Statistical properties of stimulated Raman crosstalk in WDM systems

The crosstalk variance of stimulated Raman crosstalk in wavelength-division-multiplexing (WDM) systems is derived analytically in a closed-form formula for all systems with different walkoff length. The probability density function (pdf) of stimulated Raman crosstalk is found to be lognormal distribution (Gaussian distribution in decibel scale). Both power penalty and power limit induced by Raman crosstalk are evaluated and can be applied to single- and multispan WDM systems     

Generalized root-mean-square momentum method to describe chirpedreturn-to-zero signal propagation in dispersion-managed fiber links

We present a generalized momentum method to describe evolution of the root-mean-square (rms) (averaged over time) optical pulse characteristics in dispersion-managed fiber lines. A closed system of the ordinary differential equations is derived for the rms pulse power, width, and chirp. The developed method can be useful for massive numerical simulations required to optimize wavelength-division-multiplexing dispersion-managed transmission using chirped return-to-zero format     

玻璃光纤中的瞬态受激喇曼散射

用峰功率大于10~7瓦的0.53微米微微秒光脉冲序列激发一根20米长的锗磷硅玻璃光纤,观测到稳定的15级以上斯托克斯和8级以上反斯托克斯散射。喇曼频移为430厘米~(-1)。散射光频谱范围为0.45～1.00微米。受激喇曼散射的转换效率大于50％。     

Nonlinear crosstalk due to stimulated Raman scattering in a two-channel wavelength-division-multiplexed system

The effects of stimulated Raman crosstalk on two binary PCM channels, wavelength-multiplexed in a single optical fibre, are minimised by optimising the ratio of powers launched into each channel. The longest repeater spacings that could be achieved by increasing the launched powers are thereby obtained for two WDM channels of equal group velocity.     

Quantitative analysis of Rayleigh crosstalk in Raman amplifiers

Exact and approximate analytical formulas for the inband crosstalk caused by discrete reflection followed by Rayleigh backscattering are derived. Also, a simplified expression for the double Rayleigh backscattered power is found and the total crosstalk in terms of elementary functions is calculated. Results of measurements performed in a nonzero dispersion-shifted fibre agree with theoretical predictions within 1 dB.     

Statistical analysis of crosstalk accumulation in WDM networks

Accumulation of inband crosstalk in all-optical networks is studied. By applying statistical methods, we have investigated how inband crosstalk accumulation influences the performance of optical networks of different configurations. Our study shows that there exists a delicate dependence between network topology and robustness with respect to accumulation of inband crosstalk. A method is proposed to design optical networks with optical paths satisfying a certain level of inband crosstalk performance     

Analysis of interchannel crosstalk in a dispersion-managed analog transmission link

A technique for computing the effect of cross-phase modulation (XPM) on two copropagating analog channels in an optical fiber link is presented. In this approach, the interaction between the two channels is linearized by keeping the self-phase modulation (SPM) and XPM interactions in the strong optical carrier components only at lowest order and then at the next order, deriving the effect on the modulation components of both channels when the optical carrier is strong relative to the other components of the channel. In contrast to some previously suggested approaches, it is not assumed that the pump is undistorted, and therefore, this method accurately describes distortions due to SPM, XPM, and dispersion management in both channels. This method is easily applied to systems with multiple spans employing dispersion management with loss and gain. The expressions for the received radio frequency power and crosstalk between the two channels when direct detection is used are then provided. Using this approach, new expressions for the amplitude modulation and phase modulation modes of the two channels are derived, and the way they exchange energy when SPM, XPM, and dispersion are all considered is explained. This method yields excellent agreement between theory and experimental data.     

Dynamics of stimulated Raman scattering in double-clad fiber pulse amplifiers

A systematic analysis on dynamics of stimulated Raman scattering (SRS) in highly pumped ytterbium-doped double-clad fiber amplifiers during amplification of nanosecond pulses at tens-of-kilohertz repetition rates is presented. Energy and waveform evolutions of signal and Raman pulses in the amplifiers under forward, backward and bidirectional pump are depicted respectively. In consideration of the SRS components and incurred energy loss at the amplifier output, the detrimental effects of SRS on signal amplification for three pumping methods are quantitatively compared and comprehensively illustrated upon different signal, fiber and pump conditions. To avoid the performance deterioration, some limitations are also discussed.     

Theory of optimal power budget in quasi-linear dispersion-managed fibre links

A theory of an optimal distribution of the gain of in-line amplifiers in dispersion-managed transmission systems is developed. As an example of the application of the general method, a design of the line with periodically imbalanced in-line amplification is proposed.     

高功率光纤激光器受激拉曼散射致模式不稳定研究

通过稳态速率方程和热传导方程建立了高功率光纤放大器热光耦合的有限元模型,利用该模型对受激拉曼散射致模式不稳定效应进行了数值研究。对增益光纤为25/400μm的正向泵浦激光放大器,受激拉曼散射导致激光器信号光高阶模比例上升,当高阶模的比例达到5左右时,模场发生畸变,信号光出现了百毫秒量级的模式耦合,这与实验中观察到光强波动现象一致。本文仿真模型为研究高功率光纤放大器中受激拉曼散射和模式不稳定的关系提供了分析手段。     

