采用喇曼光纤放大器的长距离光纤传输系统中双重瑞利散射噪声的抑制

本文研究了在长距离光纤通信系统中,采用多级喇曼光纤放大器的情况下,双重瑞利散射波的产生和放大过程,提出了采用在喇曼光纤放大器中加入隔离器的办法进行双重瑞利散射噪声抑制。比较信号和双重瑞利散射噪声在入隔离器前后沿传输光纤的功率变化,加入隔离器以后,双重瑞利散射噪声得到了有效地抑制,而信号所受的影响不大。     

二阶光纤喇曼放大器增益平坦性研究

针对掺铒光纤放大器(EDFA)的增益竞争特性,在Rsoft公司提供的仿真平台上搭建了长距离分布式光纤喇曼放大器实验模型.在分析泵浦光与泵浦光、泵浦光与信号光的喇曼相互作用的基础上,仿真过程中还充分考虑瑞利散射、自发散射以及信号光传输过程中非线性的影响,得到了二阶泵浦放大方式下增益平坦度与一阶泵浦功率之间的关系,发现采用二阶放大方式在改善了放大器的噪声性能的同时,也破坏了增益谱的平坦度,在实际应用中应折中考虑.     

瑞利散射对拉曼光纤放大器性能的影响及抑制措施

瑞利散射是影响拉曼光纤放大器性能的重要因素。本文系统地分析了瑞利散射对拉曼光纤放大器噪声、串扰和功率代价等性能的影响，指出优化选择泵浦功率和泵浦方式以及插入光隔离器等措施可以降低瑞利散射的影响，从而为拉曼光纤放大器的优化设计提供了依据。     

高性能喇曼光纤放大器驱动控制电路的研制

随着光通信系统传输容量的飞速增长,对光纤的通道数、传输比特率、传输带宽和传输距离都提出了越来越高的要求,促使光放大器技术向宽带、低噪声的方向发展.喇曼光纤放大器以其优越的性能引起人们的普遍关注.喇曼光纤放大器需要多个大功率激光器作为泵浦光源,这些泵浦激光器需要稳定的大电流驱动和精确温度控制才能保证整个喇曼放大器良好的工作性能.本文给出了一种喇曼光纤放大器驱动控制的实现方案,通过实际测量比较可以看到,利用该驱动控制方案实现的喇曼光纤放大器具有良好的性能指标.     

光纤喇曼放大器及其研究进展

介绍了光纤喇曼放大器(FRA)的工作原理、结构和特性,指出FRA的重点研究方向为新型光纤、大功率泵浦激光器、多泵浦喇曼放大器、混合喇曼放大器、增益均衡技术等,这些技术的发展和应用为提高FRA的性能奠定了基础,也必将使光纤喇曼放大器成为下一代光放大器的主流.     

同向与反向抽运光纤喇曼放大器的阈值比较

为分析同向抽运与反向抽运光纤喇曼放大器的阈值特性,基于已有的耦合微分方程,采用龙格库塔算法和打靶算法,数值模拟同向抽运和反向抽运光纤喇曼放大器中信号光功率沿光纤的演变过程,在此基础上根据实际情况推导出同向与反向抽运光纤喇曼放大器的阈值公式,这些公式比文献中的阈值公式更全面。然后,详细分析各个参数对同向抽运和反向抽运光纤喇曼放大器阈值特性的影响,并且对两种抽运方式的阈值进行比较,结果表明,各参量对同向和反向抽运FRA的阈值影响有相同的地方,也有不同的地方。相同参数时,反向抽运光纤喇曼放大器的阈值都大于同向抽运光纤喇曼放大器的值。结论对于光纤喇曼放大器的优化设计和实验有指导作用,为进一步的研究提供有益的参考。     

