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.     

全光网中的同频串扰

本文分析了全光网中光分插复用节点和光交叉连接节点的同频串扰问题.同频串扰分为相干串扰和非相干串扰,他们对网络性能的影响不同.我们对节点的同频串扰进行了详细的分析和理论推导,并得到了其光功率代价和同频串扰之间的数学关系.     

密集波分复用条件下的光轨网络串扰分析与仿真

光轨网络是一种能够利用成熟的光学器件实现带宽灵活分配和信息交换的新型网络.串扰是限制光轨网络的物理层性能及其扩展性的重要因素.本文讨论了典型的光轨网络节点中异频串扰和同频串扰的产生原因,理论分析了两者对光轨网络的物理层传输性能的影响.给出了3种串扰性能的评价方法.以密集波分复用技术为应用背景,分别搭建了器件隔离度为20 dB和30 dB的、具有3个节点5个波长且单波长速率为2.5 Gbps的光轨网络,仿真了串扰在光轨网络中的传播过程,并计算了光轨网络的误码率、功率代价和相对串扰.理论分析和仿真结果表明:光滤波器、解复用器和复用器是光轨网络中串扰产生的关键器件,且提高器件的隔离度等性能对于提高光轨网络的传输性能会有较显著的效果;在密集波分复用条件下,串扰对单波长速率为2.5 Gbps的光轨网络的误码率和功率代价具有显著的影响,从而限制了光轨网络实际可用的节点数目.     

密集波分复用条件下的光轨网络串扰分析与仿真

光轨网络是一种能够利用成熟的光学器件实现带宽灵活分配和信息交换的新型网络.串扰是限制光轨网络的物理层性能及其扩展性的重要因素.本文讨论了典型的光轨网络节点中异频串扰和同频串扰的产生原因,理论分析了两者对光轨网络的物理层传输性能的影响.给出了3种串扰性能的评价方法.以密集波分复用技术为应用背景,分别搭建了器件隔离度为20dB和30dB的、具有3个节点5个波长且单波长速率为2.5Gbps的光轨网络,仿真了串扰在光轨网络中的传播过程,并计算了光轨网络的误码率、功率代价和相对串扰.理论分析和仿真结果表明:光滤波器、解复用器和复用器是光轨网络中串扰产生的关键器件,且提高器件的隔离度等性能对于提高光轨网络的传输性能会有较显著的效果;在密集波分复用条件下,串扰对单波长速率为2.5Gbps的光轨网络的误码率和功率代价具有显著的影响,从而限制了光轨网络实际可用的节点数目.     

级联光交叉连接和光分插复用系统串扰研究

分析了光网络节点串扰产生的原因以及级联光交叉连接(OXC)和光分插复用(OADM)系统的串扰,对级联系统进行模拟,计算并分析了光开关隔离度、上路信号的功率差对系统误码率的影响,得出了光开关隔离度是产生串扰的主要原因、在光开关前进行功率均衡有利于提高系统误码性能等结论.     

光交换芯片中串扰的相干特性研究

以马赫-曾德尔干涉仪光开关单元组成的4×4 Benes光交换芯片为例，研究了光交换芯片中的相干问题。理论推导了光交换芯片输出端口与输入端口之间光场的变换关系，揭示了信号和串扰的产生规律，分析了光开关状态对串扰相干强度的影响。仿真研究表明：相干串扰对信号插损的影响可以忽略；在不同光开关组合状态下，光交换芯片的串扰波动可达7 dB。根据相干光束之间的相位关系，提出一种等效去除光交换芯片中串扰相干性的方法。另外，对串扰大小对通信误码率的影响进行了实验评估。     

半导体光放大器引起的串扰及其抑制技术

由于半导体光放大器(SOA)的增益饱和效应,在波分复用系统中.每个信道的增益受到复用的其它信道的影响.SOA引起的各信道之间的串扰严重限制了其应用.理论研究了SOA增益饱和效应引起的信道间串扰.数值模拟了多路信道复用时系统的误码率随复用信道数和光功率的变化情况,发现随着复用信道数的增加SOA增益饱和引起的信道间串扰越来越严重.对SOA中串扰的抑制方法进行了理论和实验研究.数值模拟发现连续光注入可以抑制输出功率的波动,从而减小误码率,当复用10个信道时,连续光注入可以使功率代价减小2 dB;实验验证了两信道的40 Gb/s系统中,注入连续光可以减少SOA引起的信道间串扰.     

OADM的设计

OADM节点是WDM光网络的关键节点之一。研究了OADM节点的实现方法,提出了一种设计方案,并讨论了光上下路开关阵列的驱动和监控的软硬件制作,完成了下路光功率监测的电路设计以及软件设计。分析了OADM节点保护倒换的原理和节点中的串扰问题。     

频谱分割波分复用无源光网络及色散影响

频谱分割是使用窄带光滤波器选择宽带光源光谱的一个切片的WDM技术,在波分复用无源光网络(WDM-PON)中采用波分复用器((MUX)进行频谱分割,能够实现光网络单元(ONU)的无色化.模型分析表明由于频谱分割的作用,使得波分复用器光通带外的频谱成分被过滤,减小了宽带光源的色散影响.在20 nm CWDM标准信道间隔下,能够以不超过1 dB的光功率代价支持155 Mb/s信号在20 km的G.652常规光纤上传输;在0.8 nm DWDM信道间隔下则能够支持2.5 Gb/s信号传输,色散引起的光功率代价低于0.5 dB.采用中心波长为1550 nm、谱宽70 nm、输出功率为-10 dBm的LED,研制了125 Mb/s速率信号直接调制的无色ONU.在信道间隔为20 nm、光纤长度为20 km的4波长WDM-PON系统上进行测试,色散等因素引起的光功率代价小于1 dB,系统光功率余量则超过5.6 dB.     

