多路干涉对光纤拉曼放大器噪声因数的影响

考虑了多路干涉与拉曼自发辐射噪声具有不同的谱分布特性，推导出信号的背向瑞利散射导致的多路干涉对光纤拉曼放大器噪声因数影响的解析表达式，给出了考虑多路干涉后光纤拉曼放大器的噪声因数的光学测量方法。分析了不同开关增益、不同输入信号功率、不同增益光纤背向瑞利散射情况下多路干涉对光纤拉曼放大器噪声因数的劣化程度。随着拉曼增益的增加，输入信号功率越大、背向瑞利散射越大，多路干涉的影响越大。     

多泵浦光纤喇曼放大器的模拟分析

通过使用综合理论模型对不同配置条件下的多泵浦分布式光纤喇曼放大器的增益谱进行了数值模拟研究,该理论模型包含了瑞利散射、放大自发辐射和不同交互效应,包括泵浦与泵浦、泵浦与信号和信号与信号之间的交互与能量转移.模拟研究了泵浦源功率、泵浦源波长间隔及光纤损耗对喇曼增益谱的影响,结果表明设计多泵浦光纤喇曼放大器需要对泵浦源功率、泵浦源波长间隔光纤损耗谱进行综合考虑,需对泵浦源功率、泵浦源波长间隔进行合理配置.在本文的泵浦源波长设定条件下,考虑实际光纤的损耗谱特性,为了获得大的增益带宽和小的增益不平坦度,短波长泵浦源和最长波长的泵浦源需要更高的泵浦功率,中间波长泵浦源的功率应较低.     

反向抽运光纤喇曼放大器增益特性分析

将打靶法和龙格库塔法两种数值计算方法相结合,对反向抽运光纤喇曼放大器中信号光和抽运光相互作用的耦合微分方程进行数值求解.在分别选取不同参量且取不同值的条件下,详细分析了光纤长度、初始信号光功率、初始抽运光功率、光纤有效面积、喇曼增益系数及光纤对信号光与抽运光的损耗等参量对增益的影响,最后提出了有效提高增益的方法.     

基于硅波导的喇曼光放大器

在硅波导上添加反向偏压的PIN结构,当波导产生受激喇曼散射时,可以将波导中双光子吸收(TPA)产生的光生自由载流子扫出波导,降低了波导的非线性损失,极大地提高了硅波导中泵浦光对信号光的喇曼增益。为了应用已经非常成熟的硅工艺,并且应用硅波导使器件小型化,根据法布里-帕罗(F-P)腔和行波放大器理论,在硅波导两端的解理面蒸镀增透膜,应用这种波导的喇曼效应设计了一种光放大器,即基于硅波导的喇曼光放大器。建立了计算放大器增益的方程,给出了不同波导长度和输入功率情况下的放大器增益,得出适当增加波导长度和泵浦光功率可以得到较高喇曼增益的结论。基于硅的光放大器有较高的饱和功率且没有泵浦源的限制,通过调整泵浦激光的波长可以放大不同波长的信号光。     

一种新颖的宽带光纤喇曼放大器优化设计方法

介绍了一种新颖的宽带光纤喇曼放大器的优化设计方法.通过研究多波长后向泵浦光纤喇曼放大器的传输方程, 分两步来确定各泵浦波的频率及输入功率的大小.首先通过模拟煺火算法迭代出满足条件的泵浦波频率,然后利用平均功率分析方法,采用四阶阿当迭代方法计算出各泵浦波输入功率的大小,从而设计出具有较宽平坦增益带宽的光纤喇曼放大器.该算法是一种简单有效的优化方法.     

双向掺铒光纤放大器的特性分析

讨论了双向掺铒光纤放大器的结构方案,利用考虑放大的自发辐和北员耗影响的双向掺铒光纤放大器稳态放大速率方程模型分析的增益与掺铒光纤长度、输入信号光功率、帛运光功率及抽运方式等参数之间的关系,研究了单向和双向等功率抽运下正反向噪声系数随正反向信号光输入功率的变化行为。     

级联掺磷光纤喇曼激光器的解析优化

讨论了二级级联喇曼光纤激光器的解析解和优化设计.通过引入几何平均功率、增益因子和归一化光纤有效长度,将描述泵浦光和斯托克斯光沿喇曼增益光纤分布的微分方程组简化成代数方程组,在对泵浦光采用线性传播近似后,获得了二级级联喇曼激光器的解析解.所获得的解析解同数值模拟结果吻合得很好.利用该解析解可方便和快速地讨论级联喇曼激光器的优化设计,计算不同泵浦功率下的最佳光纤长度、输出光纤光栅反射率和转换效率.泵谱功率越大,最佳光纤长度越短,最佳输出光纤光栅反射率越小.     

