WDM网中同频串扰的研究

串扰是波分复用(WDM)光网络中限制光交叉连接(OXC)节点容量的一个重要因素.本文分析了相干和非相干串扰对通过OXC节点的光信号的影响,给出了固定和最佳判决门限两种情况下的光功率恶化,并进行了仿真计算.结果表明相干串扰对系统的影响很大.与固定判决相比,采用最佳判决可以降低串扰影响.串扰引起的光功率恶化主要取决于复用波数M,而与输入光纤数N关系不大.为了减小串扰对网络的限制,可以在OXC节点内使用滤波器.     

Generation of optical carrier suppression millimeter-wave signal using one dual-parallel MZM to overcome chromatic dispersion

In this paper, we have proposed a novel approach to generate optical carrier suppression (OCS) mm-wave with signal only carried by one first-order sideband using a dual-parallel MZM in radio-over-fiber (RoF) system, and the transmission performance was also investigated. As the optical mm-wave signal is transmitted along the fiber, there is no time shift of the data symbols resulting from the group velocity dispersion in the fiber because the signal is only modulated on one sideband. The simulation results showed that the eye diagram keeps open and clear even when the optical mm-wave signals are transmitted over 96-km and the power penalty is about 1-dB after fiber transmission distance of 60-km, which is quite consistent with our theoretical analysis. Furthermore, the proposed OCS optical mm-wave generation approach is also used in a full-duplex RoF link based on wavelength reuse at the base station for the uplink due to another pure sideband without carrying data. The bidirectional 2.5-Gbit/s data is successfully transmitted over 40-km standard single mode fiber with less than 0.5-dB power penalty in the simulation. Both the unidirectional RoF downlink and the full-duplex RoF system have good performance.     

长距离和多模接入网络中低密度奇偶校验-正交频分复用的性能研究

研究了低密度奇偶校验编码与正交频分复用相结合的编码调制技术,从理论上分析了光纤链路中色散和频率选择性衰落的影响,并通过数值模拟仿真,比较了不同编码码率的编码调制信号在长距离单模光纤传输和多模光纤接入网络中的传输性能.仿真结果表明,采用码率为0.75的长码型非规则的低密度奇偶校验编码与正交频分复用相结合的编码调制技术更适合光纤通信系统中的长距离传输和多模接入网络.     

Impacts of dispersion maps on nonlinear distortion in distributed Raman amplified multi-span systems

The influences of dispersion maps on three major nonlinear effects (SPM, XPM and SRS) in distributed Raman amplified fiber transmission systems with periodic dispersion compensation are numerically investigated at identical nonlinear phase shift. The results show that compared with lumped amplification, distributed amplification tends to enhance the SPM/XPM induced penalties provided per span complete DC is used. However, these performance differences can be canceled out by means of optimal dispersion managements. Moreover, distributed Raman amplification can change the optimal dispersion maps for XPM effects. On the other hand, the impacts of SRS crosstalk are mainly determined by wavelength spacing and walk-off parameter, and the effects of dispersion management are quite limited. For a system with properly designed fiber dispersion characteristics, SRS induced waveform distortion can be well suppressed.     

光纤传输系统中互相位调制和受激拉曼散射串扰噪声的比较研究Ⅱ--级联传输系统

在具有级联光放大器的密集波分复用强度调制一直接检测光纤系统中，导出了包含互相位调制和受激拉曼散射共同作用的强度／相位矩阵表达式。在计算强度噪声谱的基础上，研究了互相位调制和受激拉曼散射的相互耦合并用于密集波分复用系统的噪声分析。在带色散补偿的密集波分复用级联光纤传输系统中(如80信道，信道间距50GHz)，受激拉曼散射引入的串扰噪声功率可能超过互相位调制。最后，给出了密集波分复用系统分析与设计的若干建议。     

Impact of Modulation Index on Homodyne Crosstalk in Optically Switched Networks

The impact of imperfect modulation depth on crosstalk induced penalty in optical switched systems is theoretically and experimentally investigated. A nonlinear relationship with a clear "knee" is observed, indicating an optimum modulation index of 8 dB.     

Experimental demonstration and cascadability analysis of a tunable optical buffer based on a re-circulating loop consisting of optical SSB modulator and FBG filter

We demonstrate a tunable optical buffer with variable time delays for label switching applications using an optical single sideband modulator in a fiber Bragg grating-filter loop. This optical buffer realizes payload storage with optional wavelength conversion function, providing flexibility in packet router design. Small sensitivity penalty is observed in our experiment after the payload circulating in the buffer loop three times. The cascadability of the tunable optical buffer is investigated. We provide analysis of the optical signal to noise ratio degradation due to accumulated amplified spontaneous emission noise, and the penalty caused by loss ripple and group delay ripple of the fiber Bragg grating.     

