PSO算法用于WDM系统多信道PMD补偿的研究

根据波分复用（Wavelength Division Multiplexing,WDM）系统多信道偏振模色散（Polarization Mode Dispersion,PMD）的最坏信道补偿方案,将粒子群优化（Particle Swarm Optimization,PSO）算法用于多信道的PMD补偿.在补偿最坏信道的同时,保障了其他信道的性能.并以两信道PMD补偿系统为例进行了数值模拟,得到了很好的补偿效果.     

应力对M-Z型InP/InGaAsP-EAM偏振

采用Agilent 81910A光子全参量测试仪,首次实验研究了InP/In1－xGaxAs1－yPy-MQW（Multiple-Quantum-Well,MQW）材料与衬底间因应力而产生的M-Z型光调制器的PDL影响以及由此引起的由差分群时延(Differential Group Delay,DGD)表征的偏振模色散(Polarization Mode Dispersion,PMD).研究结果表明,半导体MQW光调制器的PDL与DGD是一致的.因此在半导体光器件的制作过程中,应尽可能地减小衬底与波导芯层之间的因残存应力的存在造成对光器件的高速性能的不利影响.     

Using RLS-TEQ to reduce CP length for 20.48 Gb/s direct-detection optical OFDM transmission over 2400 km of SSMF

This paper uses a Recursive Least Squares-Time Domain Equalizer (RLS-TEQ) to reduce the Cyclic Prefix (CP) length in Direct-Detection Optical Orthogonal Frequency Division Multiplexing (O-OFDM) transmission over 2400 km of Standard Single Mode Fiber (SSMF). The RLS-TEQ can cancel the residual Inter Symbol Interference (ISI) caused by both the Group Velocity Dispersion (GVD) and the CP length being shorter than the Channel Impulse Response (CIR). Using RLS-TEQ reduces size of the CP, and consequently leading to system performance improvement.     

Comparison between DF-TEQ and LCDF-TEQ in reducing CP length for long-haul direct-detection optical OFDM transmission by computational complexity and system performance

This paper presents the comparison of using Decision Feedback Time-domain Equalizer (DF-TEQ) and Low Complexity DF-TEQ (LCDF-TEQ) to reduce Cyclic Prefix (CP) length for Optical Orthogonal Frequency Division Multiplexing (O-OFDM) transmission over 1200 km of Standard Single Mode Fiber (SSMF). Both TEQs are used immediately after the fiber channel. Numerical modeling results show that they can cancel the residual Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) caused by both the Group Velocity Dispersion (GVD) and the CP length being shorter than the Channel Impulse Response (CIR). Using these TEQs allows the reduction in size of CP, and consequently leading to system performance improvement. However, each of these TEQs adds computational complexity to the system. Therefore, the aim of this paper is to compare their performance and their computational complexities while considering different CP length and tap numbers.     

单模光纤中的二阶偏振模色散及其统计特性

用琼斯矩阵本征分析法和邦加球法,分别测量了22 km和75 km G.652单模光纤中的二阶偏振模色散,并对其平行分量、垂直分量、PCD（Polarization dependent chromatic dispersion）、消偏振项、各个分量的统计特性及其影响进行了详细的分析,得到了二阶偏振模色散随波长的分布情况及统计特性. 从统计结果可以得到,与PCD项相比,消偏振项在二阶偏振模色散中起主要作用. 该研究对二阶偏振模色散的补偿有一定的指导意义.     

一种闭环控制的错位型MEMS可调光衰减器

针对一种错位型MEMS(Micro-Electro-Mechanical Systems)可调光衰减器,基于输入输出光纤间模场的交叠积分,数值分析了径向偏差和轴向间隙同时存在的情况下,光功率衰减量与错位量和波长的关系.演示了利用闭环反馈控制系统提高器件响应线性度的显著效果.研制出样机并测量得到器件的响应时间(约1.5 ms),动态范围(约35 dB),波长相关损耗(<0.4 dB),偏振相关损耗(<0.1 dB)等关键性能参量.     

THEORETICAL ANALYSIS OF POLARIZATION MODE DISPERSION EMULATOR

The PMF (Polarization Maintaining Fiber) concatenation model is an important model in studying PMD (Polarization Mode Dispersion). In this paper, two numerical models are established based on Jones matrix and Mueller matrix. Then we perform the numerical simulation. The results indicate that the statistical probability distribution of PMD approximates the Maxwell distribution more closely with the increasing of the number of degree of freedom. The efficiency of the two ways is also discussed.     

角度调谐滤光片特性分析及膜系设计

对窄带滤光片的倾斜入射特性作了分析.斜入射时其透射通带和峰值会向短波方向移动,透射曲线的稳定性跟滤光片的间隔层结构相关,多腔间使用相同的间隔层可以保证斜入射时有稳定的峰值透射率和带宽,利用该特点可以制备角度调谐窄带滤光片.透射光S和P偏振分量的中心波长随入射角度的增大出现分离现象,产生较大的偏振相关损耗.通过搭配不同厚度的高低折射率材料作为间隔层,改变其有效折射率,使其两个偏振分量的中心波长实现重合.设计了符合密集波分复用(Dense Wavelength Division Multiplexing,DWDM)系统要求的低偏振相关损耗四腔窄带角度调谐滤光片膜系,其可调谐范围达20 nm以上,并评估了所设计角度调谐滤光片的调谐性能.     

