Design of Hybrid Optical Amplifiers for High Capacity Optical Transmission

This paper describes our design of a hybrid amplifier composed of a distributed Raman amplifier and erbium‐doped fiber amplifiers for C‐ and L‐bands. We characterize the distributed Raman amplifier by numerical simulation based on the experimentally measured Raman gain coefficient of an ordinary single mode fiber transmission line. In single channel amplification, the crosstalk caused by double Rayleigh scattering was independent of signal input power and simply given as a function of the Raman gain. The double Rayleigh scattering induced power penalty was less than 0.1 dB after 1000 km if the on‐off Raman gain was below 21 dB. For multiple channel amplification, using commercially available pump laser diodes and fiber components, we determined and optimized the conditions of three‐wavelength Raman pumping for an amplification bandwidth of 32 nm for C‐band and 34 nm for L‐band. After analyzing the conventional erbium‐doped fiber amplifier analysis in C‐band, we estimated the performance of the hybrid amplifier for long haul optical transmission. Compared with erbium‐doped fiber amplifiers, the optical signal‐to‐noise ratio was calculated to be higher by more than 3 dB in the optical link using the designed hybrid amplifier.     

DCF光纤拉曼放大器的实验研究

DCF(dispersion compensating fibre)光纤具有较高的拉曼增益系数,利用这一点可以用较短长度的DCF光纤制成分立式的光纤拉曼放大器,作为传输线路上的损耗补偿.本文在测量并计算了DCF光纤的拉曼增益系数的基础上,对分立式的DCF放大器的开关增益和噪声指数进行了测量和分析,并将分立式FRA和分布式FRA在开关增益和噪声指数方面做了比较。介绍了用不同的测量方法所造成的实验结果的差异.实验结果表明,放大介质为5 km的DCF光纤所构成的放大器,在抽运功率为800 mW的条件下,最大增益可达14.77dB,3 dB带宽为35 nm,满足作为损耗补偿的要求.     

光纤Raman放大器

本文介绍了Raman放大的机理、泵浦源及泵浦方式,分析了FRA的设计原则、增益均衡的各种方法、噪声及Raman串扰等问题,提出了可行的方案。     

Compensation of Raman-induced crosstalk using a lumpedgermanosilicate fiber Raman amplifier in the 1.571-1.591-μm region

A new method to equalize power imbalance caused by Raman-induced crosstalk among optical channels is proposed using a lumped germanosilicate fiber Raman amplifier. Evolution of optical channels through the Raman amplifier was simulated using Raman frequency modeling, which theoretically predicted simultaneous amplification and power equalization. Experimentally, a gain band with negative slope in the range of 1.571-1.591 μm was achieved in a lumped Raman amplifier pumped by a broad-band laser diode centered at 1.467 μm. We demonstrated compensation of the Raman-induced crosstalk of 5 dB accumulated along 330 km of conventional single-mode fiber     

Design of transmission optical fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering

Designed was the transmission fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering (DRBS). Basically the optical signal-to-noise ratio (OSNR) of distributed type Raman amplifier is superior to that of the lumped type Raman amplifier using a high Raman gain fiber such as dispersion compensation fiber. However, much pump power and long length of transmission fiber line are required to acquire a proper gain in the distributed type fiber Raman amplifier. Thus, compositional adjustment on the fiber for optical transmission is of benefit to reduce further the required pump power. In this regard, based on this simulation, the fluorine and germanium co-doped fiber showed a high Raman gain, high OSNR, and low DRBS.     

基于超长分布式2阶喇曼放大器的光载射频传输

为了提升光载射频传输链路的链路增益以及传输距离,采用了L波段的超长分布式2阶喇曼放大器结构对光信号进行放大。从理论上对分布式2阶喇曼放大器以及光载射频传输链路的原理进行了解释,利用信号光、1阶抽运光、2阶抽运光以及噪声之间的耦合方程组分析了它们之间的关系,并且得到了基于超长分布式2阶喇曼放大器的光载射频传输系统的1阶射频信号增益。通过数值仿真以及系统实验得到了抽运功率大小对超长分布式2阶喇曼放大器的开关增益的影响、光载射频传输系统在0GHz~7GHz范围内的频率响应及其射频增益以及该光载射频传输链路在应用超长分布式2阶喇曼放大器后的相位噪声情况。结果表明,光载射频传输在超长分布式2阶喇曼放大器的作用下获得了28.1dB的链路增益,在距离为80.94km的光链路上实现了近似无损传输,射频信号开关增益与射频信号频率无关。该研究在光载射频链路的长距离传输中有重要的应用价值。     

