Uniformly high-speed semi-open loop polarization control and PMD suppression

We propose and demonstrate a novel scheme of semi-open-loop polarization control(SOL-PC), which controls the state of polarization(SOP) with high accuracy and uniform high speed. For any desired SOP, we first adjust the initial SOP using open-loop control(OLC) based on the matrix model of a three-unit piezoelectric polarization controller, and quickly move it close to the objective one. Then closed-loop control(CLC) is performed to reduce the error and reach precisely the desired SOP. The response time is three orders faster than that of the present closed-loop polarization control, while the average deviation is on par with it. Finally, the SOL-PC system is successfully applied to realize the suppression of the polarization mode dispersion(PMD) effect and reduce the first-order PMD to near zero. Due to its perfect performance, the SOL-PC energizes the present polarization control to pursue an ideal product that can meet the future requirements in ultrafast optical transmission and quantum communication.     

偏振态的高速实时测量方法的研究

偏振态的测量在光通信领域有着重要的作用,因此越来越受到人们的关注。在分析现有方案的基础上,推导出了新的斯托克斯计算公式,以此公式为依据提出了一种能对高速变化的偏振态进行实时测量的新方案,并对可能产生的误差因素进行了分析。给出了制作实用化测量模块所要达到的器件要求和制作工艺。     

Polarization shift keying (POLSK) phase diversity homodyne system with multiplying detection in coherent optical communications

We propose a Polarization Shift Keying (POLSK) phase diversity homo-dyne system with multiplying detection in coherent optical communications. The proposed system uses only one of three Stokes parameters, which is the phase difference between two orthogonal polarizations. Although such systems using only one Stokes parameter are very sensitive to polarization fluctuation, the proposed system becomes insensitive to the linear polarization fluctuation by using the multiplying detection with a combination of in-phase and quadrature optical signal components on two orthogonal polarizations. Furthermore, insensitivity to phase noise and offset frequency and attractiveness due to homodyne type in high-speed transmissions are maintained. The most attractive feature of the proposed system is that neither a polarization controller nor electronic feedback loop for matching the state of polarization (SOP) between transmitted and local oscillator (LO) optical signals is needed. We theoretically analyze the receiver sensitivity and the power penalties of the proposed system for the cases of the elliptical SOP of received optical signals and the imbalance optical 90° hybrid.     

Use of state of polarization transparent scheme for polarization shift keying signal as optical phase conjugator to improve the transmission performance

Transmission characteristics of polarization shift keying (PolSK) signal is experimentally demonstrated in this work. Performance degradation due to transmission is improved using optical phase conjugation (OPC) technique. The wavelength converter based on the proposed state of polarization (SOP) transparent scheme for PolSK signal is effective to use it as mid-link optical phase conjugator and which is difficult to achieve using conventional wavelength conversion scheme. It is found that for fiber transmission, the performance of both of the orthogonal SOPs of the PolSK signal is different for their respective chirping characteristics which can be optimized to be similar using proposed OPC technique.     

直接检测光OFDM系统中的偏振相关损耗研究

对于高速光传输,直接检测的光正交频分复用系统（direct detection optical orthogonal frequency division multiplexing, DDO-OFDM）中的偏振相关损耗（polarization dependent loss, PDL）与偏振模色散相互作用,对系统传输带来较大影响。对DDO-OFDM系统中PDL与一阶PMD作用机理和数学模型进行了分析,并通过数字仿真加以验证。结果表明:在PDL与PMD联合作用下,对OFDM信号幅度及相位均产生影响,通过发送导频序列可有效实现信号均衡;由于输出偏振态随频率产生旋转,PMD效应一定程度上缓解PDL所致系统损伤,差分群时延为50 ps条件下,以10 Gb/s的速率在单模光纤传输480 km,DDO-OFDM系统Q值提高约0.8 dB。     

偏分复用系统中偏振模色散补偿与偏分解复用一体化方案

本文建立了偏分复用系统中偏振模色散与信号偏振态变化引起信道串扰的数学模型, 分析了偏振模色散对偏分复用信道射频功率的影响, 并提出了适用于偏分复用系统的光域偏振模色散补偿与偏分解复用同时进行的方案: 用信道的射频功率作为反馈控制信号, 监测链路中偏振模色散和偏振态变化引起的信道串扰的大小, 用改进的粒子群优化算法对偏振控制器进行自适应控制, 同时完成偏振模色散补偿与偏分解复用. 在112 Gb/s偏分复用-差分正交相移键控(PDM-DQPSK)传输系统中仿真验证了该方案的有效性. 结果表明该方案可以使112 Gb/s-PDM-DQPSK传输系统完成自适应偏分解复用的同时, 在1 dB的光信噪比代价下, 使系统对偏振模色散的容忍度提高20 ps. 关键词： 偏分复用系统 信道串扰 偏振模色散 偏分解复用     

