Bidirectional chaos synchronization and communication in semiconductor lasers with optoelectronic feedback

In this paper, a bidirectional chaos communication system based on the optoelectronic feedback semiconductor lasers (SLs) is presented, and the synchronization characteristics and the communication performances of such system are simulated numerically. The results show that the high-quality synchronization with zero lag time and simultaneous bidirectional message transmission can be realized under the suitable system parameters; the internal parameter mismatches of the lasers have influence on the synchronization quality and communication performance, but this system still possesses good robustness to parameter mismatches. Meanwhile, the security can be ensured through a suitable encoding-decoding technique.     

基于非相干光反馈半导体激光器的双向混沌通信研究

提出了一种基于非相干光反馈半导体激光器的双向混沌通信系统,数值研究了该系统的同步特性及通信性能. 结果表明,当两个激光器参数一致时,系统能获得无延时的高质量混沌同步,实现实时双向通信;当激光器内部参数失配时,系统的同步性能及通信质量会受到一定的影响,但该系统对参数失配的容忍性较好,在一定的参数失配范围内,系统仍能实现较好的双向混沌通信. 关键词： 非相干光反馈 半导体激光器 混沌同步 双向通信     

Theoretical investigations of cascaded chaotic synchronization and communication based on optoelectronic negative feedback semiconductor lasers

In this paper, a novel chaotic relay system, based on cascaded synchronization in optoelectronic negative feedback chaotic semiconductor lasers, is presented. Synchronization characteristics and the influence of parameter mismatches on synchronization performances are investigated. The results show that the complete synchronization can be achieved under suitable system parameters; internal parameter mismatches of the lasers have influence on synchronization quality, but the system possesses more robustness to parameter mismatches compared with cascaded synchronization based on coherent optical feedback. Moreover, communication related issues are also investigated. Under the additive chaos modulation (ACM) encryption scheme, encoded messages can be successfully extracted at both mediator laser (ML) and receiver laser (RL) parts; parameter mismatches of the lasers will affect messages decoding, but the influence is not strong.     

基于半导体环形激光器的高速双向双信道混沌保密通信

提出了一种利用半导体环形激光器(SRLs)的新型高速双向、双信道混沌保密通信系统. 在该系统中, 首先利用交叉双光反馈对驱动激光器的顺时针模式和逆时针模式的混沌延时特征进行抑制. 然后将此混沌信号注入到一对响应激光器对应的顺时针模和逆时针模中, 以实现带宽的增强及混沌同步. 最后基于响应激光器之间的混沌同步, 实现高速率、双向、双信道的混沌保密通信. 通过对驱动激光器在交叉双光反馈作用下的混沌特性、以及响应激光器在不同条件下的同步特性进行了相关理论和仿真研究, 结果表明: 驱动激光器在合适的交叉双光反馈作用下可以产生延时特性被良好隐藏的顺时针模式和逆时针模式混沌信号; 在该混沌信号的注入下, 响应激光器输出的混沌信号带宽可以得到明显增强; 通过设置合适注入强度值和频率失谐值, 响应激光器之间可实现高质量的等时混沌同步. 最后, 对系统的双向、双信道混沌保密通信特性进行了讨论. 当10 Gbit/s信号传输距离为10 km时, 解调信息Q因子值仍可保持在6以上.     

Two chaos synchronization schemes and public-channel message transmission in a mutually coupled semiconductor lasers system

Chaos synchronization and message transmission of a mutually coupled system consisting of two semiconductor lasers (SLs) and a partially transparent mirror (PTM) in between are investigated theoretically. Analytical results show that two types of chaos synchronization schemes, named as isochronal synchronization (IS) and leader/laggard synchronization (LLS), can be achieved by adjusting the reflectivity and position of PTM. By establishing SIMULINK model, numerical simulations illustrate that as the PTM is positioned at the center of two lasers, IS is available when the reflectivity of PTM is moderate. The LLS is achieved when the reflectivity of PTM equals to 0.5, which means feedback strength equals to coupling strength. Its lag time is just determined by the difference of feedback delay time. The investigations of mutual chaos pass filtering (MCPF) effects and the secure chaotic communication simulations indicate that IS allows real-time bidirectional message transmission on a public-channel, while LLS can achieve higher security chaotic communication by using its lag time as cryptography key. The demonstrated system can be used as a rudiment of array chaos communications system.     