Four-wave mixing between pump and signal in a distributed Raman amplifier

We observed experimentally four-wave mixing (FWM) between a 14xx-nm pump and a 15xx-nm signal in a forward-pumped distributed Raman amplifier (DRA) over 50 km of nonzero dispersion-shifted fiber with a zero dispersion wavelength of 1497 nm. The 100-mW pump Fabry-Perot (FP) spectra centered at 1440, 1450, and 1460 nm are reproduced via FWM around the single-wavelength probe signal around 1558, 1548, and 1538 nm, respectively. The suppression of DRA gain by about 2-3 dB was experimentally observed with peak FWM at minimum phase mismatching between two 14xx-nm FP pump wavelengths and two 15xx-nm signal wavelengths. This DRA gain suppression, together with the reproduced pump FP spectrum at 15xx-nm signal band, may limit the usefulness of the forward-pumped DRA, generating spectrally nonuniform FWM-induced noise floors and crosstalk in wavelength-division-multiplexed fiber-optic transmission systems.     

多泵浦增益平坦光子晶体拉曼光纤放大器

针对密集波分复用光纤通信系统中拉曼光纤放大器增益及增益谱平坦问题,提出一种采用4个泵浦光的多泵浦方式在光子晶体光纤不同位置处注入两种不同波长泵浦光的组合方式来获得拉曼光纤放大器增益更大、增益谱更加平坦的方法。这种组合方式在拉曼光纤放大器中使得光信号实现了前段放大、后段补偿,从而在拉曼光纤放大器输出端获得高增益和较平坦增益谱。模拟的结果表明:平均增益可达:26.5 dB,增益平坦度为0.046 dB。     

Noise reduction in long-haul lightwave all-amplifier systems

The overall gain of a chain of erbium-doped fiber amplifiers in a long-haul all-amplifier system would be automatically stabilized if each amplifier were operated slightly into saturation. However, with the required low level of amplifier output power which is imposed by nonlinearity in the transmission fiber, the resulting pump power becomes too low to effectively invert the gain medium of the amplifiers. Consequently, the amplifier output noise level becomes too high for proper system operation. This problem is solved by pumping the amplifiers harder so that a higher gain and higher output power are achieved. The excess gain is then counteracted by an appropriate value of post-amplifier loss. Because of the higher pump power in this case, the amplifier noise is reduced significantly. This technique is investigated theoretically, and experimental work that verifies it is reported     

具有多个点损耗的DFRA开关增益定量分析模型

基于忽略泵浦光损耗的正向拉曼光纤放大器耦合方程,推出光纤中存在多个熔接(点)损耗情况下正向(及反向)泵浦光的分布式拉曼光纤放大器(DFRA)增益的定量分析模型,进而推出由不定长光纤小段、且各小段增益系数不同、各小段之问存在熔接(点)损耗DFRA增益的定量分析模型。并针对DWDM系统的增益模型,在考虑了熔接点对信号光之间产生的泵浦作用的损耗,将上述模型进行了修订。上述两种情况下的模型,较之以往的定性的分析文献[3][4]给出定量分析公式和明确的物理解释,并指出熔接损耗点越靠近泵浦光的输入端,对DFRA拉曼开关增益的影响越大(使其越小)。为了考查模型的正确性及适用性,由具有泵浦光之间、信号光之间、泵浦光及信号光之间反相DFRA耦合方程的仿真程序进行了验证,误差不超过0.02dB。最后得出对实际DFRA设计十分有益的结论:当每3公里一个熔接点损耗系数小于0.092dB 时(实际系统中最坏情况下损耗有0.1dB),跨距小于120公里的拉曼光纤放大器的开关增益较无熔接点损耗时下降小于10%。这说明在已铺设的光纤传输系统中使用拉曼放大器是可行的,本文中具有点损耗的DFRA开关增益公式可作为实际DFRA系统设计参考标准。     

