Homoclinic chaos in a laser: synchronization and its implications in biological systems

Phase synchronization of a CO₂ laser with feedback, exhibiting homoclinic chaos, is realized by a tiny periodic perturbation of a control parameter. The deviations of the modulation frequency from the optimal one induce phase slips, thus yielding an imperfect phase synchronization. Based on the information of these phase slips, the modulation frequency can be readjusted until the phase slips are eliminated. In this way, a control loop which detects the phase slips provides an adaptive tracking of the natural frequency of the dynamical system. Moreover, we have shown that the system's susceptibility is largest when a periodic impulsive perturbation is applied near the saddle focus.     

量子阱激光器混沌相位控制同步以及编码研究

提出外部光注入多量子阱激光器激光混沌相位控制同步，及其混沌相位相移键控外调制ON/ON全光保密通信系统，数值模拟了在相位控制器控制下的激光混沌同步.通过连续ON/ON键控调制相位控制器调制通过相位控制器的激光相位相移，实现激光混沌相位相移键控连续调制，设置接收系统相位控制器，控制通过接收相位控制器的激光相位相移，以实现激光混沌解调.分别数值模拟了该系统调制速率01和05Gbit/s混沌相位相移ON/ON键控通信，进行了混沌ON/ON键控调制速率分析，以及系统参数失配和系统抗噪声扰动的数值分析. 关键词： 混沌 同步 通信 多量子阱激光器     

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     

对称双势阱玻色-爱因斯坦凝聚系统在周期驱动下的动力学相变及其量子纠缠熵表示

研究了在对称双势阱玻色-爱因斯坦凝聚体系粒子间相互作用项上外加周期调制而引起的系统动力学相变,特别地研究了该系统通向混沌的相变过程.发现在一定驱动参数下,当外加调制频率与系统固有频率达到共振时,相平面会出现不稳定性现象,即混沌.在混沌区域,粒子在各量子态随机分布,平均布居数差在零附近波动.特别地,研究表明,混沌现象的出现可以用量子纠缠熵来表征,混沌现象出现时,两种平均纠缠熵都趋于它们的最大值. 关键词： 玻色-爱因斯坦凝聚 双势阱 混沌 纠缠熵     

对称双势阱玻色-爱因斯坦凝聚系统在周期驱动下的动力学相变及其量子纠缠熵表示

研究了在对称双势阱玻色-爱因斯坦凝聚体系粒子间相互作用项上外加周期调制而引起的系统动力学相变，特别地研究了该系统通向混沌的相变过程.发现在一定驱动参数下，当外加调制频率与系统固有频率达到共振时，相平面会出现不稳定性现象，即混沌.在混沌区域，粒子在各量子态随机分布，平均布居数差在零附近波动.特别地，研究表明，混沌现象的出现可以用量子纠缠熵来表征，混沌现象出现时，两种平均纠缠熵都趋于它们的最大值.     

激光混沌串联同步以及混沌中继器系统理论研究

提出混沌通信中继器设想，建立半导体激光器激光混沌全光中继器物理模型，理论证明了激光混沌中继器系统的同步.数值实现了发射系统、中继器系统、接收系统的混沌同步，分析了系统反馈系数和同步误差以及同步时间的关系.模拟了中继器系统在激光混沌保密通信中的应用，分别给出了具有正弦信号调制频率0.2GHz和数字信号0.2Gb/s速率的混沌通信以及同步误差分析，表明混沌中继器系统确能改善和提高激光混沌通信的解码质量.分析了中继器系统的带宽和20Gb/s高速率数字信号混沌通信以及同步误差，给出了具有正弦信号调制频率0.1—2 关键词： 混沌 同步 激光器 中继器     

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.     

Collective chaos synchronization of pairs of modes in a chaotic three-mode laser

We study chaos synchronization experimentally in a modulated globally coupled three-mode laser with different modal gains subjected to self-mixing Doppler-shifted feedback, which can apply the loss modulation to individual modes at Doppler-shift frequencies. Depending on the pump power, different forms of collective chaos synchronizations were found to appear when the laser was modulated at the highest relaxation oscillation frequency, reflecting the change in cross-saturation coefficient among modes. In the present experiment, each pair of modes exhibited phase, lag, or generalized synchronization collectively according to the inherent antiphase dynamics, where these types of synchronization have already been demonstrated in two coupled chaotic oscillators in different physical systems. Information flows among oscillating modes which are established in different forms of collective chaos synchronizations were characterized by information-circulation analysis of the experimental time series. (c) 2002 American Institute of Physics.     