Chaos synchronization of optoelectronic coupled semiconductor lasers ring

In this paper, we propose a chaos synchronization configuration based on the optoelectronic coupled semiconductor lasers ring (OCSLR). The synchronization characteristics between semiconductor lasers (SLs) under unidirectional or bidirectional OCSLR are numerically investigated, and the influences of some typical internal and external mismatched parameters on synchronization are simultaneously discussed. The results show that, compared with a unidirectional OCSLR, the bidirectional OCSLR possesses better synchronization properties and robustness to the mismatched parameters. Moreover, the extraction of the encoded signals is preliminarily examined under the chaos shift keying scheme.     

链式互耦合半导体激光器的实时混沌同步

通过在互耦合外腔半导体激光器之间增加中继激光器,建立了一种链式互耦合半导体激光器混沌同步系统模型.理论分析了系统的实时混沌同步条件,数值研究了注入电流、互耦合条件、反馈条件等对系统实时混沌同步品质的影响,揭示了同步质量在反馈强度和互耦合强度二维参数空间的分布规律.结果表明:注入电流较大时,满足互耦合强度和反馈强度相同,互耦合延时和反馈延时相等,系统中所有激光器之间可同时实现稳定高品质实时混沌同步;中心激光器和边激光器之间的稳定实时混沌同步分布在在互耦合强度和反馈强度较小的区域以及互耦合强度和反馈强度相近的区域;边激光器之间由于同时接收到中心激光器实施的相同注入,能够较容易的实现稳定高品质的实时混沌同步.该系统可进一步扩展成为实现远距离的双向实时混沌同步或阵列激光器系统的实时混沌同步.     

基于1550 nm垂直腔面发射激光器的长距离双向双信道光纤混沌保密通信研究

基于同一混沌信号光注入下两个1550 nm垂直腔面发射激光器 (VCSELs) 中两对应线性偏振模式之间的混沌同步, 提出了一种可实现信息的长距离双向双信道光纤混沌保密通信的系统模型, 并对该系统的同步、双向双信道通信以及光纤信道对信息传输的影响等性能进行了相关仿真研究. 结果表明: 在由驱动混沌激光器所产生的同一混沌光注入下, 两响应激光器中对应的两线偏振模式之间均可实现高质量的等时混沌同步, 且驱动激光器与两响应激光器间的同步系数较低; 基于两响应激光器之间对应线偏振模式的高质量混沌同步, 可实现双向双信道混沌通信; 采用单模保偏光纤 (或色散位移保偏光纤) 作为通信信道, 2.5 Gbit/s信息在传输60 km (或200 km) 后解调信息的Q因子能保持在6以上. 关键词： 垂直腔面发射激光器 (VCSELs) 双向双信道 混沌通信 光纤     

Synchronization properties and effects of parameter mismatches in unidirectionally coupled chaotic vertical-cavity surface-emitting lasers

We numerically investigate the effects of parameter mismatches on chaos synchronization in vertical-cavity surfaceemitting lasers (VCSELs). We assume injection-locked chaos synchronization in a unidirectionally coupled and openloop optical feedback system. The accuracy of chaos synchronization is greatly affected by the mismatches of the device parameters and operation conditions between the two lasers. In particular, the oscillation frequency of the laser is one of the important parameters in a system of injection-locked chaos synchronization. However, the variations of the device characteristics of VCSELs are very large compared with those of other types of semiconductor lasers. We study the effects of parameter mismatches related to the oscillation frequency of VCSELs on chaos synchronization. We proved that mismatches in terms of the birefringence and the injection current play crucial roles for the quality of chaos synchronization.     