光分组交换节点中缓存器对串扰相干特性的影响

研究了光分组交换中光输出缓存器引起的排队延迟对节点串扰特性的影响，建立了节点串扰特性与缓存器长度之间关系的数学模型，结果表明，对光分组交换节点，由于缓存器的存在，串扰源数目随缓存器的长度增加而增加；串扰中，非相干串扰占多数，数目随机的相干串扰的影响较小，且当缓存器较长时，相干串扰的影响可以忽略，即可将所有串扰视为非相干。     

Coherent crosstalk in passive microring based Optical Networks-on-Chip

Optical Networks-on-Chip (ONoC) is emerging technology for future optical interconnects used in all optical networks. The electrical interconnects face lot of problems due to their inability to support higher data rates used in the System-on-Chip (SoC) technologies. Integrated optical interconnects based on SoC avoid this bottleneck with their support to higher data rates. In this paper for the first time we have studied and analyzed ONoC at physical level for the system performance based on crosstalk, BER, throughput, system frequency, and other related parameters. The investigation of ONoC performance is carried out for the multistage microring optical crossconnect on SoC for coherent WDM signals. The analysis can be used in the design of ultra-high speed photonic routers for reliable data communication and processing. The results show the dependency of a coherent crosstalk on the system frequency of SoC and also illustrate the reduction in throughput with increase in number of WDM signals due to higher probability of packet transmission. Minimum 2 dB signal to noise ratio can be obtained when crosstalk is ?25 dB with 60 wavelengths for probability of packet transmission is 0.5.     

Study on loss and crosstalk in WDM passive optical network based on spectral slicing

A model for calculating loss and crosstalk in WDM passive optical network based on spectral slicing is proposed in this paper. Through theoretical analysis and numerical calculation, the relationship between loss or crosstalk and the parameters of the system, such as the bandwidth of the light-source, the parameters of the multiplexer, the number of channels and the fraction of channel misalignment, was demonstrated.     

一种基于斜光栅辅助的非对称耦合器型光分插复用器

提出了一种基于斜光栅辅助的非对称耦合器型光分插复用器。运用复合波导的三维正交模式,对器件的三种可能的结构进行了理论分析,选出粗波导光栅型结构。利用耦合模理论,模拟了斜光栅的耦合特性并对其倾斜角进行优化设计。通过回波峰值设计法,将器件的工作波长放在波分复用信道之内,回波峰值波长放在波分复用信道之外,使得器件的性能大有提高。模拟结果表明器件的串扰可达到-30 dB,回波损耗可达到-25 dB。同时,器件的关键工艺容差较大,易于批量化生产。当斜光栅的倾斜角度在2.5°到4.5°之间时,器件的串扰低于-28 dB,回波损耗低于-22 dB。     

Transmission Characteristics of Several Kinds of Filters for WDM Optical Networking

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Dynamically selective multiwavelength cross-connect based on fibre Bragg gratings and mechanical optical switches

A dynamically selective multiwavelength cross-connect for wavelength division multiplexed (WDM) networks based on fibre Bragg gratings (FBGs) and optical switches is reported. Dynamically single- or multi-channel cross-connect functionality can be realized according to control of the optical switches and the FBGs' arrangement. Bit-error-rate performance with negligible power penalty is achieved in a 2.5Gbs-1x3 WDM channels over 100km conventional single-mode fibre (SMF) network demonstration. The characteristics of low channel crosstalk, uniform channel loss, high scalability and cascadability, and low cost of this device could provide more reconfiguration flexibility and network survivability for WDM networks.     

Power budget improvement for long-haul WDM transmission with optimum placement of SOAs

Sufficient power margin is investigated for ten-channels WDM transmission over 68,908 km by using cascaded in-line semiconductor optical amplifier for the differential phase-shift keying (DPSK) modulation format for the first time. For this, we used the structural optimization and placement scheme of semiconductor optical amplifiers (SOAs) for long-haul WDM transmission. The SOA model for in-line amplifier has low crosstalk, ASE noise power and low noise figure with sufficient gain. The impact of noise figure, amplification factor, ASE noise power, optical gain and crosstalk with signal input power for the SOA model has been illustrated, which shows that 400 mA is the optimum bias current.

We observed that the optimized optical filter bandwidth for the 100 GHz channel spacing is 0.4 nm. We observe that as we decrease the channel spacing, the quality of signal is degraded. We show that the optimum span scheme-1 is used up to a transmission distance of 68,908 km with good quality for power margin more than 24 dB. This placement scheme of SOAs shows good power budget for long transmission distance. We show the optical spectrum and clear eye diagram at the transmission distance of 68,908 km for optimum span schemes. Finally, we investigate the maximum transmission distance with decrease in channel spacing, i.e., 20 and 50 GHz.     

Modify SRS-induced crosstalk with variety of fiber in SCM–WDM transmission links

In this paper, the SRS-induced crosstalk has been evaluated in a SCM–WDM communication links at different modulation frequencies and transmission lengths for variety of fiber. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fiber, standard single mode fiber (SMF) has minimum crosstalk (−78 to −38) dB, (−55 to −33) dB and (−46 to −34) dB at modulation frequencies, transmission lengths and optical powers. Dispersion compensation fiber (DCF) has maximum crosstalk (−60 to −12) dB, (−37 to −12) dB and (−27 to −12) dB at modulation frequencies and transmission lengths.     

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.