Polarization message encoding through vectorial chaos synchronization in vertical-cavity surface-emitting lasers

We show that self-pulsating vertical-cavity surface-emitting lasers can exhibit vectorial chaos, i.e., chaos in both intensity and polarization. The achievable synchronization degree of two such lasers is high when using a continuous control scheme and unidirectional coupling. We propose a novel encryption scheme, where the phase of the vectorial field is modulated. Therefore, the total intensity of these lasers remains synchronized while the intensities in the polarization modes (de)synchronize following the phase modulation at a ps time scale. This technique allows for transmission of secure data at high bit rates that are not limited by the relaxation oscillation frequency.     

Homoclinic bifurcation in Chua’s circuit

We report our experimental observations of the Shil’nikov-type homoclinic chaos in asymmetry-induced Chua’s oscillator. The asymmetry plays a crucial role in the related homoclinic bifurcations. The asymmetry is introduced in the circuit by forcing a DC voltage. For a selected asymmetry, when a system parameter is controlled, we observed transition from large amplitude limit cycle to homoclinic chaos via a sequence of periodic mixed-mode oscillations interspersed by chaotic states. Moreover, we observed two intermediate bursting regimes. Experimental evidences of homoclinic chaos are verified with PSPICE simulations.     

高速多量子阱激光器混沌保密通信系统研究

研究了外部光注入高速多量子阱激光器激光混沌全光保密通信系统,导出系统同步方程,理论证明并数值实现了系统的同步,分析了增加反馈系数以缩短同步时间且增强系统同步稳定性的方法。研究分析了多量子阱激光器混沌隐藏和混沌键控保密通信全光调制解调系统模型,数值模拟了具有正弦调制信号的调制频率0．2GHz混沌模拟保密通信和数字信号调制速率20Gb／s的混沌数字保密通信以及调制速率0．05Gb／s混沌键控保密通信的应用,系统确实具有较高的保密性能和反破译能力;分析了混沌数字信号保密通信调制带宽20Gb／s调制解调时的同步误差以及混沌键控调制速率,系统都具有非常好的调制解调特性,且在高速混沌通信中,系统解调具有相对较小的同步误差,而1Gb／s是混沌键控通信的速率上限。     

光纤混沌双芯双向保密通信系统研究

把量子阱激光混沌耦合反馈同步系统应用于光纤保密通信中,提出光纤混沌双芯双向保密通信设想.通过耦合外部光注入多量子阱激光混沌全光耦合反馈同步系统和光纤传输信道,建立了光纤混沌双芯双向通信系统物理模型.理论和数值证明了激光混沌同步,理论分析指出光纤中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,并推导出混沌信号双芯双向传输中的非线性相移以及混沌激光功率限制和传输距离公式.数值实现了该系统在长距离二根光纤传输中的同步,详细地分析了系统同步时间随光纤传输长度的关系.模拟了调制频率06 GHz的混沌模拟通 关键词： 混沌 同步 光纤 保密通信     

Decryption characteristics in message modulation type chaos secure communication system using optical fiber ring resonators

Message modulation type chaos secure communication system using optical fiber ring resonators is analyzed numerically. It is found that the decryption characteristics degrades monotonically as the differences in parameters which are not included in the linear phase term becomes large, while they degrade periodically with a period of 2π as the differences in parameters included in the linear phase term increase. When a noise is added in the input light, the error dispersion in the message demodulation is determined by the noise level in the small parameter difference region, while the parameter differences it dominates in the large parameter difference region. Best decryption characteristics are always obtained at the minimum input power for the chaos generation, i.e., at the lowest Lyapnov exponent in chaos state in the message modulation type chaos secure communication system using optical fiber ring resonators.     

