Synchronized chaotic optical communications at high bit rates

Basic issues regarding synchronized chaotic optical communications at high bit rates using semiconductor lasers are considered. Recent experimental results on broadband, high-frequency, phase-locked chaos synchronization, and message encoding-decoding at 2.5 Gb/s are presented. System performance at a bit rate of 10 Gb/s is numerically studied for the application of three encryption schemes, namely chaos shift keying, chaos masking, and additive chaos modulation, to three chaotic semiconductor laser systems, namely the optical injection system, the optical feedback system, and the optoelectronic feedback system. By causing synchronization error in the forms of synchronization deviation and desynchronization bursts, the channel noise and the laser noise both have significant effects on the system performance at high bit rates. Among the three laser systems, the optoelectronic feedback system has the best performance while the optical feedback system has the worst. Among the three encryption schemes, only the performance of additive chaos modulation with low-noise lasers is acceptable at high bit rates.     

延时反馈双环掺铒光纤激光器互注入系统中的混沌同步研究

分析了延时反馈双环掺铒光纤(EDF)激光器互注入 系统的动态特性,并引入一种量化时间序列复杂度的评 价方法——排列熵(PE,permutation entropy),对激光器输出状 态和混沌同步质量与复杂度的关系进行讨论。研究表明,通过调节反馈 延迟时间和反馈强度可控制系统的输出状态,使系统输出为周期态和混沌态,而且利用PE熵计算激光器 输出信号的复杂度相对于分岔图同样能直观准确的反映出系统动态行为;在激光器独立工作 情况下,输出 信号的混沌区域内夹杂有较多的周期态,而在互注入情况下,混沌区域增宽且较为平坦,同 时输出信号复 杂度的PE值较高,互注入系统有利于参数选择的范围和提高混沌通信系统的安全性;提 高注入强度可 得到高质量的混沌同步,两个激光器在同步和不同步时输出信号的复杂度是 不同的,可见 研究激光器输出信号的复杂度可成为分析混沌同步质量的一种参考。     

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     

Anticipating synchronization based on optical injection-locking in chaotic semiconductor lasers

Numerical studies for anticipating chaos synchronization in semiconductor lasers with optical feedback are presented. Anticipating chaos synchronization in a delay-differential system is believed to occur when all chaos parameters between the two systems are perfectly coincident with each other. However, we find new schemes of anticipating chaos synchronization when the parameters between the two systems have mismatches. Under these conditions, the time lag between the two laser outputs is equal to that of anticipating chaos synchronization, but the physical origin of the phenomenon comes from optical injection-locking or amplification in laser systems. We show the evidence of such chaotic synchronization using trajectories in the phase space of the phase difference and the carrier density in the laser oscillations.     

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.     

ON/OFF phase shift keying for chaos-encrypted communication using external-cavity semiconductor lasers

Synchronization phenomena of two chaotically emitting semiconductor lasers subject to delayed optical feedback are investigated. The lasers are unidirectionally coupled via their optical fields. Our experimental and numerical studies demonstrate that the relative optical feedback phase is of decisive importance: a characteristic synchronization scenario evolves under variation of the relative optical-feedback phase mediating cyclically between chaos synchronization in conjunction with coherent fields, and uncorrelated states in conjunction with incoherent fields. As a key result, we propose, and numerically demonstrate, a novel ON/OFF phase shift keying method opening up new perspectives for applications in communication systems using chaotic carriers.     

