色散和非线性对新型三激光器混沌通信系统的影响

通过分步傅里叶算法对光纤传输模型——非线性薛定谔方程进行求解,研究光纤的色散和非线性对新型闭环双向三激光器混沌保密通信系统的影响。分析了在色散、非线性以及色散和非线性共同作用下,光纤传输距离对混沌信号和解调信息质量的影响。结果表明:随着传输距离增加,色散导致混沌信号展宽,展宽比率也随之增大;混沌信号同步性逐渐变差,导致解调信息质量变差。非线性不影响混沌信号的时域波形,但非线性与色散的共同作用,导致混沌信号迅速变化,混沌信号同步性迅速变差,使解调信息质量急剧恶化。     

单跨光纤长距离混沌激光保真传输实验研究

混沌激光在载波通信、密钥分发等信息安全传输领域具有巨大的应用潜力,但放大器自发辐射噪声、光纤色散以及非线性效应会降低混沌信号的保真度,进而限制单跨光纤混沌同步的距离。本文通过研究滤波器线宽、光纤色散补偿偏差以及混沌入纤功率对混沌激光传输保真度的影响,探明了单跨光纤混沌同步的极限距离,并在实验中实现了200 km单跨光纤中保真度为0.9214的混沌信号传输。以此信号为驱动,获得了同步系数为0.9043的共驱混沌同步,为长距离混沌载波通信与密钥分发的实现提供了基础。     

基于光域补偿的远距离光混沌同步

光混沌信号受限于光纤中的色散和非线性效应，难以实现远距离同步。同时，由于光注入混沌同步采用纯光域信号处理，无法与现有通信系统中的电域非线性补偿融合。因此，从非线性薛定谔方程出发，提出色散管理与基于光域的非线性管理相融合的技术方案，实现激光混沌远距离同步。然后，详细研究了不同传输距离、不同注入强度下的同步和传输特性。结果表明，在传输距离为1000 km、注入强度为0.5 mW情况下，系统能够实现信息速率为1 Gb/s的保密通信，同步载波相关系数能够达到0.97以上。     

混沌信号在色散光纤传输过程中的演化

研究了色散光纤混沌传输理论及混沌信号与色散光纤相互作用的物理机制;通过耦合激光混沌系统和色散光纤传输信道,提出了色散光纤混沌信号传输演化物理模型;提出混沌信号在色散光纤传输中的非线性演化频率啁啾和公式;着重分析光纤色散对激光混沌信号传输与演化的作用,色散能够展宽混沌信号脉冲,但不影响混沌信号的形状;色散能够改变混沌信号每个频谱分量相位,但不影响混沌信号频谱形状;色散能够改变混沌信号光场慢变场分量的变化,但不改变混沌信号包络时变特性,也不影响混沌信号脉冲的功率分布和场强分布;色散能够改变混沌吸引子在相空间整体旋转角度并使其旋转角度随光纤传输长度而发生改变,但不改变混沌吸引子在相空间中的内部结构.最后数值模拟了混沌信号在光纤传输过程中的相位、场慢变部分分量以及混沌吸引子等演化形式等.     

光纤混沌双向保密通信系统研究

本文提出光纤混沌双向保密通信设想,通过耦合光注入半导体激光器激光混沌全光耦合反馈同步系统和光纤传输信道,建立了光纤混沌双向通信系统模型,数值实现了该系统在长距离光纤传输中的同步,详细地分析了系统同步时间随光纤传输长度的关系.证明了光纤的交叉相位调制是限制激光混沌在光纤传输中同步的主要原因,导出了系统传输的非线性相移.数值模拟了具有正弦调制信号的调制频率0.5GHz混沌模拟通信和数字信号调制速率0.4Gbit/s以及20Gbit/s的混沌数字通信以及调制速率0.05Gbit/s 混沌键控通信的应用,计算出光纤混沌数字通信速率和同步误差等关系,还特别分析了系统解码特性和调制带宽,表明系统具有非常好的保密性能和具有高速率通信的能力.光纤混沌双向保密通信是可以实现的.     

离散效应对光子晶体光纤中飞秒脉冲压缩影响

为了研究离散效应对光子晶体光纤中飞秒信号脉冲压缩的影响,采用分步傅里叶方法数值求解耦合的非线性薛定谔方程,模拟了双飞秒脉冲在光子晶体光纤中的非线性传输过程;计算和分析了离散效应和非同步耦合对信号脉冲压缩的影响。结果表明,当抽运脉冲在反常色散区进行抽运,而信号脉冲在正常色散区入射时,在群速度色散、3阶色散,自相位调制及交叉相位调制联合作用下,信号脉冲在传输过程中不仅被压缩且存在最佳光纤长度;离散效应导致信号脉冲压缩因子减小,所需最佳光纤长度增加以及压缩后的脉冲频谱呈现不对称,采用非同步耦合有利于改善信号脉冲的压缩质量。     

