Nondeterministic endless control system for active polarizationcontrol

An active polarization-state control system is described for use in coherent fiber-optic communication systems. The active control system uses four piezostack fiber squeezers to enable control of the state of polarization (SOP) of the light over an unlimited range. The response time of the system is small enough to enable accurate tracking of changes in the SOP at a rate of up to 25 revolutions per second in the Poincare sphere representation. Unlimited control is achieved with a nondeterministic control algorithm. This makes the system insensitive to irregularities and unbounded instabilities of the control devices (e.g. drift). Experiments show that the SOP is accurately controlled by the system; the penalty loss due to residual mismatch in SOP is kept well below 1 dB even under dynamic circumstances     

Polarization properties of Rayleigh backscattering in single-modefibers

The state and degree of polarization (SOP, DOP) of Rayleigh backscattered light in low birefringent optical fibers was calculated using Stokes calculus. It was found that the SOP of Rayleigh backscattered light in low birefringent fiber is constant, viz. the same as the SOP of the incoming light. The DOP of Rayleigh backscattered light is one-third of the DOP of the incoming light, and not just anywhere between 0 and 100% as often mentioned in the literature. The experimental results agree with the calculations     

一种新型偏振态发生器

为了满足评价系统中光器件的光学偏振相关效应(OPRE)所需标准偏振激光光源的需要,本文提出一种新型的偏振态发生器(PSG)的实现方法,使用激光光源、线性起偏器、可旋转的1/4波片(QWP)和可旋转的1/2波片(HWP)的组合实现任意偏振态激光的产生.利用一种简便的二维平面几何方法,从理论上分析了该方案的正确性,并推导出了相应的控制算法.实验结果表明,该PSG可以提高精度产生任意偏振态,并且具有成本低、易于实现和控制算法简单等优点.     

Random-Scrambling Tunable POTDR for Distributed Measurement of Cumulative PMD

We provide the theoretical framework for a new method of distributed measurement of cumulative PMD along single-mode optical fiber links. Independent pairs of optical pulses are launched into the fiber, where each pair consists of two pulses having the same state of polarization (SOP) but two different, closely spaced wavelengths. The key aspect is that both the SOP and center wavelength of a given pair need not be correlated with those of any other pair. This random-scrambling approach is well suited for an economically designed instrument that is more robust for field applications than previously reported approaches. Since no assumed model of the distributed birefringence behavior is required, the method is suitable for any actual single-mode telecom fiber span encompassing many fiber sections of different types and origins.      

空间调制型全偏振成像系统的角度误差优化

空间调制型全偏振成像系统利用 Savart偏光镜能够将被探测目标的4个 Stokes参数 S0~S3调制在同一幅干涉图像中,从而通过单次采集便可获得完整的偏振信息。在该系统中,半波片和检偏器的角度误差对 Stokes参数的测量精度有着不可忽略的影响。文中首先给出了包含上述两种角度误差的干涉强度调制方程,根据实际系统参数,在角度误差模型的基础上分析了当入射光为自然光、0/90线偏振光、45/135线偏振光和左/右旋圆偏振光时,角度误差对空间调制型全偏振成像系统的 Stokes参数测量精度的影响。利用这四种基态偏振光的偏振测量误差,给出了任意偏振态和偏振度的入射光偏振测量误差的表征方法,最后,文中以系统测量矩阵条件数为优化目标函数,经仿真计算得出当 Savart板厚度为 23 mm时系统测量矩阵条件取得最小值为 2.06,半波片和检偏器耦合角度误差对系统偏振测量精度的影响程度最小。     

A Polarization-Stabilized Fiber-Optical Output Infrared Laser Source

In this paper, we successfully invented a polarization controlled light source for coherent or noncoherent fiber communication systems. The structure of our experiment includes 89C51 control board and feedback circuit which can stabilize states of polarization (SOPs) of output light. From the SOP modulation results, the given degree of polarization can be effectively controlled and the polarization state can be arbitrarily changed.     

