Cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in dispersion compensated WDM transmission systems

The basic mechanism of cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in a periodically dispersion compensated transmission line has been investigated. Ordinary differential equations have been derived using variational analysis to estimate the phase fluctuation and the analytical result is verified by numerical simulations based on split-step Fourier method. We therefore explore the impact of different dispersion compensation maps on phase fluctuation for 10 Gb/s and 40 Gb/s WDM transmission systems. The effects of initial pulse spacing between channels, channel spacing and residual dispersion on phase shift have been studied. We find that cross-phase modulation induced phase fluctuation can be mitigated by proper adjustment of channel spacing and/or residual dispersion.     

Theory of average pulse propagation in high-bit-rate optical transmission systems with strong dispersion management

A theory of signal transmission in high-bit-rate optical communication systems with large variations of dispersion (strong dispersion management) is presented. It is found that the averaged propagation of a chirped breathing optical pulse along the line is described by the nonlinear Schrödinger equation with an additional parabolic potential. The shape of the averaged pulse is intermediate between the sech-type soliton and a Gaussian pulse. The rapidly decaying Gaussian wings of such pulses allow denser information packing in comparison with the use of sech-type fundamental solitons.     

Experimental study on pulse propagation characteristics at normal dispersion region in dispersion flatted fibers

Pulse propagation characteristics at normal-dispersion region in dispersion-flatted-fibers are experimentally investigated by employing the second-harmonic generation frequency-resolved optical gating (SHG-FROG) method. It is found that the experimental results are consistent with the theoretical prediction. The initial optical pulse with negative chirp is compressed for nonlinear effect in the normal-dispersion fiber, and it evolves into near Gaussian pulse. Temporal width of the optical pulse decreases with the increase of the input power and propagation distance. The output pulse width for small dispersion is less than that for great dispersion at the same input power. The spectrum of the output pulse is still symmetrical about the central wavelength, and is broadened with the increase of input power. The spectral width of the output pulse is much wider than the input spectral width.     

Effects of intermodal dispersion on short pulse propagation in multi-core fibers

The effects of intermodal dispersion on ultrashort optical pulse propagation through multi-core fibers are analyzed theoretically, which has been ignored in previous studies. A three-core fiber with collinear and triangular configuration and a four-core fiber are considered. We demonstrate with numerical examples that the intermodal dispersion can cause pulse breakup effect in multi-core fibers.     

高斯脉冲在半导体光放大器中传输的解析表征

采用解析方法,在考虑材料损耗和色散的情况下,详细研究了无啁啾高斯脉冲和啁啾高斯脉冲在半导体光放大器中传输的物理过程,分析了强度增益、脉冲宽度和频率啁啾与线宽增强因子、色散系数、小信号增益特征参数及初始啁啾之间的关系。结果表明:当输入变换极限的高斯脉冲时,色散会引起增益压缩,脉冲展宽和频率啁啾;同样情况下,线宽增强因子越大,脉宽加宽越明显,输出脉冲啁啾越大,且随着线宽增强因子的增大,输出脉冲啁啾极大值向特征参数值较小的一边移动。当输入啁啾高斯脉冲时,初始脉冲啁啾越大,增益压缩越明显,啁啾系数为正时,脉冲单纯展宽,输出啁啾随特征参数的增大而逐渐减小,啁啾系数为负时,初始啁啾与群速度色散导致的啁啾相互竞争,致使脉冲先被压缩后被展宽;脉冲最窄处对应的特征参数随线宽增强因子的增大而先增大后减小,输出啁啾随特征参数的增大而经历振荡后趋于平稳。     

Mitigation of phase noise in dispersion compensated quasi-linear optical transmission systems: Analysis

We theoretically investigate the phase noise in quasi-linear optical transmission systems and study the mitigation of phase noise by properly choosing periodic dispersion compensation and amplification. Variational method is used to deduce the analytical formula for calculating the phase fluctuations of a Gaussian pulse. The analytical predictions are then checked against direct simulations by numerically solving the nonlinear Schrödinger equation. We find that stronger dispersion compensation maps can be used to reduce phase noise and it can be further mitigated by modifying the dispersion map appropriately. It is also found that shorter amplifier spacing yields lower phase noise. We also explore the effect of pre-, post- and bi-end dispersion compensation configurations on phase noise with full compensation and check the reduction of phase noise along the fiber link.     

