Cross-gain modulation in Raman fiber amplifier: experimentation and modeling

The effects of channel loss on the performance of Raman fiber amplifiers (RFA) are investigated both experimentally and theoretically. Signals from one distributed-feedback (DFB) laser and an external cavity laser (ECL) were transmitted through counterdirectionally pumped RFAs consisting of 15.6 km of dispersion compensating fiber (DCF). The ECL light was square-wave modulated at 500 Hz. At the output of the RFA, the signal of the modulated channel was eliminated with an optical band pass filter, and power fluctuations of the surviving channel were recorded with a high-speed digital oscilloscope. Power fluctuations as high as 0.45 dB with typical saturated amplifier overshoots were observed. The experimental results were confirmed by a large signal numerical analysis.     

Analysis of channel addition/removal response in all-optical gain-clamped cascade of lumped Raman fiber amplifiers

The effect of addition and/or dropping of wavelength-multiplexed channels in a network comprising three concatenated lumped Raman fiber amplifiers (LRFAs) have been analyzed by numerical simulation and verified experimentally. The first LRFA in the cascade is gain clamped using a ring-laser configuration, and the lasing power propagates through the cascade. A large-signal numerical model that incorporates time variation effects and the downstream propagation of signal, upstream propagation of pumps, and downstream and upstream propagation of amplified spontaneous emission spectral components has been used for the theoretical analysis. The LRFAs consist of 16 km of dispersion-compensating fiber counterdirectionally pumped at 1455 nm by a Raman fiber laser. Channel addition/removal is simulated by propagating through the cascade of LRFAs optical power from two laser diodes. One of them is square-wave modulated at 500 Hz, and power fluctuations of the second continuous-wave signal caused by the cross-gain saturation effect in LRFAs are monitored.     

Channel addition-removal response in all-optical gain-clamped lumped Raman fiber amplifier

Application of all-optical gain-clamped (AOGC) lumped Raman fiber amplifier (RFA) for protection of surviving channels in multiwavelength networks is investigated experimentally and theoretically. Channel addition-removal was simulated by transmitting signals of two lasers through a counterdirectionally pumped RFA consisting of 16 km of dispersion compensating fiber. Light of one of the lasers was square-wave modulated at 500 Hz; power fluctuations of the other laser caused by cross-gain modulation of the RFA were monitored at the output of the amplifier with a digital oscilloscope. An all-optical feedback loop was implemented in the form of a ring laser. Theoretical analysis of the AOGC lumped RFA is based on numerical solution of coupled propagation equations for forward and backward-propagating pumps, signals, and spectral components of amplified spontaneous emission powers.     

多波长抽运C+L波段喇曼放大器的数值模拟与分析

为了合理地设计出宽带分布式光纤喇曼放大器系统,采用理论分析与数值模拟相结合的方法,对前向抽运方式的喇曼耦合方程进行数值仿真,获得了合适的抽运源波长,从而实现了分布式喇曼光纤放大器的带宽为80nm(1530nm～1610nm).在抽运功率均匀分配的情况下,对80个信道的信号进行分布式放大,分析了不同信号、抽运功率沿光纤的...     

分布拉曼光纤放大的实验研究

采用符合ITU-T标准的G波段40信道波分复用(WDM)光源对分布式拉曼放大器(DRA)的特性进行了实验研究。对不同抽运方式及不同光纤长度的分布式拉曼放大器性能作了较为详细的报道。在抽运功率相同的条件下，选用50km单模光纤对比研究了不同抽运方式的拉曼放大器增益和噪声。通过对不同光纤长度的分布式拉曼放大器的实验研究发现，在较低抽运功率且输入信号功率较低的情况下，随着光纤长度增加，拉曼增益也增加，有效噪声系数减小。研究了分布式拉曼放大器对波分复用通信系统信噪比的改善，实验发现不同抽运功率下，拉曼放大器对系统信噪比的改善随抽运功率增加而增加，但是不成线性关系，而且最终会出现饱和。     

