10Gbit／s级联光纤放大器通信系统的传输距离

本文数值模拟了强度调制光信号在级联光纤放大器常规ＳＭＦ通信系统中的传输,在模拟中主要考虑了自相位调制、群带色散和ＡＳＥ噪声。我们使用负色散补偿光纤去补偿群速色散和自相位调制。结果表明如果色散得到很好的补偿,当放大器的间距减少到５０ｋＭ时,无误码２０５０ｋｍ传输是可能的。     

Dispersion-Compensating Fiber Raman Amplifiers With Step, Parabolic, and Triangular Refractive Index Profiles

This paper presents a comprehensive analysis of the performance of a gain-flattened coaxial fiber Raman amplifier with respect to the refractive index profile. The variation of the dispersion coefficient and the end-end gain spectrum of the coaxial fiber Raman amplifier against the core structure as a function of the step, parabolic, and triangular profiles are analyzed. The analysis shows that the dispersion coefficient is sensitive to the variation of the core structure of the fiber, whereas the effective Raman gain coefficient remains nearly constant as the structure changes. Simulations of transmissions employing the coaxial fiber Raman amplifier with the three different structures are carried out individually, and the results show that the parabolic and triangular profiles perform better than the step profile, where the parabolic profile gives the best performance over 80 km of G.652 fiber, with a transmission rate of 20 Gb/s and a gain ripple of plusmn1 dB. In addition, the analysis shows that the maximum negative dispersion wavelength of the fiber exhibits a linear relationship with the normalized core radius. Hence, a coaxial fiber Raman amplifier providing a possible operation over the L-band is proposed     

DDF色散值的阶梯曲线近似在色散管理系统中的应用

针对色散管理系统中色散渐减光纤(DDF)制造工艺复杂的缺点,设计一种色散渐减光纤的替代色散管理链路.利用两种正负色散光纤,通过设计正负色散光纤的长度来调整各个色散管理周期的平均色散值,使相邻放大器中光纤链路的色散值呈阶梯曲线状递减,从而近似代替色散渐减光纤平衡减弱的非线性效应.数值模拟结果表明色散渐减光纤的阶梯曲线近似对40Gbit/s的光传输系统性能有很大的提高作用.     

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.     

Performance comparison between DCF and RDF dispersion compensation in fiber optical CATV systems

An architecture of an externally modulated AM-VSB CATV 77-channel erbium-doped fiber amplifier (EDFA)-repeated system which use the combination of a single-mode fiber (SMF) and reverse dispersion fiber (RDF) as a dispersion compensation device is proposed and demonstrated. Compared to the conventional externally modulated fiber optical CATV systems with or without a dispersion compensation fiber (DCF), excellent performance of composite second order (CSO) /spl ges/ 78 dB accompanied by satisfied carrier-to-noise ratio (CNR) /spl ges/ 50 dB and composite triple beat (CTB) /spl ges/ 65 dB was obtained in the proposed system.     

基于非线性渐增原理获得抛物线型自相似脉冲的研究

采用理论推导和数值模拟相结合的方法研究了脉冲在指数渐增的非线性渐增光纤(NIF)中的自相似演化。结果表明,与双曲渐减的正色散渐减光纤(ND-DDF)类似,利用指数渐增的NIF也可获得具有严格线性啁啾的抛物线型自相似脉冲。同时深入研究了ND-DDF和NIF两种增益等效方式对自相似演化特性的影响,结果表明:1)等效增益决定了脉冲自相似演化的结果,等效方式决定了脉冲自相似演化进程快慢;2)在具有相等的等效增益条件下,脉冲在指数渐增NIF和双曲渐减ND-DDF中演化为相同的自相似脉冲,但是前者对脉冲的自相似演化更高效,即前者实现自相似演化所需光纤长度更短;3)两种增益等效方式所需光纤长度的关系是使得各自具有相同的光纤有效放大因子。     

Exact compensation for both chromatic dispersion and Kerr effect ina transmission fiber using optical phase conjugation

We propose a new method to compensate exactly for both chromatic dispersion and self-phase modulation in a transmission fiber, where the light intensity changes due to fiber loss and amplifier gain. This method utilizes optical phase conjugation (OPC). The pulse shape is precompensated before OPC by transmission through a fiber with large dispersion. A computer simulation demonstrates effective compensation for waveform distortion in a 40 Gb/s NRZ intensity-modulated light transmission     

