基于偏振旋转光反馈下的外光注入VCSEL产生高性能毫米波

本文提出一种基于偏振旋转光反馈下的外光注入垂直腔 表面发射激光器(VCSEL)产生高性能毫米波的方案, 并利用描述外部扰动下VCSEL动态特性的自旋反转模型(SFM), 对所产生的毫米波的特性进行了数值研究. 研究结果表明: 一个受到主VCSEL(M-VCSEL)光注入的副VCSEL(S-VCSEL)在一定条件下可以产生单周期(P1)振荡, 即在光波上调制了一个微波信号. 通过调节外光注入强度ξ_i以及S-VCSEL与M-VCSEL之间频率失谐Δν, 可以获得频率在30---60 GHz范围内连续可调的毫米波信号. 在外光注入VCSEL中引入偏振旋转光反馈, 通过选取合适的反馈强度ξ_f以及反馈延迟时间τ, 产生的毫米波信号的线宽可以得到明显窄化. 对于光注入S-VCSEL所产生的线宽为5.509 MHz的毫米波, 在引入偏振旋转光反馈后, 毫米波线宽可以降低到230.2 kHz. 本文的研究对高速光载无线(RoF)系统中优质毫米波信号的获取具有一定的参考意义.     

基于光注入半导体激光器单周期振荡的光子微波产生及全光线宽窄化

本文对基于光注入半导体激光器的单周期动力学态产生光子微波并利用光反馈压缩其线宽进行了实验研究. 研究结果表明: 通过适当调节注入参数, 能对该方法产生的光子微波频率在数十GHz范围内进行连续、大范围地调节; 通过引入光反馈并精细调节反馈强度, 光子微波的线宽能够从40—100 MHz的范围被压缩约两个数量级至300—900 kHz范围;反馈长度对光子微波的线宽几乎没有影响, 但当反馈长度精细变化时, 光子微波频率会出现一定范围内的周期性漂移.     

Tunable and broadband microwave frequency combs based on a semiconductor laser with incoherent optical feedback

Based on a semiconductor laser(SL) with incoherent optical feedback, a novel all-optical scheme for generating tunable and broadband microwave frequency combs(MFCs) is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 d B amplitude variation. For a fixed bias current, the line spacing(or repetition frequency) of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing increases with the increase in the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. In addition,mappings of amplitude variation, repetition frequency, and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.     

基于光电负反馈的光注入1550nm垂直腔面发射激光器产生窄线宽微波信号

基于1 550nm垂直腔面发射激光器在平行偏振光注入下呈现的单周期非线性动力学状态,进一步引入光电负反馈,得到了高质量的微波信号.实验研究结果表明:平行偏振光注入下,通过调节注入光的注入强度及频率,1 550nm垂直腔面发射激光器可呈现注入锁定、单周期、倍周期、混沌等多种非线性动力学状态;在合适的注入参量下,平行偏振光注入1 550nm垂直腔面发射激光器可产生光谱具有单边带结构、频率超过10GHz的光子微波信号,但该微波信号的线宽较宽(达MHz量级);进一步引入光电负反馈后,通过选取合适的光电反馈强度,可将该微波信号的线宽减小至一百多kHz(减小两个量级以上);在选择优化的反馈强度条件下,仅通过简单调节注入光强度,可实现窄线宽光子微波信号的频率在一定范围内连续可调谐.     

