基于训练序列的光OFDM相移估计与补偿方法

提出了单边带直接检测光正交频分复用(O-OFDM)传输系统的频域相位补偿方案.通过发送训练序列的方式,获取O-OFDM系统中信号的相位偏移随频率的变化规律,并依此对长距离传输色散影响的信号进行相位补偿.实现了单边带直接检测O-OFDM传输系统的频域相位补偿方案.仿真实验表明采用此方法40Gb/s信号在标准单模光纤中可传...     

通过恒包络调制提高相干光OFDM系统的光纤非线性容限

相干光正交频分复用(CO-OFDM)对光纤链路中 的色度色散(CD)和偏振模色散(PMD)具有较强的容忍性,但 是OFDM信号高峰均功率比(PAPR)的特点使其对光纤非线性效应 非常敏感,严重影响了系统传输性能。 本文提出了基于恒包络(CE)调制的方法使得系统中光信号PAPR降低为0dB,从而提高了CO-OFDM系统的非 线性传输性能。仿真结果表明,子载波采用16QAM调制的40Gbit/s单信道CE调制CO -OFDM系统,在经800km无色散补偿、欠色散补偿和周期全色散补偿 标准单模光纤(SSMF)链 路传输后,虽然较传统CO-OFDM存在约1.8dB的代价,但是系统最大 发射光功率分别提高 了6.2、9.3dB。并且,将本文方案应 用 到CO-OFDM和10Gbit/s NRZ-OOK混合传输WDM系统中,信道最大发 射光功率仍获得了5.2dB的提高。因此,本文提出的CE调制方法能有 效地提高CO-OFDM系统在不同传输环境中的光纤非线性容限。     

PSA平均光孤子系统传输性能的研究

本采用计算机系统仿真的方法，研究了应用相敏光放大器(PSA)作为在线放大器的采用平均孤子传输方案的光孤子通信系统中，泵浦光与信号光之间的相位漂移、光纤色散对光孤子通信系统传输性能的影响。仿真的结果表明：泵浦光与信号光之间的相位漂移将导致孤子幅度的下降；由于PSA增益的相敏特性，光纤色散导致孤子脉冲主瓣幅度下降，脉宽展宽，出现旁瓣。     

100 Gbit/s级联交错相位调制码型信号的传输性能

介绍了一种应用于100 Gbit/s传输系统的新型光信号调制码型--交错差分相位调制码(SDPSK).该码型的解调仅通过一个1 bit延时的马赫曾德尔延时干涉仪和一个平衡接收机即可实现.与传统的4种级联相位调制码型进行长距离传输特性比较后证明:基于NRZ码和50%占空比RZ码的SDPSK码与相同包络的DPSK码具有几乎相同的色散容限和一阶偏振模色散容限;与有相同包络的DPSK信号和差分四相相移键控码(DQPSK)信号相比,基于NRZ码和RZ码的SDPSK信号具有更高的抵抗非线性负面效应的能力:经过90 km普通单模光纤传输并采用16 km色散补偿光纤进行后置色散补偿后,通过带宽值大于125 GHz的三阶高斯滤波器检测光信号,RZ-SDPSK信号的接收性能最佳.     

相干光OFDM在高速光传输中的应用

相干光正交频分复用系统(CO-OFDM,Coherent Optical Orthogonal Frequency Division Multiplexing)可有效抑制光纤色度色散和偏振模色散,有望成为解决未来高速光传输的主流方案。这里结合光传输理论及正交频分复用系统(OFDM,Orthogonal Frequency Division Multiplex)技术原理,对CO-OFDM系统方案实现及信道等效模型进行了分析,通过数字仿真验证系统光调制器偏置点选择及信号均衡算法。理论分析和仿真结果表明,CO-OFDM系统采用单抽头频域均衡,可有效抑制光纤色散效应。光调制器偏置点选择在零点,可实现系统对OFDM信号的最佳线性调制,与传统强度调制/直接检测(IM/DD)系统比较,CO-OFDM系统品质因子有10 dB提高。     

利用普通SMF实现10Gbit＼s 信号全光长距离传输的研究

数值模拟了强度调制光信号在级联光纤放大器普通单模光纤通信系统中的传输,模拟中主要考虑了自相位调制、群速色散和自发辐射噪声,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,若色散得到很好补偿,当放大器间距减少到５０ｋｍ时,无误码２０５０ｋｍ传输是可能的。     

CO-OFDM系统中相位噪声和频偏的联合补偿

激光器频偏和相位噪声是限制CO-OFDM(相干光正交频分复用)系统性能的重要因素。文章提出了CO-OFDM系统中基于差分预编码和MCDD(多载波差分检测)算法的激光器相位噪声和频偏联合补偿方案。对CO-OFDM系统中的频偏和激光器相位噪声作用机理和基于MCDD的补偿方案机制进行了理论推导,并在不同的光信噪比、激光器频偏和线宽条件下进行了系统仿真。仿真结果表明,基于差分预编码和MCDD的联合补偿方法对CO-OFDM系统中的激光器频偏和相位噪声有较好的补偿效果和较大的补偿范围,在不引入系统开销的同时,可有效改善CO-OFDM系统性能。     

