Model for bidirectional transmission in an open cascade of opticalamplifiers

We derive a model for signal propagation and the generation and propagation of amplified spontaneous emission (ASE) in a completely open bidirectional cascade of optical amplifiers. The effect of single Rayleigh scattering of both signal and ASE is included. Our model predicts and our experiments substantially verify that the dominant gain saturating mechanism is the Rayleigh backscattered ASE centered around the 1535 nm peak in the ASE spectrum and that the spectral shape of the output ASE becomes much more sharply peaked around the 1535 nm gain peak. In an experimental open cascade of three EDFAs the ASE spectral density at the 1535 nm gain peak is increased by as much as 8-9 dB, resulting in gain compression ranging from 1-2 dB near 1550 nm to as much as 35 dB nearer 1538 nm. This combined with multiple Rayleigh scattering of the ASE around our 1538 and 1540 nm signal wavelengths results in Rayleigh scattering induced reductions of the optical signal to ASE ratio of 1-2 dB at the output of the first amplifier increasing to 36 dB at the output of the third amplifier each signal traverses     

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     

Numerical Modeling of Pulsed Raman Fiber Converters at 2 $mu{hbox {m}}$

Theoretical modeling of stimulated Raman scattering (SRS) in fibers is presented for the near-infrared band around 2 mum, where pump and Stokes wave have different absorption. This model takes into account amplified spontaneous emission (ASE), SRS towards Stokes and anti-Stokes waves, absorption of the Raman medium and Rayleigh backscattering in fibers. Depending on the fiber configuration, this model includes the cavity parameters of either external or internal mirrors at the fiber ends. Input parameters are, among others, temporal profiles of the pump radiation, absorption, and gain curve of the Raman medium. The model agrees well with experimental results obtained with a GeO₂ doped core fiber pumped by a pulsed and tunable Tm:silica fiber laser emitting around 2 mum.     

基于anti-Stokes Raman散射温度效应的温度解调理论研究

激光脉冲进入光纤中,与光纤分子相互作用,产生Raman散射和Raylei曲散射。由于Raman散射具有温度效应,其散射光强度受温度调制,可作为温度信息的载体,用于温度解调及测温系统设计。本文提出了可行的温度解调方法及理论推导,并推导出单通道和双通道条件下的测温关系,设计出两种条件下的传感器系统。     

在瑞利散射影响下分布拉曼光纤放大器噪声特性的解析解和参数优化

光纤中的瑞利散射会对分布拉曼光纤放大器的噪声特性产生不利影响。通过忽略高次瑞利后向反射的影响,给出实际情况下(信号损耗不等于抽运损耗,考虑瑞利散射影响)分布拉曼光纤放大器噪声特性的解析解。利用此解析解,对分布拉曼光纤放大器的噪声特性进行了深入讨论并提出了选择抽运功率的一般原则     

基于EDFA的分布式光纤喇曼温度解调技术

为了消除掺铒光纤放大器的放大自发辐射噪声对分布式光纤温度传感器测温精度的影响,采用精确的修正公式进行温度解调是一种有效手段。通过分析掺铒光纤放大器的放大自发辐射噪声对系统产生的影响,并将计算的中间结果代入理论公式获得了修正后的温度解调公式。实验中分别采用理论公式和修正公式对温度进行分布式测量并获得了实验数据。结果表明,修正后的温度解调公式有效补偿了掺铒光纤放大器噪声引起的误差,并显著提高了系统的信噪比和测温精度;修正公式可将系统的整体测温精度提高到1℃～2℃;此外,实验中观察到多模光纤中喇曼背向自发散射同样会出现放大现象,这与单模光纤中的情形类似,且放大喇曼自发散射依然具有理想的温度效应。     

Amplification Effect on Rayleigh Scattering and SBS in 25 km Distributed Fiber Raman Amplifier

The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fibers Raman amplifier have been researched. The signal source is a tunable narrow spectral bandwidth （〈10 MHz） ECL laser and is pumped by the tunable power 1427.2 nm fiber Raman laser. The Rayleigh scattering lines are amplified by fiber Raman amplifier, and Stokes stimulated Brillouin scattering lines are amplified by fiber Raman amplifier and fiber Brillouin amplifier. The SBS lines total gain is a production of the gain of Raman and the gain of Brillouin amplifier. In experiment, the gain of SBS is about 42 dB and the saturation gain of 25 Ion G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.     

包层抽运掺镱光纤激光器中受激拉曼散射和受激布里渊散射效应

高功率光纤激光器大多选用掺镱双包层光纤作为增益介质,由于光纤尺寸较小,极易在光纤谐振腔中产生受激布里渊散射、受激拉曼散射效应。包层掺镱双包层光纤激光器中一旦发生受激拉曼散射和受激布里渊散射效应,其产生高强度信号成为高功率光纤激光器的主要噪声来源,影响激光输出的特性和稳定性。对包层抽运掺镱光纤激光器中的受激布里渊散射和受激拉曼散射进行了实验研究,在单模双包层光纤中观察到受激布里渊散射和受激拉曼散射。实验结果表明,在光纤谐振腔中,抽运方式、谐振腔输出镜损耗、受激瑞利散射对受激布里渊散射的影响较大,尤其是受激瑞利散射为谐振腔提供了附加反馈,不仅压窄激光信号的线宽,而且使得受激布里渊散射的阈值迅速降低。     

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。     

Effect of a nonlinear photonic Crystal fiber on the noise characterization of a distributed Raman amplifier

The first experimental study of the effect of a nonlinear photonic crystal fiber (PCF) on the noise characteristics of a distributed backward-pumped Raman amplifier is reported. The PCF has a highly nonlinear Raman efficient, and a high Rayleigh scattering parameter. When an optical signal first passes through a 100-m nonlinear PCF followed by a 25-km single-mode fiber, the optical signal-to-noise ratios (OSNRs) of the amplified spontaneous emission and the double Rayleigh scattering (DRS) are improved because the high Raman gain efficiency of the PCF makes the Raman gain of the signal at the beginning of the link increase, and the signal power over the length of the transmission becomes near a constant. However, the improvement of the OSNR of DRS compared with the OSNR of amplifier spontaneous emission is limited by the large Rayleigh scattering in the PCF.     