Fast power transients in concatenated Pr3+-dopedfluoride fiber amplifiers

Amplified multiwavelength optical communication networks are prone to substantial saturation induced power fluctuations when a channel is turned on or rerouted. This perturbs amplifier gains at other wavelengths. The effects of addition and/or dropping of wavelength channels due to network reconfigurations or line failures in a multiwavelength network comprising eight concatenated Pr³⁺-doped fluoride fiber amplifiers (PDFFAs) have been studied theoretically. A large-signal numerical model which incorporates time variation effects and the downstream and upstream propagation of signal, pump and amplified spontaneous emission has been used. In an eight channel WDM network the loss of channels will cause very fast power excursions of the surviving channels. The necessary speed of the link control circuit for surviving channel protection has been investigated     

Surviving-Channel-Power Transients in Second-Order Pumped Lumped Raman Fiber Amplifier: Experimentation and Modeling

In this paper, the effect of addition and/or dropping of wavelength-division-multiplexed channels in an all- optical gain-clamped (AOGC) second-order (SO) pumped lumped Raman fiber amplifier (LRFA) has been investigated experimentally and analyzed by numerical simulation. Channel addition/ removal was simulated by transmitting ten signals through a counter-directionally pumped LRFA consisting of a 16-km-long dispersion-compensating fiber. The light from eight lasers was square-wave modulated at 500 Hz; power transients of the surviving channels caused by cross-gain modulation of the LRFA were monitored at the output of the amplifier. All-optical feedback loop was implemented in the form of a ring laser. Gain-clamping properties of the SO-pumped LRFA are compared with those of the first-order pumped LRFA having the same ON/OFF Raman gain. Theoretical analysis of the AOGC LRFA was based on numerical solution of coupled propagation equations for the backward propagating pump, signals, and both forward and backward propagating spectral components of amplified spontaneous emission powers.     

Channel addition/removal response in cascades of strongly invertederbium-doped fiber amplifiers

Signal power steady-state and transient fluctuations due to gain cross saturation in erbium-doped fiber amplifiers (EDFA's) in multiwavelength optical networks caused by addition or removal of channels due to network reconfigurations or line failures must be minimized to avoid error bursts in the surviving channels. The effects of addition and/or dropping of wavelength channels in a multiwavelength network comprising six concatenated strongly inverted two-stage EDFA's have been analyzed by numerical simulation. A large-signal numerical model which incorporates time variation effects and the downstream and upstream propagation of signal, pump and amplified spontaneous emission has been used. Power excursions caused in an eight channel wavelength division multiplexing (WDM) network by the loss/addition of one, three, or six channels will be lower than 0.6 dB if the length average normalized population density of the metastable level does not drop below 0.76. No additional measures need to be taken to limit the power excursions of the surviving channels     

Output power excursions in a cascade of EDFAs fed by multichannelburst-mode packet traffic: experimentation and modeling

A serious problem facing wavelength-division multiplexed (WDM) networks with fiber amplifier cascades is transient cross-gain saturation or gain dynamics of fiber amplifiers. Attention has been focused primarily on circuit-switched scenarios. When the number of WDM channels transmitted through a circuit-switching network varies, channel addition/removal will tend to perturb signals at the surviving channels that share all or part of the route. Even more serious bit error rate deterioration can arise in WDM packet switched burst mode networks. In this paper, we present experimental and theoretical results demonstrating the effect of fast power transients in erbium-doped fiber amplifiers (EDFAs) on packetized traffic transmitted through a chain of five EDFAs. Traffic of a local-area network has been transmitted over three channels. The effect of EDFA cross-gain saturation due to the burstiness of the traffic has been observed in a continuous-wave monitoring channel. The stabilizing effect of gain clamping of the first EDFA in the cascade has been investigated. The experimental results are extended to eight-channel WDM system using a large signal numerical analysis     

