A Theory of Polarization-Mode Dispersion of Spun Fibers

We give a compact theory of the polarization-mode dispersion (PMD) in spun fiber. For periodically spun fibers, the theory shows that the asymptotic behavior of the PMD can be predicted by a simple procedure from the two-dimensional Fourier transform of the birefringence correlation function.     

Tolerance of Duobinary and NRZ-OOK Signals to Second-Order Polarization-Mode Dispersion

The sensitivity of tightly filtered duobinary and conventional nonreturn-to zero on-off-keyed (NRZ-OOK) signals to second-order polarization-mode dispersion (SO-PMD) is assessed through extensive numerical simulations. On average, duobinary signals are significantly more sensitive to SO-PMD than to ordinary fiber chromatic dispersion (CD), whereas NRZ-OOK signals are more tolerant to SO-PMD than to CD. This seemingly contradicting behavior is explained by the difference in the frequency dependence of SO-PMD and CD. In addition, duobinary signals suffer from residual differential group delay, even after first-order PMD compensation, which is introduced between signal components that are transmitted in the launched principal state of polarization (PSP) and those that are coupled from the launched to the orthogonal PSP.     

Higher Order Polarization-Mode Dispersion in the Presence of Polarization-Dependent Loss in Optical Fiber Systems

The statistics of first- and second-order polarization-mode dispersion and statistical dependencies between corresponding quantities are investigated with regard to fiber-optic links with polarization-dependent loss (PDL). We show the occurrence of an infinite depolarization rate of the principal states of polarization (PSPs) caused by an abrupt interchange of the two PSPs with a probability that grows with the global PDL. We finally discuss the influence of the frequency resolution of measurement and simulation methods on the depolarization results     

A Framework for Evaluating the System Penalty From Polarization-Mode Dispersion Using Different Performance Monitoring Techniques

We present a theoretical framework relating system penalties from polarization-mode dispersion (PMD) to various monitoring techniques for non-return-to-zero systems. The framework includes models for string length, radio-frequency spectral power, eye opening, and degree of polarization. We validate the models experimentally and show that they are interrelated by common constants specific to the system under investigation.      

Independent and Simultaneous Monitoring of Chromatic and Polarization-Mode Dispersion in OOK and DPSK Transmission

We propose and demonstrate a novel technique for a simultaneous chromatic and first-order polarization-mode-dispersion (PMD) monitoring method using a partial bit delay Mach-Zehnder interferometer (MZI) with radio-frequency (RF) clock tone monitoring. RF clock tones at the output of the two branches of the MZI behave oppositely with increasing chromatic dispersion (CD) which improves the sensitivity of the measurement. The technique increases CD monitoring sensitivity over standard clock tone methods by a factor of two for a nonreturn-to-zero intensity modulation format and a factor of five for a differential-phase-shift-keying modulation format. The accuracy of PMD monitoring is also enhanced. Moreover, the partial bit delay allows the signal to pass through the constructive branch of the MZI with no observable degradation of the signal quality, allowing it to be normally detected by a receiver     

Virtual Generalized Mueller Matrix Method for Measurement of Complex Polarization-Mode Dispersion Vector in Optical Fibers

A virtual generalized Mueller matrix method (VGMMM) is proposed to measure the complex polarization-mode dispersion (PMD) vector in a fiber system with polarization-dependent loss or gain. VGMMM can attain the low-noise high-resolution PMD data using a relatively large frequency step, without the knowledge of input polarization states. VGMMM combines the advantages of both matrix-based methods and differentiation-based methods and overcomes their shortcomings. Experimental results on a fiber system confirm the validity and accuracy of VGMMM     

Direct Measurement of Vector Polarization-Mode Dispersion From Repeated Random Data by Use of Linear Optical Sampling

Polarization-dependent optical sampling techniques measure the complex electric field, allowing one to monitor the degrading effects of a communication channel. Here we show the ability to extract the polarization-mode dispersion of the transmission channel from a remote measurement of transmitted repeated 10-Gb/s differential phase-shift keying modulated data. This approach is independent of modulation format and data rate. We demonstrate results both with and without referencing to the laser phase. We achieve a differential group delay resolution of 0.2 ps for an unreferenced measurement.      

微波互作用系统对铯原子钟准确度的影响

本文对铯束管中微波互作用系统影响铯原子钟频率准确度的因素进行了理论分析和实验研究,提出了如何减小这些因素影响的建议和方法。     

色散补偿方式对相位调制系统中相位噪声的影响

分别推导了相位调制系统中采用色散预补偿方式和后补偿方式下非线性相位噪声的计算公式,基于此对这两种色散补偿方式下的相位噪声、功率容限以及最优信号峰值功率进行了详细的分析和讨论,结果表明:采用色散预补偿方式较后补偿方式能更有效地抑制非线性相位噪声,其对非线性相位噪声的抑制能力随着信号能量、放大自发辐射(ASE)的功率谱密度以及传输距离的增加而提高;同时,色散预补偿系统具有更高的功率容限;色散的作用使系统的最优信号峰值功率增大,最佳相移大于1rad;色散预补偿系统的最优信号峰值功率大于色散后补偿系统。     

时钟抖动和相位噪声对数据采集的影响

随着采样频率和A/D变换器位数的增加,时钟抖动和相位噪声对数据采集系统性能的影响更加显著.从相位噪声的双边带功率谱密度出发,详细分析了相位噪声和周期间抖动之间的联系,指出了相位噪声的不同频段对周期间抖动的影响,讨论了数据采集信噪比与时钟抖动和相位噪声之间的关系;并通过仿真给予定量的计算,对时钟源和数据采集系统的设计提供了一些建议;最后,利用某雷达数据采集系统进行实验,给出了相关实验结果.     