40Gb/s光纤通信系统中不同码型传输特性的实验研究

在高速光纤通信系统中码型的选择是决定系统传输质量和光谱效率的主要因素。码型的选择和信道速率、信道波长间隔、光放大器的选择、光放大器放置间隔、光纤的类型、色散管理策略等各种因素密切相关。分析了非归零码（NRZ）、归零码（RZ）和载波抑制归零码（CSRZ）码型的产生方式及特点。采用单信道和掺铒光纤放大器（EDFA）放大方式对三种码型进行了40Gb/s的100kmG.652光纤通信传输实验。比较了三种码型的系统传输持性、最佳入纤功率和不同入纤功率下的功率代价：载波抑制归零码最佳入纤功率为9dBm，功率代价小于非归零码和归零码。结果表明，在相同的色散补偿条件下，载波抑制归零码比归零码和非归零码有更优的非线性容忍度。     

级联PSA非零色散位移光纤通信系统传输性能的研究

本文通过计算机系统仿真研究了以相敏光放大器（PSA）作为中继光放大器的非零色散位移光纤通信系统的传输性能,分析了PSA系统的码间干扰（ISI）限制距离与信号速率、光纤色散、放大器间距和放大器平均输出信号功率的关系,以及PSA中泵浦光和信号光之间的相位漂移和信号脉冲波形对级联PSA光传输系统传输性能的影响。     

TDM抽运光纤拉曼放大器的色散研究

基于光纤拉曼放大器(FRA)的非线性偏微分耦合方程,采用时分复用(TDM)方式抽运,研究了多波长抽运源反向抽运时信号光在光纤中的传输特性.利用分布傅里叶变换方法数值模拟了TDM反向抽运光纤拉曼放大器的色散特性.分析了光纤的色散系数、抽运光的占空比,以及抽运源的数量变化等对光纤拉曼放大器色散的影响,研究结果为TDM抽运光纤拉曼放大器色散的进一步研究提供了参考.     

常规DSF光纤参变放大器的带宽拓宽研究

为了拓宽常规色散位移光纤(DSF)型双抽运光纤参变放大器(FOPA)的放大带宽,提出了用DSF和单模光纤(SMF)级联来构造周期色散补偿双抽运FOPA的思想。利用SMF正的二阶色散以减小DSF负的四阶色散引起的相位失配,从而达到有效拓宽FOPA放大带宽的目的。结合四波混频耦合方程对该双抽运FOPA进行仿真研究,得到拓宽为69nm的放大带宽的结果。结果表明,光纤长度一定时,采用给出的最佳补偿光纤长度进行色散补偿,可有效减小因DSF四阶色散引起的相位偏移,进而拓宽放大带宽;分多段级联进行色散补偿时,可进一步拓展放大带宽。     

Dispersion-compensator incorporated optical fiber amplifier

An optical fiber amplifier incorporating a dispersion compensator such as a dispersion compensating fiber (DCF) is proposed and examined theoretically and experimentally. The new amplifier requires only a single pump laser. In the experiment a 0.98-μm laser diode was used and the pump power was 50 mW. By utilizing remnant pump power, the amplifier can halve the loss effect of the compensator and double the apparent figure of merit of the DCF (ps/nm/dB). The noise figure of the new amplifier is not affected by inserting the DCP. A low-noise figure of 5 dB was obtained over a wide input-power range of -40 to -10 dBm     

Polarization properties of a reflective fiber amplifier employing acirculator and a Faraday rotator mirror

We present a detailed study of the polarization properties of a reflective fiber amplifier composed of a circulator, a normal single-mode Er-doped fiber and a Faraday rotator mirror. The amplifier can preserve an arbitrary input state of polarization regardless of any external perturbations, and is completely free from polarization effects. The effect of imperfections of the Faraday rotator mirror is also discussed. Finally, we demonstrate experimentally the polarization-stability of the amplifier and its ability to compensate polarization mode dispersion both in the circulator and in the single-mode Er-doped fiber     

Improvement of dispersion tolerance using phase-Modulated NRZ signals in 40-gb/s transmission systems

Compared with the conventional nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero, and chirped RZ signals by numerical simulation, a higher dispersion tolerance in the presence of fiber nonlinearities and amplifier noise has been obtained in this letter by using the phase-modulated NRZ signals. This scheme aims to improve resistance to residual dispersion by an adapted phase modulation at the transmitter.     

