DBR微腔激光器典型参数的开关调制响应及控制

以微腔激光器的典型代表垂直腔面发射半导体激光器(VCSEL)为例，选择自发辐射因子为控制参数，数值模拟了大信号深度调制情形下VCSEL的非线性动力学特性，实现了类似于边缘发射激光器的分岔，周期加倍分岔，多稳和混沌状态的稳定控制，得到分岔点位置和周期轨道与控制参数的变化关系，以及相应地调制参量和自发辐射因子的取值范围，计算结果较好地拟合了文献实验结果。     

VCSELs高阶分岔及混沌行为的参数控制

基于自发辐射在微腔激光器中的独特性,利用参数开关调制控制混沌的理论和技术,对VCSELs实施高频大信号深度调制和混沌控制的数值模拟.结果表明,提高自发辐射因子可抑制VCSELs的非线性行为,通过对自发辐射因子的开关调制,可把系统由混沌状态控制到平衡态和nP周期轨道,同时给出了VCSELS各种稳定周期态、分岔数、分岔点位置和混沌带与调控参数之间的定量关系.     

基于谱估计法的VCSEL噪声特性研究

针对VCSEL的结构特点 ,在其单模速率方程的基础上引入了Langevin噪声项 ,运用改进型的Yule -Walker谱估计方法 ,得到了在零调制电流条件下VCSEL输出光的相对强度噪声 ,频率噪声的功率谱以及小信号调制下的频率啁啾随电流孔径以及自发辐射因子等参数的变化规律。     

激光偏振技术压缩激光雷达信号动态范围

为了解决激光雷达信号的大动态范围引起远距离弱信号的失真问题,采用通过压缩信号的动态范围的方法,设计了一个利用电压调制系统透过率进而压缩激光雷达信号动态范围的方案。计算表明,系统最小透过率为4.05×10-5,可以压缩信号的动态范围达到4个数量级。利用激光雷达后向散射信号的两个方向偏振光,避免了时控光衰减器只透过一个方向偏振光的弊端。研究结果为压缩激光雷达信号动态范围提供了有价值的新方法。     

EAM-DFB基于S参量和电路模型的特性分析

针对电吸收调制器集成分布反馈激光器(EAM-DFB)的光电混合和端口散射特征,提出了包含自发辐射和俄歇复合的有源等效电路模型,及其散射参量(S参量)求取模型。通过电路级模拟在不同典型参数下的S参量,研究了EAM-DFB的工作特性。模拟得到EAM-DFB的传输参量在-25dB至-60dB内,随频率增高而减小,在调制时增大,并反映出比直调DFB更大的带宽,而反射参量随频率增高而增大,结果与已有的理论和实验吻合。同时发现,减小自发辐射因子或增大驱动电流和限制因子,反射增大传输减小,但后者的传输参量减小缓慢平坦,对调制响应有所改善。     

多次外光反馈下垂直腔面发射激光器非线性动态特性理论研究

在SIMULINK平台下建立了垂直腔面发射激光器(VCSEL)动态仿真模型，利用该模型对多次外光反馈下垂直腔面发射激光器的非线性行为进行了研究。结果表明，短外腔时，光子密度随外腔长呈周期为半激射波长的余弦关系；长外腔时，随外腔长增加，垂直腔面发射激光器依次经历混沌、多周期、倍周期和单周期区域，增大外腔反射率时同样存在这些非线性区域，但出现顺序相反。进一步得出：考虑单次反馈时由于忽略了占有较多能量的高次反馈导致上述非线性效应偏弱；增大自发辐射因子或减小线性展宽因子可抑制系统的非线性行为。     

半导体微腔激光器瞬态响应及调制特性分析

针对半导体微腔激光器的结构特点,考虑到腔量子电动力学中自发辐射增强效应,采用传统速率方程的表示形式,建立了微腔激光器的速率方程,着重讨论了微腔激光器的瞬态响应及调制特性,给出了其动态特性的仿真结果,分析了自发辐射因子、注入电流和腔长对微腔激光器的激射阈值、延迟时间、驰豫振荡频率和光输出等参量的影响,从而为改善微腔激光器的高频调制特性和优化器件结构提供了理论依据。     

半导体微腔激光器瞬态响应及调制特性分析

针对半导体微腔激光器的结构特点,考虑到腔量子电动力学中自发辐射增强效应,采用传统速率方程的表示形式,建立了微腔激光器的速率方程,着重讨论了微腔激光器的瞬态响应及调制特性,给出了其动态特性的仿真结果,分析了自发辐射因子、注入电流和腔长对微腔激光器的激射阈值、延迟时间、驰豫振荡频率和光输出等参量的影响,从而为改善微腔激光器的高频调制特性和优化器件结构提供了理论依据.     

电流调制垂直腔面发射半导体激光器混沌动力学特性

利用数值模拟的方法研究了电流调制下偏置电流和调制频率对垂直腔面发射半导体激光器(VCSEL)混沌动力学特性的影响.数值模拟结果表明,在一定的调制频率下,偏置电流较大时VCSEL处于稳定的周期一态.偏置电流较小时激光器在调制参数的某些区间会出现阵发混沌;在一定的偏置电流下,调制频率较小时,VCSEL处于稳定的周期一态,调制频率较大时系统在调制参数的某些区间会出现阵发混沌.所以偏置电流和调制频率是影响VCSEL混沌动力学特性的重要参数,可以通过适当控制偏置电流和调制频率找到系统的周期态和混沌态.     