Ultra-wide-band tellurite-based fiber Raman amplifier

We describe the first wide-band tellurite-based fiber Raman amplifier (T-FRA) for application to seamless ultra-large-capacity dense wavelength-division multiplexing (WDM) systems. First, we confirmed that the Raman scattering characteristics of the tellurite-based fiber has so large a gain coefficient and Stokes shift that we can achieve a wide-band tellurite-based fiber Raman amplifier with a shorter fiber length than when using silica-based fiber. Second, we investigated the small signal gain and the signal transmission characteristics for a high gain and high output power operation with a single-stage amplifier. Focusing on double Rayleigh scattering, we compared the high gain limit of tellurite- and silica-based fibers. We then studied the impact of nonlinear effects by measuring the bit error rate (BER) when using a two-stage amplifier with a high output power of 18.8 dBm in which we simultaneously amplified eight channel signals in the L-band located on the ITU 100-GHz grid. Finally, we designed a wide-band tellurite-based fiber Raman amplifier with a multiwavelength band pumping scheme. We constructed this amplifier with a tellurite-based fiber only 250 m in length pumped by four-wavelength-channel laser diodes, and it provided a 160-nm bandwidth with a gain of over 10 dB and a noise figure below 10 dB from 1490 to 1650 nm. We also measured the BER to confirm the transmission characteristics of the amplifier for single channel operation over the whole signal wavelength range of 160 nm. We thus confirmed that the amplifier could be employed in ultra-high-capacity WDM systems.     

基于EDFA和级联RFA的混合光纤放大器的设计

基于EDFA的理论模型和受激拉曼散射效应的分析理论,利用EDFA和RFA的增益谱互补特性,对拉曼光纤放大器(RFA)采用两根光纤级联方式,研究并设计了EDFA与级联光纤的RFA相结合的混合放大器结构.仿真结果表明:在不使用增益均衡器的条件下,所设计的混合光纤放大器在输出端得到了近似相等的输出光功率,得到了增益平坦度为0.62 dB、波长带宽为70 nm(1 550～1 620 nm)的结果,在密集波分复用光通信系统中有重要的应用价值.     

Analytical Model of Non-dispersion-limited Transient Stimulated Raman Scattering in Single-mode Silica Fiber in WDM Optical Communication System

The non-dispersion-limited analytic solutions of unidirectional N-channel transient stimulated Raman scattering (SRS) coupling wave equation which governing the propagation of the optical signals in single-mode (SM) silica fiber have been presented. Taking into account the SRS cross coupling among the N-channels, the analytic solutions are applicable to the system with arbitrary channel separation and input signal light power.     

A perturbation method for analysis of TDM-pumped fiber Raman amplifier

We propose a perturbation method for time division multiplexed (TDM) pumping fiber Raman amplifier (FRA). The method is based on the solution of Raman partial differential equations (PDEs) by a closed integral form. Taking the signals and pumps power as the interim solution and updating their values in an iterative process, Raman gain and pump/signal evolution can be calculated in any order of accuracy. In the first order of perturbation, some analytical formulas for the FRA dynamic control are obtained. Analytical formulas are employed for gain ripple minimization and also the gain clamping problem under channel reconfiguration.     

损耗对级联光纤RFA增益平坦度影响分析

增益平坦度是衡量光纤通信中喇曼光纤放大器的关键参数之一。文章从级联光纤实现喇曼增益谱平坦技术的分析理论入手, 改进了实现喇曼增益谱平坦的约束条件, 利用Matlab分析了光纤损耗对RFA增益谱平坦度的影响。结果表明: 在喇曼光纤放大器系统中, C波段各个光之间不同的损耗系数是影响增益平坦度的关键因素, 即信号光之间损耗系数的不同会引起喇曼光纤放大器的增益平坦度劣化, 各个被放大信号光之间的损耗系数相差越大, 则增益平坦度越差。     