多泵浦与光纤级联结合的宽带拉曼光纤放大器

针对传统光纤通信传输系统中拉曼光纤放大器(RFA)增益带宽不足、输出增益低且输出增益不平坦的问题,设计了一种多泵浦和光纤级联相结合的宽带拉曼光纤放大器。并且推导实现增益平坦输出时所用六个泵浦光和四段光子晶体光纤(PCF)对应参数满足的约束表达式,从理论上给出了一种提高放大器增益和增益带宽的同时保证较小增益平坦度的设计方法。最后通过Matlab数值模拟,所设计的宽带拉曼光纤放大器达到了增益带宽92 nm,平均增益39.95 dB,增益平坦度0.1447 dB。     

G652光纤中背向自发拉曼散射的增益特性

讨论了背向自发Raman散射脉冲在自生分布式G652光纤Raman放大器中传输的增益特性。实验发现，反Stokes Raman（ASR）和Stokes Raman（SR）自生分布式脉冲光纤Raman放大器的阈值抽运峰值功率是25．4W和18．0W。在入射功率为52W时，ASR和SR的增益分别为5．0dB和8．6dB。放大的反Stokes和Stokes背向自发Raman散射光时域反射（OTDR）曲线上放大的阈值时间位置随激发功率的增高前移并具有规律性。放大的ASR背向自发散射强度受光纤温度调制，具有温度效应，已应用于远程分布光纤Raman温度传感器系统。     

基于改进粒子群算法的后向泵浦RFA设计北大核心CSCD

为了满足第六代移动通信(6G)系统对光通信网络的高速率及大容量的要求,进一步提高光传输网络中光纤放大器的带宽、响应速率及放大倍数等成为目前的研究重点。在使用碲酸盐光纤作为光纤增益介质的同时,提出一种改进粒子群优化算法,通过在迭代过程中动态的调整速度、位置及惯性权重值,获得更高收敛速度,增强全局搜索的能力。应用该算法对拉曼光纤放大器的各个泵浦光参数配置进行优化、分析及仿真验证,最终设计出平均开关增益为23.738 8 dB,增益平坦度为0.209 8 dB的后向泵浦拉曼光纤放大器。结果表明,改进的粒子群优化算法对拉曼放大器泵浦光的参数配置有很强的适应性,能够获得较低的增益平坦度,对未来拉曼光纤放大器的设计具有一定的参考意义。     

色散补偿型光纤拉曼放大器的增益和噪声指数的实验研究

对S波段的色散补偿型分布式光纤拉曼放大器(FRA)进行了研制。本放大器中采用了先进的光纤拉曼激光器作为抽运源,并对5 km DCF-50 km G652光纤色散补偿型分布式FRA分别进行了前向抽运和后向抽运,测量了其前向和后向增益光谱和噪声谱,结果表明后向抽运方式在增益和噪声特性方面优于前向抽运方式。对色散补偿型分布式FRA在后向抽运方式下的增益和噪声指数随抽运功率的变化而变化的规律进行了实验研究,结果表明其增益随抽运功率的增大而增大,噪声指数随增益的增大而减小。为比较色散补偿型分布式FRA和分布式FRA在增益和噪声方面的性能,分别测量了上述两种光纤拉曼放大器在后向抽运方式下的增益谱和噪声指数谱,结果表明: 5 km DCF-50 km G652光纤制成的色散补偿型分布式FRA的增益和噪声特性,均优于由50km-G652光纤制成的分布式FRA。本文对实验结果进行了理论分析。     

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...     

Simultaneous Cancellation of Fiber Loss, Dispersion, and Kerr Effect in Ultralong-Haul Optical Fiber Transmission by Midway Optical Phase Conjugation Incorporated With Distributed Raman Amplification