基于光子晶体光纤的受激拉曼散射全光波长转换研究

基于光纤中前向瞬态受激拉曼散射效应分析理论,利用光子晶体的高非线性特性,对光子晶体光纤拉曼波长转换进行了数值分析,并建立了全光波长转换设计方案的理论模型,给出了设计原理框图及实现方法。用OptiSystem对四路探测光进行波长转换仿真,仿真结果表明:所设计的全光波长转换器同时对四路探测光实现波长转换,转换输出的信号光码型和输入泵浦信号光码型一致,并且所得到的眼图线迹清晰,眼睛张开度良好。论证了该设计方案可行。     

Complete analysis of sideband instability in chain of periodic dispersion-managed fiber link and its effect on higher order dispersion-managed long-haul wavelength-division multiplexed systems

We present for the first time a complete theoretical analysis of sideband instability (SI) that occurs when two kinds of fibers with different characteristics are concatenated to form a dispersion-managed fiber link. In the analysis, the following three cases are taken into account: case (a) when a dispersion-management period is larger than an amplification period, case (b) when the two lengths are equivalent, and case (c) when a dispersion-management period is smaller than an amplification period. We find that the SI gain peak appears at frequencies determined by the larger of the two variation periods. Moreover, for all three cases, the magnitude of the SI gain reduces with the increase in strength of dispersion management. Next, we focus on the fiber link using the combination of standard single-mode fiber and reverse dispersion fiber, which is widely used for simultaneously compensating second- and third-order dispersion. By computer simulation, it is shown that in wavelength-division-multiplexed systems, SI still induces significant degradation in channels located at frequencies where SI induced from other channels arises. By reallocating the channel frequency to avoid the SI frequency, the transmission performance is improved significantly.     

用光纤获得十级受激喇曼散射

本文报导了用多模光纤获得受激喇曼散射的实验研究。用480米长、多模、低损耗的梯度型石英光纤,用重复率为5次/秒和10次/秒、脉宽7毫微秒、功率0.7兆瓦的 YAG:Nd 倍频532毫微米的激光泵浦,获得了从546～702毫微米的十级斯托克斯受激散射。     

Statistical approach to end-to-end dispersion budgeting in single-mode fiber links using multilongitudinal-mode lasers

This paper presents a statistical analysis to the end-to-end chromatic dispersion budgeting in single-mode fiber links which employ multilongitudinal-mode laser transmitters around 1.3 or 1.55 μm regions. This is a novel approach which is relevant for upgrading the "bit rate × distance" of those already installed 400- and 565-Mbit/s fiber links.     

Analytical model for Raman noise figure in dispersion-managed fibers

We derive an exact and a closed-form approximate analytic formula for effective lumped Raman noise figure in backward-pumped dispersion-managed fibers (DMFs) of arbitrary topology. Within the single-pump small-signal amplification model, important effects such as unequal loss coefficients at pump and signal wavelengths or splice loss for the pump and the signal between the DMFs' sections are taken into account. Theoretical results agree well with the noise figure measured in a symmetric DMF. The developed approach can be used to optimize the noise performance of DMFs.     

Statistical analysis of interferometric crosstalk: theory andoptical network examples

General, statistical properties of accumulation of interferometric crosstalk due to a number of interfering signals are analyzed. The probability density function of the total crosstalk is derived as function of the sum of the incoherent crosstalk contributions associated with the interfering signals, Because the total crosstalk level can be expected to vary only slowly as compared to the time duration of one bit, the probability p that the total crosstalk exceeds a maximum tolerable value is introduced as a parameter in the crosstalk and bit error rate analysis of optical networks. General computations show that the crosstalk requirement on optical network elements may be significantly relaxed if it can be accepted that it is possible, although most unlikely, that the total crosstalk may exceed this maximum tolerable value. The statistical crosstalk model is then illustrated by investigation of optical network examples with respect to their crosstalk and transmission properties, and, finally, compared with previous crosstalk models     

分立式拉曼光纤放大器性能的试验与研究

文章介绍了分立式拉曼光纤放大器(RFA)的概念，同时给出了在高非线性光纤基础上进行分立式RFA性能测试的部分实验结果．通过实验本身，也证明了这种方案的可行性．     

乙基苯液芯光纤中受激喇曼散射产生超宽连续谱光源

本文使用乙基苯液芯光纤,获得高阶斯托克斯线,各阶线呈以红移为主的反常加宽。加宽后从一阶斯托克斯线至五阶斯托克斯线光谱联成一片,形成从562.1nm至700nm的连续超宽的相干辐射。     

Reduction of Raman MPI and noise figure in dispersion-managed fibre

Raman amplification in dispersion-managed fibre is studied experimentally. In positive-dispersion (+D)/inverse-dispersion (-D) configuration, severe multipath interference impairments at high Raman gain are observed. These are eliminated by using the +D/-D/+D configuration. In addition, the Raman gain in the +D/-D/+D configuration starts earlier in the span, improving the noise figure dramatically over conventional transmission fibres     

双向泵浦受激拉曼散射增益谱平坦光纤放大器

研究现有的拉曼光纤放大器(Raman Fiber Amplifier,RFA)增益谱平坦化技术的不足,提出一种新型的拉曼光纤放大器的设计,即双向泵浦受激拉曼散射增益谱平坦光纤放大器。利用受激拉曼散射增益谱几乎在450cm-1波数处形成的对称结构,利用前向泵浦与信号光产生的频移对信号光进行放大作用,同时利用后向泵浦与信号光产生的频移对信号光进行补偿性的放大作用,从而实现双向泵浦受激拉曼散射增益谱平坦光纤放大器的设计。通过MATLAB的仿真验证,所设计的放大器增益平坦度高,信号光功率增益大,可实现双向泵浦受激拉曼散射光纤放大器的平坦化。