远场掩模法测量单模光纤模场直径

本文根据远场均方根宽度表示的单模光纤模场直径定义,设计及制作了掩模板,导出了模场直径的测量计算公式。并对测量中可能引入的系统误差进行了分析,提出一些减小误差的方法。实现了用远场掩模法对单模光纤模场直径的测量。     

光纤模场直径精密测试系统

介绍一种由国产仪表组成的单模光纤模场直径测试系统。采采用ＩＴＵ－Ｔ标准规定的基准测试方法－－－远场扫描法，实现了微机控制自动测试。实现结果表明，该系统测试精度优于３％，满足精度高、投资省的要求，适合光纤通信领域使用。     

任意单模光波导模场半径的新定义及其与拼接损耗和色散的关系

本文给出了一种基于远场二阶矩的任意单模光波导模场半径的新定义,并给出了新定义及Hayata等的定义的远场形式。导出了两相同任意单模光波导的横向偏移损耗、角向偏移损耗与新定义及Hayata等的定义的关系式,导出了任意的各向同性单模光波导传播常数β和色散与新定义的简单关系式。光波导为圆对称时,我们的结果与已有结果完全一致。当光波导为椭圆芯光纤时,我们的公式与椭圆高斯近似的公式在形式上完全相同,只是模场半径的定义不同罢了。     

一种朗琴尺型激光光束参量测量仪

针对气体激光器细光束的尺寸参数的工业测量和质量控制，提出一种朗琴栅尺扫描ＴＥＭ００基模高斯激光光束的测量分析仪。所研制的仪器可以测量分析光斑１／ｅ２直径、横场分布和调制对比度等光束参数，特别是可以在近场测定１／ｅ２光束远场发散角。描述了该仪器的基本原理、结构及测量结果。     

单膜光纤模场直径的简易测量

单模光纤模场直径是一个非常重要的参数,其测量方法是各种各样的。这里利用极其简单的设备,通过对远场可变孔径测量来推算出模场直径,实验表明,这种方法简单可靠。假定光纤端面近场为高斯分布,由近场与远场之间的关系式直接得出距光纤端面L处的远场半径ω与近伤模伤半径ω_0之间的关系: ω=Lλ/πω,通过实验测出ω来就可得到模场直径。实验可以通过沿光轴前后移动孔径光栏的位置来找出P_(max)/e~2所对应的L值,也可以通过改变孔径来测出P(θ)     

两种扩束透镜光纤的研制与模场分析

介绍了两种对光纤端面进行修饰以扩大模场直径（MFD）的方法（加热扩散法和熔接透镜光纤法）。利用刀片远场扫描法对单模光纤（SMF）、加热扩芯光纤（TECF）与熔接透镜光纤（GIF）这两种修饰后的高斯分布光纤进行了测量比较。验证了其模场直径分别为10．700μm,13．129μm和12．7l7μm。并针对实际问题作出修正，通过对单模光纤以及上述两种扩束透镜光纤的分析，得到了相当合理的结果。说明这两种端面修饰法确实能起到扩大模场直径同时又不破坏模式分布的作用。并且验证了修正后的刀片法用于测量修饰后的光纤的各参量是非常有利的。     

用可变孔径法测试研究单模光纤的有效面积

光纤的有效面积是评价单模光纤性能指标的一个重要参数。但到目前为止，国内对这一参数的测试研究尚未同见报道。本文介绍用可变孔径法测试出各种折射率剖面结构的单模光纤的远场和近场分布，以及这些光纤的有效面积。并在实验测试的基础上，验证了ＩＴＵ－Ｔ文件中有关光纤有效面积与模场直径间的关系。同时，对目前的各种新型的Ｇ．６５５光纤的有效面积进行了较深入的测试研究。     

一种确定单模光纤远场和传输场的简单方法

本文研究了汉克尔变换核的特性。结果表明,当对变换核作合理近似后,只要测定单模光纤的模场直径和场的二阶矩,其远场和通过横向位移得到的传输场也可迅速得到确定。     

各种光纤的有效面积与模场直径之间的关系

采用波长可调谐激光光源远场扫描（FFS）法，利用高度精确的模场直径（MFD）／有效面积（Aeff）测试系统，对各种光纤的Aeff与MFD之间的关系进行了研究。结果发现，大有效面积色散位移光纤（LEDSF）的MFD和Aeff对波长的依赖性比普通单模光纤（SMF）、截止位移光纤（CSF）、色散位移光纤（DSF）和零色散位移光纤（NZDSF）大。给出了详细测量结果及测试曲线图。     

Mask测试系统的理论与实验研究

本文阐述了关于模场直径(m.f.d)的Petermann第二定义的优越性,介绍了由这一定义建立的远场掩膜测试系统;考虑到掩膜板各部分的实际透过率,修正了国外文献中m.f.d的计算公式,可以迅速、方便、准确地测定1.3μm和1.55μm处单模光纤的m.f.d。     

Mode-field diameter measurements for single-mode fibers with non-Gaussian field profiles

The mode-field diameter (MFD) of a single-mode fiber can be measured using several different techniques. The extent to which these techniques are consistent depends upon the definition used to compute the MFD and upon the fiber design. In this paper, three measurement techniques (far-field scan, offset joint, and knife-edge scan) are applied to the measurement of both conventional step-index fibers and to non-step-index dispersion-shifted fibers. Using the far-field second moment definition, which is often called the "Petermann 2" definition, measurements made using these three techniques agree to within 1.6 percent.     

