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     

半导体激光器输出混沌光的延时特性和带宽

提出一个新的方案用于抑制半导体激光器输出混沌光的延时特性并研究其带宽.在该方案中,将由伪随机信号驱动的相位调制器加到具有双路光反馈的半导体激光器的两个反馈腔中,从而构成具有双路相位调制光反馈的分布反馈半导体激光器系统.数值研究了延迟时间和反馈系数等参数对该系统输出混沌光的延时特性的影响,用自相关函数曲线中的延时特征峰的最大值表示延时特性.然后将该系统对延时特性的抑制效果和具有双路光反馈的分布反馈半导体激光器系统以及具有单路相位调制光反馈的分布反馈半导体激光器系统进行比较,结果表明本文所提出方案的抑制效果最好.进而基于能有效抑制延时特性的参数条件研究了具有双路相位调制光反馈的分布反馈半导体激光器输出混沌光的带宽,结果表明,抽运因子的增大和反馈系数的增加都能使系统输出混沌光的带宽变大.     

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.     

面发射分布反馈半导体激光器

本文详细阐述了面发射分布反馈半导体激光器(SE-DFB-LD)的基本工作原理、结构设计及其工作性能,针对国内外研究最新进展与发展现状进行了总结和评述,并在此基础上,对面发射半导体激光器的研究工作和发展趋势做出了进一步的讨论和展望。随着面发射分布反馈半导体激光器各性能指标的不断优化提升和后期加工、装调技术的逐渐成熟,其将不断满足科学研究及工业、军事等实际应用领域对半导体激光器的需求,具有很大的发展潜力。     

混沌神经网络的延时反馈控制研究

针对混沌神经网络，提出了一种改进的延时反馈控制方法. 利用该方法，当延时参数τ为奇数时，被控神经网络收敛于记忆模式以及它的反相模式的2周期上. 若选取不同的延时参数，被控网络则收敛于不同的周期态上. 关键词： 控制混沌 延时反馈控制 混沌神经网络     

光注入下外光反馈半导体激光器输出自相关特性研究

基于半导体激光器(SL)受到外部扰动(光反馈和光注入)下的速率方程组,研究了反馈系数、延迟时间、注入强度和频率失谐对半导体激光器输出混沌信号自相关特性的影响.研究表明：上述四个参量对SL输出混沌信号的自相关函数曲线的半高全宽(FWHM)以及边峰抑制比都有影响;通过合理选择各参量,可以使SL输出的混沌信号具有尖锐的自相关函数曲线分布,其FWHM可降到0.02 ns,比已有相关报道提高了一个数量级. 关键词： 半导体激光器 光反馈 光注入 自相关函数     

时变电流注入下光电负反馈垂直腔表面发射激光器的偏振双稳特性

基于光电负反馈垂直腔表面发射激光器(VCSELs)的理论模型,数值研究了时变电流注入下反馈率大小和注入电流扫描周期对VCSELs偏振双稳特性的影响.研究结果表明:增大反馈率将使双稳区域向更大电流方向移动,同时双稳区宽度增加;增大注入电流扫描周期将使双稳区宽度减小.因此,通过调整光电负反馈的大小以及注入电流的扫描周期,可实现对VCSELs偏振双稳特性的控制.     

基于光电负反馈的激光混沌串联同步系统研究

提出了一种新的混沌中继系统，该系统基于光电负反馈的激光混沌串联同步.对该系统的同步性以及激光器内部参数失配对其同步性的影响进行了研究，并与基于光反馈的激光混沌串联同步系统进行了比较.研究结果表明：当系统参量满足一定条件时，该系统能实现完全同步；当激光器内部参数失配时，其混沌同步性会受到一定的影响，但该系统的混沌同步性对参数失配的容忍性要比基于光反馈的系统好得多.     