喇曼光纤放大器的新进展

随着10Gb／s DWDM长距离传输系统的大量应用和40Gb／s技术的日趋成熟，喇曼光纤放大器的重要性日渐显露，并逐步进入商用。光器件制造商竞相研制出了性能优良的喇曼光纤放大器，主要是希望利用喇曼光纤放大器特有的分布式放大，可降低非线性影响、噪声特性好等特点，进一步推动高速，大容量，长距离光纤传输系统的发展。     

拉曼光纤放大器的一种简化模型

提出了一种多泵浦反向光纤拉曼放大器（FRA）的新型实用模型，能够给出小信号增益和噪声指数。采用数值计算泵浦光的传播规律，利用此结果解析求解信号光沿光纤的功率演化，解决了泵浦与信号光反向传输的问题。利用拟合图谱通过插值得到拉曼增益系数代替传统的将拉曼增益谱近似为三角形的方法。模型中考虑了泵浦与泵浦、泵浦与信号之间的相互作用，并包含自发拉曼散射噪声。     

两段级联宽带碲基掺铒光纤放大器特性研究

利用四能级结构速率方程组和光功率传输方程组,研究了在碲基掺铒光纤(EDTF)中内插一个光隔离器、形成两段级联的碲基掺铒光纤放大器(EDTFA)后对EDTFA性能的改善.结果表明,在给定泵浦方式、泵浦功率、纤芯掺杂浓度和输入信号功率条件下,两段级联EDTFA可以有效的抑制光纤中反向传输放大自发辐射(ASE)噪声,降低反转粒子数的消耗,从而提高信号增益、输出功率,并且降低了噪声系数.对不同光纤长度和光隔离器内插在光纤中不同位置的研究表明,当光纤为最佳长度和光隔离器在最佳位置处时,可使短波长信号增益增加10 dB,噪声系数减小1 dB,并进一步增加了放大带宽以及功率转换效率.     

光纤水听器远程传输中相干瑞利噪声的抑制

在使用窄线宽光源的干涉型光纤水听器远程传输系统中,瑞利散射通过多光束干涉引入了严重的相干噪声。分析了光纤远程传输产生的单次瑞利后向散射(RB)和双重瑞利散射(DRS)对干涉系统的影响,并使用隔离器对RB进行抑制。推导了DRS引入的相位噪声的模型,通过讨论DRS的调制特性,得出相位产生载波(PGC)技术在消除相位衰落的同时也可以大大抑制DRS产生相干噪声的结论。实验结果表明,在光纤水听器往返各25km的传输系统中,隔离器对RB产生的相位噪声抑制最大达20dB,PGC技术对DRS噪声的抑制最大达10dB。在同时抑制RB和DRS后,50km光纤传输系统中相干瑞利散射噪声的影响基本消除。     

Optimal design of multistage discrete Raman amplifiers incorporating midway isolators

Multistage discrete Raman amplifiers with midway isolators to suppress double Rayleigh backscattering are fully investigated at constant nonlinearity. The results show that placing Raman pumps at the last stage only is sufficient. For most conditions, two isolators can achieve adequate performance improvement, while more isolators only lead to slightly optical signal-to-noise ratio increase. The optimum positions of the isolators are insensitive to varied Raman gains, nonlinear phase shifts, and Rayleigh coefficients, but sensitive to different fiber lengths as well as Raman pumping schemes. Moreover, backward-pumping schemes can derive better noise performance than bidirectional pumping when using midway isolators.     

光纤中的瑞利后向散射对分布式光纤拉曼放大器噪声特性的影响

光纤中的瑞利散射会对分布式光纤拉曼放大器 (DFRAs)的放大的自发辐射 (ASE)噪声产生影响 ,并带来二次瑞利散射 (DRB)效应。得到了DFRAs中各种噪声项的解析或半解析表达式。通过此表达式深入分析了各噪声项影响分布光纤拉曼放大器性能的规律 ,并利用等价接收机灵敏度的概念讨论了瑞利散射对DFRAs噪声特性两种影响的总效果     