Ultralong lightwave systems with incomplete dispersioncompensations

Ultralong nonreturn-to-zero optical transmission systems with incomplete dispersion compensations are studied. The dispersion of transmission fiber is periodically under- or overcompensated. Postdispersion compensation (PDC) at the receiver is used to compensate for the residual dispersion caused by incomplete compensation and to tailor the signal pulse shape. Formulas estimating the change of pulse width in the absence of amplifier noise during signal transmission and after PDC are given. During signal transmission, pulse width may be compressed or broadened by the combined effect of the dispersion and self-phase modulation (SPM). The change of pulse width nearly increases with the square of the distance during signal transmission. With amplifier noise, system performance evaluated by Q factor is studied. Several types of transmission fibers are considered. The Q factor can be significantly improved by proper PDC. Signal pulse is compressed when PDC is optimized. The characteristics of the maximum Q factor and the residual dispersion are studied, in which PDC is optimized. The results show that to achieve the best system performance, fiber dispersion should be undercompensated for positive dispersion parameter and overcompensated for negative dispersion parameter. The optimal fiber dispersion lies in the range from 4 to 10 ps/km/nm for the considered systems, and the optimal ratio of residual dispersion and fiber dispersion is about 1%     

超短光脉冲通过分布式光纤放大器的传输特性

为了探讨超短光脉冲在分布式光纤放大器中的传输放大特性及影响因素,建立了光脉冲在光纤放大器中的基本传输方程,以掺镱光纤放大器为例,采用分步傅里叶变换法对放大器中光脉冲的演变进行了模拟,讨论了初始啁啾和增益色散的影响。结果表明,当光脉冲在分布式光纤放大器中传输时,光纤的色散、非线性效应均会影响脉冲的形状和频谱,光脉冲初始啁啾也会对脉冲的传输状态产生影响;对于宽频谱光脉冲,增益色散相当于一种损耗机制,应该考虑其影响。相关结果对光纤放大器的系统设计和优化具有一定的参考价值。     

Analytical study on pulse broadening in chained optical amplifiersystems

Approximate analytical formulas for root mean square pulse width evolution in fiber systems using chained optical amplifiers are derived in this paper. Effects of group velocity dispersion (GVD) and self-phase modulation (SPM) are taken into account, and the system may have axially varying parameters, such as uneven fiber dispersion including dispersion management, nonequal amplifier spacing as well as output power, etc. It is shown that the analytical formulas can be applied to the design and analysis of a wide range of practical chained optical amplifier systems, and is helpful in the understanding of the pulse distortion caused by the interaction between SPM and GVD     

Dispersion-managed solitons for 160-Gb/s data transmission

The use of dispersion-managed (DM) solitons for 160-Gb/s data transmission in fiber lines where the period of dispersion management is much shorter than the amplifier spacing is investigated through numerical simulations. It is shown that DM solitons outperform both standard solitons and “quasi-linear” return-to-zero (RZ) pulses. The dispersion tolerance is limited by pulse-to-pulse interactions and Gordon-Haus jitter and decreases with increasing transmission distance     

正常色散光纤放大器中超短脉冲的自相似演化条件

在正常色散条件下,超短光脉冲在光纤放大器中可以演化成具有线性啁啾的自相似抛物脉冲,其演化结果可影响脉冲的压缩质量.采用分步傅里叶方法数值研究了正常色散光纤放大器中,初始输入脉冲宽度、能量、光纤增益和色散系数对超短脉冲自相似演化结果的影响.发现色散长度是脉冲能否实现自相似演化的关键因素.当色散长度与光纤长度相近(几倍)时,脉冲可以实现自相似演化;两者相差越大,脉冲的自相似演化程度越差.增加初始脉冲能量可以加速脉冲的自相似演化,缩短自相似演化的距离.放大器总增益一定时,增益系数越大,脉冲受非线性扭曲的影响越大,使脉冲的自相似演化结果越差;增益系数为0.95 m-1时放大器可获得的总增益比3.8 m-1时大3.3 dB.     

5 Gbit/s, 233 km optical fiber transmission experiment employingfive semiconductor laser amplifiers

A directly modulated 1.519-μm distributed-feedback laser signal was transmitted over 233 km of single-mode fiber consisting of dispersion shifted fiber and conventional step-index fiber to minimize the dispersion penalty. The power penalty after the transmission was 0.25 dB. The results show the effectiveness of an optical amplifier repeater system for high-speed long-haul fiber optic transmission