基于双光反馈半导体激光器的单向开环混沌同步通信

利用双光反馈半导体激光器作为混沌发射源, 构建了一个单向开环混沌通信系统, 并对系统的通信性能进行了相关仿真研究. 研究表明: 通过合理选取系统参量, 双光反馈半导体激光器所产生的混沌载波能很好地抑制外腔延时特征; 发射激光器和接收激光器在强注入锁定下能实现很好的混沌同步, 并且同步性能对频率失谐具有很好的容忍性; 采用附加混沌调制加密方式, 500 Mbits/s的信号能够很好地隐藏于混沌载波中, 并可在接收端成功解调. 关键词： 半导体激光器 单向耦合 混沌通信     

双信道偏振复用保密通信系统的完全混沌同步的操控性研究

针对双信道偏振复用保密通信系统,利用线性电光效应,提出了一种新的完全混沌同步的控制方案.在该方案中,每一个线性偏振模的完全混沌同步质量随外加电场成准周期性变化.其变化规律:完全混沌同步?剧烈振荡;固定一定的外加电场,电光调制促使其完全混沌同步质量对偏置电流和反馈强度的稳健性获得极大的加强.在较大的偏置电流和反馈强度范围内,每一个线性偏振模能够实现完全混沌同步,并且调制到每一个线性偏振模的加密信号基本上能够恢复.     

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.     

In phase and antiphase synchronization of coupled homoclinic chaotic oscillators

We numerically investigate the dynamics of a closed chain of unidirectionally coupled oscillators in a regime of homoclinic chaos. The emerging synchronization regimes show analogies with the experimental behavior of a single chaotic laser subjected to a delayed feedback.     

注入半导体激光器混沌调制性能与内部相位键控编码方法研究

研究注入半导体激光混沌调制解调及其性能特性，提出外部光注入半导体激光器混沌内部相位编码方法. 小信号调制分析了系统混沌调制响应函数和解调响应函数以及解调因子，系统的调制解调响应函数以及解调因子在60MHz有一个峰值，系统在高频调制时，响应函数和解调因子明显下降. 理论推导出混沌调制解调方程，给出了小信号调制时的信息信号的解，数值分析出系统在低频有一个调制解调峰值，高频调制解调效果下降，但系统仍可以进行10⁹Hz频率调制解调. 数值模拟并证明了系统在较大的参数范围内都能实现同步，模拟了混沌调制速率200Mb/s和调制频率1.4GHz的保密通信应用. 还通过键控调制注入光的相位相移对激光混沌态进行了编码，通过同步与非同步进行混沌解码，数值模拟了具有调制速率10Mb/s的混沌相位键控编码通信应用. 关键词： 混沌 同步 激光器 相位     

Controlling hyperchaos and synchronizing periodic states in the DOPO

It has been found out that hyperchaotic behaviors can be controlled to enter periodicity state by modulating the detuned parameters in degenerated optical parameter oscillator (DOPO) with different periodic orbits from different modulation index at the same modulation frequency, or from different modulation frequency at the same modulation index. It was shown that the periodic orbits of the DOPOs modulated through sinusoid can be resulted in identical synchronization or inversed synchronization only in the case that the largest Lyapunov exponent exponent of the system is negative.PACS: 42.65.Sf     

Route to broadband optical chaos generation and synchronization using dual-path optically injected semiconductor lasers

The generation and synchronization of broadband optical chaos in dual-path optically injected (DPOI) semiconductor lasers (SLs) are numerically demonstrated. The effective bandwidth enhancement is achieved up to about 35.84 GHz, under appropriate injection strength and frequency detuning. We systematically study and compare the bandwidth enhancement in single-path optically injected SLs (SPOI-SLs) and DPOI-SLs, and find that better performance can be obtained for the latter over a larger parameter span. Furthermore, two schemes for synchronization of bandwidth-enhanced chaos generated in two similar or identical (twin) DPOI-SLs are proposed, where the twins are driven by a common DPOI signal injected from another chaotic SL. High-quality chaos synchronization, an isochronous type, is observed between the twin DPOI-SLs. Also, the effect of parameter mismatch and frequency detuning is numerically examined. The simple technique of bandwidth enhancement using dual-path injection may pave way for various applications such as high-speed random number generators (RNGs) and chaos-based communications.