Use of the mark-tracking method for optical fiber characterization

The mark-tracking method was used in the uniaxial tensile test to determine the elastic properties of optical fibers. The mark-tracking method is based on the follow-up of two markers on the specimen with the help of an image processing technique. It allows us to determine the true strain with respect to the small strains assumption (≤1%) or the finite strains (>1%) without any impact of the rigid solid movement or pulley fiber sliding on the measured strain. Both coated optical fiber and stripped fiber were subjected to the uniaxial tensile test and the cantilever beam bending test. The Young’ modulus results of the stripped fiber were found to be very similar for both tests. Thus, the mark-tracking method is adaptable to the tensile test of optical fibers and the elastic behaviors of both coated optical fiber and stripped fiber are found to be non-linear. Their Young's moduli are 22 and 79 GPa, respectively. These results revealed that those coatings play a mechanical role in fiber elongation.     

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.     

锥形光纤间耦合特性的分析与检测

将通信光纤的末端拉制成锥形，利用光信号在光纤锥形区特有的传输和耦合特性，实现了光纤的耦合、连接和分束。用耦合模理论分析了锥形光纤间的传输和耦合性质，给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果。     

锥形光纤间的耦合特性

将通信光纤的末端拉制成锥形,利用光信号在光纤锥形区特有的传输和耦合特性,实现了光纤的耦合、连接和分束.用耦合模理论分析了锥形光纤间的传输和耦合性质,给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果.     

Optical extensometer and elimination of the effect of out-of-plane motions

A novel optical extensometer is developed to estimate the local uniform strain on planar surface accurately. The proposed system consists of a shared large format lens and two image sensors, which acquire pairs of images of two isolated small regions on the object surface simultaneously. Digital image correlation (DIC) algorithm is applied to determine the relative displacement between gauge points designated on recorded pairs of images. Then local strain can be extracted after dividing the relative displacement by the scale distance. Moreover, a special experimental setup called “correction sheet” is used to eliminate the virtual strain induced by out-of-plane motions. Uni-axial tensile experiments are performed to validate the reliability and resolution of the optical extensometer, and the measurement results demonstrate that the resolution of the optical extensometer achieves 2–3 με.     

Holography based super resolution

This paper describes the simulation of a simple technique of superresolution based on holographic imaging in spectral domain. The input beam assembly containing 25 optical fibers with different orientations and positions is placed to illuminate the object in the 4f optical system. The position and orientation of each fiber is calculated with respect to the central fiber in the array. The positions and orientations of the fibers are related to the shift of object spectrum at aperture plane. During the imaging process each fiber is operated once in the whole procedure to illuminate the input object transparency which gives shift to the object spectrum in the spectral domain. This shift of the spectrum is equal to the integral multiple of the pass band aperture width. During the operation of single fiber (ON-state) all other fibers are in OFF-state at that time. The hologram recorded by each fiber at the CCD plane is stored in computer memory. At the end of illumination process total 25 holograms are recorded by the whole fiber array and by applying some post processing and specific algorithm single super resolved image is obtained. The superresolved image is five times better than the band-limited image. The work is demonstrated using computer simulation only.     

电光调制在被动综合孔径成像探测中的应用

介绍了一种新型被动综合孔径成像探测方法:视场辐射信号被接收和放大后,通过电光幅度调制将其幅度和相位信息加载到光波上,经光纤传输在末端形成阵列,通过光学系统直接成像,将视场实时恢复出来.该方法可实现工作在微波、毫米波和太赫兹波段的高分辨力实时成像探测的目的.深入分析了电光调制器在综合孔径成像探测中的应用,建立电光调制模型,讨论了在小信号调制下的电光幅度调制近似理论.通过数值计算与仿真分析,得到综合孔径成像探测中电光调制器的调制信号强度限制的有关结论.结果表明,利用上变频电光调制技术和光信息处理,所得到的成像仿真图的半峰全宽和信噪比性能都优于传统的基于下变频技术的成像仿真结果.     