开放系统中位相涨落对增益和色散的影响

本文研究了开放的简单三级级无粒子数反转激光系统中驱动场位相涨落对增益和色散的影响。发现,驱动场位相涨落将导致有限线宽,随着这个线宽的增加,增益和色散将单调地减小,当线宽不为零时,在零吸收有够产生的大折射率,这与从封闭的V型三能级系统得到的结论大不相同。     

基于FPGA的任意相位时钟管理器的设计

在通信双方为同源时钟的前提下,为保证时钟在接口处把所有数据都正确采样进来,利用Altera的综合开发平台Quartus II,实现了采样时钟相位根据输入数据相位自动调整,使采样时钟能找到最佳的采样时间来采样外来数据。任意相位时钟管理器可以产生高精度动态相位的时钟信号。     

Effects of Long-Term Clock Instability on Master-Slave Networks

Two types of master-slave networks are investigated: oneway and two-way master-slave networks. The one-way master-slave System is a generalization of the well-known hierarchical master-slave tree system. The two-way master-slave system is a novel concept. Sufficient stability conditions are given for both network types. After synchronization is achieved, the frequency drift rate of all oscillators in the network approaches the frequency drift rate of the master oscillator. The steady-state frequency differences between the oscillators and their variances are computed for six network configurations of practical interest. A performance comparison for different network connectivities shows that the two-way master-slave system with a star configuration has the best performance.     

一种低相位噪声采样时钟源的设计

分析了锁相环频率合成器与数字直接频率合成器的原理,阐述了二者性能的优劣。并在此基础上设计了一款低相位噪声的采样时钟源。该频率源结合锁相环和直接数字频率合成器的优势,在75 MHz时相位噪声可达-119 dBc@1 kHz、-116 dBc@100 kHz。     

基于双向输入型鉴相器锁相环技术的光时钟恢复系统

介绍了一类基于双向输入型鉴相器锁相环技术的时钟恢复系统。分别讨论了基于对称和非对称输入型鉴相器的时钟恢复实现方案,并提出了一种基于对称输入型鉴相器锁相环技术的解复用分离型时钟恢复方案。     

相位噪声测量在时钟偏斜测试中的应用

随着系统数据速率的提高,时钟抖动分析的需求也在与日俱增.在高速数据链路中,时钟分配器的时钟偏斜会影响系统的整体性能.分析了相位噪声和时钟抖动的对应关系,通过时域到频域的转换,实现了时钟偏斜参数的高精度测量.以一款时钟分配器为例,进行了实际测试验证.     

The Effects of Clock Drift Upon the Synchronization of Digital Communications Networks

Effects of clock drift on the performance of a discretetime control system for synchronizing all the clocks in a digital communications network are shown by a detailed analysis of the dynamic behavior of the simple case of a two-node network. With a unidirectional frequency drift of one or both oscillators, it is shown that the buffer stores eventually overflow. A more general linear control scheme is also discussed.     

基于锁相环的时钟相位插值电路设计与实现

千兆以太网收发器模拟前端的时钟恢复电路要求锁相环(PLL)能够提供"128相"等相位差的时钟信号.为了满足此要求,设计了一种相位插值电路,它在不增加四级VCO级数的基础上,对其输出时钟的相邻相位进行16插值.仿真结果表明,该插值电路使PLL的输出时钟相位从8相增加至128相,证明了电路的有效性.     

光纤光栅色散效应对相控阵天线影响的研究

研究光纤光栅色散效应对基于光栅的相控阵天线的影响,该相控阵天线基于典型的离散光纤光栅阵列的实时延迟线结构。分析表明,单边带调制方式可以有效地克服色散效应对所恢复的微波信号幅度的影响。但光纤光栅色散效应对所恢复的微波信号相位的作用仍影响实时延迟线的性能,从而改变天线阵列最大辐射方向。通过选择合适的天线元之间的距离以及提高相邻通道所对应的光纤长度差可以降低光纤光栅色散效应的影响。     

色散对ROF系统性能的影响

阐述了色散的基本原理,通过对ROF(radio over fiber)系统的研究指出,随着传输速率的升高,光纤色散会限制系统的传输性能,严重的还会造成信号的失真.在幅度调制方式(DSB调制与SSB调制)、波长数调制(单波长调制与双波长调制)及传输中对信号所造成的啁啾现象的3个不同方面,综合分析了色散对ROF系统影响,得出了SSB调制要优于DSB调制的结论,为改善ROF系统的性能提供了一定的理论基础.