硅波导受激喇曼散射放大信号光的数值模拟

提出了用连续泵浦光在硅波导中的受激喇曼散射对信号光进行放大的方法.建立了信号光和泵浦光在硅波导中传输的耦合方程,得到了计算信号光增益的理论模型.利用数值模拟结果,对泵浦功率沿波导的分布,信号光在不同波导长度以及输入功率情况下的增益等进行了分析和讨论.结果表明,适当增加波导长度和泵浦光功率可以得到较高喇曼增益的结论.     

光纤喇曼增益系数的简捷测量

基于小信号开关增益原理,采用抽运光-探测波法,利用SLD(超辐射激光二极管)作为宽带小信号探测光源,快速测量出了标准单模光纤(G.652)的频移为0.5～20 THz内的喇曼增益系数,测量结果和文献中已有的值基本吻合,所测得的光纤喇曼增益系数可用于光纤喇曼放大器的理论和实验研究,该方法同样可以对其他类型光纤的喇曼增益系数进行测量.     

双向反馈布里渊-喇曼光纤激光器输出特性

设计了一种双向反馈布里渊-喇曼光纤激光器,研究了布里渊泵浦对输出特性的影响.布里渊-喇曼光纤激光器由一段7km色散补偿光纤、1 455nm喇曼泵浦、可调谐激光器及双反馈环组成.喇曼泵浦功率固定在250mW,布里渊泵浦工作波段在喇曼峰值增益处附近,可得到较多波长数输出.随着布里渊泵浦功率增加,相邻的布里渊斯托克斯光和经背向瑞利散射的斯托克斯光之间功率差减小,同时各阶斯托克斯光平均强度增加并达到饱和.受色散补偿光纤中喇曼交叉增益影响,布里渊泵浦功率由1.8dBm增加到6.9dBm,输出多波长数先增后减.当布里渊泵浦功率为4.4dBm时,对应输出波长数最多,为37个,波长间隔0.078nm.     

Copropagating and counterpropagating pumps in second-order- pumped discrete fiber Raman amplifiers

The gains and noise figures of discrete second-order-pumped fiber Raman amplifiers utilizing copropagating and counterpropagating pump configurations were experimentally obtained, and the gain results were compared with computer simulations. It was found that the additional gain that is due to second-order Raman pumping is larger for the copropagating pumps than for the counterpropagating pumps, in agreement with simulations. In contrast to distributed second-order-pumped fiber Raman amplifiers, a slight increase in noise figure, by as much as ~1 dB was observed relative to the single-pump scheme. However, the advantages of second-order pumping in discrete amplifiers include greater flexibility in design of the gain distribution along the fiber and the ability to spectrally distribute the pump powers to avoid undesired nonlinear effects.     

Noise performance analysis of bi-directionally pumped distributed fiber Raman amplifiers with consideration of fiber nonlinearity and its impact on EDFA output OSNR

Under small-signal assumption, equivalent noise figure normalized by fiber nonlinearities (NENF) of bi-directionally pumped distributed fiber Raman amplifiers (BiDFRA) is derived. Amplified spontaneous Raman scattering noise and double Rayleigh scattering noise are both included. The relation between NENF and Raman gain, forward Raman gain percentage is investigated under different polarization factor and Rayleigh scattering coefficient. It agrees well with numerical simulation results. Based on the analytical expression, the optical signal-to-nose ratio (OSNR) improvement of hybrid pre-BiDFRA/erbium-doped fiber amplifier (EDFA) compared with sole EDFA is studied. It is shown that there is an optimum Raman gain and forward Raman gain percentage to maximize the OSNR improvement. Finally, some guidelines on BiDFRA design are proposed.     

Gain and Noise figure performance of erbium doped fiber amplifiers (EDFAs) and Compact EDFAs

In this paper, we compare the Gain and Noise figure characteristics of physical EDFAs and Compact EDFAs in an optical system consisting of cascade of both the amplifiers. We demonstrate the gain, noise figure variations of a forward pumped EDFA and Compact EDFAs as functions of Er³⁺ fiber length, injected pump power and up-conversion co-efficient. It is observed that the gain becomes constant when the length of both the amplifiers reaches above 20 m. The comparison shows that the higher gain with flatter output is obtained in case of Compact EDFAs than Physical EDFAs in a system consisting of chain of both the amplifiers. It is further investigated that the agreement between the Compact and Physical EDFA models is good up to 10 m with the no up-conversion co-efficient. Also, the noise figure obtained in case of Physical EDFA is higher than Compact EDFAs when same amplifier length is more than 20 m and then becomes constant for both the amplifiers.     

