新型三激光器结构的混沌同步特性

设计了一种新型的闭环双向三激光器混沌保密通信系统,驱动激光器基于延时外光反馈,两个参数完全相同的响应激光器在自身延时反馈和驱动激光器的驱动下实现混沌同步。建立了相应的理论模型,研究了系统的分岔特性、同步性以及内部参数失配对其同步性能的影响,并与不含自身光反馈的开环系统进行了比较。研究结果表明,当系统参数满足一定条件时,两个响应激光器的关联极值接近于1,而驱动激光器和响应激光器的相关性很小。与开环系统相比,该系统的载波带宽拓宽了约1.99GHz,对参数失配比较敏感并具有更好的保密性能。     

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。     

多变量耦合实现双环掺铒光纤激光器混沌同步

根据双环掺铒光纤激光器的理论模型,提出多变量单向耦合法实现混沌同步,对主从系统模型进行数学推导,研究不同参数条件下双环掺铒光纤激光器的混沌同步,得到实现混沌同步的条件,并在Simulink平台下动态仿真。结果表明,衰减系数不同的两个双环掺铒光纤激光器,主激光器通过定向耦合器驱动从激光器,主从系统可以实现精确混沌同步,且随着反馈强度的增大,实现系统混沌同步的时间越短,反馈强度的取值范围由衰减系数和耦合系数确定;选取不同的系统初值,主从系统可实现混沌同步,系统初值对达到混沌同步时间的影响可忽略不计;在主从系统中引入随机高斯噪声,主从系统仍可实现较好的混沌同步。     

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。     

单向耦合半导体激光器之间的混沌同步研究

研究了单向耦合半导体激光器之间的混沌同步。通过计算两个单向耦合的半导体激光器模型的Lyapunov指数,确定了耦合强度的取值范围。进一步设计了耦合控制器,使响应系统的状态变量精确同步于驱动系统。仿真模拟结果表明,该方法可快速有效地实现半导体激光器的混沌同步。     

基于对称相移键控混沌同步的高速密钥安全分发

提出一种基于对称相移键控混沌同步的高速密钥安全分发方案：混沌驱动信号对称地经过两个非平衡马赫-曾德尔干涉仪驱动无外腔反馈的响应激光器,并通过随机键控马赫-曾德尔干涉仪中的相位调制器实现相移键控混沌同步。通信双方对相移键控混沌同步时序进行双阈值量化产生随机密钥,然后交换、对比键控参数并筛选出参数相同（即键控相位相同）时的随机密钥作为一致密钥,实现密钥分发。本方案中,混沌驱动信号经过非平衡马赫-曾德尔干涉仪产生了基于延时自干涉的非线性变换,降低了驱动信号与响应信号之间的相关性（～0.25）,提高了密钥分发的安全性。此外,利用共驱无外腔反馈响应激光器构成开环同步结构,缩短混沌同步恢复时间至～1.8 ns,提高了密钥分发速率。数值仿真结果表明,在误码率为3.8×10^-3的条件下,可实现1.28 Gbit/s的高速密钥安全分发。     

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。     

单环掺铒光纤激光器的延时反馈-注入混沌同步

利用延时反馈-注入法研究了具有泵浦光强调制的单环掺饵光纤激光器的混沌同步.数值模拟表明,在合适的反馈和注入条件下,两个单环掺铒光纤激光器能够达到混沌同步.即使存在一定的高斯噪声影响,两个激光器仍然能够达到较好的同步.在此基础上,进一步研究了掺铒光纤激光器中参数不匹配情况对混沌同步的影响.     