级联光纤环的空间全偏振态统计退偏特性研究

级联光纤环退偏器具有无源、经济、高效的特点,解决了当前发展较为成熟的Lyot型退偏器对窄带光退偏失败的缺点,是具有很大发展前景的新型退偏技术。研究了通过级联光纤环的不同循环传输路径实现光的空间分解,进而实现全偏振态退偏的统计特性。分解的各光分量由于通过不同的传输路径,其输出偏振态随机分布在所有偏振状态上。通过良好地设计光纤环长,可实现各分解光分量之间互不相干,从而实现合成输出光的统计退偏。实验实现了由10级光纤环级联实现的无需偏振控制的退偏器,对带宽为1.6nm的光源可以实现偏振度小于5%的稳定退偏光的输出。     

磁光四波混频实验平台

设计一个测量光纤磁光(MO)效应和四波混频(FWM)的实验平台,具有较好的偏振控制性能,可分别采用自制的电磁偏振控制器(EMPC)和载纤螺绕环磁控装置控制输入光信号的偏振态(SOPs)和非线性光纤磁光耦合系数。实验测量了光纤四波混频闲频光功率对输入信号光偏振态椭圆率的依赖曲线,结果与理论分析一致。在此基础上,开展了连续导波光的磁光四波混频实验,测量了外加磁场对光纤四波混频闲频光功率的影响。     

Theoretical and experimental study of the dynamics ofpolarization-mode dispersion

The dynamic distribution of the state of polarization (SOP) is studied theoretically and experimentally for aerial fibers with a finite polarization-mode dispersion (PMD). A dynamic mode coupling wave-plate model is proposed to describe the SOP correlation and account for the PMD variations. It is found that the model can closely describe the experimental dynamic correlation of the SOP for an aerial fiber. A new algorithm for PMD emulation is developed     

旋转光纤中的拍长与偏振态保持能力

理论分析了旋转光纤在不同参考坐标系中的拍长及其与旋转光纤偏振态保持能力之间的关系——结果表明,旋转光纤没有确切的拍长定义,只有近似的用于描述旋转光纤偏振态保持能力的拍长计算公式。     

Polarization dependent gain in erbium-doped fiber amplifiers:computer model and approximate formulas

A computer model for polarization dependent gain (PDG) in Er-doped fiber amplifiers (EDFA) is presented. The model assumes that each erbium ion possesses an ellipsoidal gain surface and that all ion orientations are equally likely. By dividing the ions into subsets based upon orientation and computing the inversion of each subset in the presence of polarized pump and signal waves, the model predicts the dependence of the PDG induced by this polarization hole-burning (PHB) on the design of the EDFA, the signal degree and state of polarization (SOP), and the pump SOP. For moderate gain amplifiers (made from the same fiber) with the same gain peak wavelength and the same compression level, the magnitude of the PDG is nearly independent of the EDFA gain. Internal and random fiber birefringence are included to model real fibers. In fibers which cause the signal SOP to walk rapidly around the Poincare sphere, the PDG is reduced by a factor of 2/3 when compared with a linear polarization-maintained signal. Scrambled signals and partially-polarized saturating tones are also considered. Simple rules are derived for predicting the PDG of a given EDFA     

State of polarization changes: Classification and measurement

We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations.     

一种新型偏振态综合仪的实验研究

提出一种新型的偏振态综合仪的实现方案。该方案通过激光光源、线性起偏器、可旋转的1／4波片（QWP）和可旋转的1／2波片（HWP）的组合实现任意偏振态（SOP）的产生。利用二维平面几何方法,从理论上分析了该方案的正确性并推导出了相应的控制算法。实验结果表明,该仪器可以高精度产生任意SOP,且具有成本低、易于实现和控制算法简单等优点。该仪器在研究偏振相关效应对光纤通信系统和光器件的影响具有重要应用价值。     

温度对扭转光纤环性能的影响

从理论上和实验上研究了温度对扭转光纤环性能的影响.结果发现,当注入线偏振光时,扭转光纤环内存在一个弱主轴,并且其方向会随着温度的变化而偏移;而注入圆偏振光时,输出光仍然是一个比较好的圆偏振光,在同样的温度范围内,椭圆度变化很小.为进一步提高光纤大电流传感器的稳定性研究提供了一个有益的参考.     

