反馈相位随机调制消除混沌半导体激光器的外腔长信息

提出并数值证实利用反馈相位的随机调制可消除外腔半导体激光器反馈引起的时延结构. 研究发现:当反馈相位随机调制信号的速率处在0.1—1 Gbit/s范围,随机调制信号的切换幅值个数达到5时,在半导体激光器偏置电流(1.2—2.8I_th)和反馈速率(8—26 GHz)构成的参数空间中,反馈时延结构对应的外腔长信息可被有效地消除. 关键词： 半导体激光器 外腔长 反馈相位 随机信号调制     

相干长度可连续调谐的半导体激光器

实验利用光反馈的方法获得了相干长度连续可调的半导体激光光源.通过调节反馈强度及抽运电流,有效控制了光反馈半导体激光器的相干长度.其相干长度可由无反馈时的几米连续调至100 μm.同时,利用光反馈半导体激光器速率方程,数值模拟了反馈强度及抽运电流对半导体激光器相干长度的影响.实验及数值模拟均表明：通过调节反馈强度的大小可以有效控制半导体激光器的相干长度,光反馈半导体激光器的相干长度随反馈强度的增大而减小,而偏置电流对相干长度无明显影响.模拟结果与实验结果符合. 关键词： 光反馈半导体激光器 相干长度 反馈 混沌     

直接调制光反馈半导体激光器产生超宽带信号

利用直接电流调制光反馈半导体激光器产生了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.基于光反馈半导体激光器速率方程组, 数值分析了偏置电流、反馈强度对混沌UWB脉冲信号的影响.研究表明, 混沌UWB脉冲频谱的-10 dB带宽分别随着偏置电流的增大和反馈强度的增强而逐渐增加; 中心频率分别随着偏置电流的增大和反馈强度的增强而逐渐增大.实验中, 产生了中心频率为6.6 GHz, -10 dB带宽为9.6 GHz的混沌UWB信号. 进一步, 通过调节偏置电流和反馈强度, 可实现混沌UWB信号的中心频率和-10 dB带宽的可调谐输出, 实验结果和数值分析相符合.此外, 实验产生的混沌UWB信号经过34.08 km的光纤传输后, 其频谱形状几乎没有发生变化, 表明该方法所产生的混沌UWB信号对光纤色散有较大的容忍度. 关键词： 超宽带 混沌激光 光反馈 直接调制     

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     

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     

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     

光电负反馈下1550nm垂直腔表面发射激光器的动力学特性

基于激光输出的时间序列、功率谱以及相图,对1 550 nm垂直腔表面发射激光器(1 550 nmVCSELs)在光电负反馈作用下的动力学特性进行了研究.结果表明:固定偏置电流,在不同反馈强度下,光电负反馈1 550 nm VCSEL可呈现规则脉冲态、准周期态、混沌脉冲态等非线性动力学态;固定反馈强度,偏置电流取不同值时.1 550 nm-VCSEL也可呈现脉冲态、准周期态、混沌脉冲态等不同的非线性动力学状态.给出了1 550 nm VCSEL非线性动力学状态在偏置电流和反馈强度构成的参量空间分布.分析了激光器的动态演化路径,结果表明:在较小偏置电流和弱光电反馈下,激光器主要工作在稳态:随着偏置电流增加,激光器输出的动力学态通常随反馈强度的增加以规则脉冲态-准周期态-规则脉冲态的方式循环演化到混沌脉冲态;当偏置电流增加到一定值后,激光器输出的动力学态随反馈强度的增加主要以规则脉冲态准周期态混沌脉冲态的方式循环演化.     

双光反馈半导体激光混沌系统中外腔延时反馈特征的抑制

在一个双光反馈半导体激光混沌系统中,固定其中一个反馈腔镜(固定腔M₁)的反馈延迟时间以及反馈强度,实验研究了另一个反馈腔镜(可变腔M₂)的反馈延迟时间以及反馈强度对系统混沌输出的延时反馈特征的影响.研究结果表明:在可变腔M₂与固定腔M₁的反馈强度相等的条件下,改变M₂的腔长,当其腔长约等于(但不能严格等于)M₁的腔长或者腔长的一半时,系统将呈现较好地抑制延时反馈特征效果;当M 关键词： 半导体激光器 双光反馈 混沌输出 延时特征     

基于光反馈双模DFB激光器的宽带混沌信号产生

提出并数值验证了一种利用光反馈双模分布式反馈(DM-DFB)半导体激光器产生宽带混沌信号的方法.通过双纵模Lang-Kobayashi方程建立了光反馈DM-DFB半导体激光器的理论模型,探明了宽带混沌信号产生的物理机制为模式拍频,数值分析了模式间隔、偏置电流和反馈系数对混沌带宽的影响.仿真设计了双模激光器,在镜面反馈系统中,高偏置电流和强反馈强度条件下可以产生38.6 GHz的混沌信号.这一结构为宽带集成混沌源提供了一种新思路.     

基于频率失谐的光混沌同步开关的特性研究

针对实验报道的光混沌同步开关现象,建立了基于半导体激光器的光混沌同步开关的理论模型.利用该模型,数值模拟了不同外腔反馈强度和注入强度下的光混沌同步开关特性.结果表明：固定外腔反馈强度,不同注入强度下的混沌同步开关的对比度和宽度均不同;当注入强度与外腔反馈强度相同时,开关的对比度达到最大值;进一步地,当外腔反馈强度和注入强度同步增强时,混沌同步开关的对比度和宽度均单调增大. 关键词： 光混沌同步开关 半导体激光器 频率失谐 外腔反馈     

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.     