利用旋转波片组实现偏振变换器的两种新方法

偏振变换器作为一种重要的光学器件．以其高偏振变换精度、低成本、低插入损耗以及控制算法简单的特性在相干光纤通信和高速光纤通信领域具有十分重要的地位。提出了利用两个λ／4波片和一个λ／2波片的三波片组合实现任意偏振态变换的新方法。用改进的三维庞加莱球方法—偏振态投射平面的二维几何方法分别推导出了λ／4 λ／4 λ／2组合以及λ／2 λ／4 λ／4组合实现任意偏振态变换时每个波片的位置参量计算公式。研究结果表明：两个λ／4波片和一个λ／2波片的任意组合都可以实现任意偏振态的变换;用偏振态投射平面的几何方法处理偏振变换的相关问题比庞加莱球方法和矩阵处理方法简洁明了。研究结果为偏振变换器的设计提供了理论依据。     

SOP and PMD monitoring on deployed aerial optical fibres

State of polarization (SOP) and polarization mode dispersion (PMD) are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. With 184 PMD values obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47 ps and standard deviation of 0.08 ps. This small standard deviation was justification for its accuracy in measuring PMD of aerial optical fibres. A comparison is also made on the accuracy of the GINTY and the FTB-5700 on measurement of PMD of aerial optical fibres with results showing that the latter is more accurate compared to the former. The time scale over which to compensate PMD in aerial optical fibres was determined and it is slightly higher than 400 s; the decorrelation time obtained for SOPs on a particular windy and hot day. This is because the changes of the PMD vector are known to be slower than SOP changes.     

Optical properties of a three-dimensional chiral metamaterial

A three-dimensional chiral metamaterial with four-fold rotational symmetry is designed, and its optical properties are investigated by numerical simulations. The results show that this chiral metamaterial has the following features: high polarization conversion, perfect circular dichroism, and asymmetric transmission of circularly polarized light. A comparison of the results of chiral metamaterials without and with weak coupling between the constituent nanostructures enables us to confirm that the optical properties of our proposed nanostructure are closely related to the coupling between the single nanoparticles. This means that the coupling between nanoparticles can enhance the polarization conversion, circular dichroism, and asymmetric transmission. Due to the excellent optical properties, our metamaterial might have potential applications in the development of future multi-functional optical devices.     

Nonlinear repolarization in optical fibers: polarization attraction with copropagating beams

We propose a type of lossless nonlinear polarizer, novel to our knowledge, a device that transforms any input state of polarization (SOP) of a signal beam into one and the same well-defined SOP toward the output, and perform this without any polarization-dependent losses. At the polarizer output end, the signal SOP appears to be locked to the input pump SOP. The polarizer is based on the nonlinear Kerr interaction of copropagating signal and pump beams in a telecom or randomly birefringent optical fiber.     

布里渊光时域分析传感器的消偏振衰落技术

在布里渊光时域分析(BOTDA)光纤传感器中,由于受激布里渊散射的偏振相关性的影响,激励光和探测光的偏振态随机变化引起的信号起伏严重影响布里渊散射光信号的稳定测量。通过建立与偏振态有关的激励光和探测光的耦合方程,推导出接收探测光光强关于激励光和探测光偏振态的理论公式,并由此提出偏振扩展接收技术。理论分析表明,偏振扩展接收技术可以有效地抑制偏振相关信号衰落。通过对耦合方程进行模拟,验证了理论分析的正确性和偏振扩展接收技术的可行性。最后给出了采用偏振扩展接收的布里渊光时域分析实验结果,与理论分析和模拟具有较好的一致性。     

Acousto-optic polarization-dependent mode coupling in a dual-mode hollow optical fiber

We demonstrated unique polarization dependence in acousto-optic coupling in a two-mode hollow optical fiber (HOF). Local deformation of circular HOF induced by traveling acoustic wave resulted in highly birefringent optical transmission characteristics, which were experimentally analyzed for various central air-hole sizes. Potential applications for polarization-dependent devices such as polarization-dependent loss compensators and broadband polarization controllers are discussed.     

偏振模色散补偿控制中偏振度技术的性能

基于主偏振态理论，导出了光信号偏振度的解析表达式.并对40 Gb/s光传输系统中的信号偏振度受各种因素的影响进行了数值模拟，包括啁啾、脉冲形状、脉冲宽度、自发辐射噪声以及消光比等.结果表明，偏振度技术能有效地监测和控制40 Gb/s系统中小于37.5 ps的偏振模色散.而且发现就最大化偏振度技术对差分群延时的容许范围而言，脉冲的1/e强度半宽取0.45个位宽（11.25 ps）是最优的.     