Closely packed micro optical fiber arrays in laser scanning system

Closely packed optical fiber arrays are used to increase the scanning speed in some laser scanning systems, but standard optical fibers are shown to be unsuitable for these systems. In this paper, a closely packing technique of micro optical fiber arrays is presented. The fabrication and properties of micro fibers, whose diameters range from several hundred nanometers to several microns, are introduced. These micro fibers are arranged side by side in V-shaped grooves, which are fabricated by photolithography and etching techniques on silicon substrate. Comparing to standard optical fiber arrays, such closely packed micro optical fiber arrays can eliminate the dark area among output light spots and can solve the problem of high accuracy demand of exposure location. This closely packing technique is also proved to be a feasible method in practical scanning systems.     

球形光纤端面效应及其应用

本文介绍了球形光纤端面的制作方法,采用射线理论和等效透镜法分析了圆球形端面多模光纤的端面效应,并给出了两个不同端面多模光纤之间耦合的实验结果。结果表明：圆球形端面光纤具有聚光特性,与平端面相比,使用圆球形端面光纤不仅可以提高光器件之间的耦合效率,而且增大了它们之间的耦合距离,利于光路调试;可广泛应用于光源与光纤、光纤与光纤、光纤与探测器之间的耦合。     

Alignment error of arrayed beams in optical fiber array device

The alignment error of arrayed beams in optical fiber array devices is caused by structural errors of the optical fibers themselves such as error in cladding surface diameter, core offset, and the noncircularity of the cladding surface. In this study, the relations among them are analytically clarified. Moreover, by probability evaluation, the allowable structure errors for suppressing the alignment error below a certain level are calculated. The predicted yield rate below an alignment error of 0.4 μm for five beams is compared with the result of real fabrication.     

一种基于图像处理保偏双尾纤装配精度的检测方法

双尾纤相对位置的装配精度直接影响保偏双光纤准直器的保偏性能。研究和分析了双尾纤的装配精度对保偏准直器保偏性能的影响,并指出双尾纤端面"猫眼"的垂直度是主要影响因素。提出了一种保偏双尾纤装配精度的检测方法,检测系统主要由CCD摄像机、显微镜、图像采集卡和VC开发的检测处理软件等构成。还对系统中保偏双尾纤端面图像获取及图像预处理、检测光心"猫眼"坐标位置所采用的算法及"猫眼"垂直度的检测模型进行阐述,该系统检测精度优于0.5°。     

Interferometric grating method and its application in Fe-base shape memory alloy structure design

This paper presents an interferometric grating method used in measuring strain fields on a curved surface. This method can be used to determine the small and large strains with high sensitivity and has been applied successfully in Fe-base shape memory alloy (FSMA) structure design. In this study, five diffracted beam from the specimen surface produce the interferometric gratings through an optical system. Using image processing technique (fast Fourier transform with special interpolation and phase shifting technique), we have obtained the strain fields of outer surface of FSMA joint and contact pressure distribution on its inside surface which has mechanical deformation and transformation.     

双KTP内腔参量下转换产生量子相关孪生光子对

使用双ＫＴＰ晶体串接，经光学参量振荡腔内参量下转换，在３００ｍＷ泵浦功率下，获得总功率约２３ｍＷ的强度相关的孪生光束，在１．２５ＭＨｚ处其强度差噪声功率较散离噪声极限降低５０％（３ｄＢ）。     

基于反射法的光纤位移 振动传感器优化设计

采用非相干光作为光源,以平面镜为反射面,对光纤位移 振动传感器的性能进行研究。推导出光纤输出功率与测量距离的解析表达式,并详细探讨了不同光纤半径、光纤数值孔径、发射光纤和接收光纤间距、发射光纤和接收光纤轴线夹角下输出功率比与测量距离之间的内禀关系。仿真结果表明:光纤半径越小,光纤间距越大,可以测试的距离范围越小;光纤数值孔径、光纤轴线夹角越小,可以测试的距离范围越小。通过分析不同情况下,输出功率比随测量距离变化的关系,可以在实际工程应用中根据测量需要选择设计合适的传感器。此外,还对测量误差进行了分析,得到光纤轴线夹角越小,测量距离的范围越大,误差率越小,当光纤轴线夹角为0.25时,误差率约为1%。     