光反馈垂直腔面发射半导体激光器的混沌驱动同步在保密通信中的应用

基于光反馈垂直腔面发射半导体激光器(VCSELs)混沌驱动同步,提出了一种光反馈VCSELs混沌保密通信系统。通过模拟信号和数字信号在该系统的混沌保密通信的实现,验证了该系统的可行性。进一步利用该方案实现了对文字和数字图像的保密通信,并对解密图像及原始图像灰度值的差值做了相关计算。数值模拟结果说明该通信方案具有良好的解密效果。     

Modeling of optical synchronization of chaotic external-cavityVCSELs

The performance of a master-slave configuration for effecting the synchronization of chaotic vertical-cavity surface-emitting lasers (VCSELs) is studied using numerical simulations. The dynamical evolution of optically coupled VCSELs is examined using a traveling wave model which is valid in the strong optical feedback regime. It is shown that the proposed configuration is capable of effecting synchronization in a robust manner. The opportunity for exploiting synchronized chaos in secure optical communication systems is indicated     

偏振选择互注入半导体激光器的混沌同步

研究了偏振选择互注入条件下半导体激光器的同步和混沌滤波效应。将单模互注入速率方程扩展为包含两个偏振态的理论模型,并选择X偏振态作为互注入形式,不仅为激光器产生混沌和实现同步提供了条件,还可以完全抑制Y偏振光,实现了纯偏振模式同步。通过频率失调的引入,保持了激光器主从地位的稳定。研究结果表明,主从激光器实现了时差等于注入延时的混沌同步,输出功率表现出高频振荡并伴随有对称性破坏现象。对主激光器进行调制时,同步系统表现出与单向注入相似的混沌滤波效应;对从激光器进行调制时,系统的混沌滤波效应并不明显。     

Synchronization and communication using semiconductor lasers withoptoelectronic feedback

Semiconductor lasers provide an excellent opportunity for communication using chaotic waveforms. We discuss the characteristics and the synchronization of two semiconductor lasers with optoelectronic feedback. The systems exhibit broadband chaotic intensity oscillations whose dynamical dimension generally increases with the time delay in the feedback loop. We explore the robustness of this synchronization with parameter mismatch in the lasers, with mismatch in the optoelectronic feedback delay, and with the strength of the coupling between the systems. Synchronization is robust to mismatches between the intrinsic parameters of the lasers, but it is sensitive to mismatches of the time delay in the transmitter and receiver feedback loops. An open-loop receiver configuration is suggested, eliminating feedback delay mismatch issues. Communication strategies for arbitrary amplitude of modulation onto the chaotic signals are discussed, and the bit-error rate for one such scheme is evaluated as a function of noise in the optical channel     

激光耦合同步及其在光纤混沌保密通信中的应用

本文建立了光纤混沌保密通信耦合同步系统模型,实现了外部光注入分布反馈半导体激光器激光混沌在长距离光纤传输中的耦合同步,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,导出了这种传输的极限.该同步系统在长距离光纤混沌模拟和数字保密通信中的数值模拟表明,该系统确有较高的保密性能和反破译能力.光纤混沌保密通信是可以实现的.     

利用耦合时延增强激光混沌系统安全性能研究

安全性是混沌通信中的重要问题。基于一个外光反馈半导体激光器驱动两个互耦合激光器的混沌通信系统,研究激光混沌系统中反馈时延与耦合时延特征,并应用龙格-库塔法进行动态仿真。重点分析了当调节一些可控参数(耦合时延和驱动强度)时,能够改变两耦合激光器输出自相关函数中反馈时延和耦合时延幅值的差异,以此掩藏反馈时延,从而得出更优载波。仿真结果说明利用耦合时延可以增强激光混沌系统的安全性。最后给出了在优化载波后系统同步质量的讨论。     

外注入激光同步方程和在保密通信中的应用

本文建立了外部光注入半导体激光器的同步系统误差方程,实现了外部光注入波长1.31μm分布反馈激光器的两个激光混沌系统的同步,其同步误差几乎为零.成功数值模拟了该同步系统在长距离光纤传输中的同步,其同步误差随着传输距离而增加,光纤的自相位调制是限制激光混沌在光纤传输中同步的主要原因,分析了这种传输的极限,讨论了在不同传输距离上的强度噪声和相位噪声对同步误差的影响.在长距离光纤模拟和数字保密通信中应用的数值模拟表明,无论是在时域还是在频域,信息在混沌中都难以分离,确具有很高的保密性能和反破译能力.     

