混沌半导体激光器的弛豫振荡频率对随机序列速率的影响

利用光反馈半导体激光器产生的混沌激光作为随机数发生器的物理熵源, 分析了混沌信号自相关系数与随机序列游程数之间的联系, 在此基础上研究了激光器的弛豫振荡频率f_r与随机序列速率f_n在不同比值时, 序列游程数的变化情况. 研究发现, 当f_r/f_n=(2k+1)/4时, 随机序列的游程数容易满足NIST SP800-22随机数测试标准的要求. 当k=1时, 得到随机序列最大速率为f_n=4f_r/3.     

光注入提高半导体激光器混沌载波发射机的带宽

外光反馈下的半导体激光器可视为混沌载波发射机.数值研究发现，外部强光注入可以显著提高混沌载波发射机的带宽，带宽提高的程度在一定范围内与注入光的强度成正比.当外部光注入系数k_inj=0.39时，混沌载波的带宽由无光注入时的2.7GHz增大到14.5GHz，提高了5倍多.研究还发现，在相同的注入强度条件下，当注入光的频率比半导体激光器的中心频率高2—4GHz时，可实现最大限度的带宽增强.此外，适当提高半导体激光器的偏置电流也可以在一定程度上提高其产生的混沌载波的带宽. 关键词： 半导体激光器 混沌 带宽     

交叉相位调制提高半导体激光器混沌载波发射机带宽方法

提出半导体激光器混沌交叉相位调制(XPM)光反馈提高混沌载波发射机带宽方法,建立了有外腔光纤传输反馈XPM控制下的激光动力学物理模型.理论导出XPM作用下激光双反馈频率失谐公式,指出XPM产生的非线性相移影响了激光器增益和线宽增强因子,其光纤二阶非线性效应使激光振幅和相位变化更加丰富,而非线性相移的出现进一步增加了新的频率分量并使频谱展宽.数值结果表明,XPM使激光器混沌带宽增加到4倍以上,使激光混沌张弛振荡频率增加到2.85倍,其光纤长度、入纤光功率、面镜反射系数、光纤二阶非线性系数等都能影响激光混沌带宽.     

Power fluctuations of a weakly optically-injected semiconductor laser in a period-one state

The frequency spectrum and the power output of a weakly optically-injected semiconductor laser in a period-one state are investigated. It is found that the oscillations in the power output consist of three components each caused by different physical effects, namely the relaxation oscillation frequency, the detuning between master and the slave laser frequency and the photon roundtrip time. For each set of parameters the spatio-temporal dynamics are obtained and the same internal oscillations occur.     

大幅度增加弛豫振荡频率来实现毫米级外腔半导体激光器的外腔机制转换

混沌外腔半导体激光器输出明显存在弛豫振荡特征,弛豫振荡频率小于外腔振荡频率时,外腔半导体激光器输出态是短腔机制;反之,外腔半导体激光器输出态是长腔机制.首先对比分析了弛豫振荡频率为5.6 GHz,腔长对频谱有效带宽的影响.然后同时调节注入电流和载流子寿命来大幅度地增加弛豫振荡频率.最后在弛豫振荡频率为40 GHz、腔长为毫米级(4—20 mm)时,实现由短腔机制到长腔机制的转换,进而分析了外腔反馈率和外腔长对外腔半导体激光器频谱带宽的影响.分析结果表明:短腔机制下,输出混沌态不稳定,0.1 mm的偏差就会导致混沌态与非混沌态之间的转化;长腔机制下,输出混沌态稳定,输出混沌区域较大,证明长腔机制下更有益于获得宽带连续的混沌区域.在弛豫振荡频率为40 GHz、外腔长度为毫米级时,实现了外腔半导体激光器的长腔机制,从而增大了高带宽混沌的参数空间.     

Single-mode giga-hertz optical pulses generated by a self-modulation of the relaxation oscillation frequency in a semiconductor laser with subharmonic polarization-rotated optical feedback

In this research, single-mode 3.76 GHz optical pulses were generated in a Fabry-Perot type single-mode semiconductor laser with polarization-rotated optical feedback (PROF) at a round-trip feedback distance of 50.8 cm, corresponding to a feedback frequency of 0.59 GHz. Experimental results and numerical simulations revealed that the pulse generation mechanism involved a self-modulation of the laser’s relaxation oscillation frequency so that the oscillation frequency approximated to an integer multiple of the PROF round-trip feedback frequency. This effect is very different from similar experiments reported by many researchers before, in which the laser’s output was amplitude modulated by the feedback frequency and an ultra-short feedback distance was required to generate giga-hertz optical pulses. Investigations about some characteristics of the self-modulation mechanism will be reported in the paper.     

Periodic oscillation within the chaotic region in a semiconductor laser subjected to external optical injection

We report on the experimental observation of periodic windows within the chaos of the output of a semiconductor laser that is subjected to external optical injection. Continuously sampled spectra of the slave-laser output as the injection level is increased reveal the general behavior of the system as well as features that suggest that the periodic oscillation forms a distinct island within the chaotic region in the parameter space.     

掺Yb钒酸盐晶体激光振荡中的光学双稳态现象研究

研究了三种掺Yb钒酸盐晶体Yb:LuVO4,Yb:YVO4和Yb:GdVO4的激光振荡中所呈现的光学双稳态效应.以晶体所吸收的抽运功率表征的双稳区宽度ΔPabs可超过1W,在双稳区高功率一侧的边界,即激光振荡的上阈值点,出现激光输出功率的不连续变化或跃变,同时发生亚毫秒时间尺度上的大幅度强度涨落.谐振腔的输出耦合透过率、晶体长度、晶体中的热效应等对双稳态效应均具有重要影响.     