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     

基于外光注入互耦合垂直腔面发射激光器的混沌随机特性研究

通过在互耦合垂直腔面发射激光器(VCSELs)系统中增加外光注入, 建立了一种基于偏振可调光反馈VCSEL驱动互耦合VCSELs混沌系统模型, 分析了增加外光驱动对互耦合激光器随机特性的影响. 以不可预测度作为随机特性的评价指标, 采用信息论中的排列熵作为相应量化工具, 对系统输出混沌信号的不可预测性进行定量分析.数值研究了光强度、时延、偏振旋转角度以及驱动激光器与耦合激光器间的频率失谐对输出信号随机特性的影响.结果表明: 外光注入能够增大互耦合VCSELs输出混沌信号的排列熵, 即外光注入能够有效提高耦合系统的随机特性; 驱动激光器可调偏振片偏转角度调节到45° 附近, 注入强度适中, 满足耦合强度大于驱动激光器自反馈强度条件, 系统输出信号的排列熵较大; 在耦合时延与驱动激光器反馈时延不相等的同时, 增加驱动激光器与耦合激光器频率失谐, 外光注入互耦合VCSELs的随机特性能够得到进一步提高.     

1550nm-VCSELs在偏振保持光反馈和正交光注入下的偏振转换特性

基于自旋反转模型,研究了1550 nm垂直腔面发射激光器(1550 nm-VCSELs)在偏振保持光反馈和正交光注入下的偏振转换特性.结果表明:正交光注入下的从激光器会随着注入强度的增加产生偏振转换.在归一化注入电流较小时,改变反馈强度,会使从激光器发生偏振转换的注入强度出现规律不同的变化;改变频率失谐,会使从激光器发生偏振转换的注入强度出现规律相同的变化.     

基于平行偏振光注入的1550nm波段垂直腔表面发射激光器获取窄线宽光子微波的理论和实验研究

提出一种基于1550 nm垂直腔表面发射激光器(1550 nm-VCSEL)获取高质量微波信号的全光方案.在该方案中,采用波长位于VCSEL中被抑制模式的中心波长附近、振动方向与VCSEL中主导模式相同的偏振光注入(即平行注入)1550 nm-VCSEL获取高频微波,并借助双光反馈对该高频微波的线宽进行窄化.一方面,基于VCSEL的自旋反转模型,从理论上分析了采用该方案产生微波信号的可行性;另一方面,通过构建相应的实验系统,对该方案产生的微波的特性进行初步实验研究.实验结果表明:在合适的注入条件下,1550 nm-VCSEL能够产生30 GHz左右的微波信号,但该信号的线宽较宽(百兆水平);引入双光反馈后,微波线宽可被压窄两个数量级以上,得到了线宽低于1 MHz、信噪比大于40 d B的微波信号.     

外部光注入混沌激光器产生超宽带微波信号的研究

利用外部光注入混沌激光器产生了完全符合美国联邦通信委员会关于室内无线通信频谱限定的超宽带(UWB)微波信号.基于外部光注入光反馈半导体激光器的速率方程组,理论研究了外部及内部参量对半导体激光器输出混沌UWB脉冲信号的影响.研究表明,UWB信号的-10 dB带宽随着光注入强度、注入失谐量以及线宽增强因子的增大而增大,随着激光器偏置电流的增大而减小.同时,UWB信号的中心频率在5–8 GHz范围内变化.在实验中,通过设定其他参量和调节光注入强度,得到中心频率及带宽可调谐的混沌UWB微波信号,传输速率达到500 Mbit/s.实验结果与理论分析相符合. 关键词： 半导体激光器 混沌激光 光生微波技术 超宽带信号     

基于椭圆偏振光注入垂直腔表面发射激光器的正交偏振模式单周期振荡产生两路光子微波

提出了基于椭圆偏振光注入下垂直腔表面发射激光器(VCSEL)输出的正交偏振模式单周期(P1)振荡来同时获取两路光子微波的实现方案, 并进行了相关仿真研究. 结果表明: 在合适的参数条件下, 一个自由运行的VCSEL(定义为主VCSEL, M-VCSEL)可输出椭圆偏振光, 其X偏振分量和Y 偏振分量具有相同的激射频率; 将M-VCSEL输出的椭圆偏振光注入到另外一个VCSEL(定义为副VCSEL, S-VCSEL), 在给定主副VCSEL间频率失谐的条件下, 通过选择合适的注入强度可使S-VCSEL 中两个偏振分量均呈现单周期(P1)振荡, 从而可获得两正交的光子微波信号; 随着注入强度的增加, 光子微波的频率以及功率均呈现增加的趋势; 结合微波频率、功率以及输出光谱中第一边带和第二边带的幅度差在由注入强度和频率失谐所构成参数空间下的分布图, 可确定获取高品质微波信号的优化注入参数范围.     