色散补偿系统中自相位调制效应的影响

分析了自相位调制效应对正、负色散光纤中光脉冲传输的影响 ,并用数值仿真的方法研究了自相位调制效应对采用色散补偿光纤的高速率光纤通信系统性能的影响 ,获得了一些对实际色散补偿系统有参考价值的结论。     

基于光纤差分相移键控的色散补偿方案的研究

为了研究光差分相移键控(DPSK)调制格式在光纤高速传输系统中的色散补偿, 利用色散补偿光纤(DCF)的色散补偿原理, 对40Gbit/s光纤传输系统进行色散补偿, 分析了40Gbit/s单通道光纤传输系统中3种DPSK调制格式信号的频谱特性; 仿真了3种码型的色散容忍度以及3种调制格式在考虑光纤的非线性下的色散补偿方案。结果表明, 光非归零码差分相移键控(NRZ-DPSK)信号具有最好的色散容忍度, 但其受非线性的影响比较大; 33%归零码差分相移键控(33%RZ-DPSK)信号的色散容忍度差, 但其色散补偿后的效果优于NRZ-DPSK; 而载波抑制归零码差分相移键控信号对色散和非线性效应都有较好的抑制; 3种DPSK调制格式均在对称补偿2方案中色散补偿的效果最佳。此仿真研究对光DPSK信号在光纤中的色散补偿具有参考意义。     

基于光纤延迟线相位控制的相干探测方法研究

采用系统建模仿真,分析了光纤延迟线信号传输存储和相位控制机理,研究时间延迟与相位延迟关系,从时域和频域探讨光程差对光学相位匹配的影响。仿真与实验结果表明,当信号光与参考光的相位差为2nπ(n=0,1,2,……)和(2n+1)π(n=0,1,2,……)时,相干混频后的信号功率分别获得最大值和最小值。证明了光纤延迟线的时间延迟能有效补偿在传输过程中产生的相位延迟,实现了信号传输的相位控制。     

相干光OFDM系统中的相位估计分析

相干光正交频分复用(Coherent Optical Orthogonal Frequency Division Multiplexing,简称CO-OFDM)可有效降低光纤色散和偏振模色散影响,由于系统采用相干检测,对相位噪声的分析及信道估计尤为重要.文章对CO-OFDM系统数学模型进行了具体分析;OFDM作为一种特...     

一种降低相干光OFDM系统非线性效应的方法

相干光正交频分复用(Coherent optical-orthogonal frequency division multiplexing,简称CO-OFDM)可有效降低光纤色散和偏振模色散对系统的影响,是近年来光传输领域研究热点之一.但由于OFDM高的峰均值功率比(PAPR)和较窄的载波间隔(几十兆赫兹),CO-OF...     

基于OPC的高速PDM-CO-OFDM系统研究

通过理论分析和数值仿真,搭建了100Gbit/s的PDM(偏振复用)-CO-OFDM(相干光正交频分复用)系统,并使用OPC(光学相位共轭)技术对100Gbit/s的PDM-CO-OFDM系统的传输性能进行了补偿。研究表明,相位共轭技术不仅能够补偿系统的各阶色散,还能补偿非线性效应,使用OPC技术能使系统的传输距离达到1 200km,在最佳补偿距离上,使用OPC的系统Q值比使用传统的DCF(色散补偿光纤)的系统Q值大6.3dB。     

Experimental Demonstration and Numerical Simulation of 107-Gb/s High Spectral Efficiency Coherent Optical OFDM

Orthogonal frequency-division multiplexing (OFDM) is a multicarrier modulation format in which the data are transmitted with a set of orthogonal subcarriers. Recently, this modulation format has been actively explored in the field of optical communications to take advantages of its high spectral efficiency and resilience to chromatic and polarization dispersion. However, to realize the optical OFDM at 100 Gb/s and beyond requires extremely high electronic bandwidth for the electronic signal processing elements. In this paper, we investigate orthogonal-band-multiplexed OFDM (OBM-OFDM) as a suitable modulation and multiplexing scheme for achieving bandwidth scalable and spectral efficient long-haul transmission systems. The OBM-OFDM signal can be implemented in either RF domain, or optical domain, or a combination of both domains. Using the scheme of OBM-OFDM, we show the successful transmission of 107 Gb/s data rate over 1000-km standard single-mode fiber (SSMF) without optical dispersion compensation and without Raman amplification. The demonstrated OBM-OFDM system is realized in optical domain which employs 2 $times$ 2 MIMO-OFDM signal processing and achieves high optical spectral efficiency of 3.3 bit/s/Hz using 4-QAM encoding. Additionally, we perform numerical simulation of 107-Gb/s CO-OFDM transmission for both single-channel and wavelength-division-multiplexed (WDM) systems. We find that the $Q$ -factor of OBM-OFDM measured using uniform filling of OFDM subbands is in fact more conservative, in particular, is 1.2 dB and 0.4 dB lower than using random filling for single-channel and WDM systems, respectively.      

