机器视觉在光纤端面缺陷检测中的应用

传统的光纤端面缺陷检测用的是人工检测方式,这种检测方式效率很低,检测结果的主观性很强。对光纤端面缺陷使用机器视觉检测,能极大地提高检测效率和检测准确性。首先将采集到的图像通过图像处理二值化,接着对纤芯中心进行定位,然后以纤芯中心为圆心对光纤端面进行不同的圆环检测区域划分。由于光纤端面上的缺陷有可能是暗色的或者是亮色的,因此为了区分二者,对每个区域检测时需要做不同的二值处理。如果有任意一个区域的检测不能通过,则这个光纤端面就是不符合要求的。结果显示,利用机器视觉进行光纤端面检测能够快速、精确地检测出缺陷所在位置及其大小。     

光波导模场分布自动检测系统的研制

介绍了研制的一套光机电一体化的光波导模场分布自动检测系统。该系统通过光学透镜对光波导二维模场分布进行放大,并用一针孔对放大后的模场分布进行二维扫描,扫描过程中对每一点进行光电转换和A/D数据转换,传给计算机,再通过软件处理得出光波导的二维模场分布图。采用该系统成功地检测了多模光纤端面和一个条形光波导端面的模场分布。     

LPC方法提防语音信号共振峰的分析

通过对ＬＰＣ（线性预测编码）方法提取语音信号共振峰进行的研究表明,采用相一频特性与对数幅－频特性同样能提取语音信号共振峰。与对数据－频特性的二次导数相比,相－频特性的三导数有更高的频率分辨率,能更有效地解决共振峰合并的问题,撮更精确的共振峰参数。     

半导体激光器LIV测试中阈值电流的小波提取方法

针对传统半导体激光器阈值提取方法容易受噪声影响、存在重复性不好的问题,根据小波变换奇异性检测原理,提出一种采用小波变换的阈值电流提取法,其采用三阶样条函数的二倍膨胀作为光滑函数,取它的二阶导数为小波函数,并结合多尺度来对半导体激光器光功率-电流（L-I）信号中的奇异点和不规则突变点进行检测分析。实验结果表明,与传统的二段直线拟合法、一次微分法和二次微分法相比,小波提取法不受噪声影响,能够真实、准确地得到半导体激光器的阈值电流。     

用GRIN透镜斐索干涉仪检测光纤端面的质量

采用梯度折射率 (GRIN)透镜干涉仪 ,对用加热、切割和研磨三种方法获得的平面光纤端面进行质量检测 ,得到反映端面不同平整度的干涉图样。实验结果表明 ,GRIN透镜干涉仪结构简单 ,操作方便 ,可作为定性和定量检测光纤端面质量的一种新工具。     

B样条函数与图像边缘检测

介绍一种基于 B样条函数的边缘检测算子 ,该算法是利用 B样条函数对原始图像进行拟合 ,然后求拟合曲面一阶导数的模极大值或二阶导数的零交叉点来检测图像的边缘。根据 B样条函数的局部性质给出了其平滑、一阶和二阶导数的具体卷积模板 ,该算法简洁 ,便于实时处理。     

非合作情况下长码直扩卫星信号载频检测和功率估计方法

针对长码直接序列扩频卫星信号信噪比低、多普勒频率影响明显、码周期长等特点, 提出了一种非合作情况下长码直扩卫星信号载频检测和功率估计的方法。该方法通过在本地NCO中加入多普勒频率一阶导数信息来抑制多普勒频率的影响; 在检测电路中加入“超前-滞后”结构, 以防止频率测量值在频率及其一阶导数构成的二维平面上沿脊线发生偏移,并利用最小二乘方法对频率进行预测,以减小搜索范围。仿真结果表明, 所提方法能够较好地减小多普勒频率引起的估计偏差, 检测信噪比达到-21 dB。     

基于概率密度特性的高阶UT样点设计方法

针对UT变换通过非线性矩近似方程组获得样点的复杂性,提出了一种基于概率密度特性的高阶UT样点设计方法.该方法利用高斯概率密度函数导数的极值点与各种对称Sigma样点集分布相对应的特性,采用高斯概率密度函数高阶导数的极值得到Sigma样点的分布来进行Sigma样点设计,提高了估计精度.理论分析推导和仿真实验证明了该方法的有效性.     

B样条函数与图像边缘检测

介绍一种基于Ｂ样条函数的边缘检测算子,该算法是利用Ｂ样条函数对原始图像进行拟合,然后求拟合曲面一阶导数的模极大值或二阶导数的零交叉点来检测图像的边缘。根据Ｂ样条函数的局部性质给出了其平滑、一阶和二阶导数的具体卷积模板,该算法简洁,便于实时处理。     

基于OpenCV的光纤端面检测系统研究

针对光纤端面制备中各种因素的影响会导致光纤端面产生缺陷的问题,研究了一种基于机器视觉技术的光纤端面检测系统。针对光纤端面显微图像的结构特点,使用图像处理算法拟合其中的椭圆,并提出了一种基于同心椭圆约束的椭圆检测方法,挑选出纤芯和包层轮廓的拟合椭圆。依据获取的拟合椭圆参数将光纤端面划分为三个检测区域,进行分区域的瑕疵点检测和统计。全部算法使用VS2010和OpenCV开发实现。实验表明,该检测系统可以对光纤端面进行准确的质量测定。     

SPM光纤连接器端面几何参数干涉测量仪

分析了光纤连接器端面几何参数对光纤连接器性能的影响,提出了一种利用正弦相位调制(SPM)干涉仪测量光纤连接器端面几何参数的新方法。计算机模拟计算表明,这种方法能在有噪声干扰情况下高精度测量光纤连接器端面几何参数。     