Experimental Injection Map of Semiconductor Laser Submitted to Filtered Feedback

Optical injection consists in the unidirectional coupling between a “slave” laser (SL) and a “Master” laser (ML). The injected SL may exhibit different behaviors, showing frequency locking, wave mixing, relaxation regimes, period doubling, and chaos. The different regimes may be mapped on a chart where the injected power and the detuning between the slave and the master frequencies are varied. In this paper, a detailed overview of the regimes are given when the SL is submitted to both optical injection and filtered optical feedback. This last coupling is realized thanks to an extended cavity, which includes a frequency filter. When the SL is operating far from threshold (4 I_th), typical regimes mentioned for feedback-free laser are observed for all the external-cavity modes. On the contrary, when the SL operates close to threshold (1.5 I_th), it is shown that the dynamics is wealthier. New regimes, as one for which simultaneously chaos and locking occur, can be identified, in comparison to the case of a single-frequency SL.     

Multimode semiconductor laser with selective optical feedback

We study a multimode semiconductor laser subject to moderate selective optical feedback. The steady state of the laser is destabilized by a Hopf bifurcation and exhibits a period-doubling route to chaos. We also show the existence of a heteroclinic connection between a saddle node and an unstable focus that can be associated with experimentally observed multimode low-frequency fluctuations. This heteroclinic connection coexists with a chaotic attractor resulting from the period-doubling process.     

Statistical measures of the power dropout ratio in semiconductor lasers subject to optical feedback

The influence of the optical feedback ratio and bias current on the mean and the standard deviation of the power dropout ratio of low-frequency fluctuations in external-cavity semiconductor lasers has been studied experimentally. The power dropout ratio was found to increase with increasing optical feedback ratio and to decrease with increasing bias current.     

170 keV Proton radiation effects on low-frequency noise of bipolar junction transistors

In this paper, the electrical properties and low-frequency noise for bipolar junction transistors irradiated by 170?keV proton are examined. The result indicates that for the sample under proton irradiation with fluence 1.25?×?10^14?p/cm², base current I_B in low bias range (V_BE < 0.7?V) increases due to superimposition of radiation-induced recombination current, while the gain decreases significantly. Meanwhile, the low-frequency noise increases in the proton-irradiated sample. By analysis of evolution of parameters extracted from low-frequency noise power spectra, it is demonstrated that radiation-induced noise is mainly originated from carrier fluctuation modulated by generation–recombination centers (G–R centers) located at the interface of Si/SiO₂, which are introduced by proton-radiation-induced defects. It is also confirmed that the electrical properties and noise behavior of irradiated sample are mostly affected by the carrier recombination process caused by G–R centers at the interface of Si/SiO₂ than by G–R centers in EB junctions.     

Temperature dependence of turn-on time delay of semiconductor laser diode: Theoretical analysis

Temperature dependence of the turn-on time delay (t_on) of uncooled semiconductor laser diodes biased below and above threshold is analyzed in presence of data pattern effect. We show that even when the laser is biased at or slightly above threshold, the increase in temperature of operation will lead to increase in the threshold carrier (N_th) and consequently the laser diode will be biased below the threshold again and a significant value of t_on will be produced. Thus, knowledge about a value of dc-bias current required to achieve zero t_on within wide range of temperature degrees is important when considering uncooled laser diode in high-speed optical communication systems. The temperature dependence of t_on is calculated according to the temperature dependence of N_th and Auger recombination coefficient (C) and not by the well-know exponentional relationship of threshold current with temperature. The temperature dependence of N_th is calculated according to the temperature dependence of laser cavity parameters. Advanced analytical model is derived in term of carrier density, recombination coefficients and the injection current (I_inj). The validity of proposed model is confirmed by a numerical method. In addition, approximated models are included where under specified assumptions the proposed model reduces to the well-known approximate models of t_on. According to our typical values and at a specified value of modulation current, the dc-bias one (I_ib) should be increased from I_ib = I_th to I_ib ≈ 1.25 and 1.5I_th in order to achieve approximately zero t_on when the temperature increases from 25°C to 55°C and 85°C, respectively.     

A comparison of algainas and InGaAsP-based 1.3 μm semiconductor lasers using high pressure

Abstract

We have compared the effect of hydrostatic pressure on the threshold current, I_th, and lasing energy, E_lase, of 1.3 pm quantum-well devices based upon AlGaInAs and InGaAsP. Whilst we observe a very similar dependence of E_lase on pressure for the two materials, we measure strikingly different variations of I_th. By applying pressure to 1.3 μm InGaAsP lasers, I_th typically decreases by ～ 10% over 1 GPa consistent with the reduction of Auger recombination, which forms ～ 50% of I_th at room temperature. However, for the 1.3 μm AlGaInAs-based lasers, we observe an increase in I_th by ～ 8% over the same pressure range. From these results we conclude that non-radiative recombination accounts for only ～ 20% of I_th in AlGaInAs-based devices. This is in good agreement with previous temperature dependence measurements and shows why AlGaInAs-based devices exhibit a reduced temperature sensitivity of I_th which is very important for telecommunications applications.     

用半导体环形激光器产生混沌信号

提出了一种由一个分布式反馈激光器为主激光器和一个半导体环形激光器为从激光器组成的主从式激光混沌系统方案,主激光器产生的光单向注入到从激光器中,通过调整注入系数、主从激光器的失谐频率和从激光器的偏置电流,使从激光器工作在混沌状态,输出混沌信号。从基于光注入条件下的环形激光器的速率方程组入手,数值模拟了主从激光器的失谐频率、注入系数和从激光器的偏置电流3个工作参量对从激光器输出动态的影响。研究表明：外光注入条件下,半导体环形激光器可以产生混沌信号。通过分析得出:当失谐频率为3.9 GHz、注入系数为0.07、偏置电流为81 mA时,环形激光器可以产生功率谱平坦、带宽较宽的高质量混沌信号。