Link Performance Monitoring Technique for Measuring Residual Chromatic Dispersion of Optical Links

We propose a simple technique for measuring the residual chromatic dispersion (CD) of optical links based on two single-sideband tones. The residual CD was measured with an accuracy of +/- 10 ps/nm, regardless of the effect of self-phase modulation.     

光纤通信中的色散问题

介绍了光纤通信中的色散问题,并对其解决方法进行了归纳讨论。     

波分复用系统中四波混频引入光信噪比的恶化及其抑制

本文对陆上级联接掺铒光纤放大器（ＥＤＰＡ）波分复用光纤通信系统中国波混频所造成的各个光信道光信噪比的恶化提出了一套计算方法，并结合常规单模光纤及一种特殊设计的色散位移光纤进行了分析计算。结果表明：在四波混频所引入的光信噪比恶化中，因新生频率分量导致的噪声增加一般远大于光信号功率的减弱。不等信道间隔划分能有效地避免四波混频的影响，而光滤波器的带宽应在允许范围内尽量压窄。对采用色散补偿技术的级联ＥＤＦＡ波分复用系统，在同一光中继段内，使常规单模光纤置于特殊设计的色散位移光纤之前，能进一步减少四波混频带来的光信噪比的恶化。     

Nonlinear Distortion Due to Cross-Phase Modulation in Microwave Fiber-Optic Links With Optical Single-Sideband or Electrooptical Upconversion

A new analytical model is presented to study nonlinear distortion due to cross-phase modulation in dispersive and nonlinear wavelength-division-multiplexing microwave fiber-optic links. The model is not based on the pump-probe approach. Hence, it can be used to analyze a larger variety of links, including, in particular, electrooptical upconversion links. Our simulations and experiments show that the model predicts the nonlinear distortion due to cross-phase modulation quite accurately, even when the modulating microwave frequency is in tens of gigahertz and the fiber length is in tens of kilometers. Detailed analyses of the distortion due to cross-phase modulation for links with optical single-sideband modulation are presented. Measured results for optical single-sideband are shown to match our theoretical predictions very well. Our results show that the nonlinear distortion due to cross-phase modulation can be a limiting factor for optical launch power in wavelength-division-multiplexing microwave fiber-optic links; moreover, the maximum possible nonlinear distortion level for a higher frequency may be lower than that for a lower frequency. Also presented are some simple approximations for a quick estimate of the level of the nonlinear distortion     

Interchannel Crosstalk Reduction in an Analog Fiber Link Using Dispersion Management

It has previously been shown that dispersion compensation can dramatically affect the interchannel crosstalk in a multichannel analog fiber transmission link. In this work, we use a genetic algorithm to find five-segment dispersion maps that yield low crosstalk levels over two octaves of microwave-frequency bandwidth when amplitude modulation is used. The genetic algorithm suggests that optimal dispersion maps have low residual dispersion. Despite the genetic algorithm's ability to optimize dispersion maps with many fibers, it is possible to obtain similar crosstalk levels from a simpler two-segment design whose dispersion is fully compensated.     

一种克服色度色散影响的四倍频光毫米波信号产生方法

提出一种克服色度色散影响的四倍频光毫米波信号产生方法。该方法使用一个双驱动马赫曾德尔调制器,通过调整上、下两路射频信号的相位差、直流偏置点、调制系数以及基带信号增益,将数据信号仅调制到四倍频光毫米波信号的一个2阶边带上传输,解决了色度色散引起的码元走离问题,有效增加了传输距离。理论分析和仿真实验结果表明,信号在光纤中传输120 km后眼图仍然十分清晰,经过60 km传输后的功率代价约为0.45 dB。另外,基于频率再用技术,没有调制数据的另一个2阶边带信号还可以作为全双工光纤无线通信(RoF)系统的上行链路光载波,简化了基站配置。仿真实验结果表明,双向2.5 Gbit/s数据信号在光纤中传输40 km后,功率代价小于0.6 dB。     

Linearization of Phase-Modulated Analog Optical Links Employing Interferometric Demodulation

We present a linearized phase-modulated analog photonic link that utilizes parallel interferometric demodulation to suppress the third-order intermodulation distortion present in the link. By utilizing two parallel interferometers with different differential delays, we are able to balance the third-order distortion in the output photocurrent and achieve a fifth-order limited link response. We demonstrate shot noise-limited spurious-free dynamic ranges of ~ 130 dB (1-Hz bandwidth) at ~ 1 GHz for a total DC photocurrent I_dc~ 8 mA and ~ 131 dB (1-Hz bandwidth) at ~ 5 GHz for a total DC photocurrent I_dc ~ 7 mA . These results represent a nearly two order-of-magnitude improvement in dynamic range over conventional intensity- or phase-modulated analog photonic links for a fixed received photocurrent.     

