两种调制方式下主从激光器同步性能的理论研究

 以单周期信号为例,数值模拟并讨论了注入频率和注入光场波动强度对主从式半导体激光器同步性能的影响。分别通过直接调制和外部调制两种方式获得单周期信号,并采用改进的参数——相似指数评价系统的同步性能。研究结果表明：当注入强度足够大时,系统实现注入锁定同步,外部调制的相似指数大于内部调制;注入强度恒定时,同步品质几乎不受调制指数的影响,而受调制频率的影响;由于内部、外部调制引起主激光器的输出反相,两种调制方式下同步品质随调制频率的变化趋势也相反。     

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.     

Polarization switching and synchronization of mutually coupled vertical-cavity surface-emitting semiconductor lasers

Polarization switching (PS) dynamics and synchronization performances of two mutually coupled vertical-cavity surface-emitting lasers (VCSELs) are studied theoretically in this paper. A group of dimensionless rate equations is derived to describe our model. While analysing the PS characteristics, we focus on the effects of coupling rate and frequency detuning regarding different mutual injection types. The results indicate that the x-mode injection defers the occurrence of PS, while the y-mode injection leads the PS to occur at a lower current. Strong enough polarization-selective injection can suppress the PS. Moreover, if frequency detuning is considered, the effects of polarization-selective mutual injection will be weakened. To evaluate the synchronization performance, the correlation coefficients and output dynamics of VCSELs with both pure mode and mixed mode polarizations are given. It is found that performance of complete synchronization is sensitive to the frequency mismatch but it is little affected by mixed mode polarizations, which is opposite to the case of injection-locking synchronization.     

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.     

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.     

激光混沌通信中半导体激光器接收机对高频信号的滤波特性

数值研究了基于半导体激光器的混沌通信系统中构成混沌同步的接收半导体激光器对高频信号的滤波特性.分析了闭环结构的接收机对不同频率、不同幅度的加载信号的提取能力.研究发现，混沌保密通信系统对传输信号的提取能力与信号的频率有关.当信号频率较低时，闭环结构的接收机对信号的滤波效果较好；当信号频率接近半导体激光器的弛豫振荡频率时，接收机的滤波效果较差.分析结果同时表明，混沌保密通信系统中接收机对传输信号的提取质量不仅与实现混沌同步的两激光器的同步质量有关，而且依赖于传输信号的幅度. 关键词： 混沌 混沌同步 半导体激光器 滤波     

Control of dynamical instability in semiconductor quantum nanostructures diode lasers: Role of phase-amplitude coupling

We numerically investigate the complex nonlinear dynamics for two independently coupled laser systems consisting of (i) mutually delay-coupled edge emitting diode lasers and (ii) injection-locked quantum nanostructures lasers. A comparative study in dependence on the dynamical role of α parameter, which determine the phase-amplitude coupling of the optical field, in both the cases is probed. The variation of α lead to conspicuous changes in the dynamics of both the systems, which are characterized and investigated as a function of optical injection strength η for the fixed coupled-cavity delay time τ. Our analysis is based on the observation that the cross-correlation and bifurcation measures unveil the signature of enhancement of amplitude-death islands in which the coupled lasers mutually stay in stable phase-locked states. In addition, we provide a qualitative understanding of the physical mechanisms underlying the observed dynamical behavior and its dependence on α. The amplitude death and the existence of multiple amplitude death islands could be implemented for applications including diode lasers stabilization.     

Light polarization fingerprints on nonlinear dynamics of vertical-cavity surface-emitting lasers

In this paper we summarize the recent results on nonlinear dynamics of vertical-cavity surface-emitting lasers (VCSELs) which are bearing the fingerprints of the particular polarization properties of VCSELs. Due to the surface emission and cylindrical symmetry, VCSELs lack strong polarization anisotropy and may undergo polarization switching and polarization mode-hopping. This provides new specificities to the rich nonlinear dynamics induced in VCSELs by an external perturbation. We unveil both experimentally and theoretically these new specificities for the case of optical feedback, optical injection, and unidirectional synchronization between VCSELs.     

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.     

Bandwidth-enhanced chaos synchronization in strongly injection-locked semiconductor lasers with optical feedback

Bandwidth-enhanced chaos synchronization in strongly injection-locked semiconductor lasers with optical feedback is numerically studied based on laser rate equations. The bandwidth of the chaotic carrier frequency in a semiconductor laser with optical feedback is expanded roughly three times by strong optical injection compared with the bandwidth when there is no optical injection. Using a bandwidth-enhanced semiconductor laser as a chaotic transmitter and receiver, we synchronized transmitter and the receiver lasers in a complete chaos synchronization scheme.     