Comparison of soliton robustness with respect to polarization-mode dispersion with first-order polarization-mode dispersion compensated linear systems

Soliton robustness to polarization-mode dispersion (PMD) is compared, both analytically and numerically, with that of linear pulses that use first-order PMD compensation. It is found that soliton robustness to PMD is comparable with first-order PMD compensation and in some cases is even better. The effects of soliton control methods on soliton robustness to PMD were also investigated, and it was found that soliton control methods can significantly improve the soliton's robustness to PMD, particularly for long-distance systems.     

Multiscale pulse dynamics in communication systems with strong dispersion management

The evolution of an optical pulse in a strongly dispersion-managed fiber-optic communication system is studied. The pulse is decomposed into a fast phase and a slowly evolving amplitude. The fast phase is calculated exactly, and a nonlocal equation for the evolution of the amplitude is derived. In the limit of weak dispersion management the equation reduces to the nonlinear Schr?dinger equation. A class of stationary solutions of this equation is obtained; they represent pulses with a Gaussian-like core and exponentially decaying oscillatory tails, and they agree with direct numerical solutions of the full system.     

The characters of dense dispersion managed soliton in optical fiber transmission systems

The properties of ultra-short dense dispersion-managed soliton (DBMS) in optical fiber links are investigated. They show some excellent characters, such as, reducing pulse's breathing extent greatly, facing fewer mutual interactions and tolerating larger local dispersion. In general, DBMS is more stable than a conventional dispersion-managed soliton in high-capacity systems. Excessively dense dispersion compensation is more suitable for systems with weak nonlinear effect.     

单模光纤中三阶色散对超短光脉冲传输的影响

基于超短光脉冲在单模光纤中传输时高阶非线性效应的影响。应用非线性薛定谔方程(HONLS)理论,考虑光纤色散三阶效应,推导出无啁啾的高斯脉冲沿光纤传输时脉冲变化的表达式,并对理论结果进行了数值模拟与分析。结果表明,三阶色散会引起光脉冲形状发生畸变,会在其前沿或后沿附近形成非对称的振荡结构。     

A modified split—step fourier method for optical pulse propagation with polarization mode dispersion

A modified split-step Fourier method (SSFM) is presented to solve the coupled nonlinear Schroedinger equation (CNLS) that can be used to model high-speed pulse propagation in optical fibres with polarization mode dispersion (PMD). We compare our approach with the SSFM and demonstrate that our approach is much faster with no loss of pre-chirped RZ(CRZ) formats in the presence of high PMD through this approach. The simulation results show that CRZ pulses are the most tolerant to high PMD values and the extinct ratio has a great impact on the transmission performance.     

Practical design rules for single-channel ultra high-speed dense dispersion management telecommunication systems

In this work, we establish some efficient and practical design rules for the implementation of single-channel ultra-high speed (>160-Gbit/s) telecommunication systems based on dense dispersion management. Moreover, we analyze some of actual implementation issues such as slope compensation scenario, junction losses, polarization mode dispersion and chromatic dispersion fluctuations.     

Microwave propagation in dense random media

Summary Using simple, approximate arguments, we obtain a formula that relates the average spacing between peaks in the transmitted intensityvs. wave frequency distribution of a single configuration of a random distribution of scatterers to the diffusion constant, sample thickness, and effective absorption length. The value of the diffusion constant obtained this way is found to be within 20% of the value obtained via intensity-intensity autocorrelation function techniques. The author of this paper has agreed to not receive the proofs for correction.     

Generalized Hermite–Gaussian functions and pulse propagation in optical fiber systems

Chirped Hermite–Gaussian functions shows outstanding potentialities in mathematical models for linear and non linear pulse propagation in optical fibers. We propose three generalized subclasses of Hermite–Gaussian functions as natural extension to the complex domain. We exemplify the properties of these subclasses by analyzing some relevant cases of pulse oscillatory dynamics governed by nonlinear Schrödinger equation with constant or periodic coefficfients.     

Transit pulse dispersion in PVK

Time-of-flight measurement show that the hole hopping mobility in polyvinycarbazole layers is independent of thickness between 3 and 80 μm. Long-tailed transit current profiles with “knees” are observed at all thicknesses and down to ?80°C, but scale only superficially with transit time. The discrete mobility is reconciled with the transit pulse dispersion by reference to Marshall's computer model of trap-controlled transport.     

Theory of guiding-center breathing soliton propagation in optical communication systems with strong dispersion management

We present a theory of chirped breathing pulse propagation in optical transmission systems with strong dispersion management. Fast changes of pulse width and chirp over one period are given by a simple model that is verified by direct numerical simulations. An average pulse evolution in the leading order is described by the nonlinear Schr?dinger equation, with additional parabolic potential that can be a trapping (when a grating is used) or a nontrapping (without a grating) type.