基于互注入半导体激光器的混沌输出产生17.5 Gbit/s随机码

采用两个借助光纤连接的相互注入半导体激光器,实验获取了10 GHz超宽带混沌种子信号.通过8-bit模数转换器将混沌信号转换为二进制数据流,并进行进一步的逻辑异或处理和舍弃最高有效位操作,最终获得了能顺利通过美国国家标准与技术研究院(National Institute of Standard and Technology,简记为NIST)800-22标准测试以及Diehard测试,速率达17.5 Gbit/s的高速随机码. 关键词： 随机码 混沌激光 互注入半导体激光器     

利用频谱仪提取双反馈混沌半导体激光器的外腔长度密钥

光反馈半导体激光器产生的高维宽带混沌载波,应用于光混沌通信系统中.主器的外腔长度用作混沌保密通信的附加密钥.本文实验研究了光反馈混沌半导体激光器外腔长度密钥的识别.通过对长腔光反馈产生的混沌频谱进行局部放大,分析其精细结构,结果表明:无论是单反馈半导体激光器还是有不同外腔长度比的双反馈半导体激光器,都可以利用频谱仪直接提取出激光器的外腔长度信息.     

Chaos dynamics in vertical-cavity surface-emitting semiconductor lasers with polarization-selected optical feedback

We study experimentally and numerically the dynamic states of chaotic oscillations in vertical-cavity surface-emitting semiconductor lasers (VCSELs) with polarization-selected optical feedback. We identify the regimes of fully-developed chaotic states, low-frequency fluctuations (LFFs), and coexistent states of LFFs and stable oscillation for the variations of the bias injection current and the optical feedback ratio. In particular, coexistent states of LFFs and stable oscillations are observed at higher optical feedback ratio and lower bias injection current. We draw maps of dynamic states in the space of the bias injection current and the optical feedback ratio. The qualitative agreement between the theory and the experiment is found.     

Nonlinear dynamics of a directly modulated semiconductor laser with cavity detuning

A detailed numerical study of dynamical behavior of a semiconductor laser under current modulation and cavity detuning has been performed on the base of four different models of the active medium which take into account direct transitions between ground subbands, transitions with no k-selection rule between ground subbands and contribution of excited subbands in each of the above-mentioned cases. We have shown that different nonlinear regimes (period doubling, chaos, generalized bistability) can be obtained either with cavity detuning from the gain band maximum or near the laser threshold.It has been established that the shape and principal peculiarities of amplitude detuning characteristics are determined by the relation between the current modulation frequency and maximum resonance frequency of the laser.PACS numbers: 05.45.Pq, 42.55.Px, 42.65.Sf     

Analysis of linewidth and extinction ratio in directly modulated lasers for performance optimization in 10 Gbit/s CWDM systems

Direct Modulation Lasers (DMLs) have attracted increased attention during the past few years because of their intrinsic simplicity and cost-effectiveness, especially when applied to WDM metro and access networks. However, the output power waveform from a directly modulated laser is not an exact replica of the modulation current and its instantaneous optical frequency varies with time depending on the changes in optical power and the extinction ratio (ER) (an effect also known as frequency chirp). In this work, using an Optical Communication System Design Software, we have studied a directly modulated WDM 10 Gb/s system which transmission performance depends strongly on DML characteristics; simulation results have provided supplementary details about the effects of DML type (adiabatic or transient chirp dominated) as well as the effects of the optical output power. These details can provide useful design guidelines for constructing a WDM metro network.     

Influence of current pulse shape on directly modulated system performance in metro area optical networks

Due to the fact that a metro network market is very cost sensitive, direct modulated schemes appear attractive. In this paper a CWDM (Coarse Wavelength Division Multiplexing) system is studied in detail by means of an Optical Communication System Design Software; a detailed study of the modulated current shape (exponential, sine and gaussian) for 2.5 Gb/s CWDM Metropolitan Area Networks is performed to evaluate its tolerance to linear impairments such as signal-to-noise-ratio degradation and dispersion. Point-to-point links are investigated and optimum design parameters are obtained. Through extensive sets of simulation results, it is shown that some of these shape pulses are more tolerant to dispersion when compared with conventional gaussian shape pulses. In order to achieve a low Bit Error Rate (BER), different types of optical transmitters are considered including strongly adiabatic and transient chirp dominated Directly Modulated Lasers (DMLs). We have used fibers with different dispersion characteristics, showing that the system performance depends, strongly, on the chosen DML-fiber couple.     