非线性增益对外部注入半导体激光器动态行为的影响

研究了非线性增益对外部注入半导体激光器动态行为的影响。研究结果表明:非线性增益对外部注入半导体激光器的动力学行为影响极大;随着非线性增益系数的增加,激光器达到锁定时的注入系数减小,产生混沌的注入系数的范围缩小;当非线性增益系数过大时,外部注入激光器表现为混沌;非线性增益还影响外部注入半导体激光器混沌同步系统的性能,非线性增益系数越大,参数失配引起的混沌同步误差越小。     

Investigation of chaos synchronization in photonic crystal lasers

Chaotic dynamics and chaos synchronization in photonic crystal (PC) lasers with optical feedback are investigated numerically. The effect of various system parameters such as amplitude reflectivity of the external mirror “r”, external cavity length “L_e”, and injection current “I” on system dynamics is addressed in detail. Simulation results are presented using MATLAB to address system behavior. The parameters r, L_e, and I are varied over the ranges (0.05–0.25), (2.8–3.2 mm), and (1.1I_th–2I_th), respectively. The results indicate that very small parameter mismatches between the transmitter laser and receiver laser affect strongly complete chaos synchronization between them.     

Synchronization and time shifts of dynamical patterns for mutually delay-coupled fiber ring lasers

A pair of coupled erbium doped fiber ring lasers is used to explore the dynamics of coupled spatiotemporal systems. The lasers are mutually coupled with a coupling delay less than the cavity round-trip time. We study synchronization between the two lasers in the experiment and in a delay differential equation model of the system. Because the lasers are internally perturbed by spontaneous emission, we include a noise source in the model to obtain stochastic realizations of the deterministic equations. Both amplitude synchronization and phase synchronization are considered. We use the Hilbert transform to define the phase variable and compute phase synchronization. We find that synchronization increases with coupling strength in the experiment and the model. When the time series from two lasers are time shifted in either direction by the delay time, approximately equal synchronization is frequently observed, so that a clear leader and follower cannot be identified. We define an algorithm to determine which laser leads the other when the synchronization is sufficiently different with one direction of time shift, and statistics of switches in leader and follower are studied. The frequency of switching between leader and follower increases with coupling strength, as might be expected since the lasers mutually influence each other more effectively with stronger coupling.     

Role of pulse shaping in control of focus and intensity of terahertz radiation

In this work, we uncover the role of lasers pulse shaping for controlling the terahertz peaks with their separation in addition to their intensities. We have developed a mathematical model for obtaining the amplitude, frequency, and power of the emitted Terahertz radiation for the lasers whose shape is tailored based on the index and skew parameter. Then the results are compared with the case of Gaussian laser pulse in collisional plasma. We optimize the process by applying magnetic field and by varying the index of the lasers for compensating the negative influence of collisions on the THz emission. Specifically the effect of laser beam width, magnetic field and collision frequency is investigated on the electric field of the terahertz radiation and the efficiency of the mechanism.     

Synchronization of chaotic erbium-doped fibre lasers and its application in secure communication

We have investigated the synchronization of chaotic dual-ring erbium-doped fibre lasers using the delay feedback－injection scheme. Numerical simulation shows that two chaotic dual-ring erbium-doped fibre lasers can be well synchronized if the strengths of delay feedback and injection are suitable. Even though the effects of the noises and the difference between the two lasers are considered, the twins can still reach good synchronization. Secure communication could be realized using the scheme of message-masking based on the synchronization of the chaotic dual-ring erbium-doped fibre lasers.     

Controlling the leader-laggard dynamics in delay-synchronized lasers

We study experimentally the collective dynamics of two delay-coupled semiconductor lasers. The lasers are coupled by mutual injection of their emitted light beams, at a distance for which coupling delay times are non-negligible. This system is known to exhibit lag synchronization, with one laser leading and the other one lagging the dynamics. Our setup is designed such that light travels along different paths in the two coupling directions, which allows independent control of the two coupling strengths. A comparison of unidirectional and bidirectional coupling reveals that the leader-laggard roles can be switched by acting upon the coupling architecture of the system. Additionally, numerical simulations show that a more extensive control of the network architecture can also lead to changes in the dynamics of the system. Finally, we discuss the relevance of these results for bidirectional chaotic communications.     

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 semiconductor lasers by optical injection with random phase modulation

It is shown that identical synchronization of two chaotic semiconductor lasers can be achieved by injection of a common optical signal with randomly varying phase. An optical signal with randomly modulated phase is injected into two semiconductor lasers which have chaotic oscillations due to optical feedback. Strong correlation between complex intensity oscillations of the two lasers is observed even though the intensity of the common injection signal is constant. Characteristic properties of this type of synchronization are shown, in particular, the dependence of the synchronization threshold on the injection strength and the rate of phase modulation, and the dependence of the intensity correlation on the difference in phase of optical feedback.     

水泵水轮机空载开度压力脉动特性预测

为了解水泵水轮机非同步导叶启动过程空载开度下的压力脉动特性,优化机组的性能提高并网成功几率,采用RNG k-ε模型对水泵水轮机非同步导叶空载点进行模拟,并对内部流场和压力脉动特性进行了分析。结果表明,转轮与活动导叶之间的压力脉动由叶片通过频率央定,尾水管涡带的周期性旋转导致尾水管进口呈现低频压力脉动,压力脉动幅值最大处位于预开启同步导叶与转轮之间。     

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