Performance of DRA with different pumping schemes based on coupling equation

After the coupling equations of co-pumping,counter-pumping and bidirectional-pumping distributed Raman amplifiers(DRAs) are theoretically analyzed,the power distributions of these three DRAs are acquired with numerical analysis.The performance factors,such as net gain(NG),amplified spontaneous emissions(ASE) noise,double Rayleigh backscattering(DRB) noise,noise figure(NF) and optical signal noise ratio(OSNR),are discussed in depth.It can be found that the NGs of the three DRAs are almost equal.The counter-pumping scheme will induce higher ASE.And the co-pumping DRA has greater DRB noise,but its NF and OSNR are both better than the others’.Furthermore,the relations between signal power and NG,NF,OSNR are also investigated.It is shown that the NF and OSNR of the co-pumping scheme are superior to those of the other two schemes at small input signal power.The above conclusions can play a very important role in guiding the optimum design of DRA.     

光纤中点缺陷对分布光纤拉曼放大器性能的影响

阐述了考虑传输光纤中存在点缺陷损耗和反射时背向抽运光纤拉曼放大器 (B DFRA)性能的分析方法 ,计算并分析了点缺陷对增益、放大的自发拉曼散射噪声和二次瑞利散射 (DRB)噪声的影响 ,还通过带B DFRA预放器的接收终端等价接收灵敏度讨论了点缺陷作用的综合效果。     

External Optical Feedback Induced Noise in DFB Fiber Laser Sensor System

External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber DFB laser with lead fiber length from I m to 37.5 km before the onset of instabilities are shown. Rc is found to decrease with increasing lead fiber length while Sc was relatively invariable with varying fiber length. The coherent Rayleigh backscattering （CRBS） would induce neglectable noise with a lead fiber exceeding 13.5 kin. To eliminate these noises, one or two isolators should be incorporated in the system.     

Impact of double Rayleigh backscatter noise on digital and analogfiber systems

We have derived, and experimentally verified, an exact analytical expression for the noise power spectral density due to double Rayleigh backscattering in standard single mode fiber-optic transmission systems in terms of the autocorrelation function of the transmitted optical electric field. The analysis is used to examine the impact of double Rayleigh backscattering on chirped amplitude modulated-subcarrier multiplexed (AM-SCM), and optically amplified digital intensity modulated-direct detection (IM-DD) laser systems, with and without optical isolators in the link     

An All‐Optical Gain‐Controlled Amplifier for Bidirectional Transmission

A novel all‐optical gain‐controlled (AOGC) bidirectional amplifier is proposed and demonstrated in a compact structure. The AOGC function using fiber Bragg grating (FBG) pairs controls both directional signals independently, and combinations of optical interleavers and isolators suppress Rayleigh backscattering (RB) noise. The amplifier achieves high and constant gain with a wide dynamic input signal range and low noise figure. The performance does not depend on the input signal conditions, whether static‐state or transient signals, or whether there is symmetric or asymmetric data traffic on bidirectional transmission. Transmission comparison experiments between invariable symmetrical and random variable asymmetric bidirectional data traffic verify that the all‐optical gain control and bidirectional amplification functions are successfully combined into this proposed amplifier.     

Impact of Reflection Induced Noise on AM-VSB CATV Lightwave Systems

1 Introduction The lightwave CATV systems recently can provide the extremely high-fidelity transmission required by the AM-VSB video format. These systems can also provide the satisfactory performance of CNR, CSO and CTB. Such performance has been realize…     

Impact of Reflection Induced Noise on AM-VSB CATV Lightwave Systems

The effect of reflection on the performance of AM-VSB CATV lightwave systems is analyzed. Usually, there are three kinds of reflection existing in the AM-VSB CATV lightwave systems: multipath interference (MPI), double Rayleigh backscattering (DRB) and external optical feedback. The MPI and external optical feedback can be neglected owing to using the FC/APC connectors and isolated DFB lasers in the system link. It is shown theoretically and experimentally that the DRB is the limitation of the noise induced by reflection.