安全性增强的双向长距离混沌保密通信

基于混沌同步,构建安全性增强的双向长距离混沌保密通信系统。结果表明:在合适的双混沌光注入参数下,驱动激光器(DL)可以产生低时延特征(TDS)、宽带宽的混沌信号;DL输出的混沌信号注入到2个响应激光器(RLs)中,通过优化注入参数,2个RLs可输出TDS更低、带宽更宽的混沌信号,且2个混沌信号在实现高质量混沌同步的同时与DL输出混沌保持极低的相关系数(小于0.1);基于2个RLs之间高质量的混沌同步,可实现安全性增强的双向远距离混沌保密通信。采用色散位移光纤作为传输信道,20Gbit/s的信息在传输120km后,解调信息的Q因子大于6;而采用普通单模光纤作为传输信道,1Gbit/s的信息在传输140km后,解调信息的Q因子大于8。     

基于波长色散差分的色散温变效应抑制方法

为避免瑞利散射带来的信噪比劣化，光纤频率传递中多采用不同的波长进行频率信号的双向传输，因而会受到色散的影响。而在长距离的光纤频率传输系统中，还要考虑色散温变效应。理论分析了由色散温变效应带来的信号相位漂移，提出了一种可抑制色散温变效应的光纤频率传输方法，利用波长的对称关系，使三路光信号之间的色散温变效应差分抵消。研究表明，当激光器的波长间隔相等且为0.8 nm时，采用提出的频率传输方法可将色散温变效应造成的相位漂移抑制到飞秒量级，比经典的频率传输系统小近四个数量级。     

基于沃尔泰拉理论的集总光纤非线性噪声补偿

通过沃尔泰拉(Volterra)级数理论求得了非线性薛定谔方程(NLSE)的半解析解,在考虑光纤损耗、色散及非线性效应的情况下,推出了长距离在线级联掺铒光纤放大器(EDFA)光纤通信系统中信号和自发辐射噪声(ASE)之间耦合串扰的半解析表达式,得到了多跨距传输接收端输出信号和发射端输入信号之间的关系式.根据维纳(Wiener)滤波理论的时域滤波原理,在多跨距传输系统接收端设计了对非线性乘性噪声有滤波作用的维纳滤波器,并对预集总色散补偿、后集总色散补偿、分布链路色散补偿系统及一对三"跨距成比例平移对称的色散非线性同步补偿系统进行了仿真模拟研究.结果表明了提出的设计思路及方法的可行性,为进一步提高传输距离增大入纤功率提供了新的思路.     

光纤色散对WDM系统性能的限制

波分复用（ＷＤＭ）技术是增大光纤传输容量的方法，但是在高速率、长距离ＷＤＭ系统中传输性能受到限制。除了多级光纤放大器（ＥＤＦＡ）使带宽减小，噪声增大，光纤的材料色散也是对ＷＤＭ系统影响的重要因素。本文主要分析光纤色散以及有初始啁啾的脉冲、激光器的相位调制噪声、有非线性效应时光纤色散对ＷＤＭ系统传输容量的影响。     

Theoretical model of optical fiber secure communication system with chaotic multiple-quantum-well lasers

Chaotic synchronization of injected multiple-quantum-well lasers of optical fiber system and a theoretical model of optical fiber chaotic secure communication system are presented by coupling a chaotic multiple-quantum-well laser synchroniza- tion system and a fiber channel. A new chaotic encoding method of chaos phase shift keying On/Off is proposed for optical fiber secure communications. Chaotic synchronization is achieved numerically in long-haul fiber system at wavelength 1.55 μm. The effect of the nonlinear-phase of fiber is analyzed on chaotic signal and synchronization. A sinusoidal signal of 0.2 GHz frequency is simulated numerically with chaos masking in long-haul fiber analog communication at wavelength 1.55 μm while a digital signal of 0.5 Gbit/s bit rate is simulated numerically with c1haos masking and a rate of 0.05 Gbit/s are also simulated numerically with chaos shift keying and chaos phase shift keying On/Off in long-haul fiber digital communica- tions at wavelength 1.55 μm     

Performance characterization of a closed-loop chaotic communication system including fiber transmission in dispersion shifted fibers

The transmission performance of an all-optical closed-loop chaotic communication system is numerically studied, assuming various span lengths of dispersion shifted fiber between transmitter and receiver. Calculation of the mean synchronization error and Q-factor values obtained from the corresponding eye diagrams has been carried out for two encoding methods (chaotic modulation and chaos shift keying) and two repetition rates (2.4 and 5 Gbps). It is shown that transmission impairments including chromatic dispersion, fiber nonlinearity, fiber losses, and amplified spontaneous emission noise of the inline amplifiers degrade significantly the synchronization quality especially when high-bit-rate message encoding is applied. The influence of key system parameters such as launched optical power, amplifier spacing, positive or negative dispersion, etc., to the transmission performance has been investigated. Acceptable system performance can be achieved for approximately 200 km at 2.4 Gbps.     