Onset of instabilities in self-pulsing semiconductor lasers with delayed feedback

We consider the deterministic dynamics of a semiconductor laser with saturable absorber that is subject to delayed optical feedback. Alone, both the saturable absorber and delayed feedback cause the CW output to become unstable to periodic output via Hopf bifurcations. We examine the combined effects of these two destabilizing mechanisms to determine new conditions for the Hopf bifurcations. We also describe the transient as the unstable CW output evolves to the oscillatory state. A main result is that the presence of a saturable absorber can increase the sensitivity of the laser to delayed feedback. Received 1st August 2001 and Received in final form 28 November 2001     

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     

Chaos synchronization and encoding in coupled semiconductor lasers of multiple modulated time delays

We numerically investigate the synchronization performance of unidirectionally and bidirectionally coupled chaotic semiconductor lasers subject to multiple modulated time delays optical feedbacks. Moreover, by studying the autocorrelation function of the coherent feedback semiconductor laser output, we find that the signatures of time delays can be erased in systems incorporating modulated feedback time delays, which largely improve the system security. Finally, chaos masking switching (CMS) is utilized to examine the communication ability. Numerical results indicate that the messages could be successfully recovered both in unidirectionally and bidirectionally coupled lasers, which confirms the possibility of applying multiple modulated delay system in optical chaos secure communication.     

Periodic locking of chaos in semiconductor lasers with optical feedback

We show how a chaotic system can be locked to emit a periodic waveform belonging to its chaotic attractor. We numerically demonstrate our idea in a system composed of a semiconductor laser driven to chaos by optical feedback from an external cavity. The clue is the injection of an appropriate periodic signal that modulates the phase and amplitude of the intra-cavity radiation, a chaotic analogy of conventional mode-locking. The result is a time process that manifests a chaotic signature embedded in a long-scale periodic train.     

Complete chaotic synchronization characteristics of the linear-polarization mode of vertical-cavity surface-emitting semiconductor lasers with isotropic optical feedback

Based on the SFM model [M. San Miguel, Q. Feng, J.V. Moloney, Phys. Rev. A. 52 (1995) 1728.], complete chaotic synchronization characteristics of linear-polarization (LP) Mode of the vertical-cavity surface-emitting semiconductor lasers (VCSELs) with isotropic optical feedback are numerically investigated. When the propagation time τ_c of light from the transmitter to the receiver equals to the external cavity round-trip time τ, and the central frequency of the T_VCSEL matches that of the R_VCSEL, in large scale region of the feedback coefficient and the injection current where the x-polarization mode as well as the y-polarization mode obtains high synchronization quality at the same time. However, in the central frequency mismatch regions where the x- and y-polarization mode can obtain inferior synchronization quality at same time. But for τ_c ≠ τ, each LP mode of the mixed polarization modes achieved inferior synchronization quality at the same time. Besides, with big enough injection current, the output of the system with the same central frequency in two lasers is entirely governed by the y-polarization mode when the feedback coefficient and Δτ(=τ_c − τ) fixed at a certain value. So the system can realize steadily good synchronization of the completely dominant y-polarization mode. But the synchronization quality of the completely dominated y-polarization mode can be deteriorated by increasing absolute frequency detuning value. Besides, in positive frequency mismatch regions where the influence of the same frequency detuning value on the synchronization quality of the entirely governed y-polarization mode becomes smaller than in negative frequency detuning regions. At last, when τ is given and the central frequency of the T_VCSEL matches that of the R_VCSEL, the influence of the τ_c is not a simple time-shift in the time-evolution of the receiver VCSEL, which has serious influence on the complete synchronization quality of each LP mode.     

调频微片Nd:YAG激光器光回馈特性的研究

研究了调频微片Nd：YAG激光器的光回馈特性.在没有光回馈的情况下，激光频率每改变一个纵模间隔，激光器输出功率变化一个条纹.有光回馈时，同时改变激光频率和外腔相位，激光器输出功率波动频率正比于内、外腔长度之比.基于三镜腔等效模型的理论分析和实验结果相符合.并且讨论了这一现象在精密测量领域的潜在应用.