损耗对级联光纤RFA增益平坦度影响分析

增益平坦度是衡量光纤通信中喇曼光纤放大器的关键参数之一。文章从级联光纤实现喇曼增益谱平坦技术的分析理论入手,改进了实现喇曼增益谱平坦的约束条件,利用Matlab分析了光纤损耗对RFA增益谱平坦度的影响。结果表明:在喇曼光纤放大器系统中,C波段各个光之间不同的损耗系数是影响增益平坦度的关键因素,即信号光之间损耗系数的不同会引起喇曼光纤放大器的增益平坦度劣化,各个被放大信号光之间的损耗系数相差越大,则增益平坦度越差。     

基于自适应差分进化算法的拉曼放大器设计

为满足下一代6G网络对光通信网络提出的传输容量大、速率高及传输时延低的要求,本文将碲酸盐光纤作为光纤增益介质,并利用自适应差分进化(adaptive differential evolution,ADE)算法 对拉曼光纤放大器(Raman fiber amplifier,RFA) 的泵浦参数进行优化。该算法通过引入自适应算子控制变异率的大小,在保持个体多样性的同时增强全局搜 索最优解的能力。最终设计出一款覆盖100 nm带宽范围、平均增益为28.27 dB、增益平坦度为 0.65 dB的多泵浦RFA。同时,在该模型基础上分别研究了泵浦功率和光纤长度对拉曼放大器增益及增益平坦度的影响,为设计和优化多泵浦拉曼放大器模型提供了参考。     

基于双向二级喇曼抽运的偏振控制研究

为了发展具有实用价值的受激喇曼全光偏振控制方法,根据光纤中受激喇曼散射矢量理论和光纤随机双折射效应设计了基于双向二级喇曼抽运的全光偏振控制方案,构建了偏振吸引理论模型,采用严格数值迭代算法对该偏振控制方案进行了仿真分析,并完成了偏振控制方案最佳工作性能的优化设计。结果表明,当信号光波长为1550nm、功率为0.1mW、一级抽运光和二级抽运光的功率分别为1W和4W、其偏振态都为（0,1,0）、光纤长度为3km时,信号光偏振度可达0.85以上,且信号光强度波动低于35%。该方案有效降低了作用光波功率、减弱了信号光输出强度噪声,并提高了信号光输出偏振度。     

基于掺锗光子晶体光纤的可调谐多波长转换器

为了提高光网络中波长资源的使用效率,利用光纤中瞬态受激拉曼散射效应分析理论,设计了一种基于掺锗光子晶体光纤的可调谐四通道波长转换器。由于受激拉曼散射效应的增益随信号光与探测光波长之间的频移量变化,波长转换器各个转换信道波长可由探测光波长调谐。分析了泵浦信号光输入功率对多波长转换器性能的影响,结果表明:随着输入泵浦功率的增大,多路波长转换器的转换性能更好。用OptiSystem对四通道可调谐波长转换进行仿真,结果表明:所设计的波长转换器能够同时实现四通道波长转换,各信道波长可在1 511~1 569nm进行调谐。     

DWDM系统中色散对受激喇曼散射的影响

研究了光纤色散对波分复用(WDM)系统中受激喇曼散射(SRS)非线性效应的影响.提出了一种简便且物理意义明确的分析计算模型,它适合于任意输入信号、任意信道数,以及不同的色散参量.基于该模型,深入分析了两信道光纤通信系统中,各种色散参量下,色散对SRS的影响,得出了色散能减小SRS效应所引起的输出功率的波动的结论,并且给出了在不同色散参量下,输出功率标准差随距离变化的曲线.     

前向多泵浦拉曼放大器中噪声的精确分析

ASE噪声和DRBS噪声是影响拉曼光纤放大器传输性能的两个重要因素。本文运用四阶龙格-库塔法对多泵浦RFA的噪声功率进行仿真,进一步得到ASE和DRBS噪声的信噪比和噪声系数。结果表明,当光纤长度L<30 km时,ASE噪声对系统影响较大,而L>40 km时,DRBS噪声是影响系统性能的主要因素。另外,长波长的噪声比短波长信道的噪声功率更高,对系统的影响更大。当信号光波长相差24 nm时,长波长的ASE噪声饱和值至少比短波长高0.005 mW,DRBS噪声饱和值至少比短波长高0.0025 mW。