An alternative application of distributed Raman amplification (DRA) for ultralong-haul optical fiber transmission is proposed. In our study, the DRA is employed in a transmission system using midway optical phase conjugation (OPC) for amplifying an optical signal and, at the same time, for constructing signal power evolution, which is symmetrical with respect to the midpoint of the system where the OPC is performed. Then, the nonlinear signal waveform distortions that are caused by the Kerr effect, as well as fiber dispersion, are almost completely compensated by the OPC, whereas the fiber loss is compensated by the DRA. Three possible symmetrical signal power maps - a power map that has a reverse sign of the power map that is caused by lump amplification, a flat signal power map, and an arbitrary symmetrical signal power map - are numerically designed by using appropriate Raman pump powers. We show that the flat power map exhibits smaller difference from the target and a higher optical signal-to-noise ratio and requires lower pump power than the other two power maps. Numerical simulation results demonstrate that, by employing the flat power maps with a span of 40 km, a single-wavelength signal whose data rate is 160 Gb/s can be successfully transmitted over 5000 km, and the Kerr effect is sufficiently suppressed near limitation due to the nonlinear accumulation of noise. Finally, we study the feasibility of expanding our method to wavelength-division-multiplexed signal transmission by designing a DRA gain with multiple-wavelength pumping to simultaneously obtain a flat power map and a wide-and-flat gain bandwidth. By using four-wavelength Raman pumps while carefully choosing pump wavelengths and their powers, we achieve the DRA gain that simultaneously gives a fluctuation of the signal power of only 3.5%, a gain ripple of only 5.3%, and, at the same time, a gain bandwidth of as wide as 46 nm.     

Efficient Pump Depolarizer Analysis for Distributed Raman Amplifier With Low Polarization Dependence of Gain

This paper discusses a method of reducing the polarization dependence of gain (PDG) of a distributed Raman amplifier. Reducing its PDG is important for a Raman amplifier because it is higher than that of an erbium-doped fiber amplifier and can degrade transmission performance. Raman PDG is determined primarily by two factors, namely 1) polarization-mode dispersion (PMD) of the transmission fiber and 2) degree of polarization (DOP) of the pump source. The authors propose a simple analytical model to show the required pump light DOP for a given transmission fiber's PMD and the allowable PDG. For instance, a low pump DOP of 5% produces a low PDG of 0.2 dB under typical fiber PMD conditions, in which the analytical model agrees well with experiment. Subsequently, to achieve the required DOP, the pump source configuration is investigated in detail. The authors used one length of polarization-maintaining fiber (PMF) as an efficient pump depolarizer and evaluated its performance for various pump light spectra. It has been shown that the DOP following the depolarizer is determined simply by Fourier transformation of the pump light spectrum. The analysis in this paper has led to the important result that a Fabry-Perot laser diode pump with a short piece of PMF is effective in achieving a low pump DOP due to its multimode spectrum when the length of the PMF is properly adjusted for the longitudinal-mode spacing frequency. It has been verified that a Raman amplifier's PDG can be reduced by the proposed efficient depolarizer sufficiently for a PDG-reduced Raman amplifier repeater to be applicable to long-haul transmission systems     

面向6G的拉曼微结构光纤放大器设计

为了满足6G系统对未来光通信网络的要求,利用掺 GeO₂微结构光纤设计了一种多泵浦拉曼光纤放大器,该方案能够解决适用于6G系统需求的 拉曼光纤放大器中谱宽窄、输出增益低且不平坦的问题。在理论上,运用四阶龙格-库塔法 对经典拉曼耦合波微分方程进行求解;在结构上,通过合并两对具有相同波长的泵浦光,来 减少泵浦个数、简化结构,同时采用级联两段微结构光纤的方法,使信号光增益在拉曼放大 器的输出端实现前放大,后补偿。实验结果表明,在100 nm的谱宽范 围内,放大器的平均增益高达35.72 dB,增益波动小于±0. 43 dB。     

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。     

The experimental study of the effect of fiber chromatic dispersionupon IM-DD ultra-long distance optical communication systems withEr-doped fiber amplifiers using a 1000 km fiber loop

We have evaluated the transmission performance difference of ultra-long distance optical communication systems with Er-doped fiber amplifier repeaters due to fiber chromatic dispersion effect. A 1000 km fiber loop with 31 Er-doped fiber amplifiers was used for the experiments. We have changed the system zero dispersion wavelength by changing the length of the normal single-mode fiber at the end of the fiber loop, and measured the bit-error-rate after transmission. Comparison of the longest transmission distance and the width of the 9000 km transmissible window were discussed for various system zero dispersion wavelengths. The results have shown that the difference between the gain peak wavelength of the amplifier chain and the system zero dispersion wavelength caused degradation of the system performance, and the degree of the degradation was almost symmetrical from the gain peak wavelength