空间光调制器实现随机相位模板的仿真分析

为了构建基于空间光调制器的实时光学加密系统,采用仿真实验的方式,分析了在双随机相位光学加密系统中使用空间光调制器实现随机相位编码时相位编码参量对加密效果的影响。重点研究了随机相位模板中独立相位调制点的个数及相位调制范围对加密图像质量的影响,并引入相关系数来衡量加密图像和原始图像的差异。结果表明,在设定相关系数阈值为0.1的条件下,独立相位调制点个数达到128×128,相位调制范围达到2π时,加密效果较好。该结果对设计实时光电加密系统有一定指导意义。     

硅基法布里—珀罗微腔的室温发光

提出了一种新型基于法布里 -珀罗 (F- P)微腔的发光器件结构 .它采用 PECVD方法制备的非晶硅 /二氧化硅结构作为微腔中的布拉格反射腔 ,非晶碳化硅薄膜作为中间光发射层 ,通过对一维方向光子的限制 ,使发光层荧光强度增强 ,谱线变窄 .通过调节发光层和反射腔膜厚及折射率 ,可以精确控制发光峰位 .实验结果证明该结构可望实现全硅基材料的强室温可见光发射 .     

Blue lasing at room temperature in an optically pumped lattice-matched AlInN=GaN VCSEL structure

Laser action with low threshold average pump power density (~50 W - cm^-2 ) at room temperature is reported for a crack-free planar vertical cavity surface emitting laser (VCSEL) structure based on a bottom lattice-matched AllnN/GaN distributed Bragg reflector (DBR) and a top dielectric DBR. The cavity region, formed by n- and p-type GaN layers surrounding only three InGaN/GaN quantum wells, corresponds to a typical active region suitable for an electrically driven VCSEL. In addition to low threshold, a spontaneous emission coupling factor beta ~ 2 x 10^-10 is derived for this ready-to-be-processed laser structure.     

Measurement of spontaneous emission factor for injection lasers

Accurate numerical simulation of the dynamic behavior of injection lasers requires accurate values for the parameters used in physical models. One such parameter which has been difficult to measure accurately in the past is the spontaneous emission factor or degree of coupling of spontaneous emission into the lasing modes. A numerical value for this spontaneous emission factor is obtained by distortion analysis of the optical output of a biased laser modulated by a small audio frequency sine wave. This technique can be used on either single or multimode lasers, and accounts for the different behavior of the different modes. Detailed studies were done on two different multi-mode devices, under varying thermal and modulation conditions. The values obtained by this technique for the spontaneous emission factor were of the order of 10^-5and showed good agreement with the results using more conventional methods. Values of the spontaneous emission factor for different modes of the same device typically agree to within 10 percent. This is significantly better than other techniques whose results are typically good to within no better than a factor of two.     

Steady-state and transient characteristics of microcavitysurface-emitting lasers with compressively strained quantum-well activeregions

In conventional semiconductor lasers, the dimensions of the optical cavity greatly exceed the photon wavelength, and the photon density of states forms a continuum since it is essentially that of a bulk system. On the other hand, in an ideal laser, one would like to have a single optical mode coincident with the maximum in the gain spectrum of the active medium. We show that substantial density-of-states quantization and enhancement of the fraction of photons spontaneously emitted into the lasing mode can be obtained by reducing the lateral width of the surface-emitting laser. For emission at λ=0.954 μm, the threshold current density can be drastically reduced by increasing the coupling factor to a few percent. For a cavity structure width of 0.3 μm, the threshold current density is 50 A/cm², compared with 250 A/cm² for the 0.6-μm cavity. At lower still lateral widths, the cavity loses its vertical character, and confinement of the lateral optical mode rapidly deteriorates. The large-signal response of microcavity lasers is slightly improved primarily due to elimination of mode competition in intrinsically single-mode microcavities, with relaxation times close to 1 ns. The enhancement of the spontaneous emission coupling factor results in an increase of the relaxation oscillation frequency and improvement in the standard small-signal response of microcavity lasers. For J=10J_th, the -3 dB modulation frequency exceeds 40 GHz. Since low threshold current densities may be achieved in microcavity lasers, the gains in small-signal performance are primarily extrinsic, i.e., higher modulation bandwidths ace accessible for the same injection     

Modeling of the Transient Characteristics of Heterojunction Bipolar Transistor Lasers

A charge control model for the transient analysis of the bipolar transistor laser in forward active mode is developed to describe the dynamics of electron, photon and charge densities. From three coupled-rate equations, analytical expressions are obtained for the threshold base current density, the steady-state electron and photon densities, and small-signal frequency response. We find that the threshold current density decreases with increasing spontaneous emission lifetime of electrons in the quantum well as well as a linear dependence of the photon density on the base current. By optimizing the model parameters in their physical range, we show that a ${-}3$-dB bandwidth of 55 $~$GHz can be achieved for small-signal modulation of the laser. By numerically solving the rate equations, we investigate the ${-}3$-dB bandwidth under large-signal modulation to show that it remains nearly unchanged from the small-signal case. We further perform analysis of laser switching and find that the turn-on time is reduced by increasing the base current or decreasing the spontaneous emission lifetime of electrons in the quantum well.      

Characteristics of a photonic bandgap single defect microcavityelectroluminescent device

A microcavity surface-emitting coherent electroluminescent device operating at room temperature under pulsed current injection is described. The microcavity is formed by a single defect in the center of a 2-D photonic crystal consisting of a GaAs-based heterostructure. The gain region consists of two 70-Å compressively strained In_0.15Ga_0.85As quantum wells, which exhibit a spontaneous emission peak at 940 nm. The maximum measured output power from a single device is 14.4 μW. The near-field image of the output resembles the calculated TE mode distribution in a single defect microcavity. The measured far-field pattern indicates the predicted directionality of a microcavity light source. The light-current characteristics of the device exhibit a gradual turn-on, or a soft threshold, typical of single- or few-mode microcavity devices. Analysis of the characteristics with the carrier and photon rate equations yields a spontaneous emission factor β≈0.06