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。     

1.55μm喇曼温度传感器的强循环解调方法

针对1.55μm喇曼滤波器的隔离度不高的情况,提出了抑制背景噪声、热漂噪声积累、瑞利背向散射光窜扰反斯托克斯背向散射光的喇曼温度传感器的强循环解调方法。提高了系统的灵敏度、温度测量精度和稳定性;取消了恒温槽,降低了系统成本。实验表明,该解调方法使温度测量精度达到±0.05℃。     

分布光纤喇曼光子传感器系统

分布光纤喇曼光子传感器（ Ｄ Ｏ Ｆ Ｒ Ｐ Ｓ） 系统是一种实时测量空间温度场、应力场和压力场的光纤网络系统。依据喇曼散射的温度效应,自发喇曼散射光子是温度信号的载体,瑞利散射光子是应力和压力信号的载体, Ｄ Ｏ Ｆ Ｒ Ｐ Ｓ 系统是一种特殊的光纤通信机,同时也是一种光纤雷达。文章讨论了系统的结构、解调方法、 Ｌ Ｄ 波长选择、系统的信噪比     

光纤通信中的散射效应

讨论了光纤通信系统在线性和非线性条件下可能存在的各种散射效应,认为光纤的本征散射衰减不仅包括瑞利散射衰减,还包括布里渊散射和喇曼散射衰减。指出不同种类的散射效应在光纤通信中的应用。     

Piezoelectric Rayleigh Wave Excitation by Bulk Wave Scattering

The excitation of a Rayleigh surface wave on a piezoelectric crystal by the scattering of bulk waves from strips deposited on the crystal's surface is considered. Using small scatterer approximations to obtain a lower limit for the strength of excitation that can be obtained by the scattering method, the Rayleigh wave excitation resulting from the mass of the deposited strips is determined. Numerical calculations for CdS, LiNbo/sub 3/, and isotropic solids indicate that this method of excitation is feasible. Simple, small scatterer estimates for the order of magnitude of the excitation resulting from the conductivity of strips deposited on CdS and LiNbO /sub 3/suggest that the Rayleigh wave can be more strongly excited through the mass of the strips than through their conductivity. In order to evaluate the Rayleigh wave excitation, an expression has been derived that describes the excitation of elastic surface waves, guided by configurations composed of infinite, parallel layers of arbitrary piezoelectric and elastic materials, when the source of these waves are prescribed, two-dimensional force and current distributions. This expression for the surface wave excitation coefficient depends only on the source and the properties of the surface wave, and is expected to prove useful in rating a wide variety of exciting structures. For the scattering method of excitation considered here, the effect of the incident bulk wave on the strips can be represented by approximately equivalent sources, which excite the surface wave.     

基于激光散射理论的微小颗粒测量的数值分析

根据算法的准确性、稳定性和快速性原则, 讨论了Mie散射和Rayleigh散射的数值算法。将Mie散射理论及Rayleigh散射理论的Matlab数值结果与Wiscombe结果对比分析, 证明了此Matlab程序的正确性。在此基础上, 确定了当颗粒粒径参量x0.3时采用Rayleigh散射理论来确定前向某一角度范围内散射光能分布, 从中求得颗粒的粒径大小和分布, 具有比Mie散射理论算法快速性的特点。该方法为某些测试对象(颗粒与分散介质相对折射率、颗粒种类等)确定、微小颗粒的在线测量提供了理论支持。     

Determination of back-scatter coefficient from third-order Rayleigh effect in a Raman amplifier

We propose a precise measurement technique for the Rayleigh back-scattering coefficient based on a single-ended optical time-domain reflectometry trace analysis. By comparing the relative strength of the Rayleigh components-Rayleigh scattering and triple Rayleigh scattering-we show that it is possible to avoid the uncertainties associated with previous measurement techniques, achieving less than 0.1-dB error in the determination of the Rayleigh coefficient. Application of this technique to the noise characterization of the fiber Raman amplifiers will be provided at the end.     

一种简单实用的调节RFA增益平坦的方法

提出了一种用ASE宽带光源调节拉曼光纤放大器(RFA)增益平坦的简单方法.将该ASE宽带光源调节RFA增益平坦所得泵浦配置方案用于DWDM信号的放大,得到DWDM信号增益谱与相应波长处ASE信号的增益谱相近,且增益波动小于1dB.所用的方法结构简单,调节方便,可有效地调节利用RFA的DWDM系统增益平坦度,而不需要调节复杂、成本昂贵的DWDM信号源.     

分布光纤拉曼放大器多路干涉的两种新分析方法

在总结目前存在的分布光纤拉曼放大器瑞利散射噪声性能分析方法的基础上 ,提出了两种新分析方法。第一种方法给出一个简单的解析表达式。第二种分析方法是在解析式的基础上进行迭代 ,计算精度得到较大提高 ,而计算时间大大减少     

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.