白光干涉偏振模耦合分布式光纤传感器分析

分布式光纤传感器能够测量沿光纤长度上连续分布的外界量。用保偏光纤作为传感光纤的分布式光纤传感器,被测外界量引起保偏光纤中传播的两正交偏振模的相互耦合。用迈克尔逊干涉仪两臂光程差来补偿两个偏振模的光程差的方法探测传感信号。为了设计白光干涉偏振模耦合分布式传感器,根据统计光学原理分析了传感器的互相干特性。在此基础上分析了传感器的空间分辨力、光纤耦合点分辨力、最大传感光纤长度。波长1310nm、谱宽36nm的超辐射发光二极管(SLD)作光源．用色散参量为600ps／km,拍长3mm的保偏光纤的分布传感器空间分辨力和光纤耦合点分辨力分别为6cm和3mm。     

Berry phase magnification in optical microcoil resonators

We have studied the effects of the Berry phase on the linear transmission properties of optical microcoil resonators and analyzed the resonant behavior for different input polarizations and coil geometries. Contrary to previous expectations, we find that on resonance the size of the Berry phase shift can be magnified significantly, leading to a measurable polarization rotation for some geometries. Our model also considers other polarization effects including elasto-optic bend birefringence and the polarization dependent coupling coefficients, which were also previously neglected, and we still find that observable Berry phase effects persist. For example, in a three turn microcoil with a diameter of 0.2 mm, close to 100% of an initially x polarized light will be coupled into the orthogonal y polarization, due to the optical activity arising from the cumulative effects of Berry phase on resonance. More generally, the cross-polarization coupling also significantly influences the resonance extinction ratio and quality factor.     

基于半导体光放大器偏振旋转的全光缓存器

全光缓存器可实现数据包在光域内的缓存,是全光路由、伞光计算以及全光交换的关键部件之一.提出了一种基于半导体光放大器(SOA)中非线性偏振旋转(PR)的光纤环型全光缓仃器结构;提出了一种利用偏振主态(PSP)寻找两个正交线偏振态以及在线实时测量光纤中偏振态的方法.通过改变SOA的注入电流,实现了对两个正交偏振态转化的控制,利用这两个正交的线偏振态,实现了信号的"写"人和"读"出.利用该结构的缓存器,实现了2.5 Gb/s的1024 bits数据包6圈的缓存.缓存后的信号波形良好.     

Spectroscopic polarimetry with a channeled spectrum

We describe a novel method for the spectroscopic measurement of the state of polarization (SOP) of light. A pair of thick birefringent retarders is incorporated into the spectroscopic polarimeter, so the generated channeled spectrum is composed of three quasi-cosinusoidal components carrying the information about the SOP of the light that is being measured. Fourier inversion of the channeled spectrum provides significant parameters for determination of the spectrally resolved Stokes parameters of light. No mechanically movable components for polarization control or active devices for polarization modulation are used, and all the Stokes parameters can be determined at once from only the single spectrum. The effectiveness of this method is demonstrated by the generation of elliptically polarized light whose SOP varies with wave number.     

Coupling between elliptic screw polarization modes in single-mode optical waveguides with linear birefringence and regular twist of anisotropy axes in the presence of random axis twist

An analysis is made of single-mode fiber optical waveguides with linear birefringence and regular twist of anisotropy axes in the presence of random twist, which shows that, in this case, the coupling of orthogonal polarization modes having elliptic polarization in the screw coordinate system comoving with twist cannot be characterized by one coupling parameter, as differentiated from the case where constant twist is absent. In this case, the coupling between polarization modes is characterized by three independent parameters, which are different in nature and have different effects on the coupling of polarization modes. An estimate is made of the domain of applicability of the classical formula for the h parameter in single-mode fiber optical waveguides without regular twist of anisotropy axes.     

基于SOA全光偏振调制的双信道光传输系统的仿真与分析

仿真并分析了基于半导体光放大器全光偏振调制的双信道光传输系统模型.该系统分别利用两级半导体光放大器的交叉偏振调制效应(XPolM),将两路独立的强度调制的抽运光变换到一路探测光的两个正交的偏振态上,实现双通道偏振复用的全光数据传输.首先对单个半导体光放大器的动力学过程进行了理论分析,数值计算了具有不同抽运光功率的半导体光放大器对探测光偏振态的影响,进而对双半导体光放大器偏振复用系统的调制/解调原理进行了分析,模拟仿真了双半导体光放大器的双通路偏振复用的调制及解调过程,仿真结果与实验结果相符.