基于双光反馈垂直腔面发射激光器的双信道混沌同步通信

利用双光反馈垂直腔面发射半导体激光器(VCSELs) 两个正交偏振模式输出的两个混沌信号作为混沌载波, 构建了一个双信道的混沌保密通信系统, 并对该系统的通信性能进行了数值仿真研究.研究结果表明: 通过合理的选取反馈参量, 双光反馈VCSELs两个偏振模式输出的混沌信号能很好地隐藏外腔反馈延时特性; 双光反馈VCSEL两个偏振模式输出的混沌信号通过偏振保持注入到接收VCSEL中, 在强注入锁定条件下可以实现很好的混沌同步, 同步性能对频率失谐的容忍性随着注入强度的增加而加强; 在附加混沌调制加密方式下, 500 Mbit/s的信号在传输过程中能够得到很好的隐藏, 同时在接收端可以成功解调; 随着通信速率的增加, Q因子呈现下降的趋势, 但对于 6 Gbit/s的信息, Q因子仍大于6. 关键词： 垂直腔面发射激光器 双光反馈 双信道 混沌通信     

Synchronization of Chaotic Oscillations in Mutually Coupled Semiconductor Lasers

Synchronization of chaotic oscillations in mutually coupled semiconductor lasers is experimentally investigated. Synchronization of chaotic outputs from mutually injected lasers is observed not only in low frequency fluctuation regimes but also in high frequency fluctuation regions on the nano-second time scale. It is shown that the synchronization of our results is based not on complete chaos synchronization but on injection phenomena in laser systems, so called generalized chaos synchronization.     

Nonlinear dynamics and localized synchronization in mutually coupled VCSELs

Nonlinear dynamics of mutually coupled vertical-cavity surface-emitting lasers (VCSELs) are studied theoretically. We consider both identical and nonidentical cases, respectively. For identical cases, where the device parameters and the operating conditions are the same, both lasers show the same behaviors with an identical output, and some typical nonlinear states, including period-one, period-two, multi-period and chaos, are observed. However, for nonidentical cases, the symmetric behaviors are broken. Due to the mismatch of the bias current of these two lasers, the system nonlinearity is increased and the synchronization performance is degraded greatly. Nevertheless, it is found that the coupled VCSELs can still exhibit a form of localized synchronization when they operate under the periodic state introduced by either the weak coupling or the frequency detuning.     

非对称电流偏置下互耦半导体激光器的混沌同步特性研究

利用两个电流偏置在不同值的半导体激光器(SL)构建一个延时互耦系统,实验研究了两个SL的非对称偏置电流和频率失谐Δf(=f₁-f₂,f₁,f₂分别对应SL1和SL2的自由振荡频率)对系统混沌同步性能的影响.研究结果表明:对于两个振荡频率一致的SL,当两个SL的偏置电流差异较大时系统能实现较好的混沌同步;通过调节两个SL的温度,使两个SL的振荡频率失谐,对于SL1电流远大于SL2电流的情形,正频率失谐 关键词： 半导体激光器 非对称电流偏置 互耦 混沌同步     

光纤混沌相位编码保密通信系统理论研究

通过耦合激光混沌相位控制同步系统和光纤信道，提出外部光注入半导体激光器激光混沌相 位控制光纤同步以及混沌相位相移键控外调制光纤保密通信系统理论模型，数值实现了在相 位控制器控制下的远程光纤混沌同步.理论分析了光纤自相位调制对混沌信号以及对同步的 影响，导出了光纤混沌最大传输距离公式.通过连续键控调制相位控制器实现了光纤激光混 沌相位相移键控编码调制发射，设置接收系统相位控制器控制激光相位相移实现了光纤激光 混沌同步解调.数值模拟了具有比特率50Mbit/s远程光纤混沌数字编码通信系统的应用，详 细地进行了在远距离光纤传输中的系统参数失配以及系统抗噪声能力的数值分析. 关键词： 混沌 同步 光纤混沌通信 半导体激光器 相位     