Optical dispersion eigencompensators for high-speed long-haul IM/DDlightwave systems: computer simulation

This paper proposes what is believed to be the first linear optical dispersion-compensating technique capable of more effectively compensating for dispersively chirped signal than dispersively chirp-free signal. An effective digital eigen-filter approach is introduced for designing optical dispersion eigencompensators (ODECs) for compensation of the combined effects of laser chirp and fiber chromatic dispersion at 1550 nm in high-speed long-haul intensity-modulation direct-detection (IM/DD) lightwave systems. An integrated-optic synthesis of the ODEC using planar lightwave circuit (PLC) technology is proposed to enable high-speed signal regeneration. The proposed eigencompensating scheme is shown to result in the phenomenon of optical power enhancement: the combined effects of laser chirp, fiber chromatic dispersion and ODEC group delay can re-open the receiver eye further than the ideal eye-opening. The eigencompensating approach is shown to compare favorably with the Chebyshev filter technique in both the frequency and time domains     

Waveform degradation due to dispersion effects in an optical CPFSKsystem

Waveform degradation due to polarization and chromatic dispersions in a single-mode fiber is calculated for a coherent CPFSK signal. For a single-mode fiber with polarization dispersion of ⩽1 ps, chromatic dispersion almost dominates the system. However, if a fiber has polarization dispersion of more than a few picoseconds and a chromatic dispersion of less than 0.1 ps/km/nm, which can be attained by using a dispersion-shifted fiber and/or by electric dispersion compensation, polarization dispersion will restrict transmission capacity. For instance, polarization dispersion of 5 ps will restrict a bit rate by ~60 Gb/s when chromatic dispersion is fully reduced using a dispersion-shifted fiber or applying electrical equalization     

Measurement accuracy of chromatic dispersion by the modulation phase technique

A simple measuring method for the chromatic dispersion measurement is described. This technique uses group delay measurement by modulation phase of laser diodes with different wavelengths. An experiment showed that this technique is capable of measuring the chromatic dispersion of a 42.3-km single-mode fiber. The accuracy of measurement is discussed in view of fiber length, modulation frequency, and the number of employed laser diodes. The accuracy is improved when a higher modulation frequency is used and a longer fiber is measured since the detected phase fluctuation depends little on the modulation frequency and very little on the fiber length. The estimated measurement error of chromatic dispersion was 0.1 ps/km/nm for a four-laser diode system.     

基于射频信号2阶零功率的链路色散测量技术

为了适应高速率大色散光纤信道对链路色散的精确补偿要求,研究并提出了一种基于射频信号2阶零功率点的信道色散测量方案。采用信号两边带的位相差来测量光纤链路中的色散值,通过在发射端加载射频信号,可以得到接收端射频信号功率大小随链路色散值的周期性变化关系,从仿真光纤链路色散随射频信号频率的变化曲线获得接收端射频信号2阶零功率点位置。结果表明,基于射频信号2阶零功率的信号测量方案色散测量误差可控制在±10ps/nm范围内。相较于1阶零功率点,基于射频信号2阶零功率点信道色散测量方案可满足高速率、长距离大色散光纤信道对色散值的精确测量需求。     

888nm半导体抽运的60W皮秒激光振荡器模型

为了建立一个基于888nm半导体抽运的高平均功率和高效率皮秒激光振荡器的理论模型,采用模拟计算方法和谐振腔理论、ABCD定律、自洽条件以及连续被动锁模条件,利用激光晶体Nd:YVO4对波长888nm半导体抽运源的吸收特性和元件的相关参量、合适的腔模参量、实现稳定锁模的参量进行了理论分析和计算,并通过以上研究和模拟计算得到了皮秒振荡器模型的相关数据。结果表明,在120W的抽运功率下,激光器可以输出约61.5W的皮秒激光,光光转换效率51.3%。这一理论模型的建立对高平均功率和高效率皮秒激光振荡器的实验研究起着指导作用。     

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。     

Analysis of mode partition noise in laser transmission systems

Mode partition noise can be the dominant limitation on a system error rate for single-mode-fiber laser transmission systems. The distribution of power among the longitudinal modes of the laser fluctuates and, as a consequence of chromatic dispersion in the fiber, causes an amplitude fluctuation of the signal at the decision circuit in the receiver. The effect is in essence a pulse-delay fluctuation, and the error rate cannot be reduced by increasing the received signal power. We derive a simple formula describing this mode partition noise, give useful design relations, and verify the analysis by comparison with system experiments.