偏振模色散的偏振主态旋转补偿法

提出一种用以补偿一阶偏振模色散的方法通过理论分析,说明了使用偏振分离器和加入光学延迟来抑制光纤中的PMD的方法以及其存在的由于延迟偏差造成的过补偿或欠补偿由理论分析可知,通过调整输入信号偏振态的方向,可以有效改善补偿效果模拟实验证明了该方法的可行性.     

Performance of optical links with optical amplifiers

In this work a comparison between the performances of single and multichannel systems is reported for links with optical amplifiers, considering conventional and soliton signals, Time Division Multiplexing (TDM), and Wavelength Division Multiplexing (WM) techniques. The performance evaluation is obtained by means of numerical simulations taking into account the effects of the chromatic dispersion, the Kerr nonlinearity, and the ASE noise of the optical amplifiers. Both the regimes of constant and fluctuating chromatic dispersion along the link are studied. The possibility of implementing high-capacity optical systems for a high-bandwidth European network is evaluated.     

Analysis and Compensation of Polarization Mode Dispersion in Single Channel,WDM and 32-channel DWDM Fiber Optic System

One of the most serious impairments which limit the data rate in long distance and high speed transmission systems is Polarization Mode Dispersion (PMD). PMD is negligible when data rate is low (i.e. in Mb/s or few Gb/s) but it will affect the high data rate transmission systems (10^s of Gb/s, Tb/s etc.), as the pulse broadening severely distorts the signal during transmission. Thus it is necessary to compensate the PMD in both single and multichannel fiber optic transmission system due to increase in the traffic demand. This paper deals with a Deterministic Differential Group Delay (DDGD) method to compensate the PMD in single channel, by delaying the fast polarization component and wavelength independent Polarization Maintaining Fiber (PMF) method for multichannel PMD compensation. The DDGD method efficiently compensates the PMD upto 45 ps in single channel 40 Gb/s transmission systems. The State of Polarization (SOP) before and after the PMD and after compensation is analyzed by means of Poincare Sphere. By using PM Fiber method, simultaneous and effective compensation of PMD in multichannel system is achieved. Here, the simulation has been carried out for 4-channel (40 Gb/s), 8-channel (80 Gb/s), 16-channel (160 Gb/s) WDM systems and 32-channel (320 Gb/s) DWDM fiber optic system with each channel having the data rate of 10 Gb/s and the results of PMD compensation for all the channels are analyzed. It is seen that the PMD compensation is achieved upto 90 ps 87 ps, 84 ps and 80 ps in 4-channel, 8-channel, 16-channel WDM systems and 32-channel DWDM systems respectively. As very high data rate of 100 Gb/s and above are in practice now-a-days, compensation of PMD is enhanced to 1.6 Tb/s (16 × 100 Gb/s) data rate for 16-channel by PMF method and 74 ps of broadening is compensated effectively.     

High-speed transmission limitations due to Polarization Mode Dispersion

In this paper, the impacts of Polarization Mode Dispersion (PMD) on the performance of high-speed optical communication system have been reported at different bit rates. The two systems are modeled using older fibers with same PMD coefficient at different bit rates and third is with the new fiber with less PMD coefficient than that of the previous two. The attenuation, chromatic dispersion and non-linear effects have been disabled, so that all the variation of the results is due to PMD. The bit rate is varied from 2.5 to 40 Gbps and the length is varied from 1000 to 20,000 km. It is shown that the impact of PMD increases with the bit rate of system. It is also reported that the impact of PMD becomes intolerable at the bit rates of more than 40 Gbps. And also the PMD produces very minute impact on the system performance for same bit rate with the variation in the fiber length.     

The inter-modes mixing effects in Mode Group Diversity Multiplexing

Multiplexing technology in indoor optical networks with multimode fibres allows the integration of several services to the end user. The Mode Group Diversity Multiplexing technique (MGDM) in Graded-Index Multi-Mode (GI-MMF) fibre makes the system less expensive with simpler transmitters and receivers, keeping the same information capacity as other multiplexing techniques. The capacity conservation and transmission quality obtained using MGDM technique depends on the transmission conditions and the state of fibre. Bending of the fibre can affect the system by changing modes excited for the different propagation channels in the fibre. In this paper an analytical modelling method for MGDM will be presented. Improvements in system sending and receiving conditions are studied. Modelling of the fibre curvature as well as the effects of coupling patterns on the MGDM are discussed.     