Properties of Pump-Laser Modules Exposed to Polarization-Dependent and Wavelength-Selective Feedback From Fiber Bragg Gratings

The performance of fiber Bragg grating (FBG) stabilized pump-laser modules is strongly influenced by changes of the state of polarization (SOP) arising from intrinsic and/or induced birefringence of the fiber. Birefringence changes the SOP as the light propagates back and forth between laser and FBG, which are separated by a distance of 1 to 2 m. As a result, the effective wavelength-selective feedback provided by the FBG varies accordingly. Based on the steady-state solution of a set of multimode rate equations we present a new model allowing us to calculate the output characteristics of a grating-stabilized pump-laser module as function of effective feedback. An effective-reflector approach is applied to describe the external cavity between the front mirror and the FBG on the module's front side. The polarization- and wavelength-dependent effective feedback from the grating is taken into account by a feedback parameter in the equations for the effective reflector. We present an extended traveling-wave amplifier model for calculating the TE- and TM-polarized contributions to the power from all output ports of the module. Our model is verified by comparison of simulation results with experimental data for a typical FBG-stabilized pump-laser module. The output characteristics are analyzed as function of effective feedback for both the principal TE-polarization as well as the residual TM-polarization modes.     

光纤磁光效应对四波混频功率传递函数影响的理论和实验研究

根据磁光非线性光纤中导波光脉冲的四波混频(FWM )耦合模方程,数值计算了施加不同磁场时相同偏振和 接近正交偏振线偏光入射两种情况下的FWM功率传递函数(PTF),并实验测试了相 应的再生光功率最 大和最小两种起始状态下光纤磁光效应对FWM PTF的影响,实验结果与理论曲线基本 吻合。研究表明, 对光纤施加适当的磁场,有助于提升再生器的消光比性能;在接近正交偏振线偏光入射时, 再生闲频光功率随磁场的变化最为敏感。     

Angular multiplexing for multichannel communication in a single fiber

A concept of angular multiplexing of several communication channels in a relatively short step-index fiber is described. The angular dependence of the outgoing light flux and the temporal impulse response are calculated for slab waveguides and round fibers in terms of the fiber's length and the excitation conditions. Calculations of the inpulse response in the presence of mode coupling are based on a simple model which is found to be adequate for short fibers. Crosstalk levels are calculated by integrating the flux over the aperture of the detectors. Measurements of angular flux distribution, temporal impulse response, and crosstalk levels agree with theoretical prediction and validate the proposed concepts. To increase light levels, parallel excitation of each channel by several light sources is suggested and tested. Also, light collection efficiency is increased by employing lenses and annular mirrors to deflect and focus the light from each channel to small-area detectors. Given a 25 m long fiber with a coupling constant of 10^-5rad²/m, it is possible to multiplex four channels with cross-talk of about -25 dB and information rates ranging from 10⁹bits/s to 10¹⁰bits/s for each channel.     

Fast state of polarization and PMD drift in submarine fibers

We report on the measurements of state of polarization (SOP) and differential group delay (DGD) in submarine fibers. The experimental autocorrelation function shows the fastest change in both SOP and DGD is faster than 15 s, which is limited by the measurement speed. The Fourier transform is utilized to study ocean-wave-induced vibrations on submarine fibers.     

Near hexagonal close-packed optical fiber array for parallel optical interconnection

In conventional optical fiber based two-dimensional (2-D) parallel optical interconnection (POI), optical fiber arrays are aligned to 2-D light sources and detectors using precisely fabricated hole-plate or stacked V-groove plates. All these structures have problems in making positioning components and assembly with high accuracy. For polymer optical fibers with large diameter, the whole dimension of the array will be too large if they are positioned using V-grooves or hole-plate. This paper proposes a 2-D near hexagonal close-packed (NHCP) optical fiber array for 2-D POI. NHCP array has a cross-sectional profile of near-hexagonal lattice and with fibers precisely positioned at each node of lattice. Compared with perfect HCP lattice, NHCP lattice is slightly stretched in one dimension and still have all fibers with nonuniform diameter packed tightly with high packing fraction. The position of fibers in NHCP array is very important when aligned to 2-D light sources and detectors. This paper deduce the analytically expression for the probability distribution of fiber position which is related to variance of fiber diameter and structure parameters of NHCP array, and verified it by computer simulation. Experiment samples of NHCP array have been made showing that NHCP array is easy to be fabricated.     

全光纤在线偏振参量测试系统

设计和研制了一套全光纤在线偏振参量测试系统,该系统由全光纤偏振控制器、全光纤在线偏振仪等组成.系统的光路完全由光纤构成,没有插入分立器件.通过数据采集卡和Labview编程,实现了全光纤在线偏振参量测试系统对偏振态的准确控制和对斯托克斯矢量的实时、准确和高速的测量.该系统能实现对光的偏振态、偏振度、消光比和偏振相关损耗等偏振参量的测量,并能实现偏振态监控和偏振稳定的功能.