基于耦合混沌半导体激光器之间双向信号传输的研究

通过改变两个耦合混沌激光器反馈相位,实现了两激光器之间信号的双向同步传输。两个激光器之间的部分透光的平面镜可以诱导延时和混沌动力学。数值模拟考虑延迟的激光器速率方程,证明了两个激光器可以达到高质量同步。编解码的过程从信号改变两个激光器的反馈相位开始,检测两个激光器中混沌载波光功率的差,并与本地信号进行对比,最终恢复发送者传输的数字信息。根据恢复出来信号的眼图,可以看出该系统具有很高的传输质量。本方案中,窃听者即使可以得到传输信号的差值,也无法得知本地信号,因此,无法解调出发送者的信息,系统的安全传输性能得以保障。     

双环掺铒光纤激光器混沌键控保密通信系统理论模型和数值模拟

提出双环掺铒光纤激光器激光混沌键控保密通信系统及理论模型,通过调制泵浦光参数以实现混沌键控保密通信;分析了通过参数调试补偿克服系统参数失配以减小同步误差的方法:模拟了两个单环掺铒光纤激光器激光和一个双环掺铒光纤激光器激光分别在0码和1码上的混沌同步及其解码,该系统在相空间,在时域和频域都具有很好的保密性能和反破译能力。     

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     

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.     

Private Message Transmission by Common Driving of Two Chaotic Lasers

In this paper, we numerically demonstrate private data transmission using twin semiconductor lasers in which chaotic dynamics and synchronization are achieved by optical injection into the laser pair of a common, chaotic driving-signal, generated by a third laser subject to delayed optical feedback. This laser is selected with different parameters with respect to the twin pair, so that the emissions of the synchronized, matched lasers are highly correlated, whereas their correlation with the driver is low. The digital message modulates the emission of the transmitter, as in a standard CM scheme. Message recovery is then obtained by subtracting, from the transmitted chaos-masked message, the chaos, locally generated by the synchronized receiver laser. Simulations have been performed with the Lang–Kobayashi model, keeping into account both laser and photodetector noise. Private transmission has been demonstrated by investigating the effect of the parameter mismatch, between transmitter and receiver, on synchronization and message recovery.      

Demultiplexing chaos from multimode semiconductor lasers

We show numerically that the injection of two chaotic modes of a multimode semiconductor laser with optical feedback into two single-mode stand-alone semiconductor lasers leads to chaotic synchronization between the respective intensities. The effect of parameter mismatch between the transmitter and receiver lasers is examined, and it is concluded that the observed synchronization is a consequence of injection locking. Under these conditions, the possibility of using this demultiplexing scheme for message transmission is examined.     

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.     

Chaos synchronization and chaotic signal masking in semiconductor lasers with optical feedback

Theoretical and experimental investigations of chaos synchronization and its application to chaotic data transmissions in semiconductor lasers with optical feedback are presented. Two schemes of chaos synchronization-complete and generalized synchronization-are discussed in the delay differential systems. The conditions for chaos synchronization in the systems and the robustness for the parameter mismatches are studied. The possibility of secure communications based on the chaos masking technique in semiconductor lasers with optical feedback is also discussed, and message transmission of a 1.5-GHz sinusoidal signal is demonstrated. The method of bandwidth enhancement of chaotic carriers is proposed for broad-band chaos communications.     

Secure Chaotic Transmission on a Free-Space Optics Data Link

In this paper, we numerically demonstrate secure data transmission, using synchronized “twin” semiconductor lasers working in the chaotic regime, which represent the transmitter and receiver of a cryptographic scheme, compatible with free-space optics technology for line-of-sight communication links. Chaotic dynamics and synchronization are obtained by current injection into the laser pair of a common, chaotic driving-signal. Results of simulations are reported for the configuration in which the chaotic driving-current is obtained by photodetection of the emission of a third laser (driver), chaotic by delayed optical feedback in a short cavity scheme, selected with different parameters with respect to the laser pair. The emissions of the synchronized, matched lasers are highly correlated, whereas their correlation with the driver is low. The digital message modulates the pumping current of the transmitter. Message recovery is performed by subtracting the chaos, locally generated by the synchronized receiver laser, from the signal obtained by photodetection (at the receiver side) of the chaos-masked message transmitted in free space. Simulations have been performed with the Lang-Kobayashi model, keeping into account both attenuation of the optical signal in a line-of-sight configuration, and noise. Security has been investigated and demonstrated by considering the effect, on synchronization and message recovery, of the parameter mismatch between transmitter and receiver.