基于光电反馈的激光混沌并联同步系统研究

提出了基于光电反馈的激光混沌并联同步方案,对可能存在的两种同步——广义同步和完全同步进行了研究,着重讨论了激光器内部参数失配对发射与接收激光器之间以及并联接收激光器之间同步特性的影响.研究结果显示：在一定范围内,同样的内部参数失配下,并联接收激光器之间的同步效果明显优于发射激光器与接收激光器之间的同步效果. 关键词： 半导体激光器 混沌同步 光电反馈 参数失配     

Synchronization and control of chaos in coupled chaotic multimode Nd:YAG lasers

In this Letter we numerically investigate the dynamics of a system of two coupled chaotic multimode Nd:YAG lasers with two mode and three mode outputs. Unidirectional and bidirectional coupling schemes are adopted; intensity time series plots, phase space plots and synchronization plots are used for studying the dynamics. Quality of synchronization is measured using correlation index plots. It is found that for laser with two mode output bidirectional direct coupling scheme is found to be effective in achieving complete synchronization, control of chaos and amplification in output intensity. For laser with three mode output, bidirectional difference coupling scheme gives much better chaotic synchronization as compared to unidirectional difference coupling but at the cost of higher coupling strength. We also conclude that the coupling scheme and system properties play an important role in determining the type of synchronization exhibited by the system.     

Chaos synchronization and communication of mutual coupling lasers ring based on incoherent injection

A chaos secure communication system of mutual coupling lasers ring based on incoherent optical injection is proposed, in which fine tuning of optical frequency is not required compared with other schemes based on coherent optical injection. Therefore the secure communication scheme is attractive for experimental investigation. The dynamics of semiconductor lasers in the coupling ring are examined. Numerical investigations indicate that zero lag synchronization can be achieved under equal coupling time and strength of mutual coupling. Furthermore, by chaos shift keying (CSK), secure communication is simulated with a random bit stream of 1.0 Gbit/s. The results confirm the possibility of applying incoherent schemes of mutual coupling lasers ring to realize chaotic secure communication.     

Feedback Induced Instability and Chaos in Semiconductor Lasers and Their Applications

Semiconductor laser with feedback is an excellent model for nonlinear optical system which shows chaotic dynamics. It is interesting not only from the fundamental physical study but also application standpoints of view. The dynamics of feedback induced instability and chaos, especially for optical feedback, and their applications are reviewed in this paper. The model of such a system is described by the laser rate equations. At first the dynamic behaviors of feedback induced instability and chaos in semiconductor lasers are discussed on the basis of the theory and experiments. Instability and chaos may be stabilized by the method of chaos control. Then we apply the method to suppress the noise induced by the feedback in a semiconductor laser. The synchronization of chaos between two similar systems is also an important issue in chaos applications and we discuss secure communications based on chaos synchronization. Some other examples of applications of feedback induced chaos are also described.     

Bidirectional communication using delay coupled chaotic directly modulated semiconductor lasers

Chaotic synchronization of two directly modulated semiconductor lasers with negative delayed optoelectronic feedback is investigated and this scheme is found to be useful for efficient bidirectional communication between the lasers. A symmetric bidirectional coupling is identified as a suitable method for isochronal synchronization of such lasers. The optimum values of coupling and feedback strength that can provide maximum quality of synchronization are identified. This method is successfully employed for encoding/decoding both analog and digital messages. The importance of a symmetric coupling is demonstrated by studying the variation of decoding efficiency with respect to asymmetric coupling.     

Conversion between anticipating and lag chaos synchronization induced by different bias current levels in mutually delay-coupled semiconductor lasers

Based on a mutually delay-coupled semiconductor lasers (SLs) system, through adjusting the bias current of a SL and fixing that of the other one, the conversion between anticipating and lag chaos synchronization of this system has been experimentally observed for the first time. Experimental results show that for two SLs with the similar operation parameters, the SL biased at a relatively higher current level plays a leader role due to its relatively higher output power. Considering that the SL with a higher bias current level will oscillate at a longer wavelength, the SL with a longer wavelength becomes the leader, which provides a synchronization conversion scheme via by purely electronic current drive. Furthermore, the corresponding theoretical analyses have been given, and show that whether the SL with a longer or shorter wavelength becomes the leader mainly depends on the approach of the driving of frequency detuning between the two SLs.