Analysis of Chromatic Dispersion Variation in Optical Fiber under Large Stretching

In the frame of a large-stroke optical fiber delay line implementation, using the ability of silica fibers to induce large and variable group delay when they are stretched, we intend to express theoretically the evolution of second-order chromatic dispersion versus fiber stretching. Both an experimental analysis and a numerical analysis are presented in this paper. The main result consists of the observation of a linear variation of the second-order chromatic dispersion versus a 0 to 32-cm group delay variation. The numerical simulation exhibits a discrepancy of 10% with respect to the experimental results.     

几种计算光纤色散特性的数值方法

应用解超越方程法、矩阵微扰法、伽辽金法和有限差分法计算光纤色散特性。大量的计算实例表明：它们都能快速、准确地计算光纤色散特性。     

Phase Shift Technique for the Measurement of Chromatic Dispersion in Optical Fibers Using LED's

A sinusoidal technique is reported, which allows simple and accurate measurements of chromatic dispersion in optical fibers. It is based on the phase shift which a sinusoidally modulated light beam undergoes while traveling along a fiber when its wavelength is changed. The choice of a multiple LED's source permits the continuous spectral covering from 750 to 1600 nm; easily available instrumentation and devices are needed for the measurement setup. The technique is reported in detail by showing results obtained in multimode fibers; statistical evaluation of its accuracy and a comparison with conventional methods are carried out. An accuracy of a few picosecond in relative delay and of /spl I.chemc/1 ps/nm /spl dot/ km in chromatic dispersion are demonstrated, that compare very favorably with the existing techniques.     

Erbium Amplifier Dynamics in Wireless Analog Optical Links With Modulator Bias Optimization

Modulator bias optimization is a technique used to improve the transmitted radio-frequency power of amplified analog optical links. However, when bias optimization is used, the mean optical power at the modulator output is dependent on the amplitude of the modulation signal. In this letter, we show how fluctuations of the modulation signal power, in conjunction with the dynamic behavior of the erbium optical amplifier, can deteriorate the transmission of data frames compliant to the 802.11 a/g IEEE protocol. Optical and electrical compensating methods, based on mean power clamping at the modulator output, are proposed, and their efficiency in restoring a high-quality transmission is demonstrated     

A Contribution to Study the Effect of Multipath Coherent Crosstalk Due to Optical Network Nodes on DPSK Signals

Multipath coherent crosstalk, due to multiple replicas of the main signal in optical networks, is examined in terms of the potential impact on the performance of optical differential phase-shift keying signals. Analytical expressions are derived and presented for both the moment generating function of the decision variable and the average error probability. A detailed comparison with incoherent crosstalk is also performed. Using symbol-conditioned analysis for this crosstalk, it is shown that for low optical signal-to-noise ratio penalties, the coherent crosstalk is more damaging than the incoherent one.     

啁啾光脉冲在高阶色散控制光纤链中的稳定传输

基于一种二阶和三阶色散补偿的光纤级联系统模型 ,用数值法对啁啾皮秒光脉冲作了传输模拟。结果表明 ,完全补偿的高阶色散控制系统消除了三阶色散所引起的脉冲边沿部的振荡 ,减弱了脉冲峰的时间移动 ;另外 ,在确定的配置下 ,给输入脉冲附加一最佳的频率啁啾 ,可使得色散控制孤子稳定传输。脉冲宽度和啁啾以及光强度都围绕在初始值附近波动 ,在每个补偿周期末端 ,基本恢复到初始值 ;最佳啁啾的选取与二阶色散的配置有关 ,与三阶色散的配置无关 ;文中画出了 10 0Gbit/s码率的 64位随机高斯光脉冲序列在完全补偿系统中传输 10 0 0 0km后的眼图。由清晰的眼图可知 ,这种完全补偿系统减弱了脉冲之间的相互作用     

Chromatic Dispersion Induced Semi Optical Pulse Stretching Approach to Beam Steering Applications of Phase Array Antenna