Analysis of the Optical Amplifier Noise Effect on Electrooptically Generated Hyperchaos

A theoretical analysis regarding the determination of the optical amplifier noise effect on the performance of optical chaos communications using semiconductor lasers with electrooptical feedback is carried out. Analytical expressions for the synchronization error and the signal-to-noise ratio of the extracted message are obtained and verified by extensive numerical simulations. Fiber transmission simulations are also carried out to identify under which circumstances the amplifier noise effect is the dominant impairment.     

光反馈垂直腔面发射半导体激光器的混沌驱动同步

基于光反馈垂直腔面发射半导体激光器动力学模型,通过分析光子数密度随光反馈强度变化的分岔情况,确定了激光器处于混沌态时的参数区间。利用混沌信号驱动同步方案,实现了两个被驱动激光器的精确混沌同步,并通过对两个被驱动激光器相关系数的分析,确定了它们达到精确混沌同步的参数区间。研究了参数失配对同步的影响,结果表明该同步方案有很好的稳健性。     

半导体激光器的混沌驱动同步

利用混沌驱动同步法研究了在电流调制下的半导体激光器的混沌同步。首先数值计算了系统最大Lyapunov指数随调制强度的变化情况,确定了激光器处于混沌态的参数区间。然后分别实现了同地激光器系统和异地激光器系统的混沌驱动同步。响应激光器间相关系数的数值计算表明,两种激光器系统均能达到很好的混沌同步。以三个响应激光器为例,将响应系统推广到多个激光器,并且实现了两种激光器系统的混沌同步。     

Analysis and characterization of the hyperchaos generated by a semiconductor laser subject to a delayed feedback loop

We characterize the chaotic dynamics of semiconductor lasers subject to either optical or electrooptical feedback modeled by Lang-Kobayashi and Ikeda equations, respectively. This characterization is relevant for secure optical communications based on chaos encryption. In particular, for each system we compute as a function of tunable parameters the Lyapunov spectrum, Kaplan-Yorke dimension and Kolmogorov-Sinai entropy.     

Synchronization of chaotic lasers by optical feedback forcryptographic applications

We propose a new scheme for synchronization of the optical chaos generated by a semiconductor laser subjected to external reflection. The scheme is based on optical feedback and will be analyzed from the viewpoint of static and dynamic properties and of robustness to external perturbations and noise. An application to cryptographic communications (chaotic shift keying) is finally proposed     

Characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback

We numerically investigate the detailed characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback. The emission of the dominant TE mode of a drive laser is rotated 90 deg and fed back to the laser with time delay. The polarization-rotated TE mode is also injected with time delay into the TM mode of a second laser. Two types of synchronization with different time-lags are found, as in the case for synchronization in semiconductor lasers with nonrotated optical feedback. However, a significant difference to the nonrotated optical feedback case is that neither of the two types of synchronization requires matching of optical carrier frequency between the two lasers.     

Synchronized chaotic mode hopping in DBR lasers with delayedopto-electric feedback

We propose and demonstrate a scheme for generating synchronized chaotic mode hopping in two wavelength-tunable lasers. Chaotic mode hopping resulting in large hops in wavelength is induced by delayed feedback of an electrical signal proportional to the intensity of the laser output which passes through an optical filter. Mode hopping among up to 11 modes was experimentally observed and optical signals in each wavelength band show a different on-off modulation time series. Analysis of the time series indicates high dimensionality. By using a unidirectional coupling method that injects part of the output of one laser into another, we can synchronize the chaotic mode hopping of two separate lasers and obtain synchronized chaotic on-off modulation patterns in multiple corresponding wavelength bands. The robustness of the synchronization with respect to the parameter mismatch and the effects of the coupling strength are investigated. The chaotic mode hopping dynamics and synchronization are well described with a numerical model that includes the characteristics of the laser tuning and the filter transmission. A multiplexed data transmission scheme using chaotic carriers is proposed and experiments demonstrate that multiple messages can be simultaneously recovered when chaos synchronization is achieved