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     

微波管中离子张弛振荡的混沌现象

微波管中离子张弛振荡引起的噪声对其工作性能有很大影响，已成为微波管领域研究的焦点之一.用包络方程描述电子束特性，用离散的宏粒子模型描述离子特性，在此基础上编写了一维粒子模拟程序，对行波管与速调管模拟，得到张弛振荡的时间序列；将振荡看作是一个复杂非线性动力学系统的响应，分析了离子张弛振荡时间序列的功率谱、重构相图及Lyapunov指数，指出离子张弛振荡具有混沌性质，为研究离子张弛振荡的控制与带有离子振荡噪声信号的处理提供了参考. 关键词： 张弛振荡 粒子模拟 微波管 混沌     

Characterization of semiconductor laser frequency chirp based on signal distortion in dispersive optical fiber

In the paper, the simple method of laser chirp parameters estimation is presented. It is based on measuring time-domain distortions of chirped signal transmitted through dispersive fiber and finding laser chirp parameters by matching measured distortions to calculated ones. Experiments undertaken with 1.55 μm telecommunication grade distributed feedback (DFB) lasers and standard single-mode fiber are described, together with some practical remarks on measurement setup and main conclusions.     

Phase synchronization in a two-mode solid state laser: Periodic modulations with the second relaxation oscillation frequency of the laser output

Phase synchronization (PS) in a periodically pump-modulated two-mode solid state laser is investigated. Although PS in the laser system has been demonstrated in response to a periodic modulation with the main relaxation oscillation (RO) frequency of the free-running laser, little is known about the case of modulation with minor RO frequencies. In this Letter, the empirical mode decomposition (EMD) method is utilized to decompose the laser time series into a set of orthogonal modes and to examine the intrinsic PS near the frequency of the second RO. The degree of PS is quantified by means of a histogram of phase differences and the analysis of Shannon entropy.     

用滑模变结构控制方法实现外腔反馈式半导体激光器的混沌控制

通过增加外腔反馈式半导体激光器的激光反馈时间，使系统处于混沌状态，再采用滑模变结构控制方法实现这种激光器的混沌控制.该方法的优点是系统既能很快地获得稳定的输出激光，又能根据工程需要实现激光输出功率强度的灵活调整.理论分析和数值计算结果表明控制结果具有很强的稳定性和鲁棒性.研究结果对改善实际激光系统稳态输出的快速性、输出功率的灵活可调性和能量转换效率有较好的参考价值. 关键词： 混沌 外腔反馈式半导体激光器 滑模变结构控制 外腔长度     

金原子的放大自发辐射脉冲的弛豫振荡

首次报道了由金原子发出的波长627.8nm的放大自发辐射脉冲具有弛豫振荡.得出其在时间域和频率域的规律.这种振荡可能是高增益脉冲辐射系统的一种普遍现象.     

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     

利用半导体激光器环产生27 GHz的平坦宽带混沌激光

关键词： 激光器 混沌 宽带 环形结构     

Experimental characterization of DFB and FP chaotic lasers with strong incoherent optical feedback

We have experimentally investigated chaotic power oscillations in single-longitudinal mode DFB and multi-longitudinal mode FP lasers as a function of incoherent optical feedback strengths of up to 42%. We have demonstrated the existence of chaos in the output oscillations of both laser types using classical experimental tools such as RF spectrum, standard deviation, and maximum Lyapunov exponent, which all increase with increasing of feedback strength for both in single-longitudinal mode DFB lasers and multi-longitudinal mode FP lasers. It is also shown that power switching among longitudinal modes of multimode FP semiconductor laser is a considerable portion of the chaotic power oscillations for both strong and weak incoherent optical feedback.     

New nonlinear dynamics in a semiconductor laser with optical self—feedback

We demonstrate a new kind of instability of the external cavity semiconductor laser,In some parameter regimes,the external cavity system will produce short and strong optical pulses in aperiodic intervals.This instability also shows low-frequency characteristics.     

Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry–Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry–Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation.     

半导体激光器混沌输出的延时特征和带宽

外腔延时特征和带宽是影响混沌激光应用的两个重要参量.本文将一个单路光反馈的半导体激光器输出的激光部分地注入到另一个双路滤波光反馈的半导体激光器中,从而构成一个具有外光注入的双路滤波光反馈半导体激光器系统,即主从激光器系统,用于抑制混沌激光的延时特征并研究其带宽.数值研究了外光注入系数、反馈强度、抽运因子和滤波器带宽对系统输出混沌激光的延时特征的影响,然后将该系统对延时特征的抑制效果和具有外光注入的单路光反馈半导体激光器系统、具有外光注入的双路光反馈半导体激光器系统、具有外光注入的单路滤波光反馈半导体激光器系统以及无光注入双路滤波光反馈半导体激光器系统进行对比和分析,结果表明本文提出的方案对延时特征的抑制效果最好.然后在本文提出的具有外光注入的双路滤波光反馈半导体激光器系统中,延时特征被有效抑制的参数条件下研究系统输出混沌激光的带宽,结果表明,通过适当选择参数的取值,本文提出的方案可以提高系统输出混沌激光的带宽.