Spallation analysis is one of important research directions in impact dynamics. By combining the newly developing Peridynamics (PD) theory, the spallation phenomenon of concrete is numerically simulated using C language and MATLAB programming. The factors that may affect the spalling are verified: the type of pulse load, the geometric size of the model and the action time of pulse load. The dynamic response of spallation of three-dimensional concrete columns under different pulse loading forms (rectangular pulse, triangular pulse and exponential pulse) is analyzed. (1) Under the same impulse effect, only one spalling occurs in the rectangular pulse, and no multiple spallation occurs when the pulse amplitude increase. Exponential and triangular pulses can produce multiple spallation phenomena, and the time for the first spallation phenomenon is rectangular pulse?<?triangle pulse?<?exponential pulse. (2) The effect of the same linear triangle pulse on spalling of concrete columns with different lengths (100 mm, 200 mm and 300 mm) is analyzed. The triangle pulse can cause single or multiple spallation, which is related to the length and size of the model. (3) Finally, by changing the number of time steps of the pulse load, the different spalling phenomena of triangular pulses are analyzed. The thickness of the first layer increases significantly with the increase of the action time.

     

Limitation Due to Signal-Clipping in Linearized Microwave-Photonic Links

Microwave-photonic links with ideally linear transfer functions (class A or B) are limited by distortion due to signal clipping. This limitation is investigated theoretically and through numerical simulation, with results for up to 50 input carriers confirming analytic results based on a Gaussian input distribution. An ultimate clipping-free dynamic range of 183.5 dB - Hz is predicted for an ideal class-B link, up to 70 dB greater than achieved with conventional links.     

The Nonlinear Impairments Due to the Data Correlation Among Sub-Carriers in Coherent Optical OFDM Systems

Resulted from the narrow frequency interval, the nonlinear impairments are strongly related with the data correlation of the optical orthogonal frequency division (OFDM) symbol in coherent optical OFDM (CO-OFDM) system, which is very different from the traditional WDM optical communication systems. The concept of normalized accumulative correlation coefficient (NACC) is proposed to evaluate the data correlation of the OFDM symbol. The parameter phi is presented to describe the influence of the systematic physical configuration on the nonlinear impairments. The dependence of the nonlinear impairments on the data correlation is investigated and revealed analytically. Closed form expressions are presented to calculate the noise spectrum, total nonlinear noise energy and noise signal ratio (NSR) under the condition that phi les 0.2, which is valid for most practical CO-OFDM system. The NSR is proportional to the NACC and phi². Simulation results are well consistent with analytical calculations when phi les 0.2.     

Fast Characterization of Dispersion and Dispersion Slope of Optical Fiber Links Using Spectral Interferometry With Frequency Combs

We demonstrate fast characterization ( $sim$1.4 $mu hbox{s}$) of both the dispersion and dispersion slope of long optical fiber links ( $sim$25 km) using dual quadrature spectral interferometry with an optical frequency comb. Compared to previous spectral interferometry experiments limited to fiber lengths of meters, the long coherence length and the periodic delay properties of frequency combs, coupled with fast data acquisition, enable spectral interferometric characterization of fibers longer by several orders of magnitude. We expect that our method will be useful to recently proposed lightwave techniques like coherent wavelength-division multiplexing and to coherent modulation formats by providing a real-time monitoring capability for the link dispersion. Another area of application would be in stabilization of systems which perform frequency and timing distribution over long fiber links using stabilized optical frequency combs.      

Generation of Flat Supercontinuum in a Single-mode Optical Fiber with a Convex Chromatic Dispersion Profile

A single-mode optical fiber with a convex chromatic dispersion profile is proposed for generating a flat supercontinuum(SC).The fiber has normal dispersion and the dispersion parameter D(λ,z) is a convex function of wavelengths.It is shown from the numerical results that the chromatic dispersion,the flatness of the dispersion curve and the pump conditions have significant effect on SC generation.A flat and broad SC without strong residual pump component can be obtained when the pump wavelength is set in the...     

以太网中多模光纤系统色散问题的解决方案

由于目前以太网中敷设的多模光纤系统存在严重的色散问题,限制了其在10 Gb/s以太网中的应用,因此如何有效地降低多模光纤的色散是10 Gb/s多模光纤以太网应用的关键.对目前用于解决10 Gb/s多模光纤以太网中色散问题的技术进行了归类,分析了各种技术的优缺点.