Tailoring Chirped MoirÉ Fiber Bragg Gratings for Wavelength-Division-Multiplexing and Optical Code-Division Multiple-Access Applications

The design and fabrication of chirped Moiré fiber Bragg gratings (CMGs) are presented, which can be used in either (1) transmission as passband filters for providing wavelength selectivity in wavelength-division-multiplexed (WDM) systems or (2) reflection as encoding/decoding elements to decompose short broadband pulses in both wavelength and time in order to implement an optical code-division multiple-access (OCDMA) system. In transmission, the fabricated CMGs have single or multiple flattened passbands (< 0.5 dB ripple) and exhibit > 12 dB isolation and near constant in-band group delay. It is shown that these filters do not produce any measurable dispersion-induced power penalties when used to provide wavelength selectivity in 2.5 Gbit/s systems. It is also demonstrated how CMGs can be used in reflection to encode/decode short pulses from a wavelength-tunable mode-locked Er-doped fiber laser.     

Impact of Modulation Index on Homodyne Crosstalk in Optically Switched Networks

The impact of imperfect modulation depth on crosstalk induced penalty in optical switched systems is theoretically and experimentally investigated. A nonlinear relationship with a clear "knee" is observed, indicating an optimum modulation index of 8 dB.     

基于超结构光纤光栅和非线性放大环镜的OCDM系统

实验研究了基于超结构光纤布喇格光栅的40 Gbit/s×2的光码分复用系统,利用非线性放大环镜对系统解码输出脉冲进行了整形和噪音抑制.在非线性放大环镜非线性开关特性的作用下,解码输出脉冲的宽度由7.7 ps压缩至3.6 ps,干扰噪音得到了有效地抑制,实验中环镜的输入功率约为6 mW.结果表明,采用非线性放大环镜能够提高超结构光纤光栅光码分复用系统的性能,这种有效抑制噪音的高速全光编解码还可以应用于光标签交换网络.     

Nonlinear Crosstalk Suppression in WDM-SCM Systems

The mechanism of nonlinear crosstalk in WDM-SCM fiber communication systems is investigated. Then the crosstalk suppression method of complementary modulation of twin carriers is introduced and discussed. Aiming at the limitation of this method, a new method named symmetric carrier complementary modulation is presented, and it has shown satisfactory effect in crosstalk reduction.     

A multi-channel full-duplex 60-GHz-band radio-over-fiber system

We propose and simulate a novel full-duplex radio-over-fiber system using a single light source at central station (CS). The scheme is employed to generate 60-GHz optical millimeter wave at CS for down-link transmission while the same optical carrier is reused at base station for up-link connection. There is no additional laser source for the upstream data generation in the base station. The bidirectional full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF). The power penalty for the down-link data after transmission over 40 km SMF is less than 0.6 dB, while for the up-link data, the power penalty after transmission over 40 km SMF is neglected. This system shows good performance over long-distance delivery and has important applicable value in high radio frequency (RF) sector and multi-channel full-duplex system.     

System degradation due to phase error induced crosstalk in WDM optical networks employing arrayed waveguide grating multi/demultiplexer

The phase error induced crosstalk within arrayed waveguide gratings (AWG) have been investigated theoretically as well as simulation. For WDM system, a crosstalk level of −21.9 dB causes a power penalty of 1 dB for 64 channels and less than 0.5 dB for 16 channels and 32 channels, respectively. For crosstalk level of −30 dB and below, the power penalty is negligible. Crosstalk due to phase error also causes higher power penalty at higher bit rate. Bit rate of 10, 20 and 40 Gbits/s causes power penalty of 1 dB with crosstalk level of −41.5, −46.25 and −49 dB, respectively.     

