Guided-wave characteristics of optical graded-index planarwaveguides with metal cladding: a simple analysis method

The guided mode characteristics of metal-clad graded-index waveguides are generally determined by complex eigenvalue equations or perturbative methods. However, these methods either require several iterations in the complex plane or are only suited to the class of waveguides whose guided field can be described analytically. We describe a method of calculating complex propagation constants for metal-clad graded-index waveguides under very general but weakly guiding conditions. The method, based on Galerkin's formalism using trigonometric basis functions, allows arbitrary inhomogeneous and complex refractive index profiles. Applications to three generally used waveguide models show our approach to be in good agreement with other analytical or numerical methods     

A refined WKB method for symmetric planar waveguides withtruncated-index profiles and graded-index profiles

An accurate method is proposed, based on a modified version of the WKB method in quantum mechanics, for evaluating the propagation constants and field distribution of symmetric planar waveguides with a truncated-index and graded-index profile. Simple formulas are given for calculating the dispersion characteristics including those for the truncated parabolic and exponential profile, and results are much more accurate than those of the ordinary WKB method, especially in the near cutoff regions. This method also can be extended to other more complicated cases     

Theoretical investigation on the dispersion of graded-index polymeroptical fibers

Various experiments on polymer optical fibers (POF's) suggest that they present a large transmission capacity, but this is not confirmed by the standard theory. In this paper we present a full dispersion model based on evaluating the frequency response of the fiber instead of the direct calculation of the pulse broadening from the moments of the impulse response. The mathematical formalism is firstly displayed and subsequently applied to the graded-index POF made with polymethylmethacrylate (PMMA). The simulation results show that the baseband bandwidth is indeed enhanced due to the strong differential mode attenuation (DMA)     

Ray-tracing technique for evaluating the dispersion characteristics of graded-index cylindrical fibres

A method which uses ray-tracing techniques and modal relations is sketched for the determination of the dispersion characteristics of cylindrical fibres with radial graded-index distribution. Examples of the results obtained are described, which show how it is possible, applying this procedure, to fully analyse propagation in optical fibres with any refractive-index distribution.     

Multimode fibers for compensating intermodal dispersion of graded-index multimode fibers

This paper proposes a novel type of multimode dispersion compensation fiber (MM-DCF) by which the intermodal dispersion of multimode fibers (MMFs) can be effectively compensated. A theoretical model that precisely calculates the group velocities of a target MMF and its MM-DCF and the power coupling between the two fibers is applied to confirm the proposal presented here. As a demonstration of the operation of the MM-DCF, an MMF optimized for transmission at a wavelength of 850 nm is compensated by the MM-DCF, and its overfilled launch bandwidth at a wavelength of 1300 nm is enhanced from 0.62 to 2.56GHz/spl middot/km.     

Influence of a central depression on the dispersion characteristics of a graded-index profile

Ray-tracing techniques and modal relations are utilised for evaluating the dispersion characteristics of multimode fibres with a quasiparabolic profile having a central depression. The results show that the dispersion increases with the dimensions of the depression; however, such an increase may be negligible if the dimensions of the depression approach those corresponding to realistic preforms produced by the c.v.d. technique.     

A method for the analysis of biaxial graded-index optical fibers

The problem of wave propagation in a biaxial graded-index fiber with circular symmetry is considered. The problem is formulated in terms of four first-order differential equations for the tangential components of the electric and magnetic fields. A general solution method for solving systems of differential equations is presented. This solution method is then used to solve the system of equations for a particular example of a biaxial graded-index fiber. Numerical results for the propagation constant in the fiber are given     

Detailed error estimates for first order WKB calculation method

Using evanescent wave theory combined with nonlinear transformation techniques, very accurate upper and lower limits of the exact results for modal propagation constants and group delays are obtained for a near parabolic graded-index optical fibre. Comparing to a first order WKB solution we find WKB errors in group delays of 3?10 ps/km compared to the exact results, the fundamental mode specifying the worst case.     

A numerical method for the analysis of single-mode low-dispersion graded-index fibers

A numerical integration method for the calculation of the time dispersion of optical-fiber modes is introduced and used to determine the parameters of single-mode graded-index silica-based fibers for the 1.55-μm band. The method gives an accuracy on the order of 0.001 ps/km/nm, and it was possible to quantify the error in assuming the overall time dispersion to be the sum of the material and waveguide dispersions. The analysis indicates that when large material dispersion is to be neutralized by waveguide dispersion, the outer diameter of the cladding must be increased to avoid higher microbending losses. When the difference between the refractive indices at the center of the core and in the cladding decreases, the ratio between the cladding and core diameters must be increased.     

A modified WKB method for the improved phase shift at a turningpoint

With the presence of an index or/and index slope discontinuity in a planar waveguide, the phase shift at the turning point which is near or at the discontinuity is no longer a constant (π/2) as in the conventional WKB method. In this paper, we present analytical expressions of this phase shift. Not only the index discontinuity, but also the index slope discontinuity have been taken into account in deriving these expressions. Numerical results show a significant improvement over the conventional WKB method after a modified phase shift has been used. According to our results, the phase shift is π/6 instead of π/2 or zero at the cutoff for a waveguide with a truncated index profile. As a by-product, we found a more accurate phase shift expression for the total internal reflection at an index discontinuity where the index slopes on both sides of the discontinuity have been considered     

基于XTCE标准的通用型航天器系统数据处理方法研究

基于航天器研制过程中需要对不同种类不同格式的系统数据进行统一描述的目的,采用XTCE建立通用型的航天器系统数据处理方法,通过使用某型号航天器地面系统数据管理软件进行地面试验,得出该系统数据处理方法的使用可以实现航天器系统数据交换格式规范性和通用性的结论。提高航天器系统数据解析和处理的效率和可靠性,为航天任务中的信息交换处理提供了便利的方法和新的思路。     