Effect of Cascading Amplification Stages on the Performance of Serial Hybrid Fiber Amplifier

Abstract

This study demonstrates simulation and experimental validation of a wideband serial hybrid Raman/erbium-doped fiber amplifier. Two configurations are adopted; in type A, a Raman amplifier is the first stage, and in type B, an erbium-doped fiber amplifier is the first stage. At low input signal power, the average gain level is 20 dB with a flat gain bandwidth of 40 nm for both configurations. The noise figure in type B is dominated by the erbium-doped fiber amplifier and produces lower values and flatter spectra than in type A. The gain of the proposed hybrid amplifiers is affected more by the second amplification stage.     

多波长双向抽运光纤拉曼放大器的优化设计

通过合理分析提出了便于计算多波长双向抽运光纤拉曼放大器信号及噪声功率的实用数值模型,给出求解信号和噪声功率的快速算法。在定义抽运方向度为前向抽运功率与总抽运功率值的比值后,通过对计算结果的分析发现信道平均放大自发辐射噪声功率随着抽运方向度的提高而单调递减;而信道平均双重瑞利散射噪声功率相对抽运方向度的变化曲线始终成U字形。不同的增益下存在对应的最优抽运方向度,在此抽运方向度下放大器总噪声最低。进而考虑在信号非线性失真的条件下提出了抽运方向度优化的衡量指标。优化后的多波长双向抽运方式不仅能保证对所有信道的平坦放大,而且其综合性能明显高于后向抽运方式。     

掺铒光纤放大器的理论模拟与全局分析

基于Giles模型并考虑了ASE噪音,对各种泵浦方式下的掺铒光纤放大器(EDFA)进行了数值模拟.提出了一种新的分析方法(增益噪音指数全局分析法),直观有效地分析了EDFA的增益和噪音指数与掺铒光纤长度和泵浦功率的依赖关系,并对各种EDFA的性能作了全面的比较.     

Fundamentals of optical amplifiers

The minimum noise figure of linear phase-insensitive amplifiers is 3 dB, according to the constraint of the uncertainty principle. Laser amplifiers, parametric amplifiers and Raman amplifiers obey the general quantum limit in an ideal case. A degenerate parametric amplifier is a phase-sensitive linear amplifier, and thus is a noiseless amplifier with a noise figure of 0 dB. The noise figure degradation in a practical amplifier and the signal-to-noise ratio design of an optical amplifier system are presented. Several other amplifier characteristics, such as signal gain, frequency bandwidth and saturation output power, are also discussed.     

Gain ripple minimization in fiber Raman amplifiers based on variational method

In this paper, the variational method is employed for minimizing the gain ripple of multi-wavelength fiber Raman amplifiers. The variance of gain spectrum of the fiber Raman amplifier is regarded as the cost function, restriction on total pump power and average gain is given as the constraints of the minimization problem. It is shown that the minimization problem with any necessary constraints on the pump powers, average gain and signal to noise ratio, is reduced to a two-point boundary value problem. The method gives the entire possible local and global solutions. The method is applied to different examples of fiber Raman amplifiers with different lengths from 25 km to 100 km and different numbers of pumps from 4 to 20 to determine the pump powers and wavelengths for minimum gain ripple. It was obtained for a 100 km fiber Raman amplifier the gain ripple can be about 0.1 dB with on-off gain more than 20 dB.     

抽运方式对混合拉曼光纤放大器性能的影响

通过实验比较了前向抽运拉曼光纤放大器与掺铒光纤放大器组成的混合放大器、后向抽运拉曼光纤放大器与掺铒光纤放大器组成的混合放大器的性能。实验采用75km标准单模光纤作为增益介质。采用20信道(符合ITU-T建议的波分复用信号)，波长为1537．377～1560．605nm，作为混合放大器的测试信号。20信道总功率-2．86dBm，每一信道用2．5Gb／s、码长2^7-1的非归零码通过电吸收调制器(EA)进行外调制。实验结果表明，前向抽运方式混合放大器的性能优于后向抽运方式的混合放大器，其中噪声系数的改善值为2．28～6．55dB。采用前向抽运时，各信道的增益同后向抽运相比，增加值均大于5dB。但不论采取那种抽运方式，采用混合放大的形式，各信道的光信噪比均大于26．9dB。