Return loss characteristics of optical fiber connectors

This paper describes the return loss characteristics for four typical contact type connectors: perpendicular and oblique endface connectors employing either physical contact or contact via index matching material. The high index layer on the polished fiber endface and the index matching material, which are important connector parameters, are investigated by measuring the return loss from one perpendicular fiber endface coated with the material and by etching the fiber endface. It is useful to apply two materials with different refractive indices to derive the refractive index and thickness of high index layers on perpendicular fiber endfaces. The index matching material we use has a refractive index of 1.467 at 20°C and a thermal coefficient of -2.9×10^-4/°C at 1.3 μm. We performed return loss calculations and experiments of the four contact type connectors. The worst value at any temperature from -40 to 80°C can be estimated, by measuring the return loss of these connectors at room temperature     

Efficient power coupling from a 980-nm, broad-area laser to asingle-mode fiber using a wedge-shaped fiber endface

A theoretical and experimental study of an efficient technique for coupling a broad-area laser to a single-mode fiber without the use of bulk optical components was carried out. The technique uses a wedge-shaped fiber endface to approximate a cylindrical lens action to correct for the phase mismatch between the curved laser beam wavefront and the planar fiber beam. A theoretical formula for the coupling efficiency in the absence of both angular and transverse misalignments is derived. By optimizing the wedge angle and the axial separation between the laser facet and the fiber endface, a maximum coupling efficiency of 47%, compared to 20% for the square endface, achieved, resulting in 15.2 mW of power in the single-mode fiber. The fabrication process consists of a simple polishing procedure requiring a wedge-shaped polishing tool and is highly reproducible     

Fibre probe far-field technique for mode-field diameter measurementof single-mode fibres

A far-field pattern (FFP) technique using an optical fibre probe to measure the mode-field diameters of single-mode fibres is described. The endface separation between the test fibre and the probe fibre can be reduced to a tenth of the fibre/detector separation in the conventional scanning detector method     

Loss and reflectance of standard cylindrical-ferrule single-modeconnectors modified by polishing a 10° oblique endface angles

It is shown that the reflectance performance of existing, cylindrical, keyed, single-mode fiber connectors can be significantly improved by polishing 10° oblique endfaces. This results in a maximum of -60 dB to less than -70 dB reflectance. Due to the resulting air gaps and hence multiple beam interference, the average insertion loss increase compared to physical-contact-type connectors is 0.43 dB. This is in excellent agreement with the predicted value of 0.45 dB for this type of joint. In cases where insertion loss performance is not the limited factor, this straightforward modification of standard cylindrical connectors shows potential for use in bidirectional and/or analog AM transmission systems. When the additional insertion loss cannot be tolerated, design changes in endface profiles and keying features may also be required. If fiber-to-fiber endface contact can be achieved, the same excellent reflectance performance will be achieved even with the presence of a modified index layer on the endface     

光纤连接器制作中的端面处理技术

插入损耗和回波损耗是光纤连接器最重要的光学指标,而影响这两个光学指标的主要因素包括光纤连接器端面质量和对准光纤的横向位移、间隙及角位移等.讨论了光纤连接器插入损耗的主要因素,对横向位移产生的插入损耗进行了理论分析及实验验证,所得到的实验值与计算值基本吻合.同时对单模光纤连接器端面研磨工艺与其光学指标的关系进行了大量的实验和理论分析,研究了光纤端面质量与回波损耗的关系,优化了适合工业生产光纤连接器的端面研磨工艺.     

A new scheme of conical-wedge-shaped fiber endface for coupling between high-power laser diodes and single-mode fibers

A new scheme for the lensed fiber employing a conical-wedge-shaped fiber endface (CWSFE) for coupling between the high-powered 980-nm laser diodes and single-mode fibers (SMFs) is proposed. The CWSFE was fabricated by following grinding and polishing techniques and then through heating in a fusing splicer to form an elliptical microlens endface. A coupling efficiency of 84% has been demonstrated. The higher coupling efficiency of the CWSFE lensed fiber was attributed to the better matching of both the elliptical Gaussian field distribution and the aspect ratio between the laser source and the fiber. In comparison to other fabrication techniques of lensed fiber used in high-power diode lasers, the advantages of this novel CWSFE structure are the ability to control over two axial curvatures and a small fiber offset through grinding and polishing processes to form a good elliptical endface. The results of this study have led to the development of a simple and reproducible fabrication process for achieving a high-yield and high-coupling CWSFE structure that is suitable for use in commercial high-power pump laser modules.     

Design of enhanced MT-RJ type connector for physical contact

An enhanced MT-RJ type connector was constructed employing a compact two-fiber ferrule in a newly designed housing for high-density optical duplex connection. The ferrule and the connector housing is designed to achieve physical contact (PC). As a result, the connectors we fabricated perform very well and provide ease of operation by means of direct core endface contact between the plugs. This connector is highly effective for use in the duplex connection of advanced optical networks.     

Transmitted power variations in single-mode fiber joints withobliquely polished endfaces

An experimental and theoretical study of multiple-beam interference effects at oblique endface airgap joints, with endfaces oriented parallel to each other, is discussed. It was found that although excellent return loss performance can be obtained by using such joints, large variations in the transmitted power can result in small changes in endface separation. Compared to the case of nonoblique endfaces, endface separation between the successive fringes in oblique endfaces increases by a factor which depends on the oblique angle and the refractive index of the gap material