光纤OFDM系统中的色散补偿技术研究

为了减小光纤的色度色散对光纤正交频分复用（OFDM）系统性能的影响,提出了将无线通信中的信道估计器引入光纤OFDM系统进行信道估计的色散补偿方法。在理论上分析了光纤的色度色散对于传输OFDM信号的影响,并在实验中采用梳状导频的形式,在每个OFDM码元的特定的子载波上插入导频,在接收端通过基于最小平方（LS）原则的LS估计器进行信道估计,得到了OFDM光纤传输的信道幅度响应和相位响应,通过使用LS估计器,直接调制的光OFDM信号在单模光纤中传输200km,误比特率低于10-6 ,功率代价小于2dB。结果表明,高频子载波较低频子载波更容易受到色散的影响,在光纤OFDM系统中引入信道估计器进行信道估计能够有效补偿由色度色散带来的相位偏移和幅度衰减。     

Electronic Dispersion Compensation

The performance of different electronic equalization and processing schemes for 40- and 10-Gb/s optical transmission over single-mode fiber (SMF) are discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion (PMD). In addition, the impact of fiber nonlinearity and modulation format on equalization is also investigated. The main objective of this paper is to present an overview and a comparison of the performances rather than a detailed explanation of the principles of the different equalization schemes. The equalizers which will be covered are analog equalizer (feedforward and decision feedback type), maximum likelihood sequence estimator (MLSE), electronic precompensation, coherent/intradyne detection with digital signal processing (DSP) equalization, DSP-based optical orthogonal frequency division multiplexing (OFDM), and turbo equalization.     

Phase Noise Effects on High Spectral Efficiency Coherent Optical OFDM Transmission

There are three major advantages for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) transmission using digital signal processing. First, coherent detection is realized by digital phase estimation without the need for optical phase-locked loop. Second, OFDM modulation and demodulation are realized by the well-established computation-efficient fast Fourier transform (FFT) and inverse FFT. Third, adaptive data rates can be supported as different quadrature amplitude modulation (QAM) constellations are software-defined, without any hardware change in transmitter and receiver. However, it is well-known that coherent detection, OFDM, and QAM are all susceptible to phase noise. In this paper, theoretical, numerical, and experimental investigations are carried out for phase noise effects on high spectral efficiency CO-OFDM transmission. A transmission model in the presence of phase noise is presented. By using simulation, the bit error rate floors from finite laser linewidth are presented for CO-OFDM systems with high-order QAM constellations. In the experiments, the phase noise effects from both laser linewidth and nonlinear fiber transmission are investigated. The fiber nonlinearity mitigation based on receiver digital signal processing is also discussed.     

An improved channel estimation algorithm for CO-OFDM system and its performance analysis

We present an extra processing added to conventional least square （LS） channel estimation to further improve its per- formance in coherent optical orthogonal frequency division multiplexing （CO-OFDM） system. The influence of noise, chromatic dispersion and polarization mode dispersion on the performance of the proposed algorithm is analyzed. The simulation results show that the improved algorithm has better performance and lower complexity.     

Performance evaluation of (D)APSK modulated coherent optical OFDM system

Performance of amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency division multiplexing (CO-OFDM) with and without differential encoding is investigated. Numerical simulations based on 40 Gbit/s single-channel and 5 ^* 40 Gbit/s wavelength division multiplexing transmission are performed, and the impacts of amplified spontaneous emission noise, laser linewidth, chromatic dispersion, and fiber nonlinearity on the system performance are analyzed. The results show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, although 16(D)APSK modulated optical OFDM signal has a lower tolerance towards amplified spontaneous emission (ASE) noise, it has a higher tolerance towards fiber nonlinearity such as self-phase modulation (SPM) and cross-phase modulation (XPM): the optimal launch power and the corresponding Q² factor of 16(D)APSK modulated OFDM signal are respectively 2 dB and 0.5 dB higher than 16QAM modulated optical OFDM signal after 640 km transmission, both in single-channel and WDM CO-OFDM systems. Although the accumulated CD decreases the peak-to-average power ratio (PAPR) during transmission, 16(D)APSK modulated OFDM signal will still remain an advantage compared with 16QAM modulated OFDM signal up to 1000 km single-channel transmission, meanwhile relaxing the needs for training symbols and pilot subcarriers and consequently increase the spectral efficiency.