Novel dispersion compensation method for cross-coupling measurement in PM-PCF based on OCDP

For polarization maintaining photonic crystal fiber (PM-PCF), the cross-coupling measurement can be severely affected by interferogram broadening, due to the large inter-mode chromatic dispersion. In this paper, a novel dispersion compensation method is proposed to mitigate the influence, including a frequency domain algorithm and investigation of the dispersion coefficient for a phase packet in algorithm. A numerical simulation and measurement of birefringence as a function of wavelength reveal that the dispersion coefficient in PM-PCF is much larger than that in PANDA-PM fiber. After compensation, the accuracy of coupling strength measured can be restored and spatial resolution is improved. Experiments show the compensation provides high accuracy with average relative error less than 0.31% and spatial resolution improved 4.1 times.     

Simplified method for passive optical network in-service fibre-fault monitoring based on fibre Bragg gratings

The fibre-fault monitoring is a crucial network element, especially for passive optical networks. In this work is presented and demonstrated experimentally a simplified method for the optical access network monitoring, based on fibre Bragg gratings, deployed near vulnerable network locations. We experimentally demonstrated the use of this technique in a four-branch PON with a maximum span of 60 km, with the FBG monitors placed in several positions along the network. From the experimental results, the proposed method applicability is set for up to 90-km-long networks. Since this method does not require active optical devices, it could be applied in extended reach networks, with reduced implementation costs, which is an advantage to other monitoring methods.     

目视万能工具显微镜的影像测量应用研究

在传统目视万能工具显微镜的基础上,使用光学CCD代替人眼采集图像,增加光栅尺和数显表替代原来的投影式读数器,实现了工件测量CCD图像与光栅尺数据的计算机自动采集。根据CCD图像、光栅尺数据及笛卡尔坐标系理论,建立了测量尺寸与光栅尺数据和图像工件边缘位置的数学模型。应用中值滤波、阈值分割对工件图像进行预处理,采用最小二乘法提取工件边缘的位置和方向,并在此基础上结合工件测量数学模型计算得到了被测工件尺寸。     

An chromatic dispersion monitoring method based on spectral-shift of SOA

A remnant dispersion monitoring method based on spectral-shift of SOA in high speed optical communication system with CSRZ format and single channel speed of 40 Gbit/s is proposed. The system performance can be optimized by careful choosing bandwidth and center wavelength of the optical fiber grating filter. The dynamical monitoring range is ±60 ps/nm and the monitoring precision is about 5 ps/nm. This method can be suitable for the application in dynamical dispersion compensation of high speed optical communication systems.     

一种降低渐变折射率反射膜表面电场的方法

为了解决渐变折射率反射膜表面电场不为0,容易造成表面损伤的问题,提出了反射相移补偿方法,即不引入另外界面,在渐变折射率反射膜表面增加一层适当厚度的均匀膜,来降低渐变折射率反射膜的表面电场。结果表明,该方法确实降低了渐变折射率反射膜的表面电场;缺点是导致了渐变折射率反射膜中心波长的略微漂移,但该漂移相比于反射带宽而言可以忽略。该研究对制备高损伤阈值的渐变折射率反射膜具有参考价值。     

A universal method for directivity synthesis

A completely new synthesis method, the successive approximation method, is developed. By introducing a control function and a step-by-step approach program various directivity functions can be obtained in which the peaks of the sidelobes and specified zeros fit within a specified curve. This method is applicable to any form of array. Numerical calculations have been done to illustrate its applications: determining optimum current distribution of linear arrays, unequally spaced arrays, steering the main beam through current excitation, etc.     

基于电流传输器的数字可编程电压模式双二次通用滤波器的分析综合法

提出了一种基于第二代电流传输器的数字可编程电压模式双二次滤波器的分析综合方法.由该方法无需元件匹配就能实现电压模式低通、带通、高通、带阻及全通5种滤波输出.使用传输门开关电路实现了数字可编程滤波器.所实现的电路具有高输入阻抗、电路结构简单,所有无源元件接地、灵敏度很低的特点,可应用于模数混合集成电路.     

啁啾光纤光栅色散补偿方案研究

设计了利用啁啾光纤光栅(CFG)对10Gbit／S光信号进行色散补偿的仿真模拟系统,该模拟系统研究了5种不同的色散补偿方案对系统误码率的影响,选出了最佳的一种补偿方案,模拟研究了入纤光功率对系统误码率的影响,结论是在保持光探测器接收功率不变的条件下,入纤光功率越高,误码率越大．对于最佳色散补偿方案,入纤光功率为6dBm时既能保证较高的传输功率又有较好的误码性能。     

基于异步幅度抽样的高速光信号色散监测方法

针对目前异步幅度统计直方图（AAH）对色散监测范围小、灵敏度低的缺点,提出一种基于异步幅度抽样（AAS）的色散监测方法,定义无量纲色散监测参数G,将色散与其他损伤因子分离开。使用 OptiSystem9.0 软件搭建了200Gbps DP-16QAM 监测系统,在不同信噪比和占空比下进行色散监测仿真实验,探讨了信噪比和占空比对该方法的监测精度的影响,并对色散监测误差进行了分析。仿真结果表明基于该参数的色散监测方法受噪声因子影响小、精确度高,能实现在0~600 ps/nm 全范围内对色散的有效监测,为在更高阶调制信号的光纤通信系统中进行色散监测管理提供一定的参考。