线宽增强因子对光反馈半导体激光器混沌信号生成随机数性能的影响

基于光反馈半导体激光器产生的宽带混沌信号作为物理熵源生成物理随机数已得到广泛研究.线宽增强因子的存在会导致半导体激光器出现大量不稳定动态特性,因此,本文着重研究半导体激光器的线宽增强因子对生成随机数性能的影响.数值仿真结果表明:随着线宽增强因子的增加,光反馈半导体激光器输出混沌信号的延时峰值逐渐减小、最大李雅普诺夫指数逐渐增大.基于不同线宽增强因子下产生的混沌信号提取随机数,并利用NIST SP 800-22软件对生成随机数的性能进行测试.测试结果表明,选取线宽增强因子较大的半导体激光器产生混沌信号作为物理熵源易于生成性能良好的随机数.     

Sensitivity to external optical feedback of circular-side hexagonal resonator microcavity laser

The sensitivity to fault reflection is very important for larger dynamic range in fiber fault detection technique. Using time delay signature (TDS) of chaotic laser formed by optical feedback can solve the sensitivity limitation of photodetector in fiber fault detection. The TDS corresponds to the feedback position and the fault reflection can be detected by the laser diode. The sensitivity to feedback level of circular-side hexagonal resonator (CSHR) microcavity laser is numerically simulated and the feedback level boundaries of each output dynamic state are demonstrated. The peak level of TDS is utilized to analyze the sensitivity. The demonstration is presented in two aspects:the minimum feedback level when the TDS emerges and the variation degree of TDS level on feedback level changing. The results show that the CSHR microcavity laser can respond to the feedback level of 0.07%, corresponding to -63-dB feedback strength. Compared to conventional distributed feedback laser, the sensitivity improves almost 20 dB due to the shorter internal cavity length of CSHR microcavity laser. Moreover, 1% feedback level changing will induce 1.001 variation on TDS level, and this variation degree can be influenced by other critical internal parameters (active region side length, damping rate, and linewidth enhancement factor).     

Analytical expressions for the intensity and frequency noise of an individual mode in a multimode semiconductor laser with external optical feedback

Analytical expressions are derived for the intensity and frequency noise of each individual mode in a multimode semiconductor laser with external optical feedback. It is shown that in a two-mode laser the side-mode effect on the intensity noise is enhanced by the optical feedback which gives the maximum linewidth narrowing.     

有效压缩增益开关DFB激光器光谱线宽的注入时间窗口

实验与理论研究了外光注入种子脉冲有效压缩增益开关DFB激光器光谱线宽的注入时间窗口.发现只有在增益开关光脉冲建立之前约100 ps的时间窗口内，注入种子脉冲方可以有效压缩增益开关DFB半导体激光器光谱线宽, 并且线宽随着注入光强度的增加而减小，可产生低啁啾的近变换极限的超短光脉冲.实验证实，在此时间窗口内注入种子脉冲，增益开关DFB激光器的光谱线宽从0.46 nm压缩至0.08 nm，时间带宽积从2.46降低至0.70.同时理论研究了增益开关DFB半导体激光器的光谱线宽压缩与种子脉冲的注入时间及强度的关系.     