通过以太无源光网的射频电视传送技术

论述了1550 nm射频电视(CATV)通道与1490 nm数据通道的相互干扰问题。针对1490 nm光波通过光纤中受激拉曼效应对1550 nm光波的非线性串扰和1550 nm光波通过粗波分复用(CWDM)分波器对1490 nm光波的线性串扰提出了理论计算公式,进行了定量分析和计算。结果表明,数据非线性串扰可使射频电视系统低频端的载噪比下跌9 dB;而在常规融锥型粗波分复用分波器情况下,射频电视线性串扰可使数据光接收机的光功率代价达到2.5dB。最后指出了克服串扰的方法,如以太空闲字符扰码和高隔离度粗波分复用等。     

A detailed analysis of cross-phase modulation effects on OOK and dpsk optical WDM transmission systems in the presence of GVD,SPM, and ASE noise

A performance analysis is carried out to evaluate the effect of cross-phase modulation (XPM) on a dispersion-managed 20 Gb/s optical wavelength-division multiplexing (WDM) transmission system using either the on-off keying (OOK) or the different-phase-shifting keying (DPSK) modulation, in the presence of the group-velocity dispersion (GVD), self-phase modulation (SPM), and amplified spontaneous emission (ASE). It is found that to achieve a bit error rate (BER) of 10⁻⁹ at a distance of 160 km, a 1.0 dB XPM power penalty is incurred for input channel power of 3 dBm in the OOK transmission and 7 dBm in the DPSK transmission. The power penalty increases with input channel powers and is inversely proportional and exhibits oscillations with respect to the channel separation. The oscillation is evenly spaced for the DPSK but not for the OOK and suggests the presence of optimum separation values. The XPM penalty decreases when a high dispersion fiber is used and increases linearly with increasing dispersion slope. Small residual dispersion can reduce the penalty of nonlinear effects.     

基于综合光学调制技术的光纤无线双向通信系统设计

提出并研究了一种使用单光源的光纤无线双向传输系统.该系统只需在中心站配置一个可调谐激光器,以产生频率恒定的激光光源,通过综合光学调制（频率调制、强度调制）技术将基带信号调制到光载波上,最终形成60 GHz毫米波下行信号|同时,相同的光载波在基站被重用,作为上行链路传输光源.系统结合光载波重用技术和综合调制技术特点,合理利用资源,基站结构更为简化.仿真结果表明,该系统可以将速率达2.5 Gbit/s的数据在单模光纤中双向传输20 km,功率代价小于0.5 dB,相对已有的技术方案,该传输系统在传输功率、传输距离、传输性能方面具有明显优势.     

光纤传输系统中互相位调制和受激拉曼散射串扰噪声的比较研究Ⅰ--单级传输系统

在密集波分复用强度调制直接检测光纤系统中 ,导出了包含互相位调制和受激拉曼散射共同作用的强度/相位矩阵表达式。在计算强度噪声谱的基础上 ,研究了互相位调制和受激拉曼散射的相互耦合并用于密集波分复用系统的噪声分析。分析表明 ,受激拉曼散射主要引入低频串扰噪声 ,而互相位调制主要引入高频串扰噪声。相邻较近信道引入的串扰噪声主要来源于互相位调制 ,相邻较远信道引入的串扰噪声主要来源于受激拉曼散射。在单级传输 (无色散补偿 )系统中 ,系统性能一般首先受到互相位调制的限制     

实现20Gbit/s的OTDM孤子信号56km色散位移光纤的传输

在国内最先采用孤子的方式将8×2.5Gb/s的OTDM信号在色散位移光纤中传输了56.1km,对8×2.5Gb/s的OTDM进行解复用后进行了误码测量,系统功率代价为2.9dB.系统采用增益开关半导体激光器作光孤子源,高Q电滤波方式提取时钟,非线性光学环路镜解复用。孤子脉冲最大半宽度为20ps,传输光纤平均色散1.2ps/nm/km。     

单边带调制ROF链路中交叉相位引起的非线性串扰

利用非线性薛定谔方程,推导计算了基于光学单边带调制的光载射频链路中交叉相位调制引起的非线性串扰,建立了新的分析模型,并和抽运探测法进行了比较.该模型可以用来分析不同的ROF链路,特别是波分复用光电上转换链路.得到了单链路和波分复用链路的传输眼图.信道中由交叉相位调制引起的非线性串扰和调制频率,泵浦和探测能量,光纤长度以及信道间隔等有关,通过仿真验证了理论分析.     

Add/drop applications in fiber ring networks based on a reconfigurable optical add/drop multiplexer in a re-circulating loop

A periodic add/drop system in a fiber ring network was investigated using a reconfigurable optical add/drop multiplexer (ROADM) in a re-circulating fiber loop. After seven cascaded add/drop nodes at every 150 km along the transmission, at bit error ratio (BER) equals to 10⁻⁹ and data rate of 10 Gbps, we observed a 2.5 dB power penalty for the passing through channels with 1050 km transmission distance, and 0.3 dB sensitivity penalty variation for the periodic add/drop channels at every 150 km, respectively.