Broadband 2 × 2 free-space optical switch using electronically controlled liquid lenses

To the best of our knowledge, proposed is the first liquid lens technology-based 2 × 2 free-space optical switch using a pair of Electronically Controlled Variable Focus Lenses (ECVFLs). By independently controlling the focal lengths of two cascaded liquid ECVFLs, the two input optical beams are spatially adjusted to couple to their respective output beam ports. At 633-nm, the experimental switch demonstrates 26.3 dB crosstalk, 23.0 dB within-channel isolation, 1.1 dB optical loss, and 0.2 dB Polarization Dependent Loss (PDL). A 0.2 dB Wavelength Dependent Loss (WDL) is measured over 633-nm and 514-nm wavelengths. A 1 × 2 optical-fiber coupled switch version is also tested. The proposed switch can be useful in free-space laser systems as well as fiber-based modules.     

基于正交频分复用的水声通信中克服频率偏移影响的方法

OFDM(正交频分复用)是一种适合于在频率选择性衰落信道中进行高速传输的技术。水下信 道中存在着严重的多普勒频率偏移,限制了这种技术在水下的应用。本文分析了频率偏移对OFDM 系统性能的影响,提出了利用循环前缀补偿频率偏移引起的相位偏移方法来克服频偏的影响。试验 证明了这种方法的有效性。     

Bandwidth Allocation Method by Service for WDM EPON

A WDM(Wavelength Division Multiplexing) EPON(Ethernet Passive Optical Network) is an economical and efficient access network that has attracted significant research attention in recent years. A MAC(Media Access Control) Protocol of PON is based on TDMA(Time Division Multiple Access) basically, we can classify this protocol into a fixed length slot assignment method suitable for leased line supporting Qos(Quality of Service) and a variable length slot assignment method suitable for LAN/MAN with the best efforts. In this paper, we present bandwidth allocation method by service for WDM EPON and verify this method by simulation results.     

正交频分复用在水声通信中频率同步的研究

正交频分复用（OFDM）通信系统对频率偏移比较敏感，容易导致系统性能急剧下降。水声通信中存在着严重的多普勒频率偏移，限制了OFDM技术在水下的应用。本文仿真分析了频率偏移对OFDM系统的性能影响，提出了一种适用于水声通信的频率同步方法。本方法不仅可以对固定的频率偏移进行估计，也可以对连续变化的频率偏移进行估计。仿真表明，本方法具有较高的频偏估计精度和大的频偏估计范围。湖试结果也表明，采用这种方法可有效地进行频偏估计。     

蚀刻衍射光栅波分复用器件的设计与模拟

近年来光通信飞速发展,波分复用技术(WDM)是满足要求的有效手段.密集波分复用技术已经得到成功商用,其扩展信息传输容量的能力也在不断增强.作为波分复用中最关键的器件,蚀刻衍射光栅(EDG)是平面波导密集波分复用器件中很有发展潜力的一种.本文分析了EDG器件的解复用原理,参量设计,工艺过程.文章最后,建立了一个光栅干涉的简单模型,对设计好的器件参量进行模场形状、谱响应、色散等光栅性能的模拟,得到基本的器件解复用特性,并加以分析.     

Performance comparison of various modulation schemes over free space optical (FSO) link employing Gamma–Gamma fading model

Free Space Optics (FSO) is an emerging line-of-sight technology intending to provide last-mile solution to the network problem where fiber technology is not feasible. The use of Wavelength Division Multiplexing (WDM) technology for FSO is inspired due to the demand for broadband communication. This technique has brought a revolution because the system data capacity is enhanced by simply adding more number of channels and reducing the channel spacing without having the need of more than one FSO link. By reducing the channel spacing to an appropriate level, Dense Wavelength Division Multiplexing (DWDM) based FSO systems are also be attained and are reported by various research works. FSO finds applications in vast areas like backhaul networks for cellular communication, disaster recovery, LAN–LAN connectivity, high-definition TV, MAN-extension, video transmission, medicine industry and surveillance. However, its usage is limited due to the serious challenges of link vulnerability to weather and atmospheric turbulence-induced fading. This paper is based on a WDM-FSO system. An 8-channel WDM based FSO system is proposed and performance is evaluated on widely accepted modulation schemes under weak, moderate and strong turbulence conditions. Gamma–Gamma fading model is employed for atmospheric turbulence modelling. The system is simulated on OptiSystem 14.0.     

Performance enhancement of 10 Gb/s direct modulation optical OFDM by external optical injection

We show experimentally and by simulation a performance enhancement of a directly modulated 10 Gb/s optical Orthogonal Frequency Division Multiplexing (OFDM) system due to external optical injection. The experiment is performed back to back and over 12 km of single mode fiber. The injection extends the range of linear operation of the laser and therefore extends the usable bandwidth for direct modulation formats which are susceptible to nonlinearity, such as OFDM. Nonlinearity in the system and its reduction due to injection are estimated by means of a two tone test. Additionally the performance enhancement on OFDM systems was verified in both simulation and experimentally by the comparisons of the average Bit Error Rate (BER) and Error Vector Magnitude (EVM).