短外腔偏振旋转光反馈下1550nm垂直腔面发射激光器的动力学特性研究

基于扩展的自旋反转模型,对短外腔偏振旋转光反馈下1550 nm垂直腔面发射激光器的动力学特性进行了数值仿真和理论分析.研究结果表明:增加反馈强度会导致多个偏振开关现象出现,中等反馈强度下呈现丰富的动力学状态,譬如单周期、倍周期、准周期及混沌态,增加注入电流使Y方向线偏振模的工作区域被压缩;随着反馈延迟时间的增加,在弱光反馈时,偏振模跳变现象将会以特定的频率发生,施加中等的反馈强度将会导致模式跳变的频率增加,并且出现各种新的动力学状态,包括拍频单周期、拍频脉冲包络、拍频准周期和拍频混沌态.新动力学行为的出现是由于短外腔区激光器的动力学特性对相位变化非常敏感,从而使外腔模式间的拍频效应发挥了关键作用.此外还发现各种动力学状态之间会伴随模式间的跳变而发生相互跳变.     

Effect of intrinsic optical feedback on the intersubband optical properties of spherical quantum dots

Optical feedback due to mutual relation between local field effect and intersubband transition in quantum dots is investigated for the first time. In this regard, dielectric function of quantum dots is considered up to the third order of nonlinearity. It is found that near the resonance, the intensity inside the dot is a function of frequency, which is determined by the optical feedback. This effect changes the magnitude of optical nonlinearity and its symmetry around the transition energy. The results indicate that the magnitude of the dielectric function decreases at frequencies below the transition frequency because of concentration of electric field inside the dot and vice versa. It is also shown that this effect is enhanced by increasing the intensity and resonance contribution in the dielectric function.     

基于次谐波调制光注入半导体激光器获取窄线宽微波信号的实验研究

实验研究了处于单周期振荡的光注入半导体激光器在频率等于单周期振荡频率一半的1/2次谐波调制下所产生的微波信号的特性.实验结果显示:在合适的注入条件下,处于单周期(P1)振荡的光注入半导体激光器可输出频率可达26.5 GHz、光谱具有单边带结构的光生微波信号,但微波信号的线宽比较宽(MHz量级);通过采用频率为单周期振荡频率一半的次谐波信号调制光注入半导体激光器,可将微波线宽从十几MHz压缩到几十k Hz.进一步分析了次谐波调制信号的功率以及频率对微波信号的相位噪声的影响,并在由次谐波调制信号的功率和频率构成的参数空间绘制出了能实现次谐波频率锁定的分布区域.     

Experimental investigations on the external cavity time signature in chaotic output of an incoherent optical feedback external cavity semiconductor laser

Chaotic dynamics of a semiconductor laser subject to incoherent optical feedback (IOF) are experimentally investigated, and the external cavity time are retrieved and measured from intensity time series of the laser output by using self-correlation function and the mutual information. Through moderating feedback strength and injection current of the laser, the external cavity time signature of the laser chaotic output is effectively attenuated, and then the security of such chaos encryption system can be assured to a certain degree.     

Conceal time-delay signature of chaotic vertical-cavity surface-emitting lasers by variable-polarization optical feedback

Time-delay (TD) signatures of chaotic outputs generated by vertical-cavity surface-emitting lasers (VCSELs) are investigated quantitatively by using two proposed estimators, the peak signal to mean ratio (PSMR) calculated based on the auto-correlation function, and the valley signal to mean ratio (VSMR) calculated based on an information-theory-based estimator, the permutation entropy (PE) function. The VCSELs subject to variable-polarization optical feedback (VPOF) are considered, and the effects of polarizer angle, feedback strength, feedback delay and injection current are discussed. When the feedback strength is small, the TD signatures for the fully developed chaotic outputs of VCSELs can be well concealed for all polarizer angles. While for large feedback strength, the TD signatures cannot be concealed for any polarizer angle. However, for moderate feedback strength, the TD signatures of VCSELs with VPOF at intermediate polarizer angles can be better concealed than those of VCSELs with conventional polarization-selected optical feedback. Thus, the VCSELs with VPOF are extremely interesting for the security-enhanced chaotic optical communication systems.     

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.