Improvements to the variable aperture method for measuring themode-field diameter of dispersion-shifted fibers

The variable aperture system for measuring single-mode fiber mode-field diameter is modified to provide accurate measurements of dispersion-shifted fibers. The system's numerical aperture (NA) is increased by using a spherical mirror and a large aperture wheel with 23 apertures out to 0.556 NA. Petermann's second mode-field diameter (MFD) definition is calculated with Simpson's rule numerical integration. The industrialized high-NA variable aperture method in the far field (VAMFF) system is accurate to within 1%, with a measurement standard deviation of less than 0.5%. Flexibility for measuring various fiber designs over a range of wavelengths is also a key feature. It is concluded that the industrialized high-NA VAMFF system is an excellent MFD measurement bench because of its precision, accuracy, and versatility     

New approach for determining non-Gaussian mode fields of single-mode fibres from measurements in far field

The far-field RMS width of a single-mode fibre is shown to be related to the first derivative of the power passed through a circular aperture. This relationship allows a direct determination of Petermann's recent definition of mode field radius from data collected using the far-field variable-aperture technique.     

Determining the mode-field diameter of single-mode optical fiber: An interlaboratory comparison

The National Bureau of Standards, in cooperation with the Electronic Industries Association, conducted an interlaboratory measurement comparison among fiber manufacturers. Evaluated were transverse splice offset, near-field, far-field, and variable aperture far-field methods for determining mode-field diameter. Measurements were performed on five single-mode fibers at both 1300- and 1550-nm wavelengths. At 1300 nm, agreement was fairly good with the average one standard deviation being 0.15 μm for mode-field diameters in the8-11 mum range. Distinct systematic differences among various techniques were observed at 1550 nm where mode distributions are not as Gaussian.     

Analysis of mode-field measurements using orthogonal polynomials

Mode-field measurements can be analyzed using a sum of orthogonal polynomials as the fitting function. This method is demonstrated theoretically and experimentally for the mode-field diameter (MFD) measurement of single-mode fibres using the transverse-offset (TO) technique. The fit error is reduced by an order of magnitude in comparison with an ordinary Gaussian fit, and is limited by instrumental noise. Using the Petermann 2 definition, expressions for the MFD and its estimated error are derived. The convergence of the method is demonstrated experimentally. It is shown that the MFD is independent of the chosen range of TO values. In the limit of a large range of equidistant X_i values, the orthogonal polynomials are Hermite-Gaussian polynomials. The transformation from TO field transmission coefficient to strip integrated far-field power can then be carried out easily, and the polynomial coefficients can be used for characterization of the field distribution     

Mode-field diameter of single-mode fiber by knife-edge scanning in the far field

Knife-edge scanning has been applied to the far-field patterns of both matched-clad and depressed-clad single-mode fiber at 1300 nm. The method offers several advantages as compared with other techniques. The mode-field diameter (MFD) has been derived according to a Gaussian fitting procedure, and values agree closely with those obtained with the other standardized procedures.     

Propagation constant and waveguide dispersion of single-mode fibersmeasured from far-field

Wavelength-dependent measurements of the far-field pattern can be evaluated to yield a mode-field radius. It was recently proposed to fit these data to a formula that contained all the parameters necessary to construct an empirical relation for the wavelength dependence of the propagation constant. The authors report on the feasibility of this technique, using actual measurement data. They discuss the calculation of the waveguide dispersion from the measured mode-field radius. In both cases the choice of the empirical fitting function proves to be of great importance     

单模光纤模场半径快速测量仪的设计及制作

用FPGA可编程控制器来控制步进电机带动放置在光纤端面远场区域的一个透光圆孔屏障沿光轴线移动,从而调节PIN光电管接收到的光信号强度.用锁相放大器来提高光电信号的信噪比,信号被快速采样后输入FPGA控制器,经过数据处理后显示所测单模光纤的模场半径.测量仪具备较好的测量精度和重复精度.     

Suitable definition of mode field diameter in view of splice loss evaluation

The definition of the mode field diameter is investigated theoretically and experimentally from a practical viewpoint of the splice loss estimation. The difference of mode field diameter defined by various definitions becomes larger as theV-value decreases. This tendency agrees with the experimental result. As a result, the definition of mode field diameter obtained from RMS width of far-field intensity is useful.     

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