Measurements of complex degree of spatial coherence at the end face of an optical fiber

The phase and modulus of the complex degree of spatial coherence at the exit end face of an optical fiber are measured with the help of a real-time data processing computer. Interference fringes produced by superimposing wavefronts of the image of the end cross-section are scanned by a linear photodiode array to calculate the one dimensional value of spatial coherence. Evolution of phase measured at the different positions in the fringe pattern reveals that the phase is intimately related to modal structures of the propagating field in an optical fiber supporting a small number of guided modes.     

偶氮化合物中级联作用引起的高阶多波混频的研究

用三维简并四波混频的实验装置，在偶氮化合物中观察到了多波混频效应，在接收屏上，除了三个泵浦光斑，还观察到了由于多波耦合产生的另外１４个排列整齐的信号光斑，这个现象可望被广泛用光计算，信息处理和光互连中。     

Polarization maintaining fibers for application in magnetic field measurements

Optical fibers may be applied in measurements of electrical current, particularly as so-called optical current transformers. Electric current sensors, in which optical fibers are used are small, light, cheap and safe. Their sensitivity is, however, due to the restricted magnetootpic properties of optical fibers, rather small. Moreover, these sensors are susceptible to deformations of the optical fiber. An increase of their sensitivity consists in lengthening the distance of optical fiber on which the magnetic field acts. However, this can lead to an increase of disturbances caused by changes of internal stresses. The negative effects can be reduced by applying optical fibers with a higher magnetooptic sensitivity and a lower susceptibility to mechanical stresses and deformations. The present paper deals with side-hole optical fibers with a decreased birefringence reducing the susceptibility to deformations. The optical fibers consist of a multicomponent glass with a higher value of the refractive index, thanks to which the sensitivity to the effect of the external magnetic field is increased. In future such optical fibers are planed to be applied in magnetooptic sensors.     

小F数衍射微透镜阵列光学性能研究

本文基于小光点扫描,在国内首次提出了一种测试小F数衍射微透镜阵列光学性能的方法.利用光通信用半导体激光器和探测器建立了一套测试系统,并对所研制的大阵列,小单元尺寸的多相位菲涅耳衍射微透镜阵列的衍射效率和点扩散函数进行了测试.结果表明,衍射微透镜实际衍射光斑比理论衍射受限光斑扩展不大,8相位和16相位石英微透镜的衍射效率分别高达80.2%和87.5%,说明本实验室对多相位的设计理论和制作工艺已基本掌握,满足应用的要求.     

制导光纤强度的依赖关系

分析研究制导高强度光纤强度8个方面的依赖关系，指出光纤强度降低的关键原因是光纤中存在着缺陷即表面微裂纹。因此，必须从制造工艺、制造环境入手，严格控制减少微裂纹方能制造出过2％筛选应变的高强度光纤。     

真空条件下激光诱导光纤损伤特性研究

实验研究并分析了调Q Nd:YAG 脉冲激光诱导光纤损伤特性.设计了在真空条件下全石英光纤传输1064 nm 脉冲激光实验.通过将激光注入光纤端面气压降低到10—100 Pa, 光纤端面击穿阈值提高到大气环境下的185 倍.结合光纤端面损伤形貌分析可知,光纤端面损伤主要是由于激光驻波场和烧蚀共同作用的结果,光纤端面或内部大量的缺陷降低了光纤抗激光损伤的能力.在真空条件下由于光纤端面光学击穿阈值的提高,激光诱导光纤损伤特性又表现出了另外一种损伤模式——光纤初始输入段损伤.它发生在光纤输入段附 关键词： 激光损伤 光束传输 真空 石英光纤