which the fiber with an outside diameter d_e (outside diameter or primary coating) are laid without tension, with a slight excess length. The slots with a depth h are helical or alternated helical, providing the possibility of additional excess length, and the fiber can be “cabled” directly without stresses. A central strength member with a diameter Dp reinforces the cylindrical rod, ensuring the mechanical and thermal qualities.     

Mechanical and optical properties of silver-halide infrared transmitting fibers

This article presents a review of the optical and mechanical properties of infrared transmitting fibers extruded from single crystals of silver-halides at the Applied Physics Group in Tel-Aviv University during the last decade. The optical properties of Agcl_xBr_1-x crystals and fibers include the spectral transmission window, laser power transmission, the change of the power distribution traveling along the fiber, and the laser-induced breakdown. The mechanical properties include the investigation of the ultimate tensile strength (UTS), hardness, and the elastic strain limits of these fibers and their composition dependence. The mechanical properties that involve single and multiple bending of fibers in the plastic and the elastic strain limits are also described.     

The Structure and Properties of Polyamide/Liquid Crystal Polymer Blends

Melt blended polyamide (PA)/liquid crystal polymer (LCP) blends were prepared and their structures and properties were studied. The tensile strength and impact strength of the PA/LCP blends increased with increasing small amount of LCP content. Compared with a pure PA sample, there was a 17.7% increase in the tensile strength and a 45.5% increase in the impact strength when the LCP content was less than 10%. On the other hand, the Vicat softening temperature decreased with increasing the LCP content. Differential scanning calorimetry (DSC) showed that small addition of LCP was beneficial to increase the crystallinity of PA component for PA/LCP blends and the melting peak for the PA component of PA/LCP blends shifted to lower temperature with increasing LCP content. Scanning electron microscopy (SEM) displayed a layered structure existing in the injection moldings of PA/LCP blends with the LCP crystals having a preferred orientation along the melt flow direction in the sub-skin, shearing layer, and core region. The increased crystallinity of PA component and preferred orientation structure of LCP phase were beneficial to increase the mechanical properties of the PA/LCP blends.     

Role of weak interface to retain high strength of fiber in monofilamentary SiC fiber/titanium-aluminide composite

The tensile strength of monofilamentary weakly bonded SiC fiber/γ-TiAl intermetallic compound matrix composite, prepared by the sputtering method, was measured and analysed using a fracture mechanical technique. The main results are summarized as follows: (1) The fracture of TiAl occurred prior to that of fiber, resulting in formation of circumferential cracks on the fiber. Interfacial debonding occurred during tensile test, resulting in long pull-out of the fiber. (2) The strength of the fiber in the TiAl matrix was nearly the same as that of the bare fiber. (3) The fracture mechanical analysis showed that (i) the interfacial debonding grows unstably upon initiation and (ii) the stress distribution in the fiber in the cross-section, where the matrix is fractured, approaches to that of bare fiber with increasing debonded length. The reason why the fiber strength was maintained in spite of the formation of cracks on the fiber surface due to the premature fracture of the matrix was accounted for by the fully blunted crack-tip from the above calculation result.     

高体分SiC_p/Al复合材料螺纹性能的测试

从SiCp/Al复合材料性能分析着手,讨论了预置件法、焊接法和粘接法等在空间遥感器研制中常用的联接方法的优缺点,提出了在高体积分数（体分）SiCp/Al复合材料上直接加工螺纹,并加装钢丝螺套的方法来改善螺纹联接性能。对在某高体分SiCp/Al复合材料上加工的M4、M5螺纹进行了拉伸测试,结果表明：加装钢丝螺套前,复合材料螺纹有被拉脱现象;加装钢丝螺套后,M4螺纹、螺杆在3 000～4 000 N被拉断;M5螺纹、螺杆在8 000～9 000 N被拉断,测试后两种规格的螺纹状态良好,可以满足实际应用对该材料拉伸强度的要求,其已应用于工程项目中。     

Characterization of microscopic failure process and deformation in glass/nylon composites by micro-grid method

Tensile tests are performed on short glass fiber reinforced nylon-6 composite specimens with an open hole. The specimens with four different fiber surface treatments are used. Fiber weight fractions are 10% and 30%. It is found that the dependence of tensile strength on the diameter of hole is different for different fiber weight fractions. To explain the difference in tensile strength, in-situ observation of microscopic failure process around an open hole is conducted. The micro-grids are printed on the specimen surface to observe the microscopic deformation and fracture clearly. The difference in microscopic failure process due to the difference in fiber surface treatment and fiber weight fraction are observed, which explains the difference in tensile strength qualitatively. In addition, micro-grid methods are applied to measure the axial strain distribution in a short fiber in a real composite. The shear-lag prediction is compared with the experimental results. The fiber axial strain distribution obtained by the micro-grid methods is found to agree well with the shear-lag prediction until extensive interfacial debonding occurs.